Perfusion & Diffusion: Animal Models
Thursday 23 April 2009
Room 312 16:00-18:00


Josette Chen and Afonso C. Silva

16:00 739. Hybrid Diffusion Imaging (HYDI) in a Brain Model of Dysmyelination
    Yu-Chien Wu1,2, Andrew L. Alexander2, Ian D. Duncan3,4, Aaron S. Field4,5
Radiology , University of Wisconsin-Madison, Madison, WI, USA; 2Waisman Laboratory for Brain Imaging & Behavior, University of Wisconsin-Madison, Madison, WI, USA; 3Medical Science, University of Wisconsin-Madison, Madison, WI, USA; 4Radiology, University of Wisconsin-Madison, Madison, WI, USA; 5Biomedical Engineering, University of Wisconsin-Madison, Madison, WI, USA
    Fractional anisotropy (FA) in the diffusion tensor imaging (DTI) is commonly used as a measure of white matter (WM) integrity. However, FA is also highly sensitive to such factors as non-Gaussian diffusion, crossing fibers and imaging noise, which may degrade its specificity. It has recently been proposed that the radial diffusivity is highly related to WM myelination. Alternatively, PDF measures in the diffusion spectrum imaging (DSI), e.g. Po and MSD, may provide additional information about WM microstructure. In this longitudinal study, the dysmyelinating shaking pup model was studied using both the DTI and DSI acquired from a hybrid diffusion imaging.
16:12 740. Untangling a Fiber Bundle Knot - Preliminary Results on STN Connectivity Using DTI and HARDI on Rat Brains
    Ellen Brunenberg1, Vesna Prckovska1, Bram Platel2, Gustav Strijkers1, Bart ter Haar Romeny1
Biomedical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands; 2Biomedical Engineering, University Hospital Maastricht, Maastricht, Netherlands
    Deep Brain Stimulation of the subthalamic nucleus (STN) for Parkinson’s Disease improves the motor function, but cognitive and emotional side effects occur. These can be minimized by an accurate location of the STN motor part, analyzing the connections with other brain areas. In this study, we compare DTI and HARDI glyphs around the rat STN. The HARDI glyphs are more heterogeneous than the mostly oblate DTI glyphs. We observe crossings in the lateral STN, while a linear configuration can be seen medially. We may thus distinguish the lateral motor part and the medial cognitive/emotional part of the rat STN.
16:24 741. Diffusion Tensor Imaging and Micro-Computed Tomography Based Three Dimensional Stereotaxic Atlas of the Adult C57BL/6J Mouse Brain Corrected for Postmortem Tissue Deformation
    Manisha Aggarwal1, Jiangyang Zhang2, Michael I. Miller1,3, Susumu Mori2,4
Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, USA; 2Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, MD, USA; 3Center of Imaging Science, Johns Hopkins University, Baltimore, MD, USA; 4F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, USA
    A microCT and DTI based three dimensional stereotaxic atlas of the adult C57BL/6J mouse brain was developed, with correction of postmortem tissue distortion due to specimen fixation. A population-averaged in vivo MRI brain template was developed with estimates of anatomical variability, and was used as the reference for nonlinear deformation of the ex vivo data, to generate a distortion-corrected DTI atlas with high anatomical fidelity. The distortion-corrected DTI atlas was incorporated into the stereotaxic coordinate frame. Compared to existing histology based atlases, the distortion corrected microCT-DTI atlas provides a more accurate representation of the adult C57BL/6J brain anatomy.
16:36 742. Mild Hypoxic-Ischemic Injury in the Neonatal Rat Brain: Longitudinal Evaluation of the White Matter Using Diffusion Tensor MR Imaging
    Silun Wang1, Ed. X. Wu2,3, Kexia Cai2,3, Ho-Fai Lau2,3, Pek-Lan Khong1
Department of Diagnostic Radiology, The University of Hong Kong, Hong Kong, Hong Kong; 2Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Hong Kong; 3Department of Electrical and Electronic Engineering, The University of Hong Kong
    We evaluated longitudinally mild hypoxic-ischemic (HI) induced white matter (WM) damage in a neonatal rat model using DTI and correlated the DTI indices with histological evaluations. Results showed significantly decreased FA and increased ¦ËˇÍ in the injured WM reflected dysmyelination. The longitudinal changes of increasing FA, decreasing ¦ËˇÍ, and no change in ¦Ë// in both injured and control WM suggests continued myelination. Furthermore, differences in FA and ¦ËˇÍ between injured and control WM decreased longitudinally. Our results demonstrated that mild HI induced WM damage continues to mature with partial recovery post-HI, and this could be reflected by DTI in vivo.
16:48 743. Diffusion Weighted Magnetic Resonance Imaging of Neuronal Activity in the Hippocampal Slice Model
    Brian Hansen1, Jeremy Flint2,3, Peter Vestergaard-Poulsen1, Stephen J. Blackband2,3
Center of Functionally Integrative Neuroscience, University of Aarhus, Aarhus, Denmark; 2Department of Neuroscience, University of Florida, Gainesville, FL, USA; 3The McKnight Brain Institute, University of Florida, Gainesville, FL, USA
    Functional magnetic resonance imaging (fMRI) has become the leading modality for studying the working brain but the spatiotemporal resolution of the method is somewhat limited. Therefore, alternative MR-based methods for detection of brain activity have been proposed and investigated. Studies have reported functional imaging based on diffusion weighted (DW) MRI. The basis for such DW fMRI is believed to be the sensitivity of DW MRI to changes in tissue micro-structure. However, it remains unclear whether the observed signal changes reflect cell swelling related to neural activation, residual vascular effects, or a combination of both. Here we present evidence of a detectable activity related change in the diffusion weighted MR-signal from the cellular level in live hippocampal slices in the absence of vasculature. Slices are exposed to several substances and the effects evaluated and compared.
17:00 744. DKI Visualizes Hippocampal Alterations in the Chronic Mild Stress Ratmodel
    Rafael Delgado y Palacios1, Marleen Verhoye1,2, Johan Van Audekerke1, Dirk Poot2, Jan Sijbers2, Ove Wiborg3, Annemie Van der Linden1
Bio-Imaging Lab, University of Antwerp, Antwerp, Belgium; 2Vision Lab, University of Antwerp, Antwerp, Belgium; 3Centre for Basic Psychiatric Research, Aarhus Psychiatric University Hospital, Aarhus, Denmark
    Depression is a serious and disabling disorder. However, the exact pathophysiology of depression is not clearly understood. The chronic mild stress ratmodel is a well established animal model. In the hippocampus and the corpus callosum and capsula externa of this model, we used diffusion kurtosis imaging (DKI) as a measure of tissue’s microstructure. We found changes in the hippocampus of mean and radial kurtosis in the CMS rats in comparison with control rats, suggesting possible stress-induced CA3 apical dendrite atrophy, dendritic regression in granule and CA1 pyramidal cells and reduction of mossy fiber terminals volume and surface area.
17:12 745. Myocardial Remodeling in Chronic Porcine Model: A DT-MRI Study Using the Toroid-Based Representation
    Choukri Mekkaoui1, Marcel P. Jackowski2, Donald P. Dione1, Francis G. Spinale3, Albert J. Sinusas1
Yale University, New haven, CT, USA; 2University of Sao Paulo, Brazil; 3Medical University of South Carolina, USA
    The toroid-based representation of MR diffusion tensor fields was used to investigate structural and fiber angle remodeling at 2- and 8-weeks post-MI compared to normal hearts. Toroidal DT-MRI indices provide a means for a non-destructive, regional quantification of hearts post-MI. Results suggest that structural changes attributed to left ventricular (LV) remodeling involve both the infarcted and non-infarcted LV myocardium. The ongoing tissue reorganization process is underscored by a concomitant alteration in diffusivity, anisotropy and myocardial fiber inclination in the remote territory between 2- and 8-weeks post-MI. The toroid-based parameters revealed a structural dynamic modification as a function of time post-MI.
17:24 746. In-Vivo Hadamard Encoded Continuous Arterial Spin Labelling (H-CASL)
    Jack A. Wells1,2, Mark F. Lythgoe2,3, David Gadian2, Roger Ordidge1, David L. Thomas1
Advanced MRI Group, University College London, London, UK; 2RCS Unit of Biophysics, UCL Institute of Child Health, London, UK; 3Centre for Advanced Biomedical Imaging, University College London, London, UK
    Recently, Hadamard encoding techniques have been applied to the CASL labelling pulse to efficiently image small boli of tagged arterial blood water at a range of post-labelling delay times. In this study we demonstrate that this method can be successfully applied in-vivo to accurately measure cerebral blood flow and arterial transit time (äa) in the rat brain. We have modified the ASL quantification model to take account of the new encoding approach that can measure the first inflow of labeled blood into the tissue. We demonstrate an improvement in the precision of the äa estimates compared to the standard method.
17:36 747. Vessel Size Imaging with Iron Oxide and with Gadolinium: A Comparative Study in Rodent
    Nicolas Pannetier1,2, Benjamin Lemasson3,4, Thomas Christen1,2, Régine Farion1,2, Christoph Segebarth1,2, Chantal Remy1,2, Emmanuel Luc Barbier1,2
Inserm, U836, Grenoble, F-38043, France; 2 Université Joseph Fourier, Grenoble Institut des Neurosciences, UMR-S836, Grenoble, F-38043, France; 3Oncodesign Biotechnology, Dijon, France; 4 Inserm, U836, Grenoble, F-38043, France
    Vessel Size Index (VSI) is a powerful tool for characterizing tumor vessel diameters and their evolution under therapy. VSI has been obtained either using a Gd-bolus or at steady-state using iron oxide particles. In this study we compared the VSI obtained with Gd and with iron using either a dynamic approach (first passage) or a steady state approach. Data were acquired in rats bearing a glioma model. The case of Gd-loaded tumor was also considered. This study suggests that monitoring the first passage of a Gd-bolus with a double-echo EPI sequence is well suited to assess VSI in humans.
17:48 748. Gd-DTPA-Enhanced MRI Revealed Leakage at Aqueous-Vitreous Interface Upon Ocular Hypertension
    Kevin C. Chan1,2, Qing-ling Fu3, Kwok-fai So3, Ed X. Wu1,2
Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Hong Kong SAR, China; 2Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong SAR, China; 3Department of Anatomy, The University of Hong Kong, Hong Kong SAR, China
    This study aims to employ in vivo contrast-enhanced MRI to evaluate the ocular transport upon an induction of ocular hypertension in the right eye in a rat model of chronic glaucoma. Following systemic administration of Gd-DTPA solution, our results showed a progressive T1-weighted signal increase in the anterior vitreous body of the glaucomatous eye but not the control eye, suggestive of the leakage of Gd-DTPA at the aqueous-vitreous interface. These findings may explain the sources of changing biochemical compositions in the glaucomatous chamber components, which may implicate the cascades of neurodegenerative processes in the retina and the optic nerve. Our findings of the early Gd-DTPA signal enhancements in the anterior vitreous body than the preretinal vitreous provided a noninvasive marker for the disease. More importantly, this approach could have direct clinical applications and can be readily translated to humans.