MRI-GUIDED SPECT MEASUREMENTS OF MEDIAL TEMPORAL-LOBE BLOOD-FLOW IN ALZHEIMERS-DISEASE

In this study, we assessed the accuracy and reliability of MRI-guided SPECT measurements of medial temporal lobe blood flow in Alzheimer's d isease (AD). Methods: Interactively aligned three-dimensional MP-RAGE MRI and Tc-99m-HMPAO SPECT images were used for MRI-guided measurement of medial temporal robe CBF in eight control subjects and eight patie nts with probable AD. Intraoperator reliability was assessed by repeat ed alignment and measurement by one experienced operator. Accuracy was assessed by examining two subjects with fiducial markers. Results: Th e alignment error was less than 1 SPECT pixel size (3.5 mm) and the co efficient of variation in repeated measures of medial temporal-to-cere bellar CBF ratios was 3.2%, The difference in mean medial temporal-to- cerebellar CBF ratios between eight control subjects and eight AD pati ents was 12%. Also by using three-dimensional seed-grow defined health y brain reference regions, there were significant differences between control subjects and AD patients in medial temporal blood flow. Furthe rmore, the volumes of the MRI-defined medial temporal ROIs were smalle r in the AD patients. The best separation between AD patients and cont rol subjects was achieved by combining MRI measurements of atrophy and SPECT measurements of CBF. Conclusion: These data show that the accur acy and reliability of MRI-guided SPECT measurements of medial tempora l CBF clearly allow the detection of changes in AD. Also, a direct com parison of structural and functional changes is possible by this metho dology, which might improve the early diagnosis of AD.