Jones, D.K.: Studying connections in the living human brain with diffusion MRI. Cortex 44(8), 936-952

Cardiff University Brain Research Imaging Centre, School of Psychology, Cardiff University, Cardiff, Wales, UK.
Cortex (Impact Factor: 5.13). 09/2008; 44(8):936-52. DOI: 10.1016/j.cortex.2008.05.002
Source: PubMed


The purpose of this article is to explain how the random walks of water molecules undergoing diffusion in living tissue may be exploited to garner information on the white matter of the human brain and its connections. We discuss the concepts underlying diffusion-weighted (DW) imaging, and diffusion tensor imaging before exploring fibre tracking, or tractography, which aims to reconstruct the three-dimensional trajectories of white matter fibres non-invasively. The two main classes of algorithm - deterministic and probabilistic tracking - are compared and example results are presented. We then discuss methods to resolve the 'crossing fibre' issue which presents a problem when using the tensor model to characterize diffusion behaviour in complex tissue. Finally, we detail some of the issues that remain to be resolved before we can reliably characterize connections of the living human brain in vivo.

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    • "Anatomical connectivity between brain regions can be measured (or rather approximated) using diffusion magnetic resonance imaging. It delineates the likelihood of white-matter fiber bundles traced to link brain regions (Johansen-Berg and Rushworth, 2009; Jones, 2008). The number of samples reaching any voxel/vertex in the gray matter or, more frequently, the likelihood of passing through brain white matter then provides the connectivity profile of a particular voxel/vertex or node in the ROI. "
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    ABSTRACT: Regional specialization and functional integration are often viewed as two fundamental principles of human brain organization. They are closely intertwined because each functionally specialized brain region is probably characterized by a distinct set of long-range connections. This notion has prompted the quickly developing family of connectivity-based parcellation (CBP) methods in neuroimaging research. CBP assumes that there is a latent structure of parcels in a region of interest (ROI). First, connectivity strengths are computed to other parts of the brain for each voxel/vertex within the ROI. These features are then used to identify functionally distinct groups of ROI voxels/vertices. CBP enjoys increasing popularity for the in-vivo mapping of regional specialization in the human brain. Due to the requirements of different applications and datasets, CBP has diverged into a heterogeneous family of methods. This broad overview critically discusses the current state as well as the commonalities and idiosyncrasies of the main CBP methods. We target frequent concerns faced by novices and veterans to provide a reference for the investigation and review of CBP studies.
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    • "DTI is a non-invasive imaging technique sensitive to the movement of water molecules in nervous tissue (Jones, 2008). When unrestricted, water diffuses randomly, whereas it is hindered in its movement in highly organized tissue such as collections of nerve fibers composing white matter. "
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    • "As network functionality is critically dependent on the white matter connections between cortical brain regions, analysis of its microstructure is likely to enhance our understanding of the neurodevelopmental origins of psychopathy. Diffusion tensor imaging (DTI) is a noninvasive technique that is increasingly used to examine subtle changes in the microstructural organization of white matter pathways (Jones, 2008). In DTI studies, structural connectivity is most commonly quantified as fractional anisotropy (FA), an index roughly representing the proportion of diffusion in the direction parallel to the axonal bundle (axial diffusivity, AD) relative to perpendicular diffusion (radial diffusivity, RD). "
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