Alexander Beckett, An Vu, Scott Schillak, Lawrence Wald, David Feinberg

Coil arrays using smaller loop sizes allow increased signal close to the coil array. Such coil arrays with a large number of channels allow increased SNR across a large area of cortex, and accelerated imaging comparable to commercially available high-channel coils, with particularly good performance close to the coil array. These gains in SNR allow high-resolution (0.5mm isotropic) EPI

Sajad Hosseinnezhadian, Roberta Frass-Kriegl, Sigrun Goluch, Michael Pichler, Jürgen Sieg, Marie Poirier-Quinot, Luc Darrasse, Ewald Moser, Jean-Christophe Ginefri, Elmar Laistler

In view of building a flexible 7T 2D coil array for cardiac MRI at 7 T, transmission line resonators (TLRs) with and without decoupling ring are investigated. Using 3D EM simulation and MR measurements for single elements, it could be shown that the presence of the decoupling ring does not perturb significantly the  $$$B_1^+/\sqrt{P_{input}}$$$ distribution of the TLR. 3D gradient echo images for both TLRs with and without decoupling rings have been acquired. No significant degradation in the image quality due to the presence of the decoupling ring was observed.

Matthew Wilcox, Stephen Ogier, Sergey Cheshkov, Ivan Dimitrov, Craig Malloy, Steven Wright, Mary McDougall

Biomarkers detectable by carbon-13 NMR spectroscopy have known correlations with breast cancer characterization, but in vivo 13C spectroscopy has been limited by low SNR. To counteract this, a 16-element receive coil and isolating preamplifier box was constructed for carbon-13 spectroscopy of the breast at 7 Tesla. The array was characterized on the bench and showed good results in terms of ease of tuning, low element-to-element coupling and Q values. Scanner testing using the coil was preliminary but showed successful 1H and 13C transmission and that array elements were individually able to acquire spectra.

Wolfgang Loew, Christopher Ireland, Matthew Lanier, Brynne Williams, Matthew Batie, Yu Li, Randy Giaquinto, Ron Pratt, Charles Dumoulin

A novel three-layer frame was developed to enable scalable phased-array coils.  The geometry of the three-layer frame allows a single 12-element tile to dock with up to four identical tiles.  When adjacent tiles are docked, the overlap of coils in adjacent tiles is identical to the coil overlap within a tile.  Two phased-arrays setups using 12-element tiles and integrated balun coil technology were constructed.  The first contained two separate tiles and the second had two interconnected tiles. The phased-array coils were evaluated with phantom imaging experiments and with multiple in-vivo experiments.

Jérémie Clément, Rolf Gruetter, Özlem Ipek

Searching for optimal RF coil array for whole-brain MR applications, central-fed dipole was compared with fractionated dipole in a single and RF coil array configurations with combination of loop coils in measurements and electromagnetic field simulations in terms of B₁⁺ transmit efficiency, field uniformity, SAR and mutual coupling in an array. High transmit field performances were shown over the cerebral cortex by using phase-only shimming with six center-fed dipoles with two loops RF coil array on experimentally measured B₁⁺-maps and anatomical MR images.

Suchit Kumar, Young-Seung Jo, Jeong-Hee Kim, Chulhyun Lee, Chang-Hyun Oh

In ultra-high-field magnetic resonance imaging (UHF-MRI), body imaging suffers from B1 inhomogeneity due to relatively short wavelength. A range of new radio frequency (RF) coil designs has been proposed to overcome this problem. As previously reported, dipole antenna had been proposed to address this B1+ inhomogeneity problem for body imaging. In this paper, structural adjustment of dipole antenna has been tried for parallel transmission to improve overall B1+ homogeneity. Surface dipole antennas with several structures are tried and compared with our top-hat dipole antenna array reported previously. Also, static RF shimming was employed to evaluate the B1 uniformity.

Kyle Gilbert, Joseph Gati, Peter Zeman, David Schaeffer, Stefan Everling, Ravi Menon

An eight-channel RF coil was developed for imaging the common marmoset at 9.4T. The coil was adjustable in width to accommodate different head sizes while maintaining high SNR, thereby facilitating the study of larger cohorts of animals. Tuning and matching of the coil did not require adjustment over the range of potential head sizes. EPI time series were acquired, showing minimal geometric distortion with a two-fold reduction factor. A two-fold reduction factor could be achieved in both the left-right and anterior-posterior directions.

Kyle Gilbert, Joseph Gati, L Klassen, Stefan Everling, Ravi Menon

A 15-channel receive coil, in conjunction with a 2-channel transmit coil, was developed for imaging the common marmoset at 9.4T. The high channel count produced low geometry factors while accelerating in EPI acquisitions, thereby reducing geometric distortions with minimal impact on the SNR. This demonstrates the utility and feasibility of employing higher channel counts for functional imaging of the marmoset.

Wen-Yang Chiang, Cecil Yen, Mary McDougall, Afonso Silva

A 10-element head RF coil array was developed for imaging the brain of awake marmosets. A soccer ball design was used to improve whole brain coverage and parallel imaging acceleration when compared to our previous designs. Coil clip and PLA cement were introduced to help place the small coil elements on surfaces of irregular shape and optimize geometric decoupling. The matching network provided independent adjustments of tuning, matching, active detune and preamp decoupling, greatly simplifying the construction of coil arrays in space-limited applications.  Molded-in foam padding was also introduced to provide additional comfort during awake marmoset imaging.

Michael Beck, Dennis Parker, J Hadley

A ladder and overlapped phased array coils were constructed with the same number of channels and overall dimensions to see how much of a SNR performance difference there was between the two coil construction techniques.  The results show that between 2 and 12 cm within a cylindrical phantom the difference between SNR was less than 3%.  With negligible performance difference the ladder array can be a viable alternative to overlapped arrays if a simpler coil construction process is desired.

Neha KOONJOO, Bryce Primavera, Jason Stockmann, Thomas Witzel, Lawrence Wald, Matthew Rosen

Highly-resolved proton imaging is challenging in the millitesla regime. With the aim of enhancing our previous single-channel spiral head coil for operation at 276 kHz, a quadrature head coil was designed, comprised of 2 layers (inner and outer) producing orthogonal B1 fields. Images acquired with the new quadrature coil had the same signal magnitude when compared to the single-channel coil. However, the expected √2-factor signal enhancement in combined SNR was not fully realized due to a 30% higher noise floor observed in one quadrature. Improvements in gradient amplifier filtering will significantly improve the SNR.

Vishal Kampani, Randall Jones, Hal Charles, Natalie Hussey

To create a dual-tuned (¹H & ¹⁹F) receive-only surface coil array for pulmonary functional imaging. This satisfies an unmet clinical need because there is currently no widely accessible 3D measure of regional lung function.  As a result, the current standard of care for diagnosis and evaluation of lung disease relies nearly exclusively on global measures such as spirometry. The technical significance of this proposal is that the implementation of parallel imaging for ¹⁹F MRI would provide a means to shorten breath hold times with marginal SNR impact as well as facilitate the development of real time free breathing image acquisitions.

Iulius Dragonu, Craig Buckley, Matthew Robson, Aaron Hess

Ultra-high-field (UHF) provides higher SNR than conventional, clinically available field strengths. However, UHF suffers from heterogeneous transmit B₁⁺ fields. At 7 T, the shortened transmit radio-frequency (RF) wavelengths have a similar value to the dimensions of the human head/thorax which may result in signal cancellation and local signal dropouts. In this paper, we propose a novel imaging scheme based on simultaneous excitation with all transmit channels. Controlled aliasing is used to encode each transmit channel independently which we term Tx-CAIPIRINHA.

Tx-CAIPIRINHA has been demonstrated in-vivo. The concept uses the linear superposition of B₁⁺ fields via the excitation flip angle which only holds true in the low flip angle regime. When normalizing to transmit efficiency, Tx-CAIPIRINHA achieved a marginally higher SNR than B₁⁺ shimming, demonstrating the constructive combination of transmit sensitives throughout the image.

Jan Paska, Martijn Cloos, Graham Wiggins

Body imaging at 7T is challenging due to wavelength effects, a low sensitivity in deep tissue1, and a large variation in body sizes across the patient population. A common approach is to use close fitting coils or dipoles2,3,4, which exhibit a high transmit and receive sensitivity and are fairly load independent, but lack the easy handling  necessary for routine clinical use.   We aim to construct an RF coil array for general purpose body imaging for routine use that is robust, easy, and safe to handle, while retaining adequate sensitivity in the deeper regions. Given these boundary conditions, we settled on a stand-off design5 with an RF shield. Thus, consciously sacrificing some sensitivity to improve handling and safety. After extensive optimization we converged to an optimal coil array consisting of a transceive dipole array complemented with a birdcage array for reception only. The array was completed and a sensitivity analysis with respect to body sizes was performed.

Manuela Rösler, Markus Weiger, David Brunner, Thomas Schmid, Romain Froidevaux, Klaas Pruessmann

Two major challenges for MRI of short-T2 tissues are creating large gradient strengths and avoiding signal contamination from hardware parts, in particular the RF coils. In this work, to enable short-T2 MRI with a dedicated insert gradient coil, an RF birdcage coil was designed with a) minimized background signal and b) optimized B1 field to prevent aliasing associated with the limited monotonic range of the gradient.

Aidin Arbabi, Dulcie Vousden, Leigh Spencer Noakes, Jun Dazai, Shoshana Spring, John Sled, Jason Lerch, Mark Henkelman, Brian Nieman

Multiple-mouse MRI was implemented on a 7-Tesla magnet with four Cryogen (liquid helium)-cooled radio frequency probes. The high signal-to-noise ratio offered by the probes enabled spatial resolutions of 60 μm isotropic in <2 hours, a significant improvement for in vivo anatomical imaging of the mouse brain. Several 3D pulse sequences including FLASH/MP2RAGE/RARE were implemented for multiple-mouse acquisition. Manganese-enhanced T1-weighted images were obtained at two different resolutions of 60 μm and 75 μm. Results demonstrate the combined benefits of cryogen-cooled coils and multiple-mouse MRI. 

Jorge Chacon-Caldera, Alexander Fischer, Matthias Malzacher, Lothar Schad

Increasing signal-to-noise-ratio (SNR) in prostate MRI could facilitate the diagnosis and characterization of prostate cancers. In this work, we built a quadrature posterior surface array that aims to increase local SNR at the prostate. The coil was compared to 3 and 9 channels of the standard spine array using phantom measurements. Respectively, SNR gains of 12 and 9% were obtained using a realistic region-of-interest (ROI). Further work will be undertaken to translate the SNR gains to in-vivo prostate imaging at 3T. 

Wenming Li, Shu Du, Jianmin Wang

New design of flexible surface coil was presented. Voltage-controlled variodes instead of trimmers are used for remote coil frequency adjustment; λ/4 impedance transforming circuit are used to enable remote detune, thus detune circuits with big rigid components are moved out from the antenna part. By doing this, the antenna is covered by soft foam seamlessly which improved the flexibility significantly. Design was tested on four-element arrays. Experiments on both phantom and invivo testing show good results with this design.

Natalia Gudino, Qi Duan, Jacco de Zwart, Stephen Dodd, Joe Murphy-Boesch, Peter van Gelderen, Jeff Duyn

On-coil current-source switch-mode amplification presents high power efficiency, allows direct control of the transmit field (B1), and decoupling of elements through the amplifier output impedance. These are important advantages over conventional remote voltage-mode quasilinear amplification that should allow more efficient and safer implementation of a multi-channel transmit system. Following this approach, we present an optically controlled transceiver design that was used for initial safety assessment of the technology toward the implementation of a high channel-count pTx array for brain imaging at high-field. We acquired human brain images with this technology at 7T

Jiaming Cui, Chenhao Sun, Dheyaa Alkandari, Steven Wright

This abstract reports a switchable coil element which uses “forced current excitation”.  The coil consists of three aligned rungs, with a total length of 37 cm.  Any one or more of three rungs can be easily selected to provide a variable length or position field-of-view.   The forced current approach ensures equal current on the selected rungs to give a uniform field distribution along the length of the field-of-view. Bench measurements demonstrate the expected efficiency improvement when only a single rung is selected and the uniform field pattern.   

Ana Luisa Neves, Redha Abdeddaim, Stefan Enoch, Jerome Wenger, Johann Berthelot, Anne-Lise Adenot-Engelvin, Nicolas Mallejac, Franck Mauconduit, Lisa Leroi, Alexandre Vignaud, Pierre Sabouroux

The influence of air fraction on the permittivity of BaTiO₃ aqueous mixtures was assessed, with the aim of obtaining high permittivity mixtures. For extremely saturated mixtures (>50%v/v), the air fraction of the mixture plays a great role in determining ε_r, and by applying high pressure it is possible to go beyond the maximal value described in dielectric shimming literature. A BaTiO₃ 1cm-thick pad was manufactured (ε_r =470) and tested in a 7T MRI, as well as a conventional saturated pad (≈40%v/v, ε_r=200). Results show an overall signal improvement when using higher permittivity pads and the possibility to reduce pad-thickness.

Till Huelnhagen, Ariane Fillmer, Antje Els, Florian Schubert, Bernd Ittermann, Thoralf Niendorf

Respiratory motion induced B₀ field fluctuations, constitute a challenge for B₀ sensitive CMR like spectroscopy.  Accommodating CMRS in a single breath-hold is elusive if not prohibitive. Motion corrected approaches under free breathing were demonstrated to substantially improve CMRS. Yet, B₀ field fluctuations over the respiratory cycle may compromise spectral resolution and data integrity. A compensation strategy like dynamically updated first order shims synchronized with the respiratory motion, offers the potential to enhance spectral quality and permits scan time shortening. This work details respiratory motion induced B₀ fluctuations in the interventricular septum and examines the capability of linear shimming for compensation of myocardial B₀ fluctuations.

Ashvin Bashyam, Matthew Li, Michael Cima

Single-sided NMR has the potential for broad utility, especially as a portable diagnostic for disorders in fluid regulation. These sensors require a remote, high field, uniform magnetic field to achieve sufficient sensitivity. We demonstrate a new magnet geometry, the Unilateral Linear Halbach, that combines design principles from sweet-spot and linear Halbach magnets to achieve this goal. Sensitivity analysis using finite element analysis produces a generalized framework for Unilateral Linear Halbach design. Experimental validation through the fabrication of a magnet assembly shows close agreement with the simulated magnetic field. Unilateral Linear Halbach magnets increase the sensitivity, portability, and versatility of single sided NMR.

Peter Ross, Lionel Broche, Gareth Davies, David Lurie

Fast-field cycling MRI is a novel technique that involves cycling the main magnetic field during image acquisition. By doing this, information on the magnetic field dependence of parameters such as the T₁relaxation time can be investigated and exploited as a new form of endogenous image contrast. In this abstract we present progress on a new human-scale fast field-cycling MRI system with a detection field of 0.2 T.

Ruben Pellicer-Guridi, Michael Vogel, David Reutens, Viktor Vegh

Superconducting quantum interference devices (SQUIDs) are highly sensitive magnetometers and they have found application in ultra-low field MRI. However, they require cryogenics and their noise performance is hindered by external noise sources and the strong fields employed in pre-polarised MRI experiments. Air-core magnetometers provide an attractive alternative, as they are highly sensitive, robust and relatively cheap to manufacture. Our goal is to provide of a method to optimise the sensitivity of these devices. In this work we propose an accurate numerical model and the use of a genetic algorithm to consider previously unexplored coil configurations.

Chao Luo, Xiaoqing Hu, Xiaoliang Zhang, Xin Liu, Ye Li

In this paper, we designed and fabricated a kind of metamaterial with 9×9 cells, which bent on phantom and inserted to a birdcage volume coil to investigate the performance for 3T MRI. The results of simulations and phantom experiments agreed with each other very well indicate that the proposed metamaterial is able to increase the B1+ fields in some region closed to the surface of phantom. This improvement of B1+ fields will benefit to 3T MRI targeted clinical applications.

Christian Mirkes, G. Shajan, Ali Aghaeifar, Irena Zivkovic, Kai Buckenmaier, Klaus Scheffler

Multiple local shim coils can be used to improve the B₀ homogeneity at ultra-high field. In this work, a dual-layered multi-channel B₀ and RF coil setup is presented that allows a flexible design of the shim coil without influencing the RF performance. It is shown that a 16 channel B₀ coil in combination with a standard 2^nd order spherical harmonics (SH) shim system can achieve  a higher degree of B₀homogeneity than a 3^rd order SH shim system in the case of whole-brain shimming.

Markus Weiger, Johan Overweg, Manuela Rösler, Romain Froidevaux, Franciszek Hennel, Bertram Wilm, Alexander Penn, Urs Sturzenegger, Wout Schuth, Menno Mathlener, Martino Borgo, Peter Boernert, Christoph Leussler, Roger Luechinger, Benjamin Dietrich, Jonas Reber, David Brunner, Thomas Schmid, Laetitia Vionnet, Klaas Pruessmann

Zero-echo-time (ZTE) techniques enable imaging of tissues with very short T2s, e.g. bone or myelin. Their performance directly scales with gradient strength G, which depends on the target T2 and spatial resolution. With present-day gradients the spatial resolution for T2s on the order of 100 μs is limited to several millimetres. To improve the resolution, considerably higher gradient strengths are required. As a further challenge of ZTE sequences, the strong gradients are applied with full duty cycle. The goal of this work was to develop a gradient coil that meets these challenges, offering very high amplitude at full duty cycle.

Nicolas Arango, Jason Stockmann, Thomas Witzel, Lawrence Wald, Jacob White

Accurate B0 shimming with close-fitting coil arrays can improve brain imaging at 3T and 7T, but slice-optimizing the shimming during acquisition requires fast redistribution of dozens of multi-amp coil currents.  Our open-source, low-cost ($80/channel) driver system can redistribute fifty amps to thirty-two coils in milliseconds, with milliamp accuracy.  The system uses an easily reprogrammed microcontroller, optical fiber isolation, and thirty-two current-feedback coil-drivers (described previously). When used to drive sixty-four slice-specific sets of currents in a novel 32-coil shim array, stretching in an EPI brain scan was substantially reduced, without introducing driver artifacts.

Paul Chang, Sahar Nassirpour, Anke Henning

Real-time B0 feedback has been shown to be beneficial for the controlling of B0 fluctuations. However, update rates that have been reported are slow (~100ms) and either use pre-emphasis to correct for the coupling and faster dynamics of the system or only use control the frequency 

We show that for faster update rates (±1ms) pre-emphasis (i.e. dynamic decoupling) is not required and that static decoupling can perform equally well or better.

Paul Chang, Sahar Nassirpour, Anke Henning

High-order dynamic B0 shimming has been shown to improve the shim quality for multi-slice acquisition schemes. However, for gradient intensive sequences, eddy currents become a major problem and pre-emphasis is required. The pre-emphasis can be done flexibly with the use of digital filters as they can drive arbitrary-shaped waveforms and are scalable to a larger number of channels.

In this work, we design and implement a system to perform dynamic B0 shimming with digital pre-emphasis with a very fast update rate. The setup is then tested for performing pre-emphasis on a 9.4T scanner. 

David Brunner, Jonas Reber, Simon Gross, Klaas Pruessmann

Tight temperature control of various devices is required to guarantee highly stable experimental conditions. E.g. B₀ field shifts induced by heating of shim irons or gain changes induced in preamplifiers can be avoided by oven controlling the critical components of the device. Furthermore, a recently presented approach of active shimming with controlled magnetic materials requires tight temperature control of a large count of devices in parallel in the bore.  For such applications, we present a 14 channel, low power, MR compatible temperature measurement and control system which can be parallelized for a scalable channel count. 

Soheil Taraghinia, Koray Ertan, Ergin Atalar

Phase-shifted Pulse Width Modulation (PWM) technique is implementable in stacked and parallel configuration of the H-bridge gradient amplifiers. However, in the gradient array systems where one stage amplifier is sufficient to drive each element, phase-shifted PWM is not feasible. In this work, similar technique is implemented by utilization of the coupling between the elements of the array and finding the optimized phases for each channel in order to have minimum current ripples. This method is tested for different gradient fields and high ripple reduction percentages achieved both in simulations and experiments.

Zhi Hua Ren, Wenshen Zhou, Shao Ying Huang

A magnetic resonance imaging (MRI) for outdoor in-situ scanning is promising for biological studies. Here we propose a portable MRI system in which both the magnet array and the transceiver coil can be physically opened and closed. This is for imaging long objects in situ where cutting the object and fitting it into a bore for scanning is not an option. A convertible magnet array is designed where the force to open and to close the magnet array is minimized based on an analytical solution. Meanwhile, a convertible solenoid coil is proposed as an RF transceiver coil. 

Matthew Bourne, Robin Dykstra, Sergei Obruchkov

To lower the entry barrier for MRI system development, an open source PXIe platform consisting of IP for peripheral boards, an associated linux device driver and example system controller and peripheral boards were developed. The design was capable of performing system controller initiated DMA transfers in both directions with a maximum block size of 8MB. The hardware design was greatly simplified by mounting FPGA modules from Avnet onto custom PXIe compatible carrier boards. The modules from Avnet contained a System on a Chip device from Xilinx consisting of a dual core ARM processor and FPGA fabric.

Josip Marjanovic, Jonas Reber, Lars Kasper, Benjamin Dietrich, David Brunner, Klaas Pruessmann

The demand for higher image quality led to a significant increase in the number of parallel receive coils and to the addition of sensor systems such as magnetic field monitoring probes to MR systems, boosting the demand for many high quality receive channels. Furthermore, new methods increasingly require high acquisition duty cycles and bandwidths setting new requirements on data traffic and real-time capabilities. We present a flexible, scalable receiver system addressing those issues demonstrated on an example of concurrent imaging and field monitoring with real-time processing of synchronized streams of coil and trajectory data, as required by modern reconstruction algorithms.

Xianchun Zeng, Chunqi Qian

To improve the detection sensitivity of MRI, a Wireless Amplified NMR Detector (WAND) is developed to image surrounding vessels from inside the esophagus. This cylindrical detector is a double frequency resonator with a single metal wire that is self-connected by a pair of varactors. It can convert wirelessly provided pumping power into amplified MR signals. When the detector is inserted inside the esophagus, vessel walls of the vertebrate artery and basal artery can be identified with greatly improved clarity. This detector will be useful to characterize subtle lesions in inflamed vessels. 

Andreas Port, John Pauly, Fraser Robb, Greig Scott

As MRI array counts expand, there is growing interest in moving more of the receive electronics onto the array, the ultimate goal being wearable, and cordless arrays. This places severe constraints on the maximum feasible power consumption per channel. We explore low power front-end topologies employing passive mixers. If combined with low-power high resolution successive approximation ADCs or continuous time sigma delta ADCs, receive arrays at only 100mW per channel may be feasible.

Jonathan Lu, Pascal Stang, Fraser Robb, John Pauly, Greig Scott

One step in making wireless MRI possible is to sync the clocks at both the transmit side hardware that plays out the pulse, and the receive chain that processes the FID data. A discrepancy between the timing of the two clocks will lead to jitter that amounts to artifacts in the MRI image. In this work, we demonstrate a method to transfer a wireless clock without creating jitter artifacts in an MRI image.

Dan Madularu, Chathura Kumaragamage, Axel Mathieu, Praveen Kulkarni, M. Rajah, Alain Gratton, Jamie Near

We describe the fabrication and performance of a chronic in situ coil system designed to allow focal brain stimulation in awake rats while acquiring highly resolved MRI data. We developed a subcutaneously implantable receive-only surface radiofrequency coil to be fitted immediately adjacent to the rat skull surface during the cannulation procedure. SNR performance of the coil was superior to three commercially-available coils, in some instances by a factor of three. Widespread BOLD was observed in response to bicuculline and morphine microinfusions. This approach enables mapping the functional response to highly targeted stimuli such as microinfusions or optogenetics.

Eric Der, Vyacheslav Volotovskyy, Boguslaw Tomanek, Jonathan Sharp

TRASE is a k-space encoding method for low cost MRI that replaces conventional imaging gradients with a switchable RF transmit array. TRASE echo train sequences require rapid switching between transmit elements to cycle through up to six different phase gradient encoding fields. In vivo image resolution is currently limited because long (~500μs) refocusing pulses render the echo train sequence vulnerable to T₂ losses. Here we present a design for a high power PIN diode driver circuit capable of robust and rapid switching of short (~100μs) high power pulses for a 24cm coil. Results from 0.2T experiments are shown.

J.M. Sousa, Håkan Ahlström, Mathias Engström, Mark Lubberink

Zero-Echo Time (ZTE) has been proposed as an alternative attenuation method for PET-MR brain imaging. However, the filtering effects on these ZTE AC maps have not been explicitly discussed, in relation to effects on reconstructed and corrected images, and that is what we aim to develop in this study.

Wyger Brink, Zhiyi Wu, Andrew Webb

A simple head-sized phantom has been developed to produce realistic B₁ and B₀ features and electrical loading conditions, as a tool for the evaluation of MR techniques and RF validation in high field MR systems.

Ayano Enomoto, Gadisetti Chandramouli, Alan Koretsky, Chunqi Qian, Murali Cherukuri, Nallathamby Devasahayam

Improvement in sensitivity is required to detect the weak signals with Fourier transform Electron Paramagnetic Resonance (FT-EPR). In the proposed method, the signal from a wireless coil filled with sample was enhanced by using pumping coil in the regular EPR system. In this study, we achieved approximately 6-fold of improvement in signal intensity compared with conventional FT-EPR system under the simulated condition of animal body. We will also show the results of oximetry using the LiPc in, in vivo applications to measure tissue oxygenation. 

Taoming Liu, Dominique Franson, Nate Lombard Poirot, Russell Jackson, Nicole Seiberlich, Mark Griswold, Murat Cavusoglu

This paper presents a Jacobian-based inverse kinematics and open-loop control method for an MRI-guided magnetically-actuated steerable intravascular catheter system. The catheter is directly actuated by magnetic torques generated on a set of current-carrying micro-coils embedded on the catheter tip by the magnetic field of MRI scanner. The Jacobian matrix is derived from a three dimensional kinematic continuum model of the catheter deflection. The inverse kinematics are numerically computed by iteratively applying the inverse of the Jacobian matrix. Experimental evaluation compares a catheter prototype’s desired trajectory to the actual trajectory.

Md Shahadat Hossain Akram, Craig Levin, Takayuki Obata, Genki Hirumi, Taiga Yamaya

PET inserts for the existing MRI systems are showing great potential for widespread and affordable low-cost simultaneous PET/MR imaging that would otherwise improve the PET sensitivity due to the proximity of detectors to the imaging region. To avoid electromagnetic interference between PET and MRI components, PET detectors are enclosed in Faraday shield cages. A electrically floating PET insert enables us to use MRI built-in body RF coil instead of using separate custom designed RF coil with the PET insert. This study experimentally evaluates different PET geometries and different design factors for efficient RF penetration through the floating-PET insert.  

Stephen Ogier, Hongli Dong, Steve Wright, John Bosshard

There are many approaches to simultaneous multi-nuclear spectroscopy, but the simplest and potentially the most elegant involves sending all frequencies through a single broadband amplifier into a single-port, multi-tuned coil.  This abstract examines a complication in this approach, that of early saturation of the amplifier due to the need to amplify two signals simultaneously.  A simple solution, staggering the RF pulses a small amount to avoid the overlapping of their peaks, is shown to largely avoid the problem.

Lucia Navarro de lara, Roberta Frass-Kriegl, Jürgen Sieg, Andreas Renner, Michael Pichler, Sigrun Goluch, Thomas Bogner, Ewald Moser, Thomas Beyer, Wolfgang Birkfellner, Michael Figl, Elmar Laistler

A 24 channel head and neck coil for PET/MR with an integrated moving radioactive source is presented to enable transmission measurements for accurate attenuation mapping.

Shimul Saha, Alena Shchelokova, Ioannis Sotiriou, Alexey Slobozhanyuk, Maria Koutsoupidou, Elena Cellitti, Helena Cano-Garcia, Pavel Belov, Andrew Webb, George Palikaras, Efthymios Kallos

We present in vivo results from a metasurface structure comprising an array of brass wires embedded in a high epsilon and low loss medium. The metasurface was used to scan humans in a 1.5T MRI scanner and demonstrated enhancement of the signal-to-noise ratio up to 200% in the area-of-interest close to the metasurface.

Sebastian Rupprecht, Buddhi Tilakaratne, Chris Messner, Christopher Sica, Michael Lanagan, Wei Chen, Qing Yang

Ultra-high dielectric constant (uHDC) materials were established as an effective B1 shimming and enhancement tool in MRI. A dielectric material operates at certain frequency range and enhances fields at an anticipated resonance frequency. We trimmed a rectangular dielectric block such that the fundamental frequency mode of the block resonated at 3 T, and compared it with a similarly sized non-resonant block. Both cases were coupled with a transmit receive surface coil resonant at 123.2 MHz. The effect of the surface coil area on the B₁ field enhancement was explored to optimize the dielectric and coil configuration.

Michel Geahel, Ludovic de Rochefort, Jean-Christophe Ginefri, Luc Darrasse, Cornelis van der Beek, Javier Briatico, Marie Poirier-Quinot

In MRI, high-temperature superconducting (HTS) radio frequency (RF) coils have been shown to greatly improve the signal-to-noise ratio. The nonlinear behavior of superconducting materials as a function of the emitted RF power is, nowadays, one of the principal technological obstacle limiting the use of these materials on a wider scale. It could be overcome by using HTS coil in reception mode only. Here we characterize these non-linear properties and use them to decouple the HTS coil during transmit mode. This preliminary study is a promising approach to use the highly sensitive HTS coils in reception mode only.

Jorge Chacon-Caldera, Matthias Malzacher, Alexander Fischer, Lothar Schad

Partially orthogonal RF resonators (Parti-coils) is a novel concept in which RF coils are extended in an orthogonal direction. This increases overlap distance between elements. Therefore, coil density can be optimized. We show alternative geometrical coil configurations in array design using Parti-coils and compare them to an array of traditional planar coils using numerical simulations. Parti-coils enhanced the flexibility in array design, increased the overlap distance between coils by a maximum 3.2-fold, decreased next-nearest neighbor coupling by more than 6dB, showed up to 6.6% higher |B1-|_acc. penetration depth, and a factor 1.05 increase of |B1-|_acc. at a ROI.

Jiaming Cui, Romina Del Bosque, Ivan Dimitrov, Sergey Cheshkov, Mary McDougall, Craig Malloy, Steve Wright

This work describes a forced-current-excitation (FCE) bilateral breast coil, modified for the insertion of a 32-channel receive array for 1H imaging and spectroscopy at 7T. A previous design of the bilateral quadrature volume coil employed RF shielding which prevented the insertion of a receive array with the associated hardware and cabling. The modified bilateral coil uses twinaxial cable for the FCE-enabling quarter-wave transmission lines, allowing balanced signal transmission and eliminating the need for the shields. The results include uniform bilateral excitation, an increase in efficiency as compared to the shielded coil, and successful installation of the 32-channel receive array.

Dheyaa Alkandari, Neal Hollingsworth, Chung-Huan Huang, Jiaming Cui, Steven Wright

We report a volume coil consisting of 16 bowtie slot elements arranged in eight independent modules.  The slot coils provide several interesting advantages over conventional elements.   In particular they demonstrate a high degree of Intrinsic coupling between modules, making this array ideally suited for use in parallel transmit using conventional amplifiers.  Additionally,  all match and tune elements, baluns and feedlines are concealed between two ground planes, shielding the imaging volume from stray electric fields.  Imaging results are shown at 4.7 Tesla demonstrating isolated patterns and a broad coverage in volume coil mode. 

Michael Twieg, Mark Griswold

Recent work has shown the use of shim and gradient coil arrays for dynamic shimming and novel spatial encoding methods. These arrays require precise current source drivers with high power and bandwidth. Because of these demands, shim and gradient arrays are typically driven with amplifiers which are located outside the magnet bore due to constraints on power dissipation, radiofrequency interference (RFI), or magnetic materials. Here we present a highly efficient digitally-controlled switchmode current driver. We demonstrate that it is feasible to shield the RFI from the receive chain while avoiding ferrous materials and large heatsinks.

Yun-Kyoung Ko, Han Lim Lee, Chang-Hoon Choi, N. Jon Shah

MRI RF channels refer to the pathways of received signals and the availability of multiple channels allows one to access multi-channel array coils. To control the use of different coils, MRI usually utilises a crossbar-type switch matrix system that interactively connects the selected coil as an input and corresponding analogue-to-digital converters as an output. However, since the RF wavelength decreases with increasing B₀, impedance in RF pathways varies in accordance with wavelength. This results in signal loss and in degraded image quality. In this study, we proposed an RF loss compensation technique for the switch matrix and verified its performance.

Michael Ohliger, Cornelius von Morze, Jermey Gordon, Peder Larson, Daniel Vigneron

Accurate RF coil localization is important for hyperpolarized 13C MRI. Fiducial markers can be constructed from 55Mn and localized using projection imaging. This study examines the minimum number of projections necessary to localize the markers subject to the known distances between markers. This would potentially allow marker localization to be automated as part of prescan.

Juan Diego Sánchez Heredia, Daniel Højrup Johansen, Rie Beck Hansen, Esben Søvsø Szocska Hansen, Christoffer Laustsen, Vitaliy Zhurbenko, Jan Henrik Ardenkjær-Larsen

In this study, we describe a method to obtain improved preamplifier decoupling for receive-only coils. The method relies on the better decoupling obtained when coils are matched to an impedance higher than 50 Ω. Preamplifiers with inductive imaginary impedance and low real impedance, increases the effectiveness of the decoupling. A 2-channel ¹³C array of 50 mm loop coils show an increase of Q-factor of the coils from 247 to 365. The measured SNR, using two small phantoms, demonstrated a similar improvement.

Takenori Oida, Yuki Kaga, Tetsuya Yamamoto, Tetsuo Kobayashi

Shmaryu Shvartsman, James Dempsey, Tom Chmielewski, Gerald Fought, Michael Hernandez, Iwan Kawrakow, Amit Sharma

We report on successful testing of a novel magnetic and RF shielding technology for a 6MeV Linac for MRI guided radiation therapy system.  It allows complete decoupling of the Linac and its components from the MRI system. A low field region is created where the Linac can be operated without any problems. The system is compact and allows positioning of all magnetically and RF sensitive Linac components on a rotating Gantry and treat patients from any angle.  

Nicola Bertolino, Thy Nguyen, Dhaval Shah, Robert Zivadinov, Marcello Alecci, Ferdinand Schweser

PET-MRI imaging sets the stage for truly novel imaging approaches, but preclinical hybrid systems, characterized by ultra-high static magnetic field and small bore diameter, are still in the proof-of-concept stage. In this study, we developed an optimized RF coil/shield setup for an ultra-high field compatible prototype PET ring that can be retrofitted to conventional small-animal MRI systems. In particular an original shielding solution was designed and tested with the purpose of maximizing coil efficiency, usable space inside the detector, and PET sensitivity.

Darshan Keelara, ThejasVishnu Ramesh, Syed Saad Siddiq, Padma Chennagiri, Samarth Singh, Shivaprasad Chikop, Shreyas Indurkar, Sairam Geethanath

Image Signal to Noise Ratio (SNR) and resolution are significant challenges in ultra-low field MRI. A single channel transmit coil and a 4-channel phased array was developed for wrist to operate at 9.5mT. The current work involves integration with the DDS module for verifying functionality. Future work is to develop phased array for head MRI.

Paul Chang, Sahar Nassirpour, Anke Henning

B0 shimming methods are becoming more sophisticated. Methods such as multi-coil shimming, dynamic B0 shimming with pre-emphasis and real-time feedback all require additional hardware to drive the shim coils.

In this work, we present a novel general-purpose embedded platform for controlling any of the above mentioned shim systems. Control software can be developed on Linux, while low-level scripts are used for optimal control of hardware interfaces.

Aziz Ulug, Weidong Luo, Sebastian Magda

Automated segmentation algorithms have been used more and more frequently for research and clinical purposes.  There are available software packages that can determine volumes of brain structures and lesions.  While signal to noise ratio in volumetric images is one of the determinants in the accuracy of such software, the effect of noise to the output results is usually not well described.  We have studied effects of increased noise variance and denoising in evaluating the performance of automated segmentation tool using a synthetic phantom, one human dataset with artificially added noise, and 46 subjects scanned twice.

Matthias Malzacher, Jorge Chacon-Caldera, Alexander Fischer, Lothar Schad

Sodium MRI keeps becoming  more interesting for multiple studies and clinical applications due to its capability to provide information on tissue viability.  This information would be highly valuable in the clinical routine.We analyze technical possibilities to allow pushing sodium MRI into clinical use. In particular, we investigate approaches for transmitting and receiving sodium and proton signals using the same hardware. One main target of these approaches is to be fully compatible with standard 3T MRI systems without decreasing significantly the performance of proton imaging. We prove the feasibility for such systems. Yet, some drawbacks have to be taken into account.