PET Scan (Positron Emission Tomography)
A nuclear medicine imaging technique that detects metabolic activity in the body using radioactive tracers. PET scans are used with radiolabelled peptides for diagnostic imaging — gallium-68 DOTATATE PET identifies somatostatin receptor-positive neuroendocrine tumours for treatment with lutetium Lu-177 dotatate.
Technical Context
PET detects gamma rays from positron-emitting radiotracers. The radiotracer is injected IV → distributes to tissues → positron emission → annihilation with electron → two 511keV gamma photons at 180° → detected by ring detector. Common tracers: FDG (18F-fluorodeoxyglucose — glucose metabolism, used in oncology for tumour staging), Ga-68 DOTATATE (somatostatin receptor imaging — the companion diagnostic for Lu-177 dotatate PRRT), Ga-68 PSMA (prostate cancer imaging — companion for Lu-177 vipivotide tetraxetan), and various research tracers. Ga-68 DOTATATE PET/CT: sensitivity >90% and specificity >95% for SSTR-positive NETs — superior to conventional CT/MRI and older scintigraphy (OctreoScan). The theranostic paradigm: same targeting peptide (DOTATATE) used with diagnostic isotope (Ga-68, positron emitter for PET) and therapeutic isotope (Lu-177, beta emitter for PRRT), enabling selection of patients most likely to benefit from targeted radionuclide therapy.