Carel C. van Leeuwen¹, Bart R.E. Steensma¹, Dennis W.J. Klomp¹, Cornelis A.T. van den Berg¹, and Alexander J.E. Raaijmakers^1,2
1University Medical Center Utrecht, Utrecht, Netherlands, ²Biomedical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands

A coax cable dipole antenna with gaps in the shield supports flat current profiles on the outside of the shield. A simulation study is performed to further optimize the design of this flexible so-called ‘coax dipole antenna’. MR thermometry measurements are performed using a single antenna and a homogeneous phantom. The coax dipole antenna causes 18% lower peak heating than a fractionated dipole antenna. An array of eight coax dipole antennas is used to generate T2-weighted images and B1 maps of the prostate of three volunteers, where the coax dipoles achieve the same B1 as an array of fractionated dipoles.

Yue Zhu^1,2, John C Gore^1,2,3,4, and Xinqiang Yan^1,2
1Vanderbilt University Institute of Imaging Science, Nashville, TN, United States, ²Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN, United States, ³Biomedical Engineering, Vanderbilt University, Nashville, TN, United States, ⁴Electrical and Computer Engineering, Vanderbilt University, Nashville, TN, United States

We designed a continuously adjustable Bailey splitter/combiner with a sliding mechanism. This device has a good input matching of < -18dB and a low insertion loss of about -0.5dB. The sliding mechanism allowed easy handling and precise adjustments. The resistor free design eliminated the potential safety concern from the previous Ratio Adjustable Power Splitter circuits. We obtained good agreements between predicted and measured transmit field maps with the Bailey splitter/combiner.

Raphaela Czerny¹, Michael Obermann¹, and Elmar Laistler^1
1High Field MR Center, Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria

As flexible form-fitting RF coils can provide enhanced receive sensitivity in MRI, various coil design approaches have been studied recently, including coaxial and stranded wire coil elements. While stranded wire coils are electrically identical to conventional rigid copper loop coils, coaxial transmission line resonators are self-resonant and do not require additional components along the conductor. The goal of this work was to compare flexible receive-only stranded wire coils and coaxial coils in terms of Q-factors, inter-element coupling, noise correlation, and SNR.

Sirihaas Gaddipati¹ and Xiaoliang zhang^2
1University at Buffalo, Buffalo, NY, United States, ²Biomedical Engineering, University at Buffalo, Buffalo, NY, United States

In traditional magnetic resonance imaging (MRI) design, ideal coil overlapping is used to minimize coupling between nearest-neighbor coils, and low input impedance preamplifiers are used to isolate the relatively weak coupling. Modern-day MR systems use phased array coils constructed out of low impedance resonant loops. Inside such arrays, electrodynamic interactions between elements must be carefully balanced[1]. However, to make the complex sensitivities of phased-array coils sufficiently distinct in parallel spatially-encoded MRI, needed an overlapping between coils. This electromechanical balancing act becomes increasingly difficult as the number of receive elements grows for optimal performance, leading to geometrical puzzles of profound complexity.

Don Straney¹, Clarissa Zimmerman Cooley^1,2, and Matthew S Rosen^1,2,3
1Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, United States, ²Harvard Medical School, Boston, MA, United States, ³Department of Physics, Harvard University, Cambridge, MA, United States

An active transmit/receive (T/R) switch based on reed relays shows promise in overcoming the previous limitations at low field of both passive and active T/R switches.  We aim to provide a design for other low-field researchers to use which handles a wide range of frequencies (DC to 3.4 Mhz) and power levels (<1 mW to 2 kW pulsed) in a simple, low-parts-count device which is easy to reproduce.

Giuseppe Carluccio^1,2 and Christopher Michael Collins^1,3
1Radiology, Center for Advanced Imaging Innovation and Research (CAI2R), New York, NY, United States, ²Radiology, Bernard and Irene Schwartz Center for Biomedical Imaging, New York, NY, United States, ³Bernard and Irene Schwartz Center for Biomedical Imaging, New York, NY, United States

High-Permittivity materials have been recently used to shape the B1 field distribution to enhance SNR and transmit efficiency. So far, these materials have been mainly applied to increase SNR in the head. In this work, through numerical simulations, we explore the possibility to use high-permittivity pads to improve the signal in the chest. The pads are positioned between the model of the coils (8 TEM transmit coils and 24 receive loops) and of the human body. Our simulations show that some improvement can be obtained by adding the pads to the coils.

Sam-Luca J.D. Hansen¹, Markus W. May¹, Mirsad Mahmutovic¹, Manisha Shrestha¹, Anpreet Ghotra¹, Matthäus Poniatowski¹, and Boris Keil^1
1Institute of Medical Physics and Radiation Protection, TH Mittelhessen University of Applied Sciences, Gießen, Germany

We demonstrated a highly efficient B₁⁺to-SAR dipole antenna for ultrahigh-field MRI which consists of a double-folded ladder structure. The antenna was simulated and bench tested. The antenna has a high impedance which provides low mutual coupling between other antenna elements. Ultimately, this characteristic possibly allows to construct antenna array for pTx.

Alireza Sadeghi-Tarakameh¹, Bahram Khalichi², Xiaoping Wu¹, Gregory J. Metzger¹, and Yigitcan Eryaman^3
1Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, MN, United States, ²Department of Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey, ³University of Minnesota, Minneapolis, MN, United States

Utilizing receive and transmit array coils with improved SNR/SAR performance is crucial to realizing the full potential of ultra-high field (UHF) MRI. In this work, we optimize a previously introduced antenna (NODES) to improve its SNR and SAR performances for 7T cardiac MRI applications.

Jose EC Serralles¹, Elfar Adalsteinsson^2,3, Lawrence L Wald⁴, and Luca Daniel^1
1Computational Prototyping Group (CPG), Research Laboratory of Electronics (RLE), Department of Electrical Engineering and Computer Science (EECS), Massachusetts Institute of Technology (MIT), Cambridge, MA, United States, ²Department of Electrical Engineering and Computer Science (EECS), Massachusetts Institute of Technology (MIT), Cambridge, MA, United States, ³Institute for Medical Engineering and Science (IMES), Massachusetts Institute of Technology (MIT), Cambridge, MA, United States, ⁴Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States

Algorithmic design of coil arrays in MRI is typically considered desirable but computationally intractable. In this work, we demonstrate that it is in fact feasible to programmatically optimize over the design of a coil array to achieve a metric-of-interest, such as slice homogeneity in the transmit field. We build on previous work by employing global optimizers in several of the key steps in the optimization procedure. We demonstrate the effectiveness of this approach via a couple of numerical examples.

Paul Nobre¹, Gwenaël Gaborit^2,3, Raphaël Sablong¹, Lionel Duvillaret³, and Olivier Beuf^1
1Univ. Lyon, INSA-Lyon, Université Lyon 1, UJM-Saint Etienne, CNRS, Inserm, CREATIS, UMR 5220, U1206, Villeurbanne, France, ²Université de Savoie, IMEP-LAHC, UMR 5130, Le Bourget-du-Lac, France, ³KAPTEOS, Sainte-Hélène-du-Lac, France

The large majority of receiver clinical MR coil are using cables between the resonant coil and Connector plug. To remove possible induced currents on the cable’s shield, circuits such as RF traps are distributed along the cable. This is done to ensure patients’ safety during the exam. RF-traps are difficult to miniaturize and are not fit for inner coils such as endoluminal coils. Optical fibers would be a smart option to get rid of this critical drawback but this requires electro-optical conversion devices. This abstract presents the first images obtained at 7T with an electro-optical conversion based on Pockel’s effect.

Gary Zabow¹, Stephen Dodd², and Alan Koretsky^2
1Applied Physics Division, National Institute of Standards and Technology (NIST), Boulder, CO, United States, ²NINDS, National Institutes of Health (NIH), Bethesda, MD, United States

Planar meander-line coils have been proposed as ideal surface coils because they should, theoretically, create highly uniform  fields over planes of essentially unlimited area.   Experimentally, however, field uniformity of planar meander-line coils is often worse, not better, than even simple loop surface coils.   This presentation shows why existing predictions of meander-line coil fields and imaging performance are misinterpreted and how coil geometries can be simply corrected to better match theory.  In particular, it is shown how a single extra turn of wire can increase  field uniformity by at least an order of magnitude, allowing for uniform, large-area near-surface imaging.

Devavrat Likhite¹, Rob Amerling¹, Leon Lee¹, and Saban Kurucay^1
1GE Healthcare, Waukesha, WI, United States

In the recent times, cleaning protocols after every patient, regular disinfection of medical equipment and use of single-use devices have become a common practice. MRI equipment has been one of the most difficult imaging modalities to clean. Here, we present a simple technique that uses UV light to disinfect the MRI system, without the use of any external power or connecting cables. This technique uses the power from the MRI system and thereby provides a simple and wire-free UV disinfection solution that does not need external electrical source.

Dennis Philipp¹, Endri Stoja², Simon Konstandin¹, Robin Wilke¹, Diego Betancourt², Thomas Bertuch², Juergen Jenne^1,3, Reiner Umathum^1,3, and Matthias Guenther^1,4
1Fraunhofer MEVIS, Bremen, Germany, ²Fraunhofer FHR, Wachtberg, Germany, ³German Cancer Research Center DKFZ, Heidelberg, Germany, ⁴MR Imaging and Spectroscopy, Faculty 01, University of Bremen, Bremen, Germany

Smart metasurfaces, special two-dimensional metamaterial devices, have a huge potential to drastically improve imaging efficiency in MRI and are a promising tool to overcome some of the limitations which are hampering technological advances in the field. The design, simulation, and experimental verification of thin, smart, non-linear metasurfaces is presented, which yield an up to eightfold enhanced signal-to-noise ratio in 3T MRI. The smart metasurface is a system of two inductively coupled structures, one of which has a non-linear, incident power-dependent behavior. On-bench characterization and MRI scans with a homogeneous phantom and a kiwi fruit prove the functionality and working principle.

Aditya Ashok Bhosale¹ and Xiaoliang Zhang^1
1Biomedical Engineering, State University of New York, Buffalo, Buffalo, NY, United States

Self-decoupled radiofrequency coils reduce the electromagnetic coupling between the coil elements and eliminate the use of complex decoupling technologies. The use of a small value capacitor (Cmode) in a self-decoupled coil helps in eliminating the coupling between coil elements but causes a large electric field across the Cmode capacitor1.which may potentially cause a safety problem during imaging. In this study, we propose the use of a high dielectric sheet to reduce the electric field across the capacitor and thereby reducing the higher SAR in the subject.

Tania del Socorro Vergara Gomez^1,2, Marc Dubois^1,2,3, Pierre Jomin², Megdouda Benamara³, Djamel Berrahou³, Elodie Georget³, Tryfon Antonakakis³, David Bendahan¹, Frank Kober¹, Stefan Enoch², and Redha Abdeddaim^2
1Aix Marseille Univ, CNRS, CRMBM, Marseille, France, ²Aix Marseille Univ, CNRS, Centrale Marseille, Institut Fresnel, Marseille, France, ³Multiwave Imaging, Marseille, France

Abdominal imaging at 3T suffers from B₁⁺ inhomogeneities due to radiofrequency (RF) wavelength reduction. High permittivity dielectric pads have been introduced as suitable solution to this problem. Such pads can require up to a few kilograms of ceramic powder usually dispersed in water. This could be detrimental to patient comfort during examination. Here we present a new approach based on thin, lightweight and flexible metasurface pads. The pads are shown to improve transmit and receive efficiency together with SNR in vitro. 

Zachary Colwell¹, Djaudat Idiyatullin², Lance DelaBarre², Thomas Vaughan³, Michael Garwood², and Sung-Min Sohn^1
1School of Biological and Health Systems Engineering, Arizona State University, Tempe, AZ, United States, ²Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN, United States, ³Zuckerman Institute, Columbia University, New York, NY, United States

Simultaneous Transmit and Receive (STAR) requires high decoupling between the RF transmitter and receiver. Current methods for this include, but are not limited to: geometric isolation, active RF leakage cancellation and metamaterial decoupling. The presented method uses a passive, four-port, tunable canceller circuit to achieve upwards of 40 dB of isolation between a quadrature transmit coil pair and the single receiving coil for a 1.5T system.

Christoph Michael Schildknecht¹, Markus Weiger¹, Romain Froidevaux¹, and Klaas Paul Pruessmann^1
1Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zürich, Switzerland

For short-T2 MRI measurements, fast T/R switches that can handle high RF power are of paramount importance. In this work, we present a T/R switch based on GaN MOSFETs that switches in tens of nanoseconds and can handle a peak power of more than 1000W.

Mike Twieg^1
1Hyperfine Research, Guilford, CT, United States

RF switches occupy many roles in MRI RF systems, including spoiling, damping, transmit/receive (T/R) switches, digital tuners, and crossbar switches. For high field MRI, PIN diodes are the switching device of choice, but at low field strength FETs are attractive. However, implementing the typical drive circuitry for the switch is difficult at lower frequencies. Here we describe a novel drive circuit suitable for a broad frequency range. It does not rely on any ferrous materials, or any high frequency oscillating circuits, and is thus suitable for use on the coil.

Wonje Lee¹, Fraser Robb², John Pauly³, Shreyas Vasanawala¹, and Greig Scott^3
1Pediatric Radiology, Stanford University, Palo Alto, CA, United States, ²GE Healthcare, Aurora, OH, United States, ³Electrical Engineering, Stanford University, Palo Alto, CA, United States

We assess the effect of UWB antenna arrangement within a simulated bore environment that includes a pediatric human phantom using system fidelity factor calculations for wireless data link integrity

Julian Adolfo Maravilla¹, Karthik Gopalan¹, Ana Claudia Arias¹, and Michael Lustig^1
1EECS, UC Berkeley, Berkeley, CA, United States

Recent advances in coil design and fabrication have allowed for flexible and thermoformed coil arrays. However, the weak solder joints and rigid design of traditional variable capacitors used with these coils greatly limit their flexibility. Here, we propose the Flexible Tunable Capacitor (FTC), a high-Q, flexible, easily tunable variable capacitor. This design uses an array of small low-loss parallel plate capacitors adjustable with small step sizes by exploiting series and parallel combinations. This work proposes a basic design that offers a wide range of capacitor values (0.5 pF to 7 pF) suitable for 3T and 7T coils.