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Multi-Scale Diffusion Tractography Guided by Entropy Spectrum Pathways

V. Galinsky, L.Frank
IEEE Trans Med Imaging, vol. 34, issue 5: 1177-1193, May 2015

Geometrical Optics using Entropy Spectrum Pathways (GO ESP) framework allows simultaneous estimation of the local diffusion and the global fiber tracts and provides a number of advantages over the traditional local approaches, such as Diffusion Tensor Imaging (DTI) or various flavors involving the Ensemble Average Propagator (EAP) in simplified diffusion models.

GO ESP framework computes the maximum entropy trajectories between locations that depend upon the global structure of the multi-dimensional and multi-modal diffusion field sampled by multi b-shell multi q-angle Diffusion Weighted Imaging (DWI) data expanded in spherical waves. The equilibrium and transitional probabilities computed by the framework incorporate both local and global properties of the field and represent better measures for characterization of the information flow than the traditional fractional anisotropy and diffusion tensor eigenvectors.

The multiparametric tractography uses the forward integration of the probability conservation with geometrical optics-like ray tracing procedure and is able to trace multiple fibers following the analogy with multiple convective modes guided by a global structure of the entropy spectrum coupled with a small scale local diffusion.

Different scales included in transitional probabilities facilitate correct tracing of fibers through areas of complicated fiber architectures where multiple fibers cross.  A number of recent studies suggests that more than 90% of human brain DTI data may be composed of this "difficult" areas with fibers crossing at angles of 40 or more degrees.  The ability to perform quantitative local diffusion estimation and global tractography in the presence of such complex fiber architectures thus has profound implications for the utility of DTI data in both basic neuroscience and clinical applications.

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