ABR Nuclear Radiology cheat sheet

Photoelectric absorption probability varies approximately with Z^3/E^3; it dominates at low photon energies and high atomic number, producing a photopeak in spectra.

Compton scattering probability depends on electron density and dominates in soft tissue for nuclear medicine photons; scattered photons blur images and raise background.

Pair production requires photon energy of at least 1.022 MeV, so it is irrelevant for Tc-99m and most PET photons but matters for high-energy therapy photons.

NaI(Tl) light output is about 38,000 photons per MeV; at 140 keV the photopeak is broad, with typical energy resolution around 6-7%.

Collimator resolution improves with longer holes and smaller hole diameter, but sensitivity falls; septal thickness must prevent penetration at the imaged photon energy.

PET coincidence detection uses 511 keV annihilation photons; random coincidences increase with the square of activity, while timing resolution improves time-of-flight localization.

Paralyzable dead time causes observed count rate to peak and then fall as activity rises; nonparalyzable dead time causes observed rate to approach a plateau.

Iterative reconstruction with attenuation and scatter correction reduces streak artifacts and improves quantitation compared with filtered backprojection in SPECT and PET.

Mo-99/Tc-99m generators use an alumina column; Tc-99m is eluted with 0.9% saline, and Mo-99 breakthrough must not exceed 0.15 kBq per MBq Tc-99m.

Alumina breakthrough in generator eluate must be limited to 10 micrograms per milliliter; excess aluminum can alter labeling and biodistribution.

Radiochemical purity is the fraction of radioactivity in the desired chemical form; it is measured by chromatography and must meet the kit specification.

Tc-99m pertechnetate has a 6-hour half-life and 140 keV gamma; stannous ion reduces pertechnetate so it can bind to kit ligands.

Tc-99m MDP binds bone mineral; Tc-99m sulfur colloid is taken up by reticuloendothelial cells; Tc-99m MAA is trapped in pulmonary capillaries.

F-18 FDG has a 110-minute half-life and is trapped after hexokinase phosphorylation; F-18 NaF binds bone and is used for skeletal PET.

Ga-68 DOTATATE and Ga-68 PSMA bind somatostatin receptors and prostate-specific membrane antigen, respectively; Ga-68 has a 68-minute half-life.

Radiopharmaceutical quality control includes appearance, pH, particle size where relevant, sterility, endotoxin, and radionuclidic purity before administration.

ALARA uses time, distance, and shielding; exposure from a point source falls with the inverse square of distance.

NRC occupational dose limits are 50 mSv/year total effective dose equivalent, 150 mSv/year lens dose, and 500 mSv/year extremity dose.

The public dose limit is 1 mSv/year; a declared pregnant worker has a 5 mSv limit to the embryo-fetus over gestation.

A written directive is required for I-131 sodium iodide doses greater than 30 microcuries and for certain other therapeutic administrations.

Patient release after radiopharmaceutical therapy is permitted when the dose to any other individual is unlikely to exceed 5 mSv, with written instructions.

The MIRD schema estimates absorbed dose by multiplying source-region residence time by S values for target regions.

Decay is calculated with A = A0 e^(-0.693 t/T1/2); shielding is planned with half-value and tenth-value layers for the specific photon energy.

Survey meters must match the radiation type and energy; Geiger-Mueller detectors are sensitive but may saturate, while ionization chambers provide dose-rate measurements.

FDG PET patient preparation includes fasting, blood glucose control, and uptake time near 60 minutes; insulin can alter myocardial and tumor uptake.

FDG distributes physiologically to brain, myocardium, liver, spleen, kidneys, bowel, and urinary tract; brown fat and muscle uptake are common pitfalls.

SUVmax is time-dependent and affected by partial volume, lesion size, glucose, and reconstruction; SUL peak is less sensitive to body composition.

Deauville scoring compares lymphoma uptake with mediastinal blood pool and liver; scores 1-3 are generally negative and 4-5 positive.

PERCIST response requires a 30% decrease in SUL peak and an absolute decrease of at least 0.8 SUL units in the target lesion.

PSMA PET shows physiologic uptake in salivary and lacrimal glands, liver, spleen, kidneys, and bowel; PSMA is also expressed in some nonprostate tumors.

Ga-68 DOTATATE uptake is physiologic in pituitary, spleen, liver, kidneys, and adrenals; the Krenning score grades somatostatin receptor uptake.

PET/CT artifacts include misregistration from breathing, attenuation-correction errors from metal, and partial-volume loss in small lesions.

Tc-99m sestamibi and tetrofosmin are lipophilic cations taken up by mitochondria; myocardial uptake tracks perfusion and viability with little redistribution.

Tl-201 uptake depends on Na/K-ATPase and perfusion; it redistributes over time, so stress and delayed images can show ischemia or scar.

Exercise stress is preferred when feasible; adenosine, regadenoson, and dipyridamole are vasodilators, while dobutamine is used when vasodilators are contraindicated.

Reversible perfusion defect indicates ischemia; fixed defect indicates scar, and reverse redistribution can occur with subendocardial infarction or artifact.

Gated SPECT provides ejection fraction, wall motion, and thickening; post-stress stunning can produce transient regional dysfunction.

Rb-82 has a 75-second half-life and N-13 ammonia has a 10-minute half-life; both PET tracers allow flow quantification and attenuation correction.

Viability is suggested by Tl-201 rest-redistribution uptake or FDG perfusion-metabolism mismatch; matched defects suggest scar.

Tc-99m PYP cardiac uptake graded 2 or 3, confirmed with SPECT, supports transthyretin amyloidosis after AL amyloidosis is excluded.

Thyroid uptake with I-123 or Tc-99m pertechnetate is elevated in Graves disease and low in subacute thyroiditis or exogenous thyroid hormone.

A hot thyroid nodule with suppressed surrounding uptake usually indicates an autonomously functioning nodule and has low malignancy risk.

Parathyroid sestamibi imaging uses dual-phase or subtraction technique; SPECT/CT improves localization of adenomas before surgery.

Hepatobiliary IDA scintigraphy shows gallbladder nonvisualization in acute cholecystitis; morphine augmentation can shorten the study.

GI bleeding is imaged with Tc-99m sulfur colloid for rapid detection or Tc-99m tagged red cells for longer monitoring.

MAG3 is secreted by tubules and is preferred for renal function and obstruction; DTPA measures glomerular filtration.

Captopril renography is positive when renal function declines after ACE inhibition, suggesting renovascular hypertension.

V/Q scintigraphy is positive for pulmonary embolism when a perfusion defect is mismatched with normal ventilation; matched defects suggest lung disease.

Tc-99m MDP bone uptake reflects osteoblastic activity and blood flow; three-phase imaging adds flow and blood-pool information.

A superscan shows diffusely increased skeletal uptake with faint kidneys and soft tissues, suggesting widespread metastases or metabolic bone disease.

Prosthetic joint infection is evaluated with labeled leukocytes, often combined with sulfur colloid marrow imaging to distinguish marrow from infection.

In-111 oxine or Tc-99m HMPAO labeled leukocytes migrate to infection and inflammation; sensitivity is lower for chronic or spinal infection.

Gallium-67 accumulates in infection, inflammation, and tumor; normal uptake includes liver, spleen, marrow, salivary glands, lacrimal glands, and bowel.

FDG PET/CT is useful for fever of unknown origin, vascular graft infection, and spinal infection, but uptake is nonspecific.

Diabetic foot osteomyelitis is suggested by labeled leukocyte uptake in bone or by FDG uptake that persists after antibiotic therapy.

Bone scan is sensitive but not specific; SPECT/CT improves anatomic localization and distinguishes facet, sacroiliac, and dental disease.

Tc-99m HMPAO and ECD brain perfusion SPECT show regional cerebral blood flow; absent cerebral uptake supports brain death when clinical criteria are met.

I-123 ioflupane DAT SPECT shows reduced striatal uptake in Parkinsonian syndromes; a normal scan argues against degenerative Parkinsonism.

FDG brain PET shows temporoparietal hypometabolism in Alzheimer disease and frontal or temporal patterns in other dementias.

Amyloid PET tracers bind cortical amyloid; a negative scan makes Alzheimer disease unlikely, while a positive scan can occur in normal aging.

I-131 therapy for thyroid cancer uses remnant ablation or adjuvant doses; dosimetry can limit activity for extensive metastases.

Lu-177 DOTATATE peptide receptor radionuclide therapy delivers beta and gamma radiation to somatostatin receptor-positive neuroendocrine tumors.

Y-90 microsphere liver therapy requires lung shunt fraction measurement; high shunt increases pulmonary radiation risk.

Ra-223 is an alpha emitter used for bone metastases in prostate cancer; Lu-177 PSMA therapy targets prostate-specific membrane antigen.