DTI tractography

Even though it is not closely connected to CIS, I was fascinated by a relatively new brain visualization technique, the Diffusion Tensor Imaging (DTI). Google can show many of the incredible images created by analyzing and clustering the neurons. There is a free software, the MedINRIA that can help creating these images, and open source platform 3D Slicer has also got a recent tractography plugin. (Their picture on the right shows the lateral connections of the brain.)
Wikipedia describes briefly the technology behind it: "Tractography is performed utilizing Diffusion Weighted Imaging, an MR technique which is sensitive to the diffusion of water in the body, and can be used to reveal its 3D shape. Free diffusion occurs equally in all directions. If the water diffuses in a medium having barriers, the diffusion will be uneven. In such a case, the relative-mobility of the molecules from the origin has a shape different from a sphere. This shape is often modeled as an ellipsoid, and the technique is then called Diffusion Tensor Imaging. Barriers can be many things --cell membranes, axons, myelin, etc; but in white matter the principal barrier is the myelin sheath of axons. Bundles of axons provide a barrier to perpendicular diffusion and a path for parallel diffusion along the orientation of the fibers. This is termed "anisotropic" diffusion. Anisotropic diffusion is expected to be increased in areas of high mature axonal order. " So the water diffusion gives an idea of approximate fiber orientation. By data analysis techniques we can track the principal diffusion direction and estimate fiber trajectories in white matter. By automatically grouping fibers into structures, we can visualize physiological structures, highly interconnected and functionally integrated regions in the brain.


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