This paper mainly includes three parts: Method development and its application for the analysis of cingulum; Subdivision of splenium using the traced fiber from tractography; Clinical application in some psychiatric diseases with diffusion tensor image. A scale-invariant parameterization method by arc-angle was proposed to study the cingulum, specifically, which is one of the most prominent white matter fiber tracts of the limbic system. This method can establish better anatomical correspondence of cingulum across subjects than the methods ever used. Using this improved fiber-based scheme, we found a significant left-greater-than-right asymmetry pattern in most segments of cingulum bundle, except the most posterior portion of cingulum, in DTI datasets of normal right-handed subjects. Further, another normal left-handed subjects were recruited to explore the microstructure of bilateral cingulum bundles associated with handedness. The statistical results showed a remarkable left-greater-than-right asymmetry pattern of anisotropy in most segments of cingulum bundles except the most posterior segment, for both right-handers and left-handers. Very interestingly, higher anisotropy of the right-hander than the left-hander was found in the bilateral cingulum bundles. An indirect approach was developed to subdivide the splenium of corpus callosum on mid-sagittal slice of diffusion tensor image (DTI). In this framework, the subdivision was implemented by clustering splenium voxels with some feature derived from the geometric properties of its crossing fiber. Some preliminary and reasonable result indicated the potential applicability of this approach. We have applied diffusion tensor image to the analysis of white matter in some psychiatric diseases, and some meaningful finding was obtained. 1). For the analysis of callosum corpus in schizophrenia, there were no significant differences between first-episode schizophrenics and controls in FA and ADC for each sub-regions of callosum corpus. But the isthmus area of the patients was significantly smaller than that of the controls. 2). For the analysis of whole brain in schizophrenia, we found that FA in white matter of the patients was lower than controls at the cerebral peduncle, frontal regions, inferior temporal gyrus, medial parietal lobes, hippocampal gyrus, insula, right anterior cingulum bundle and right corona radiata. 3). For the analysis of white matter and gray matter in Alzheimer’s disease, the results showed that the location of lower FA in AD patients were close to those of cortical volume reduction in some sites, but some white matter abnormalities (mainly the right superior parietal lobule, bilateral superior longitudinal fasciculi and cerebral peduncles) were structurally distant from the atrophic cortices. This indicated that white matter abnormality might be an independent factor in the progress of Alzheimer’s disease.
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