Abstract
Fractional anisotropy (FA) and mean diffusivity (MD) are the most frequently used metrics to investigate white matter impairments in mental disorders. However, these two metrics are derived from intra-voxel analyses and only reflect the diffusion properties solely within the voxel unit. Local diffusion homogeneity (LDH) is a newly developed inter-voxel metric which quantifies the local coherence of water molecule diffusion in a model-free manner. In this study, 94 schizophrenia patients and 91 sex- and age-matched healthy controls underwent diffusion tensor imaging (DTI) examinations. White matter integrity was assessed by FA, MD and LDH. Group differences in these metrics were compared using tract-based spatial statistics (TBSS). Compared with healthy controls, schizophrenia patients exhibited reduced FA and increased MD in the corpus callosum, cingulum, internal capsule, fornix and widespread superficial white matter in the frontal, parietal, occipital and temporal lobes. We also found decreased LDH in the corpus callosum, cingulum, internal capsule and fornix in schizophrenia. Our findings suggest that both intra-voxel and inter-voxel diffusion metrics are able to detect impairments in the anisotropic white matter regions, and intra-voxel diffusion metrics could detect additional impairments in the widespread isotropic white matter regions in schizophrenia.
Highlights
Diffusion tensor imaging (DTI) is commonly used to investigate white matter (WM) alterations in the human brain [1,2]
The decreased fractional anisotropy (FA) and increased mean diffusivity (MD) were mainly located in the corpus callosum, cingulum, internal capsule, fornix and widespread superficial white matter in the frontal, parietal, occipital and temporal lobes
We found that schizophrenia patients exhibited reduced FA and increased MD in the corpus callosum, cingulum, internal capsule, fornix and widespread superficial white matter in the frontal, parietal, occipital and temporal lobes
Summary
Diffusion tensor imaging (DTI) is commonly used to investigate white matter (WM) alterations in the human brain [1,2]. Based on the diffusion tensor model, fractional anisotropy (FA) and mean diffusivity (MD) are the most frequently used metrics to characterize the diffusion of water molecules [3,4]. FA represents a normalized ratio of diffusion directionality, while MD quantifies the bulk mobility of water molecules; these indices provide information on white matter integrity from different perspectives. Several studies have reported that inter-voxel diffusion metrics are informative and useful [5,6,7]. These inter-voxel metrics are able to reveal significant region-specific white matter alterations in some neuropsychical diseases and provide useful information for computer-aided diagnosis, inter-voxel and intra-voxel metrics have shown inconsistent findings [7,8,9]
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