ABNM Nuclear Medicine cheat sheet

Photoelectric absorption varies approximately with Z^3/E^3 and dominates at low photon energies and high atomic number; Compton scattering depends on electron density and dominates in soft tissue from about 100 keV to 1 MeV.

Pair production requires photon energy above 1.022 MeV; the positron and electron subsequently annihilate, producing two 511 keV photons.

Decay formulas: A = A0 e^(-λt); T1/2 = ln2/λ; mean life = 1/λ = 1.443 × T1/2.

Gamma-camera collimator resolution R ≈ d(Le + L)/Le, where d is hole diameter, Le is effective hole length, and L is source-to-collimator distance; sensitivity increases with d^2 and decreases with Le^2.

NaI(Tl) energy resolution is about 6-7% at 140 keV; a ±10% energy window around the 140 keV photopeak is typical for 99mTc imaging.

NRC occupational limits: 50 mSv/y total effective dose, 150 mSv/y lens dose, 500 mSv/y extremity dose; public limit is 1 mSv/y.

Radiation protection follows time, distance, and shielding; point-source intensity obeys the inverse-square law, so doubling distance reduces exposure rate to one quarter.

Dead time causes count loss at high activity; paralyzable systems show count-rate decline at very high rates, while nonparalyzable systems plateau.

99Mo/99mTc generator: 99Mo (66 h) decays to 99mTc (6 h); saline elution removes pertechnetate from an alumina column; transient equilibrium is approached after about 24 h.

99mTc decays by isomeric transition to 99Tc, emitting a 140 keV gamma ray; it has no significant particulate emission and a 6-hour physical half-life.

Kit labeling depends on stannous ion reduction of pertechnetate; radiochemical purity is measured by chromatography, and common impurities are free pertechnetate and hydrolyzed reduced technetium.

18F-FDG is a glucose analog taken up by GLUT transporters and phosphorylated by hexokinase; FDG-6-phosphate is trapped because it cannot continue through glycolysis.

18F has a 110-minute half-life and decays by positron emission; the positron annihilates to yield two 511 keV photons emitted approximately 180 degrees apart.

99mTc-MAA particles are 10-100 micrometers and lodge in pulmonary capillaries; they are used for lung perfusion imaging, and particle number is limited in pulmonary hypertension or right-to-left shunt.

Common renal agents: 99mTc-DTPA is filtered by glomeruli; 99mTc-MAG3 is secreted by tubules; 99mTc-DMSA binds proximal tubules and is used for cortical imaging.

Iodine-123 and iodine-131 have different imaging roles: I-123 (13.2 h) is used for diagnostic thyroid imaging, while I-131 (8.02 d) is used for therapy and some imaging.

V/Q scan interpretation: perfusion defect with normal ventilation is a mismatch and raises PE probability; matched defects are less specific and often reflect parenchymal disease.

99mTc-MDP bone scan is acquired 2-4 hours after injection; increased uptake reflects osteoblastic activity and blood flow, and a superscan shows diffuse skeleton uptake with faint kidneys.

Three-phase bone scan includes flow, blood-pool, and delayed images; cellulitis increases all phases, while osteomyelitis typically shows focally increased flow, blood pool, and delayed uptake.

Myocardial perfusion SPECT uses 99mTc-sestamibi or tetrofosmin; stress and rest images assess ischemia, and gated acquisitions provide left ventricular function and wall motion.

Renal captopril renography is positive when an ACE inhibitor worsens renal function or delays excretion on the affected side; it is used to assess renovascular hypertension.

99mTc-IDA hepatobiliary imaging: gallbladder nonvisualization after 4 hours supports acute cholecystitis; biliary leak appears as extrabiliary tracer accumulation.

99mTc-RBC is used for gastrointestinal bleeding; 99mTc-pertechnetate is used for Meckel diverticulum and thyroid imaging; 99mTc-sestamibi is used for parathyroid and myocardial imaging.

SPECT reconstruction often uses iterative ordered-subset expectation maximization with attenuation correction and scatter correction; filtered backprojection is faster but noisier.

In PET, a positron annihilates with an electron to produce two 511 keV photons emitted nearly 180 degrees apart; coincidence detection identifies an annihilation event.

Clinical PET crystals include BGO, LSO, LYSO, and GSO; LSO and LYSO have fast decay and high light output, while BGO has higher stopping power but slower timing.

SUV = decay-corrected tissue activity concentration / (injected activity / body weight); SUV is affected by plasma glucose, uptake time, body composition, and reconstruction.

18F-FDG PET patient preparation includes fasting for at least 4-6 hours, avoiding vigorous exercise, and controlling blood glucose; insulin can shift FDG into muscle and reduce tumor uptake.

PET/CT artifacts include CT attenuation-correction mismatch from patient motion, metallic implants, and contrast; misregistration can create false uptake or false-negative regions.

Deauville five-point scale compares lymphoma FDG uptake with mediastinal blood pool and liver; scores 1-3 generally indicate complete metabolic response.

Common PET tracers: 18F-NaF for bone; 68Ga-DOTATATE for somatostatin receptors; 68Ga-PSMA for prostate cancer; 82Rb or 13N-ammonia for myocardial perfusion.

Quantitative PET metrics include SUVmax, SUVmean, metabolic tumor volume, and total lesion glycolysis; PERCIST uses SUL and a threshold change for response.

131I emits beta particles and a 364 keV gamma ray; it treats hyperthyroidism and differentiated thyroid cancer by concentrating in thyroid tissue and delivering local radiation dose.

Radioiodine remnant ablation after thyroidectomy requires adequate TSH stimulation, usually by levothyroxine withdrawal or recombinant TSH, and a low-iodine diet before treatment.

177Lu-DOTATATE targets somatostatin receptor-positive neuroendocrine tumors; standard kidney protection uses amino acid infusion, and dosimetry may guide activity.

223Ra is an alpha emitter for bone metastases; the standard regimen is 50 kBq/kg every 4 weeks for 6 doses, with monitoring for myelosuppression and diarrhea.

90Y microspheres are delivered by hepatic arterial infusion for liver tumors; beta radiation provides local dose, and lung shunt fraction is assessed to limit pulmonary exposure.

89Sr and 153Sm are bone-seeking agents for painful skeletal metastases; both can cause myelosuppression, and blood counts are monitored before and after treatment.

Release criteria after radioiodine therapy depend on measured dose rate and retained activity; written instructions address close contact, children, pregnancy, and travel.

Pregnancy is a contraindication to most radionuclide therapy and diagnostic radioiodine; breastfeeding interruption depends on the radiopharmaceutical and must follow published guidance.