This method is particularly hampered by voxels containing multiple fiber orientations such as crossing, bending or fanning fibers (Jbabdi and Johansen-Berg 2011). 2000) uses the diffusion tensor model (i.e., estimating one principal direction in each voxel) to reconstruct fiber tracts in the brain. The classical approach of diffusion tensor (DT)-based deterministic tractography (Basser et al. This may lead to biased characterization of connectome topology, particularly in the presence of false positive tract reconstructions (Drakesmith et al. However, the anatomical accuracy of diffusion-weighted tractography, which infers neuronal pathways from tissue water diffusion direction, continues to be a matter of controversy, and reconstructing connectomes with both high sensitivity and high specificity remains challenging (Sporns et al. 1999 Jones 2008 Jbabdi and Johansen-Berg 2011). 2013).ĭiffusion MRI-based tractography has offered exclusive means to map structural connections non-invasively in animal and human brain, and is considered a very useful and powerful technique to unravel the human connectome at meso- and macro-level (Le Bihan et al. 2012), the BRAIN project (NIH 2014), the Brainnetome Project (Jiang 2013) and the CONNECT project (Assaf et al. 2012) involve ongoing efforts in large-scale multicenter projects, such as the Human Connectome Project (Van Essen et al. 2014), rat (Schmitt and Eipert 2012), macaque (Stephan et al. Accurate connectome reconstructions at micro-, meso- and macro-scale in other species, including Drosophila (Chiang et al. So far, a complete connectome has been mapped only for C. Unraveling the human connectome is a great challenge (Poldrack and Farah 2015) and its reconstruction would be a fundamental breakthrough in neuroscience (Sporns et al. Connectomes can provide crucial insights into brain functioning in health and disease as (changes in) structural connections underlie at least part of functional and behavioral phenotypes (Sporns et al. This field aims to construct comprehensive maps of all neuronal elements and their connections in different organisms, including a wide range of mammalian species. Mapping brain-wide structural connectivity has become an important goal in neuroscience and is the primary focus of the field of connectomics (Sporns et al. Hence, connectome reconstruction benefits from varying parameter settings and combination of tractography methods to account for anatomical variation of neuronal pathways. Despite the potential of CSD-based and global tractography to handle complex fiber orientations at voxel level, reconstruction accuracy, especially for long-distance connections, remains a challenge. Similar patterns and trade-offs were found, when we applied spherical deconvolution informed filtering of tractograms, streamline thresholding and group-based average network thresholding. Furthermore, performance of all tractography methods decreased with increasing spatial distance between connected regions. There was a parameter range trade-off between sensitivity: 0.06–0.63 interhemispherically and 0.22–0.86 intrahemispherically and specificity: 0.99–0.60 interhemispherically and 0.99–0.23 intrahemispherically.
All tested tractography methods generated considerable numbers of false positive and false negative connections. Therefore, we validated whole brain structural connectome reconstructions based on ten ultrahigh-resolution dMRI rat brain scans and 106 cortical regions, from which varying tractography parameters were compared against standardized neuronal tracer data. Our study aimed to determine the accuracy of connectome reconstruction for three dMRI-based tractography approaches: diffusion tensor (DT)-based, CSD-based and global tractography. Recently, sophisticated methods including constrained spherical deconvolution (CSD) and global tractography have been developed to improve tract reconstructions through modeling of more complex fiber orientations. However, dMRI-based tractography indirectly measures white matter tracts, with suboptimal accuracy and reliability. Diffusion MRI (dMRI)-based tractography offers unique abilities to map whole-brain structural connections in human and animal brains.
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