CAMRT Nuclear Medicine cheat sheet

Decay law: A = A0·e^(−λt), where λ = ln2/T½; activity falls by half every half-life regardless of starting activity.

Common isotope half-lives: Tc-99m 6.02 h, F-18 109.8 min, Ga-68 67.7 min, I-123 13.2 h, I-131 8.02 d, Tl-201 73 h, In-111 2.80 d, Lu-177 6.65 d.

Mo-99/Tc-99m generator: Mo-99 (T½ 66 h) decays to Tc-99m; elution efficiency falls and Tc-99m breakthrough must be tested per eluate before patient use.

Radiopharmaceutical localization: MDP binds bone hydroxyapatite; DTPA and MAG3 are renal tubular/glomerular agents; MIBI and tetrofosmin track perfusion and mitochondrial membrane potential.

V/Q scan interpretation uses modified PIOPED II: high-probability pattern is ≥2 large mismatched perfusion defects; a normal perfusion scan excludes PE.

Sentinel node and thyroid imaging rely on particle size and uptake: filtered sulfur colloid (~100 nm) for nodes, larger colloid for liver/spleen, pertechnetate for thyroid and Meckel diverticulum.

Dose-limiting radiation protection: ALARA, time-distance-shielding; Tc-99m has 140 keV gamma (good for gamma camera), F-18 511 keV annihilation photons require PET coincidence detection.

Effective half-life: 1/Teff = 1/Tphys + 1/Tbio; used to estimate retained activity and dosimetry over time.

Radiopharmacy quality control: radiochemical purity by chromatography, pH, clarity, and sterility; Tc-99m pertechnetate must be clear and colorless with no visible particulates.

Gamma camera components: collimator (defines resolution/sensitivity), NaI(Tl) crystal, photomultiplier tubes, pulse-height analyzer, and computer; energy window centered on photopeak.

Collimator choice: low-energy high-resolution for Tc-99m; medium-energy for In-111 and I-123; high-energy for I-131; pinhole for small organs such as thyroid.

Spatial resolution improves with closer patient-to-collimator distance and smaller hole diameter, but sensitivity decreases as resolution improves.

Photopeak energy windows: Tc-99m 140 keV (±10%), I-123 159 keV, F-18 511 keV, I-131 364 keV; scatter correction uses a lower-energy window.

PET detection uses coincidence of two 511 keV photons emitted 180° apart; time-of-flight improves SNR, and attenuation correction is required for quantification.

SPECT reconstruction: filtered back-projection is fast but noisy; iterative OSEM reduces noise and artifacts, and CT-based attenuation correction improves uniformity.

Image quality metrics: uniformity (flood field), spatial resolution (line spread function), sensitivity (cps/MBq), and energy resolution (~10% FWHM for NaI).

Dead time and pulse pile-up at high count rates cause count loss and spectral shift; paralyzable vs nonparalyzable models describe the response.

Radiation dose quantities: absorbed dose in gray (1 Gy = 1 J/kg), equivalent dose in sievert using radiation weighting (photons = 1), effective dose sums tissue-weighted doses.

Occupational limits (ICRP): 20 mSv/y averaged over 5 years, 50 mSv in any single year; public limit 1 mSv/y; extremity 500 mSv/y.

Pregnancy: confirm pregnancy status before high-dose studies; I-131 is contraindicated in pregnancy and breastfeeding; lactation interruption depends on radiopharmaceutical.

Time, distance, shielding: dose rate falls with inverse square of distance; lead shielding is effective for low-energy photons but not for 511 keV PET photons.

Personnel monitoring uses TLD or OSL dosimeters; ring badges for extremity dose; ALARA program includes audit and dose investigation levels.

Radioactive waste: decay-in-storage until activity is indistinguishable from background before disposal; sharps and contaminated materials segregated.

Patient release criteria: residual activity and dose rate at 1 m guide discharge instructions; avoid prolonged close contact with children and pregnant persons.

Emergency spills: contain, mark, absorb, and decontaminate; survey with a Geiger-Mueller or scintillation detector and document the event.

Myocardial perfusion: stress/rest SPECT with Tc-99m sestamibi or tetrofosmin; reversible defect indicates ischemia, fixed defect indicates scar.

Bone scan: Tc-99m MDP uptake reflects osteoblastic activity and blood flow; three-phase scan (flow, blood pool, delayed) distinguishes cellulitis from osteomyelitis.

Renal scan: Tc-99m DTPA for GFR, MAG3 for tubular secretion and transplant evaluation; captopril renography for renovascular hypertension.

Thyroid: Tc-99m pertechnetate uptake and I-123 scan; hot nodule suppresses surrounding tissue, cold nodule requires further evaluation.

V/Q scan: Technegas or DTPA aerosol for ventilation, Tc-99m MAA for perfusion; mismatched defects suggest pulmonary embolism.

PET/CT: F-18 FDG reflects glucose metabolism; patient preparation includes fasting and glucose control; brown fat and infection are false-positive pitfalls.

GI bleeding: Tc-99m labeled RBC scan detects intermittent bleeding; Meckel scan uses pertechnetate and appears as focal uptake in the right lower abdomen.

Lymphoscintigraphy and sentinel node: intradermal filtered sulfur colloid, dynamic imaging, and gamma probe localization intraoperatively.

Therapy: I-131 for hyperthyroidism and thyroid cancer, Lu-177 DOTATATE for neuroendocrine tumors, and Y-90 microspheres for hepatic tumors; verify pregnancy status and dosimetry.