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Introduction
Published in Shoogo Ueno, Bioimaging, 2020
A method of spin diffusion measurements was introduced by Stejskal and Tanner in 1965 (Stejskal and Tanner, 1965), and around 20 years later, diffusion-weighted imaging and DTI have been well developed for clinical use by the efforts of many investigators (Le Bihan et al., 1986, Turner and Le Bihan, 1990, Le Bihan et al., 1992, Basser et al., 1994). Recent advances in diffusion MRI and DTI have become powerful tools to visualize structures of neuronal fibers and neuronal networks in the human brain.
Artifacts and Pitfalls in Diffusion MRI
Published in Ioannis Tsougos, Advanced MR Neuroimaging, 2018
Especially regarding high b-value diffusion MR imaging, which provides enhanced contrast compared to “regular” diffusion MRI, motion is a definite drawback and has to be dealt with. The most frequently adopted approach is to use image registration techniques to coregister each DW image to the first image collected (the B0) using it as a reference image. According to Ben Amitay et al. (2012), given the orientational sensitivity of the DW-MRI signal, cost functions such as cross correlation and least-squares (used for intramodal coregistration) are ineffective while cost functions such as mutual information (Studholme et al., 1999) or its normalized variant (Haselgrove and Moore, 1996) are used successfully.
Mapping the Injured Brain
Published in Yu Chen, Babak Kateb, Neurophotonics and Brain Mapping, 2017
Chandler Sours, Jiachen Zhuo, Rao P. Gullapalli
Diffusion MRI has long been used as an important tool in studying neurological disorders because it provides in vivo measurements of tissue microstructure changes that are unable to be detected using conventional CT or MR imaging. Diffusion tensor imaging (DTI) entails measuring water diffusion in at least six directions to obtain an appropriate representation of a diffusion tensor, describing the preferential diffusion direction and an ellipsoidal diffusivity profile. Briefly speaking, common measurements in DTI include mean diffusivity (MD) and apparent diffusion coefficient, which both measure the average magnitude of diffusivity, and fractional anisotropy (FA), which measures the disproportion of diffusion along the three principal axes of the diffusion ellipsoid. The diffusion properties of different brain tissues (GM, WM, CSF) exhibit unique structural properties. Diffusion in CSF is similar to free diffusion in water, so MD is extremely high (~3 × 10−3 mm2/s) and FA is almost 0. Diffusion in GM is generally nondirectional or isotropic because it is mostly composed of neurons and glial cells (FA < 0.2). On the other hand, in WM, diffusion is highly anisotropic due to the myelinated axons, which restrict water diffusion in the direction perpendicular to the axon. Therefore, axial diffusivity (AD, diffusion measured along the axon) can be as much as seven times the radial diffusivity (RD, diffusion measured perpendicular to the axon averaged across two axes) (FA ~ 0.45–0.8) (Song et al., 2003). Figure 14.1 shows an example of water diffusion in WM axons and the effect of axon membrane injury to water diffusion, which leads to increased RD and reduced FA.
A critical review on the impact of built environment on users’ measured brain activity
Published in Architectural Science Review, 2021
Sameh Azzazy, Amirhosein Ghaffarianhoseini, Ali GhaffarianHoseini, Nicola Naismith, Zohreh Doborjeh
Over the last few decades, a marked increase in interest in understanding neuropsychological mechanisms of human behaviour has spurred an eruption of innovative methods to measure and interpret brain activities. This approach is considered more technologically advanced as it depends on sophisticated instruments to scan the human brain. According to Duffau (2011); Eberhard (2009); Gegenfurtner et al. (2017), there are different methods to map the brain structure and activity and each has a favourable purpose (Figure 4): Structural Imaging which provides representation of the brain structure by: Computerized Tomography (CT): It computes several X-rays from different angles to plot a two-dimensional horizontal section of the brain (Bear, Connors, and Paradiso 2016).Magnetic Resonance Imaging (MRI): Like the CT but instead it uses a strong magnetic field to plot at a higher resolution and more sections than CT (Duffau 2011).Water Diffusion MRI (dMRI). This is more advanced and allows mapping of the brain wiring (Duffau 2011).Functional imaging techniques which can provide functional information on different parts of the brain: Positron Emission Tomography (PET): This measures the blood flow to determine the activity of the brain tissue (Bear, Connors, and Paradiso 2016)Functional MRI (fMRI): This is more advanced and accurate, it uses the same concept as PET but measuring the local blood flow (Duffau 2011).