Quantitative approaches to dopaminergic brain imaging

During the last three decades dopaminergic brain imaging has emerged from a dedicated research tool to a widespread and routinely used application. The rationale behind this development is on the one hand the well known pathologic involvement of the dopaminergic pathway in various neuro-psychiatric diseases, and on the other hand the increasing availability of specific radioligands for picking up pre- and postsynaptic dopaminergic key functions. In particular the commercial availability of SPECT tracers but also the growing number of positron emission tomography/computed tomography (PET/CT) imaging devices has contributed to the steadily increasing number of diagnostic applications. In an era aiming for accurate diagnosis in the early and even preclinical stage of disease, refined methodologies are required to detect even subtle changes. In this context quantification of dopaminergic functions more and more gains importance. Whereas earlier visual assessment was considered sufficient to characterize findings, today refined quantitative tools have the potential to deliver information beyond. This review briefly addresses the development of quantitative methods for dopaminergic brain imaging, from simple manual ratio based applications to various automated methodologies, some of them including tools for correction of physical parameters such as scatter and septal penetration and partial volume effects. Voxel based analysis methods will be covered and also kinetic analyses will be briefly touched. The main focus is directed at SPECT rather than PET methodologies due to the clinical impact of the first. Finally, some thoughts regarding the impact of standardization and harmonization of protocols for imaging and processing will be discussed, including the use of normal data bases for reference.