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 va lues for Tc-99m-HMPAO in various regions of the normal brain after ali gnment and registration to a standard shape and size, and to validate the automated image registration (AIR) program for SPECT-to-SPECT tran sformation. Methods: Thirty subjects took part in this study. Techneti um-99m-HMPAO brain SPECT and x-ray-CT scans were acquired. SPECT image s were normalized to an average activity of 100 counts/pixel. Intersub ject accuracy was evaluated on brain images of 17 normal subjects (mea n 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 ov erlaid on reference images to determine the overlap areas. Intrasubjec t accuracy was evaluated by realigning 20 degrees rotated brain images with an index calculated as: overlap area/(overlap area + nonoverlap area). Anatomical variability between realigned target and reference i mages was evaluated by measurements on corresponding x-ray-CT scans, r ealigned using transformations that were established by the SPECT imag es. Realigned brain SPECT images of 30 normal subjects (mean age = 50. 7 +/- 18.7 yr), including those subjects examined in the accuracy vali dation 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 mea n images prepared by the human brain atlas (HBA) standardization techn ique on a voxel-by-voxel basis to generate T maps. Results: Accuracy i ndices were 0.98 +/- 0.006 and 0.99 +/- 0.002 for the intersubject and intrasubject evaluations, respectively. The maximum anatomical variab ility was 4.7 mm after realignment. Paired Student's t-test comparison s of mean HBA and AIR images revealed statistically significant differ ences for the deep white matter, pens and occipito-temporal regions. T hese differences could be explained by variation in the population bei ng studied and the protocol for data handling by AIR and HBA. Conclusi on: AIR aligns and registers brain SPECT images with acceptable accura cy, without the necessity of MRI or x-ray-CT scans.