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Electrical Brain Stimulation to Treat Neurological Disorders
Published in Bahman Zohuri, Patrick J. McDaniel, Electrical Brain Stimulation for the Treatment of Neurological Disorders, 2019
Bahman Zohuri, Patrick J. McDaniel
Protons in different body tissues return to their normal spins at different rates, so the scanner can distinguish among various types of tissue. The scanner settings can be adjusted to produce contrasts between different body tissues. Additional magnetic fields are used to produce three-dimensional images that may be viewed from different angles. There are many forms of MRI, but diffusion MRI and functional MRI (fMRI) are two of the most common.
Diffusion Imaging in Brain Tumors and Treatment Response
Published in Andrei I. Holodny, Functional Neuroimaging, 2019
Shareef Riad, Andrei I. Holodny, Suresh K. Mukherji
The key to understanding diffusion MRI is realizing that it is fundamentally different from routine MR sequences such as T1 and T2 and, in fact, conceptually easier to understand. T1- and T2-weighted images are generated from the time it takes for molecules to return to their original resting state after undergoing a series of excitations. Diffusion MRI is based on visualizing the relative speeds at which water molecules diffuse through tissue.
DiffusionWeighted Magnetic Resonance Microscopy
Published in Luisa Ciobanu, Microscopic Magnetic Resonance Imaging, 2017
Another application of diffusion MRI is the measurement of neuronal activity Diffusion based functional MRI (DfMRI) studies have been reported in human subjects (Le Bihan, 2006) and animal models (Tsurugizawa, 2013). The hypothesis behind DfMRI is that transient neuronal network morphological changes (e.g., cell swelling) accompanying neuronal activity lead to a detectable decrease in the apparent diffusion coefficient of the tissue. As of today there is no general consensus on whether this hypothesis is true, and the precise origin of the DfMRI signal is still unclear MRM investigations hold the potential to identify the morphological changes occurring at the cellular level during neuronal activation and establish whether or not they are correlated to the detected diffusion MR signal changes. Such studies, typically performed on tissue samples, present several advantages. First, they avoid confounding factors such as blood flow blood oxygenation changes, motion artifacts related to breathing or anesthesia effects. Second, they significantly simplify result interpretation by reducing the complexity of the networks investigated.
Neurosurgical applications of tractography in the UK
Published in British Journal of Neurosurgery, 2021
Sebastian M. Toescu, Patrick W. Hales, Martin M. Tisdall, Kristian Aquilina, Christopher A. Clark
Tractography derived from diffusion MRI is a useful tool in the arsenal of the modern neurosurgeon. In this UK-based survey of practising neurosurgeons, we show that predominantly DTI-based reconstructions are used, that tumour resection remains the most frequent use of the technique, and that large tracts such as the corticospinal tract are most frequently identified. The results point out a number of limitations with the technique, many of which are inherent, such as inaccuracy in representing underlying anatomy, and intra-operative brain shift. The advent of iMRI and rapid-acquisition high angular resolution imaging may mitigate some of the perceived limitations of tractography described in this report. We urge units using tractography to adopt standardised procedures for tract reconstruction, and hope that broader collaboration in the field can lead to the development of ‘best practice’ in this area.
Cellular and extracellular white matter alterations indicate conversion to psychosis among individuals at clinical high-risk for psychosis
Published in The World Journal of Biological Psychiatry, 2021
Felix L. Nägele, Ofer Pasternak, Lisa V. Bitzan, Marius Mußmann, Jonas Rauh, Marek Kubicki, Gregor Leicht, Martha E. Shenton, Amanda E. Lyall, Christoph Mulert
The diffusion MRI-based free-water imaging technique addresses these limitations by decomposing the diffusion signal into two compartments (Pasternak et al. 2009). The first compartment models the fractional volume of isotropic, unrestricted diffusion in the extracellular space (free-water, FW) which can be responsive to pathologies such as edoema and atrophy (Pasternak et al. 2012; Lyall et al. 2018). The second compartment models hindered/restricted diffusion in close proximity to cellular membranes, from which FA of the tissue (FAT) is derived, reflecting more closely changes in myelination and axonal membrane health than the conventional DTI metric FA (Pasternak et al. 2009). By differentiating these compartments this model has proven to be successful in providing new insights to potential biological mechanisms underlying the observed FA reductions in schizophrenia (Pasternak et al. 2012, 2015; Lyall et al. 2018).
Impact of Amblyopia on the Central Nervous System
Published in Journal of Binocular Vision and Ocular Motility, 2020
Nathaniel P. Miller, Breanna Aldred, Melanie A. Schmitt, Bas Rokers
However, in recent decades, advances in magnetic resonance imaging (MRI) methods have enabled more precise in vivo assessment of the structure and function of the brain beyond the retina. Functional integrity can be assessed using functional MRI (fMRI) in which neural activity is estimated based on metabolic demand via blood oxygen level-dependent (BOLD) signals.35 Structural integrity can be assessed with voxel-based morphometry (VBM) or diffusion MRI (dMRI). VBM is based on MRI intensity differences produced by different kinds of brain tissue and can assess local gray and white-matter volume. Diffusion MRI measures the diffusion of water molecules in tissue, enabling the identification of white-matter pathways in the brain and the estimation of their structural integrity.