Fig. 2.
PET principle: imaging agents used for PET are radioactive probes emitting positively charged anti-electrons (positrons). The positron travels a short distance (∼1–3 mm) before it annihilates with any electron to give two photons of 511 keV travelling under a mutual angle of 180°. It is this pair of coincident high energy photons that underly the PET principle allowing in vivo quantitative 3D imaging through coincident detection using a gantry of multiple detectors around the patient