The Future of Psychopharmacology and Positron Emission Tomography

Abstract

Positron emission tomography (PET) is a brain imaging technique which is at least 1000 times more sensitive than nuclear magnetic resonance (NMR). Today NMR can produce images of structures of the brain, but whether or not functional NMR will become clinically relevant still has to be proven. PET can give information about functional events in the brain of individual living patients. In PET, probes are used to study brain function. These probes are introduced into the central nervous system by intravenous injection, having been selected to follow and participate in the various aspects of biochemical processes in the brain that are to be studied. The probes are ordinary organic molecules which can be followed when labelled with a specific type of isotope called a positron emitting isotope. Ordinary radioactive isotopes cannot be used since the radiation from such isotopes does not pass through the skull bone. But positrons, the particles which are released from disintegrating positron emitting isotopes, can be recorded because when they collide with electrons in the tissue, gamma radiation is produced by the annihilation of antimatter and matter. The gamma radiation moves from the inside of the brain out toward the detection devices, which can be placed in rings around the head. Thus, PET is a technique by which the emission of gamma radiation from compounds labeled with specific isotopes is studied. These isotopes also have the advantage of being short-lived.