Comparison between brain CT and MRI for voxel-based morphometry of Alzheimer's disease

The voxel‐based morphometry (VBM) technique using brain magnetic resonance imaging (MRI) objectively maps gray matter loss on a voxel‐by‐voxel basis after anatomic standardization. In patients with Alzheimer's disease (AD), reductions of gray matter volume, mainly in the medial temporal structures, have been reported; however, inhomogeneity and geometric distortion of the field intensity hampers the reproducibility of MRI. In the present study, we developed a novel computed tomography (CT)‐based VBM method and used this technique to detect volume loss in AD patients as compared with normal controls. The results were compared with MRI‐based VBM using the same subjects. Pittsburgh Compound B (11C‐PIB) positron emission tomography (PET)/CT was performed and two experts in neuro‐nuclear medicine judged whether regional amyloid β load was consistent with a diagnosis of AD. Before the injection of 11C‐PIB, high‐quality CT scans were obtained using the same PET/CT equipment. MRI was performed within a mean interval of 25.1 ± 8.2 days before the PET/CT scan. Using statistical parametric mapping 8 (SPM8), the extracted gray matter images from CT and MRI were spatially normalized using a gray matter template and smoothed using a Gaussian kernel. Group comparisons were performed using SPM8 between five 11C‐PIB‐positive patients with probable AD and seven 11C‐PIB‐negative age‐matched controls with normal cognition. Gray matter volumes in the bilateral medial temporal areas were reduced in the AD group as compared with the cognitively normal group in both CT‐based VBM (in the left; P < 0.0001, cluster size 2776 and in the right; P < 0.0001, cluster size 630) and MRI‐based VBM (in the left; P < 0.0001, cluster size 381 and in the right, P < 0.0001, cluster size 421). This newly developed CT‐based VBM technique can detect significant atrophy in the entorhinal cortex in probable AD patients as previously reported using MRI‐based VBM. However, CT‐VBM was more sensitive and revealed larger areas of significant atrophy than MR‐VBM.