Analysis of four dopaminergic tracers kinetics using two different tissue input function methods

The integrity of the dopaminergic system can be studied using position emis sion tomography. The presynaptic tracers [C-11]-methylphenidate and [C-11]d ihydrotetrabenazine (DTBZ) are used to investigate the dopamine transporter availability, the dopamine vesicular transporter integrity; the postsynapt ic tracers [C-11]-raclopride and [C-11]-Schering 23990 (SCH) are used to pr obe the D2 and D1 receptors. These are reversible tracers, where the bindin g potential (BP) = B-max/K-d often is used to quantify the amount of their specific binding to the sites of interest. The simplified tissue input meth ods to calculate BP are attractive, since they do not require a blood input function. The suitability and performance of two such methods were evaluat ed: the Logan graphical tissue method, and the Lammertsma reference tissue method (RTM). The BP estimates obtained with the two methods were nearly id entical in most cases, with similar reliability and reproducibility indicat ing that all four tracers satisfy the assumptions required by each method. The correlations among the fitted parameters obtained from the RTM were est imated and were found not to introduce noticeable bias in the RTM BP and R- 1 estimates. R-1 showed low intersubject and intrasubject variability. The k(2) estimate showed good reliability for SCH with cerebellar input functio n and DTBZ with occipital input function.