PhysicsPulseTM
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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%.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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).
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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?
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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 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.
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.
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.
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.
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.