[Prediction of progression in patients with mild cognitive impairment using IMP-SPECT]

To examine the difference in functional brain imaging between mild cognitive impairment (MCI) and normal aging, we measured rCBF on functional brain imaging using 123I-IMP single photon emission computed tomography (IMP-SPECT) in 19 MCI patients who progressed to develop AD on follow-up and 23 probable Alzheimer's disease (AD) patients as well as 15 age-matched normal subjects. Baseline MMSE score was 25.3 (SD 1.2) in the MCI group and 17.5 (SD 3.3) in the AD group. The regions of interest (ROI) in the posterior cingulate gyrus, frontal, temporal and parietal cortices were drawn on the image of IMP-SPECT with reference to an individual MRI image. The rCBF ratio was calculated using ROI value in the cerebellum as a reference. Voxel-based analysis was also preformed using statistical parametric mapping (SPM). The rCBF ratio in the posterior cingulate gyrus was significantly reduced in the MCI group (mean 0.956, SD 0.080) and the AD group (mean 0.833, SD 0.118) compared to that in the normal group (mean 1.083, SD 0.084). In the frontal, temporal and parietal cortices, the rCBF ratio was significantly reduced only in the AD group compared to the normal group. At a fixed specificity of 80%, the diagnostic sensitivity in the discrimination between MCI patients and normal subjects was 80.5% when using rCBF ratio in posterior cingulate gyrus. In the SPM analysis, significant reduction of the rCBF in MCI group was observed only in the posterior cingulate gyrus, compared with normal subject group. Our results suggest that MCI patients presenting with a posterior cingulate hypoperfusion are at higher risk for transition from MCI to clinically recognizable AD.