AbstractThere are two types of imaging instruments, single-photon emission computed tomography (SPECT) and positron emission tomography (PET) that use radiopharmaceuticals for the diagnosis of brain disorders. Brain perfusion imaging agents, labeled either with123I or99mTc, are useful in detecting various cerebral vascular abnormalities, such as stroke and transient ischemia with SPECT. The management of other neurological disorders (i.e., in Alzheimer's, epilepsy, schizophrenia, and head trauma patients) may also be benefitted by these agents. The exact trapping mechanisms and their relationships with potential clinical applications still remain to be elucidated. Imaging studies using18F fluorodeoxyglucose with PET is currently the most promising diagnostic tool for the evaluation of local glucose metabolism related to various disease states, such as Alzheimer's disease, brain tumor, and epilepsy. In the past few years significant progress has been made in the design and characterization of new CNS neuronal and postsynaptic receptor imaging agents for PET and SPECT. The new diagnostic agents are aimed at measurements of localization and changes of neuronal function. It is likely that these types of agents have potential for clinical application, especially in the diagnosis of psychiatric disorders that do not involve morphological changes.