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In neuroscience, tractography is a 3D modeling technique used to visually represent nerve tracts using data collected by diffusion MRI. It uses special techniques of magnetic resonance imaging (MRI) and computer-based diffusion MRI. The results are presented in two- and three-dimensional images called tractograms. In addition to the long tracts that connect the brain to the rest of the body, there are complicated neural circuits formed by short connections among different cortical and subcortical regions. The existence of these tracts and circuits has been revealed by histochemistry and biological techniques on post-mortem specimens. Nerve tracts are not identifiable by direct exam, CT, or MRI scans. This difficulty explains the paucity of their description in neuroanatomy atlases and the poor understanding of their functions. The most advanced tractography algorithm can produce 90% of the ground truth bundles, but it still contains a substantial amount of invalid results. Tractography is performed using data from diffusion MRI. The free water diffusion is termed "isotropic" diffusion. If the water diffuses in a medium with barriers, the diffusion will be uneven, which is termed anisotropic diffusion. 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. Anisotropic diffusion is expected to be increased in areas of high mature axonal order. Conditions where the myelin or the structure of the axon are disrupted, such as trauma, tumors, and inflammation reduce anisotropy, as the barriers are affected by destruction or disorganization. Anisotropy is measured in several ways.

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Hierarchical Microstructure Informed Tractography

Alessandro Daducci, Gabriel Girard, Maxime Descoteaux

Background: Tractography uses diffusion magnetic resonance imaging to noninvasively infer the macroscopic pathways of white matter fibers and it is the only available technique to probe in vivo the st

MARY ANN LIEBERT, INC2021

On the cortical connectivity in the macaque brain: A comparison of diffusion tractography and histological tracing data

Jean-Philippe Thiran, Gabriel Girard, Maxime Descoteaux, Giorgio Innocenti, Tim Bjørn Dyrby

Diffusion-weighted magnetic resonance imaging (DW-MRI) tractography is a non-invasive tool to probe neural connections and the structure of the white matter. It has been applied successfully in studie

2020

On the intrahemispheric connectivity of the monkey: a diffusion tractography and tract tracing analysis

Gabriel Girard, Maxime Descoteaux, Giorgio Innocenti

In this work, we compare diffusion tractography with neuronal retrograde tract tracing of the frontal, cingulate and parietal areas of the monkey. In this work, we compare diffusion tractography with

International Society for Magnetic Resonance in Medicine2019

Connectome

A connectome (kəˈnɛktoʊm) is a comprehensive map of neural connections in the brain, and may be thought of as its "wiring diagram". An organism's nervous system is made up of neurons which communicate through synapses. A connectome is constructed by tracing the neuron in a nervous system and mapping where neurons are connected through synapses. The significance of the connectome stems from the realization that the structure and function of the human brain are intricately linked, through multiple levels and modes of brain connectivity.

Neuroanatomy

Neuroanatomy is the study of the structure and organization of the nervous system. In contrast to animals with radial symmetry, whose nervous system consists of a distributed network of cells, animals with bilateral symmetry have segregated, defined nervous systems. Their neuroanatomy is therefore better understood. In vertebrates, the nervous system is segregated into the internal structure of the brain and spinal cord (together called the central nervous system, or CNS) and the routes of the nerves that connect to the rest of the body (known as the peripheral nervous system, or PNS).

Tractography

Attention: it is also necessary to register at https://tinyurl.com/edsan2022 in addition to signing up for the course. The "Examples of Data Science Applications in Neuroimaging" (EDSAN) course i

Focuses on neural anisotropy directions in deep learning and their impact on model accuracy.

Explores molecular profiling for determining neuronal densities and the correlation with reconstructed circuits.

Explores neuronal connectivity patterns, connection probabilities, and experimental techniques used to study synaptic connectivity.