Nuclear Medicine: Radiopharmacy, Instrumentation, and Clinical Practice
Radiopharmacy fundamentals
A candidate must know how a radionuclide generator works, especially the Mo-99/Tc-99m system: Mo-99 decays to Tc-99m, which is eluted as sodium pertechnetate. Understand parent/daughter half-lives (66 h vs 6 h), transient equilibrium, and the meaning of eluate breakthrough testing for Mo-99 and alumina. Know that Tc-99m emits a 140 keV gamma ray and that its short half-life and generator availability make it the workhorse tracer. Be able to relate radiopharmaceutical choice to physiology: MDP for bone, sestamibi for myocardial perfusion and parathyroid, MAG3 or DTPA for renal function, sulfur colloid for liver/spleen and marrow, MAA for lung perfusion, and iodine-123 or pertechnetate for thyroid.
Instrumentation and quality control
Understand the gamma camera: collimator geometry (parallel-hole, pinhole, diverging), photomultiplier tubes, energy window setting around the photopeak, and the trade-off between sensitivity and resolution. Know why scatter correction and energy peaking matter, and the purpose of daily flood/energy checks, uniformity correction, and center-of-rotation testing. SPECT adds tomographic reconstruction; PET relies on coincidence detection of annihilation photons and requires attenuation correction. Recognize artifacts: patient motion, collimator damage, and inappropriate windowing.
Traps and worked rule
Questions often swap tracer and indication, or ask which collimator suits a small organ (pinhole for thyroid). Another trap is decay math: students forget that activity falls by half per half-life. Worked example: starting with 800 MBq of Tc-99m (6 h half-life), after 18 hours three half-lives have passed, so activity is 800/8 = 100 MBq. Rule of thumb: count half-lives first, then divide; never subtract linearly. Also remember dose optimization and ALARA principles when discussing administered activity.