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      Anisotropic cerebral vascular architecture causes orientation dependency in cerebral blood flow and volume measured with dynamic susceptibility contrast magnetic resonance imaging

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          Abstract

          <p class="first" id="d14698994e249">Measurements of cerebral perfusion using dynamic susceptibility contrast magnetic resonance imaging rely on the assumption of isotropic vascular architecture. However, a considerable fraction of vessels runs in parallel with white matter tracts. Here, we investigate the effects of tissue orientation on dynamic susceptibility contrast magnetic resonance imaging. Tissue orientation was measured using diffusion tensor imaging and dynamic susceptibility contrast was performed with gradient echo planar imaging. Perfusion parameters and the raw dynamic susceptibility contrast signals were correlated with tissue orientation. Additionally, numerical simulations were performed for a range of vascular volumes of both the isotropic vascular bed and anisotropic vessel components, as well as for a range of contrast agent concentrations. The effect of the contrast agent was much larger in white matter tissue perpendicular to the main magnetic field compared to white matter parallel to the main magnetic field. In addition, cerebral blood flow and cerebral blood volume were affected in the same way with angle-dependent variations of up to 130%. Mean transit time and time to maximum of the residual curve exhibited weak orientation dependency of 10%. Numerical simulations agreed with the measured data, showing that one-third of the white matter vascular volume is comprised of vessels running in parallel with the fibre tracts. </p>

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          Most cited references34

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          High resolution measurement of cerebral blood flow using intravascular tracer bolus passages. Part I: Mathematical approach and statistical analysis.

          The authors review the theoretical basis of determination of cerebral blood flow (CBF) using dynamic measurements of nondiffusible contrast agents, and demonstrate how parametric and nonparametric deconvolution techniques can be modified for the special requirements of CBF determination using dynamic MRI. Using Monte Carlo modeling, the use of simple, analytical residue models is shown to introduce large errors in flow estimates when actual, underlying vascular characteristics are not sufficiently described by the chosen function. The determination of the shape of the residue function on a regional basis is shown to be possible only at high signal-to-noise ratio. Comparison of several nonparametric deconvolution techniques showed that a nonparametric deconvolution technique (singular value decomposition) allows estimation of flow relatively independent of underlying vascular structure and volume even at low signal-to-noise ratio associated with pixel-by-pixel deconvolution.
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            MR contrast due to intravascular magnetic susceptibility perturbations.

            A particularly powerful paradigm for functional MR imaging of microvascular hemodynamics incorporates paramagnetic materials that create significant image contrast. These include exogenous (lanthanide chelates) and endogenous (deoxygenated hemoglobin) agents for mapping cerebral blood volume and neuronal activity, respectively. Accurate interpretation of these maps requires an understanding of the biophysics of susceptibility-based image contrast. The authors developed a novel Monte Carlo model with which the authors quantified the relationship between microscopic tissue parameters, NMR imaging parameters, and susceptibility contrast in vivo. The authors found vascular permeability to water and the flow of erythrocytes to be relatively unimportant contributors to susceptibility-induced delta R2. However, pulse sequence, echo time, and concentration of contrast agent have profound effects on the vessel size dependence of delta R2. For a model vasculature containing both capillaries and venules, the authors predicted a linear volume fraction dependence for physiological volume changes based on recruitment and dilation, and a concentration dependence that is nonlinear and pulse sequence dependent. Using the model, the authors demonstrated that spin echo functional images have greater microvascular sensitivity than gradient echo images, and that the specifies of the volume fraction and concentration dependence of transverse relaxivity change should allow for robust mapping of relative blood volume. The authors also demonstrated excellent agreement between the predictions of their model and experimental data obtained from the serial injection of superparamagnetic contrast agent in a rat model.
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              Tracer arrival timing-insensitive technique for estimating flow in MR perfusion-weighted imaging using singular value decomposition with a block-circulant deconvolution matrix.

              Relative cerebral blood flow (CBF) and tissue mean transit time (MTT) estimates from bolus-tracking MR perfusion-weighted imaging (PWI) have been shown to be sensitive to delay and dispersion when using singular value decomposition (SVD) with a single measured arterial input function. This study proposes a technique that is made time-shift insensitive by the use of a block-circulant matrix for deconvolution with (oSVD) and without (cSVD) minimization of oscillation of the derived residue function. The performances of these methods are compared with standard SVD (sSVD) in both numerical simulations and in clinically acquired data. An additional index of disturbed hemodynamics (oDelay) is proposed that represents the tracer arrival time difference between the AIF and tissue signal. Results show that PWI estimates from sSVD are weighted by tracer arrival time differences, while those from oSVD and cSVD are not. oSVD also provides estimates that are less sensitive to blood volume compared to cSVD. Using PWI data that can be routinely collected clinically, oSVD shows promise in providing tracer arrival timing-insensitive flow estimates and hence a more specific indicator of ischemic injury. Shift maps can continue to provide a sensitive reflection of disturbed hemodynamics. Copyright 2003 Wiley-Liss, Inc.
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                Author and article information

                Journal
                Journal of Cerebral Blood Flow & Metabolism
                J Cereb Blood Flow Metab
                SAGE Publications
                0271-678X
                1559-7016
                January 06 2017
                March 2017
                July 21 2016
                March 2017
                : 37
                : 3
                : 1108-1119
                Affiliations
                [1 ]Department of Pediatrics, Division of Neurology, University of British Columbia, Vancouver, Canada
                [2 ]UBC MRI Research Centre, University of British Columbia, Vancouver, Canada
                [3 ]Department of Physics, University of Heidelberg, Heidelberg, Germany
                [4 ]Department of Radiology and Hotchkiss Brain Institute, University of Calgary, Calgary, Canada
                [5 ]Department of Physics and Astronomy, University of British Columbia, Vancouver, Canada
                [6 ]Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands
                [7 ]Department of Radiology, University of British Columbia, Vancouver, Canada
                [8 ]Division of Neurology, Department of Medicine, University of British Columbia, Vancouver, Canada
                Article
                10.1177/0271678X16653134
                5363485
                27259344
                8e0e94d9-d360-4b1a-b6fb-1fa54f1718d2
                © 2017

                http://journals.sagepub.com/page/policies/text-and-data-mining-license

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