SPECT imaging of dopamine D2 receptors was performed using 123I-labeled 2'-iodospiperone (2'-ISP).
Methods: Iodine-123-2'-ISP was administered to 12 normal subjects. Serial SPECT scans were obtained in six normal subjects for kinetic studies and static SPECT images were obtained in four normal subjects. Two additional normal subjects had serial whole-body imaging to calculate radiation dosimetry.
Results: Serial SPECT scans demonstrated rapid initial brain uptake followed by gradual washout from the cerebral cortex and cerebellum, while the activity in the basal ganglia was stable for 2 hr and gradually decreased thereafter. There was fast clearance of blood activity with rapid conversion of 2'-ISP to the hydrophilic metabolites. The basal ganglia-to-frontal cortex ratio increased with time and plateaued between 2 and 4 hr postinjection. The basal ganglia-to-frontal cortex ratio obtained during this period demonstrated an age-dependent decrease similar to other D2 ligands.
Conclusion: 2'-ISP can be used for mapping dopamine D2 receptors in human brain with SPECT. The relatively high background activity, however, suggests that further modification of the compound may be needed prior to widespread clinical use.