Advances in functional and structural MR image analysis and implementation as FSL.

Information processing in the cerebral cortex involves interactions among distributed areas. Anatomical connectivity suggests that certain areas form local hierarchical relations such as within the visual system. Other connectivity patterns, particularly among association areas, suggest the presence of large-scale circuits without clear hierarchical relations. In this study the organization of networks in the human cerebrum was explored using resting-state functional connectivity MRI. Data from 1,000 subjects were registered using surface-based alignment. A clustering approach was employed to identify and replicate networks of functionally coupled regions across the cerebral cortex. The results revealed local networks confined to sensory and motor cortices as well as distributed networks of association regions. Within the sensory and motor cortices, functional connectivity followed topographic representations across adjacent areas. In association cortex, the connectivity patterns often showed abrupt transitions between network boundaries. Focused analyses were performed to better understand properties of network connectivity. A canonical sensory-motor pathway involving primary visual area, putative middle temporal area complex (MT+), lateral intraparietal area, and frontal eye field was analyzed to explore how interactions might arise within and between networks. Results showed that adjacent regions of the MT+ complex demonstrate differential connectivity consistent with a hierarchical pathway that spans networks. The functional connectivity of parietal and prefrontal association cortices was next explored. Distinct connectivity profiles of neighboring regions suggest they participate in distributed networks that, while showing evidence for interactions, are embedded within largely parallel, interdigitated circuits. We conclude by discussing the organization of these large-scale cerebral networks in relation to monkey anatomy and their potential evolutionary expansion in humans to support cognition.

The organization of the human cerebral cortex estimated by intrinsic functional connectivity

https://cogns.northwestern.edu/cbmg/TBSSNI2006.pdf

Tract-based spatial statistics: voxelwise analysis of multi-subject diffusion data.

Anisotropic water diffusion in neural fibres such as nerve, white matter in spinal cord, or white matter in brain forms the basis for the utilization of diffusion tensor imaging (DTI) to track fibre pathways. The fact that water diffusion is sensitive to the underlying tissue microstructure provides a unique method of assessing the orientation and integrity of these neural fibres, which may be useful in assessing a number of neurological disorders. The purpose of this review is to characterize the relationship of nuclear magnetic resonance measurements of water diffusion and its anisotropy (i.e. directional dependence) with the underlying microstructure of neural fibres. The emphasis of the review will be on model neurological systems both in vitro and in vivo. A systematic discussion of the possible sources of anisotropy and their evaluation will be presented followed by an overview of various studies of restricted diffusion and compartmentation as they relate to anisotropy. Pertinent pathological models, developmental studies and theoretical analyses provide further insight into the basis of anisotropic diffusion and its potential utility in the nervous system.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/nbm.782

The basis of anisotropic water diffusion in the nervous system – a technical review

The relationship between brain structure and complex behavior is governed by large-scale neurocognitive networks. The availability of a noninvasive technique that can visualize the neuronal projections connecting the functional centers should therefore provide new keys to the understanding of brain function. By using high-resolution three-dimensional diffusion magnetic resonance imaging and a newly designed tracking approach, we show that neuronal pathways in the rat brain can be probed in situ. The results are validated through comparison with known anatomical locations of such fibers.

Three-dimensional tracking of axonal projections in the brain by magnetic resonance imaging.

https://www.cell.com/biophysj/pdf/S0006-3495(94)80775-1.pdf

MR diffusion tensor spectroscopy and imaging.

/pdf/estimation-of-the-effective-self-diffusion-tensor-from-the-2gokefhpqs.pdf

Estimation of the Effective Self-Diffusion Tensor from the NMR Spin Echo

Analytical Expressions for the b Matrix in NMR Diffusion Imaging and Spectroscopy

Diffusion tensor imaging (DTI) provides intravoxel microstructural and microdynamic information about tissues that reflects their physiological state. The authors use DTI to assess changes in water mobility in an in vivo model of cerebral ischemia in cats. They use four estimated scalar quantities: the 3 principal diffusivities (/spl lambda//sub 1/, /spl lambda//sub 2/, and /spl lambda//sub 3/) and the T/sub 2/-weighted NMR signal (A(0)), as features with which to segment both normal and pathological tissues. While the authors can use these parameters to discriminate between normal and ischemic white and gray matter in cats, they are evaluating their use to distinguish between reversibly and irreversibly damaged tissues during stroke and other white matter diseases. >

D. Lebihan

Papers

MR diffusion tensor spectroscopy and imaging.

Estimation of the Effective Self-Diffusion Tensor from the NMR Spin Echo

Analytical Expressions for the b Matrix in NMR Diffusion Imaging and Spectroscopy

MR diffusion tensor imaging of ischemic brain in vivo