scholarly journals Optimizing the fitting initial condition for the parallel intrinsic diffusivity in NODDI: An extensive empirical evaluation

2019 ◽  
Author(s):  
Jose M. Guerrero ◽  
Nagesh Adluru ◽  
Barbara B. Bendlin ◽  
H. Hill Goldsmith ◽  
Stacey M. Schaefer ◽  
...  
Keyword(s):  
White Matter ◽  
Gray Matter ◽  
Empirical Evaluation ◽  
Free Water ◽  
B Value ◽  
Tissue Type ◽  
Estimated Parameters ◽  
Diffusion Weighting ◽  
Model Residuals ◽  
And Diffusion

AbstractPurposeNODDI is widely used in parameterizing microstructural brain properties. The model includes three signal compartments: intracellular, extracellular, and free water. The neurite compartment intrinsic parallel diffusivity (d‖) is set to 1.7 µm2⋅ms−1, though the effects of this assumption have not been extensively explored. This work seeks to optimize d‖ by minimizing the model residuals.MethodsThe model residuals were evaluated in function of d‖ over the range from 0.5 to 3.0 µm2⋅ms−1. This was done with respect to tissue type (i.e., white matter versus gray matter), sex, age (infancy to late adulthood), and diffusion-weighting protocol (maximum b-value). Variation in the estimated parameters with respect to d‖ was also explored.ResultsResults show the optimum d‖ is significantly lower for gray matter relative to 1.7 µm2⋅ms−1 and to white matter. Infants showed significantly decreased optimum d‖ in gray and white matter. Minor optimum d‖ differences were observed versus diffusion protocol. No significant sex effects were observed. Additionally, changes in d‖ resulted in significant changes to the estimated NODDI parameters.ConclusionFuture implementations of NODDI would benefit from d‖ optimization, particularly when investigating young populations and/or gray matter.

scholarly journals Brain Substrates of Time-Based Prospective Memory Decline in Aging: A Voxel-Based Morphometry and Diffusion Tensor Imaging Study

2020 ◽  
Vol 31 (1) ◽  
pp. 396-409
Author(s):  
Alexandrine Morand ◽  
Shailendra Segobin ◽  
Grégory Lecouvey ◽  
Julie Gonneaud ◽  
Francis Eustache ◽  
...  
Keyword(s):  
Diffusion Tensor Imaging ◽  
White Matter ◽  
Prospective Memory ◽  
Gray Matter ◽  
Diffusion Tensor ◽  
Imaging Study ◽  
Age Related ◽  
Young Subjects ◽  
Anterior Prefrontal Cortex ◽  
And Diffusion

Abstract Time-based prospective memory (TBPM) allows us to remember to perform intended actions at a specific time in the future. TBPM is sensitive to the effects of age, but the neural substrates of this decline are still poorly understood. The aim of the present study was thus to better characterize the brain substrates of the age-related decline in TBPM, focusing on macrostructural gray matter and microstructural white matter integrity. We administered a TBPM task to 22 healthy young (26 ± 5.2 years) and 23 older (63 ± 5.9 years) participants, who also underwent volumetric magnetic resonance imaging and diffusion tensor imaging scans. Neuroimaging analyses revealed lower gray matter volumes in several brain areas in older participants, but these did not correlate with TBPM performance. By contrast, an age-related decline in fractional anisotropy in several white-matter tracts connecting frontal and occipital regions did correlate with TBPM performance, whereas there was no significant correlation in healthy young subjects. According to the literature, these tracts are connected to the anterior prefrontal cortex and the thalamus, 2 structures involved in TBPM. These results confirm the view that a disconnection process occurs in aging and contributes to cognitive decline.

Cognition and gray and white matter characteristics of presymptomatic C9orf72 repeat expansion

Neurology ◽  
2017 ◽  
Vol 89 (12) ◽  
pp. 1256-1264 ◽  
Author(s):  
Janne M. Papma ◽  
Lize C. Jiskoot ◽  
Jessica L. Panman ◽  
Elise G. Dopper ◽  
Tom den Heijer ◽  
...  
Keyword(s):  
Diffusion Tensor Imaging ◽  
White Matter ◽  
Gray Matter ◽  
Diffusion Tensor ◽  
Gray Matter Volume ◽  
Repeat Expansion ◽  
White Matter Integrity ◽  
Matter Volume ◽  
Presymptomatic Stage ◽  
And Diffusion

Objective:To investigate cognitive function, gray matter volume, and white matter integrity in the presymptomatic stage of chromosome 9 open reading frame 72 repeat expansion (C9orf72RE).Methods:Presymptomatic C9orf72RE carriers (n = 18) and first-degree family members without a pathogenic expansion (healthy controls [HC], n = 15) underwent a standardized protocol of neuropsychological tests, T1-weighted MRI, and diffusion tensor imaging within our cohort study of autosomal dominant frontotemporal dementia (FTD). We investigated group differences in cognitive function, gray matter volume through voxel-based morphometry, and white matter integrity by means of tract-based spatial statistics. We correlated cognitive change with underlying gray or white matter.Results:Our data demonstrate lower scores on letter fluency, Stroop card I, and Stroop card III, accompanied by white matter integrity loss in tracts connecting the frontal lobe, the thalamic radiation, and tracts associated with motor functioning in presymptomatic C9orf72RE compared with HC. In a subgroup of C9orf72RE carriers above 40 years of age, we found gray matter volume loss in the thalamus, cerebellum, and parietal and temporal cortex. We found no significant relationship between subtle cognitive decline and underlying gray or white matter.Conclusions:This study demonstrates that a decline in cognitive functioning, white matter integrity, and gray matter volumes are present in presymptomatic C9orf72RE carriers. These findings suggest that neuropsychological assessment, T1-weighted MRI, and diffusion tensor imaging might be useful to identify early biomarkers in the presymptomatic stage of FTD or amyotrophic lateral sclerosis.

scholarly journals Estimating intra-axonal axial diffusivity in the presence of fibre orientation dispersion

2020 ◽  
Author(s):  
Amy FD Howard ◽  
Frederik J Lange ◽  
Jeroen Mollink ◽  
Michiel Cottaar ◽  
Mark Drakesmith ◽  
...  
Keyword(s):  
White Matter ◽  
Fibre Orientation ◽  
Free Water ◽  
Orientation Distribution ◽  
B Value ◽  
Axial Diffusivity ◽  
High B Value ◽  
Axonal Compartment ◽  
Two Parameters

AbstractBy analysing the diffusion MRI signal, we can infer information about the microscopic structure of the brain. Two parameters of interest - the intra-axonal axial diffusivity and fibre orientation dispersion - are potential biomarkers for very different aspects of the white matter microstructure, yet they are difficult to disentangle. The parameters covary such that, if one is not accurately accounted for, the other will be biased. In this work we use high b-value data to isolate the signal from the intra-axonal compartment and resolve any degeneracies with the extra-axonal compartment. In the high b-value regime, we then use a model of dispersed sticks to estimate the intra-axonal axial diffusivity and fibre orientation distribution on a voxelwise basis. Our results in in vivo, human data show an intra-axonal axial diffusivity of ~ 2.3 – 3 μm2/ms, where 3 μm2/ms is the diffusivity of free water at 37°C. The intra-axonal axial diffusivity is seen to vary considerably across the white matter. For example, in the corpus callosum we find high values in the genu and splenium, and lower values in the midbody. Furthermore, the axial diffusivity and orientation dispersion appear negatively correlated, behaviour which we show is consistent with the presence of fibre undulations but not consistent with a degeneracy between fanning fibres and axial diffusivity. Finally, we demonstrate that the parameter maps output from Neurite Orientation Dispersion and Density Imaging (NODDI) change substantially when the assumed axial diffusivity was increased from 1.7 to 2.5 or 3 μm2/ms.

Abstract T P89: Unilateral Cerebral Atrophy Secondary to Extracranial Carotid Stenosis

Stroke ◽  
2014 ◽  
Vol 45 (suppl_1) ◽  
Author(s):  
Shahram Khalid ◽  
Navid Seraji-bozorgzad
Keyword(s):  
White Matter ◽  
Carotid Stenosis ◽  
Gray Matter ◽  
Statistical Significance ◽  
Cerebral Atrophy ◽  
Tissue Type ◽  
Total Brain Volume ◽  
Brain Images ◽  
Asymptomatic Patients ◽  
Bilateral Carotid

Background: Moderate to severe or bilateral carotid stenosis is associated with cerebral atrophy and cognitive decline. Prior studies have evaluated global atrophy and its correlation with the degree of stenosis. It is unclear whether carotid stenosis can lead to unilateral cerebral changes. Objective: To evaluate for unilateral cerebral atrophy in asymptomatic patients with moderated to severe extracranial unilateral carotid stenosis. Methods: Subjects were selected from patients who had undergone carotid vascular imaging and MRI of the brain, from January 2007 to January 2013 at our institution. Patients with history of TIA or ischemic stroke were excluded. Carotid stenosis (CS) group consisted of patients with unilateral moderate to severe carotid stenosis (n=9). Patients without any stenosis (n=5) were used as controls. T1-weighted brain images (FOV 256 x 256 x128, resolution 1.5 x 1.5 x 5 mm) were registered to Talairach space using FSL software. Non-brain tissue was removed using the BET module. Segmentation into gray matter (GM), white matter (WM), and cerebrospinal fluid (CSF) was done with the FAST tool. Total brain volume (TBV) was calculated as the sum of three tissue types (GM + WM + CSF). Total number of voxels in each hemisphere was calculated for GM, WM and CSF. Index of Asymmetry (IoA), was defined as the absolute value of inter-hemispheric voxel difference divided by TBV. IoA for each tissue type was compared between subjects and controls using Student’s t-test. Results: Mean age was 63.7±7.8 and 57.4 ±6.0 for the CS and control groups, respectively. Average gray matter IoA for CS was significantly increased compared to controls (1.4% v. 0.7, p < 0.02). Average white matter IoA was similar between the groups (0.6% v. 0.7%, p< 0.36). There was a trend for increased CSF IoA in the CS group compared to controls, but it did not reach statistical significance (1.8% v. 0.9%, p < 0.10). Conclusion: Moderate to severe carotid stenosis can lead to unilateral cerebral atrophy in the absence of other neurological symptoms. Further prospective studies with larger cohorts of the patients are required.

FT-IR microspectroscopic analysis of diseased white matter brain tissues

1995 ◽  
Vol 53 ◽  
pp. 968-969
Author(s):  
Steven M. Le Vine ◽  
David L. Wetzel
Keyword(s):  
White Matter ◽  
Gray Matter ◽  
Twitcher Mouse ◽  
Grid Pattern ◽  
Marked Contrast ◽  
Spatially Resolved ◽  
Ft Ir ◽  
Ir Microspectroscopy ◽  
Chemical Evidence

In situ FT-IR microspectroscopy has allowed spatially resolved interrogation of different parts of brain tissue. In previous work the spectrrscopic features of normal barin tissue were characterized. The white matter, gray matter and basal ganglia were mapped from appropriate peak area measurements from spectra obtained in a grid pattern. Bands prevalent in white matter were mostly associated with the lipid. These included 2927 and 1469 cm-1 due to CH2 as well as carbonyl at 1740 cm-1. Also 1235 and 1085 cm-1 due to phospholipid and galactocerebroside, respectively (Figs 1and2). Localized chemical changes in the white matter as a result of white matter diseases have been studied. This involved the documentation of localized chemical evidence of demyelination in shiverer mice in which the spectra of white matter lacked the marked contrast between it and gray matter exhibited in the white matter of normal mice (Fig. 3).The twitcher mouse, a model of Krabbe’s desease, was also studied. The purpose in this case was to look for a localized build-up of psychosine in the white matter caused by deficiencies in the enzyme responsible for its breakdown under normal conditions.

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