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.
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.
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.
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.
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.
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New York repealed and replaced 10 NYCRR Part 16 effective July 22, 2026, and the new Part contains section 16.65, the state's first rule written specifically for cone beam CT.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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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).
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.