DUAL-ISOTOPE BRAIN SPECT IMAGING FOR MONITORING COGNITIVE ACTIVATION - PHYSICAL CONSIDERATIONS

The physical considerations of using dual isotope brain SPECT imaging to monitor blood flow changes during cognitive activation studies were investigated. These factors included field uniformity, spatial resolu tion and crosstalk. Serial dual isotope single photon emission compute d tomographic (SPECT) studies of a test tube phantom and an anthropomo rphic brain phantom filled with Tc-99m and I-123 were made over a 10 h period. The reconstructed counts in the Tc-99m and I-123 windows were corrected for crosstalk and were plotted as a function of time. The p lotted data from each window decreased over time with a half-life char acteristic of each radionuclide. The relative difference between true I-123 and Tc-99m region counts has to be of the order of 10% to be sta tistically significant at the P<0.05 level.