Quantification and visualization of defects of the functional dopaminergicsystem using an automatic algorithm

In SPECT, the binding of radiotracers in brain areas is usually assessed by manual positioning of regions of interest (ROIs). The disadvantages of thi s method are that it is an observer-dependent procedure and that it may not be sensitive for assessing defects significantly smaller than the ROI. To circumvent these limitations, we developed a fully automatic three-dimensio nal technique that quantifies neuronal radiotracer binding on a voxel-by-vo xel basis. Methods: To build a model of normal I-123-labeled N-omega-fluoro propyl-2 beta-carbomethoxy-3 beta-(4-iodophenyl)nortropane (FPCIT) binding, 17 studies of healthy volunteers were registered to the same orientation. After registration, the specific-to-nonspecific binding ratio was calculate d for each voxel of the striatal volumes of interest (VOIs). The mean and S D of that binding ratio were then calculated on a voxel-by-voxel basis. For the analysis of 10 healthy volunteer studies (control group) and 21 studie s of drug-naive patients with Parkinson's disease, the registration and cal culation of the specific-to-nonspecific [I-123]FPCIT binding ratio were per formed by the same method. Subsequently, a voxel of the striata was classif ied as a diminished [I-123]FPCIT binding ratio if its value was lower than the mean -2 x SD. For each subject, the defect size, the relative number of voxels with a diminished binding ratio and the binding ratio of the whole striatal VOIs were calculated and compared with the binding ratio as assess ed by the traditional ROI method. Results: The results of the automatic met hod correlated significantly with the results of the traditional ROI method . Furthermore, for the ipsilateral side, the automatically calculated defec t size had less overlap between the patient and the control group than the traditionally calculated binding ratio. Conclusion: The method presented qu antifies [I-123]FPCIT binding ratio automatically on a voxel-by-voxel basis , by comparison with a model of healthy volunteers. We have shown that it i s appropriate to use the automatic method as a replacement for the traditio nal manual method, which enables us to study the localized dopaminergic deg eneration process in Parkinson's disease more precisely and without any int er- or intraobserver variability.