scholarly journals Modelling conduction delays in the corpus callosum using MRI-measured g-ratio

2018 ◽  
Author(s):  
S. Berman ◽  
S. Filo ◽  
A. A. Mezer
Keyword(s):  
White Matter ◽  
Corpus Callosum ◽  
Quantitative Mri ◽  
Biophysical Model ◽  
Diameter Distribution ◽  
Conduction Delay ◽  
Axon Diameter ◽  
Healthy Human ◽  
G Ratio

AbstractConduction of action potentials along myelinated axons is affected by their structural features, such as the axonal g-ratio, the ratio between the inner and outer diameters of the myelin sheath surrounding the axon. The effect of g-ratio variance on conduction properties has been quantitatively evaluated using single-axon models. It has recently become possible to estimate a g-ratio weighted measurement in vivo using quantitative MRI. Nevertheless, it is still unclear whether the variance in the g-ratio in the healthy human brain leads to significant differences in conduction velocity. In this work we tested whether the g-ratio MRI measurement can be used to predict conduction delays in the corpus callosum.We present a novel framework in which the structural properties of fibers (i.e. length and g-ratio, measured using MRI), are incorporated in a biophysical model of axon conduction, to predict conduction delays of long-range white matter fibers. We applied this framework to the corpus callosum, and found conduction delay estimates that are compatible with previously estimated values of conduction delays. We account for the variance in the velocity given the axon diameter distribution in the splenium, mid-body and genu, to further compare the fibers within the corpus callosum.Conduction delays have been suggested to increase with age. Therefore, we investigated whether there are differences in the g-ratio and the fiber length between young and old adults, and whether this leads to a difference in conduction speed and delays. We found small but significant differences between the predicted delays of the two groups in the motor fibers of the corpus callosum. We also found that the motor fibers of the corpus callosum have the fastest conduction estimates. Using the axon diameter distributions, we found that the occipital fibers have the slowest estimations, while the frontal and motor fiber tracts have similar estimates.Our study provides a framework for predicting conduction latencies in vivo. The framework could have major implications for future studies of white matter diseases and large range network computations. Our results highlight the need for improving additional in vivo measurements of white matter microstructure.

scholarly journals In vivo measurement of axon diameter distribution in the corpus callosum of rat brain

Brain ◽  
2009 ◽  
Vol 132 (5) ◽  
pp. 1210-1220 ◽  
Author(s):  
Daniel Barazany ◽  
Peter J. Basser ◽  
Yaniv Assaf
Keyword(s):  
Corpus Callosum ◽  
Rat Brain ◽  
Diameter Distribution ◽  
Axon Diameter ◽  
In Vivo Measurement

scholarly journals Body mass index, time of day, and genetics affect perivascular spaces in the white matter

2020 ◽  
Author(s):  
Giuseppe Barisano ◽  
Farshid Sepehrband ◽  
Nasim Sheikh-Bahaei ◽  
Meng Law ◽  
Arthur W. Toga
Keyword(s):  
Body Mass Index ◽  
White Matter ◽  
Body Mass ◽  
Structural Changes ◽  
Large Population ◽  
Time Of Day ◽  
Perivascular Spaces ◽  
Healthy Human ◽  
Magnetic Resonance Imaging Mri

AbstractThe analysis of cerebral perivascular spaces (PVS) using magnetic resonance imaging (MRI) allows to explore in vivo their contributions to neurological disorders. To date the normal amount and distribution of PVS in healthy human brains are not known, thus hampering our ability to define with confidence pathogenic alterations. Furthermore, it is unclear which biological factors can influence the presence and size of PVS on MRI. We performed exploratory data analysis of PVS volume and distribution in a large population of healthy individuals (n = 897, age = 28.8 ± 3.7). Here we describe the global and regional amount of PVS in the white matter, which can be used as a reference for clinicians and researchers investigating PVS and may help the interpretation of the structural changes affecting PVS in pathological states. We found a relatively high inter-subject variability in the PVS amount in this population of healthy adults (range: 1.31-14.49 cm3). We then identified body mass index, time of day, and genetics as new elements significantly affecting PVS in vivo under physiological conditions, offering a valuable foundation to future studies aimed at understanding the physiology of perivascular flow.

scholarly journals Body mass index, time of day, and genetics affect perivascular spaces in the white matter

2020 ◽  
pp. 0271678X2097285
Author(s):  
Giuseppe Barisano ◽  
Nasim Sheikh-Bahaei ◽  
Meng Law ◽  
Arthur W Toga ◽  
Farshid Sepehrband
Keyword(s):  
Body Mass Index ◽  
White Matter ◽  
Body Mass ◽  
Structural Changes ◽  
Large Population ◽  
Time Of Day ◽  
Perivascular Spaces ◽  
Healthy Human ◽  
Magnetic Resonance Imaging Mri

The analysis of cerebral perivascular spaces (PVS) using magnetic resonance imaging (MRI) allows to explore in vivo their contributions to neurological disorders. To date the normal amount and distribution of PVS in healthy human brains are not known, thus hampering our ability to define with confidence pathogenic alterations. Furthermore, it is unclear which biological factors can influence the presence and size of PVS on MRI. We performed exploratory data analysis of PVS volume and distribution in a large population of healthy individuals (n = 897, age = 28.8 ± 3.7). Here we describe the global and regional amount of PVS in the white matter, which can be used as a reference for clinicians and researchers investigating PVS and may help the interpretation of the structural changes affecting PVS in pathological states. We found a relatively high inter-subject variability in the PVS amount in this population of healthy adults (range: 1.31–14.49 cm3). The PVS volume was higher in older and male individuals. Moreover, we identified body mass index, time of day, and genetics as new elements significantly affecting PVS in vivo under physiological conditions, offering a valuable foundation to future studies aimed at understanding the physiology of perivascular flow.

scholarly journals Analysis of White Matter Damage in Patients with Multiple Sclerosis via a Novel In Vivo MR Method for Measuring Myelin, Axons, and G-Ratio

2017 ◽  
Vol 38 (10) ◽  
pp. 1934-1940 ◽  
Author(s):  
A. Hagiwara ◽  
M. Hori ◽  
K. Yokoyama ◽  
M. Nakazawa ◽  
R. Ueda ◽  
...  
Keyword(s):  
Multiple Sclerosis ◽  
White Matter ◽  
White Matter Damage ◽  
G Ratio

Corpus Callosum Measurement as an in Vivo Indicator for Neocortical Neuronal Integrity, but not White Matter Pathology, in Alzheimer's Disease

2000 ◽  
Vol 903 (1 VASCULAR FACT) ◽  
pp. 470-476 ◽  
Author(s):  
HARALD HAMPEL ◽  
STEFAN J. TEIPEL ◽  
GENE E. ALEXANDER ◽  
BARRY HORWITZ ◽  
PIETRO PIETRINI ◽  
...  
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
White Matter ◽  
Corpus Callosum ◽  
White Matter Pathology

scholarly journals Bundle-Specific Axon Diameter Index as a New Contrast to Differentiate White Matter Tracts

2021 ◽  
Vol 15 ◽  
Author(s):  
Muhamed Barakovic ◽  
Gabriel Girard ◽  
Simona Schiavi ◽  
David Romascano ◽  
Maxime Descoteaux ◽  
...  
Keyword(s):  
White Matter ◽  
Internal Capsule ◽  
Mean Value ◽  
Axon Diameter ◽  
Posterior Limb ◽  
Weighted Magnetic Resonance Imaging ◽  
The Central Nervous System ◽  
Index Value ◽  
White Matter Connectivity

In the central nervous system of primates, several pathways are characterized by different spectra of axon diameters. In vivo methods, based on diffusion-weighted magnetic resonance imaging, can provide axon diameter index estimates non-invasively. However, such methods report voxel-wise estimates, which vary from voxel-to-voxel for the same white matter bundle due to partial volume contributions from other pathways having different microstructure properties. Here, we propose a novel microstructure-informed tractography approach, COMMITAxSize, to resolve axon diameter index estimates at the streamline level, thus making the estimates invariant along trajectories. Compared to previously proposed voxel-wise methods, our formulation allows the estimation of a distinct axon diameter index value for each streamline, directly, furnishing a complementary measure to the existing calculation of the mean value along the bundle. We demonstrate the favourable performance of our approach comparing our estimates with existing histologically-derived measurements performed in the corpus callosum and the posterior limb of the internal capsule. Overall, our method provides a more robust estimation of the axon diameter index of pathways by jointly estimating the microstructure properties of the tissue and the macroscopic organisation of the white matter connectivity.

scholarly journals Apparent thinning of human visual cortex during childhood is associated with myelination

2019 ◽  
Vol 116 (41) ◽  
pp. 20750-20759 ◽  
Author(s):  
Vaidehi S. Natu ◽  
Jesse Gomez ◽  
Michael Barnett ◽  
Brianna Jeska ◽  
Evgeniya Kirilina ◽  
...  
Keyword(s):  
White Matter ◽  
Temporal Cortex ◽  
Mean Diffusivity ◽  
Brain Regions ◽  
Tissue Growth ◽  
Quantitative Mri ◽  
Childhood Development ◽  
Cortical Thinning ◽  
Ventral Temporal Cortex

Human cortex appears to thin during childhood development. However, the underlying microstructural mechanisms are unknown. Using functional magnetic resonance imaging (fMRI), quantitative MRI (qMRI), and diffusion MRI (dMRI) in children and adults, we tested what quantitative changes occur to gray and white matter in ventral temporal cortex (VTC) from childhood to adulthood, and how these changes relate to cortical thinning. T1 relaxation time from qMRI and mean diffusivity (MD) from dMRI provide independent and complementary measurements of microstructural properties of gray and white matter tissue. In face- and character-selective regions in lateral VTC, T1 and MD decreased from age 5 to adulthood in mid and deep cortex, as well as in their adjacent white matter. T1 reduction also occurred longitudinally in children’s brain regions. T1 and MD decreases 1) were consistent with tissue growth related to myelination, which we verified with adult histological myelin stains, and 2) were correlated with apparent cortical thinning. In contrast, in place-selective cortex in medial VTC, we found no development of T1 or MD after age 5, and thickness was related to cortical morphology. These findings suggest that lateral VTC likely becomes more myelinated from childhood to adulthood, affecting the contrast of MR images and, in turn, the apparent gray–white boundary. These findings are important because they suggest that VTC does not thin during childhood but instead gets more myelinated. Our data have broad ramifications for understanding both typical and atypical brain development using advanced in vivo quantitative measurements and clinical conditions implicating myelin.

scholarly journals Does powder averaging remove dispersion bias in diffusion MRI diameter estimates within real 3D axonal architectures?

2021 ◽  
Author(s):  
Mariam Andersson ◽  
Marco Pizzolato ◽  
Hans Martin Kjer ◽  
Katrine Forum Skodborg ◽  
Henrik Lundell ◽  
...  
Keyword(s):  
White Matter ◽  
Diffusion Mri ◽  
Ex Vivo ◽  
Dynamic Properties ◽  
High Signal ◽  
Axon Diameter ◽  
Signal To Noise ◽  
B Values ◽  
Wide Range

Noninvasive estimation of axon diameter with diffusion MRI holds potential to investigate the dynamic properties of the brain network and pathology of neurodegenerative diseases. Recent methods use powder averaging to account for complex white matter architectures, such as fibre crossing regions, but these have not been validated for real axonal geometries. Here, we present 120-313 μm long segmented axons from X-ray nano-holotomography volumes of a splenium and crossing fibre region of a vervet monkey brain. We show that the axons in the complex crossing fibre region, which contains callosal, association, and corticospinal connections, are larger and exhibit a wider distribution than those of the splenium region. To accurately estimate the axon diameter in these regions, therefore, sensitivity to a wide range of diameters is required. We demonstrate how the q-value, b-value, signal-to-noise ratio and the assumed intra-axonal parallel diffusivity influence the range of measurable diameters with powder average approaches. Furthermore, we show how Gaussian distributed noise results in a wider range of measurable diameter at high b-values than with Rician distributed noise, even at high signal-to-noise ratios of 100. The number of gradient directions is also shown to impose a lower bound on measurable diameter. Our results indicate that axon diameter estimation can be performed with only few b-shells, and that additional shells do not improve the accuracy of the estimate. Through Monte Carlo simulations of diffusion, we show that powder averaging techniques succeed in providing accurate estimates of axon diameter across a range of sequence parameters and diffusion times, even in complex white matter architectures. At sufficiently low b-values, the acquisition becomes sensitive to axonal microdispersion and the intra-axonal parallel diffusivity shows time dependency at both in vivo and ex vivo intrinsic diffusivities.

Abstract 3575: Oligodendrocyte Proliferation and Improved Myelination Following Human Embryonic-Derived Neural Stem Cell Treatment in an Experimental Model of Cerebral Palsy

Stroke ◽  
2012 ◽  
Vol 43 (suppl_1) ◽  
Author(s):  
Tenille Smith ◽  
Sahar Rosenblum ◽  
Nancy Wang ◽  
Sam Lawrence ◽  
Kendrick Wang ◽  
...  
Keyword(s):  
Cerebral Palsy ◽  
Stem Cell ◽  
White Matter ◽  
Corpus Callosum ◽  
Neural Stem Cell ◽  
Functional Recovery ◽  
White Matter Injury ◽  
Motor Disability ◽  
Hypoxia Ischemia

Introduction: Cerebral palsy (CP) is the most common cause of motor disability in children, and chronic deficits are associated with white matter injury. Neonatal hypoxic-ischemic insults, an important cause of CP, induce oligodendrocyte apoptosis and impair normal myelin development. No CP treatments target myelination making regenerative medicine a promising research frontier. We investigated the effect of human embryonic-derived neural stem cell (NSC) treatment on oligodendrocytes and myelination following hypoxia-ischemia (HI). Methods: Neonatal Wistar rat pups underwent left CCA ligation followed by placement in 8% O2 at 37°C on post-natal day 7 (P7). Following T2w MRI on P9, immunosuppressed pups received intra-arterial transplant of 500k fLuc/eGFP transduced NSCs or saline on P10. BrdU was administered intraperitoneally from P11 - P18. In vivo bioluminescence images (BLI) were obtained 1 - 10 days (d) after injection. Myelination was evaluated using luxol fast blue (LFB) and myelin basic protein (MBP) staining 10 and 30 d after treatment. Oligodendrogenesis was quantified using BrdU staining in conjunction with Olig2, NG2, and CC1. RT-qPCR was performed on neonatal brain isolates and NSC mRNA. Luminex immunological assay was used to quantify NSC protein secretion. Functional recovery was assessed using the novel object recognition (NOR) task at P30. Results: Stroke size between groups was not significantly different 3, 10, and 30 d after treatment. BLI demonstrated significant NSC homing to the ischemic hemisphere days 1 - 7 (p=0.001) after transplant. Histology confirmed initial NSC localization to corpus callosum and cortex with migration into external capsule and corona radiata 30 d after transplant. NSC-treated pups had significantly more BrdU+ cells near the lateral ventricle (p=0.036) and in the corpus callosum (p=0.020) than controls. In addition to more Olig2+ and NG2+ cells in the striatum, NSC-treated pups had significantly more BrdU+/Olig2+ cells in the corpus callosum (p<0.05) than controls 30 d after treatment. LFB and MBP staining demonstrated greater myelination 10 and 30 d after treatment in corpus callosum (p=0.022, p<0.05) and striatum (p=0.017, p=0.001) of NSC-treated pups. Stat3 (2.82), IL-6 (1.48), and IL-6Rβ (1.73) mRNA was upregulated in the brains of NSC-treated pups. Proteomic and mRNA data confirm NSC expression of VEGF (17.9pg/mL, 4.35) and CXCL1 (3.6pg/mL, 10.27). NSC-treated pups performed better on NOR (p=0.016). Conclusions: Intra-arterial NSC transplant after hypoxia-ischemia results in NSC engraftment into white matter tracts, increased oligodendrocyte proliferation, and improved myelination. NSC-derived proteins may drive the distinct changes in gene expression occurring in the brain after NSC treatment and may mediate functional recovery via activation of endogenous self-repair mechanisms, including oligodendrogenesis.

Sign in / Sign up

Export Citation Format

Share Document