ISMRM 24th Annual Meeting & Exhibition • 07-13 May 2016 • Singapore

Scientific Session: Novel Concepts in MR Technology

Tuesday, May 10, 2016
Room 331-332
16:00 - 18:00
Moderators: Stuart Crozier, Thomas Witzel

DC plasma coils for MRI
Vincent Oltman Boer1 and Esben Thade Petersen1
1Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital Hvidovre, Hvidovre, Denmark
Coupling between conducting structures is one of the major design limitations for in-bore MRI equipment. Here we show how switchable plasma conductors can be used in a direct current (DC) MR coil for B0field manipulation. This can be applied in for example B0 shimming, signal de-phasing or ultimately even gradient coil design.

Integration of Miniaturized Ultrasound and Single-Sided, Low-Field MRI
Cheng Chen1, Mason Greer1, Michael Twieg1, Mark A. Griswold1,2, and Soumyajit Mandal1
1Department of Electrical Engineering and Computer Science, Case Western Reserve University, Cleveland, OH, United States, 2Department of Radiology, Case Western Reserve University and University Hospitals of Cleveland, Cleveland, OH, United States
Ultrasound (US) and magnetic resonance (MR) are two well-established imaging modalities with largely complementary contrast mechanisms. We propose and experimentally evaluate the feasibility of a fundamentally new tool; miniaturized two-dimensional (2-D) US collocated with a one-dimensional (1-D) single-sided MR system for bimodal imaging in portable or wearable form factors. The proposed system will be capable of scheduling both measurements in real-time, thus enabling closed-loop operation in which the output of one sensor is used to optimize the operation of the other.  We study the feasibility of such a system and show preliminary experimental results obtained by combining a commercial US imaging system with a custom single-sided planar MR sensor.

Traveling Internal Plane-wave Synthesis for Uniform B1(+) in High Field MRI
Adam W Anderson1
1Biomedical Engineering, Vanderbilt University, Nashville, TN, United States
Image quality in high field MRI is limited by B1 inhomogeneity. This work describes a new approach to improving B1 homogeneity using parallel transmission. Rather than transmitting a conventional traveling wave, which is diffracted and reflected by the human body, thereby creating a non-uniform internal field, the new method seeks a solution to the inverse problem—what external field produces a traveling plane wave within the body? Simulations suggest dramatic improvements in B1 homogeneity can be obtained given a sufficient number of transmitted field modes. 

Magnetic Pebbles – Materials with Controllable Magnetism for Compact, Low-Power Shim Units
David Otto Brunner1, Simon Gross1, Jonas Reber1, and Klaas Paul Pruessmann1
1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland
B0 shimming with very high channel count encounters many implementation problems due to the size and current handling requirements of the shim units. Here we present an approach using distributions of ferromagnetic materials with controllable magnetic moments to generate shim fields. These units are small, require only low currents and can hence be implemented in large numbers into RF receive arrays.

Size-adaptable “Trellis” receive array concept for knee imaging
Graham C Wiggins1, Bei Zhang1, and Barbara Dornberger2
1Center for Advanced Imaging Innovation and Research (CAI2R) and Center for Biomedical Imaging, New York University School of Medicine, New York, NY, United States, 2Siemens Healthcare, Erlangen, Germany
For optimal performance an array should conform closely to the anatomy being imaged. Knee coils typically have rigid formers which must be large enough to accommodate most subjects, but which necessarily are not optimal for small ones. We present here a cylindrical surface coil array which can adapt in size while maintaining good tuning, match and decoupling. It is built on a trellis-like structure which controls the configuration and morphs the surface coils.

Doppler Ultrasound Triggering for Cardiac Magnetic Resonance Imaging at 7 Tesla
Fabian Kording1, Christian Ruprecht1, Bjoern Schoennagel1, Mathias Kladeck Kladeck1, Jin Yamamura1, Gerhard Adam1, Juliane Goebel2,3, Kai Nassenstein2, Stefan Maderwald3, Harald Quick3,4, and Oliver Kraff3
1Department of Diagnostic and Interventional Radiology, University Medical Center Hamburg, Hamburg, Germany, 2Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital, University Duisburg-Essen, Essen, Germany, 3Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany, 4High Field and Hybrid MR Imaging, University Hospital, University Duisburg-Essen, Essen, Germany, Essen, Germany
Cardiac synchronization for magnetic resonance imaging at ultra-high-field MRI remains a challenge as disturbances in the inherent electrical measurement of the ECG increase with field strength. An ultrasound transducer and transmission line was developed and the feasibility of Doppler Ultrasound as an alternative method for cardiac synchronization was evaluated in terms of safety concerns, signal and image quality. The transmission line and transducer did not disturb the transmit RF field or image homogeneity and were approved for RF safety. Doppler Ultrasound was successfully applied for cardiac synchronization without signal disturbances and represents a promising alternative for ultra-high field CMR.

The Multi-Pole Antenna Array
Qi Duan1, Natalia Gudino1, and Hellmut Merkle1
1Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, United States
In this work, we propose concepts of transmit arrays based on combination of monopole and dipole antennas and their variations for high field imaging. Based on these concepts, transmit arrays for a variety of applications can be derived based on parameters such as desired and possible transmit field-of-view, number of available transmit ports, etc. For illustration purpose, a special case of the second order array, a.k.a. the Trident antenna, was built for spine or posterior cortex imaging and tested on phantom at a 7T scanner.

A High-Speed, High Power T/R Switching Frontend
David Otto Brunner1, Lukas Furrer2, Markus Weiger1, Werner Baumberger2, Thomas Schmid1, Jonas Reber1, Benjamin Emanuel Dietrich1, Bertram Jakob Wilm1,3, Romain Froidevaux1, and Klaas Paul Pruessmann1
1Institute for Biomedical Engineering, University of Zurich and ETH Zurich, Zurich, Switzerland, 2ZSN Center for Signal Processing and Communications, University of Applied Sciences Winterthur, Winterthur, Switzerland, 3Skope Magnetic Resonance Technologies, Zurich, Switzerland
Dead-times after the excitation pulse of the order of 1 µs are required for imaging approaches for short T2 compounds such as UTE, ZTE or SWIFT. Here we present a multi-channel T/R interface box employing symmetrically biased T/R switches which, in conjunction with a novel diode driver, provide signal rise times of 350 ns. The unit further comprises fiber-optic triggering, biasing, and malfunction detection. Its performance is demonstrated by low artefact ZTE scans with 500 kHz at 7T.

N-path frequency mixers for ultra-high density receive arrays
Michael Twieg1, Soumyajit Mandal1, and Mark A Griswold1,2
1Electrical Engineering and Computer Science, Case Western Reserve University, Cleveland, OH, United States, 2Radiology, Case Western Reserve University, Cleveland, OH, United States
Dense MRI receiver arrays face challenges associated with RF cabling, power consumption, and space required by on-coil RF LNAs. On-coil frequency mixers and ADCs have been proposed as solutions to these challenges. Here we propose the use of passive N-path mixers implemented in CMOS for on-coil frequency conversion. We demonstrate a prototype fabricated in a 0.5µm CMOS process, and compare its measured and simulated performance. We also show simulations of a similar design in 65nm CMOS with greatly improved performance. The improved version may handle multiple RF channels on a single chip, and eliminates the need for RF LNAs entirely.

Progress Toward a Portable MRI System for Human Brain Imaging
J. Thomas Vaughan1, Bert Wang2, Djaudat Idiyatullin1, Sung-min Sohn1, Albert Jang1, Lance DelaBarre1, and Michael Garwood1
1Center for Magnetic Resonance Research - University of Minnesota, Minneapolis, MN, United States, 2Wang NMR, Inc, Livermore, CA, United States
Critical magnet, imaging physics, RF and gradient technology were built and tested to demonstrate the feasibility of a portable 1.5T MRI system for imaging the brain in real world environments.  Feasibility is demonstrated.

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