Table 5 Assumptions of PET/SPECT imaging

Radioactive tracers are composed of radioactive nucleotides linked to different ligands. The nucleotides emit positrons (PET) or photons (SPECT) from the tracer, which allows determining the tracer’s location. When the ligand is a hydrophilic plasma protein such as albumin, the tracer provides a measure of extravasation just like most MRI contrast agents. When the ligand binds specific molecular targets, such as TSPO, they can be used to elucidate specific pathophysiological processes.