Diffusion tensor imaging

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Functional MRI is a noninvasive diagnostic test that measures small changes in blood flow as a person performs tasks while in the MRI scanner. It detects the brain in action e. It has an advantage over other imaging studies that focus only on the structure of the brain. Diffusion tensor imaging DTI detects the white matter fibers that connect different parts of the brain. These imaging studies help to map specific brain areas before surgery.

Diffusion tensor imaging

Diffusion tensor imaging DTI allows a live look into the microstructure of white matter in the brain and is an important complement to volumetric studies of specific structures such as the amygdala. DTI may be particularly informative for the study of autism because it has been speculated that white matter the connections between neurons defects may be even more pronounced than gray matter defects for affected individuals. Furthermore, in contrast to gray matter, white matter volume continues to increase across childhood and adolescence, thus allowing for analyses of growth curves and changes specific to the microstructure of axons. See papers by Courchesne, et al. Studies that utilize DTI technology generally describe two characteristics of white matter within a particular "voxel" in the brain:. Diffusion imaging takes advantage of the fact that the myelin sheath surrounding an axon restricts the diffusion of water perpendicular to the axon, while allowing relatively free diffusion of water parallel to the axon. This partially restricted motion is referred to as anisotropic diffusion, and carries a theoretical maximum value of 1. In contrast, completely free diffusion of water, as is found in ventricles, is said to be isotropic and theoretical. FA values should be near zero. As a concept, fractional anisotropy FA is thought to reflect both the size and number of myelinated axons and the coherence of axonal orientation Neil, et al. Thus, low FA values may suggest decreased fiber density, reduced myelination of fiber tracts or less directionally coherent organization of fibers within a voxel. White matter injuries such as a stroke result in low FA values, and studies have shown a correlation between low FA values and reduced cognitive performance Skranes, et al. FA values also decrease as a consequence of healthy aging Kochunov, et al. In contrast, high FA values are thought to reflect coherently bundled, myelinated fibers oriented along the axis of greatest diffusion or a general increase in the size or number of myelinated axons within a particular voxel.

Note that the transformation matrixes generated should only be applied to the scalar images. Although this ADC concept has been extremely successful, especially for clinical applications, it has been challenged recently, as new, more comprehensive models of diffusion in biological tissues have been introduced. Since both diffusion tensor imaging consist in registration procedures, they can be implemented as one single step.

Diffusion Tensor Imaging DTI studies are increasingly popular among clinicians and researchers as they provide unique insights into brain network connectivity. However, in order to optimize the use of DTI, several technical and methodological aspects must be factored in. These include decisions on: acquisition protocol, artifact handling, data quality control, reconstruction algorithm, and visualization approaches, and quantitative analysis methodology. Herein, we provide a straightforward hitchhiker's guide, covering all of the workflow's major stages. Ultimately, this guide will help newcomers navigate the most critical roadblocks in the analysis and further encourage the use of DTI.

Advanced magnetic resonance MR neuroimaging modalities are becoming more available and useful as their value in the diagnosis and prognosis of central nervous system diseases is more fully studied and understood. Specifically, diffusion tensor imaging DTI has become increasingly studied and utilized in recent years. It has become incorporated by many radiologists into routine clinical practice, with most research performed on traumatic brain injury TBI. DTI is a variant of diffusion-weighted imaging DWI that utilizes a tissue water diffusion rate for image production. The first application of DWI to the human brain was performed in and since has become the gold standard for detecting acute stroke. DTI does not require contrast and is available on almost all modern MR scanners with relatively quick scan times for this sequence. Random thermal motion, or Brownian motion, is water molecular diffusion in three-dimensional 3D space. Isotropy is defined as uniformity in all directions, and when applied to water molecules, isotropy occurs when the diffusion of water is entirely uninhibited such as water movement in a glass of water. Anisotropy is when there is a directionality in the diffusion of water present, and the movement of water is no longer random such as water movement along straws placed in a glass. The greater the anisotropy, the more directional and linear the diffusion of water molecules.

Diffusion tensor imaging

Thank you for visiting nature. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser or turn off compatibility mode in Internet Explorer. In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript. Diffusion tensor imaging is a magnetic resonance imaging method that measures the diffusion patterns of molecules in biological tissue. These patterns provide information on the microscopic structure of the tissue. The technique is commonly used to image neuronal fibre tracts. Whether connectivity in white matter detected by functional MRI relates to underlying electrophysiological synchronization is unclear.

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This deviation from a free diffusion behavior is what makes diffusion MRI so successful, as the ADC is very sensitive to changes in tissue microstructure. Correction of motional artifacts in diffusion-weighted MR images using navigator echoes. This vector can be color-coded, yielding a cartography of the tracts' position and direction red for left-right, blue for superior-inferior, and green for anterior-posterior. Neuroimage 52, — The main disadvantage of glyph visualization is that it only allows intrinsic individual profiles rather than global characterization of the tensor data. A common deterministic algorithm used and implemented in the main DTI processing packages is Fiber Assignment by Continuous Tracking FACT defining specific anatomic tracts based on ROIs assuming that fiber orientation is uniform within a voxel and changes abruptly in the boundaries of it Mori et al. Method of utilizing water in magnetic resonance imaging. MR diffusion kurtosis imaging for neural tissue characterization. Spatial normalization of diffusion tensor MRI using multiple channels. Diffusion and perfusion magnetic resonance imaging: Applications to functional MRIch. We expect that the field will benefit from many future advances in diffusion imaging and analysis. Pierpaoli C, Basser PJ. However, its use for the assessment of highly-organized body systems outside the CNS, where anisotropy can facilitate early detection of pathology, has been gaining favor in recent years.

Introduction: Studies have shown that adolescents with moderate hypoxic-ischaemic encephalopathy HIE may have specific cognitive deficits, especially reduced speed of information processing. The aim of our study was to confirm these earlier findings find out whether the degree of impairment in speed of information processing correlates with the degree of white-matter impairment as measured by diffusion tensor imaging DTI. Methods: Thirty-three participants mean age 18y 5mo, SD 12mo; 19 male with mild or moderate HIE and 32 neurotypical adolescents mean age 17y 10mo, SD 12mo, 18 male completed a comprehensive neuropsychological battery measuring short-term memory, inhibition, speed of information processing, long-term visual and verbal memory.

Implications of bulk motion for diffusion-weighted imaging experiments: effects, mechanisms, and solutions. Another application area of DWI is in oncology. Neuroimage 51, — Fernandez, A. Brain Cogn. As a final take-home message, WM integrity assumptions must always be made with extreme caution Beaulieu, ; Jones et al. Method of utilizing water in magnetic resonance imaging. Some people are sensitive to the contrast agent and may develop an allergic reaction. Imaging 38, — IEEE Trans. Molecular diffusion, tissue microdynamics and microstructure. Neuroimage 39, 62— Shifting from region of interest ROI to voxel-based analysis in human brain mapping.