Tracking and validation techniques for topographically organized tractography

Abstract

Topographic regularity of axonal connections is commonly understood as the preservation of spatial relationships between nearby neurons and is a fundamental structural property of the brain. In particular the retinotopic mapping of the visual pathway can even be quantitatively computed. Inspired from this previously untapped anatomical knowledge, we propose a novel tractography method that preserves both topographic and geometric regularity. We make use of parameterized curves with Frenet-Serret frame and introduce a highly flexible mechanism for controlling geometric regularity. At the same time, we incorporate a novel local data support term in order to account for topographic organization. Unifying geometry with topographic regularity, we develop a Bayesian framework for generating highly organized streamlines that accurately follow neuroanatomy. We additionally propose two novel validation techniques to quantify topographic regularity. In our experiments, we studied the results of our approach with respect to connectivity, reproducibility and topographic regularity aspects. We present both qualitative and quantitative comparisons of our technique against three algorithms from MRtrix3. We show that our method successfully generates highly organized fiber tracks while capturing bundle anatomy that are geometrically challenging for other approaches.

Connectivity gradients on tractography data: Pipeline and example applications

“…However, the major white matter fibers of the brain itself have some topographical organization. The clearest case of this is the organization of the corpus callosum which is topographically organized in the anterior posterior axis, connecting specific parts of the cortex with their contralateral homolog (Genç, 2011 ), but overlapping gradients of connectivity have also been observed in coronal cross sections of the optic radiation (Aydogan & Shi, 2016 ; Aydogan & Shi, 2018 ; Kammen, Law, Tjan, Toga, & Shi, 2016 ). The optic radiation plays a key role in the retinofugal pathway that connects the retina to the primary visual cortex (V1) through the lateral geniculate nucleus (LGN).…”

“…This type of organization has now been shown to not only be present in many parts of the brain and across vertebrates—suggesting that there is an evolutionary advantage to it—but also to have functional relevance for behavior (Marquand, Haak, & Beckmann, 2017 ; Tinsley, 2009 ). The topographic regularity of the connections themselves has also seen a recent surge of interest, with studies showing that the axons connecting topographical maps conserve the same spatial pattern along their entire trajectory (Aydogan & Shi, 2016 , 2018 ; Wang, Aydogan, Varma, Toga, & Shi, 2018 ).…”

Challenges for Tractogram Filtering

“…Most tractography methods already include restrictions on the shape of streamlines, such as maximum local curvature or minimum and maximum length. Moreover, some tractography methods include geometry priors at a higher level [4,15]. Since these rules are usually included in state-of-the-art tractography approaches, there has been less need for filtering methods implementing this idea.…”

Mapping Short Association Fibers in the Early Cortical Visual Processing Stream Using In Vivo Diffusion Tractography

“…The detailed map of the connections in the macaque visual system ( Felleman and Van Essen 1991 ; Van Essen et al 1992 ) has been used for validation of ex vivo DWI tractography in macaque ( Azadbakht et al 2015 ). Moreover, the retinotopic organization of the optic radiation tract projecting into V1 was used for validation of a tractography method ( Aydogan and Shi 2018 ). Therefore, these well-known connectivity patterns in the early cortical visual processing stream, comprising V1 and V2, can be considered a suitable test bed for in vivo U-fiber connectivity mapping using diffusion MRI tractography.…”