PhysicsPulseTM
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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).
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Siemens CT Reconstruction Kernels Decoded
A practical guide to Siemens SOMATOM CT reconstruction kernels: how kernel naming and resolution index work, and how kernel selection affects sharpness, noise, and quantitative accuracy.
CT 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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 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.
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.
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.
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.
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.
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.
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.
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.