R. Adam Horch^1,2 and John C. Gore^1,2
1Department of Radiology & Radiological Sciences, Vanderbilt University, Nashville, TN, United States, ²Vanderbilt University Institute of Imaging Science, Nashville, TN, United States

3D printing with selective metallization is demonstrated as a new means to fabricate RF coils for solution-state NMR. Current capabilities allow construction of mm-scale solenoids with integral sample chambers for self-contained NMR probes, and 3D-printed microcoils are imminent given ongoing advances in technology. The unique properties of 3D printing enable facile construction of potentially thousands of coils at low cost, giving way to large coil arrays for high-throughput NMR and novel coil geometries.

Roberta Kriegl^1,2, Jean-Christophe Ginefri², Marie Poirier-Quinot², Zhoujian Li², Luc Darrasse², Ewald Moser^1,3, and Elmar Laistler^1,3
1Center for Medical Physics and Biomedical Engineering, Medical University, Vienna, Vienna, Austria, ²IR4M (Imagerie par Résonance Magnétique Médicale et Multi-Modalités), UMR8081 CNRS, Université Paris Sud, Orsay, Essonne, France, ³MR Centre of Excellence, Medical University, Vienna, Vienna, Austria

A novel design scheme for monolithic transmission line resonators (TLRs) used as NMR surface probes is presented. The multi-turn multi-gap TLR design provides an additional degree of freedom for adjusting the TLR geometry, and therefore enables more accurate optimization of current distribution, and B₁pattern. It also promotes the use of multi-turn TLR technology for high-field applications requiring a large FOV, which has not been possible up to now due to the low self-resonance frequency of these coils. Here, we compare three different multi-turn multi-gap TLRs designed for ¹H imaging at 7 T by 3D electromagnetic simulations and MRI experiments.

Jonathan Y Lu¹, Kamal Aggarwal¹, Thomas Grafendorfer², Fraser Robb³, John M Pauly¹, and Greig C Scott^1
1Electrical Engineering, Stanford University, Stanford, CA, United States, ²Advanced Coils, GEHC Coils, Stanford, CA, United States, ³GE Healthcare, Aurora, OH, United States

We demonstrate a novel Q-spoiling method using a depletion mode Gallium Nitride (GaN) HEMT device. This device, when unbiased, ideally acts as a short and when biased with a negative gate-to-source voltage acts as an open switch. Using this device, we constructed a coil that is Q-spoiled when unpowered and at resonance with an applied gate to source voltage. Compared with the conventional Q-spoiling method using a PIN diode, the new circuit requires less power and yields comparable SNR coil measurements. In addition, the default Q-spoiled state allows greater safety benefits, and easier decoupling with multiple coils.

Andreas Pfrommer¹ and Anke Henning^1,2
1Max Planck Institute for Biological Cybernetics, Tuebingen, Germany, ²Institute for Biomedical Engineering, UZH and ETH Zurich, Zurich, Switzerland

Parallel imaging is intrinsically limited by Maxwell’s equations. A complete set of vector solutions to the Helmholtz equation consists of both curl-free and divergence-free fields. In this study we investigated the contribution of electric-type current patterns to UISNR for different voxel positions and acceleration factors in a spherical model at 9.4T. For moderate acceleration the electric mode increased UISNR by maximally 55%. For very high acceleration, however, UISNR was mostly caused by the magnetic mode. The reason for this might be the much faster growing power loss of the electric mode with respect to the expansion order.

Gang Chen^1,2, Daniel Sodickson¹, and Graham Wiggins^1
1Center for Advanced Imaging Innovation and Research (CAI2R) and Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, United States, ²The Sackler Institute of Graduate Biomedical Science, New York University School of Medicine, New York, NY, United States

For a body-sized phantom at 7 Tesla, the ideal current patterns for curl-free current modes display V-shaped distributions due to the need for phase evolution along the axial direction (z) to account for propagation delays to or from the central region of interest. Previous studies have shown that either bending the electric dipole into a V or shortening a straight dipole helps to mitigate destructive interference of signal, and therefore to increase transmit efficiency or SNR, at the central point of interest. Here we describe a novel 3D curved electric dipole antenna design constructed on a dielectric substrate to compensate for propagation delays and increase central B1+ efficiency.

Rita Schmidt¹ and Andrew Webb^1
1Radiology, Leiden University Medical Center, Leiden, Netherlands

In previous work the concept of using high permittivity materials to increase the strength and homogeneity of the B1 field has been shown at 3T and 7T. However, it was also shown that at ultrahigh field instead of a monotonic sensitivity improvement, high permittivity pads can also be a source of local signal decreases due to wavelength effects within the material. In this study we investigate how the wavelength effects can be mitigated by using a low order prefractal geometry for the dielectric pad, which maintains the overall coverage of the pad, but gives an increase in sensitivity and homogeneity.

Gillian G Haemer^1,2, Christopher M Collins^1,2, Daniel K Sodickson^1,2, and Graham C Wiggins^1
1The Center for Advanced Imaging Innovation and Research, and the Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, United States, ²The Sackler Institute of Graduate Biomedical Sciences, Department of Radiology, New York University School of Medicine, New York, NY, United States

Previous work has shown that high permittivity materials (HPMs) placed between the coil and the sample can improve SNR, transmit efficiency, and RF homogeneity. However dielectric resonances in any HPM placed close to a transmit/receive coil may create an adverse affect when tuning and matching RF coils. By visualizing the dielectric resonant modes and testing various ways to reduce their effect on the coil we explore one practical aspect of HPM use.

Simone Angela Winkler¹, Jason P Stockmann², Paul A Warr³, Boris Keil², Lawrence L Wald^2,4, and Brian K Rutt^1
1Dept. of Radiology, Stanford University, Stanford, CA, United States, ²A. A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts, United States, ³Department of Electrical & Electronic Engineering, University of Bristol, Clifton, United Kingdom, ⁴Harvard-MIT Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States

Combining RF and B0 shim functions into a single array is an appealing approach which allows highly flexible matrix B0 shimming while preserving closely fitting, high channel count receive array elements. The standard approach is to add chokes to bypass all loop capacitors to allow the DC current to flow around the loop, but this introduces additional loss, heating, RF field perturbation, bulk and construction complexity. We report on the analysis (by theory, simulation, and experiment) of several new combined RF-shim element designs, with particular focus on SNR performance. We particularly investigated two new loop designs – concentric and coaxial types – and compared these to the standard chokes and RF-only loop types. We conclude that both new loop types provide viable solutions for RF-shim loop architectures at 7T.

Dean Darnell¹, Trong-Kha Truong¹, and Allen Song^1
1Brain Imaging and Analysis Center, Duke University, Durham, North Carolina, United States

It is a challenge to correct small spatial variations in B0 inhomogeneities with current B0 shimming implementations due to a lack of shimming spatial resolution. Building upon the Integrated Parallel Reception, Excitation and Shimming (iPRES) concept, this study improves the spatial resolution by increasing the number of independent magnetic fields available for each RF coil. Initial experiments show that the additional magnetic fields introduced for shimming show a notable improvement in B0 homogeneity root-mean-square error relative to the original iPRES design.

Isabelle Saniour¹, Anne-Laure Perrier², Reina Aydé¹, Gwenaël Gaborit^2,3, Lionel Duvillaret³, and Olivier Beuf^1
1Université de Lyon, CREATIS, CNRS UMR 5220, Inserm U1044, INSA-Lyon, Université Lyon 1, Villeurbanne, France, ²Université de Savoie, IMEP-LAHC, UMR 5130, Le Bourget-du-Lac, France, ³KAPTEOS, Sainte-Hélène-du-Lac, France

The use of metallic coaxial cables in MRI could induce local high Specific Absorption Rate (SAR). Optical fiber link could be a promising alternative to coaxial cables for MRI to ensure patient safety. A novel type of an endoluminal receiver coil ensuring optical transmission of NMR signal and optical detuning is designed. Firstly, the conversion of the NMR electrical signal into an optical signal is based on Pockels effect and ensured by an Electro-Optical (EO) waveguide added to the coil according to the applied electric field. Then, the decoupling of the coil is done optically using photodiodes placed on the coil that provide the DC decoupling current.