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Disorders Affecting White and Gray Matter:
Published in Swati Goyal, Neuroradiology, 2020
“Dawson’s fingers” refer to initial finger-like thin and linear hyperintensities along the medullary veins, followed by ovoid/elliptical configuration, arranged perpendicularly to the lateral ventricles, extending radially outward and best visualized on sagittal images. CE-MRI − incomplete peripheral enhancement around active lesions (“open ring” sign − open component represents the GM side of the lesion, and the enhancing component represents the WM side of the lesion).Double inversion recovery (DIR) sequences use two inversion times and better delineate cortical lesions by suppressing both WM and CSF signals.Magnetization transfer imaging calculates the ratio (MTR), which is a marker of myelin disorder, a reduction in which favors the diagnosis of multiple sclerosis.DTI − increased fractional anisotropy (FA) and diffusivity values.
Quantitative imaging to guide mechanism-based modeling of cancer
Published in Ruijiang Li, Lei Xing, Sandy Napel, Daniel L. Rubin, Radiomics and Radiogenomics, 2019
David A. Hormuth, Matthew T. McKenna, Thomas E. Yankeelov
Diffusion tensor imaging (DTI) is a variant of diffusion weighted-MRI (DW-MRI) that can be used to assess the magnitude and direction of water diffusion in tissue. In DTI, pulsed gradients are applied along at least six non-collinear directions to estimate the diffusion coefficient of water in those directions and build the diffusion tensor at each voxel. Structures such as white matter or muscles which are well organized exhibit anisotropic diffusion, while tumor regions typically exhibit more isotropic diffusion. DTI measurements are commonly used to characterize structural connectivity through tractography which follows the path of the dominant diffusion direction in highly anisotropic tissues (i.e., white matter tracts). The fractional anisotropy index which ranges from 0 (fully isotropic diffusion) to 1 (fully anisotropic diffusion) is often used to assess the degree of diffusion anisotropy within a region. The diffusion tensor is useful in biophysical models as the tensor can be used to define the direction of tumor cell movement or assist in defining the movement of tumor cells along white matter tracts. A detailed review of DTI can be found in (Sundgren et al. 2004).
Precision Imaging of Prostate Cancer
Published in Ayman El-Baz, Gyan Pareek, Jasjit S. Suri, Prostate Cancer Imaging, 2018
DTI has been widely used in clinical applications, especially in neuro- and musculoskeletal imaging. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values provided from DTI data reflect the degree of water diffusion restriction in different tissue. Pathological processes may cause change in normative FA values and disruption of fibers in tractography. The feasibility of performing DTI of the prostate had been demonstrated by some studies; and DTI tractography can successfully visualize fiber tracts around the prostate [58]. DTI tractography might be applicable to the estimation of structures of the prostate [59], the characterization of prostate cancer [60], and monitoring prostatic structural changes under radiotherapy [61].
Neuroimaging in professional combat sports: consensus statement from the association of ringside physicians
Published in The Physician and Sportsmedicine, 2023
Newer MRI technology and acquisition sequences have improved the sensitivity of the MRI for detecting the stigmata of TBI, but not all sequences are routinely adopted or performed in clinical contexts, and some are presently strictly related to research due to high rates of false positives and false negatives. Among these is diffusion tensor imaging (DTI). Traumatic axonal injury is characterized by a reduction in fractional anisotropy (FA) on DTI. Magnetization transfer imaging (MTI), which applies radio frequency power only to the protons in the macromolecules of tissues rather than the protons in water, can add sensitivity to an MRI [1,8,9]. Magnetic source imaging (MSI), using a combination of MRI and magnetoencephalography (MEG), was found to be superior to using only an MRI in the detection of TBI [1,8,9]. Proton magnetic resonance spectroscopic imaging (1 H-MRSI) has been found to be a sensitive tool in detecting axonal injury in the corpus callosum of TBI patients [1,8,9]. Susceptibility-weighted imaging (SWI) and functional MRI (fMRI) techniques including arterial spin labeling (ASL) which can demonstrate changes in regional brain activation are newer MRI methods for better detection of TBI and microhemorrhages [8,9].
Diffusion tensor imaging and auditory tractography to evaluate cochlear implant candidacy: a pilot study
Published in Acta Oto-Laryngologica, 2023
Badr E. Mostafa, Yasser Abdel Azim, Lobna Elfiky
The microstructural integrity and orientation of white matter tracts in the brain can be evaluated by diffusion tensor imaging (DTI). The entire length of white matter structures of interest can be visualized three-dimensionally and their functional integrity evaluated. Two main measures can be inferred, fractional anisotropy (FA) which allows the generation of white matter fiber maps, and mean diffusivity (MD) which provides a specific surrogate of changes associated with myelination and the intrinsic characteristics of the axons. Reduced FA is believed to underlie diminished microstructural integrity. If reduced FA is accompanied by an increase in MD, results are more likely to be driven by alteration in brain tissue [2,4–6]. DTI was studied in different hearing disorders, tinnitus and as a predictor of outcomes in patients undergoing cochlear implantation [3,7–12].
Altered connectivity of default mode and executive control networks among female patients with persistent post-concussion symptoms
Published in Brain Injury, 2023
Jimmy K. Y. Wong, Nathan W. Churchill, Simon J. Graham, Andrew J. Baker, Tom A. Schweizer
In addition to altered brain function, persistent symptoms are likely due to microscopic injury of white matter tracts, which form the neuroanatomical substrate for inter-regional communication (7). To assess such “structural connectivity” noninvasively, diffusion tensor imaging (DTI) may be used to assess changes in tissue microstructure, based on patterns of regional water diffusion predominantly in white matter fiber tracts. Metrics of interest include mean diffusivity (MD), characterizing the overall diffusion rate; and fractional anisotropy (FA), characterizing the tendency for water to diffuse in a preferred direction along the length of axons. Some studies also examine axial diffusivity (AD), which measures diffusion along the preferred direction, and radial diffusivity (RD), which measures diffusion perpendicular to the preferred direction. In previous studies of mTBI, patients have typically exhibited reduced FA and increased MD and RD, identified at an average of 1 week to 1 month post-injury (17–20). These DTI parameters may also provide insight into the mechanisms of injury and affected white matter tracts that give rise to altered brain function post-concussion.