Regional atrophy in the brain of lissencephalic mouse lemur primates: measurement by automatic histogram-based segmentation of MR images.

Age-related regional cerebral atrophy was evaluated in a small lissencephalic primate, model of cerebral aging. Twelve mouse lemurs (Microcebus murinus), ages 1.9-10.9 years (maximum life span: 12 years), were studied. 3D inversion-recovery fast spin-echo MR images (isotropic resolution = 234 mum) were recorded at 4.7 T with a surface coil actively decoupled from the transmitting birdcage probe. The surface coil-related sensitivity gradient was corrected by normalization with images from an agar and NaCl phantom. An automatic statistical segmentation technique based on a classification-maximization algorithm was tested on digital phantoms that mimicked the brain and applied to the 3D brain images. Segmented 3D maps that displayed gray matter, white matter, and cerebro-spinal fluid (CSF) voxels were computed. The ventricles and peri-encephalic spaces were categorized into 14 regions, defined on brain atlases on the basis of cytoarchitectural and anatomical criteria. The volume of CSF voxels belonging to each of these regions was calculated as an index of regional atrophy. Dilation of the mammillary fossa was an early event in the aging process. CSF accumulation within the occipital, parieto-temporal, temporal, and frontal ventral peri-encephalic spaces was particularly marked in the oldest animals that also displayed ophthalmologic alterations.