The PET Revolution in the Neurosciences

Abstract

Positron emission tomography (PET) has the potential of revolutionizing clinical neurosciences, by making it possible for the first time to measure in vivo chemistry in the living human brain, expressing the results in absolute units of meters, kilograms, and seconds (the MKS system). When we can measure the rate of a chemical process in a region of the brain, there is the possibility of at least two diseases, one in which the rate of the chemical process is abnormally slow, and another in which the process is abnormally fast. PET studies of brain chemistry fall into two categories: substrate metabolism and information transfer. Advances in the use of simple probe detector systems are being used to monitor the response of a given patient to drug treatment, and to reduce the incidence of untoward side effects. PET can at times detect abnormalities before anatomical changes have occurred, for example, in epilepsy, Huntington’s disease or cerebrovascular disease. In patients with epilepsy and brain tumors, PET scanning provides information useful in the planning and monitoring of surgical treatment. PET can be used to determine whether there is an epileptic focus, or in patients with tumor, to assess the effectiveness of surgery, radiation and chemotherapy. PET scanning can document the extent of tumors, and progression or regression with different forms of treatment. Up to now, treatment has been based primarily on histopathological examination of biopsies; biochemical characterization may be an even better way to classify tumors. Studies of patients with stroke indicate that metabolic abnormalities seen on PET frequently are more extensive than the corresponding CT findings, and the pattern of metabolic abnormalities in PET correlates with the clinical syndrome and with the degree of eventual recovery. Abnormal D2 dopamine receptor concentrations have been found in the caudate and putamen of many patients with psychotic depression. PET studies have brought about a whole new approach to biological psychatry.