Positron emission tomography: ligand imaging.

Since it was first used to image the brain in 1976, positron emission tomography (PET) has been utilized in a wide range of neurologic and psychiatric applications. From cerebral metabolism to receptor concentration, various PET imaging techniques involving a host of radiopharmaceuticals have provided insight into countless facets of both the normal and diseased brain. Although the majority of these radiopharmaceuticals are still limited to the realm of research, one PET ligand in particular has gained widespread clinical use: (18)F-fluorodeoxyglucose, a radiolabeled analog of glucose, has become an exceedingly prevalent clinical tool for the measurement of metabolism in organs throughout the body, including the brain. In recent years, a number of novel PET ligands have also made it through the US Food and Drug Administration approval process and been used clinically. However, gaining approval is by no means the only challenge facing these radiopharmaceuticals. Traversing the blood-brain barrier is a formidable obstacle in drug delivery, and accurately modeling tracer kinetics and correcting for the partial-volume effect are among the difficult tasks that remain once the ligand reaches its intended target. Even so, the use of PET imaging in neurology and psychiatry can be expected to expand in the coming years as novel radiopharmaceuticals continue to be developed.