Gradients, Shims & Novel Systems
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Friday 11 May 2012
Room 105-106  10:30 - 12:30 Moderators: Frederik T. Goldie, Peter T. While

10:30 0696.   Concept and realization of high strength gradients for the Human Connectome Project
Ralph Kimmlingen1, Eva Eberlein1, Peter Dietz1, Sabrina Kreher1, Johann Schuster1, Jörg Riegler1, Volker Matschl1, Volker Schnetter1, Andreas Schmidt1, Helmut Lenz1, Ernst Mustafa1, Daniel Fischer1, Andreas Potthast1, Ludwig Kreischer 1, Michael Eberler1, Franz Hebrank1, Herbert Thein1, Keith Heberlein1, Philipp Hoecht1, Thomas Witzel2, Dylan Tisdall2, Junqian Xu3, Essa Yacoub3, Gregor Adriany3, Edward Auerbach3, Steen Moeller3, David Feinberg4, Dietmar Lehne1, Lawrence L. Wald2,5, Bruce Rosen2,5, Kamil Ugurbil3, David van Essen6, Van Wedeen2, and Franz Schmitt1
1Siemens Healthcare, Erlangen, Germany, 2Martinos Center for Biomedical Imaging, Dept. of Radiology, Massachusetts General Hospital, Boston, United States, 3Center for Magnetic Resonance Research, University Minnesota, Minneapolis, United States, 4Helen Wills Inst. of Neurosc., UC Berkeley, CA, United States, 5Harvard-MIT Division of Health Sciences Technology, Cambridge, United States, 6Dept. of Anatomy and Neurobiology, Washington U, St. Louis, United States


10:42 0697.   
Minimum maximum temperature gradient coils: experimental analysis
Peter T. While1, Michael Poole2, Larry K. Forbes1, and Stuart Crozier2
1School of Mathematics and Physics, University of Tasmania, Hobart, Tasmania, Australia, 2School of Information Technology and Electrical Engineering, University of Queensland, Brisbane, Queensland, Australia

The problem of gradient heating is addressed using a method reported elsewhere for designing gradient coils with minimum maximum temperature. The behaviour of four prototype coils is analyzed through experiment and compared to a minimum power coil and another coil designed with minimum maximum current density. Each minimaxT coil is designed to perform optimally for a specific set of thermal parameters. A thermal imaging camera is used to record temperature data for all coils at thermal equilibrium. Results show that with reasonable estimates of coil parameters the minimaxT method generates coils with improved thermal performance and considerably lower maximum temperature.

10:54 0698.   
Monoplanar gradient system for imaging with nonlinear gradients
Sebastian Littin1, Daniel Gallichan1, Anna Masako Welz1, Andrew Dewdney2, Feng Jia3, Chris Cocosco1, Jürgen Hennig1, and Maxim Zaitsev1
1Dept. of Radiology, Medical Physics, University Medical Center Freiburg, Freiburg, Germany, 2Siemens Healthcare, Erlangen, Germany, 3Freiburg Institute for Advanced Studies (FRIAS), University Freiburg, Freiburg, Germany

Here we present the design and show the process of building a high performance nonlinear monoplanar PatLoc gradient system (FlatLoc). This hand build system is dedicated for imaging the heart, abdomen and pelvis and was successfully implemented in our 3T whole-body scanner and first images were acquired.

11:06 0699.   
Practical design of a high-power, high-homogeneous, actively-shielded, Bo insert coil, capable of +/- 1.0 T field-shifts and stand-alone, low-field imaging
Chad Tyler Harris1, William B Handler1, and Blaine A Chronik1,2
1Physics and Astronomy, University of Western Ontario, London, Ontario, Canada, 2Imaging Research Laboratories, Robarts Research Institute, London, Ontario, Canada

In this work we present a practical design of a high-powered, actively-shielded, small-animal, variable-field MR system capable to temporally pulse magnetic fields up to +/- 1.0 T, yet with sufficient homogeneity for signal detection for fields up to 0.25 T. This system could be used as a high-power insert system withing superconducting magnets for dreMR imaging, or as a stand-alone prepolarized/low-field small-animal MRI system.

11:18 0700.   
A stand-alone system for concurrent gradient and RF sequence monitoring
Benjamin Emanuel Dietrich1, David Otto Brunner1, Christoph Barmet1, Bertram Jakob Wilm1, and Klaas Paul Pruessmann1
1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland

Magnetic field monitoring with NMR probes enables the observation of the spatio-temporal field evolution during MR experiments. This work presents a method that allows a comprehensive measurement of all the externally induced magnetic fields relevant for the spin dynamics in the system.

11:30 0701.   
A 64 channel receive-only field camera for eddy current and trajectory calibration
Veneta Tountcheva1, Boris Keil1, Thomas Witzel1, Dylan Tisdall1, Philipp Hoecht2, and Lawrence L. Wald1,3
1A.A. Martinos Center for Biomedical Imaging, MGH, Harvard Medical School, Radiology, Charlsetown, MA, United States, 2Siemens Medical Solutions USA Inc., Charlsetown, MA, United States, 3Harvard-MIT, Div. of Health Science and Technology, Cambridge, MA, United States

64ch receive-only field camera has been built to study the spatial and temporal evolution of the magnetic field in the presence of eddy currents and gradient trajectories. The field camera consists of 64 small solenoids in a 4 x 4 x 4 grid, each with a small (0.9mm diameter) water sample in a capillary plugged with susceptibility matched material. The camera was validated with field maps acquired after inducing eddy currents on the x-, y-, z-gradients at different time delays. The eddy currents frequency offsets have been mapped out as a function of position and time delay for each x-, y-, z-gradients allowing determination of the eddy current gradients and gradient cross term’s time constants and amplitudes for either pre-emphasis adjustment or inclusion in image reconstruction methods.

11:42 0702.   Real-Time Shim Feedback for Field Stabilization in Human MRI Systems
Y. Dürst1, B. J. Wilm1, B. E. Dietrich1, S. J. Vannesjö1, and K. P. Pruessmann1
1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland

Field changes stemming from various sources such as temperature drifts, physiological motion, or any other external effects can severely degrade results of MRI/MRS experiments. We implemented a real-time feedback system where NMR field probes are employed to measure magnetic field variations and actively compensate field changes using the shim coils of a whole-body. Successful field stabilization has been achieved in three experimental situations of varying effect strength, update rate, and spatial order of the field control.

11:54 0703.   
A new PET insert for simultaneous PET/MR small animal imaging
Hans F Wehrl1, Konrad Lankes1,2, Mosaddek Hossain1, Ilja Bezrukov1,3, Chih-Chieh Liu1, Petros Martirosian4, Gerald Reischl1, Fritz Schick4, and Bernd J Pichler1
1Department for Preclinical Imaging and Radiopharmacy, University of Tuebingen, Tuebingen, Germany, 2Bruker BioSpin MRI, Ettlingen, Germany, 3Max Planck Institute for Intelligent Systems, Tuebingen, Germany, 4Section on Experimental Radiology, University of Tuebingen, Tuebingen, Germany

A new small animal PET/MR system is presented with a performance comparable to stand alone commercial solutions. A detailed evaluation of the mutual interference as well as the PET and MR characteristics is given. Additional in vivo imaging data shows the huge potential of simultaneous PET/MR.

12:06 0704.   
Single-Sided Spectrometer for Magnetic Nanoparticle Detection
Lisa Bauer1, Michael Twieg2, Matthew Riffe3, Yong Wu1, Robert Brown1, and Mark Griswold1,4
1Department of Physics, Case Western Reserve University, Cleveland, Ohio, United States, 2Department of Electrical Engineering and Computer Science, Case Western Reserve University, Cleveland, Ohio, United States, 3Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio, United States,4Department of Radiology, Case Western Reserve University, Cleveland, Ohio, United States

Magnetic Particle Imaging (MPI) is a new imaging method that relies on the harmonic response of magnetic nanoparticles to external, oscillating magnetic fields. The emergence of MPI has placed an emphasis on the ability to detect, characterize and distinguish magnetic nanoparticles in different environments, but conventional bore-type spectrometers limit the physical dimensions of nanoparticle sample holders and the environment in which the samples can be measured. This compact, single-sided spectrometer provides an alternative to conventional spectrometers, allowing nanoparticle detection from arbitrary sample holders.

12:18 0705.   Imaging without Gradients: First In Vivo MR Images using the TRASE RF Imaging Method
Jonathan C Sharp1, Qunli Deng1, Vyacheslav Volotovskyy2, Randy Tyson1, Donghui Yin2, Richard Bernhardt2, Scott King2, and Boguslaw Tomanek1
1Institute of Biodiagnostics (West), National Research Council of Canada, Calgary, Alberta, Canada, 2Institute of Biodiagnostics, National Research Council of Canada, Winnipeg, Manitoba, Canada

TRASE is an MRI acquisition method which traverses k-space using refocusing pulses applied with phase-gradient RF transmit fields. Only a single transmit channel is used, and the switched-B0 gradient system is not required. TRASE in vivo images were collected at 0.2T using a novel RF transmitter coil array, capable of producing 2-axis encoding. TRASE-encoding was used in-plane (2D), with B0-phase encoding (1D) to encode orthogonally. We collected the first in vivo TRASE images (of wrist and knee). The results are encouraging and a step towards the development of a low-cost MR imaging technology.