A particularly sensitive step in the quantification of SPECT images of the dopamine transporter (DAT) is a correct delineation of the region of interest (ROI). In this study, we primarily compared the reproducibility of the following different approaches for ROI delineation in SPECT images of the DAT: the use of manual delineation (MD) on high-count striatal slides directly on the SPECT image, ROI delineation based on individual MR images (MRD), and oversized striatal ROIs-that is, the striatal volume of interest (SVI), as described previously. We also assessed the ability of the different approaches to identify striatal pathology in patients with parkinsonism.
Methods: Eight patients with highly variable reductions in cerebral DAT availability were SPECT-scanned twice with (123)I-labeled N-(3-iodoprop-(2E)-enyl)-2beta-carboxymethoxy-3beta-(4'-methylphenyl) nortropane bolus infusion setup and once with an MRI scanner. For SPECT/MRI coregistration, we used external fiducial markers visible on both MRI and SPECT. With the MD and MRD methods, the outcome parameters for DAT availability were the binding potentials and the ratio at equilibrium of specifically bound radioligand to nondisplaceable radioligand in tissue (BP(ND)). For the SVI method, the outcome parameter was the specific binding ratio (SBR).
Results: No statistically significant difference in striatal BP(ND) intraobserver reproducibility was seen among any of the 3 methods. The intraobserver reproducibility average +/- SD for MD was 7.0% +/- 4.1%; for MRD, 5.7% +/- 5.4%; and for SVI, 6.7% +/- 6.0%. Mean intrasubject variability, as determined from the test-retest scans, did not differ with the 3 delineation methods used. The average (+/-SD) intrasubject variability of striatal BP(ND) was 11.9% +/- 10.0% with MD and 14.6% +/- 15.3% with MRD. With the SVI method, the intrasubject variability of striatal specific binding ratio was 10.0% +/- 10.2%. BP(ND) values obtained with the MD and MRD methods were similar (paired t test, P > 0.4).
Conclusion: In patients with reduced striatal DAT binding, the reproducibility of the outcome from ROI MD is comparable to both that obtained by delineation of ROI on individual MR images, followed by coregistration to the SPECT image, and that obtained with the SVI-based approach.