The reasoning
- Positron emission → annihilation with an electron after ~1–2 mm → two 511 keV photons at ~180° → coincidence detection by a detector ring (no collimator needed; higher sensitivity and resolution than SPECT, ~4–6 mm).
- FDG kinetics: GLUT transporters (GLUT1/3 up‑regulated in tumours) → hexokinase phosphorylates to FDG‑6‑P → not a substrate for phosphoglucose isomerase and low glucose‑6‑phosphatase in tumours → metabolic trapping (Warburg effect).
- Patient preparation: fast 4–6 h, blood glucose ideally < 150–200 mg/dL, rest in a quiet warm room (reduces muscle and brown fat uptake), imaging at ~60 min.
- SUV = tissue activity concentration ÷ (injected activity / body weight). SUVmax > 2.5 was a classic "suspicious" cut‑off for lung nodules, but SUV varies with glucose, timing, body habitus, partial volume and scanner. Use it for trends (Deauville 5‑point scale in lymphoma, PERCIST for response), not as a binary test.