Room 355 BC

13:30 - 15:30

Moderators:

Yoram Cohen, Samuel J. Wharton

Cynthia Wisnieff¹, Pascal Spincemaille², and Yi Wang^1
1Cornell Univerisity, New York, New York, United States, ²Weill Cornell Medical College, New York, New York, United States

In this work we examine the similarities between the orientation dependent nature of diffusion, magnetic susceptibility and relaxation rate. It is found that highly structured areas, such as the white matter, have the most common structural information in these orientation dependent processes consistent with the known structure and magnetization of white matter. In the estimation of susceptibility anisotropy was found that, when either diffusion and relaxation rate tensor information was used in the constrained susceptibility tensor reconstruction, similar estimates of magnetic susceptibility anisotropy could be obtained.

Marco Reisert¹, Elias Kellner¹, Henrik Skibbe¹, and Valerij Kiselev^1
1Medical Physics, University Medical Center, Freiburg, Baden-Württemberg, Germany

Diffusion-sensitized magnetic resonance imaging provides information about the nerve fiber bundle geometry of the human brain. While the inference of the underlying fiber bundle orientation only requires single q-shell measurements, the absolute determination of their volume fractions is much more challenging. This work uses a conservation law for fiber orientation densities that can infer the absolute fraction. In this study we show by simulations on a pseudo ground truth phantom that for complex, brain-like geometries the method is able to infer the densities correctly. In-vivo results with 81 healthy volunteers scanned with a clinical feasible protocol are plausible and consistent.

Flavio Dell'Acqua^1,2, Istvan Bodi³, David Alexander Slater¹, Marco Catani^1,4, and Michel Modo^5,6
1NATBRAINLAB, Department of Neuroimaging, King's College London, Institute of Psychiatry, London, United Kingdom, ²NIHR Biomedical Research Centre for Mental Health at South London and Maudsley NHS Foundation Trust, King’s College London, Institute of Psychiatry, London, United Kingdom, ³Department of Clinical Neuropathology, King's College Hospital, London, United Kingdom,⁴NATBRAINLAB, Forensic and Neurodevelopmental Sciences, King's College London, Institute of Psychiatry, London, United Kingdom, ⁵McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, ⁶Department of Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States

Although a detailed cytoarchitectural description of the human brain by histology is long established, a comprehensive description of its connections ranging from major white matter pathways to small short-range fascicles remains elusive. Diffusion MR histology and micro-tractography offers a three-dimensional description of tissue cytoarchitecture at a mesoscale level. These methods produce quantitative information that, coupled with high-resolution visualisation of small fibres, fills the gap between large-scale network mapping and microscopic histology. We believe that this approach, applied to a fixed post-mortem cerebellum, represents an essential step forward in the understanding of the human brain and cerebellar connectivity and its functions.

Way Cherng Chen^1,2, Sean Foxley¹, and Karla Miller^1
1FMRIB Centre, University of Oxford, Oxford, Oxon, United Kingdom, ²Magnetic Resonance Imaging Group, Singapore Bioimaging Consortium, Singapore, Singapore, Singapore

The orientation dependence of non-linear GRE phase evolution in white matter (WM) was investigated in this study. GRE phase time course was obtained from in-vivo experiments and correlated to WM fiber orientation information obtained from DTI. A realistic geometric magnetic susceptibility model of WM microstructure was then used to predict the dependence of the non-linear phase evolution on orientation of WM fibers to B0. The striking similarity between simulation and experimental results showed that susceptibility compartmentalization is the driving force of this higher order signal characteristic.

Chunlei Liu^1,2 and Wei Li^1
1Brain Imaging and Analysis Center, Duke University, Durham, NC, United States, ²Radiology, Duke University, Durham, NC, United States

Using a multipole analysis in the Fourier spectral space, we developed a high-resolution method that enables the quantification of tissue’s magnetic response with a set of multipole susceptibility tensors of various ranks. The Fourier spectral space, termed p-space, can be generated by applying field gradients or equivalently by shifting the k-space data in various directions. We performed p-space susceptibility tensor imaging in simulation and on mouse brains ex vivo, illustrating capabilities of mapping white matter fiber orientations. These experiments demonstrate that multipole tensors may enable practical mapping of tissue microstructure in vivo without rotating subject or magnetic field.

Dan Wu¹, Jiadi Xu², Xiaoying Cai³, Peter C.M. van Zijl^2,4, Susumu Mori^2,4, and Jiangyang Zhang^4
1Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, United States, ²F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States, ³Department of Biomedical Engineering, Tsinghua University, Beijing, Beijing, China, ⁴Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, MD, United States

We performed in vivo high resolution HARDI of the mouse brain on an 11.7T system. By reducing the field of view using spatially selective RF pulses, we were able to focus on targeted brain structures. The technique allowed us to accomplish 3D high resolution HARDI (60 diffusion directions) in two hours in the mouse hippocampus at 0.1 mm isotropic resolution and the mouse cerebellum at 0.125 mm isotropic resolution. Using this localized HARDI approach, we were able to visualize complex tissue microstructure and local neuronal circuitry of the live mouse brain.

Peter van Gelderen¹, Hendrik Mandelkow¹, Jacco A. De Zwart¹, and Jeff H. Duyn^1
1AMRI, LFMI, NINDS, National Institutes of Health, Bethesda, MD, United States

MR measurements and model calculations suggest that the magnetic susceptibility of myelin is anisotropic, and this property strongly affects T2* relaxation and its orientation dependence in white matter of human brain. Direct measurement of this anisotropic susceptibility by MRI is in principle possible, but practically difficult and potentially confounded by effects from microscopic tissue compartmentalization. Therefore, we present an independent measurement of anisotropic susceptibility based on the torque experienced by white matter in a spinal cord sample suspended in a homogeneous 7T field.

Russell Dibb^1,2, Wei Li³, Gary Cofer¹, and Chunlei Liu^3,4
1Center for In Vivo Microscopy, Duke University Medical Center, Durham, NC, United States, ²Biomedical Engineering, Duke University, Durham, NC, United States, ³Brain Imaging & Analysis Center, Duke University Medical Center, Durham, NC, United States, ⁴Radiology, Duke University Medical Center, Durham, NC, United States

Characterizing the effect of paramagnetic contrast agents and field strength on magnetic susceptibility image contrast aids in the effective use, comparability, and consistency of susceptibility mapping to quantify myelination using MR histology. In this study, we generate field-normalized magnetic susceptibility maps of the adult mouse brain perfused with six different concentrations of paramagnetic contrast agent and at three magnetic field strengths. We verify that the susceptibility-field strength relationship is linear and quantify the linear effect of gadolinium contrast agent on improving the apparent susceptibility contrast between white and gray matter. We propose that this contrast arises due to the decaying signal contributions of a complex white matter water pool structure.

Evren Ozarslan^1,2, Cheng Guan Koay³, Timothy M. Shepherd⁴, Michal E. Komlosh^2,5, Mustafa Okan Irfanoglu^2,5, Carlo Pierpaoli², and Peter J. Basser^2
1Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, United States, ²STBB, PPITS, NICHD, National Institutes of Health, Bethesda, MD, United States,³Department of Medical Physics, University of Wisconsin, Madison, WI, United States, ⁴Department of Radiology, New York University Langone Medical Center, New York, NY, United States,⁵Center for Neuroscience and Regenerative Medicine, USUHS, Bethesda, MD, United States

We propose a quantitative, efficient, and robust framework for representing diffusion-weighted MRI data obtained in q-space, and the corresponding mean apparent propagator (MAP) describing molecular displacements in r-space. We also define and map novel quantitative descriptors of diffusion that can be computed robustly using this MAP-MRI framework. Our approach employs a series expansion of basis functions with anisotropic scale parameters. Consequently, the technique subsumes DTI and reconstructions are performed in an anatomically consistent reference frame. Experiments on excised marmoset brain specimens demonstrate that MAP-MRI provides several novel, quantifiable parameters that capture previously obscured intrinsic features of nervous tissue microstructure.

Assaf Horowitz¹, Daniel Barazany¹, Ido Tavor¹, Moran Berenstein¹, Galit Yovel², and Yaniv Assaf^1
1Neurobiology, Tel Aviv University, Tel Aviv, Israel, Israel, ²School of psychology, Tel Aviv University, Tel Aviv, Israel, Israel

Previous ex-vivo studies, performed on exited nerve, had shown that the Axonal Conduction Velocity (ACV) of myelinated fibres is proportional to its diameter (1). Recent studies have succeeded to measure the rat brain (2) and the human brain (3) axon diameter distribution (ADD) in-vivo, using AxCaliber - a diffusion MRI methodology (4). In this study we succeeded to show a correlation between human visual callosal fibers’ ADD to its ACV which was measured through EEG recording and behavioral tasks.