ISMRM 21st Annual Meeting & Exhibition 20-26 April 2013 Salt Lake City, Utah, USA

Relaxometry & Parameter Mapping
Wednesday 24 April 2013
Room 151 AG  13:30 - 15:30 Moderators: Maria I. Altbach, Sean C. L. Deoni

13:30 0459.   
Cellular Compartment Specific T2* Relaxation in White Matter
Pascal Sati1, Peter van Gelderen2, Afonso C. Silva3, Daniel S. Reich1, Hellmut Merkle4, Jacco A. De Zwart2, and Jeff H. Duyn2
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.

13:42 0460.   
Non-Invasive Investigation of the Compartmentalization of Iron in the Human Brain
Ferdinand Schweser1,2, Jan Sedlacik3, Andreas Deistung1, and Jürgen R. Reichenbach1
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.

13:54 0461.   
Exchange Rate Selective Imaging Using T1lower case Greek rho Dispersion
John T. Spear1,2, Zhongliang Zu2,3, and John C. Gore3,4
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.

14:06 0462.   Efficient Tissue Permittivity and Conductivity Mapping Using Standard MR Images -permission withheld
Seung-Kyun Lee1, Selaka Bandara Bulumulla1, and Ileana Hancu1
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.

14:18 0463.   
in vivo Imaging of Electrical Properties of Human Brain Using a Gradient Based Algorithm
Jiaen Liu1, Xiaotong Zhang1, Sebastian Schmitter2, Pierre-Francois Van de Moortele2, and Bin He1,3
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.

14:30 0464.   
Volumetric Measurement of Human Brain T1 in vivo Using Pulsed Pseudo Random Amplitude Modulation
Xiaowei Zou1,2 and Truman R. Brown2
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.

14:42 0465.   
T1 Estimation for Aqueous Iron Oxide Nanoparticle Suspensions Using a Variable Flip Angle SWIFT Sequence
Luning Wang1, Curtis Andrew Corum2, Djaudat Idiyatullin2, Michael Garwood2, and Qun Zhao1
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).

14:54 0466.   
Improved T1 Relaxometry with NMR Field Probes: Demonstration of Contrast Agent Characterization
Simon Gross1, Benjamin E. Dietrich1, Christoph Barmet1,2, and Klaas P. Prüssmann1
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.

15:06 0467.   
Triple Echo Steady State (TESS) Relaxometry
Rahel Heule1, Carl Ganter2, and Oliver Bieri1
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.

15:18 0468.   
Effects of Diffusion on High Resolution Quantitative T2 MRI
Wendy Oakden1 and Greg J. Stanisz2
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.