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Hybrid Nanosystems
Published in Carla Vitorino, Andreia Jorge, Alberto Pais, Nanoparticles for Brain Drug Delivery, 2021
Pablo Vicente Torres-Ortega, Laura Saludas, Jon Eneko Idoyaga, Carlos Rodríguez-Nogales, Elisa Garbayo, María José Blanco-Prieto
The use of HNs based on magnetic NPs incorporated within an organic matrix is attractive for PD treatment. For example, Ji et al. developed an interesting strategy based on Fe3O4 magnetic nanoliposomes loaded with nimodipine [36]. In this study, magnetic NPs demonstrated unique properties to guide these nanoliposomes to the targeted tissue by the application of an external magnetic field [36]. In addition, authors incorporated into the study a diagnostic value known as fractional anisotropy (FA), which is a useful measure of brain connectivity [37]. It was previously shown that the FA values measured by MRI may be related to microstuctural changes which happen in the substantia nigra [38]. Ji et al. observed a higher FA value and number of positive TH cells after intraperitoneal administration of the magnetic nanoliposomes in the 6-hydroxydopamine (6-OHDA) PD rat model compared to the free nimodipine and control groups [36]. Along similar lines, other studies have found a decrease in the FA associated with dopaminergic neuron loss [39, 40]. These results support the point that these HNs have a significant potential to cross the BBB and to provide a neuroprotective effect, constituting a promising targeting therapy for PD.
Anatomical and Biological Imaging of Pediatric Brain Tumor
Published in David A. Walker, Giorgio Perilongo, Roger E. Taylor, Ian F. Pollack, Brain and Spinal Tumors of Childhood, 2020
Rob A. Dineen, Shivaram Avula, Andrew C. Peet, Giovanni Morana, Monika Warmuth-Metz
DTI is an advanced MRI technique that is based on diffusion of water molecules as in DWI but also provides information on the direction of motion of the water molecule, enabling it to obtain microstructural parameters of the gray and white matter. The scan duration is longer than that of DWI as the diffusion gradient is applied in six or more directions. Whilst the image resolution can be improved using various methods, including increasing the number of gradient directions, these methods can prolong the scan time, increasing the chances of motion-related artefact. The parameters will therefore need to be optimized for children depending on the need (clinical versus research). Water molecules in normal white matter diffuse preferentially along the principal axis of axons in an anisotropic fashion (isotropic diffusion represents equal diffusion in all directions). Fractional anisotropy (FA) is a measurement derived from exploiting the anisotropic diffusion and reflects the alignment and integrity of the white-matter fibers. Measurement of diffusion can also be quantified as longitudinal or axial diffusivity (AD), which represents diffusivity along the principal axis, radial diffusivity (RA), the average diffusivity in the two minor axes, and mean diffusivity, which represents average diffusivity in all three axes.22,23
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.
Corpus Callosal Microstructure Predicts Bimanual Motor Performance in Chronic Stroke Survivors: a Preliminary Cross-Sectional Study
Published in Topics in Stroke Rehabilitation, 2023
Rini Varghese, Brianna Chang, Bokkyu Kim, Sook-Lei Liew, Nicolas Schweighofer, Carolee J. Winstein
Microstructural status was quantified as the fractional anisotropy (FA) index. The FA index is a composite measure reflecting the three-dimensional directional characteristics of diffusion in each voxel, serving as a proxy for fiber orientation.18,19,20 It is computed as a normalized fraction of the eigenvalues derived directly from voxel-wise fitted tensors, and ranges from 0 (isotropic diffusion, spherical in shape) to 1 (anisotropic diffusion, ellipsoidal in shape). The FA composite measure works particularly well for directionally homogenous, well-aligned fibers such as those of the CC, especially after thresholding for edge effects. In a random subset of stroke survivors (n = 20), we validated the FA index generated in the standard-space CC mask with those in the native FA maps and found no difference in mean FA between the two spaces. Results from these comparisons and bootstrap analyses are provided in Supplement S4.
Intimate partner violence and brain imaging in women: A neuroimaging literature review
Published in Brain Injury, 2023
Jirapat Likitlersuang, David H. Salat, Catherine B. Fortier, Katherine M. Iverson, Kimberly B. Werner, Tara Galovski, Regina E. McGlinchey
Diffusion-weighted imaging is another domain of MRI that can be used to create the contrast image of the diffusion of water molecules within the brain tissue. The diffusion tensor imaging (DTI) is one of the DWI sequences that can evaluate the white matter tractography (3D modeling) of nerve fibers as well as microstructural tissue properties. Specifically, the degree in anisotropy or degree of directionality of water molecules movement within the brain can be extracted. Fractional anisotropy (FA) is a scalar value from 0 to 1 and in diffusion imaging described the fiber density, axonal diameter, and myelination in the brain white matter. A value of one indicates fluid flow in one direction without any restriction (anisotropic), while a value closer to zero indicates leaky axon and unrestricted flow in all directions (isotropic). In other words, the reduced FA value may indicate an alteration of the integrity of the white matter tracts (Figure 2).
The role of diffusion tensor imaging in characterizing injury patterns on athletes with concussion and subconcussive injury: a systematic review
Published in Brain Injury, 2021
Maryam Tayebi, Samantha J. Holdsworth, Allen A. Champagne, Douglas J. Cook, Poul Nielsen, Tae-Rin Lee, Alan Wang, Justin Fernandez, Vickie Shim
Various DTI metrics were compared between SRC or subconcussed participants and the control subjects who were healthy individuals or uninjured athletes. Fractional Anisotropy (FA) were studied in 55 papers, Mean Diffusivity (MD) in 33, Axial Diffusivity (AD) in 23, Radial Diffusivity (RD) in 21, tractography in 9, and Apparent Diffusion Coefficient (ADC) and trace in 4 studies. 31 cross sectional investigations were conducted among active players (who were under 30 years old and categorized as high school, collegiate, or professional players), which compared these groups with healthy control subjects. 14 studies showed that the FA did not change in both the acute and chronic phase of injury. However, 11 studies found an increase in FA, while 7 found a decrease in FA (Figure 3). MD exhibited a different trend; most studies (N studies = 11) showed a reduction in MD in the acute and chronic phases, whereas 3 papers found an increase, and 5 found stability in MD (Figure 4). As for AD, an equal number of studies found this index to either decrease or constant (Nstudies = 8 each) (Figure 5). Seven papers found RD to decrease and six found no change in this parameter, while no increase reported in any paper (Figure 6). Eight papers focused exclusively in retired athletes (Figure 7), and – as in the active athletes – similar trends and variability of the aforementioned DTI metrics can be found.