White matter quantification in a model of schizophrenia mice using microscopic Diffusion Tensor Imaging

Methods Preparation – 12 mice (6 wild-type (WT) and 6 KO) were perfused and fixed in 4% paraformaldehyde solution. Acquisition – Ex vivo experiments were performed at 7.0T on a Bruker Avance III console with 600 mT/m maximum gradient strength using a volume/surface cross RF coil. Anatomical T2 weighted images were first acquired as a pilot image to place 7 slices of 0.7 mm in the coronal plane between -3.2 mm and 2.7 mm relative to the bregma. Diffusion sequence was a spin echo sequence (TE/TR equal to 35/2 000 ms) in which two identical diffusion gradients were applied with a duration of 5 ms and a separation time of 35 ms. 6 different gradient diffusion directions ([1 1 0],[1 -1 0],[0 1 1],[0 1 -1],[1 0 1],[-1 0 1]) with a b-value of 1000 s/mm were used. The FOV and the plane resolution were set to 30 x 30 mm and 59 x 59 μm respectively. Total time of the DTI acquisition was about 12 hours with a number of averages equal to 12. Data Analysis – DTI analysis was done using house software implemented in Matlab (The MathWorks, Inc., Natick, MA). For each slice, an ROI of all the brain was manually selected. After DTI reconstruction fractional anisotropy (FA) maps and principal eigenvectors were calculated and color maps were obtained. Corpus callosum and dorsal fornix were segmented using a FA value threshold of 0.35 and a principal eigenvector in the X-Y plane / Z plane. Post-commissural fornix was selected by drawing a ROI.