Optimization of automated quantification of I-123-IBZM uptake in the striatum applied to parkinsonism

Evaluation of therapies for parkinsonism by dopamine receptor SPECT require s a reproducible, optimized quantitation technique. This study presents a n ew, objective, automated technique for semiquantitative analysis of dopamin e receptor density, as applied to the differential diagnosis of parkinsonis m. Methods: Dopamine receptor density measured by I-123-iodobenzamide (IBZM ) SPECT was retrospectively analyzed in nonidiopathic parkinsonism (NIPS), in Parkinson's disease (PD), and in healthy volunteers (n = 19, 38, and 13, respectively). A mean template was created from coregistered control studi es. Registration errors were assessed using studies with simulated binding deficits. Patient studies were registered to the mean template, and striata l binding was calculated from a corresponding map of 3-dimensional regions of interest (ROIs). The striatal binding ratio and deficits determined by v oxelwise comparison with the normal template were investigated and tested w ith various 3-dimensional ROI sizes and positions. Separation of patient gr oups was determined by t score after automatically processing all studies. Results were compared with manual ROI analyses. Results: The automatic meth od was completely reproducible in 64 of 70 cases. The best diagnostic discr iminator was the minimum binding ratio of the 2 striatal nuclei, with the f ollowing values: NIPS, 1.33 +/- 0.13; PD, 1.50 +/- 0.12; healthy volunteers , 1.49 +/- 0.08 (+/-SD). The deficit size from voxelwise analysis was: NIPS , 20.5 +/- 8.2 ml; PD, 9.5 +/- 8.3; healthy volunteers, 8.9 +/- 6.0 (+/-SD) . The accuracy, measured by receiver operating characteristic areas, was 0. 85 +/- 0.05, 0.77 +/- 0.06, and 0.80 +/- 0.06 (+/-SE) for the optimal predi ctor (automated) and 2 blinded observers (manual), respectively. Conclusion : A new 3-dimensional, automated technique has been developed to semiquanti tate receptor density that dramatically improves reproducibility. The optim al diagnostic discriminator of parkinsonism determined by the automatic tec hnique has good accuracy compared with the manual technique.