A TECHNIQUE TO LOCALIZE ACTIVATION IN THE HUMAN BRAIN WITH TECHNETIUM-99M-HMPAO SPECT - A VALIDATION-STUDY USING VISUAL-STIMULATION

This study extends and validates a system for localizing brain activit y changes based on fiducial markers, coregistration of SPECT and MRI s tructural images and atlas/MRI-assisted localization. Methods: Ten nor mal subjects underwent Tc-99m-HMPAO SPECT during a resting eyes-closed baseline measurement and during visual stimulation (8-Hz reversing ch eckerboard). SPECT scans were registered with MRI scans obtained from each individual using a fiducial-based system that minimized z-axis an d rotational errors, and registration was further refined along the x- and y-axes by superimposing corresponding axial SPECT and MRI slices. Regions of interest (ROIs) were located on MRI slices with the aid of an atlas. Corresponding loci on SPECT slices were chosen and incremen tally adjusted such that the center of a ROI was located precisely at the maximum of activity in the visual cortex or the cortical gray matt er ribbon. Results: Activity in the calcarine cortex increased by 44.3 9% during visual stimulation (p < 0.001). Adjustment of ROI location i n accordance with local activity maxima yielded superior results to a method relying strictly on atlas/MRI localization. Premotor cortex act ivity declined by 16.91% on the right (p < 0.01) and 13.85% on the lef t (p > 0.05), whereas no changes occurred in the somatosensory cortex. Conclusion: Changes in visual cortical activity were most comparable to previous functional MRI studies but also congruent with PET and SPE CT findings. Using the locus of peak activity to aid in defining corti cal ROIs improves the signal-to-noise ratio by reducing noise related to inevitable minor registration errors.