Pharmacological implications for neuroreceptor imaging

Neuroreceptor imaging is increasing in nuclear medicine. New generations of radioligands will be developed that will allow us to study neurotransmitter systems not studied before. In data interpretation, however, links will have to be made with the number of counts acquired in the image and the real radioactivity in the brain and then, via the specific activity (and known metabolic characteristics), with the concentration of the ligand. From this point, links will have to be made, via kinetic modelling, with receptor density and, if possible, with receptor affinity, with the final link with brain function at a neurophysiological level. In this article several properties of receptor pharmacology and function are discussed that might help with the interpretation. It is argued that there is a complex relationship between the data, as is apparent in the images recorded and the underlying pharmacology of the receptor. Caution should be exercised, however, when in drawing conclusions about the receptor status and the possible implications on pathophysiology.