EVALUATION OF BRAIN ACTIVITY IN FDG PET STUDIES

Purpose: A tool (Gemini) was developed for quantifying regions of inte rest (ROIs) in registered MR and PET data. Its use was validated throu gh phantom and simulated studies. Method: Hot spheres were imaged in a phantom (3:1 and 5:1 target-to-nontarget ratios). The computerized 3D Hoffman brain phantom was used to simulate PET studies. Spherical loc al activity features of two diameters (4 and 10 mm) and five intensiti es (5, 15, 25, 50, and 100% increase over gray matter) were added to t he data in the thalamus and Brodmann area 37. The data were reprojecte d into sinograms and blurred with a 7 mm kernel. Poisson noise was add ed, and the sinograms were then reconstructed and analyzed using both SPM96 and Gemini spherical ROIs. Results: Based on phantom and simulat ed data, the 95th percentile of intensity within a Gemini ROI afforded a reasonable joint optimization of variance (reliability) and accurac y (validity). SPM96 and Gemini results were similar for the larger (10 mm) feature, but in this application, Gemini was more sensitive than SPM96 for the small feature (4 mm). Conclusion: Gemini, a tool for dis play and measurement of spherical ROIs in registered PET and MR data, is precise and accurate for testing hypotheses of differences in local ized brain activity, comparing favorably with SPM96.