In vivo Assessment of the Human Nigrostriatal Dopaminergic System Using Positron Emission Tomography

Direct biochemical functional analysis of implanted cells in human brain during life is not possible. However, one can obtain specific regional cerebral biochemical information using special radiotracer techniques and positron emission tomography (PET). The information carriers are tracer substances, labelled with short-lived positron emitting radionuclides (e.g. C or SF), which, after administration to healthy volunteers or patients, are distributed in space and time according to their pharmacokinetic properties. Comparison of the time course of count rates in brain regions with specific tracer uptake to those in brain reference regions allows quantification of specific tracer uptake in terms of metabolic trapping or binding to receptor sites. Quantification may be attempted through application of rigorous mathematical kinetic models or via simple but robust measures like ratios of count rates between two brain regions. Several PET radiotracers now exist to investigate various aspects of the dopaminergic nigrostriatal neurotransmitter system. Pathophysio