Quantitative evaluation of striatal I-123-FP-CIT uptake in essential tremor and parkinsonism

The aim of this study was to quantitatively evaluate the striatal uptake in 3 groups of patients: essential tremor (ET), drug-induced parkinsonism (DIP), and Parkinson disease (PD), using a voxel-based methodology and volumes of interests (VOIs) analysis.

Sixty patients from the Neurology Department Movement Disorders outpatient clinic in a tertiary hospital with I-123-FP-CIT SPECT were selected. After a clinical follow-up period of 2 years, a final clinical diagnosis of DIP was established for 20 patients (first group); 20 patients were diagnosed with ET (second group), and the third group was made up of 20 patients with a qualitatively pathologic SPECT who were diagnosed with PD.Once processed, DIP studies were spatially normalized to Montreal Neurologic Institute space and an average image was computed to create an I-123-FP-CIT SPECT template using statistical parametric mapping (SPM). Then all the I-123-FP-CIT images from all groups (DIP, ET, and PD) were registered to the new template. VOIs were defined in a digital atlas in Montreal Neurologic Institute space (caudate nucleus, putamen, and occipital cortex). Finally, mean counts were extracted from all VOIs and putamen-occipital and caudate-occipital ratios were computed. Analysis of variance tests were performed with all ratios.A SPM study of patterns evaluated the efficacy of the automated technique to determine whether the significant differences among groups corresponded to the same regions that the method purported to evaluate.

The analysis of variance test revealed significant differences between DIP and ET as compared with PD, both in the putamen and in the caudate nucleus. There were significant differences between DIP and ET populations only in the putamen but not in the caudate.The SPM found a lower uptake in the PD group in comparison with the ET and DIP groups. Therefore, in the organic parkinsonism cases, the most significant changes in uptake decrease were found in the putamen nuclei when compared with the DIP and the ET cases. No significant changes were observed between the ET and DIP groups.

This study provides a fairly simple, reproducible, and useful methodology to be applied in everyday practice to quantify the studies of dopamine transporters using FP-CIT.We present the different ratios for putamen and caudate nucleus for 3 different groups with FP-CIT images. We obtained an optimal discrimination threshold value between the reference population and the pathologic population for the putamen ratio.