Reproducibility of [123I]PE2I binding to dopamine transporters with SPECT

The iodinated cocaine derivative [(123)I]PE2I is a new selective ligand for in vivo studies of the dopamine transporter (DAT) with SPECT. Recently, a bolus/infusion (B/I) protocol for [(123)I]PE2I measurements of DAT density was established [Pinborg LH et al. J Nucl Med 2005;46:1119-271]. The aims of this study were, firstly, to evaluate the test-retest variability using the B/I protocol and, secondly, to evaluate the B/I approach in a new group of healthy subjects using two outcome parameters, BP(1) (C(ROI)/C(plasma)) and BP(2) (C(ROI)/C(REF)).

Seven healthy subjects were subjected to [(123)I]PE2I SPECT scanning twice. For both studies, the two outcome parameters BP(1) and BP(2) were calculated based on two different methods for region of interest (ROI) delineation, namely manual delineation and probability map-based automatic delineation with MRI co-registration.

With manual delineation, striatal test-retest variability (absolute difference between first and second scan as a percentage of the mean) of BP(1) and BP(2) was 13.9% (range 1.8-35.7%) and 4.1% (range 0.5-9.7%) respectively. The probability map-based automatic delineation resulted in striatal test-retest variability of 17.2% (range 4.3-40.5%) and 5.2% (range 0.1-10.9%) respectively. The B/I approach provided stable brain activity from 120 to 180 min post injection in both high- and low-count regions with a mean % change/hour in striatal BP(2) of 10.6.

[(123)I]PE2I SPECT with the B/I approach yields a highly reproducible measure of striatal dopamine transporter binding. The appropriateness of a B/I protocol with a B/I ratio of 2.7 h (i.e. with a bolus worth 2.7 h of infusion) was confirmed in an independent sample of healthy subjects.