PhysicsPulseTM
NRC Reciprocity: Form 241 Across State Lines
Reciprocity is how an Agreement State licensee legally does licensed work outside its home state without holding a second full license. Under 10 CFR 150.20, a general license and an NRC Form 241 authorize temporary work in NRC jurisdiction; work in another Agreement State runs through that state's own reciprocity process. The rules on filing, fees, the 180-day limit, and what reciprocity does not cover decide whether a traveling program is compliant.
Pb-212 Targeted Alpha Therapy: Physics & Dosimetry
Lead-212 is an in vivo generator alpha emitter: it delivers one high-LET alpha per decay through its short-lived daughter chain, with a 10.64-hour half-life convenient for radiopharmaceutical shipping and dosing. This guide covers the decay physics, MIRD-style dosimetry, the 203Pb imaging surrogate, and the radiation-safety wrinkle its 2.6 MeV daughter photon creates.
Grid-Less Radiography: Scatter Correction Software
Software scatter correction estimates and subtracts scattered radiation after the exposure, letting a facility drop the anti-scatter grid on selected radiographic exams. It can preserve contrast and cut patient dose, but its performance depends on body size and clinical task, so it needs a physicist-led validation rather than a blanket switch.
MRI Safety Program: ACR Zones and Roles
An MRI safety program controls four invisible hazards through zones, trained personnel, and implant screening. Here is how to build one around the 2024 ACR Manual on MR Safety and the Joint Commission's 2026 imaging goal — and where a medical physicist fits as your MR Safety Expert.
Amyloid and Tau Brain PET: SUVR and Centiloid
Amyloid and tau PET have moved from research tools to clinically actionable tests, especially with anti-amyloid therapies. Reliable interpretation depends on harmonized quantification: the Centiloid scale anchors amyloid burden on a common 0–100 axis, but it only works when scanner calibration, reconstruction, and analysis pipelines are controlled. This is squarely a medical physics problem.
Coronary Artery Calcium Scoring: Agatston & Dose
Coronary artery calcium (CAC) scoring turns a non-contrast ECG-gated chest CT into a quantitative cardiovascular risk marker. The Agatston score, its volume and mass companions, and the CAC-DRS reporting system are only as trustworthy as the acquisition protocol behind them — which is why standardized technique, HU calibration, and reproducibility limits are a medical physics problem, not just a reading-room one.
Radiation Survey Meter Selection Guide
Not all radiation survey meters answer the same question. Learn how GM meters, ion chambers, hybrid meters, x-ray survey sensors, and imaging survey meters work so you can match the right instrument to contamination control, leakage surveys, and shielding verification.
Pediatric Nuclear Medicine Dosing Explained
Pediatric nuclear medicine dosing balances diagnostic image quality against the heightened radiosensitivity of children. This guide explains weight-based administered-activity scaling, minimum activities, and the North American consensus guidelines—including the 2024 update—and walks through worked dose calculations and the regulatory framework that governs administered activity in children.
CT Dose Index Monitoring: RDSR, DRLs, and the ACR DIR
A CT radiation dose index monitoring (RDIM) program is an enterprise system that automatically captures DICOM Radiation Dose Structured Reports from every scan, benchmarks the results against diagnostic reference levels and the ACR Dose Index Registry, and turns that data into protocol optimization and outlier review.
PET/MR Radiation Safety: Hot Lab Meets the Magnet
A PET/MR suite stacks two unrelated hazard domains in one room: positron-emitting tracers and 511 keV photons governed by NRC radiation rules, and an always-on magnet governed by ACR accreditation and the Joint Commission. Neither program covers the other, so a combined suite needs both an RSO-led radiation-safety program and an MRMD/MRSO/MRSE-led MR-safety program, coordinated so the hot-lab workflow does not fight the ACR four-zone model.
Lu-177 PSMA Therapy: Dosimetry & Safety
Lu-177 PSMA-617 (Pluvicto) is a beta-emitting radioligand therapy for PSMA-positive metastatic castration-resistant prostate cancer. Because Lu-177 pairs a therapeutic beta particle with imageable low-energy gammas, treatment planning couples MIRD-based organ dosimetry — where the kidneys and salivary glands are the dose-limiting organs — with an outpatient radiation-safety workflow built on patient-release calculations, contamination control, and NRC medical-use requirements.
Metal Artifact Reduction in CT: How MAR Works
Metal artifact reduction (MAR) preserves image quality, HU accuracy, and clinical confidence in diagnostic CT, radiation therapy planning, and hybrid PET/CT and SPECT/CT workflows.
The 2026 NRC Rulemaking Wave: What Medical-Use Licensees Need to Know
Between April and July 2026 the NRC issued five proposed rules reaching medical-use licensees under Executive Order 14300. Two of them amend 10 CFR Part 35 at the same time — one rewrites patient release and caregiver dose, the other overhauls authorized-user training. ALARA would be replaced by a graded approach to dose management with an explicit cost-benefit test.
Cardiac SPECT MPI: Physics, OSEM, and QC
Cardiac SPECT myocardial perfusion imaging combines radiopharmaceutical selection, gamma-camera acquisition, iterative reconstruction, attenuation and scatter correction, and ECG-gated LVEF analysis into a complex imaging chain where each step has its own quality-control requirements. A well-run cardiac SPECT MPI program aligns radiopharmaceutical protocols, daily and weekly QC, reconstruction parameters, and artifact awareness with ASNC, SNMMI, NEMA, and AAPM guidance.
MRI Acoustic Noise and Gradient PNS Safety
MRI acoustic noise and gradient-induced peripheral nerve stimulation are two physiologic hazards driven by the same switched gradient coils. Both are managed through IEC 60601-2-33 operating modes, the strength-duration dB/dt limit, mandatory hearing protection above 99 dBA, and documented physicist review — not by trusting that the scanner console will always keep the patient safe.
Lost Dosimeter? Reconstructing the Dose of Record
A lost or damaged dosimeter does not erase the requirement to keep a dose of record. NRC rules require the licensee to assign a defensible occupational dose using a reasonable estimate—from coworker data, area monitoring, or workload reconstruction. This guide walks through the methods, the math, and the recordkeeping that make the estimate stand up to inspection.
New York Dental CBCT Rule: Part 16 Explained
New York repealed and replaced 10 NYCRR Part 16 effective July 22, 2026, and the new Part contains section 16.65, the state's first rule written specifically for cone beam CT. For a dental practice outside New York City it means a written QA program, acceptance and annual testing by a New York State licensed medical physicist, patient dose posted at the operator console, and accreditation by January 22, 2028. Inside the five boroughs a different rulebook applies.
Tc-99m MDP Bone Scintigraphy: Technique and QC
The Tc-99m MDP bone scan remains the workhorse of skeletal nuclear medicine. Its diagnostic power rests on physics: chemisorption of diphosphonate onto bone mineral, a 140 keV photon well matched to the gamma camera, delayed imaging that lets soft tissue clear, and SPECT/CT that turns a hot spot into an anatomic diagnosis. This guide connects each step to the acquisition parameters and QC that keep the study reliable.
Full-Spine Scoliosis Radiography: Dose & Image Quality
Full-spine scoliosis radiography is a dose-optimization problem disguised as an image-quality problem. Because young patients are imaged repeatedly over years of growth, the projection (PA versus AP), the acquisition technology (stitched digital radiography versus EOS slot-scanning), filtration, and the image-quality target set by Cobb-angle measurement all combine to determine cumulative radiation risk. This guide connects the physics to a defensible protocol.
Pregnant Radiation Worker: Dose Limits
A pregnant radiation worker can continue working safely in most medical radiation environments, but only under a deliberate program: voluntary written declaration, the 5 mSv embryo/fetus dose limit, fetal dosimetry, and ALARA controls. The decision to declare is the worker's alone, and the radiation safety program's job is to make the safe path the easy path.
Instructions to Workers: 10 CFR Part 19 & Form 3
10 CFR Part 19 is the worker-facing side of the NRC's radiation rules: the notices a licensee must post, the instructions workers must receive, and the dose reports they are entitled to. It is one of the most commonly cited gaps at inspection, precisely because it is easy to assume it is handled. This guide covers what Part 19 requires, including NRC Form 3, the 1 mSv instruction threshold, and worker dose reports.
Radionuclide Cisternography with In-111 DTPA
Radionuclide cisternography uses intrathecally injected indium-111 DTPA — the only FDA-approved intrathecal radiotracer — to image cerebrospinal fluid flow over 24 to 72 hours. Its 67-hour half-life and dual 171 and 245 keV photopeaks make delayed imaging feasible but demand a medium-energy collimator and correct dual-window setup. The study answers three questions: is there a CSF leak, is this normal-pressure hydrocephalus, and is the shunt patent.
Photon-Counting CT: Physics, Image Quality & Dose
Photon-counting detector CT (PCD-CT) replaces the scintillator-photodiode chain of energy-integrating detectors with direct-conversion semiconductors that count individual X-ray photons and sort them by energy. The result is near-elimination of electronic noise, ultra-high spatial resolution, inherent spectral data on every scan, and real dose-efficiency gains — but it also changes how physicists approach acceptance testing, CT-number accuracy, and QC.
Radiopharmaceutical Extravasation: Dose & Reporting
Radiopharmaceutical extravasation deposits part of an injected dose into soft tissue instead of the bloodstream, and in significant events the local absorbed dose can reach several gray. This is a radiation-safety and dosimetry problem: knowing when to identify, quantify, document, and report an extravasation protects patients and keeps a nuclear medicine program defensible.
Lu-177 Theranostics Dosimetry: MIRD and SPECT/CT
Lu-177 dosimetry turns a therapy isotope into a measurable absorbed dose. This guide explains the MIRD schema, quantitative SPECT/CT, organ-at-risk doses for Lutathera and Pluvicto, and why FDA labels stay fixed-activity while physicists push for personalization.
Mammography AEC (Phototimer) Performance QC
On a digital mammography unit the automatic exposure control (AEC) chooses target, filter, kVp, and mAs for every patient, so it sets both image quality and dose. AEC (phototimer) performance QC confirms the system holds a stable signal-to-noise ratio as breast thickness changes, repeats reliably, and keeps mean glandular dose within the MQSA limit — evaluated against the 2018 ACR Digital Mammography QC Manual and enforced through the FDA EQUIP inspection program.
SPECT Scatter Correction: TEW, DEW, and Beyond
Compton-scattered photons blur SPECT images and inflate apparent activity, so scatter correction is essential wherever SPECT is used quantitatively — from Tc-99m perfusion to Lu-177 dosimetry. Triple-energy-window (TEW) and dual-energy-window (DEW) methods estimate the scatter in the photopeak from adjacent energy windows and subtract it, while model-based and Monte Carlo methods reconstruct the scatter directly.
Radiation Protection Survey: Shielding Check
A radiation protection survey is the post-construction verification that closes the loop on a shielding design: the physicist measures dose rates in occupied areas around a newly installed x-ray, CT, or radioactive-material room, scales the measurements to realistic weekly workload and occupancy, and confirms the as-built barriers meet NCRP design goals and regulatory dose limits before clinical use begins.
Contrast-Enhanced Ultrasound: Physics & Safety
Contrast-enhanced ultrasound images microbubbles, not tissue, and that inverts the usual output settings: the exam runs at very low mechanical index to keep the bubbles intact. Understanding the mechanical index, the acoustic-output ceilings, and the microbubble physics is what makes CEUS both diagnostic and safe.
Cath Lab Shielding Design: NCRP 147 and 168
Interventional and cardiac catheterization suites are a distinctive shielding problem: the useful beam is always intercepted by the image receptor, so structural barriers are designed almost entirely against scattered and leakage radiation. High workloads, long fluoroscopy times, and an operator standing beside the patient make the cath lab both a structural-shielding and an occupational-protection challenge. A defensible design combines NCRP Report No. 147 secondary-barrier methods, NCRP Report No. 168 dose-management guidance, and verified operator shielding.
Rb-82 Generator Quality Control
A Sr-82/Rb-82 generator delivers a 75-second cardiac PET tracer on demand, but its long-lived parent, Sr-82, can bleed into the patient dose. Rb-82 generator QC is the daily strontium-breakthrough test — plus elution technique, calibration, and recordkeeping — that keeps Sr-82 and Sr-85 below the NRC limits in 10 CFR 35.204 and prevents the kind of overexposure documented in past breakthrough incidents.
CTDI Measurement: CT Dose QC With a Pencil Chamber
CTDI measurement is how a medical physicist confirms that a CT scanner's displayed dose is real. Using a 100-mm pencil ionization chamber in 16 cm and 32 cm PMMA phantoms, the physicist measures CTDI100 at the center and periphery, combines them into CTDIw and CTDIvol, compares the result against the scanner-displayed value and ACR reference levels, and documents the agreement a defensible dose program depends on.
RSO Role: Duties, Authority, and Qualifications
What a Radiation Safety Officer actually does — the authority and responsibilities of 10 CFR 35.24, the 35.50 qualification pathways, ALARA and investigational levels, the Radiation Safety Committee for broad-scope licenses, and the annual program review that keeps a license in good standing.
Contrast-Enhanced Mammography: Physics and QC
Contrast-enhanced mammography (CEM) pairs a low-energy image that looks like a standard mammogram with a high-energy exposure to build an iodine-only recombined image. This guide explains the dual-energy physics around the iodine K-edge, the mean glandular dose penalty, the CNR and figure-of-merit metrics that drive QC, and how CEM fits inside the MQSA and manufacturer-QC framework.
F-18 Fluoroestradiol (FES) PET for ER+ Breast Cancer
F-18 fluoroestradiol (FES) PET/CT noninvasively maps estrogen receptor expression across all sites of disease at once. Approved as Cerianna in 2020, it complements FDG PET by imaging receptor status rather than glucose metabolism, guiding endocrine therapy decisions in recurrent or metastatic ER-positive breast cancer, resolving inconclusive lesions, and revealing receptor heterogeneity that a single biopsy can miss.
PET/MR Attenuation Correction: The Bone Problem
Attenuation correction is the hardest quantitative problem in PET/MR. Unlike PET/CT, MR signal does not map to 511 keV attenuation, and bone and lung are invisible to standard Dixon sequences. This guide explains MR-based attenuation correction methods, the resulting SUV bias, and how ZTE/UTE and deep-learning pseudo-CT approaches close the gap.
Authorized User Training & Experience (10 CFR 35)
Before a physician can order radiopharmaceutical therapy or a physicist can calibrate a therapy unit, they must be named on the radioactive material license as an authorized user or authorized medical physicist. 10 CFR Part 35 Subpart J defines two routes to that status — board certification and a training-and-experience pathway — each with specific hour and case requirements and preceptor attestation.
Photon-Counting CT: Image Quality and Dose
Photon-counting detector CT replaces scintillator-based energy-integrating detectors with semiconductors that count and energy-resolve individual X-ray photons. The result is lower electronic noise, higher spatial resolution, improved iodine contrast, always-on spectral data, and the opportunity to lower radiation dose — but the physics and QC differ enough from conventional CT that acceptance testing and protocol design need a fresh look.
Radiation Safety Training Programs
A radiation safety training program is the documented system that instructs workers before they begin radiation work and refreshes them annually, as required by 10 CFR 19.12. This guide explains who must be trained, the regulatory basis, effective content, recordkeeping, competency assessment, and how training is examined during NRC and Agreement State inspections.
Gamma Camera Uniformity QC: Floods and Limits
Flood-field uniformity is the daily heartbeat of gamma camera QC. This guide covers what integral and differential uniformity measure, the difference between intrinsic and extrinsic floods, how counting statistics set the required count density, and how to read the NEMA numbers before an artifact reaches a patient study.
SPECT Reconstruction: FBP vs Iterative OSEM
SPECT image reconstruction turns raw projection data into cross-sectional images two ways: analytic filtered back projection (FBP), which is fast but noisy and cannot model physics, and iterative OSEM, which converges on a statistically consistent image while modeling attenuation, scatter, and collimator blur. Understanding both is essential to reading, optimizing, and quantifying modern SPECT and SPECT/CT.
Ultrasound Elastography QC: Physics and QA
Ultrasound elastography turns a shear wave measurement into a stiffness number, and that number drives clinical decisions. A defensible QC program confirms the value is accurate against a known phantom, repeatable within tolerance, and reported with the reliability criteria and system-specific context that make it comparable over time.
Y-90 Radioembolization Radiation Safety
Yttrium-90 radioembolization is a pure beta-emitting therapy, and its radiation safety program looks nothing like a gamma-emitter's. This guide explains Y-90's decay physics, why low-Z shielding and contamination control matter more than lead walls, the dose-assay and post-procedure survey workflow, patient release, and the NRC and Agreement State framework for a defensible program.
Dental CBCT Quality Control: AAPM TG-261 Guide
Dental and maxillofacial CBCT quality control is now anchored by AAPM Task Group Report 261. A defensible QC program combines acceptance testing, routine image-quality checks (uniformity, noise, CNR, spatial resolution, geometric accuracy), radiation-output measurement, and dose optimization tied to state regulations and manufacturer specifications.
MUGA and LVEF: Count-Based Ejection Fraction
The gated blood pool scan (MUGA/ERNA) measures left ventricular ejection fraction from counts, not geometry, which is why it remains the most reproducible LVEF tool for detecting small serial changes in cancer patients on cardiotoxic therapy. This guide explains the count-based physics, the acquisition, and where MUGA still beats echo.
NRC Enforcement: Violations & Civil Penalties
When the NRC finds a violation, what happens next follows a defined process: the violation is classified by significance, dispositioned as a minor violation, a non-cited violation, or a cited Notice of Violation, and — for the most significant cases — assessed for a civil penalty or made the subject of an order. Understanding that escalation ladder is what lets an RSO respond correctly instead of overreacting or underreacting.
CT Iterative & Deep-Learning Reconstruction
CT reconstruction has moved from filtered back projection through hybrid and model-based iterative reconstruction to deep-learning reconstruction (DLR). Each class changes noise magnitude, noise texture, spatial resolution, and low-contrast detectability differently, so dose-reduction claims must be judged with task-based image-quality metrics, not noise alone.
Sewer Disposal of Radioactive Material
Releasing licensed radioactive material into the sanitary sewer is permitted under 10 CFR 20.2003, but only within tight limits. The material must be readily soluble or dispersible, the monthly average concentration must stay below Appendix B Table 3 values, mixtures must satisfy a sum-of-fractions test, and total annual releases are capped. This guide explains the rule, the math, the records, and the common RSO mistakes.
Total-Body PET and Long Axial FOV Scanners
Total-body and long axial field-of-view PET scanners cover 106 cm to 194 cm of the patient in a single position instead of the roughly 15-26 cm of a conventional system. That geometry raises coincidence sensitivity by about an order of magnitude, which a facility can spend on faster scans, lower injected activity, delayed low-count imaging, or whole-body dynamic kinetics — but only with the right acceptance testing and quantitative calibration.
CT Number (Hounsfield Unit) Calibration and Accuracy QC
CT number accuracy is the quantitative backbone of CT. Hounsfield units anchor density-based diagnosis, dose calculation, attenuation correction, and reconstruction. This guide explains how HU is defined, why water and material accuracy drift, the tolerances used in ACR accreditation and AAPM TG-66, and how a defensible CT number QC program is built and documented.
Sentinel Events vs Serious Reportable Events
Sentinel events and serious reportable events are converging. Here is what the January 1, 2027 Joint Commission–NQF alignment means for hospital safety reporting, and for radiology, MRI, nuclear medicine, and radiation therapy.
SPECT/CT Quality Control Program
SPECT/CT quality control is the scheduled program of gamma camera and tomographic tests—uniformity, center of rotation, spatial and energy resolution, sensitivity, and CT co-registration—that keeps a hybrid system performing to specification and ready for accreditation.
Minimum Detectable Activity for Contamination Surveys
Minimum detectable activity (MDA) is the smallest amount of radioactivity a counting setup can reliably distinguish from background — the statistical floor that decides whether a contamination survey can actually see the limit it must enforce.
PET Spatial Resolution and Positron Range
PET spatial resolution is not set by the reconstruction algorithm alone — it is bounded by physics: the finite size of the detector element, the ~0.5° non-collinearity of annihilation photons, and the distance a positron travels before it annihilates. Positron range is the term that changes most between radionuclides, which is why an F-18 image is sharper than a Ga-68 or Rb-82 image on the very same scanner.
Cone-Beam CT Dose: Why CTDI Falls Short
Cone-beam CT (CBCT) uses a wide cone of radiation and a flat-panel detector, so the conventional 100 mm CTDI pencil chamber underestimates the true dose. A defensible CBCT dose program blends the right metric for the platform — CTDI for narrow beams, AAPM TG-111 equilibrium-dose methods for wide beams, and kerma-area product for C-arm and dental systems — with realistic protocol optimization and routine QC.
Flat-Panel Detector QC: Uniformity & Dead Pixels
Flat-panel detector quality control confirms that a digital radiography receptor produces a uniform, low-noise image with an acceptable number of defective pixels. Signal nonuniformity, SNR nonuniformity, anomalous pixels, lag, and ghosting are the receptor-level tests that keep detector artifacts from mimicking or masking pathology, and AAPM TG-150 and TG-151 define how physicists and technologists check them.
Patient Gonadal & Fetal Contact Shielding
For half a century, lead gonadal and fetal contact shields were standard practice in diagnostic radiography. AAPM, NCRP, ACR, and RSNA now recommend discontinuing them as a routine practice — because the benefit is negligible, the shields are usually mispositioned, and they can interfere with automatic exposure control and obscure anatomy in ways that increase dose and force repeats. This is a policy change every RSO and imaging facility has to manage.
Zr-89 ImmunoPET: Physics and Dosimetry
Zirconium-89 immunoPET matches a 78.4-hour physical half-life to the multi-day pharmacokinetics of antibodies, enabling whole-body PET days after injection. But the same nuclide carries a low positron branching ratio and an intense 909 keV prompt gamma that shape image quality, quantification, patient dose, and staff radiation safety in ways F-18 imaging never demands.
Radioactive Waste in Nuclear Medicine
A practical, answer-first guide to managing radioactive waste in nuclear medicine — decay-in-storage, sanitary-sewer release, licensed disposal and transfer, and return-to-supplier — with the worked decay math, a pathway comparison table, and the NRC and Agreement State rules that govern each route.
Dual-Energy CT: Physics and Quality Control
Dual-energy (spectral) CT acquires attenuation data at two effective energies so the scanner can separate materials, quantify iodine, and synthesize virtual monoenergetic and virtual non-contrast images. Those quantitative outputs only stay trustworthy when a medical physicist tests material decomposition, VMI CT-number accuracy, and iodine quantification against AAPM TG-291 and TG-299 guidance.
Count Rate and Dead Time in Nuclear Medicine
Every counting detector misses events when they arrive too close together. In nuclear medicine this dead time caps usable count rate and, at high activities, biases images and quantitative dosimetry. This guide covers the paralyzable and non-paralyzable models, the NEMA count-rate tests, the 20% count-loss benchmark, and where it matters clinically.
Low-Level Waste Classification: 10 CFR Part 61
Most nuclear-medicine waste never reaches a disposal site because decay-in-storage handles it, but the material that outlives the 120-day rule must be classified under 10 CFR 61.55 as Class A, B, or C. This guide explains the waste-classification tables, the sum-of-fractions rule, and how decay-in-storage and Part 61 fit together.
Mean Glandular Dose in Mammography
Mean glandular dose (MGD) is the accepted metric for breast dose in mammography because the glandular tissue is the radiosensitive target. MGD cannot be measured directly; it is estimated by multiplying a measured incident air kerma by published conversion factors that depend on breast thickness, glandularity, and beam quality. This guide explains the Dance and Boone formalisms, the 3.0 mGy MQSA limit, and how a medical physicist verifies dose during the annual survey.
Y-90 PET/CT After Radioembolization
Y-90 is a near-pure beta emitter, yet a tiny internal-pair-production branch lets PET/CT image the microsphere distribution after radioembolization with better resolution and quantitative accuracy than bremsstrahlung SPECT. This guide covers the decay physics, why the images are count-starved, the local deposition dosimetry method, and the QC that makes post-therapy dose numbers defensible.
Stochastic vs Deterministic Radiation Effects
Stochastic effects such as cancer are modeled as having no dose threshold, so their probability rises with dose while severity does not. Deterministic tissue reactions such as cataract and skin injury have practical thresholds, and their severity climbs with dose once the threshold is crossed. The distinction is the physics behind every dose limit, ALARA decision, and patient risk conversation.
FDG PET/CT for Cardiac Sarcoidosis
Cardiac FDG PET/CT lives or dies on dietary preparation. The goal is to starve normal myocardium of glucose so that inflammatory cells light up against a dark background. This guide explains the substrate-suppression physics, compares dietary protocols with published suppression rates, works through SUV quantitation, and covers dose and QC for a defensible cardiac sarcoidosis program.
Repeat-Reject Analysis in Digital Radiography
Repeat-reject analysis is a core radiography quality-control tool: every rejected image is a patient exposure that produced dose but no diagnosis. A defensible program standardizes reject reasons, tracks rates by projection and technologist, and feeds the findings back into training and protocol fixes — guided by AAPM TG-305.
Radiation Risk Communication in Imaging
Communicating imaging radiation risk well means neither inflating it nor dismissing it. Effective dose is a population planning quantity, not an individual risk prediction; at diagnostic doses the modeled risk is small and uncertain, and the benefit of an indicated exam almost always dominates. A defensible script leads with benefit, frames dose against natural background, and answers the patient's real question.
DXA Precision and Least Significant Change
A follow-up bone density result is only meaningful if the change exceeds the measurement error of the test. DXA precision assessment quantifies that error at each skeletal site, and the Least Significant Change (LSC) converts it into the smallest BMD change a facility can call real with 95% confidence. This guide explains how to run a precision study, compute the LSC correctly, and use it to read serial scans.
Renal Scintigraphy: Split Function & GFR
Renal scintigraphy turns a dynamic renogram into two numbers a clinician acts on: split (relative) renal function and glomerular filtration rate. Both depend on getting the physics right — region-of-interest counts corrected for background and for kidney depth. This guide walks through the quantification, the camera-based Gates GFR method, and where the accuracy is won or lost.
Diagnostic X-Ray Room Shielding: NCRP 147
Diagnostic X-ray room shielding follows NCRP Report 147, which sets weekly air-kerma design goals, distinguishes primary from secondary barriers, and converts a required transmission into a lead or concrete thickness using workload, use factor, occupancy, distance, and the Archer transmission model.
Siemens CT Reconstruction Kernels Decoded
A practical guide to Siemens SOMATOM CT reconstruction kernels: how kernel naming and resolution index work, and how kernel selection affects sharpness, noise, and quantitative accuracy.
Lu-177 DOTATATE PRRT for Neuroendocrine Tumors
Lu-177 DOTATATE (Lutathera) is the somatostatin-receptor peptide receptor radionuclide therapy for gastroenteropancreatic neuroendocrine tumors, delivered as four 7.4 GBq cycles. Behind each administration is a specific physics and radiation-safety workflow: amino-acid renal protection, dose-limiting kidney and marrow dosimetry, Lu-177 decay characteristics, and patient release under 10 CFR 35.75. This guide walks through the physics that makes PRRT safe and effective.
USP 825: Radiopharmaceutical Compounding Safety
USP General Chapter 825 is the compounding standard written specifically for radioactive drugs. It defines how nuclear pharmacies and nuclear medicine departments prepare, compound, dispense, and repackage radiopharmaceuticals safely—reconciling the sterile-compounding engineering controls of USP 797 with the radiation-safety realities of short half-lives, contamination control, and NRC and FDA oversight. This guide explains the chapter's scope, its place among the USP compounding chapters, and how a facility builds a compliant program.
CT Tin Filtration: Spectral Shaping and Dose
Tin (Sn) spectral filtration hardens the CT x-ray beam by removing low-energy photons that add dose but little diagnostic signal in high-contrast tasks. For unenhanced, high-contrast studies such as lung cancer screening, sinus CT, and stone protocols, spectral shaping can cut effective dose by roughly half while preserving diagnostic image quality — but it is a task-specific tool, not a universal setting, and its dose accounting has subtleties every physicist should understand.
F-18 FDG PET/CT Dose Optimization
FDG PET/CT image quality is set by the product of injected activity and acquisition time, not activity alone. Because randoms grow with the square of activity while trues grow linearly, more dose eventually stops helping — the fix is often time, not activity.
Airborne Effluent Releases and Public Dose
Nuclear medicine, PET, and cyclotron facilities routinely release small amounts of radioactive gases and vapors to the environment through hoods and stacks. NRC regulations set a clear framework: a 100 mrem per year public dose limit, a separate 10 mrem per year constraint on air emissions, and two accepted ways to demonstrate compliance, including an effluent-concentration method keyed to Appendix B. Understanding which limit applies, and how the sum-of-ratios method works, keeps a release program defensible.
Intraoperative Gamma Probe QC & Performance Testing
The handheld gamma probe is the instrument a surgeon trusts to find a sentinel node or a parathyroid adenoma, yet it is often the least QC'd device in the department. NEMA NU 3-2004 defines the sensitivity, spatial and angular resolution, energy resolution, and shielding tests that keep a probe dependable in the operating room.
Contrast-Detail QC for Digital Radiography
A contrast-detail phantom like the CDRAD 2.0 answers the question exposure index cannot: at this dose, how small and faint an object can this radiography system actually show? The inverse image quality figure (IQFinv) turns that threshold into one number for optimization, but it is a blunt instrument for small dose differences and belongs alongside DQE, exposure index, and reject analysis, not instead of them.
Breastfeeding Interruption After Radiopharmaceuticals
Some radiopharmaceuticals appear in breast milk and can deliver an ingestion dose to a nursing infant. Interruption recommendations are chosen to keep the infant's effective dose below about 1 mSv, following NRC Regulatory Guide 8.39 and ICRP Publication 106, with radionuclide-specific periods ranging from none to complete cessation for I-131 sodium iodide.
Cumulative Patient Radiation Dose Tracking
Patients who undergo many imaging studies can accumulate a cumulative effective dose above 100 mSv, the level at which the IAEA-convened study of recurrent imaging says organ doses are typically in a range at which radiation effects are of concern. There is no regulatory dose limit for patients, so tracking, justification, and optimization — not a hard cap — are the tools. This is what cumulative dose means, how to compute it, and how to build a program around it.
Gamma Camera Testing with NEMA NU-1
NEMA NU 1 defines how gamma camera performance is measured and reported, from intrinsic spatial resolution and energy resolution to flood-field uniformity, sensitivity, count-rate behavior, and SPECT center of rotation. Understanding these parameters lets a medical physicist separate acceptance testing from routine QC and catch detector drift before it reaches patients.
Digital Breast Tomosynthesis (DBT) QC
Digital breast tomosynthesis (DBT) adds limited-angle acquisition and slice reconstruction to mammography, and with it a layer of tomosynthesis-specific QC. This guide covers DBT acceptance testing, reconstructed in-plane and z-axis resolution, artifact spread, AEC reproducibility in tomo mode, average glandular dose for tomo and combo acquisitions, and how it all maps onto MQSA and the manufacturer's QC manual.
RPT Shielding for Lu-177, Ra-223, and Ac-225
RPT shielding is a radionuclide- and workflow-specific radiation safety review. Lu-177, Ra-223, and Ac-225 differ in photon emissions, contamination pathways, waste handling, patient workflow, and shielding needs, so each therapy program needs its own source-term, occupancy, and operational-control assessment.
Diagnostic Reference Levels: A Practical Guide
Diagnostic reference levels (DRLs) are benchmark dose values used to flag imaging protocols that deliver unusually high or low radiation dose for a given exam. This guide explains how DRLs and achievable doses are derived from survey data, how to compare a facility's median dose to national benchmarks, and how to use DRLs as the first step in dose optimization rather than as patient dose limits.
PET/CT ACR Accreditation Phantom QC
The ACR PET phantom is the accreditation test that proves a PET/CT scanner recovers accurate SUV and resolves small structures. It measures background SUV near 1.0, hot-cylinder contrast recovery, and cold-rod visibility so a laboratory can defend that its quantitative reads mean what they claim across scanners and over time.
Airborne Radioactivity Areas and Ventilation
An airborne radioactivity area is a regulatory designation with a precise definition tied to the derived air concentration and DAC-hours. Managing it is mostly an engineering-controls problem: ventilation, fume hoods, and negative pressure keep airborne concentrations and internal dose ALARA, with posting, air sampling, and bioassay closing the loop.
Low-Dose CT Lung Cancer Screening: Dose & QC
Low-dose CT lung cancer screening balances a very low radiation dose against the noise budget needed to find small nodules. The ACR CT Accreditation Program and CMS cap CTDIvol at 3.0 mGy for a standard-sized patient, and a defensible screening protocol pairs that dose ceiling with tube-current modulation, reconstruction, and QC that hold image quality steady across body sizes.
NRC Part 35 Recordkeeping Requirements
A compliant medical-use radiation safety program is only as good as its records. This guide maps the 10 CFR Part 35 Subpart L recordkeeping requirements — which record each activity generates, the exact retention period, and the Part 20 cross-references — so RSOs and nuclear medicine departments can build a records system that survives an NRC or Agreement State inspection.
Gamma Camera Energy Resolution & Photopeak QC
A gamma camera's energy resolution and photopeak calibration decide how well it separates true photopeak events from scatter. Energy resolution is the full width at half maximum of the photopeak expressed as a percentage of the photon energy — typically 9–10% for Tc-99m — and it drives the energy window that controls contrast, count rate, and uniformity.
GI Bleeding Scintigraphy: Tc-99m RBC Imaging
Technetium-99m labeled red blood cell scintigraphy detects and localizes active gastrointestinal bleeding at rates far lower than catheter angiography can, and its ability to image intermittently over hours is a real physical advantage. Getting it right depends on red blood cell labeling efficiency, continuous dynamic (cine) acquisition, and disciplined interpretation — supported by SPECT/CT when localization is uncertain.
DXA Bone Densitometry QC: Precision and LSC
A DXA scanner only produces clinically useful bone mineral density when its calibration is stable and its precision is known. Daily phantom scans track calibration drift, an in-house precision study converts measurement noise into a least significant change, and only changes larger than the LSC should be called real. This guide walks through the physics, the math, and the ISCD/ACR rules that make serial DXA defensible.
Radiation Area Posting and Labeling Rules
Radiation area posting and labeling under 10 CFR Part 20 Subpart J is one of the most frequently cited—and most fixable—areas of radiation safety. This guide explains the dose-rate thresholds that define radiation, high radiation, and very high radiation areas, the exact sign wording required, container labeling rules, and how to classify an area from a survey measurement using inverse-square geometry.
Shipping Radioactive Material: DOT 49 CFR
Shipping and receiving radioactive material is governed by DOT 49 CFR Parts 171–173, NRC 10 CFR Part 71, and the IATA Dangerous Goods Regulations for air. This guide explains package types, White-I/Yellow-II/Yellow-III labeling, the Transport Index, surface dose-rate and contamination limits, hazmat training, and the receiving survey under 10 CFR 20.1906.
Cu-64 DOTATATE PET/CT for Neuroendocrine Tumors
Copper-64 DOTATATE (Detectnet) is an FDA-approved somatostatin-receptor PET agent for neuroendocrine tumors. Its 12.7-hour half-life allows centralized production and unit-dose distribution, while its low positron energy gives F-18-like spatial resolution — a different physics profile from generator-produced Ga-68 DOTATATE that changes logistics, image quality, and QC.
Mobile Radiography Radiation Safety
Distance is the dominant control in mobile radiography. Because scatter falls with the square of distance, stepping from 1 meter to 2 meters cuts staff dose to roughly one quarter — which is why the 2-meter rule anchors bedside, ICU, OR, and NICU practice. This guide covers scatter geometry, shielding, technique and AEC limits on portable units, exposure-index QC, pediatric considerations, and the FDA-plus-state regulatory framework that governs X-ray machines.
Fluoroscopy Peak Skin Dose & SRDL Monitoring
Peak skin dose is the dose quantity that predicts radiation-induced skin injury in fluoroscopically guided interventions. Reference air kerma and kerma-area product are the practical surrogates displayed on the console, but they are not the same as skin dose. A defensible program uses NCRP 168 substantial-radiation-dose-level triggers, documents dose metrics, and follows up high-dose cases.
Public Dose Limits Under 10 CFR Part 20
The NRC caps radiation dose to individual members of the public at 1 mSv (100 mrem) per year and 0.02 mSv in any one hour in an unrestricted area. Meeting those limits is not enough — a licensee must be able to demonstrate compliance through surveys, calculations, or effluent monitoring, and design shielding and controls to a stricter ALARA goal. This guide explains the limits, the definitions behind them, and how to prove compliance.
PET Partial Volume Effect & Recovery Coefficients
The partial volume effect is the systematic blurring-driven bias that makes small lesions on PET look less intense than they truly are. Because of finite scanner resolution, activity spills out of small objects and background spills in, so SUV is underestimated for structures smaller than roughly two to three times the system resolution. Recovery coefficients quantify and correct that bias — and understanding them is essential to defensible quantitative PET.
Cardiac CT Dose Optimization: Coronary CTA
Coronary CT angiography once delivered 12 mSv or more, but prospective ECG-triggering, tube voltage reduction, ECG-based current modulation, high-pitch acquisition, and iterative or deep-learning reconstruction now bring most studies to a few millisieverts — often below 1 mSv — without sacrificing diagnostic accuracy. Getting there means matching acquisition mode to heart rate and rhythm, right-sizing tube parameters, and verifying dose against benchmarks.
PET Occupational Dose: Managing 511 keV
PET staff dose is a 511 keV problem. F-18 delivers roughly seven times the dose rate per unit activity of Tc-99m, so the same handling habits that keep a general nuclear medicine technologist safe are not enough in PET. This guide covers the physics of 511 keV exposure, extremity and whole-body dose data, shielding, and the ALARA controls that keep PET staff within limits.
Joint Commission Diagnostic Imaging Requirements
The Joint Commission's diagnostic imaging requirements are the accreditation backbone that most hospitals actually operate under. They govern CT radiation-dose recording, fluoroscopy dose review and the 15 Gy sentinel-event threshold, MRI safety and access control, and the annual imaging-equipment evaluation by a qualified medical physicist. This guide maps the requirements to a defensible compliance program.
Brain FDG-PET for Dementia and Epilepsy
Brain FDG-PET maps regional glucose metabolism to support the differential diagnosis of dementia and the presurgical localization of epilepsy. Patient preparation, a resting uptake environment, consistent reconstruction, and semiquantitative analysis against a normal database all shape whether the metabolic pattern is read correctly.
Fetal Dose in Medical Imaging: Thresholds
Fetal (conceptus) dose is the radiation dose absorbed by the developing embryo or fetus during a maternal imaging exam. Below roughly 50 mGy there is no measurable increase in malformation or pregnancy-loss risk, and most diagnostic exams fall far below that level—so an informed dose estimate, not reflexive avoidance or termination, should drive patient management.
PET Randoms, Dead Time, and NECR
PET count-rate performance is a balance of physics working against each other: true coincidences build the image, random coincidences grow with the square of activity, and dead time throws away counts when the detectors are busiest. The Noise-Equivalent Count Rate (NECR) folds all three into one figure of merit. This guide explains randoms, dead time, and NECR, and why more injected activity is not always more signal.
Mammography QC and MQSA: Annual Survey
Mammography QC under MQSA is a layered program: daily-to-annual technologist tasks plus an annual medical physicist survey of dose, image quality, AEC, kVp, HVL, and artifacts. Each unit must stay accredited, FDA-certified, and within the mean glandular dose limit.
ALI, DAC & Internal Dose Limits (10 CFR 20)
Internal radiation dose limits are hard to apply directly, so 10 CFR 20 converts them into two practical quantities: the annual limit on intake (ALI) and the derived air concentration (DAC). This guide explains how ALI and DAC are defined in Appendix B, how DAC-hours track intake against the occupational dose limit, when individual monitoring is required, and how the SUM of internal and external dose forms the total effective dose equivalent.
NRC Inspection Prep: An RSO Checklist
NRC and Agreement-State inspectors review the entire 10 CFR Part 35 program — credentials, dosimetry, QC records, sealed-source inventory, surveys, and written directives — not just individual procedures. This guide walks RSOs and program managers through every inspection element, from document binder preparation to corrective-action responses, so the program is ready before the inspector arrives.
FDG PET/CT for Infection and Inflammation
FDG is not just an oncology tracer. Activated leukocytes and macrophages are avid glucose consumers, so FDG PET/CT has become the method of choice for a wide range of infectious and inflammatory disorders — from prosthetic valve endocarditis to cardiac sarcoidosis to fever of unknown origin. But the study only works when patient preparation, uptake time, quantification, and interpretation pitfalls are handled with the same rigor a physicist brings to any quantitative PET exam.
CT Brain Perfusion: Radiation Dose Optimization
CT brain perfusion (CTP) is a dynamic, same-slab acquisition that repeatedly irradiates a fixed volume to build cerebral blood flow, volume, and mean-transit-time maps. Because the tissue is scanned dozens of times, cumulative skin and lens dose can approach deterministic thresholds unless tube voltage, tube current, sampling interval, and total scan duration are chosen deliberately and monitored against dose-notification limits.
Size-Specific Dose Estimate (SSDE) in CT
SSDE corrects the scanner-reported CTDIvol for patient size, giving a far better estimate of the dose actually delivered. This guide explains the AAPM Report 204 and 220 methods, water-equivalent diameter, conversion factors, a worked example, and how to use SSDE in CT protocol management and accreditation.
NESHAP Air Emissions: Do Medical Sites Comply?
The blunt answer for most medical facilities is that EPA's NESHAP Subpart I for radionuclide air emissions no longer applies to you. EPA rescinded it for NRC and Agreement State licensees in 1996 after finding the NRC program provides an ample margin of safety. What actually binds a medical facility's air emissions is the NRC 10 CFR 20.1101(d) 10 mrem/yr constraint and the 100 mrem/yr public dose limit — this article explains who owes what.
SPECT/CT Attenuation Correction Explained
SPECT/CT attenuation correction uses the co-acquired CT to build a patient-specific map of photon attenuation, scale it to the emission energy, and recover the counts lost to absorption inside the body. It is essential for quantitative SPECT and for artifact-free cardiac and bone imaging, but it introduces its own failure modes — misregistration, truncation, and metal artifacts — that a medical physicist has to detect and control.
MRI Geometric Distortion: Sources and QC
MRI geometric distortion is spatial misregistration of anatomy caused by gradient nonlinearity, main-field inhomogeneity, and object-induced susceptibility and chemical-shift effects. A QC program that separates system distortion from sequence and patient distortion keeps MRI geometrically accurate for accreditation, quantification, and MR-guided treatment.
Electronic Personal Dosimeters (EPDs)
Electronic personal dosimeters give staff a real-time dose and dose-rate readout with audible alarms, making them powerful ALARA and eye-lens tools in interventional and nuclear medicine settings. But an EPD is not automatically the legal dose of record, it can misbehave in pulsed fluoroscopic fields, and it complements rather than replaces accredited passive dosimetry. This guide explains the physics, the standards, and how to deploy EPDs correctly.
The Radiation Safety Committee Explained
The Radiation Safety Committee is the governance body that holds a medical radioactive-material program accountable. Required for licensees with multiple types of medical use, it brings authorized users, the RSO, nursing, and management to one table to oversee ALARA, dose trends, new uses, and program changes — turning radiation safety from one person's job into an institutional commitment.
Ga-68 PSMA PET/CT: Physics, SUV, and QC
Ga-68 PSMA PET/CT images prostate cancer by targeting prostate-specific membrane antigen. Its physics — a 68-minute half-life, high-energy positrons, and on-site generator production — drives the imaging workflow, the SUV quantification chain, and the radiopharmaceutical and scanner quality control a defensible program must document.
Nationally Tracked Sources and the NSTS
The National Source Tracking System is the NRC's cradle-to-grave ledger for the most dangerous sealed sources — Category 1 and Category 2 quantities of radioactive material. This guide explains what makes a source nationally tracked, the close-of-next-business-day transaction reporting on NRC Form 748, the annual inventory reconciliation, and how NSTS tracking differs from 10 CFR Part 37 security and its aggregation rule.
Ga-68 DOTATATE PET/CT for Neuroendocrine Tumors
Ga-68 DOTATATE PET/CT maps somatostatin-receptor expression to detect and stage neuroendocrine tumors and select patients for Lu-177 DOTATATE therapy, and its Ga-68 physics, SUV calibration, and Krenning-score reporting decide whether the result can be trusted.
Stereotactic Breast Biopsy QC
Stereotactic breast biopsy places a needle at a mammographically detected target using paired angled projections to compute depth. A quality-control program built around a localization-accuracy test — verifying the device reaches the target within about a millimeter — plus image quality, dose, and mechanical checks is what keeps the procedure both accurate and low-dose.
DR Exposure Index (EI) and Deviation Index
The exposure index is not a patient dose. Under IEC 62494, the exposure index (EI) estimates detector air kerma, the target exposure index (EIT) defines the intended operating point, and the deviation index (DI) reports how far each exposure landed from target. Used correctly, the EI/EIT/DI triad is a feedback tool for ALARA and repeat-rate reduction — not a dose metric.
F-18 Flurpiridaz Cardiac PET Perfusion Imaging
Flurpiridaz F-18 is the first fluorine-18 PET myocardial perfusion tracer approved in the United States. Its 110-minute half-life allows unit-dose delivery from a regional PET pharmacy and true exercise stress, while its low positron energy sharpens image quality and supports absolute myocardial blood flow quantification. This guide explains the physics, the phase 3 evidence, dosimetry, and the QC and regulatory context for adopting it.
Occupational Dose Records & NRC Form 5
Occupational radiation dose recordkeeping is where many otherwise-strong radiation safety programs get cited. The rules live in 10 CFR 20 Subparts L and M: what you record on NRC Form 5, how long you keep it, when you must report to the NRC, and when you must report to the worker. This guide organizes the recordkeeping and reporting requirements, the retention periods, and the dose quantities that make up a defensible occupational dose record.
Breast MRI QC and ACR Accreditation
Breast MRI accreditation rests on two linked image streams: phantom QC that proves the scanner is stable, and clinical images that prove the protocol resolves and enhances small lesions. This guide walks through the ACR Breast MRI Accreditation Program, the weekly and annual QC tests, the physics of SNR, uniformity, and fat suppression, and how a qualified medical physicist keeps a program defensible.
Written Directives in Nuclear Medicine
A written directive is the dated, signed order an authorized user must complete before certain radiopharmaceutical therapies and I-131 administrations. This guide explains 10 CFR 35.40 and 35.41: when a directive is required, what it must contain, the oral-directive 48-hour rule, the verification procedures, and how directives prevent medical events.
V/Q Lung Scintigraphy: Physics & Dosimetry
Ventilation–perfusion (V/Q) lung scintigraphy is built on a deliberate physics trade-off: Tc-99m macroaggregated albumin transiently occludes a tiny fraction of the pulmonary microvasculature to map perfusion, while Xe-133 gas, Tc-99m DTPA aerosol, or Technegas maps ventilation. This guide covers the particle-number safety margin, radiopharmaceutical physics and dosimetry, Xe-133 room-ventilation controls, and why V/P SPECT outperforms planar imaging.
SMPTE Pattern Monitor QC for Radiology
How to evaluate the SMPTE test pattern for diagnostic monitor QC, satisfy ACR CT Quality Control requirements, and protect accurate image interpretation.
Radiation Protection for Fluoroscopy Staff
Interventional and cath-lab staff work beside a patient who becomes the dominant source of scattered radiation, and they accumulate some of the highest occupational doses in medicine. Protecting them is a physics problem — scatter geometry, inverse-square distance, lead attenuation — layered onto a regulatory framework in which the eye-lens dose limit is actively diverging between the NRC and international bodies.
I-131 MIBG Therapy: Physics and Safety
I-131 metaiodobenzylguanidine (MIBG) delivers targeted beta radiation to norepinephrine-transporter-expressing tumors — pheochromocytoma, paraganglioma, and neuroblastoma. This guide explains the nuclear-medicine physics: I-131 decay, why thyroid blockade is mandatory, bone marrow as the dose-limiting organ, MIRD-based dosimetry, the FDA-approved high-specific-activity product Azedra, and the NRC patient-release framework under 10 CFR 35.75 and Regulatory Guide 8.39.
ACR CT Accreditation Phantom QC
The ACR CT accreditation phantom packs CT-number accuracy, low-contrast resolution, uniformity, and high-contrast resolution into four modules. Passing it means measuring contrast-to-noise ratio, HU accuracy, and uniformity against the ACR CT Quality Control Manual criteria, at a CTDIvol below the ACR reference limits.
Radioactive Package Receipt and Wipe Testing
Every radioactive material package arriving at a medical facility must be monitored for external radiation and surface contamination on a defined schedule. A wipe test converts a count-rate reading into removable activity per unit area, which is compared against DOT and NRC limits. This guide explains the survey procedure, the wipe-test math, the action levels, and the records that keep package receipt defensible.
PET Uptake Time: Why It Affects SUV and Quality
A PhysicsPulse guide to PET uptake time, why the injection-to-scan interval governs SUV accuracy, lesion contrast, and reproducible follow-up imaging.
Doppler Ultrasound QC: Flow and Velocity Testing
Doppler quality control is the part of an ultrasound QC program that checks the flow measurement chain, not just the grayscale image. Velocity accuracy, Doppler sensitivity and penetration, sample-volume registration, and clutter-filter behavior each fail differently, and each needs a test device—flow phantom, string phantom, or moving target—plus a documented baseline and action level tied to ACR and AIUM accreditation expectations.
Decay-in-Storage of Radioactive Waste (35.92)
Decay-in-storage (DIS) is the most practical disposal pathway for short-lived medical radioactive waste. Under 10 CFR 35.92 a licensee may hold byproduct material with a half-life of 120 days or less until a surface survey with a suitable meter on its most sensitive scale, no interposed shielding, cannot distinguish it from background — then dispose of it as ordinary trash after removing all radiation labels.
C-11 PET Radiopharmaceuticals: Physics and Use
Carbon-11 is a positron emitter with a ~20.4-minute half-life, which makes it one of the most demanding radionuclides in clinical PET. That single number forces an on-site cyclotron, batch synthesis with decay during production and QC, no shipping, and dose-on-demand scheduling. This guide covers C-11 nuclear and positron physics, production via the 14N(p,α)11C reaction, the main tracers (C-11 choline, acetate, methionine, and PiB), quality control under USP and cGMP, decay-correction math, and the radiation-safety implications of a rapid-decay positron emitter.
Mammography Compression QC: Force and Dose
Mammographic compression is a quality-control parameter, not just a comfort setting. Compression force, paddle behavior, and compressed-breast-thickness accuracy directly change mean glandular dose, image sharpness, and dose reproducibility. This guide explains the physics of force versus pressure, what MQSA and the ACR require, and how a defensible compression QC program is built and documented.
F-18 PSMA PET/CT: Piflufolastat Imaging
Fluorine-18–labeled PSMA agents such as piflufolastat F-18 and flotufolastat F-18 pair the well-behaved physics of fluorine-18 — a 110-minute half-life and a short positron range — with prostate-specific membrane antigen targeting. The longer half-life enables unit-dose distribution without an on-site generator, and the low positron energy supports near scanner-limited spatial resolution, which together shape logistics, image quality, and quantitative QC differently from gallium-68 PSMA-11.
Radioactive Material Spill Response Procedures
A radioactive material spill is a time-sensitive contamination event, and the response depends on whether it is classified as minor or major. This guide explains the major-versus-minor spill criteria, the NRC spill-kit and step-by-step response, decontamination and survey verification, removable-contamination action levels, and the reporting and program requirements an RSO must build in advance.
Holmium-166 Radioembolization Physics
Holmium-166 microsphere radioembolization pairs a therapeutic beta emitter with an imageable gamma line and paramagnetic behavior, so the same particle that treats the tumor can be quantified by SPECT, CT, and MRI. This guide covers Ho-166 decay physics, the scout-dose work-up, personalized dosimetry targets, imaging quantification, and how it differs from Y-90.
Pediatric Fluoroscopy Dose Optimization
Children are more radiosensitive and have longer lifetimes for effects to appear, so pediatric fluoroscopy dose optimization is a distinct discipline. Low pulse rates, last-image-hold, tight collimation, grid removal, and air-gap magnification are the levers that cut dose without losing the diagnostic information the study exists to provide.
Cardiac CT Temporal Resolution and Motion
Temporal resolution is the shutter speed of cardiac CT. It is set by gantry rotation time, the reconstruction geometry (half-scan, dual-source, or multi-segment), and heart rate, and it determines how much coronary motion blur survives in a coronary CT angiogram. This guide explains the physics, the numbers, and how a medical physicist evaluates and optimizes it.
Nuclear Medicine Hot Lab Design and Safety
The hot lab is where nuclear medicine radiation safety is won or lost. A defensible design sizes shielding, workflow zoning, contamination control, and instrumentation to the actual radionuclides handled — Tc-99m, F-18, I-131, and Lu-177 each pose different external-dose and contamination problems — and verifies the built room with a post-construction survey.
Digital Radiography Lag and Ghosting QC
Lag and ghosting are the two temporal artifacts of a flat-panel digital radiography detector: lag is residual signal carried from a prior exposure, while ghosting is a change in detector sensitivity from exposure history. They arise from charge trapping in amorphous-silicon and selenium receptors and scintillator afterglow, and left unchecked they can mimic or mask anatomy. This guide explains the physics, the measurement methods, and how AAPM TG-150/TG-151 acceptance and ongoing QC keep them under control.
Radium-223 (Xofigo) Therapy: Physics & Safety
Radium-223 dichloride (Xofigo) is a calcium-mimetic, bone-seeking alpha emitter used to treat symptomatic bone metastases in castration-resistant prostate cancer. Its physics — a short-range, high-LET alpha cascade with very low photon yield — makes contamination control, accurate activity measurement, and correct written-directive and patient-release handling the central radiation-safety tasks, not structural shielding.
Computed Radiography Imaging Plate QC
Computed radiography turns a reusable storage-phosphor plate into a digital image, but the same reusability that makes CR economical also lets plate defects, incomplete erasure, and exposure drift accumulate silently. A disciplined QC program — grounded in AAPM Task Group 10, the IEC exposure index, and deviation-index monitoring — catches those problems before they reach a diagnostic image.
NRC Medical-Use License Amendments
A radioactive material license is a living document. Adding an authorized user, a new radionuclide, a new room, or a higher possession limit can require a license amendment before the change—while other changes need only a notification. This article maps 10 CFR 35.13 against 35.14, works a possession-limit example, and shows how to keep a medical-use license current and defensible.
MRI Diffusion ADC Quantitative QC
The apparent diffusion coefficient (ADC) is only a biomarker if it is reproducible. A quantitative DWI QC program uses a temperature-controlled diffusion phantom, fixed b-values, and QIBA bias and repeatability tolerances to prove an ADC number means the same thing across scanners, sites, and time.
Dosage Determination Under 10 CFR 35.63
Before any unsealed radiopharmaceutical is administered, 10 CFR 35.63 requires the licensee to determine and record its activity — by direct measurement in a calibrated dose calibrator or by decay correction from a licensed preparer — and generally to keep it within 20% of the prescribed dosage. This short, deceptively simple regulation is where dose-calibrator QC, recordkeeping, written directives, and medical-event avoidance all converge.
Radioactive Seed Localization Radiation Safety
Radioactive seed localization (RSL) implants a small I-125 sealed source into a non-palpable breast lesion so a surgeon can find and excise it with a gamma probe. It is a low-dose, well-tolerated alternative to wire localization, but it is a use of licensed radioactive material: it requires an NRC or Agreement State license under 10 CFR 35.1000, authorized-user training, written directives, seed accountability from receipt through pathology, and a robust lost-seed procedure.
CT Dose Check: Notification & Alert Values
CT Dose Check is a scanner safety feature, defined by NEMA XR-25 and embedded in NEMA XR-29 (MITA Smart Dose), that warns operators before a planned scan exceeds a preset CTDIvol or DLP. Notification values catch single high-dose series, alert values catch potentially serious cumulative exposures, and both work best when a medical physicist sets them to match local protocols rather than leaving factory defaults in place.
FAPI PET Imaging: Ga-68 and F-18 Physics
FAPI PET targets fibroblast activation protein on cancer-associated fibroblasts rather than glucose metabolism, so it images tumors with high contrast, no fasting, and low background in brain, liver, and the GI tract. The physics differs by radionuclide: Ga-68 is generator-based, F-18 gives sharper resolution and batch distribution, and a shared DOTA chelator opens a theranostic path.
Radiation Dose Quantities & Units Explained
Absorbed dose, equivalent dose, and effective dose answer different questions, use different weighting factors, and are easy to confuse. This guide defines each quantity and its SI unit, works the ICRP 103 math, explains the operational quantities used in monitoring, and clarifies why the NRC's 10 CFR Part 20 quantities differ from the current ICRP recommendations.
Double Dosimetry: Effective Dose for IR Staff
A single badge cannot capture effective dose for a partially shielded interventional worker: worn over the apron it overestimates, worn under it underestimates. Double dosimetry uses one collar badge and one under-apron badge, then combines the two readings with a validated algorithm to estimate effective dose and satisfy occupational dose limits.
MRI Gradient and Eddy-Current QC
The gradient system encodes MRI spatial information, so a miscalibrated or poorly compensated gradient distorts geometry and biases quantitative values like the ADC. This guide explains gradient calibration, gradient nonlinearity, and eddy-current compensation, the QC tests that detect problems in each, and why the ACR phantom is only part of the picture.
Quantitative Myocardial Blood Flow with Cardiac PET
Quantitative myocardial blood flow adds absolute, per-gram perfusion numbers to the relative pictures of cardiac PET. By acquiring a dynamic scan, sampling the arterial input, and fitting a kinetic model, the physicist and physician recover rest and stress flow in mL/min/g and their ratio, myocardial flow reserve. Done rigorously, it uncovers balanced multivessel disease and microvascular dysfunction that relative perfusion alone can miss, but only if tracer physics, dynamic acquisition, and model fitting are controlled.
ALARA Investigational Levels for Occupational Dose
Investigational Levels I and II are the ALARA action thresholds a radiation safety program sets below the regulatory occupational dose limits, so a rising dose triggers review long before anyone approaches a legal limit. This guide explains the two-tier concept, how licensees typically derive quarterly values as fractions of the 10 CFR 20.1201 limits, who reviews what, and how to document the program under NRC Regulatory Guide 8.10 — with a worked calculation and an example table.
PET Bayesian Penalized-Likelihood Reconstruction
Bayesian penalized-likelihood (BPL) reconstruction — GE's Q.Clear — lets PET images fully converge while a penalty term controls noise, improving contrast recovery, small-lesion detectability, and SUV accuracy over early-stopped OSEM. This guide explains the relative difference prior, the beta and gamma parameters, how to choose beta, and why EARL harmonization and consistent settings matter for quantitative reads.
Automatic Exposure Control in Radiography QC
Automatic exposure control terminates a radiographic exposure when the detector has received enough radiation for a diagnostic image. AEC quality control links a regulatory reproducibility requirement, detector-tracking performance, and the digital exposure index so that consistent image quality is delivered at the lowest reasonable dose across patient size, kVp, and field configuration.
Medical Event Reporting: 10 CFR 35.3045
A medical event is not the same as patient harm — it is a regulatory definition. Under 10 CFR 35.3045, specific dose and percentage thresholds, wrong-patient or wrong-radiopharmaceutical administrations, and leaking sources trigger mandatory notification of the NRC, the referring physician, and the patient on a strict timeline. Knowing the thresholds and building a written-directive workflow that prevents them is core RSO work.
Y-90 Radioembolization Dosimetry Methods
Y-90 radioembolization (SIRT) treats liver tumors with millions of beta-emitting microspheres. This guide explains the decay physics, the three dosimetry methods (BSA, MIRD mono-compartment, and partition model), Tc-99m-MAA mapping and lung shunt limits, and the radiation-safety and regulatory framework under 10 CFR 35.1000.
The MIRD Schema for Internal Dosimetry
The MIRD schema is the standardized framework nuclear medicine uses to estimate the radiation absorbed dose delivered to organs and tissues by internally administered radiopharmaceuticals. At its core, absorbed dose equals time-integrated activity multiplied by a radionuclide- and geometry-specific S value. This guide explains the equations, the biokinetic and physical inputs, the software, and how the schema supports modern theranostics dosimetry.
Mobile C-arm Fluoroscopy QC and Radiation Safety
Mobile C-arms move between operating rooms and rarely get the same physics scrutiny as fixed fluoroscopy, yet they operate close to staff and can deliver high skin dose. This guide covers the QC tests, dose-rate limits, image-quality checks, dose-display verification, and OR scatter-protection practices that keep a mobile C-arm program safe and defensible.
Cabinet X-ray & Specimen Radiography Safety
Cabinet x-ray systems — including the intraoperative specimen radiography units used in breast-conserving surgery — are self-shielded, interlocked enclosures held to FDA's 21 CFR 1020.40 performance standard. A defensible program pairs the federal leakage, interlock, and warning-signal requirements with state radiation-machine registration and routine radiation surveys.
Dental Intraoral & Panoramic Radiography QC
Dental radiography is the highest-volume X-ray procedure in the country, yet its quality control is often the least formalized. Intraoral and panoramic units still need documented beam-quality, collimation, exposure-reproducibility, and receptor checks, and the current framework — NCRP Report No. 177, FDA performance standards, and state rules — sets the tolerances a defensible dental QC program has to meet.
Fluoroscopy Spatial Resolution & Low-Contrast QC
Fluoroscopy image-quality QC pairs two measurements: limiting high-contrast spatial resolution, tested with a line-pair pattern, and low-contrast detectability, tested with a contrast-detail phantom. Neither number means anything without the dose rate that produced it, so a defensible fluoroscopy survey trends resolution, contrast, and air kerma rate together against a documented baseline.
Patient Release After Radiopharmaceutical Therapy
Patient release after radiopharmaceutical therapy is governed by a dose-based limit, not an activity cutoff. This guide explains the 10 CFR 35.75 5 mSv (0.5 rem) release criterion, the three NUREG-1556 / Reg Guide 8.39 methods of demonstrating compliance, the patient-specific dose calculation with effective half-life and an occupancy factor, the 1 mSv written-instruction trigger, and the records you must keep — with a worked I-131 example.
Gallium-67 Citrate Imaging: Physics and QC
Gallium-67 citrate is a classic multi-photopeak SPECT agent whose physics still teaches the fundamentals: a four-line electron-capture emitter that demands a medium-energy collimator, a triple energy-window acquisition, and 48-to-72-hour imaging. This guide covers Ga-67 decay data, collimator and window selection, dosimetry, protocol design, and where Ga-67 still fits now that FDG PET/CT has taken most of its indications.
Thyroid Bioassay for Radioiodine Workers
Radioiodine concentrates in the thyroid, so a worker who inhales or ingests I-131 can accumulate a meaningful committed dose to a single organ from a small intake. A thyroid bioassay — a direct measurement of radioiodine in the neck — is the primary tool for detecting and quantifying that intake. This article explains when a bioassay program is required, how measurements are timed and interpreted, and how the committed dose is derived under NRC rules.
Ultrasound Transducer QC: Dead Elements
The ultrasound transducer is the most-handled, most-damaged, and least-tested component in the imaging chain. Dropped probes, delaminated lenses, cracked cables, and dead array elements degrade the image silently, and standard B-mode phantom scanning misses most of it. A defensible transducer QC program combines physical inspection, phantom uniformity, in-air reverberation analysis, and — where available — electronic element testing, at a frequency that reflects how fast probes actually fail.
HIDA Scan and Gallbladder Ejection Fraction
Hepatobiliary scintigraphy (the HIDA scan) images bile flow with a Tc-99m iminodiacetic-acid tracer and quantifies gallbladder contraction as the gallbladder ejection fraction. Standardized sincalide infusion, morphine augmentation, and correct counting technique are what make the study reproducible and clinically decisive.
Building an ALARA Program for a Medical Facility
ALARA — keeping radiation dose as low as reasonably achievable — is a regulatory expectation, not a slogan. A defensible ALARA program defines management commitment, dose constraints, investigational levels, time-distance-shielding controls, monitoring, training, and periodic review. This guide explains how to build one that satisfies NRC or Agreement State requirements and actually reduces dose.
Antiscatter Grids: Scatter, Contrast & Dose
An antiscatter grid is a contrast-versus-dose trade: it absorbs scattered photons before they reach the detector, raising radiographic contrast, but it also attenuates some primary radiation, so technique and patient dose must rise to keep the image. Choosing grid ratio, frequency, and focusing — and knowing when to remove the grid — is a physics decision driven by patient thickness, scatter-to-primary ratio, and the imaging task.
WBC Infection Imaging: In-111 & Tc-99m HMPAO
Radiolabeled autologous white blood cell (WBC) scintigraphy remains a reference standard for imaging occult infection and inflammation. The choice between Tc-99m HMPAO and In-111 oxine is a physics and workflow decision — photon energy, half-life, labeling efficiency, image quality, and radiation burden all differ — and the labeling quality-control steps are what make the study diagnostic.
Survey Meter Calibration Programs
A survey instrument is only as trustworthy as its calibration. A defensible program covers full calibration before first use, annually, and after repair; routine constancy and operational checks between calibrations; NIST-traceable standards; and documentation that survives an inspection. This guide explains the regulatory basis, the math, and how to build the program.
PET/CT Daily QC and Scanner Calibration
PET/CT is a quantitative imaging modality, so its quality control program has to protect both image quality and the numerical accuracy of the SUV. This means layering daily detector and CT checks, periodic normalization and uniformity tests, and a scanner-to-dose-calibrator cross-calibration that ties measured activity concentration back to a traceable standard — all documented to meet ACR, NEMA, and accreditation expectations.
Radiographic Beam Alignment & Collimation QC
Beam alignment and collimation QC confirm that the light field, the x-ray field, and the image receptor agree. When they drift apart, patients receive dose to tissue that is never imaged, edges of anatomy get clipped, and repeat exposures climb. This guide covers the 21 CFR 1020.31 congruence tolerance, the test-tool method, and how a physicist documents it.
Syringe and Vial Shielding in Nuclear Medicine
Syringe and vial shields are the front line of extremity and whole-body dose control in nuclear medicine. Because attenuation is energy-specific, a 2 mm tungsten shield that is more than adequate for Tc-99m barely dents F-18's 511 keV photons, which need 5 to 8 mm of tungsten. Choosing the right material and thickness, and understanding where shields help the fingertips least, is core radiation-safety physics for any hot lab.
DaTscan (I-123 Ioflupane) SPECT Imaging
DaTscan (I-123 ioflupane) SPECT visualizes striatal dopamine transporter density to separate neurodegenerative parkinsonism from essential tremor and other non-degenerative causes. Getting it right depends on correct thyroid blocking, careful acquisition, gamma-camera QC, and a sound understanding of semiquantitative striatal binding ratios. This guide covers the physics, protocol, and clinical interpretation.
Y-90 Bremsstrahlung SPECT/CT Imaging & Dosimetry
Yttrium-90 is a nearly pure beta emitter, so post-radioembolization imaging relies on the faint bremsstrahlung X-rays produced as those betas slow down. This guide explains why bremsstrahlung SPECT/CT is hard, how to choose the energy window and collimator, how quantitative correction enables post-therapy dosimetry, and how it compares to Y-90 PET.
Fluoroscopy QC and FDA Dose-Rate Limits
The annual fluoroscopy physics survey verifies that a fluoroscope's air kerma rate stays within the FDA federal limits, that automatic exposure rate control and high-level control behave correctly, that the displayed dose values are accurate, and that image quality is adequate. It combines a regulatory output-rate check with image-quality and dose-management evaluation.
MRI Fat Suppression and Chemical Shift QC
Fat suppression and chemical shift are two faces of the same 3.5-ppm fat-water frequency difference. This guide explains the physics of CHESS, SPAIR, SPIR, STIR, Dixon, and water excitation, the chemical-shift misregistration artifact, worked frequency and inversion-time math, and how a medical physicist keeps fat suppression uniform and defensible during MRI accreditation.
High Radiation Area Access Controls
A high radiation area is not just a posting problem — it triggers engineered access controls under 10 CFR 20.1601, and a very high radiation area demands additional measures under 20.1602. This guide covers the exact dose thresholds, the control options a licensee may choose, where these areas arise in medical facilities, and how the RSO documents compliance.
MRI SAR and RF Safety: Limits and Monitoring
Specific absorption rate (SAR) is how MRI quantifies the risk of radiofrequency tissue heating. This guide explains what SAR means, the IEC 60601-2-33 operating-mode limits and temperature basis behind it, how the FDA significant-risk thresholds relate, why B1+rms matters for implants, and how a medical physicist verifies RF safety during acceptance and annual testing.
Tc-99m PYP Cardiac Amyloidosis Imaging
Technetium-99m pyrophosphate (PYP) scintigraphy noninvasively diagnoses transthyretin cardiac amyloidosis (ATTR-CM). A reliable study depends on standardized acquisition, mandatory SPECT to separate myocardial retention from blood pool, the heart-to-contralateral (H/CL) ratio and Perugini grade for interpretation, and exclusion of light-chain amyloidosis — each a place where physics and protocol discipline decide whether the result can be trusted.
MRI Relaxometry: T1/T2 Mapping Phantom QC
Quantitative T1 and T2 mapping turns MRI signal into physical relaxation times, but the numbers drift with sequence, field strength, vendor, and temperature. A phantom-based relaxometry QC program measures bias and repeatability against reference values so mapping results are comparable across scanners and over time.
Extremity Dosimetry in Nuclear Medicine
Nuclear medicine staff receive their highest radiation doses to the fingertips while drawing, dispensing, and injecting radiopharmaceuticals. This guide covers the extremity dose limit, ring-badge monitoring and placement, why ring dosimeters underestimate fingertip dose, and the practical controls that keep hands ALARA.
Rubidium-82 Cardiac PET Myocardial Perfusion
Rubidium-82 cardiac PET is a generator-based myocardial perfusion technique with a 76-second tracer, pharmacologic stress, and the ability to quantify absolute myocardial blood flow and flow reserve. Its short half-life drives fast, low-dose imaging but demands strict generator QC, daily strontium-breakthrough testing, and careful attention to timing, motion, and quantification.
MRI SNR and RF Coil Quality Control
Signal-to-noise ratio is the single most sensitive indicator of MRI receive-chain health. This guide explains how SNR is defined, the NEMA measurement methods, why the single-image background method fails under parallel imaging, and how a physicist uses SNR and coil QC to catch failing RF coils before they reach patients.
Dual-Energy Subtraction Chest Radiography
Dual-energy subtraction (DES) chest radiography acquires low- and high-kVp images and combines them to produce separate soft-tissue and bone images, suppressing overlying ribs so pulmonary nodules and other findings are easier to see. Choosing between two-shot and single-exposure detectors, managing the added dose and image noise, and verifying decomposition quality are all medical-physics decisions that determine whether DES actually improves detection.
Postmortem Radiation Safety After Radionuclide Therapy
When a patient dies soon after radiopharmaceutical therapy, the radioactivity does not stop at the door. Autopsy, embalming, burial, and cremation each create their own exposure and contamination pathways for pathologists, morticians, and the public. This is the radiation safety officer's framework for estimating residual activity, deciding what precautions apply, and closing a regulatory gap that no single U.S. rule fully covers.
CZT Cardiac SPECT: Physics and Performance
Dedicated cadmium-zinc-telluride (CZT) cardiac SPECT cameras replaced the rotating Anger head with stationary solid-state detectors purpose-built for the heart. Direct conversion sharpens energy resolution, multiplies system sensitivity several fold, and enables large reductions in acquisition time and patient dose — while opening the door to dynamic SPECT and quantitative myocardial blood flow. This guide connects the detector physics to measurable performance.
Dynamic PET and Tracer Kinetic Modeling
A standardized uptake value is one number from one time point; dynamic PET follows the tracer through blood and tissue and separates delivery from trapping. Tracer kinetic modeling turns that time course into physiological parameters such as the net influx rate Ki and the total distribution volume, using compartment models, an input function, and graphical methods like Patlak and Logan analysis. Long-axial-field-of-view scanners now make whole-body dynamic imaging and non-invasive input functions practical.
PET/CT Scatter Correction Explained
Scattered coincidences make up a third or more of the events in a modern 3D PET scan, and left uncorrected they flood the image with a low, diffuse background that destroys quantitative accuracy. Scatter correction — usually single-scatter simulation — estimates and removes that background so SUVs mean what they claim to mean.
Managing the Contaminated Patient
A radioactively contaminated patient arriving at a hospital is first a patient and only second a radiation problem. This guide explains how an RSO and medical physicist prepare the emergency department to stabilize the patient, control contamination, estimate internal intake, apply FDA-approved decorporation agents, and keep staff dose low, grounded in NCRP and IAEA guidance.
F-18 FDOPA PET: A Multi-Target Tracer
F-18 FDOPA is one of the most versatile PET tracers in clinical use — a fluorinated amino-acid analog of L-DOPA that images dopaminergic nerve terminals in parkinsonism and amino-acid transport in neuroendocrine tumors, congenital hyperinsulinism, and gliomas. Its physics, the carbidopa premedication decision, quantification methods, and dosimetry all differ by indication, so a defensible FDOPA program is really several protocols under one tracer name.
MRI B0 Homogeneity & Center Frequency QC
Static magnetic field (B0) homogeneity and center (resonant) frequency are the two quiet parameters behind nearly every MRI image quality problem a physicist is asked to troubleshoot. When B0 drifts or becomes non-uniform, fat suppression fails, spectral fat-sat swaps to water, EPI distorts, and geometric accuracy degrades. This guide explains how B0 homogeneity and center frequency are measured, what AAPM TG-325 recommends, and how to build a defensible MRI QC program around them.
Tc-99m DMSA Renal Cortical Scintigraphy
Tc-99m DMSA renal cortical scintigraphy binds to proximal tubular cells and images functioning cortex, making it the reference test for renal scarring and differential renal function. A defensible study depends on correct geometric-mean quantification with background subtraction, SPECT or pinhole imaging in children, weight-based pediatric activity, and documented dose-calibrator and radiochemical-purity QC.
Effective Dose & ICRP Tissue Weighting Factors
Effective dose is the most used and most misused quantity in radiation protection. It weights organ-level equivalent doses by ICRP 103 tissue weighting factors to produce a single whole-body index of stochastic risk. This guide explains how equivalent dose and effective dose are computed, the current tissue and radiation weighting factors, how they changed from ICRP 60, and the crucial limits on using E to estimate an individual patient's risk.
SPECT Center of Rotation: Calibration and QC
SPECT center-of-rotation (COR) calibration aligns the camera's electronic matrix with the true mechanical axis of rotation. An uncorrected COR error blurs reconstructions, creates ring or tuning-fork artifacts, and can mimic perfusion defects on cardiac SPECT. This guide covers the physics, the point-source test, NEMA NU 1-2023 and AAPM guidance, tolerances, and QC frequency.
KAP Meter Calibration & QC for Fluoroscopy
The kerma–area-product (KAP) meter is the workhorse of fluoroscopy dose monitoring, but a displayed number is only as good as its calibration. This guide explains what KAP measures, why it is distance-invariant, how calibration coefficients and beam-quality corrections are established, the ±35% displayed-dose accuracy requirement, and the QC a medical physicist performs to keep the numbers defensible.
Radiopharmacy Aseptic Technique and QC
A radiopharmacy must do two hard things at once: keep doses sterile and keep staff dose low. Aseptic technique, engineering controls, and quality control under USP <825>, <797>, and <823> hold that balance — protecting patients from microbial and endotoxin contamination while respecting the ALARA constraints unique to radioactive drugs.
Dental and CBCT Room Shielding (NCRP 177)
Dental radiography has historically needed little added structural shielding because workloads are low and beams are small. Cone-beam CT changes that assumption: higher output, isotropic scatter, and larger fields of view can push a busy operatory past the uncontrolled-area design goal. This guide walks through the NCRP 177 and NCRP 147 framework, a worked barrier estimate, and when a dental facility actually needs a shielding review.
Digital Subtraction Angiography Image Quality QC
Digital subtraction angiography (DSA) turns a small iodine signal into a diagnostic image by logarithmically subtracting a mask from contrast-filled frames. Its image quality is governed by quantum noise, mask registration, and detector performance rather than by raw dose, so a defensible QC program measures subtraction contrast, signal-to-noise, misregistration behavior, and air kerma rate together — not one in isolation.
Gastric Emptying Scintigraphy: Standard Method
Gastric emptying scintigraphy is only reliable when it is standardized. The SNMMI 3.0 solid-meal protocol fixes the meal, the imaging times of 0, 1, 2, and 4 hours, and the quantification: geometric mean of anterior and posterior counts, decay-corrected, expressed as percent gastric retention. Gastric retention above 10% at 4 hours indicates delayed emptying.
PET Normalization and Detector Efficiency
PET normalization corrects for the fact that every line of response has a slightly different intrinsic detection efficiency. Without it, a uniform source produces non-uniform images, ring and diagonal artifacts appear, and SUV is systematically wrong. This article explains direct and component-based normalization, the normalization scan, worked coefficient math, and how normalization QC protects quantitative accuracy.
Planned Special Exposures Under 10 CFR 20.1206
A planned special exposure is the narrow, tightly controlled mechanism that lets a licensee authorize a worker to exceed the annual occupational dose limits in an exceptional situation. This guide explains the 10 CFR 20.1206 dose caps, the preconditions, the prior-dose determination, and the recordkeeping and reporting that make a PSE defensible.
Brain Perfusion SPECT: HMPAO and ECD Imaging
Brain perfusion SPECT with Tc-99m HMPAO or Tc-99m ECD maps regional cerebral blood flow by trapping a lipophilic tracer in proportion to perfusion at the moment of injection. Diagnostic image quality depends on radiopharmaceutical stability, correct energy windowing and collimation, reliable center-of-rotation and uniformity QC, and attenuation and scatter correction — plus, increasingly, semiquantitative comparison to a normal database.
X-Ray Output QC: Reproducibility & Linearity
X-ray output reproducibility and linearity are two of the most fundamental radiographic QC tests. Reproducibility confirms that repeated exposures at a fixed technique deliver a consistent air kerma, and linearity confirms that air kerma per mAs stays constant as tube-current and time stations change. Both are anchored in the FDA performance standard 21 CFR 1020.31 and verified by a qualified medical physicist.
Skin Dose from Radioactive Contamination
Skin contamination is a dose problem a personnel badge never sees. When a radionuclide lands on skin, the dose that matters is the shallow-dose equivalent to the sensitive basal layer at 7 mg/cm², averaged over 10 cm², and it is dominated by beta and low-energy photon emissions that never reach a deep-dose dosimeter. This guide explains how skin dose is defined, how it is assessed with VARSKIN-class tools, the regulatory limit and averaging rules, and the practical response that keeps a spill from becoming a recordable dose.
PET/CT Respiratory Gating & Motion Management
Respiratory motion blurs PET/CT images of the lung bases and upper abdomen, lowering measured SUV and misregistering the attenuation-correction CT. This guide explains phase and amplitude gating, external-device versus data-driven signals, the count-statistics trade-off, and how motion management improves quantification and radiotherapy planning.
Diagnostic Ultrasound QC: AAPM/ACR Program
A structured ultrasound QC program protects image quality, validates transducer integrity, and satisfies ACR and AIUM accreditation requirements. This guide covers the full test set — from transducer element dropout and depth of penetration to distance-accuracy and in-air reverberation — along with test frequencies, action levels, phantom selection, and documentation practices based on AAPM TG-1 and TG-128.
The Radioactive Drug Research Committee (RDRC)
The Radioactive Drug Research Committee (RDRC) is the FDA-approved pathway under 21 CFR 361.1 for basic research with radioactive drugs without an IND. This guide explains RDRC scope, the pharmacologic and radiation dose limits for adults and minors, committee composition, subject and reporting rules, and how RDRC approval fits alongside the IRB and the facility's radioactive-material license.
Quantitative SPECT/CT: Calibration & SUV
Quantitative SPECT/CT converts reconstructed counts into an absolute activity concentration in becquerels per milliliter, unlocking SUV in SPECT and patient-specific dosimetry for radiopharmaceutical therapy. Getting there requires a traceable system calibration factor, CT-based attenuation and scatter correction, resolution recovery, partial-volume correction, and rigorous QC — because vendor algorithms can otherwise disagree by more than 100%.
CT Automatic Tube Voltage Selection (Auto-kV)
Automatic tube voltage selection (auto-kV) uses the CT topogram to pick the tube potential that delivers the required image quality at the lowest dose, exploiting the sharp rise in iodine contrast at lower kVp. It is distinct from tube-current modulation, it is powerfully effective for contrast-enhanced and angiographic tasks, and — critically — it can raise dose for the wrong task, so it needs task-aware setup and physicist oversight.
The Linear No-Threshold (LNT) Model
The linear no-threshold model assumes cancer risk rises in direct proportion to dose with no safe threshold. It is the scientific backbone of dose limits and ALARA, and recent expert reviews continue to endorse it for radiation protection while acknowledging its low-dose uncertainty.
Ra-223 Dichloride Therapy for Prostate Cancer
Radium-223 dichloride (Xofigo) is an alpha-emitting, bone-seeking therapy that prolongs survival in metastatic castration-resistant prostate cancer with symptomatic bone metastases. This guide covers alpha radiobiology, the 55 kBq/kg dosing regimen, the ERA-223 abiraterone restriction, contamination control, and the medical physicist and RSO role.
Pediatric CT Dose: Image Gently and SSDE
Children are more radiosensitive than adults and have longer life expectancy for radiation effects to express, so adult CT settings overdose them. Pediatric CT dose optimization right-sizes kVp, tube current, and reconstruction to patient size using Image Gently principles and size-specific dose estimates (SSDE).
NRC Occupational Dose Limits: 10 CFR Part 20
10 CFR Part 20 sets the federal radiation dose limits every NRC and Agreement State licensee must meet: the 5 rem annual TEDE limit for workers, separate lens and skin limits, the embryo/fetus limit for a declared pregnant worker, and the public dose limits. This guide explains each limit, the monitoring thresholds that trigger dosimetry, and how ALARA goes beyond the numbers.
Cyclotron Production of Fluorine-18 for PET
Fluorine-18 is the workhorse of clinical PET, and almost all of it is made on a medical cyclotron via the 18O(p,n)18F reaction on enriched water targets. This guide explains the production physics, saturation yield, targetry, automated radiochemistry, and the FDA, USP, and NRC framework that governs PET radiopharmaceutical production and release.
MRI ACR Phantom QC: The Seven Tests
The ACR MRI accreditation phantom is the backbone of an MRI quality control program. The large and small phantoms support seven standardized image-quality tests plus system-level checks, run weekly by technologists and annually by the MR medical physicist, each with defined pass criteria and action levels.
Annual Radiation Protection Program Audit
The annual radiation protection program review required by 10 CFR 20.1101(c) is not a paperwork ritual. It is a performance-based audit of both the content and the real-world implementation of your radiation safety program, and it is one of the first things an NRC or Agreement State inspector asks to see.
OSL vs TLD Personnel Dosimeters: Physics and QC
OSL and TLD personnel dosimeters both store energy from radiation in crystal traps and release it as light for readout, but they differ in how that light is stimulated, whether the signal survives reanalysis, and how they respond to photon energy. Understanding the luminescence physics behind each — and the NRC monitoring thresholds and NVLAP performance testing that govern them — is what lets a radiation safety program choose and use them defensibly.
Tc-99m Generator QC: Mo-99 Breakthrough Testing
A PhysicsPulse reference on the Mo-99/Tc-99m generator—how transient equilibrium drives elution timing, what every eluate QC test checks, and the molybdenum and aluminum breakthrough limits the NRC and USP require before a dose reaches a patient.
ACR Digital Mammography Phantom QC
The ACR Digital Mammography Phantom image test is a core quality-control check: technologists and the medical physicist score simulated fibers, speck groups, and masses against defined pass criteria. This guide explains the ACR DM Phantom, how scoring works, why the criteria differ from the legacy screen-film phantom, and how observer variability affects results.
Gamma Camera Collimator Selection Guide
The collimator is the resolution-limiting component of every gamma camera, and it forces an unavoidable trade-off: any change that sharpens images costs sensitivity, and vice versa. Choosing correctly means matching hole geometry and septal thickness to the photon energy of the radionuclide while balancing count rate against spatial resolution for the clinical task. This guide covers the physics, the math, and the QC that keep the choice defensible.
CT Bowtie Filters: Dose and Image Quality
The CT bowtie filter is a beam-shaping filter that adds attenuation toward the edges of the fan beam so the detector sees a more uniform signal across a roughly elliptical patient. Done right, it lowers peripheral skin dose and stabilizes noise; but its benefit depends entirely on patient centering, filter selection, and scan-field-of-view choice, and miscentering can quietly erase the advantage.
Sealed Source Leak Testing & Inventory
Sealed source leak testing and physical inventory are two of the most routine, and most commonly cited, obligations in a materials license. Leak testing confirms a source is intact by wiping it and checking for removable contamination above the 185 Bq (0.005 microcurie) limit; the semiannual inventory confirms every source is accounted for. This guide explains the 10 CFR 35.67 requirements, the exemptions, the recordkeeping rules, and how an RSO builds a defensible program.
CT Image Quality QC: MTF, NPS, and Detectability
CT image quality is more than a single resolution number. Spatial resolution (MTF/TTF), image noise and its texture (NPS), and low-contrast detectability together describe how well a scanner reproduces anatomy. With iterative and deep-learning reconstruction now standard, contrast-to-noise ratio alone can mislead, and task-based metrics give a more honest picture of clinical performance.
Dose Calibrator QC: The Four Required Tests
Dose calibrator quality control is the program of four tests—constancy, accuracy, linearity, and geometry—that proves a nuclear medicine clinic measures patient dosages correctly. Each test checks a different failure mode, runs on a different schedule, and is tied to NRC and license expectations.
MRI Parallel Imaging: g-Factor and SNR
Parallel imaging accelerates MRI by undersampling k-space and unfolding the aliasing with coil sensitivity information, but speed is never free. The signal-to-noise ratio falls by a factor of the square root of the acceleration and again by the spatially varying g-factor, a coil-geometry term that is always at least one. Understanding both terms is what separates a defensible protocol and QC program from cargo-cult acceleration settings.
Occupational Eye-Lens Dose in Fluoroscopy
The lens of the eye is one of the most radiosensitive tissues in the body, and interventional fluoroscopy operators can accumulate enough scatter dose to risk cataract. After ICRP lowered the recommended occupational eye-lens limit to 20 mSv per year, monitoring with the Hp(3) quantity, leaded eyewear, ceiling-suspended shields, and good technique became central to staff radiation protection — even though the U.S. NRC limit remains 150 mSv per year.
Surface Contamination Limits & Equipment Release
Releasing surveyed equipment for unrestricted use is a routine but frequently misunderstood radiation safety task. The classic surface contamination values, the dose-based license-termination criterion, and the separate transport limits answer different questions. This guide explains the numbers, why Regulatory Guide 1.86 was withdrawn but its values persist, how to convert a smear count to removable contamination, and how to build a defensible equipment-release procedure.
NEMA NU 2 PET/CT Performance Testing
NEMA NU 2 is the common language of PET/CT performance. It defines reproducible measurements of spatial resolution, sensitivity, scatter fraction and count-rate performance (including NECR), accuracy of corrections, image quality, and time-of-flight resolution, so that scanners can be compared, accepted, and monitored against vendor specifications on an apples-to-apples basis.
Ultrasound Thermal & Mechanical Index Safety
The Thermal Index (TI) and Mechanical Index (MI) are the two on-screen safety indices that let sonographers keep diagnostic ultrasound output as low as reasonably achievable. This guide explains how TI and MI are defined, derated, displayed under the Output Display Standard, and bounded by FDA Track 3 acoustic-output limits.
Caregiver Dose After Radiopharmaceutical Therapy
When a patient is released after I-131 or Lu-177 therapy, the radiation source goes home. Family members, caregivers, and visitors can receive dose from the released patient, and a defensible program manages it with the right dose constraints and written instructions. This guide explains the 5 mSv release criterion, the 1 mSv instruction trigger, the comforter-and-carer constraint, and how to keep household doses ALARA.
I-131 Therapy for Hyperthyroidism: Dosimetry
Radioiodine (I-131) is a definitive therapy for hyperthyroidism, but choosing the administered activity is a physics decision as much as a clinical one. This article compares fixed and calculated (uptake-corrected) dosing, works through the concentration and absorbed-dose formulas, and connects the calculation to NRC written-directive and patient-release requirements.
Fluoroscopy Dose Management: Air Kerma and KAP
Fluoroscopy dose management uses reference air kerma, kerma-area product, and peak skin dose to track patient exposure, flag substantial radiation dose levels, and prevent deterministic skin injury during fluoroscopically guided interventions.
Radiochemical Purity and TLC/ITLC QC
Radiochemical purity is the fraction of a radiopharmaceutical's activity that is in the desired labeled chemical form. Thin-layer chromatography (TLC/ITLC) separates the labeled product from free pertechnetate and hydrolyzed-reduced technetium so a clinic can prove a kit is fit for the patient before it is injected.
Lead Apron QC: Testing and Rejection Criteria
Protective aprons only work if they are intact. This guide covers lead apron integrity testing: inspection methods, dose-based rejection criteria for holes and tears over critical organs, lead-equivalence standards under IEC 61331, inspection frequency, and how to build a defensible protective-garment QC program.
CT Noise Power Spectrum & Task-Based Image Quality
A single noise standard deviation cannot describe modern CT. The noise power spectrum captures noise magnitude and texture, the task transfer function captures resolution under clinical conditions, and the detectability index combines them into a task-based measure of low-contrast performance. AAPM TG-233 and ICRU Report 87 formalize this framework for acceptance testing, commissioning, and protocol optimization on iterative and deep-learning reconstruction.
External Dose Control: Time, Distance, Shielding
Time, distance, and shielding are the three levers that control external radiation dose, and each one is quantifiable. Dose is proportional to time, falls with the inverse square of distance, and drops exponentially through shielding. Understanding the math turns ALARA from a slogan into a set of decisions a radiation safety program can defend against the 10 CFR Part 20 dose limits.
Ac-225 Targeted Alpha Therapy: Physics & Safety
Actinium-225 targeted alpha therapy exploits the short range and high linear energy transfer of alpha particles to kill tumor cells while sparing nearby tissue. Its four-alpha decay chain, recoiling radioactive daughters, and low-but-nonzero photon output make Ac-225 a distinctive physics, dosimetry, and radiation-safety problem that differs from Lu-177 and Ra-223 therapy.
Mammography CNR and SDNR Quality Control
Contrast-to-noise ratio (CNR) and signal-difference-to-noise ratio (SDNR) are the core quantitative image-quality metrics in the ACR Digital Mammography QC program. They tie detector signal, noise, and radiation dose together into a single number the medical physicist tracks over time to catch drift before it reaches the reading room.
CT Image Artifacts: Causes and Correction
CT artifacts are not random image noise. Beam hardening, photon starvation, motion, metal, ring, cone-beam, and partial-volume artifacts each arise when a specific reconstruction assumption is violated, and each has a distinct signature, cause, and correction. Recognizing the mechanism is what lets a technologist, radiologist, or physicist decide whether the finding is disease or a data error, and whether the fix belongs in the protocol, the algorithm, or the scanner's QC program.
Reporting Radiation Incidents to the NRC
NRC regulations set specific, tiered timeframes — immediate, 24-hour, and 30-day — for reporting radiation overexposures, lost or stolen licensed material, and doses that exceed regulatory limits. Knowing which threshold triggers which report, and having the phone numbers and written-report content ready before an event, is a core radiation safety officer responsibility.
N-13 Ammonia Cardiac PET Perfusion Imaging
N-13 ammonia is a cyclotron-produced PET myocardial perfusion tracer with a 9.97-minute half-life, high first-pass extraction, and a short positron range that yields excellent image quality and quantitative myocardial blood flow. Its physics, on-site production logistics, and QC set it apart from Rb-82 and F-18 flurpiridaz.
CT Slice Thickness QC and Sensitivity Profiles
The reconstructed CT slice thickness is not a physical cut through the patient but the full width at half maximum of the slice sensitivity profile (SSP): the scanner's response along the z-axis. Understanding how the SSP is shaped by beam collimation, detector configuration, helical interpolation, and reconstruction determines how a physicist verifies slice width, why thin slices cost noise, and how partial-volume averaging limits small-lesion contrast.
Part 37 Access Authorization and T&R
Physical barriers protect a Category 1 or 2 source from the outside, but an insider with keys is a different problem. 10 CFR Part 37 Subpart B answers it with an access authorization program: background investigations, fingerprinting, and a reviewing official who decides who is trustworthy and reliable enough for unescorted access.
F-18 Fluciclovine PET/CT for Prostate Cancer
F-18 fluciclovine (Axumin) is a synthetic amino-acid PET tracer for suspected prostate cancer recurrence after treatment. Its physics — a low-energy positron, a 109.77-minute half-life, and rapid amino-acid kinetics — shapes a pelvis-first acquisition that must beat bladder activity, and its detection rate climbs steeply with PSA.
Radiation Protection Program Under 10 CFR 20.1101
The written radiation protection program required by 10 CFR 20.1101 is the umbrella document that ties together ALARA, dose limits, surveys, records, and the annual review. It is the first thing an NRC or Agreement-State inspector asks to see, and a program that exists only on paper is a common finding. This guide covers what 20.1101 requires, how the four subsections fit together, and how to build a program that is scaled to your licensed activities and actually implemented.
Lymphoscintigraphy & Sentinel Node Mapping
Sentinel lymph node mapping succeeds or fails on the physics of the injected tracer: particle size governs nodal migration, administered activity and decay govern how much signal survives to the operating room, and a well-tuned gamma camera plus a calibrated probe turn that signal into an accurate map. This guide connects the radiopharmaceutical choice, imaging protocol, dosimetry, and QC that make lymphoscintigraphy defensible.
Anode Heel Effect in Radiography: Physics & QC
The anode heel effect is a predictable, geometry-driven variation in x-ray beam intensity along the cathode-anode axis. It is strongest with large fields, short source-to-image distances, and steep anode angles, and it can bias exposure, image quality, and the detector exposure index. Understanding its physics lets technologists position patients to their advantage and lets a medical physicist confirm beam uniformity during acceptance and routine QC.
Radioactive Gas Handling and Effluent Control
Radioactive gases and aerosols used in ventilation imaging behave differently from a bottle of liquid technetium: a noble gas like xenon-133 delivers dose by external submersion, spreads through a room's air, and leaves through the ventilation system rather than being contained on a benchtop. Safe programs rely on negative-pressure rooms, closed delivery systems, charcoal traps, air monitoring, and effluent control keyed to the 10 CFR Part 20 limits.
Radiopharmaceutical Dosimetry with ICRP 128
Every diagnostic nuclear medicine study delivers a patient radiation dose that scales with the administered activity through a radiopharmaceutical-specific dose coefficient. ICRP Publication 128 is the current compendium of those coefficients. This guide explains how effective dose is estimated, how to use the coefficients, where they are heading, and what it means for justification and optimization.
Focal Spot Size Measurement in Radiography QC
Focal spot size controls geometric sharpness in radiography. This guide explains the line-focus principle, the pinhole, slit, and star-resolution measurement methods standardized in IEC 60336 and NEMA XR-5, the nominal-focal-spot tolerance limits, focal spot blooming, and how a medical physicist folds focal spot testing into acceptance and annual QC.
Pulsed Fluoroscopy: Dose Reduction QC
Pulsed fluoroscopy is the single most effective operator-controlled lever for lowering patient and staff dose during fluoroscopically guided procedures. But the savings are not simply proportional to pulse rate: automatic dose-rate control raises dose per pulse at low frame rates to preserve image quality, so a defensible dose-reduction program pairs pulse-rate selection with QC of dose per pulse, air kerma rate, and displayed dose metrics.
MARSSIM Final Status Surveys Explained
A MARSSIM final status survey is how a facility proves a site is clean enough to release. This guide walks through the NUREG-1575 Revision 2 framework: survey-unit classification, derived concentration guideline levels, the Sign and Wilcoxon Rank Sum tests, the Data Quality Objectives process, and the worked statistics that decide whether a survey unit passes.
I-123 MIBG Imaging: Collimators & H/M Ratio
I-123 MIBG imaging looks simple until the numbers move: the same patient can read a heart-to-mediastinum ratio of 1.4 on a low-energy collimator and 1.8 on a medium-energy one. High-energy I-123 photons penetrating collimator septa are why collimator choice, energy windows, and cross-calibration decide whether an H/M ratio is comparable across cameras and studies.
CT Patient Centering: Dose and Image Quality
Centering the patient at CT isocenter is one of the cheapest dose-reduction tools in the department. When the patient sits below isocenter, the bowtie filter and the localizer-driven automatic exposure control both work against you—raising surface dose while degrading image noise. This article explains the physics, quantifies the penalty, and gives a practical QC and workflow checklist.
Contamination Monitoring in Nuclear Medicine
Contamination monitoring — routine surveys, personnel frisking, hand-foot monitors, and wipe tests — is the daily backbone of a nuclear medicine radiation safety program. Doing it defensibly means choosing the right instrument for each radionuclide, setting action levels that make sense, and proving your survey can actually detect the contamination limit through a minimum detectable activity calculation, not just waving a probe and hoping.
Tc-99m MAA Lung Shunt Fraction for Y-90
Before Y-90 radioembolization, a Tc-99m MAA scan estimates how much of the injected dose would shunt to the lungs. That lung shunt fraction sets the lung dose, drives activity reduction or a treatment hold, and — done on planar instead of SPECT/CT — is often overestimated enough to deny a treatable patient.
Nuclear Medicine Area Surveys: 35.70 & 20.1501
A nuclear medicine survey program has two engines: the end-of-day ambient dose-rate survey required by 10 CFR 35.70 in written-directive areas, and the broader radiation and contamination surveys required by 10 CFR 20.1501. Knowing which rule drives which survey, with what instrument, frequency, and action level, keeps the program defensible.
Ge-68/Ga-68 Generator Quality Control
The Ge-68/Ga-68 generator supplies gallium-68 for PET radiopharmaceuticals such as Ga-68 DOTATATE and Ga-68 PSMA. Its quality control centers on germanium-68 breakthrough testing, radionuclidic and radiochemical purity, metal-ion impurities, and elution performance, judged against compendial and labeled specifications so the eluate is safe to radiolabel and inject.
X-Ray Beam Filtration and Spectral Shaping
Beam filtration removes low-energy x-ray photons that add skin dose without forming the image. This guide explains inherent, added aluminum, and spectral copper or tin filtration, the beam-hardening physics with worked math, the measured dose savings, and the FDA and IEC filtration requirements a medical physicist verifies.
NRC Broad Scope Licenses: Types A, B, and C
A broad scope license under 10 CFR Part 33 lets an institution add radionuclides, uses, and authorized users through its own Radiation Safety Committee instead of filing an NRC amendment for every change. That flexibility comes with weighty responsibility: Types A, B, and C differ in quantity limits, committee requirements, and the depth of program a licensee must run to earn and keep the authority.
Radioactive Spill Response in Nuclear Medicine
A practical, answer-first guide to radioactive spill response and decontamination in nuclear medicine, covering containment, survey-to-contamination math, wipe-test action levels, waste handling, and NRC and state regulatory compliance.
Fluoroscopy Air Kerma Rate Limits & ADRC
Fluoroscopic equipment can only push its entrance air kerma rate so high: 21 CFR 1020.32 caps it at 88 mGy/min, or 176 mGy/min under high-level control. Automatic dose rate control (ADRC) drives output toward that ceiling to keep the image usable. Understanding both is essential to fluoroscopy QC, dose management, and avoiding skin injury.
Occupational Radiation Exposure Monitoring
A practical guide to designing and maintaining an effective occupational radiation monitoring program in healthcare—from dosimeter selection and badge placement to ALARA investigation levels and NRC recordkeeping.
I-124 PET Imaging and Thyroid Dosimetry
I-124 is a long-lived positron emitter that lets PET/CT measure radioiodine uptake and project lesion absorbed dose before I-131 therapy. Its complex decay scheme — a low positron branch, high positron energy, and abundant prompt gamma rays — makes accurate quantification a physics problem, not a push-button one.
CT Automatic Tube Current Modulation (ATCM)
Automatic tube current modulation (ATCM) is the single most important dose-management tool on a modern CT scanner. It adjusts the X-ray tube current in real time to patient attenuation, lowering dose to thin regions and projections while holding image noise near a user-selected target. Understanding the noise index, reference mAs, and modulation strength is essential to using ATCM correctly and to verifying it during the annual physics survey.
Lead Shielding Design for CT and PET/CT
How medical physicists design lead shielding for CT, fluoroscopy, interventional radiology, PET/CT, and radionuclide therapy—covering workload, use factor, occupancy, distance, the NCRP 147 transmission equation, tenth-value-layer barrier thickness, and a worked numeric example under 10 CFR 20.
CTDIvol and DLP Explained: CT Dose Metrics
A clear, answer-first guide to CT dose metrics—CTDIw, CTDIvol, DLP, SSDE, and effective dose—with the formulas, a worked numeric example, the limitations of each index, and how technologists and physicists use them to optimize protocols and meet ACR and Joint Commission requirements.
Y-90 Ibritumomab (Zevalin) Radioimmunotherapy
Y-90 ibritumomab tiuxetan (Zevalin) is an anti-CD20 radioimmunotherapy for B-cell non-Hodgkin lymphoma. Because Y-90 is a high-energy, pure beta emitter with no primary gamma, its physics — weight-based dosing, a platelet-driven activity cap, bremsstrahlung-only external field, and straightforward outpatient release — differs sharply from gamma-emitting therapies, and the medical physicist and RSO have to plan the program around those emissions.
Radioactive Material License Renewal
Renewing a radioactive material license is not a formality. Under the NRC's timely-renewal rule (10 CFR 2.109), filing a complete renewal at least 30 days before expiration keeps the license in effect while the application is reviewed. A defensible renewal reconciles possession limits, authorized users, procedures, and the ALARA program with how the facility actually operates.
Parathyroid Scintigraphy: Sestamibi & SPECT/CT
Parathyroid scintigraphy localizes hyperfunctioning glands before minimally invasive parathyroidectomy. Tc-99m sestamibi can be imaged with a dual-phase washout technique or a dual-tracer subtraction technique, and adding SPECT/CT raises sensitivity and pins the gland to an anatomic location. The physics — tracer kinetics, collimator choice, tomographic timing, and dosimetry — decides whether the surgeon gets a usable map.
X-Ray Tube Heat Loading and Thermal Management
An X-ray tube converts about 99% of the electron beam energy into heat and only about 1% into X-rays, so thermal loading, not radiation output, is usually what limits how fast and how long a system can scan. Understanding heat units, anode and housing heat capacity, cooling curves, and tube rating charts explains focal-spot degradation, throughput throttling in high-volume CT and interventional work, and several recurring QC findings.
Type A and Type B Packages: A1/A2 Limits
Whether a shipment of radioactive material can travel in a Type A package or requires a robust Type B package comes down to two numbers: A1 for special-form material and A2 for normal-form material. Those limits are set nuclide by nuclide in 10 CFR Part 71 and 49 CFR 173.435, derived from the IAEA Q-system dose criteria, and combined for mixtures with the sum-of-fractions rule. Getting the package type right is a core radiation-safety and compliance duty for any facility that ships or receives isotopes.
Decommissioning a Radioactive Materials License
Closing a radioactive-materials program and terminating an NRC or Agreement State license is a defined, dose-based process. The licensee must decommission the use area, demonstrate that residual radioactivity meets the radiological criteria for license termination through a final status survey, and document compliance using derived concentration guideline levels and detection-capable instrumentation.
Well Counter QC for Bioassay and Wipe Tests
The scintillation well counter is the low-activity workhorse of a nuclear medicine department—it counts wipe tests, I-131 thyroid bioassays, and blood samples. Its quality control is a small set of interlocking tests: energy peaking, chi-square constancy, efficiency (sensitivity) calibration, background, and minimum detectable activity. Each rests on counting statistics, and each protects a different regulatory or clinical decision.
Fluoroscopy Magnification Modes and Patient Dose
Selecting a fluoroscopic magnification (zoom) mode shrinks the field of view and improves visibility of fine detail, but it also raises the entrance air kerma rate. Because the automatic dose-rate control drives the input dose up to keep image-receptor signal constant, dose rate rises roughly with the inverse square of the field-of-view diameter, so magnification is one of the most consequential operator choices for patient skin dose.
Sentinel Node Surgery: Staff Radiation Safety
Sentinel lymph node biopsy injects only tens of megabecquerels of Tc-99m, so measured doses to surgeons, scrub staff, and pathologists sit far below regulatory limits. But 'very low' is not 'zero': a defensible program still needs dose data, specimen-handling rules, and a documented ALARA basis for why the operating-room team is not classified as radiation workers.
Gamma Camera Sensitivity QC
System sensitivity — the count rate a gamma camera records per unit of source activity — is a fundamental performance measure that ties directly to image quality, acquisition time, and quantitative accuracy. Measuring it correctly means decay-correcting the source activity, subtracting background, and comparing the result against the NEMA baseline and manufacturer specification. Trending sensitivity over time is one of the clearest early warnings of a degrading collimator, crystal, or detector.
Fluoroscopy HVL and Beam-Quality QC
Half-value layer (HVL) is the single number that describes how hard, or penetrating, a fluoroscopic X-ray beam is, and it sits at the center of both patient dose and regulatory compliance. A beam that is too soft delivers skin dose that never reaches the detector, while a properly filtered beam — often hardened with added copper — protects the patient without sacrificing the image. Measuring HVL correctly, comparing it to the FDA minimum, and trending it are core parts of a defensible fluoroscopy QC program.
The ICRP System of Radiological Protection
Nearly every radiation-protection rule an imaging or nuclear medicine program follows traces back to one framework: the ICRP system of radiological protection, built on three principles — justification, optimization, and dose limitation — and on the effective-dose quantity. Understanding the framework, and knowing where it does and does not apply, is what turns a checklist of limits into a coherent safety program.
PET Detectors: Crystals, SiPMs, and TOF
Every PET image begins as a flash of light in a scintillator crystal. This guide explains how crystal properties—light yield, decay time, density, and effective Z—and the transition from photomultiplier tubes to silicon photomultipliers determine energy resolution, coincidence timing, and the time-of-flight capability that sharpens modern PET, and how those detector fundamentals connect to NEMA acceptance testing.
Half-Value Layer and kVp QC in Radiography
Half-value layer (HVL) and kVp accuracy are core acceptance and annual QC tests for radiographic units. HVL confirms the beam is adequately filtered to protect the patient, while kVp accuracy, output reproducibility, and linearity confirm the generator delivers the technique it displays. This guide explains the physics, the FDA 21 CFR minimums, the tolerances physicists apply, and how the tests are performed.
Patient Radiation Alarms After Nuclear Medicine
Patients who have had a nuclear medicine study or radionuclide therapy can set off sensitive radiation detectors at airports, borders, and secure buildings for days to months afterward. NRC Regulatory Guide 8.39 expects licensees to warn them and, when appropriate, issue a wallet card documenting the treatment.
FDG PET/CT in Lymphoma: Deauville Response
Response assessment in FDG-avid lymphoma runs on a deceptively simple physics foundation: the Deauville five-point scale compares residual tumor uptake to two internal references — the mediastinal blood pool and the liver. Making that visual score reproducible across scanners and time points depends on standardized acquisition, SUV quantification, and the harmonization that lets a scan today be compared to a scan three months ago.
CT Beam Collimation, Efficiency, and Overranging
The z-axis width of the CT x-ray beam is wider than the images it produces. Penumbra at the beam edges lowers geometric efficiency, and helical overranging irradiates tissue beyond the planned scan. Both effects add dose that never contributes to the reconstructed image, and both are measurable, reportable QC parameters a medical physicist should track.
Nuclear Medicine Department Shielding Design
Shielding a conventional nuclear medicine department that runs on Tc-99m is a different problem from shielding a PET suite: 140 keV photons are far less penetrating than the 511 keV annihilation photons of PET, so distance, layout, and workflow usually matter more than lead. This guide explains the sources, design goals, dose-rate constants, and barrier calculations, with a worked example that shows why conventional nuclear medicine rooms rarely need structural lead.
Siemens PET Flow (FlowMotion) Explained
A PhysicsPulse guide to Siemens PET Flow (FlowMotion) continuous bed motion: how it improves image uniformity, quantitative SUV accuracy, and workflow compared with step-and-shoot PET, and how technologists optimize protocols.
CT Colonography: Low-Dose Protocol Optimization
CT colonography is a structural screening test performed on healthy, asymptomatic adults, so its physics goal is unusual: produce a diagnostic study for polyp detection at the lowest achievable radiation dose. Reaching that target means engineering the supine-and-prone protocol around automatic exposure control, kVp, reconstruction, and the noise-versus-dose relationship rather than copying a diagnostic abdomen technique.
Neutron Safety at PET Cyclotron Facilities
A PET cyclotron is the one place in a medical imaging enterprise where fast neutrons dominate the radiation safety picture. Proton-induced reactions during F-18 production create an intense neutron field and activate the vault, targetry, and even the air — hazards that behave nothing like the 511 keV photons downstream, and that demand neutron-specific dose quantities, shielding, and monitoring.
PET PSF Reconstruction: Resolution Recovery
Point spread function (PSF) reconstruction, or resolution modeling, sharpens PET images by putting the scanner's measured blur into the system model. It improves contrast recovery and lesion detectability, but it also introduces edge overshoot (Gibbs) artifacts and can make small-lesion SUVs less reproducible. Understanding when PSF helps and when it distorts quantification is essential for defensible PET reporting and harmonization.
CT Protocol Optimization: Dose, Quality, and ACR
How to balance diagnostic image quality against minimal radiation dose in CT—using AEC, kV optimization, and iterative reconstruction—while meeting ACR and Joint Commission requirements.
Florida Radiation Safety Rules for Imaging Centers
What imaging centers in Florida must do to comply with radiation safety regulations, from 64E-5 equipment registration and personnel licensure to annual physics evaluations and inspections.
Meckel Diverticulum Scintigraphy with Tc-99m
A bleeding Meckel diverticulum is the most common congenital anomaly of the gastrointestinal tract, and Tc-99m pertechnetate scintigraphy remains the noninvasive test of choice for locating the ectopic gastric mucosa that causes it. This guide explains the radiopharmaceutical mechanism, the imaging protocol, the premedication that improves sensitivity, and the physics and dosimetry a nuclear medicine team should understand.
Radiographic kVp Accuracy & Reproducibility QC
Tube potential (kVp) sets beam quality, subject contrast, and a large share of patient dose, so an inaccurate or unstable kVp quietly degrades images and inflates exposure. This guide explains what kVp accuracy and reproducibility mean, how they are measured, the tolerances a medical physicist applies, and the practical steps that keep a radiographic generator in specification.
Radiation Safety for Inpatient I-131 Therapy
When a radioiodine therapy patient cannot be released under the 5 mSv limit, they must be hospitalized — and that decision brings a specific set of radiation safety duties under 10 CFR 35.315: a private room and bath, radioactive-materials posting, visitor limits, contamination control, staff dosimetry, and monitoring of every item that leaves. This guide walks through the physics of I-131, the release calculation, room preparation, and the ALARA program that keeps caregivers, visitors, and the public within dose limits.
Time-of-Flight PET: How TOF Improves SNR
Time-of-Flight (TOF) PET uses photon timing differences to localize annihilation events more precisely, improving image quality, quantitative SUV accuracy, and scan efficiency.
ACR Accreditation Physics Requirements
A practical guide to ACR accreditation physics requirements, covering modality-specific testing, tolerances, documentation, and submission for CT, MRI, PET, nuclear medicine, mammography, and ultrasound—plus the qualified medical physicist's role.
PET/CT Shielding Calculations: TG-108 and NCRP 147
PET/CT shielding is a mixed-modality problem: the injected patient, hot lab, uptake rooms, scanner room, and CT subsystem can all contribute to adjacent-area dose. A defensible design combines PET-specific TG-108 methods, CT shielding principles from NCRP 147, realistic workload and occupancy assumptions, and post-construction verification.
SPECT Jaszczak Phantom QC: Resolution & Contrast
A gamma camera can pass every planar quality-control test and still produce poor tomographic images if reconstruction, center-of-rotation, and uniformity are not right. The Jaszczak-style SPECT phantom — cold rods, cold spheres, and a uniform region in one water-filled cylinder — is the single acquisition that reveals reconstructed spatial resolution, contrast detectability, and tomographic uniformity together, which is why it anchors both routine SPECT QC and ACR accreditation.
Geometric Unsharpness & Magnification in Radiography
Every radiographic image is a shadow, and every shadow has a blurred edge. Geometric unsharpness — the penumbra cast by a finite focal spot — scales with magnification, so focal spot size, source-to-image distance, and object position together determine how sharp a radiograph can be. Understanding the simple geometry behind that blur is the foundation of technique optimization, magnification radiography, and focal-spot quality control.
Xenon-133 Ventilation Study Radiation Safety
A xenon-133 ventilation study introduces a radioactive noble gas that the patient exhales into room air. Unlike a spill of liquid activity, gaseous Xe-133 becomes an airborne and submersion hazard, so radiation safety depends on a xenon trap, a negative-pressure room, controlled exhaust, and airborne-concentration limits from 10 CFR Part 20.
PET and Radiopharmaceutical Therapy Isotopes Reference
A Physics Pulse reference guide to the most common PET and radiopharmaceutical therapy isotopes—their decay physics, photon and particle emissions, clinical applications, and the radiation safety practices that keep technologists and patients protected.
CT Gantry, Table, and Alignment QC
CT geometric QC verifies that the alignment lights, table motion, and gantry tilt place the imaged volume exactly where the operator intends. Small errors in laser accuracy, table increment, or tilt propagate into mis-localized slices, dose-length errors, and failed accreditation, so these mechanical checks belong in every CT quality control program.
NRC Radioactive Material License: Medical Use
A practical guide to obtaining and maintaining an NRC or Agreement State radioactive material license for medical use, covering 10 CFR Part 35 use categories, the NRC Form 313 / NUREG-1556 application, RSO and Authorized User requirements, ALARA, source security, amendments, and ongoing compliance.
F-18 FLT PET: Imaging Tumor Proliferation
3'-deoxy-3'-[18F]fluorothymidine (FLT) is a PET tracer that reports cellular proliferation rather than glucose metabolism. Trapped by thymidine kinase 1 in the salvage pathway, FLT uptake correlates with Ki-67 and offers higher tumor specificity than FDG in some settings — but lower absolute uptake and complex kinetics demand careful quantification.
CT Helical Pitch: Dose and Image Quality
Helical pitch ties table speed to radiation dose and image noise in CT. Whether increasing pitch lowers dose depends entirely on how the scanner handles tube current, so pitch must be read together with the mA scheme, not in isolation.
Common Radiation Safety Violations to Avoid
A practical guide to the radiation safety violations most often cited during imaging and nuclear medicine inspections, mapped to the exact 10 CFR Part 20 and Part 35 sections, with the root causes and corrective actions that keep facilities off the enforcement list.
Bone-Pain Palliation: Sr-89, Sm-153, and Ra-223
Bone-seeking radiopharmaceuticals deliver targeted radiation to osteoblastic skeletal metastases. The beta emitters strontium-89 and samarium-153 palliate pain, while the alpha emitter radium-223 both palliates and extends survival in metastatic castration-resistant prostate cancer. Their physics — emission type, energy, half-life, tissue range, and marrow dose — drives the differences in efficacy, myelotoxicity, and radiation safety, and each requires a written directive and a defensible dosimetry and release plan.
MRI B1 & Flip-Angle Transmit Calibration QC
The flip angle a sequence actually delivers depends on the transmit B1 field, and B1 is never perfectly uniform. Transmitter-gain calibration and B1 mapping — using the double-angle method, actual flip-angle imaging, Bloch-Siegert, or DREAM — verify that prescribed flip angles are the ones tissue experiences, protecting contrast, quantitative accuracy, and SAR estimates.
Buildup Factor and Broad-Beam Gamma Shielding
The simple exponential attenuation law describes only narrow-beam, good-geometry conditions. Real shielding barriers see broad beams, where scattered photons that survive the barrier add to the dose on the far side. The buildup factor is the multiplicative correction that accounts for those scattered photons, and ignoring it can underestimate transmitted dose by a factor of two or more.
PET SUV Quantification and QC
The standardized uptake value (SUV) turns a PET image into a quantitative measurement, but an SUV is only as trustworthy as the calibration and protocol behind it. SUV depends on accurate activity assay, body weight, uptake time, blood glucose, decay correction, and a valid cross-calibration between the dose calibrator and the scanner. This guide explains the SUV equations, the dominant error sources, and the QC that keeps serial and multicenter SUVs comparable.
Image Intensifier vs Flat-Panel Detector Physics
The image intensifier (II) and the flat-panel detector (FPD) are two different physical ways to turn a fluoroscopic X-ray beam into a moving image. They behave differently on nearly every quality-control parameter a physicist measures — spatial resolution, contrast and veiling glare, field uniformity and geometric distortion, DQE, lag and ghosting, and dose response — so an annual survey has to be matched to the receptor technology in the room.
Mobile Nuclear Medicine Service: NRC Compliance
A mobile nuclear medicine service brings byproduct material and imaging to a client's site under the mobile provider's own radioactive material license. 10 CFR 35.80 sets the compliance backbone: a management letter from each client, instrument checks before use at every address, area surveys before leaving, and defined records — all layered on Part 20 dose limits, DOT transport rules, and Agreement State reciprocity.
Conjugate-View Planar Quantification in Dosimetry
The conjugate-view method uses paired anterior and posterior gamma-camera images to convert counts into absolute activity, correcting for the attenuation that makes a raw planar count depth-dependent. Its geometric-mean core is elegant: the geometric mean of two opposed views is, to first order, independent of source depth, which is why the technique remains a workhorse for time-activity curves and internal dosimetry.
Digital Radiography Detectors: Direct vs Indirect
Flat-panel digital radiography detectors split into two families defined by how they turn X-rays into signal: direct-conversion photoconductors such as amorphous selenium, and indirect-conversion scintillators such as cesium iodide coupled to amorphous silicon. That single design choice propagates through spatial resolution, noise, detective quantum efficiency, and dose efficiency, and it should shape how a physicist specifies, tests, and troubleshoots a DR system.
Operational Dose Quantities Explained
Effective dose and equivalent dose protect people, but neither can be measured directly on a worker or with a survey meter. Operational quantities — the personal dose equivalents Hp(10), Hp(3), and Hp(0.07), and the area quantities H*(10) and H'(0.07) — are the measurable surrogates built to estimate the protection quantities conservatively. Understanding what each depth means, how a conversion coefficient links a measured field to a reported dose, and how the operational quantities map to the NRC's deep, lens, and shallow dose equivalents is the foundation of every occupational monitoring program.
CT-Based Attenuation Correction in PET/CT
CT-based attenuation correction converts the CT image into a 511 keV attenuation map so PET activity can be quantified. This guide explains the bilinear HU-to-mu conversion, the artifacts it can introduce — metal, contrast, respiratory mismatch, truncation — and the QC that keeps SUV quantification trustworthy.
Medical Display QC: DICOM GSDF and TG-270
A medical display is the last link in the imaging chain — a perfectly acquired image can still be misread on a miscalibrated monitor. This is how the DICOM Grayscale Standard Display Function and AAPM TG-270 keep diagnostic displays perceptually consistent, and what a physicist actually measures.
Respiratory Protection for Airborne Radioactivity
When engineering controls cannot fully contain airborne radioactive material, respirators become the last line of defense against internal exposure. This guide explains the ALARA hierarchy of controls in 10 CFR 20 Subpart H, the assigned protection factors in Appendix A, the DAC-hour intake math, and the program elements — fit testing, bioassay, air sampling, and medical clearance — that a compliant respiratory protection program requires.
Radionuclide Cystography for Reflux
Direct radionuclide cystography detects vesicoureteral reflux by instilling a small activity of a technetium-99m radiopharmaceutical into the bladder and imaging the tract continuously during filling and voiding. Its two defining advantages are physical: continuous acquisition captures the transient reflux that intermittent fluoroscopy can miss, and instilling a non-absorbed tracer keeps the effective dose very low. Understanding the counting physics, the dosimetry, and the trade-off against fluoroscopic cystography is what lets a nuclear medicine team choose and defend the right study for a child.
Doppler Ultrasound Physics: Aliasing & Nyquist
Aliasing is the most common and most misread artifact in spectral and color Doppler. It is not an equipment fault: it is a direct consequence of sampling a Doppler signal with a pulsed system, and it appears whenever the Doppler-shift frequency exceeds the Nyquist limit of half the pulse repetition frequency. Understanding the Doppler equation, the depth–velocity trade-off, and the handful of controls that shift the Nyquist limit is what separates a confident velocity measurement from a misdiagnosis.
Radioactive Source Security: 10 CFR Part 37
10 CFR Part 37 sets security requirements for category 1 and category 2 quantities of radioactive material. Compliance turns on aggregating your sources against the Appendix A thresholds, granting unescorted access only to trustworthy and reliable individuals, maintaining security zones with monitoring and immediate detection, coordinating with local law enforcement, and protecting material in use and transit.
Thyroid Uptake Measurement: RAIU & Probe QC
The radioactive iodine uptake test quantifies the fraction of administered iodine trapped by the thyroid at a fixed time. A defensible RAIU result depends on a calibrated uptake probe, a decay-corrected standard, correct neck-to-standard geometry, background and tissue-attenuation correction, and an understanding of the radionuclide used, so the percent uptake supports a correct diagnosis and therapy dose.
MRI Image Artifacts: Identification & QC
MRI artifacts are systematic signal errors from the scanner, the sequence, or the patient. Recognizing the mechanism behind ghosting, chemical shift, susceptibility, Gibbs ringing, aliasing, and RF artifacts lets the physicist separate a hardware fault from an expected physics effect and keep the ACR phantom QC program defensible.
Scintillation Detectors in Radiation Safety
Sodium iodide scintillation detectors convert gamma energy into light, then into a measurable charge pulse whose height encodes photon energy. That energy discrimination, combined with high detection efficiency, makes NaI(Tl) the instrument of choice for wipe-test counting, low-level contamination surveys, and thyroid or well-counter measurements that a Geiger-Mueller tube would miss.
In-111 Pentetreotide SRS: Physics and QC
In-111 pentetreotide (OctreoScan) somatostatin receptor scintigraphy localizes somatostatin-receptor-positive neuroendocrine tumors using a gamma emitter that decays by electron capture with 171 and 245 keV photopeaks. A defensible study depends on medium-energy collimation, dual-photopeak energy windows, correct administered activity, standardized 4- and 24-hour imaging, and camera QC anchored to nuclear-medicine physics standards and NRC materials rules.
Mammography Half-Value Layer & Beam-Quality QC
Half-value layer is the core beam-quality metric in mammography quality control: it is the aluminum thickness that halves air kerma, it must meet the MQSA minimum of kVp/100 + 0.03 mm Al measured with the compression paddle in the beam, and it feeds directly into the normalized glandular dose used to report mean glandular dose. This guide covers the measurement method, MQSA and ACR compliance, target/filter beam qualities, and the physics that ties HVL to filtration, contrast, and patient dose.
X-Ray Machine Registration & State Inspections
The regulation of diagnostic X-ray machines confuses many facilities because it splits across agencies: the FDA sets federal performance standards on the equipment itself, states register and inspect the machines in use, and the NRC governs only radioactive material — not machines. This guide maps who regulates what, the key 21 CFR 1020 dose and leakage limits, how state registration and inspection work, and where MQSA imposes a federal physicist survey.
F-18 Sodium Fluoride Bone PET/CT: Physics & QC
F-18 sodium fluoride (NaF) is a bone-seeking PET tracer that images osteoblastic activity with far higher resolution and target-to-background than Tc-99m bone scintigraphy. This guide covers the tracer physics and kinetics, SUV quantification and attenuation-correction pitfalls, patient dosimetry using ICRP coefficients, and the QC and cross-calibration a defensible NaF PET/CT program needs.
MR Spectroscopy (MRS) Quality Control
Magnetic resonance spectroscopy measures tissue chemistry rather than anatomy, and its results are only as trustworthy as the shimming, water suppression, localization, and quantification behind them. This guide covers the physics of clinical proton MRS, the sequences and metabolites that matter, chemical-shift displacement and linewidth, and a practical quality-control program that keeps spectra defensible.
Background Radiation: Natural and Man-Made Sources
Background radiation is the baseline against which every occupational, public, and patient dose is judged. In the United States the average person receives about 6.2 mSv per year, split almost evenly between natural sources — dominated by radon — and man-made sources, now dominated by medical imaging. Understanding this breakdown is the foundation of radiation risk communication and ALARA.
PET SUV Harmonization and EARL Accreditation
A standardized uptake value is only meaningful if it means the same thing on every scanner. Because point-spread-function and time-of-flight reconstruction can inflate SUVs by tens of percent, the same patient can produce different numbers on different systems. SUV harmonization programs such as EANM Research Ltd (EARL) constrain scanner performance with phantom-based recovery-coefficient and calibration specifications so that quantitative PET is comparable across sites and over time.
CT Effective Dose Estimation with DLP k-Factors
CTDIvol and DLP describe scanner output, not patient risk. Effective dose links a CT exam to stochastic detriment using region-specific k-factors and ICRP tissue weighting factors, while organ dose is the quantity that actually governs risk. This guide shows how to convert DLP to effective dose correctly, where the k-factor method breaks down, and how to communicate CT dose without overstating individual risk.
Securing Licensed Material: 10 CFR 20.1801/20.1802
Securing and controlling licensed material is one of the most frequently cited requirements in NRC and Agreement State inspections. 10 CFR 20.1801 governs stored material and 20.1802 governs material in use. Both apply to every quantity of licensed material a facility possesses, not just the large sources covered by Part 37, and both come down to a simple test: is the material either secured or under someone's constant watch?
Effective Half-Life in Nuclear Medicine Dosimetry
Effective half-life is where physics meets physiology: it merges a radionuclide's fixed physical decay with the patient-specific biological clearance that removes activity from an organ. Because absorbed dose scales with the time-integrated activity, and that integral is governed by the effective half-life, this single quantity often controls how much dose an organ receives in both diagnostic imaging and radiopharmaceutical therapy.
Iodine Contrast Physics: K-Edge, kVp, and CT
Iodinated contrast enhances on CT because iodine's K-edge sits at about 33 keV, right where the diagnostic X-ray beam has abundant photons and the photoelectric effect is strong. That single fact explains why lowering tube potential boosts iodine attenuation, why low-kVp protocols can cut both dose and contrast volume, and why iodine's energy-dependent attenuation is the basis of dual-energy CT.
Beta & Bremsstrahlung Shielding for Beta Emitters
Shielding a pure beta emitter is counterintuitive: lead can make the hazard worse. Because high-Z materials convert stopped beta particles into penetrating bremsstrahlung x-rays, the correct approach is to stop the betas with a low-Z material first, then add high-Z shielding only for the residual bremsstrahlung.
Molecular Breast Imaging: CZT Cameras & Dose
Molecular breast imaging (MBI) uses a dedicated cadmium-zinc-telluride gamma camera and Tc-99m sestamibi to detect functional tumor uptake, giving it real supplemental value in mammographically dense breasts. Its clinical case depends on physics: direct-conversion detectors, optimized collimation, and dose reduction that brought the effective dose down to a screening-acceptable range.
Copper Filtration for Fluoroscopy Dose Reduction
Added copper filtration removes the soft, low-energy photons in a fluoroscopic beam that deposit skin dose without improving the image. Modern interventional systems switch copper thickness automatically to cut entrance skin dose substantially, at the cost of higher tube loading. This guide explains the physics, the measured dose savings, and how a physicist verifies it.
Gas-Filled Radiation Detectors
Ionization chambers, proportional counters, and Geiger-Muller tubes are all gas-filled detectors, but they operate in different regions of the same voltage curve — and that single difference decides which instrument belongs on a survey. A physicist who understands the six-region curve knows why an ion chamber reads accurate dose rate, why a GM pancake finds contamination, and why using the wrong one produces a dangerously wrong number.
Counting Statistics in Nuclear Medicine
Radioactive decay is random, so counts from a stable source are, to a good approximation, Poisson distributed: the standard deviation of N counts is √N, and the fractional uncertainty is 1/√N. That single relationship governs image noise, how long to acquire, whether a QC device is behaving, and the smallest activity a counter can detect. Understanding it is the difference between trusting a number and being misled by one.
Ultrasound Spatial Resolution QC
Ultrasound spatial resolution has three directional components — axial, lateral, and elevational — each set by a different part of the pulse-echo physics. Where resolution testing is performed, a defensible program measures all three on a tissue-mimicking phantom, tracks them against the transducer's baseline, and treats a change as a prompt to investigate, alongside the uniformity, artifact, and mechanical-integrity checks that detect most transducer faults.
Whole-Body Counting and In Vivo Bioassay
In vivo bioassay measures radioactivity inside the body directly, using shielded detectors to assess internal dose from an intake. This guide explains whole-body, lung, and thyroid counting, the minimum detectable activity math that sets a program's sensitivity, calibration with anthropomorphic phantoms, and how committed effective dose is derived for occupational monitoring.
PERCIST: Quantitative PET Tumor Response
PERCIST 1.0 turns FDG PET into a reproducible measure of tumor treatment response using SULpeak in a fixed 1.2-cm region, a liver reference threshold, and a 30 percent change rule. This guide explains the SUL math, the response categories, the scanner calibration and protocol consistency it demands, and why it outperforms size-based criteria.
Detective Quantum Efficiency in Digital Radiography
Detective quantum efficiency (DQE) is the single best summary of how efficiently a digital X-ray detector converts incident dose into usable image information. It combines spatial resolution (MTF), image noise (NPS), and detector dose response into one frequency-dependent curve, standardized for measurement by IEC 62220-1-1. Understanding DQE helps facilities compare detectors, defend dose reductions, and interpret acceptance-testing reports.
Gamma-Ray Constant & Point-Source Dose
The specific gamma-ray constant — modernized as the air-kerma rate constant — is the single number that converts the activity of a photon-emitting radionuclide into a dose rate at one meter. Combined with the inverse-square law and broad-beam shielding, it is the everyday tool a radiation safety officer uses to estimate external dose from vials, waste, sealed sources, and treated patients.
Gamma Camera Bar Phantom Resolution QC
A four-quadrant bar phantom is the routine weekly check of a gamma camera's spatial resolution and linearity: AAPM Report 177 recommends the extrinsic image with a Co-57 sheet source, and lists the intrinsic image (uncollimated detector, point source) as an alternative. This guide explains what the test measures, how bar visibility maps to FWHM, how uniformity and linearity interact, the tolerances that matter, and how routine bar-phantom QC fits into a defensible acceptance and annual-survey program.
Entrance Skin Dose (ESD) in Radiography
Entrance surface dose is the workhorse patient-dose quantity in general radiography. It is built from three measurable ingredients — tube output, inverse-square geometry, and the backscatter factor — and it links directly to diagnostic reference levels and, at the high end, to deterministic skin effects. This guide shows how ESD is defined, calculated, measured, and used.
Self-Contained Irradiator Radiation Safety
A self-contained blood or research irradiator hides a very large sealed source behind heavy shielding. It is not a Part 36 irradiator, its Cs-137 source is a Part 37 security concern, and its dose delivery drifts with source decay — three facts that shape the whole radiation safety program.
I-131 Therapy for Thyroid Cancer
I-131 therapy for differentiated thyroid cancer spans three distinct intents — remnant ablation, adjuvant treatment, and treatment of known disease — each with different administered activities. This guide explains the nuclear-medicine physics: fixed-activity versus dosimetry-guided dosing, patient preparation, post-therapy SPECT/CT, effective half-life, and MIRD blood dosimetry.
Pediatric Radiography Dose Optimization
Children are smaller and more radiosensitive than adults, so an adult radiographic technique is rarely the right starting point. Optimizing pediatric radiography means matching kVp, mAs, added filtration, grid use, collimation, exposure-index targets, and shielding practice to body size and clinical task — reducing entrance dose while preserving the diagnostic image quality the exam was ordered to provide.