Heterogeneity of posterior limbic perfusion in very early Alzheimer's disease

PURPOSE: This study was designed to quantify the heterogeneity of cerebral perfusion on SPECT images in elderly controls and Alzheimer's disease (AD) patients in mild stage using a three-dimensional fractal analysis (3D-FA). MATERIAL AND METHOD: Seventy-five patients with possible and probable AD based on the NINCDS/ADRDA criteria, and thirty-one elderly controls underwent 99mTc-HMPAO SPECT scanning. Dementia severity was assessed using the clinical dementia rating (CDR). Patients with CDR scores of 0.5 (n=33) were classified as "very early" and those with CDR 1 (n=42) as "early". We delineated the SPECT images using 2 cutoffs (35% and 50% cutoffs of the maximal voxel radioactivity) and measured the number of voxels in the areas included by the contours obtained with each cutoff level. The fractal dimension (FD) was calculated by relating the logarithms of cutoff level and the number of voxels. Posterior limbic images were reconstructed at 30 degrees positive to the coronal plane, and posterior limbic FD was calculated. RESULT: Posterior limbic FD for early AD, very early AD, and control groups were 1.03+/-0.16, 1.02+/-0.17, and 0.87+/-0.14 (P=0.001 versus early AD group, P=0.001 versus very early AD). Use of the posterior limbic FD and the ratio of posterior limbic FD to total FD separated very early AD patients from controls with a sensitivity of 76% and a specificity of 81%. CONCLUSION: 3D-FA indicated significant differences in the heterogeneity of CBF distribution between patients with AD in mild stage and elderly controls. Posterior limbic FD may be useful for easily and objectively distinguishing patients with very early AD from aging people.