PET Radiopharmaceuticals
What this domain tests
This domain covers production, biodistribution, dose preparation, and QC of PET drugs, especially F-18 FDG, plus generator and cyclotron agents. Questions often combine decay math with patient-preparation rules.
Core rules
- F-18 has a 109.8-minute half-life and is cyclotron-produced by the 18O(p,n)18F reaction. FDG is a glucose analog: GLUT transporters bring it into cells, hexokinase phosphorylates it to FDG-6-phosphate, and low phosphatase activity traps it, so uptake reflects glucose metabolism.
- Fasting for 4–6 hours, hydration, and avoidance of vigorous exercise reduce confounding muscle uptake. High blood glucose or recent insulin can lower tumor uptake and alter biodistribution; follow institutional glucose cutoff.
- Typical FDG adult dose is about 5–15 mCi (185–555 MBq), with a 45–60 minute uptake period. Void before imaging to reduce bladder activity.
- Other agents: Ga-68 DOTATATE (somatostatin receptor), Ga-68 PSMA (prostate), Rb-82 chloride (myocardial perfusion; 76-second half-life, generator), N-13 ammonia (~10 minutes), F-18 NaF (bone), amyloid tracers.
- QC includes visual inspection, pH, radiochemical purity (often TLC, ≥90%), radionuclidic purity, sterility, endotoxin, and half-life verification.
Worked example
A vial contains 740 MBq F-18 FDG at 10:00. At 11:00, activity = 740 × 0.5^(60/109.8) = 740 × 0.685 ≈ 507 MBq. If the prescribed dose is 370 MBq, the volume must be recalculated from the current concentration, not the calibration-time concentration.
Traps
Do not use decay-uncorrected activity for dosing. Do not assume FDG uptake equals malignancy-infection, inflammation, and brown fat also take it up. Rb-82 and Ga-68 come from generators, but their half-lives and elution rules differ.