Current Development of Neuroimaging Using PET Techniques

Abstract

Positron emission imaging was developed more than 50 yrs ago, when Dr. Gordon Brownell did the first clinical brain imaging with his scanner in1951 on 8-year old girl to detect a brain tumor. Detection and localization of brain tumors was the main application area of the positron emission imaging for the following 20 years. The isotopes like 72As, 64Cu and 68Ga were used as imaging agents. When the cyclotrons came available in the hospital environment in 1970s, 15O and 11C labeled gases replaced the long-lived isotopes. These studies were based on blood flow and oxygen metabolism and are still used in a variety of neurological applications. New area of neuroimaging started, when radiolabeling techniques developed to produce compounds to investigate metabolic and specific biochemical (receptor and/or enzyme) functions in the brain. This development established in vivo neurochemistry, which is presently one of the most active research areas in neuroimaging. Presently the mostly used radiolabels in PET imaging are 11C and 18F, which can be detached to the imaging ligand through radiosyntheses. The main application areas of PET imaging for diagnosis and research include neurodegeneration, stroke, drug addiction, brain activation, epilepsy, inflammation, cancer, and drug development. The application area is continuously increasing based on radiopharmaceutical development. The first significant breakthrough in in vivo neuroimaging happened after introducing of radioligands to image dopamine transporters. Even these ligands are not generally approved for clinical diagnosis; they are used world wide as research tools in neurodegenerative disorders, especially in Parkinson’s diseases (PD) as well as drug abuse. Presently world wide interest is to develop specific ligands for diagnosis of Alzheimer’s disease and several imaging ligands are in clinical trials. Other active radiopharmaceutical developments include ligands for serotonergic and metabotropic glutamate receptor systems.