Study The Relationship Of Structure And Function Of Brain By Combining MR Diffusion Tensor Imaging And Functional Magnetic Resonance Imaging

Part â…  Study of visualization techniques of cerebral white matter fiber tracts for diffusion tensor dataPurpose: To describe the 2D and 3D visualization techniques of the cerebral white matter fiber tracts for diffusion tensor data, and to search for the best FA threshold and ROI method of tactography for the corticospinal tract (CST). Material and methods: DTI of the brain was performed in 5 normal volunteers using SE echo-planar imaging, then 2D display maps and 3D tractography was generated by the software of DTVâ…¡. Single and two-ROI menthods and different FA thresholds were applied for tractography of CST. Results: Different visualization modes of CST for diffusion tensor data displayed .The anisotropy and direction can be displayed in the directional encoded color map (DEC). Of the 2D visualization modes, DEC map is better than FA map and ellipsoid map in displaying the CST. The tractography of CST using two-region-of-interest (ROI) method and 0.25 of FA threshold were in good accord with the anatomy of CST. The fibers of CST and other fiber tracts overlapped while using one-ROI method. The tractogaphy of CST was affected by the noise using the FA threshold of 0.15, and partial subcortical fibers of CST could not display using FA threahold of 0.35 and 0.45. Conclusion: We determined that the two-ROI method is superior to the one- ROI method, and 0.25 of FA threshold is best for visualizing the CST for tractography.Part â…¡ Study the relationship of both structure and function in visual system by combining DTI and fMRIPurpose: To demonstrate the feasibility of combining DTI and fMRI maps to show fiber tract anatomy in relation to activations and to quantitate anisotropy in white matter tracts and functionally activated regions. Material and methods: DTI and fMRI were performed in 10 normal volunteers (6 men, 4 women; mean age 38.5 years). Functional activity was generated using flashing checkerbord (12 visual angle) at 8 Hz. For imaging processing, fMRI analysis was performed with the software of SPM99, and DTI with the software of DTV â…¡. The activated maps were overlayed upon FA maps and DEC maps using the software of MRIcro. FA values weremeasured within activated regions and in the optic radiations. Results: All subjects showed activations in primary visual cortex, and with V5 activations in 5 and LGN activations in 3. Overlay of fMRI maps upon FA maps revealed that activated voxels were almost exclusively in regions of low anisotropy. FA values within activated reagions were much lower than that of optic radiations. Overlay of fMRI maps on to DEC maps showed that the optic radiation fiber tracts linked the activated LGN and primary visual cortices directly in 3 cases. Conclusion: Activated regions had lower FA value than optic radiation, supporting that most BOLD signal changes occurs within the relatively isotropic cotical grey matter. The combination of both techniques can also help demonstrating functional connectivity between different cortices and subcortical areas directly. Part III Combinatin of fMRI and DTI in the disease of posterior visual pathwaysPurpose: We used the combination of fMRI and DTI to explore the structure-function relationship in the disease of posterior visual pathways, to explore the anatomic basis for the abnormal visual response. Materials and Methods: 11 patients (3 gliomas, 4 meningiomas, 3 metastasis. 1 stroke ) involving either cortical or subcortical visual pathways were investigated by combining fMRI and DTI. FMRI was performed by flashing checkerbord (12 visual angle) at 8 Hz. For imaging processing, fMRI analysis was performed with SPM99, and DTI and tractography with the software of DTV II . Fractional anisotropy (FA) of optic radiations and activatited volume (VOXELs) of primary visual cortices (VI and V2) were measured and analyzed both at the affected side and the contralesional side. Relative FA (rFA) and relative activated volume (rVOXELs) were also caculated. 3D tractography of optic radiations succeeded in 3 cases. Results: FA values had significantly statistical difference between affected side and the contralesional side of optic radiations (P<0.001). The spatial extent of fMRI activations of primary visual cortex decreased in the affected side comparing with the contralesional side (P<0.001).We analyzed the activated maps of visual cortex and FA changes of optic radiations,and found that the rVOXELs correlated with the changes rFA ( r = 0.711, p=O.O32 ) in 9 posterior diseases.Conclusion: fMRI responses of visual cortex correlate with the integrity of the optic radiation except for the visual cortex, and the result support the hypothesis...