Vincent Oltman Boer¹ and Esben Thade Petersen^1
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.

Cheng Chen¹, Mason Greer¹, Michael Twieg¹, Mark A. Griswold^1,2, and Soumyajit Mandal^1
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.

Adam W Anderson^1
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. 

David Otto Brunner¹, Simon Gross¹, Jonas Reber¹, and Klaas Paul Pruessmann^1
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.

Graham C Wiggins¹, Bei Zhang¹, and Barbara Dornberger^2
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.

Fabian Kording¹, Christian Ruprecht¹, Bjoern Schoennagel¹, Mathias Kladeck Kladeck¹, Jin Yamamura¹, Gerhard Adam¹, Juliane Goebel^2,3, Kai Nassenstein², Stefan Maderwald³, Harald Quick^3,4, and Oliver Kraff^3
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.

Qi Duan¹, Natalia Gudino¹, and Hellmut Merkle^1
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.

David Otto Brunner¹, Lukas Furrer², Markus Weiger¹, Werner Baumberger², Thomas Schmid¹, Jonas Reber¹, Benjamin Emanuel Dietrich¹, Bertram Jakob Wilm^1,3, Romain Froidevaux¹, and Klaas Paul Pruessmann^1
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.

Michael Twieg¹, Soumyajit Mandal¹, and Mark A Griswold^1,2
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.

J. Thomas Vaughan¹, Bert Wang², Djaudat Idiyatullin¹, Sung-min Sohn¹, Albert Jang¹, Lance DelaBarre¹, and Michael Garwood^1
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.