PROPORTIONAL ANATOMICAL STEREOTAXIC ATLAS FOR VISUAL INTERPRETATION OF BRAIN SPET PERFUSION IMAGES

A semi-automatic method was developed to determine the anterior (AC) a nd posterior (PC) commissures on brain single-photon emission tomograp hic (SPET) perfusion images, and then to draw the proportional anatomi cal Talairach's grid on each axial SPET image. First, the AC-PC line w as defined on SPET images from the linear regression of four internal landmarks (frontal pole of the brain, inferior limit of the anterior c orpus callosum, sub-thalamic point and occipital pole). Second, the SP ET position of AC and PC points on the AC-PC line was automatically de termined from measurements made on hard copies of magnetic resonance ( MR) images of the patients. Finally, a proportional Talairach's grid w as automatically drawn on each axial SPET image. To assess the accurac y of localization of AC and PC points, co-registered technetium-99m he xamethylpropylene amine oxime SPET and MR images from 11 subjects were used. The mean displacements between estimated points on SPET and tru e points on MRI (Delta x=sagittal, Delta y=frontal and Delta z=axial d isplacement) were calculated. The mean displacements (in mm) were Delt a x=-1.4+/-1.8, Delta y=-1.7+/-3.3 and Delta z=-1.1+/-2.5 for AC, and Delta x=-1.8+/-1.8, Delta y=0.3+/-3.2 and Delta z=-1.3+/-2.7 for PC. T hese displacements represented an error of less than 5 mm at the anter ior or posterior pole of the brain or at the vertex. Intra- and inter- observer comparisons did not reveal significant differences in mean di splacements. Thus, this semi-automatic method results in reproducible and accurate stereotactic localization of SPET perfusion abnormalities , This method can be used routinely for repeat follow-up studies in th e same subject as well as in different individuals without requiring S PET-MRI co-registration.