Room 151 AG

13:30 - 15:30

Moderators:

Maria I. Altbach, Sean C. L. Deoni

Pascal Sati¹, Peter van Gelderen², Afonso C. Silva³, Daniel S. Reich¹, Hellmut Merkle⁴, Jacco A. De Zwart², and Jeff H. Duyn^2
1Translational Neuroradiology Unit, Neuroimmunology Branch, National Institute of Neurological Disorders and Stroke, Bethesda, Maryland, United States, ²Advanced MRI Section, Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, Bethesda, Maryland, United States, ³Cerebral Microcirculation Unit, Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, Bethesda, Maryland, United States, ⁴Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, Bethesda, Maryland, United States

T2* relaxation and its orientation dependence were studied in marmoset monkeys and humans at high field. Measurements were analyzed with multi-component fitting and compared to simulations to account for the organization of myelin at the cellular and molecular levels. Our findings suggest the possibility to identify myelin water, and to distinguish between axonal and interstitial water based on R2* signal decay and frequency shift (Δf) information.

Ferdinand Schweser^1,2, Jan Sedlacik³, Andreas Deistung¹, and Jürgen R. Reichenbach^1
1Medical Physics Group, Institute of Diagnostic and Interventional Radiology I, Jena University Hospital - Friedrich Schiller University Jena, Jena, Germany, ²School of Medicine, Friedrich Schiller University Jena, Jena, Germany, ³Neuroradiolology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany

Abnormal accumulation of iron in the brain is known to be associated with several neurodegenerative diseases such as multiple sclerosis or Parkinson’s disease. In this contribution we show how a combination of R₂^* mapping and QSM can be used to infer on the compartmentalization of brain iron in vivo.

John T. Spear^1,2, Zhongliang Zu^2,3, and John C. Gore^3,4
1Department of Physics and Astronomy, Vanderbilt University, Nashville, TN, United States, ²Vanderbilt University Institute of Imaging Science, Nashville, TN, United States, ³Department of Radiology, Vanderbilt University, Nashville, TN, United States, ⁴Vanderbilt University, Nashville, TN, United States

A novel technique is explained for producing chemical exchange rate dependent images and describes how to analyze these images to calculate exchange rates for model systems. Samples containing Glucose and Creatine were imaged and analyzed to calculate exchange rates of 5,750 Hz and 499 Hz respectively, which are reasonably close to previously reported values in the literature. This technique can theoretically be extended to calculate exchange rates of separate pools in mixtures as well, which will be of great interest moving forward.

Seung-Kyun Lee¹, Selaka Bandara Bulumulla¹, and Ileana Hancu^1
1GE Global Research, Niskayuna, NY, United States

We demonstrate a method in which tissue electrical properties are estimated from standard MR images alone, without need for dedicated B1 mapping. The method is based on rearrangement of the Helmholtz equation applied to B1+ and B1– into a form in which MR-measurable quantities are separated out. The non-measureable term, which defines the error in our method, is exactly zero in the limit B1+ = B1–, and grows quadratically with the fractional difference between B1+ and B1–. The method is applied to conductivity and permittivity mapping in a water-oil phantom and in-vivo conductivity measurement in a volunteer’s leg.

Jiaen Liu¹, Xiaotong Zhang¹, Sebastian Schmitter², Pierre-Francois Van de Moortele², and Bin He^1,3
1Biomedical Engineering, University of Minnesota, Minneapolis, Minnesota, United States, ²Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, United States, ³Institute for Engineering in Medicine, University of Minnesota, Minneapolis, Minnesota, United States

Being able to image tissue electrical properties—conductivity and permittivity—in vivo using MRI, Electrical Properties Tomography (EPT) has drawn considerable interests from the community. Currently, most EPT studies have focused on the homogeneous Helmholtz equation based method, whereas the ignored gradient term of electrical properties could potentially carry rich information for a more reliable reconstruction. In this study, a new gradient-based algorithm, called G-algorithm, for EPT was developed, and initial feasibility was demonstrated through in vivo human brain experimentation at 7T.

Xiaowei Zou^1,2 and Truman R. Brown^2
1Columbia University, New York, NY, United States, ²Medical University of South Carolina, Charleston, SC, United States

This work presents a novel method named pulsed Pseudo Random Amplitude Modulation (PRAM)for T1 measurement, and validates it on T1 phantoms. Both phantom and human results confirm that this method agrees well with the conventional inversion recovery method. Without fast imaging acceleration, the scan time per slice (128x128 matrix size) on human brain is 1.5s.

Luning Wang¹, Curtis Andrew Corum², Djaudat Idiyatullin², Michael Garwood², and Qun Zhao^1
1Department of Physics and Astronomy, University of Georgia, Athens, GA, United States, ²Department of Radiology, University of Minnesota, Minneapolis, MN, United States

Quantitative estimation of T1 is a challenging but important task inherent to many applications involving intrinsic or exogenous contrast agents in magnetic resonance imaging (MRI). Super-paramagnetic iron oxide (SPIO) nanoparticles have been used as T2 or T2* contrast agents, and as such, produce negative (reduced signal) contrast. Alternately, increasing numbers of recent studies have reported ways to generate T1-weighted positive contrast using the SPIO contrast agents. In the present work, the T1 values of water containing SPIO contrast agents were measured by sweep imaging with Fourier transformation (SWIFT) using variable flip angles (VFA-SWIFT).

Simon Gross¹, Benjamin E. Dietrich¹, Christoph Barmet^1,2, and Klaas P. Prüssmann^1
1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland, ²Skope Magnetic Resonance Technologies, Zurich, Switzerland

The observation of longitudinal nuclear magnetization with NMR field probes is a fast and sensitive method for the characterization of T1-relaxation times. Changes in the properties of the NMR field probes and geometrical considerations lead to an increase in sensitivity of a factor of ten. A field measurement resolution of 50 pT was reached, enabling robust and precise fitting of signals acquired in single shot experiments.

Rahel Heule¹, Carl Ganter², and Oliver Bieri^1
1Department of Radiology, University of Basel Hospital, Basel, Switzerland, ²Department of Radiology, Klinikum rechts der Isar, Technische Universität München, Munich, Germany

A variety of SSFP methods have been proposed so far and are known in the literature for fast relaxometry, but all of them are sensitive to B1, and show some more or less pronounced mixed T2/T1 sensitivity. In this work, a new rapid relaxometry method is introduced based on a triple echo steady state (TESS) approach. Relaxometry with TESS is not biased by T2/T1, is insensitive to B0 heterogeneities, and, surprisingly, for T2 not affected by B1 field errors. As a result, the new proposed method is of high interest for fast and reliable relaxometry in the clinical routine.

Wendy Oakden¹ and Greg J. Stanisz^2
1Medical Biophysics, University of Toronto, Toronto, ON, Canada, ²Imaging Research, Sunnybrook Research Institute, Toronto, ON, Canada

As resolution increases, so does unwanted diffusion sensitization from imaging and spoiler gradients. Quantitative T2 (qT2) is especially problematic as this effect increases with each echo, decreasing the measured T2 noticeably as voxel size decreases below 0.5x0.5mm². Measured T2 becomes orientation dependent in the presence of anisotropic diffusion. Fully refocused imaging gradients can mitigate the problem, as can minimizing spoiler gradients and measuring diffusion in order to calculated corrected T2 values. Decreasing spoiler gradient schemes affect qT2 non-linearly and can result in an overestimation of myelin water fraction as well as precluding simple arithmetic correction of T2.