Mean regional cerebral blood flow images of normal subjects using Technetium-99m-HMPAO by automated image registration

The purpose of this study was twofold: to calculate relative uptake values for ^99mTc-HMPAO in various regions of the normal brain after alignment and registration to a standard shape and size, and to validate the automated image registration (AIR) program for SPECT-to-SPECT transformation. Methods: Thirty subjects took part in this study. Technetium-99m-HMPAO brain SPECT and x-ray-CT scans were acquired. SPECT images were normalized to an average activity of 100 counts/pixel. Intersubject accuracy was evaluated on brain images of 17 normal subjects (mean age = 64.9 ± 8.7 yr). These images were aligned and registered to a standard size and shape with the help of AIR. Realigned images were overlaid on reference images to determine the overlap areas. Intrasubject accuracy was evaluated by realigning 20°, rotated brain images with an index calculated as: overlap area/(overlap area + nonoverlap area). Anatomical variability between realigned target and reference images was evaluated by measurements on corresponding x-ray-CT scans, realigned using transformations that were established by the SPECT images. Realigned brain SPECT images of 30 normal subjects (mean age = 50.7 ± 18.7 yr), including those subjects examined in the accuracy validation study, were used to generate mean and s.d. images. Images based on the mean value of each voxel (n = 30) were compared with other mean images prepared by the human brain atlas (HBA) standardization technique on a voxel-by-voxel basis to generate T maps. Results: Accuracy indices were 0.98 ± 0.006 and 0.99 ± 0.002 for the intersubject and intrasubject evaluations, respectively. The maximum anatomical variability was 4.7 mm after realignment. Paired Student's t-test comparisons of mean HBA and AIR images revealed statistically significant differences for the deep white matter, pons and occipito-temporal regions. These differences could be explained by variation in the population being studied and the protocol for data handling by AIR and HBA. Conclusion: AIR aligns and registers brain SPECT images with acceptable accuracy, without the necessity of MRI or x-ray-CT scans.