728 research outputs found
Incorporating white matter microstructure in the estimation of magnetic susceptibility in ex-vivo mouse brain
Accurate estimation of microscopic magnetic field variations induced in
biological tissue can be valuable for mapping tissue composition in health and
disease. Here, we present an extension to Quantitative susceptibility mapping
(QSM) to account for local white matter (WM) microstructure by using our
previously presented model for solid cylinders with arbitrary orientations to
describe axons in terms of concentric cylinders. We show how multi-gradient
echo (MGE) and diffusion MRI (dMRI) images can be combined to estimate an
apparent scalar susceptibility. Experiments in mouse brains acquired at
ultrahigh field shows the mesoscopic contribution due to WM microstructure to
be substantial, with a magnitude up to 70% of the total frequency shift in
highly anisotropic WM. This in turn changed estimated susceptibility values up
to 56% in WM compared to standard QSM. Our work underscores how microstructural
field effects impact susceptibility estimates, and should not be neglected when
imaging anisotropic tissue such as brain WM.Comment: 33 pages, 7 figure
To mask or not to mask? Improving QSM quality by accounting for spatial frequency distributions and susceptibility sources
Estimating magnetic susceptibility using MRI depends on inverting a forward
relationship between the susceptibility and measured Larmor frequency. However,
an often-overlooked constraint in susceptibility fitting is that the Larmor
frequency is only measured inside the sample, and after background field
removal, susceptibility sources should only reside inside the same sample. Here
we test the impact of accounting for such effects in susceptibility fitting and
demonstrate that such effects should not be ignored.Comment: 22 pages, 5 figure
Isolated Gallbladder Rupture Due to Blunt Abdominal Trauma
Traumatic injury to the extrahepatic biliary system is rare and usually diagnosed at laparotomy when it is
associated with other visceral injuries. Isolated gallbladder rupture due to blunt abdominal trauma is even
rarer. The clinical presentation of gallbladder injury is variable, resulting in a delay in diagnosis and
treatment. Awareness to the possibilty of trauma to the extrahepatic biliary system enables early surgical
intervention and eliminates the high morbidity associated with delated diagnosis
The Larmor frequency shift of a white matter magnetic microstructure model with multiple sources
Magnetic susceptibility imaging may provide valuable information about
chemical composition and microstructural organization of tissue. However, its
estimation from the MRI signal phase is particularly difficult as it is
sensitive to magnetic tissue properties ranging from the molecular to
macroscopic scale. The MRI Larmor frequency shift measured in white matter (WM)
tissue depends on the myelinated axons and other magnetizable sources such as
iron-filled ferritin. We have previously derived the Larmor frequency shift
arising from a dense media of cylinders with scalar susceptibility and
arbitrary orientation dispersion. Here we extend our model to include
microscopic WM susceptibility anisotropy as well as spherical inclusions with
scalar susceptibility to represent subcellular structures, biologically stored
iron etc. We validate our analytical results with computer simulations and
investigate the feasibility of estimating susceptibility using simple iterative
linear least squares without regularization or preconditioning. This is done in
a digital brain phantom synthesized from diffusion MRI (dMRI) measurements of
an ex vivo mouse brain at ultra-high field.Comment: 70 pages, 14 figure
The Molecular Clockwork of the Fire Ant Solenopsis invicta
This is an open-access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication
Associations between cardiorespiratory fitness, physical activity and clustered cardiometabolic risk in children and adolescents: the HAPPY study
Clustering of cardiometabolic risk factors can occur during childhood and predisposes individuals to cardiometabolic disease. This study calculated clustered cardiometabolic risk in 100 children and adolescents aged 10-14 years (59 girls) and explored differences according to cardiorespiratory fitness (CRF) levels and time spent at different physical activity (PA) intensities. CRF was determined using a maximal cycle ergometer test, and PA was assessed using accelerometry. A cardiometabolic risk score was computed as the sum of the standardised scores for waist circumference, blood pressure, total cholesterol/high-density lipoprotein ratio, triglycerides and glucose. Differences in clustered cardiometabolic risk between fit and unfit participants, according to previously proposed health-related threshold values, and between tertiles for PA subcomponents were assessed using ANCOVA. Clustered risk was significantly lower (p < 0.001) in the fit group (mean 1.21 ± 3.42) compared to the unfit group (mean -0.74 ± 2.22), while no differences existed between tertiles for any subcomponent of PA. Conclusion These findings suggest that CRF may have an important cardioprotective role in children and adolescents and highlights the importance of promoting CRF in youth
Linear spanning sets for matrix spaces
Necessary and sufficient conditions are given on matrices , and , having entries in some field and suitable dimensions, such that the linear span of the terms over is equal to the whole matrix space.
This result is then used to determine the cardinality of subsets of when is a finite field
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