Nuclear Medicine Physics and Protection
Core concepts
Know radiopharmaceuticals (Tc-99m, F-18 FDG, I-131, Ga-68), their half-lives and emissions, and how they localize. Understand gamma camera physics (collimator, scintillator, photomultiplier), PET/CT principles (annihilation, coincidence detection), and the difference between diagnostic and therapeutic nuclear medicine. Know contamination control, patient release criteria, and the handling of radioactive waste. Understand time, distance, and shielding for high-energy photons (e.g., F-18 requires more shielding).
Traps
Questions test half-life values (Tc-99m ~6 h, F-18 ~110 min, I-131 ~8 d). Don't confuse diagnostic I-123 with therapeutic I-131. Watch for contamination vs exposure-internal contamination is a different hazard. Remember that PET photons (511 keV) need denser shielding than Tc-99m. Patient release criteria and instructions are commonly tested. Syringe shields and vial shielding reduce extremity dose.
Worked example / rule of thumb
Tc-99m T½ = 6 h; after 24 h (4 half-lives) activity = 1/16 of initial. Rule of thumb: count half-lives and divide by 2^n; for F-18 (~110 min), two half-lives ≈ 3.7 h.