Zhenyu Zhou1,2, Weihong Guo3, Tianyu Tang2, Wei Liu1, Bradley S. Peterson1, Yijun Liu2, Dongrong Xu1
1MRI Unit, Psychiatry, Columbia University, New York, NY, USA; 2Psychiatry, University of Florida, Gainesville, FL, USA; 3Mathematics, University of Alabama, Tuscaloosa, AL, USA
A new Diffusion Anisotropy Index R4 is developed for characterizing the degree of fiber crossing in DTI data, using a measure of apparent diffusion coefficient and a method based on spherical harmonic series. We then used R4 to investigate the relationship between diffusion anisotropy and multiple fibers crossing within individual voxels. Group differences of FA and R4 were computed respectively based on DT-MRI data of six autistic children and six healthy controls. We found that in the autistic population, brain regions where fibers are highly crossing (corpus callosum/lateral ventricle and arched fiber/precentral gyrus) are featuring with high R4 and low FA values simultaneously, indicating possibly a different mechanism other than pathological abnormality in white matter that causes low FA.