|Diffusion Imaging of Tissue Microstructure|
|Diffusion Tensor Imaging Detects Mossy Fiber
Sprouting in Rat Hippocampus After Status Epilepticus
Teemu Petteri Laitinen1, Jari Nissinen1, Asla Pitkänen1, Olli H.J. Gröhn1
1University of Kuopio, Kuopio, Finland
The ability of diffusion tensor imaging to detect mossy fiber sprouting in dentate gyrus was studied in two different animal models of epilepsy. Our results show that the volume and fractional anisotropy of dorsal dentate gurys, determined from FA maps, is increased six months after status epilepticus when compared to healthy control animals. Histological evaluation showed significant increase in the density of mossy fiber sprouting during epileptogenesis in the diseased animals, consistent with the DTI results. The results of this study suggest that mossy fiber sprouting can be detected using DTI.
Quantitative Comparison of Fiber Properties from DTI,
HARDI and Light Microscopy
Ann S. Choe1, 2, Xin Hong1, 2, Daniel C. Colvin1, 2, Iwona Stepniewska2, zhaohua Ding1, 2, Adam W. Anderson1, 2
1Vanderbilt University Institute of Imaging Science, Nashville, Tennessee, USA; 2Vanderbilt University, Nashville, Tennessee, USA
Measurements of fiber orientation and coherence were made using diffusion tensor imaging (DTI), high angular resolution diffusion imaging (HARDI), and light microscopy of myelin stained tissue sections. Quantitative comparisons of these data show the strengths and limitations of diffusion MRI in revealing microscopic fiber structure in the brain.
Direct Correlation Between Diffusion
Tensor Imaging and Electron Microscopy of the Fornix in Humans with
Temporal Lobe Epilepsy
Luis Concha1, Daniel J. Livy1, Donald W. Gross1, B. Matt Wheatley1, Christian Beaulieu1
1University of Alberta, Edmonton, Canada
Biophysical mechanisms of water diffusion anisotropy in nervous tissue have been studied in animal models and post-mortem human brain; however, there are no direct studies of fresh human white matter. Diffusion tensor imaging in-vivo and follow-up electron microscopy of the same white matter tract is required in humans. The fornix (principal output of hippocampus) was excised during surgery for intractable temporal lobe epilepsy and analyzed quantitatively with electron microscopy. White matter micro-structure was correlated with pre-operative diffusion tensor parameters. Higher extra-axonal fraction and lower axonal density were related to reduced diffusion anisotropy and increased perpendicular diffusivity of the fornix.
In-Vivo Measurement of the Axon Diameter Distribution
in the Rat’s Corpus Callosum
Daniel Barazany1, Peter J. Basser2, Yaniv Assaf1
1Tel Aviv University, Tel Aviv, Israel; 2National Institutes of Health, Bethesda, Maryland, USA
The axon diameter distribution (ADD) is an important anatomical feature of nerve fascicles. In this work, we use AxCaliber- a new diffusion MRI based framework, to extract the ADD within the corpus callosum (CC) of the rat, in vivo. By altering the diffusion time and diffusion weighting we could fit the data to extract the ADD for each image voxel. With this methodology we were able to segment the CC to at least 5 distinct regions each one them characterized by a unique ADD. The ADD of each region corresponded with the known anatomical morphology of the corpus callosum.
Recognition of Grey Matter and Parallel Versus
Crossing Fibre Bundles Within White Matter Using HARDI Data and a
Supervised Learning Algorithm
Susanne Schnell1, Björn Wolf Kreher1, Jürgen Hennig1, Hans Burkhardt2, Valerij Kiselev1
1University Hospital Freiburg, Freiburg, Germany; 2Albert-Ludwigs University Freiburg, Freiburg, Germany
In the present study, we recall methods from pattern recognition problems aiming at recognition of three different tissue types: grey matter and fibre crossing bundles versus parallel fibre bundles in white matter by using high angular resolution diffusion imaging (HARDI) and T1-weighted MRI. We engage a support vector machine, which has demonstrated a robust performance in a number of applications. HARDI data are represented by rotational invariant weights of low-order spherical harmonics. The method was systematically tested in simulations and successfully applied to an in vivo data set.
Q-Ball Imaging of the Spinal Cord
Julien Cohen-Adad1, 2, Maxime Descoteaux3, Rachid Deriche3, Serge Rossignol1, Richard D. Hoge4, Habib Benali2
1GRSNC, Department of Physiology, Faculty of Medicine, Université de Montréal, Montreal, Canada; 2INSERM U678, Université Pierre et Marie Curie (Paris VI), CHU Pitié-Salpêtrière, Paris, France; 3Odyssée Project Team, INRIA/ENPC/ENS, INRIA Sophia Antipolis, France, France; 4Unité de Neuroimagerie Fonctionnelle, CRIUGM, Université de Montréal, Montreal, Canada
We applied q-ball imaging (QBI) in an ex vivo spinal cord to investigate how this technique might recover various fiber crossing in the spinal cord. We compared the added value of QBI over DTI. We showed that QBI can recover crossing fiber information in the ex vivo spinal cord, where the DTI approach is limited. To our knowledge, this is the first QBI study demonstrating the benefits of QBI for observing longitudinal, dorso-ventral and commissural fibers in the spinal cord.
Examining Tumor Microstructure with
Temporal Diffusion Spectroscopy
Daniel C. Colvin1, Mark D. Does1, Zou Yue1, C Chad Quarles1, John C. Gore1, Thomas E. Yankeelov1
1Vanderbilt University Institute of Imaging Science, Nashville, Tennessee, USA
The increasing use of diffusion MRI, in both research and clinical settings, has emphasized the need for a more quantitative understanding of the pathophysiological factors affecting water diffusion rates on microscopic scales. While currently employed pulsed gradient spin echo (PGSE) methods are sensitive to restrictions of water displacements on the order of several microns (10-6 meters), the ADC of tissues is affected by interactions occurring on much smaller scales. By employing oscillating gradient spin echo (OGSE) techniques, these microscopic dimensions may be probed and variations in tissue microstructure, as may occur in tumors responding to therapy, may be assessed.
Changes in Pinnation Angle and Fiber Length of
Muscles Under Plantar- And Dorsi-Flexion and Force Production - In-Vivo,
DTI Based Fiber Tractography in Humans
Shantanu Sinha1, chandan mishra2, David Shin3, Ryuta Kinugasa4, John Hodgson3, Reggie V. Edgerton3, Usha Sinha5
1UCSD, San Diego, California , USA; 2UCSD, San diego, California , USA; 3UCLA, USA; 4UCSD, USA; 5SDSU, USA
DTI-based Fiber tracking of different muscle groups in the human lower leg was performed in-vivo under conditions of rest, plantar-(PF), dorsi(DF)-flexion and active force production. Pennation angles were shown to increase upon plantarflexion in soleus and Medial Gastronemius(MG), and remains nearly same upon dorsiflexion with respect to the normal rest state. Fiber lengths also decreased both in soleus and MG upon PF and DF These results are in concurrence with previous ultrasound studies.
A Comparison of In Vivo and Ex Vivo Diffusion Tensor
Imaging in the Same Patient
Jennifer Andrea McNab1, Natalie L. Voets1, G Douaud1, Ned Jenkinson2, Tipu Aziz2, Karla L. Miller1
1University of Oxford, Oxford, UK; 2University of Oxford, UK
A method is presented for high-resolution 3D diffusion tensor imaging (DTI) in whole, human, fixed brain on a clinical scanner. Whereas previous post-mortem studies have focused on animal brains or small sections of human tissue, this study presents the highest resolution, whole human brain DTI yet reported. Using a rare case study that includesin vivo and ex vivo DTI in the same patient, a direct comparison is made between in vivo and ex vivo anisotropy patterns, illustrating the visualisation of additional structure in the high resolution post-mortem images.
Diffusion Tensor Spectroscopy of Myo-Inositol in
Jacob Ellegood1, Chris C. Hanstock1, Christian Beaulieu1
1University of Alberta, Edmonton, Canada
Diffusion Tensor Spectroscopy (DTS) of myo-inositol (mI) has not been measured previously in human brain, although due to its compartmentalization in glial cells it may have different diffusion properties than N-acetyl aspartate in neurons and axons. Using high b values (~5000 s/mm2) and a two point measurement, the fractional anisotropy value of mI was determined to be elevated in a subcortical white matter region, rather unexpectedly, when compared to an occipital gray matter region in human brain.