Xinqiang Yan, John Gore, William Grissom

7T scanners currently are not equipped with body coils, so for MR imaging of relatively short coverage along the z-direction (head, knee and prostate), local transmit coils with standing-wave behavior are commonly used to achieve high efficiency. For MR imaging that requires long coverage such as the legs, traveling wave MRI is potentially a competitive choice since it is extremely simple to implement and enables large FOV imaging. In this study, we propose a coverage-adjustable transmit coil which combines the concepts of traveling-wave and standing-wave. The new design exhibits excellent efficiency over short regions, but maintains the ability to cover longer areas for MR imaging of the legs or whole body.

Manushka Vaidya, Daniel Sodickson, Christopher Collins, Riccardo Lattanzi

We show that the ideal surface current patterns maximizing internal signal-to-noise ratio (SNR)  are composed of a) signal-optimizing current patterns which maximize the signal sensitivity without considering sample noise, and b) “dark mode” current patterns which minimize sample noise without affecting signal. For a central voxel in a spherical sample, the absence of dark mode current patterns on an encircling sphere suggests that optimally tracking the precessing spin while ignoring sample noise is sufficient to achieve the best possible SNR. For an off-center voxel, however, the dark mode current patterns form high magnitude localized currents that efficiently minimize sample noise.

Stephanie Yong, Boguslaw Tomanek, Jonathan Sharp

TRASE is a k-space encoding method that uses RF transmit phase gradient fields to achieve mm-level resolution. However, image quality is critically dependent upon the efficient generation of B₁ fields with uniform magnitude and strong phase gradients. We present a new family of phase gradient coil designs based upon a solenoid twisted about a transverse axis. Four twisted solenoids wound on a single cylindrical former are sufficient to encode two spatial dimensions. The design has many attractive geometric, electrical and magnetic characteristics, including the ability to encode in the B₀-direction, previously not possible for transverse-B₀ magnet geometries.

Gillian Haemer, Manushka Vaidya, Christopher Collins, Daniel Sodickson, Graham Wiggins

A helmet shaped coil former made of high permittivity material is simulated with an 8 channel transmit/receive coil as an evaluation step towards coil construction. The addition of the high permittivity material improves performance in both transmit and receive but the choice of a permittivity that is too high may lead to undesired split-resonance effects.

Jinfeng Tian, Xiaoping Wu, Brian Hanna, John Strupp, Kamil Ugurbil, Gregor Adriany, J. Vaughan

A complete MRI RF simulation has at least two parts involved: S-parameter optimization including frequency tuning, impedance matching and channel decoupling, and RF field generation. Previous EM-Circuit co-simulation work used every port data for field synthesis. In this abstract, the speeding factor, or the CPU/GPU time reduction factor, of the co-simulation method against the traditional broadband calculation, is present. We also compared the accuracy of field synthetization from every port data, vs. from every channel data, and propose a highly automatic optimal simulation flow that offers best field accuracy, minimum computer disk space and memory requirement, and fast data processing.

J. W. Radder, S. Moeller, G. Adriany, P.-F. Van de Moortele, B. Tramm, E. Auerbach, K. Ugurbil

Simulation results are presented for 64-channel phased arrays operating at frequencies of 296.5 MHz (7T) and 447 MHz (10.5T) with 4.5 cm element loop diameters.  FDTD simulations were performed per channel to obtain B1 receive fields of the coil array placed around a 2 mm resolution voxel anatomical head model.  Sum-of-squares B1 efficiency maps show improved performance of the array at 10.5T compared to 7T over the whole head region.

Gillian Haemer, Nicole Wake, Martijn Cloos, Christopher Collins, Daniel Sodickson, Graham Wiggins

An alternative approach for generating a digital model of an RF coil is described that avoids the use of geometric priors and ensures structural accuracy. This approach is demonstrated on a helmet-shaped transmit-receive coil, and the resulting simulations are compared to experimental data.

Yang Gao, Weidao Chen, Jinfeng Tian, Yi Sun, Gang Chen, Anna Roe, Xiaotong Zhang

For monkey brain functional MR imaging, sufficient SNR is essential to reveal significant functional activities. Through a series of numerical simulation, we have demonstrated that under 7T environment, to image macaque brain whose size is much smaller than the natural resonate dimension of a dipole antenna, combining dipole and loop can feasibly provide considerably high SNR in both local cortical and deep brain regions. It is believed that such design will effectively benefit functional MRI over macaque with much enhanced signal quality.

Yang Gao, Weidao Chen, Xiaotong Zhang

We have calculated the ultimate SNR at a particular voxel located at monkey cortex through finding the optimized expansion coefficient. Our proposed method enables us to find the relative contribution of divergence free and curl free in UISNR at particular position in the realistic model.

Anh Tran, Sergey Makarov, Harshal Tankaria

Respiratory motion is an important problem in Magnetic Resonance Imaging (MRI), contributing to image blurring during data acquisition and coil detuning. Using the concept of an ideal (perfectly matched and tuned at all available ports) RF transmit coil and the VHP-Female v4.0 dynamic CAD model, we estimate the detuning of a full-body RF coil detuning during the respiratory cycle. Our results show that the computed resonant capacitance values change by at most 0.5%.

Yoshihisa Soutome, Shin-ichiro Suzuki, Hideta Habara, Takahide Shimoda, Yoshitaka Bito

The value of ring capacitors in elliptical birdcage coil (EBC) should be varied gradually according to the location of the ring capacitor in order to generate uniform B₁⁺ field distribution. Usually, it is difficult to adjust the value of the ring capacitor precisely by using fixed capacitors, because the value of the fixed capacitor is discretized. To realize the easy fabrication of EBC, we have designed EBC with constant ring-capacitor value at 1.5T. Simulation and experimental results indicated that the designed EBC generated uniform B₁⁺ field distribution and showed the same transmission efficiency as the conventional EBC.

Xinqiang Yan, Xiaoliang Zhang, John Gore, William Grissom

Traveling-wave MRI has robust matching performance and capability for large field-of-view (FOV) imaging. However, the efficiency of traveling-wave MRI is much lower than conventional methods, which limits its application. One way to improve  the efficiency is to place local wireless resonators around the subject. The feasibility of this approach has been demonstrated in previous works using a single small loop. However, it is not clear whether other kinds of coils (such as electric dipoles) can be used as local elements, and it is not clear how much the improvements can be maintained in human imaging using an array design. By using wireless local loop coil and transverse dipole arrays, the transmit efficiency (B₁⁺) of traveling-wave MRI can be improved by 3.4-fold in the brain and 2-fold in the knee. The coil types (loops or dipoles) should be carefully chosen for brain or knee imaging to maximize the improvement since they exhibit different types of coupling to the TE₁₁ mode, and the enhancement depends on the local body configuration

Hong-Hsi Lee, Daniel Sodickson, Riccardo Lattanzi

Ultimate intrinsic SNR (UISNR) is the theoretically highest SNR for given geometry and electrical properties, independent of the coil design. Here, we introduce an analytic exact expression to calculate the UISNR at the sphere center, enabling to directly analyze the dependence on main magnetic field, sample geometry and electric properties. The analytic expression can approximate the UISNR near the center with < 5% error. This work can enable people without access to the full simulation code to calculate UISNR and use it, for example, as an absolute reference to assess the performance of head coils with spherical phantoms.

Zhi Hua Ren, Shao Ying Huang

Permanent magnet array is a welcome option to provide main magnetic field for portable magnetic resonance imaging (MRI). In this abstract, we propose an efficient and fast optimization method which can optimize the filed strength and homogeneity for the design of permanent magnet arrays. The magnetic field of permanent magnets with the interference of irons is calculated by applying boundary integral method (BIM). For optimization, genetic algorithm particle swarm optimization (GAPSO) is applied which offers highly diversified options and converges fast. A permanent magnet array is optimized with significantly improved performance, and it will be built for low-field portable MR imaging. 

Ian Connell, Ravi Menon

To-date, increasing interest in adapting dipole antennae for imaging at ultra-high field strengths has spawned the design and construction of many dipole-based RF arrays. However, increased electric-field interactions between dipole-to-sample and dipole-to-dipole provide an implementation barrier due to mutual coupling and load-sensitivity. This study presents an analysis of dipole-to-dipole coupling and implements a filter design method to isolate dipole elements in a highly-conformal array designed for human brain imaging at 7 Tesla.

Zhipeng Cao, Xinqiang Yan, Jun Ma, William Grissom

A novel parallel transmit array design method is proposed that integrates both Maxwell and Bloch equations. The method is demonstrated to be better than traditional coils in dynamic multiband shimming and reduced field-of-view imaging scenarios to achieve better excitation accuracy and lower RF energy deposition, as well as robustness across multiple subjects and excitation schemes.

Jonathan Lu, Fraser Robb, John Pauly, Greig Scott

In this work, we demonstrate wireless Q-spoiling of an MRI surface coil in a 1.5T scan using commercial Linx LR series modules. These modules send a digital data stream wirelessly using an On-Off-Keying (OOK) protocol and a carrier frequency of 418MHz. With the simple Linx modules for wireless scanner state detection, it becomes possible to perform tasks such as wirelessly Q-spoiling MRI receive coils and beginning readout of receive coil data. Such steps are necessary for the ultimate goal of wireless MRI.

Roland Müller, Harald Möller

Noise figure measurements have the reputation of being intricate and needing special equipment. Here, we will demonstrate that a simple setup involving an RTL-SDR dongle achieves convenient results. It requires, besides the inexpensive dongle, only common equipment, which should be available in all MRI coil labs.

Daniel Højrup Johansen, Juan D. Sanchez-Heredia, Vitaliy Zhurbenko, Jan H. Ardenkjær-Larsen

This abstract presents two preamplifier designs for ¹³C imaging optimized either for single or array coil usage. For single coil usage the preamplifier is designed to minimize noise yielding a noise figure of 0.25 dB. For array coils coupling between elements is a problem when the input impedance of the preamplifier is high. Hence the main contribution of this work is a low resistance, inductive input impedance preamplifier yielding better decoupling for array coils, while maintaining acceptable gain (20 dB) and noise figure (0.75 dB).

Agazi Tesfai, Johannes Fischer, Ali Özen, Michael Bock

MRI of short T₂* samples is possible with ultra-short echo time sequences (UTE) which can be further improved using dedicated RF coils optimized for short-TE imaging. This work compares the performance of a commercial wrist coil with two custom-built coils (birdcage, solenoid) for UTE imaging of a mummy hand (low water content, short T₂*), and an in-vivo measurement of a human hand in which short-T₂* tissues such as tendons are highlighted by UTE image subtraction.

Nikolai Avdievich, Ioannis Giapitzakis, Anke Henning

Tight-fit multi-channel ultra-high field (UHF, >7T) transceiver (TxRx) phased arrays improve transmit (Tx) efficiency in comparison to larger Tx-only arrays. However, tight-fit TxRx-arrays may require matching for each subject. To evaluate a potential use of tight-fit TxRx-arrays without matching, we investigated both numerically and experimentally an effect of a strong mismatch on performance of a 9.4T 8-channel human head TxRx-array. We demonstrated that mismatching caused only ~5% decrease of the B₁⁺ field, while may have stronger effect on the maximum local SAR. Additionally it also effects the SNR distribution. While overmatching favors SNR, undermatching may enhance Tx-efficiency evaluated as B₁^+/√SAR_10g.

Xinqiang Yan, John Gore, William Grissom

To overcome B1 inhomogeneities and technological difficulties in building large-sized volume resonators, multi-channel arrays are commonly used for transmission at ultra-high fields. One of the main challenges in designing transmit arrays is to minimize the coupling among coil elements. The induced current elimination (ICE) method, which uses additional resonator elements to cancel coils’ mutual electromagnetic (EM) coupling, has proven to be a simple and efficient approach to decouple loop, stripline and dipole arrays. However, in previous embodiments the decoupling elements acted as “magnetic-walls”, blocking the magnetic field and leading to MR signal loss near the elements. In this study, we improved the ICE method to avoid the signal cancellation by using overlapped and perpendicular decoupling loops.

Angelo Galante, Marco Fantasia, Piero Sebastiani, Antonello Sotgiu, Marcello Alecci

We show, by Finite Elements Modelling, the tuning and matching feasibility of a highly coupled parallel transmission (PTx) array by means of two degrees of freedom (two capacitances values) and decouple them a posteriori. This approach could be useful to simplify the design of PTx arrays avoiding complex procedures to geometrically and/or electrically decouple the elements. The procedure is stable for small parameters changes and this suggests a possible experimental verification of the results.

Anna A. Hurshkainen, Anton V. Nikulin, Stanislav B. Glybovski, Irina V. Melchakova, Pavel A. Belov, Benoit Larrat, Elodie Georget, Stefan Enoch, Pierre Sabouroux, Ana L. Neves, Redha Abdeddaim

In order to acquire image or MR spectra at two different nuclei dual-frequency RF-coils are used. Conventional approaches of tuning and matching a coils at several frequencies employ expensive non-magnetic capacitors which also introduce dissipative losses. We propose an alternative method of tuning and matching the coils at multiple desired frequencies. This method is based on resonant excitation of hybridized eigenmodes of periodic structures of metal strips. The proposed method allows one to build cheap coil with reduced dissipative losses resonating on two different frequencies simultaneously.

Sören Johst, Sascha Brunheim, Marcel Gratz, Harald Quick, Mark Ladd, Stephan Orzada

In this work we present phantom and in-vivo pTx excitation results acquired with a 32-channel add-on pTx system based on a 1-channel 7T MRI system. The add-on system uses custom-built I/Q modulators and custom-built amplifiers located inside the magnet room. The single exciter channel is split into 32 sub-channels, whereby the modulators control the phase and amplitude of the individual pTx RF pulses. The modulators and pre-calculated pTx gradients are synchronized via trigger signals generated in the imaging sequence. With the 32-channel pTx system, reduced FOV imaging of the lumbar vertebrae during free breathing was possible.

Jin Jin, Ewald Weber, Kieran O’Brien, Aurelien Destruel, Bassem Henin, Craig Engstrom, Stuart Crozier

This paper presents the initial in vivo imaging results from a new unilateral 8-channel pTx transceive array designed and constructed for 7 T MRI of the hip joint. With subject-specific RF shims, 3D sequences (DESS and MEDIC) provided sufficient coverage, uniform image intensity and excellent contrast. The RF techniques employed in the construction of the array promote efficient use of RF power, enabling turbo spin echo sequences with full coverage of hip joint to be performed with adequate excitation. Comprehensive and conservative RF safety procedures ensure that local RF energy absorption is well below regulatory limits.

Thomas Fiedler, Martina Flöser, Stefan Rietsch, Stephan Orzada, Harald Quick, Mark Ladd, Andreas Bitz

The RF shimming performance of a 32-channel remote body coil is compared to ideally and non-ideally decoupled local and remote arrays consisting of 8 and 16 channels by evaluation of the singular values as well as evaluation of the RF shimming performance in axial and coronal slices with L-curves. For high-field body imaging, multi-ring remote coil arrays provide high degrees of freedom for RF shimming and can achieve higher B1+ homogeneity, especially for coronal slices. However, to utilize the full RF shimming potential of remote multi-ring transmit arrays, high local SAR has to be taken into account during safety assessment.

Kyle Gilbert, Joseph Gati, Ravi Menon

A 32-channel receive coil with variable-density element distribution, in conjunction with an 8-channel transmit coil, was developed for imaging of the occipital-parietal regions of human brain at 7T. Spatial SNR maps demonstrate targeted sensitivity to the peripheral occipital pole, with a smoothly varying SNR proximal to this region. The temporal SNR of the occipital-parietal coil attained 35% higher SNR in the visual cortex than a whole-head coil.

Tales Santini, Narayanan Krishnamurthy, Sossena Wood, Shailesh Raval, Yujuan Zhao, Anthony Fischetti, Minseok Koo, Howard Aizenstein, Tamer Ibrahim

This work presents the design of a 64-channel double-rowed head coil (16 octagons with 4 Tx channels on each octagon).  The magnetic field ( ) and the specific absorption rate (SAR) generated by the new coil were then compared with the TEM and 16-channel Tic Tac coils using Finite-Difference Time Domain (FDTD) simulations. Preliminary data shows significant improvements in all of performance parameters: coefficient of variation (CV) = 14.9% (  field distribution) and maximum/minimum (Max/Min) = 2.45 (  field intensity) across the whole head above and including the cerebellum; and peak/average SAR = 4.97/1.51 W/Kg/10g.  

Nikolai Avdievich, Ioannis Giapitzakis, Anke Henning

Tight-fit ultra-high field (UHF) (>7T) surface loop transceiver (TxRx)-phased arrays improve transmit (Tx) efficiency in comparison to Tx-only arrays built larger to accommodate for receive (Rx)-only array inserts. However, the number of elements in TxRx-arrays is restricted by the number of available RF Tx-channels (commonly 8 or 16), which limits the Rx-performance. A prototype of a 16-element array, which consists of 8 TxRx-surface loops circumscribing a head and 8 additional “vertical” Rx-only loops positioned in the center of each TxRx-loop perpendicularly, was constructed. This addition improves the Rx-performance substantially and has a minimal effect on both the Tx-efficiency and maximal local SAR.

Joseph Corea, Balthazar Lechene, Shreyas Vasanawala, Ana Clauda Arias, Micheal Lustig

The current landscape of pediatric body MRI lacks dedicated high-density arrays, especially for small children. Therefore many centers use existing arrays designed for adults. These arrays are much larger than the patients, reducing the effective number of elements. Adult arrays are heavy for children and are supported by additional padding, increasing the distance from the patient and reducing image quality. Here, we present an appropriately sized blanket-like array designed from patient data for torso and chest/abdominal imaging of 0-2 and 3-5 year olds respectively. This pediatric array is fabricated using screen-printed electronics to produce an extremely lightweight and flexible coil.

Greig Scott, Fraser Robb, John Pauly, Pascal Stang

For add on receiver electronics, and wireless receiver coils, a major challenge is the synchronization of on-coil digitizers without a physical connection to the scanner. We propose that a digitizer that multiplexes the RF pulse and FID to an ADC can then use the transmit data to phase and frequency correct the MRI image data. We demonstrate frequency estimator and pulse sequence frequency tracking feasibility with a test bench that synthesizes the wireless MRI data acquisition and artifact-free image reconstruction.

Ettore Meliadò, Alexander Raaijmakers, Peter Luijten, Cornelis van den Berg

One of the most demanding challenges with ultra-high field MRI is the SAR_10g assessment during a multi-channel transmit MRI examination. A worst-case estimate is often used. In this work a fast method is presented to assess the upper bound of the maximum SAR_10g for body coil arrays with knowledge on only the power distribution among the channels. The performance is assessed for prostate imaging at 7T using our database with 23 realistic subject-specific models. The mean overestimation factor is 1.58 and the mean reduction in overestimation is 0.75 compared to a recently presented alternative estimation method.

Ryan Brown, Oleksandr Khegai, Prodromos Parasoglou

MRI provides the unique ability to study metabolic and microvasculature functions in skeletal muscle using phosphorus and proton measurements. However, the low sensitivity of these techniques can make it difficult to capture dynamic muscle activity due to the temporal resolution required for kinetic measurements during and after exercise tasks. We developed a dual-nuclei coil array to enable proton and phosphorus MRI of the human lower extremities with SNR more than double that of a birdcage coil in the gastrocnemius muscles. This enabled the local assessment of phosphocreatine recovery kinetics following a plantar flexion exercise using an efficient sampling scheme with a 6 s temporal resolution. The integrated proton array demonstrated image quality approximately equal to that of a clinical state-of-the-art knee coil, which enabled fat quantification and dynamic blood oxygen level-dependent measurements that reflect microvasculature function.

Bei Zhang, Gang Chen, Martijn Cloos, Zidan Yu, Jerzy Walczyk, Christopher Collins, Ryan Brown, Riccardo Lattanzi, Daniel Sodickson, Graham Wiggins

Inspired by recent theoretical work indicating that z-oriented currents could capture most of the optimal SNR and outperform loops in reception at high frequencies, we constructed and evaluated a close-fitting dense dipole receive-only head array with 29 elements. The array was combined with a dual-channel transmit birdcage for experiments. SNR was good throughout a head phantom at 7T and outperformed a commercial head coil in regions above and below the center. Future work will focus on detuning mechanisms for dipole elements to enable safe in-vivo measurements.

Ewald Weber, Craig Engstrom, Kieran O’Brien, Aurelien Destruel, Bassem Henin, Jin Jin, Stuart Crozier

This paper presents the initial in vivo imaging results from a new open 8-channel pTx transceive array designed and constructed for 7 T MRI of the knee and ankle joints. The open design of the coil provides easy access and conformable accommodation of both joints, while enabling the joints to be imaged at multiple angles for enhanced pathological assessment. With individualized RF shims, the array provided full coverages and uniform excitations for both joints, demonstrated with high quality 2D TSE and 3D GRE (DESS and MEDIC) images.

Leeor Alon, Christopher Collins, Daniel Sodickson, Riccardo Lattanzi

Slotted antennas were demonstrated to be highly efficient coils for ultra high field magnetic resonance imaging. In this work, we elucidate the performance of such antennas using the ideal current patterns theoretical work.

Bart Steensma, M. Ertürk, Kamil Ugurbil, Luijten Peter, Dennis Klomp, van den Berg Nico, Gregory Metzger, Alexander Raaijmakers

The combined use of loops and dipoles as transmit elements is investigated at 7 T and 10.5 T. A 8 channel loop/8 channel dipole setup is compared to a 16 channel dipole setup at both field strengths. It is found that combining loops and dipoles enhances transmit performance at both field strengths. The 8 loop/8 dipole transmit setup is the best performing setup at both field strengths. Additionally, increasing the channel count from 8 to 16 channels provides an almost 50% reduction in SAR_10g/(B₁⁺)² at 10.5 T.   

Elizaveta Motovilova, Yang Gao, Zhihua Ren, Xiaotong Zhang, Shao Ying Huang

This study presents a numerical evaluation of a novel RF coil array for human head imaging at 7T. The 8-element coil was developed using a metamaterial concept. As the main advantage of a metamaterial transmission line is that the uniformity of RF-magnetic near field does not dependent of the TL’s physical length, we applied this meta-TL concept to a loop in order to achieve a larger coverage of B₁⁺-field. Numerical comparison to conventional designs demonstrate an improved B₁-field homogeneity of the proposed coil. Preliminary experimental studies show a reasonable agreement with simulations.

Bernhard Gruber, Arjan Hendriks , Cezar Alborahal, Bas Brussen, Tim Leiner, Gustav Strijkers, Dennis Klomp, Martijn Froeling

High-density coil arrays can be used to accelerate MRI. Here we present the results from measurement-based extrapolations of a 256 Channel Cardiac Array Coil obtained by 16 sequential scans of a 16 Channel Array to assess acceleration performance and sensitivity constraints for 3T MRI. With element sizes of 55 mm x 33 mm, tissue load remains dominant at the 3T Larmor frequency of water, while SENSE accelerations can go up to 20-fold at low g-factors. These results motivate the design of a 256 channel cardiac array for accelerated 3T MRI.

Suk-Min Hong, Chang-Hoon Choi, Jörg Felder, Arthur Magill, N. Shah

A dipole antenna achieves good isolation from a loop coil when it is located over the centre of a loop coil. Such an arrangement can be used as a dual-tuned coil, by tuning the dipole and the loop to the ¹H and X frequencies, respectively. At 3 T, however, the length of a dipole antenna is too long to be of use for brain applications. In this study, we bent the dipole antenna around the head to overcome the length problem. We then evaluated the feasibility of combining two dipole antennae and a 4-loop array for ¹H/³¹P application.

YongHyun Ha, Arthur W. Magill, Chang-Hoon Choi, N. Jon Shah

In this work we investigate the transmit and receive performance of a probe employing such switching, using a simple loop coil tuned to 45 and 169 MHz for the detection of ²³Na and ¹H, respectively, at 4T. PIN diode switched-capacitor networks work well under forward bias, but perform poorly in reverse bias. Specifically, a high reverse bias voltage is required to allow operation over a realistic range of RF transmit voltages. This makes such switched-capacitor networks unsuitable for use in transmit probes. However, they can be used in receive-only probes, because the voltages present on the loop are much smaller.

YongHyun Ha, Chang-Hoon Choi, N. Jon Shah

In this work, we designed a double-tuned ¹H/²³Na four-ring birdcage coil with a modification that entailed folding the outer end-rings by 90 degrees to overcome the available space limitation. And  ²³Na SNR of the folded four-ring birdcage coil reached more than 93% of that obtained with the single-tuned birdcage coil. One benefit of folded four-ring birdcage coil compared to conventional four-ring birdcage coil is that there is no space restriction. This helps to build double-tuned coils that have a smaller diameter, leading to higher filling factors.

Victor Taracila, Louis Vannatta, Robert Rainey, Miguel Navarro, Aleksey Zemskov, Fraser Robb

In MR coils or MR table there are multiple cables. Their presence is not desirable because they distort the B1 field; therefore multiple RF traps are distributed along the cable length to minimize induced cable currents. Tuning and performance of the MR cable traps’, also called cable baluns, on the cable are always difficult to predict, because the cable shape and position may vary. A coaxial half-wave cavity resonator is shown to be a precise tool to test cable balun assembly. It facilitates precise measurement of a balun’s coupling to the cable, its loss, and coupling to neighboring baluns.

karthik lakshmanan, Ryan Brown, Christopher Collins, Graham Wiggins

RF coils for multi-nuclear imaging require scanner-specific front-end interfaces that can limit their compatibility to one particular scanner platform. On the other hand, an intermediate interface that allows legacy coil compatibility with modern scanner architecture can be valuable in large institutions that operate a variety of scanners. In this work we describe the tools to build an intermediate interface with electronically controlled low-loss RF and DC signal pathways to provide a flexible means to route signals between the coil and scanner. While the tools are generally applicable to a variety of platforms, we focus on enabling compatibility between legacy multinuclear coils and a current scanner platform.

Stefan Rietsch, Stephan Orzada, Sarah Handtke, Sascha Brunheim, Mark Ladd, Harald Quick

Receive-only (Rx) radiofrequency (RF) arrays are widely used in the clinical environment at 1.5 and 3T. At 7T, there is by default no integrated RF body coil. Yet, a 32-channel Tx/Rx body coil built into a 7T MRI system was recently presented. Consequently, this paves the way for 7T body imaging using this coil for Tx and local coils to receive the RF signal. In this work we present a 32-channel Rx-only coil for 7T and evaluate SNR boost and acceleration capabilities of one 4-channel building block.

Stefan Rietsch, Stephan Orzada, Andreas Bitz, Marcel Gratz, Mark Ladd, Harald Quick

Remote radiofrequency (RF) body coils are broadly used as built-in body RF coils for signal transmission in clinical MR systems at 1.5 and 3T. For ultra highfield MR at 7T, remote body coils in conjunction with pTx systems have recently been presented. In this work we present a modified micro stripline RF element with meanders and investigate the performance of a 7T remote RF transmit array for body imaging applications featuring 8 of these elements concerning coupling, degrees of freedom within the B₁⁺ fields, distribution of losses, power efficiency, and SAR efficiency.

Abdullah Amin, Bhumi Bhusal, Tanvir Baig, Robert Deissler, Laith Sabri, Ozan Akkus, Michael Martens

Control of strain development in an MgB₂ based full body MRI magnet is a challenge towards realizing a conduction cooled system. It is possible to alter the strain development in an MRI magnet by modifying the coil winding support conditions and by varying the winding stress on the wire across the layers. A multiscale multiphysics model is employed to study the strain comparison by varying support conditions and winding prestress. Results conclude, radial support with constant winding prestress generates about 50% less stress and 42% less strain compared to no mandrel support.

Tijl van der Velden, Quincy van Houtum, Vincent Boer, Peter Luijten, Jeroen Siero, Dennis Klomp

In this work, a method is presented where a whole-body gradient system corrects for eddy currents induced by an unshielded gradient insert coil. A single-axis unshielded gradient breast insert coil was positioned in a 7 tesla whole body MR system. Field cameras were used to analyze the eddy currents and validate the proposed method.

Ali Aghaeifar, Irena Zivkovic, Christian Mirkes, Theodor Steffen, Klaus Scheffler

The homogenization of static magnetic field (B0) is necessary for MR imaging. The unwanted B0 inhomogeneity becomes more pronounced in ultra high field, and the scanner's inbuilt shim setup can not compensate the B0 fluctuation as is needed. Here we propose to use combined setup of the multi-coil approach and the scanner's shim setup to achieve higher homogeneity of B0 field. We employed custom-built multi-coil for slice-wise shimming in combination with the scanner's shim setup for global shimming. The results show improvement about 50% compare to dynamic shimming alone in the most of the slices.

Shahin Pourrahimi, Jerome Ackerman, John William, Nadder Pourrahimi, Alexey Kaplan

In a project to develop a compact MRI limb scanner for orthopedic and metabolic bone disease applications we developed a three-bore 1.5T magnet with the following design goals: ability to operate the magnet in a small point-of-care space, elimination of liquid cryogens for installation or operation, a comfortable patient experience while scanning knees, ability to tilt the magnet to accommodate patients rather than requiring patients to accommodate to the magnet, and capability for conventional and solid state proton and phosphorus MRI for metabolic bone disease assessment.

Jiazheng Zhou, Pu-Yeh Wu, Jason Stockmann, Fa-Hsuan Lin

We used numerical simulations to study the relationship between attainable field homogeneity and the number as well as the orientation of shim coils in a multi-coil shim array. We found that, constrained the same number of shim coils, arranging shim coils in three orthogonal directions can provide the best shimming. Inspired by simulations, we propose a design of the integrated RF-shim coil at 3 T to place shim and RF coil orthogonally.

Hector Sanchez Lopez, Luca Zilberti, Oriano Bottauscio, Mario Chiampi, Xiaodong YANG, Yajie XU

This work presents a new shielding method capable to reduce E-peak field values by minimizing the infinite norm of the induced current density. The target volume (“organ”) is surrounded by a conductive surface “shell” where the infinite norm of the induced current density is minimized thereby producing a uniform distribution of the E-field inside the target volume and its surrounding. The method was effectively applied in the design of a whole body gradient coil with E-field control. E-field reduction larger than 10% are registered in a human phantom model. Further reductions in E-field is possible by compromising the coil performance.

Daniel Martire, William Handler, Colin McCurdy, Justin Peterson, Blaine Chronik

A method to design and numerically optimize a gradient field exposure system for testing medical devices is presented. Magnet windings are modelled as small current elements in space, and dimensions of a coil capable of emulating the switching rate and strength of MRI gradient fields are chosen by a grid search of parameter space. A buildable option capable of achieving 1.2% homogeneity over an 8 cm DSV, a slew rate of 246 T/s, and a maximum field shift of 68 mT was determined to be sufficient for our application and for satisfying relevant elements of ISO/TS 10974.

Koki Matsuzawa, Katsumi Kose, Yasuhiko Terada

 Designing gradients coils with arbitrary geometries has been realized by matrix inversion optimization techniques. Use of a truncated singular value decomposition (SVD) is promising because magnetic field accuracies are controlled by choosing the appropriate SVD eigenmodes. However, in the SVD method, the gradient performances, such as inductance and power dissipation, cannot be optimized. Here we proposed a new strategy to optimize a desired coil performance. A key feature is the use of a genetic algorithm to optimize the appropriate combination of SVD eigenmodes. The concept is demonstrated for a biplanar geometry, and would be readily applicable to arbitrary geometries.

Reina Ayde, Claude Fermon

Mixed sensors coupled to tuned flux transformer could more effective than classical tuned coils in detecting MRI signals on a very low field range. In order to compare later on their effectiveness, first, a very low field head MRI system (8.4 mT) is developed. Homogeneity, gradients strength, excitation and reception coils were adjusted. A homogeneity of 84 ppm was achieved in a quasi-open configuration. The amplitude of each gradient was 100 times lower than at high field but sufficiently high to achieve a resolution of less 2 mm x 2 mm x 2 mm. Images with a 3D imaging acquisition without pre-polarization technique nor magnetic shielding room were achieved.

Koki Matsuzawa, Katsumi Kose, Yasuhiko Terada

Small gradients are ideal in performance. Vertical-field MRI systems use biplanar gradient coils, and the coil sizes are no smaller than the magnet gap. Here we propose the oval geometry for gradient coils for vertical-field MRI to increase coil performance, Oval coils could be smaller than biplanar coils with maintaining the high accessibility and gradient linearity. Moreover, oval coils are preferable from the viewpoint of heating problems, because the gradient heat is efficiently cooled by air. In this study, we designed and constructed oval gradient coils for a 0.3 T, open MR scanner, and demonstrated the validity of the concept.

Irena Zivkovic, Iliya Tolstikhin, Bernhard Schoelkopf, Klaus Scheffler

At high magnetic fields B0 inhomogeneities are more pronounced and B0 shimming becomes very important. Dynamic or slice based shimming always provides better results than global or shimming in a volume. For shimming in a small volume, we propose a setup composed of irregularly shaped coils. Performances of the proposed setup are compared to performances of the configuration composed of only loop elements. The setup with irregular coils shows improved performances over the setup containing only loop elements. Future work should validate performances of the proposed setup on different volume sizes and different brain’s B0 maps.

Tijl van der Velden, Carel van Leeuwen, Erik Huijing, Martino Borgo, Peter Luijten, Dennis Klomp, Jeroen Siero

A lightweight insert gradient coil was constructed for high resolution brain imaging. The coil was designed as a single-axis unshielded coil to accelerate EPI readouts. The resulting coil weighs 45 kg and can be quickly positioned in the scanner by two persons. Theoretically, a gradient strength of 210 mT/m can be achieved with a slew rate of 1088 T*m^-1*s^-1 when driven at 400V/600A. In a 7 tesla scanner, an efficiency of 0.35 mT*m^-1*A^-1 with a slew rate of 800 T*m^-1*s^-1 was measured. Experiments on five healthy volunteers resulted in no experiences of nerve stimulation.

Moriel NessAiver

As part of mandated yearly performance evaluations on over 120 GE, Siemens, Philips and Toshiba 1.5T scanners, the ACR phantom was used to make 2555 measurements of RF slice profiles and thicknesses.  Aggregated slice profiles are plotted showing clear differences between vendors both in terms of ‘squareness’ and FWHM thickness.  With a target slice thickness of 5.0 mm the measured thicknesses ranged from 4.21 to 6.65 mm!  The affect that interslice gap has on measured profiles (RF crosstalk) is demonstrated for T1 weighted sequences.  A very surprising dependence of measured thickness on slice position on the ACR phantom is demonstrated. 

Jonathan Weine, Florian Maier, Daniel Polak, Reiner Umathum

Methods for simultaneous excitation and acquisition enable measurements of signals with ultrashort T2* relaxation times. In this work, a method was developed and implemented to analogously compensate leakage of the excitation pulse into the receiver channel due to imperfections in coil tuning and the quadrature hybrid utilized in cSWIFT setups. The setup was enhanced with an embedded system, a vector modulator and a summing unit to subtract the leakage from the signal. Feasibility of the real-time compensation was demonstrated. Leakage was reduced by up to -40 dB.

Michael Muelly, Paul Stoddard, Shreyas Vasanwala

MRI has advantages compared to other radiologic modalities in terms of tissue visualization, versatility, and lack of risks associated with ionizing radiation. However, cost of MRI is often the limiting factor favoring other modalities. Using historical scanner data and a Monte Carlo type discrete event simulation, we investigated how estimating exam length on the basis of patient demographics and dynamic block lengths affect mean patient wait times and schedule fill rate. In our simulation we are able to significantly lower mean patient wait times and optimize the schedule fill rate, which would theoretically result in lower cost per exam while enhancing patient satisfaction.

Yee Eun Kim, Thomas Neuberger, Gangchea Lee, Lara LaDage

In this work, Eastern Fenced lizards, a non-model species known for high neurogenesis, were used to explore the extent of adult brain plasticity after exposing the animals to a complex environment and inmates. To conduct this study a MR setup for in-vivo lizard imaging was designed, constructed and tested. High resolution baseline in-vivo three dimensional lizard brain MR microscopy data sets were acquired and analyzed. The high quality of the images will allow to detect any brain volume changes after exposing the lizards to the enriched environment and having them scanned a second time.

Huijun Yu, Mohamed Hamed, Sebastian Littin, Feng Jia, Stefan Kroboth, Maxim Zaitsev

An open source waveform generator based on Pulseq (open-source pulse sequence programming environment) for emerging matrix coils was developed, with the channel count of up to 64. The FPGA development board integrated with USB3.0 is used to store the waveform data and generate the waveform in real-time when external trigger signal is activated. The generator software was written in Python 2.7 with a queue structure.

Michael Muelly, Paul Stoddard, Shreyas Vasanwala

The complexity of MR scanners results in significant variability in the quality of images produced, in some cases requiring clinical expertise to recognize suboptimal images. Deep convolutional neural networks are an emerging technique with potential clinical applications. We aim to investigate whether deep convolutional neural networks could be trained for three MR image quality control classification tasks: 1) Recognize adequacy of MR elastography wave propagation, 2) determine whether rectal gas susceptibility artifact obscuring the prostate is present, and 3) determine scan technique in unlabeled images. Using the Inception v4 deep convolutional neural network we found high classification accuracy for two out of these three problems suggesting the potential to automate certain aspects of MR quality control.

Sossena Wood, Tales Santini, Narayanan Krishnamurthy, Shailesh Raval, Tamer Ibrahim, PhD

In this work, a developed refillable multi-compartment 3D-printed head phantom (established from MRI scans obtained in-vivo) was compared to a homogeneous commercial spherical phantom, the phantom itself with homogeneous loading in all of its compartments and in-vivo (the same volunteer on whom the phantom was based).  Through B1 mapping and SAR analysis within an RF coil, the heterogeneous multi-compartment head phantom results were most accurate to the in-vivo volunteer.

Floris Jansen, Mark Fries, Tuoyu Cao, Mehdi Khalighi, Chang Kim

Accurate quantitation in PET requires good stability of the detector gain. The challenging thermal environment of the detector in a PET/MR system (proximity to gradients, induced eddy currents, heat from RF shield, ...) makes accurate temperature compensation important. Current solutions rely on characterization of detector response together with real time temperature measurement for a predictive (open loop) gain control. This work presents a method of gain control that operates in real time by analyzing spectral information of singles events, permitting closed loop gain control in the presence of temperature gradients or count rate variations.

Filiz Filci, Aylin Dogan, Gokhan Cansiz, Bulent Sen, Volkan Acikel, Ergin Atalar

In this study, prototype hardware of FPGA Controlled Multi-Channel All-Digital Transmitter for Parallel Magnetic Resonance Imaging is presented. The transmitter system consists of a RF power amplifier and a digital signal generator to feed each channels and a user interface computer to control the signal type, amplitude, phase, and frequency of targeted pulse. Digital signal generator uses a novel method which is IQ Pre-Modulation Delta Sigma Modulation Based Digital Single Side Band modulator and enables frequency, phase, and amplitude modulation schemes. The prototype hardware is produced to feed a 12-channel RF-coil, thus RFPA module consists of 12-PA are implemented.  

Samarth Singh, Darshan Keelara, Chennagiri Padma, Rashmi Rao, Imam Shaik, Sairam Geethanath

A cost-effective RF Signal Transmit-Receive chain with independent transmit and receive coil was designed with inexpensive off-the-shelf electronic components, costing around 175 US dollars. A Direct Digital Synthesizer (DDS) module was controlled using an Arduino Uno R3 microcontroller board. RF pulses were timed to precision using Arduino IDE, and the 405 kHz sine wave required to operate a 9.5 mT system was pulsed to a transmit coil. This signal was detected successfully by a custom-made surface coil. While the transmit, pulse was at 1.12Vpp from the DDS module, the surface coil successfully picked up a 1.75 Vpp signal.

HUI HAN, John Stager, Hsin-Jung Yang, Na Zhang, Sizhe Guo, Zhuoqi Li, Yicheng Wang, Debiao Li

We propose a new general MR coil concept with integrated RF and Bo shimming applicable to almost all MRI coils and systems. Innovative geometrical decoupling methods are proposed to bring the distance between separate shim and RF loops to zero millimeters and to make shim loops physically free from the RF loops. Therefore, both RF and shim coils can be in close proximity to the subject and be designed independently to maximize the performance of each function. It also opens a new window to integrate shim and RF coils or other coils in the constricted scanner bore space. 

Jonathan Howard, Rexford Newbould

A significant limiting factor for electronic devices within the scanner room is the electromagnetic interference (EMI) that they generate. Also, electromagnetic radiation from the scanner can interfere with the safe operation of electronics in close proximity to the scanner. We describe the development of an approach that enables researchers to fabricate inexpensive and reliable shielded enclosures without access to extensive engineering facilities. Our investigation explores the relative advantages and disadvantages in the design and construction of three different shielded enclosures and concludes with a performance evaluation by measuring the frequency dependent attenuation of electromagnetic signal intensity.

Aurélien Massire, Henitsoa Rasoanandrianina, Thorsten Feiweier , Manuel Taso, Aude-Marie Grapperon, Shahram Attarian, Maxime Guye, Jean-Philippe Ranjeva, Annie Verschueren, Virginie Callot

Amyotrophic lateral sclerosis (ALS) may benefit from unique contrasts and high-spatial resolutions provided by ultra-high field brain MRI. This also stands for spinal cord; nevertheless spinal cord imaging at 7T has lagged considerably behind brain investigations until recently. In this work, we propose a multi-parametric quantitative MR imaging protocol (T₁, T₂*, DTI, CSA), in an acquisition time compatible with clinical research (50min), to comprehensively investigate spinal cord diffuse alterations in neurodegenerative diseases such as ALS. With imaging along the whole cervical cord and medulla, theses multi-parametric acquisitions have the potential to provide new insights for the study of ALS.

Bixia Chen, Toshinori Matsushige, Markus Kraemer, Philipp Dammann, Sören Johst, Stefan Maderwald, Marc Schlamann, Harald Quick, Mark Ladd, Ulrich Sure, Karsten Wrede

Collateral networks in Moyamoya angiopathy (MMA) have a complex angioarchitecture. Delineation of deeply seated collateral networks (DSCNs) and image quality were prospectively evaluated in 10 patients using 7 Tesla TOF MRA and MPRAGE in comparison with conventional DSA. Seventy DSCNs were detected in DSA, 79 in TOF MRA, and 54 in MPRAGE. Detection of DSCNs was significantly better in TOF MRA than in DSA and MPRAGE. TOF MRA and DSA image quality were comparable, both were better than MPRAGE. Delineation of DSCN pathways in MMA using 7 Tesla TOF MRA was excellent and comparable to DSA.

Mark Chiew, Wenwen Jiang, Peder Larson, Brian Burns, Peter Jezzard, Albert Thomas, Uzay Emir

In this study, we have developed and demonstrated a GOIA-semi-LASER sequence with density-weighted (DW)-concentric rings trajectory (CRT) that performs robustly at 7 Tesla and within a clinically feasible acquisition time. DW-CRT has been validated in a series of phantom experiments and its feasibility assessed in a healthy volunteer with an in-plane resolution of 5×5 mm². Experiments qualitatively demonstrate the advantage of DW-CRT over uniformly-weighted (UW)-CRT in terms of its improved resolution and reduced contamination of spectra from neighboring voxels. 

Sigrun Goluch, Roberta Frass-Kriegl, Michael Pichler, Martin Gajdošík, Juergen Sieg, Ewald Moser, Martin Meyerspeer, Martin Krššák, Elmar Laistler

Carbon-13 (¹³C) MR spectroscopy (MRS) requires RF coils enabling acquisition at two different Larmor frequencies, namely at the ¹H frequency (f_1H=297.2 MHz) for scout imaging, B₀ shimming and proton decoupling, as well as at the ¹³C frequency (f_13C=74.7 MHz) for acquisition of the carbon spectra at 7T. In this work we present preliminary data on the development of a dual tuned ¹³C/¹H coil array for calf muscle studies at 7 T, including simulation, bench and MR measurements in a glucose phantom.

Luc van Vught, Robert de Meel, Jedrzej Burakiewicz, Stijn Genders, Martine Jager, Irene Notting, Jan Verschuuren, Hermien Kan, Jan-Willem Beenakker

Current diagnostic tools fail to accurately assess the condition of the eye muscles and orbital fat in ocular diseases. We have developed a high-resolution 7 Tesla quantitative MRI-protocol of the eye and evaluated its clinical value for Graves' orbitopathy and myasthenia gravis. The scan protocol proved to be robust against eye-motion and extra-ocular muscles were easily segmented from the orbital fat. Patient data showed elevated muscle fat fractions for both conditions compared to healthy subjects. Since the method quantifies the condition of the tissues, which otherwise can only be assess via an invasive biopsy, it  potentially is an efficient technique to assess treatment response.

Tamer Ibrahim, Tales Santini, Shailesh Raval, Narayanan Krishnamurthy, Sossena Wood, Jung-Hwan Kim, Yujuan Zhao, Xiaoping Wu, Essa Yacoub, Howard Aizenstein, Tiejun Zhao

Several major obstacles still face neuro UHF imaging including scanning and preparation time for every subject (for TX arrays) and RF intensity limitations due to increased local/global power deposition. The solutions provided and compared in this work represent non-subject specific configurations (combined mode NOVA coil system, PTX NOVA coil system operating in quadrature, and combined mode 16Tx/32Rx Tic-Tac-Toe coil system) and subject specific configurations (PTX NOVA coil system RF-shimmed for each subject). Experimental results shows significant drop in the B1+ field intensity in the left temporal lobe and cerebellum in the NOVA coil systems, issue alleviated with the Tic-Tac-Toe design.

Han-Joong Kim, Hyunwoo Song, Sang-Doc Han, Phil Heo, Donghyuk Kim, Yeonjin Choi, Kyoung-Nam Kim

In this study, a bilateral monopole antenna was proposed to have ring element of existing ring-monopole as common ground and to consist of two interlocking monopole antennas along z-axis to improve lopsided |B₁| field toward the ground plate. Geometry of the proposed bilateral monopole antenna was optimized with EM simulation then optimized antenna was compared with a transceiver array coil and a birdcage coil for quality verification. Even with worse power consumption, the proposed bilateral monopole antenna can be an alternative for existing RF coils such as transceiver array coil and birdcage coil due to its improved |B₁⁺| field uniformity.

Christian Bruns, Tim Herrmann, Markus Plaumann, Chang-Hyun Oh, Chulhyun Lee , Suchit Kumar, Johannes Bernarding

In order to provide a system, which allows imaging of ¹⁹F MR contrast agents, an in-house-built ¹⁹F/¹H transmit/receive system for 7 T was successfully tested in a human whole-body 7 T MRI system. This system enables the measurement of concentrations of 1.85 mM. For this approach we used a ¹⁹F tuned coil which provided still enough signal gain at the proton frequency to allow ¹H imaging for comparison. This showed the possibility of using ¹⁹F as contrast agents with a quite simple coil design in comparison to other dual tuned approaches.

Gangchea Lee, Navid Gandji, Seokwon Jung, Elena Semouchkina, Michael Lanagan, Thomas Neuberger

High performance Radio Frequency resonators (RF resonators) produce strong and homogeneous magnetic fields. Due to their large sizes, patch antennas have hardly been considered to be used as RF resonators in Magnetic Resonance Imaging (MRI), especially at high fields. In this work, a newly developed miniaturized patch antenna with high dielectric material plugs was designed, simulated, built and tested at 14.1 T. The simulated and experimental magnetic fields were compared to confirm the performance of the fabricated patch antenna as a RF resonator for MRI.

Syu-Jyun Peng, Yue-Loong Hsin

We proposed a method to precisely visualize subdural strip and grid electrodes in relation to underlying Brodmann’s area labeled cortical gyration. We transformed a reference brain labeled with Brodmann’s areas to match individual brain. Then we registered the digitalized electrodes from post-implant CT onto the anatomically labeled brain MRI.

Huajie Jiao, Rongrong Zhu, Kaining Shi, Yong Yang, Weiheng He

Summary: Exophthalmos caused by muscle thickening and fat increasing in orbit is the typical symptom in hyperthyroidism, which impairs multiple systems as the auto-immune disease. From this study, we found the increase of percentage of fat and T2* value using the fat quantification analysis package, which indicate the accumulation and differentiation of fat-oriented cells, inflammation cells infiltration and collagen mucous change. Therefore, the characteristics of fat change in orbit can be evaluated by the transverse six-echo proton density fat fraction (PDFF) sequence (mDIXON-quant) technique in early-stage hyperthyroidism without significant manifestation of eyes.

Gangchea Lee, Jeongin Choi, Eberhard Munz, Ibrahim Ozbolat , Michael Lanagan, Thomas Neuberger

High resolution, and high Signal to Noise Ratio (SNR) images in Magnetic Resonance Imaging (MRI) require long imaging times. In this work a setup for two separate shielded scroll coils with a common gradient and magnet was introduced to produce two independent three dimensional MRI data sets for MR microscopy. The RF coils and shields were designed, fabricated, and tested. 3-D printed cell samples were imaged using the fabricated set up. Overall, two samples could be acquired with a larger field of view and a similar SNR in the same time compared to a single sample in a solenoid.

Michael Woletz, Sigrun Goluch, Allan Hummer, Christian Windischberger

Tissue-equivalent phantoms with well-defined T₁- and T₂-relaxation behaviour are often required for sequence optimisation and quality control purposes. Based on numerous T₁ and T₂measurements at 3T and 7T with varying concentrations of Agarose and gadopentetate dimeglumine (Magnevist), we herein present a formula for creating phantoms with T₁-values between 700 ms and 3000 ms and T₂-values between 30 ms to 250 ms at both field strengths. 

Bixia Chen, Toshinori Matsushige, Sören Johst, Stefan Maderwald, Lale Umutlu, Ulrich Sure, Harald Quick, Mark Ladd, Karsten Wrede

General advantages of ultra-high-field MRI at 7 T in cerebral arteriovenous malformations (AVM) imaging have been shown recently. This prospective clinical study (10 adult patients) aims to evaluate signal characteristics of AVM feeders, nidus and drainage using 7 T MRI (TOF, MPRAGE, SWI). AVM feeders, nidus and drainage were evaluated by 2 raters. Additionally, AVMs were segmented manually and signal intensity histograms were calculated for the extracted feeders, nidus and drainage, respectively. As previously shown, 7 T MRI has excellent imaging results regarding vessel delineation in AVMs. However, identification of the AVM architecture remains challenging due to signal heterogeneity.

Vitaliy Zhurbenko, Vincent Boer , Esben Petersen

High field MRI coils are often based on transmission line resonators. Due to relatively short wavelength of RF fields, such coils produce uneven field patterns. Here we show, that it is possible to manipulate magnetic field patterns of microstrip resonators in both planes (sagittal and transverse) segmenting stripe and ground plane of the resonator with series capacitors. The design equations for capacitors providing symmetric current distribution are derived. The performance of two types of segmented resonators are investigated experimentally. To authors’ knowledge, a microstrip resonator, where both, strip and ground plane are capacitor-segmented, is shown here for the first time.

A S M Zahid Kausar, David Reutens, Ewald Weber, Viktor Vegh

Birdcage coils have a number of limitations, especially at ultra-high field. Monopole antenna arrays have been proposed as an alternative to birdcage coils, as the design is simpler and they do not use capacitors. We evaluated the potential of using monopole arrays for 3T and 7T MRI brain scans. To be able to benchmark performance, we compared the field produced by the monopole array with the field produced by the birdcage coil. We show that monopole arrays can potentially achieve better field homogeneity and sensitivity than the birdcage coil. We fabricated a monopole array and demonstrated decoupling between individual monopoles. 

Atefeh Kordzadeh, Nicola De Zanche

This abstract introduces the TEM horn antenna as an efficient element for imaging the human body at high fields. The horn was designed for 200.4 MHz, simulated in HFSS adjacent to a torso-size phantom, and fabricated using 3-D printing. Transmit/receive imaging measurements were performed at 4.7T. Flip angle maps are compared to the simulation results.

Kurt Bockhorst, Jarek Wosik, Ponnada Narayana

We report on the performance and development of a 300-MHz (7 T) cryogenic receive- only surface coil for MRI of rat brain. Practical performance limits of the cryo-coil were tested such as SNR gains at 55 K for a 19 mm in diameter Cu coil and its frequency stability over long (up to a few days) scans. 3D-RARE isotropic images of ex-vivo rat brain up to 512 slices with outstanding isotropic resolution of 34 μm were acquired showing structural details not seen with conventional small animals coils. In addition, a comparison of such images with matching histological plates is discussed.

Sang-Doc Han, Hyunwoo Song, Phil Heo, Han-Joong Kim, Donghyuk Kim, Yeonjin Choi, Yeunchul Ryu, Kyoung-Nam Kim

With the facilitated approach of ultra-high frequency (UHF, over 7T) magnetic resonance imaging (MRI) system, multi-nuclei (MN)-MRI can be regarded as one of critical means for diagnose due to its capability of acquiring non-invasive metabolic information^{1, 2}. In this study, a radiofrequency (RF) coil that can selectively receive two nuclei signals, the proton (¹H) and the sodium (²³Na), by controlling PIN diodes is proposed. Since ¹H images show clear anatomical structure where ²³Na show critical in-vivo metabolisms, acquired MN magnetic resonance (MR) images using the proposed MN RF coil have capabilities to assist diagnose visually³.

Bu Park, Sunder Rajan, Joe Murphy-Boesch, William Koch, Charity Stagg, Brent McCright

Numerical simulations and experimental verification of the feasibility are shown to improve B₁ uniformity of a commercial ¹⁹F RF coil with addition of a secondary resonator using inductive coupling without changing the RF coil at 7.0T animal MRI. The designed resonator was placed on the opposite side of the imaging object from the ¹⁹F surface coil to improve the field uniformity. Numerical simulations and related experiments using a ¹⁹F phantom show significant improvement of |B₁⁺| and image uniformity, i.e., about 26%. The mouse leg image of ¹⁹F/¹H with the designed resonator is shown as an example of potential pre-clinical applications.

Gang Chen, Christopher Collins, Daniel Sodickson, Graham Wiggins

At clinical field strengths, the contribution of coil noise is often characterized by the Q-ratio, the ratio of the loaded Q and unloaded Q. Because of the inconsistent contribution of radiation loss and frequency drift in unloaded and loaded cases, it is difficult to characterize the body noise dominance of a dipole antenna by conventional Q ratio at 7T. Here we propose a new approach using a measure of Q when a dipole antenna is well shielded. The shielded/loaded Q ratio estimates the relative noise contribution from coil loss, similar to unloaded/loaded Q ratio for surface coil at low frequencies.

Tales Santini, Junghwan Kim, Sossena Wood, Narayanan Krishnamurthy, Shailesh Raval, Tamer Ibrahim

7T Foot and ankle has been previously explored1.  A four-channel Tic-Tac-Toe (TTT)  transmit-only (Tx-only) array2,3 and a four-channel receive-only array were developed and combined to demonstrate the feasiability of high signal-to-noise ratio (SNR) foot and ankle imaging at 7T MRI.  The experimental measurements of magnetic field distribution responsible for excitation (B1+) is in agreement with the finite-difference time-domain (FDTD) simulations and the SAR is within the FDA safety limits for the entire lower leg and foot (peak SAR ~ 7W/Kg/10g of tissue, average SAR ~ 1W/Kg/10g of tissue per continuous average field B1+ = 1.97uT).  In-vivo proton density TSE and T2DESS images were acquired.

Mingyan Li, Ewald Weber, Jin Jin, Yasvir Tesiram, Thimo Hugger, Simon Stark, Feng Liu, Sven Junge, Stuart Crozier

This work investigates the feasibility of incorporating an additional RF element to the rotating RF coil (RRFC) to improve imaging performance. The transmit profiles of the two-element rotating coil array were optimised by adjusting the interference patterns formed by two channels with varied relative phase. Combined with the previously developed rotating imaging scheme, an optimal relative phase was determined to produce an image uniformity of 93%. 

Andrew Leynes, Yiran Chen, Subramaniam Sukumar, Duan Xu, Xiaoliang Zhang

The development and test of a triple-nuclear surface coil for simultaneous 1H, 13C, and 31P small animal imaging at 14.1 Tesla.

Eric Fiveland, Julia Prusik, Renee Linton, Jeffrey Ashe, Julie Pilitsis, Ileana Hancu

A detector for measuring and predicting the on/off state of cycling deep brain stimulation (DBS) was developed and tested in 6 patients.  3-electrode EKG measurements, amplified by a commercial bio-amplifier, were used as input for a custom electronics box (e-box). The e-box transformed the DBS waveforms into transistor-transistor logic (TTL) pulses and recorded their timing.  Following locking to each patient’s individual waveform, the e-box was shown to predict stimulation onset with an average absolute error of 112ms, 30 minutes after disconnecting from the patients.   Using this detector, stimulation can be accurately synchronized to fMRI acquisitions.

Jeroen Gemert, Wyger Brink, Andrew Webb, Rob Remis

High-permittivity pads can be used to improve B₁⁺ homogeneity and intensity in neuroimaging and body applications. Normally, finding the “optimal” pad for a specific region of interest involves evaluating many different pad designs using electromagnetic simulations, which is a very time-consuming approach taking hours to days of computation time. We propose a nonlinear optimization method based on model order reduction that allows us to design high-permittivity pads in less than 30 seconds.

Rita Schmidt, Assaf Tal, Andrew Webb

Magnetic resonance spectroscopy is a powerful technique for in-vivo measurement of metabolites, however its sensitivity is limited due to very low concentration of the metabolites. This is especially valid for studies of neurotransmitters such as glutamate and GABA. In this study, a new hybrid metasurface comprising of conducting strips and agar-gel was designed to improve MR sensitivity at 3T. The metasurface forms a compact and flexible pad which is placed in the vicinity of the region of interest. The measurements focused on MRS acquisitions including PRESS and MEGA-PRESS, showing an improvement in SNR of a factor of 1.75, 2 cm from the pad.  

Mingyan Li, Jin Jin, Ewald Weber, Yasvir Tesiram, Thimo Hugger, Simon Stark, Sven Junge, Feng Liu, Stuart Crozier

Precise image recovery for the rotating coil requires sensitivity estimation and iterative algorithm to remove motion artifact, but inaccurate sensitivity estimation can affect image reconstruction accuracy. Previously we developed a radial sampling scheme for the RRFC which avoids sensitivity mapping procedures by manipulating oversampled central k-space data. However, the overall reconstruction inaccuracy results from relatively sparse sampled outer k-space still remained. As a more robust and preferred imaging scheme in routine MRI scans, the Cartesian trajectory will be employed to develop an imaging scheme for the RRFC to overcome the abovementioned limitations and further reduce motion artifact.

Wyger Brink, Jan Paska, Jiying Dai, Jeroen van Gemert, Gang Chen, Graham Wiggins, Rob Remis, Christopher Collins, Andrew Webb

Dielectric materials enable additional control of the RF field in a particular RF coil. In this work we present a hybrid domain decomposition method, which allows for an efficient analysis of dielectric materials in the presence of coupled RF coil structures or coil array configurations.

Dean Darnell, Jonathan Cuthbertson, Yixin Ma, Naomi Morales-Medina, Sebastian Luce, Allen Song, Trong-Kha Truong

Implementation of wireless communications in an MRI scanner will reduce the complexity of the scanner by decreasing the number of wired connections and connectors. To enable wireless communication in the scanner, a new RF coil design is proposed which allows RF currents at the Larmor and wireless data frequencies to flow on the same coil element, thus enabling simultaneous MRI image acquisition and wireless data transfer with the same coil. 

Patrick Vogel, Stefan Herz, Philip Dietrich, Thomas Kampf, Volker Behr, Thorsten Bley

A percutaneous transluminal angioplasty (PTA) is a procedure to widen stenotic blood vessels in medical conditions such as coronary heart disease or peripheral artery disease. With the assistance of fluoroscopic guidance and radiopaque contrast agents, guidewires and balloon catheters are used to treat vascular stenoses. Magnetic Particle Imaging (MPI) is a very fast and sensitive tomographic imaging modality with the potential of real-time radiation-free 3D imaging. In this work the feasibility of performing a MPI-guided PTA in artificial stenoses with a traveling wave MPI scanner is demonstrated.

Gaspar Delso, Roie Manavaki, Florian Wiesinger, David Goldhaber, Floris Jansen

We present an evaluation, across multiple clinical sites, of the impact of prescan variability on head attenuation maps based on zero echo time imaging.

Dean Darnell, Devin Willey, Sebastian Luce, Allen Song, Trong-Kha Truong

Integrated parallel reception, excitation, and shimming (iPRES) coil arrays enable RF excitation/reception and localized B₀ shimming with a single coil array, but so far use an external DC power supply and require a B₀ map and a shim optimization for each subject, which takes additional time. Here, we propose a novel iPRES head coil array powered by an on-board MR-compatible battery that delivers fixed DC currents optimized in advance to shim an average subject's brain. This stand-alone, plug-and-play system does not require any subject-specific shim optimization, thus enabling a wider adoption of iPRES in clinical applications.

Chang-Hoon Choi, Lutz Tellmann, Jörg Felder, Christoph Lerche, N. Jon Shah

In a simultaneous MR-PET experiment, an RF resonator for MRI is placed inside the field-of-view of the PET scanner. Attenuation caused by RF coil components can cause severe artefacts in PET images if not adequately corrected. Although it may be possible to minimise subject-specific attenuation and scatter effects, correcting those due to the RF coil is still a challenging task. In this work, we have designed and constructed a number of RF coils constructed utilising a variety of copper conductors and evaluated their characteristics from the MR and PET points of view.

Frank Preiswerk, Cheng-Chieh Cheng, Pei-Hsin Wu, Lawrence Panych, Bruno Madore

Clinical cardiac MRI typically requires the use of electrocardiogram (ECG) leads to detect R-waves and synchronize the MRI acquisition accordingly. The magnetohydrodynamic effect can corrupt the ECG signal, sometimes making R-wave detection difficult, especially at higher field strengths. We are proposing here a practical and low cost ultrasound-based solution for detecting cardiac activity in a manner immune to the presence and strength of the B0 field. Equivalence was shown in cases where ECG gating worked well. In the future, the approach should prove most helpful as an alternative to ECG when the latter proves impractical, especially at higher field strengths.

Steen Moeller, Naoharu Kobayashi, Gregor Adriany, Djaudat Idiyatullin, Mike Garwood, Edward Auerbach

The development of a programmable high-speed triggering to enable progress in implementation of SWIFT on a Siemens scanner. First in-vivo images, at 50khz, using a linear T/R coil.

Alek Nacev, Ryan Hilaman, Sahar Jafari, Sagar Chowdhury, Lamar Mair, Pavel Stepanov, Dhruv Patel, Irving Weinberg

Directing magnetic nanoparticles to sites within biological tissues requires both strong magnetic field gradients and accurate images of the particles and underlying anatomy. Most modern MR imaging systems require always-on magnetic field sources such as permanent magnets or superconducting coils. These field sources limit the ability to control magnetic particles within the imaging volume. Due to these field sources having a high strength always-on magnetic field, there are additional safety concerns when attempting to integrate these sources into an intraoperative arena. We built a new magnetic field source design that is capable of adjusting its magnetic field strength while retaining a low power usage to improve portability.

Radim Barta, Andrei Ghila, Satyapal Rathee, B Fallone, Nicola De Zanche

Aluminum and copper conductors are compared for constructing radiologically transparent MRI surface coil detectors for use in a hybrid MRI - linear accelerator. Radiation dose to skin can cause serious reactions and skin dose is enhanced when materials are placed in the radiation beam. Therefore increases in skin dose due to surface coils must be minimized by optimized construction. A copper conductor causes a three-fold increase in skin dose compared to a similar thickness aluminum conductor. An aluminium coil (20μm thick) was used to image a phantom, yielding 93% of the SNR achieved with a copper tape coil (32μm thick).

Kelly Byron, Fraser Robb, Shreyas Vasanawala, John Pauly, Greig Scott

A compact wireless power transfer (WPT) system being used to power wireless patient coils would require a compact power amplifier that can operate inside the MRI bore.  A Class-EF power amplifier is designed and implemented that uses air-core inductors and is capable of driving the coupled resonant coils used for WPT with similar efficiency to a system that uses a large and expensive power amplifier that is outside the scan room.  This new power amplifier is very compact and is also very cost-effective.

Malathy Elumalai, Joshua Slade, Huadong Zheng, Thomas Mareci

Magnetic Resonance Imaging at higher field strengths has several design challenges that must be addressed for optimal performance and image resolution. We have developed a cantilever system that is suspended in the magnet to eliminate phase noise that are produced due to vibrations generated by gradient coils. The cantilever system has features such as detachable quadrature RF coils, animal cradle system with in-built water & anesthesia and tuning/matching capability outside the bore. The system is not only centered in all three axes but also has tuning capability in the z-direction from outside the bore so we could move the subject in and out to center in the bore.

Adam Maunder, Graham Norquay, Madhwesha Rao, Jim Wild

Monitoring of the ¹²⁹Xe polarization by NMR during spin-exchange optical pumping (SEOP) is vital for quality control and for experimental investigations into optimizing system running parameters. In this study, we present a  compact NMR spectrometer designed to improve user flexibility and reduce cost for online polarimetry on a ¹²⁹Xe SEOP system. A Java-based user interface was developed to control the system with an Arduino based hardware control. The performances of the user interface and hardware in routine ¹²⁹Xe NMR spectrometer measurements are demonstrated herein.

Arne Berneking, Adam Mehina, N. Jon Shah

The goal of this study is to demonstrate hybrid MR/PET scanner design optimization methods from an RF coil perspective with a focus on UHF MRI. Here, coil performances are investigated depending on different shielding distances to present simulation and measurement methods to include RF coil performances into the hybrid MR/PET scanner design. Moreover, integration of PET detector shielding and RF coil shield is investigated. The results of this study clarify that a trade of between a compact design, PET and RF coil performances is necessary and that RF coil performances can be optimized by an integrated shielding with an optimized configuration.

John Zhen, Robin Dykstra, Sergei Obruchkov

Magnetic Resonance Imaging has established itself as indespensible utility in health sector for over 3 decades, yet remained inflexible in its form factor. By taking advantage of modern advances in miniturisation and improved efficiency of electronic devices along with the developments of single sided magnet probes this abstract presents a handheld, battery powered portable MR spectrometer system which can be used for tissue analysis and sample charectarisation outside of an imaging suite.

Mohammad Mehdi Khalighi, Tuoyu Cao, Mark Fries, Timothy Deller, Floris Jansen, Gary Glover

In a simultaneous ToF-enabled SiPM PET/MR scanner, eddy currents induced by the changing gradient field lead to increased temperature around the PET detectors; this can change the detector gain and shift the position of the photopeak in the spectrum, reducing accuracy of the reconstructed image. Conventionally, peak stability is achieved by thermal monitoring system and adjusting the gain based on the temperature.  A more accurate gain control algorithm is presented, which analyzes the spectrum of single events detected on each device. Reconstructed activity of a PET phantom in extreme MR gradient switching is measured to remain stable, better than 0.5%.

Xiaoqi Wang, Hong Bai, Yadong Cui

A first attempt in utilizing the state of art visualizing technology - Virtual Reality to read MR angiography images. 

Frank Preiswerk, Jiarui Cai, Cheng-Chieh Cheng, W. Hoge, Pei-Hsin Wu, Lawrence Panych, Bruno Madore

Voltage or laser-light triggers are often used to synchronize auxiliary devices to the MR acquisition process. A very simple RF antenna and associated circuit is proposed here instead. The device is used here to trigger ultrasound probe firings, as part of a hybrid ultrasound-MRI system, but could be used for other purposes as well. Compared to scanner-generated triggers, advantages include: 1) vendor- and software release-independent, 2) available in the scan room, 3) no change to product sequences needed, and 4) the little device proved handy for pulse sequence debugging as well.

Andreas Pohlmann, Jason Millward, Paula Ramos Delgado, Daniel Marek, Didier Wecker, Ralph Wissmann, Helmar Waiczies, Thoralf Niendorf, Sonia Wacizies

MRI using i.v. administered fluorine-19 loaded nanoparticles (NPs) allows the tracking of inflammatory cell migration. The inherently low SNR limits the precise localization of 19F-labeled inflammatory cells, because large voxel sizes are needed to collect sufficient signal. To overcome this, we show here the first use of a novel 19F cryogenic quadrature RF surface probe at ultrahigh field to substantially boost SNR beyond that of state-of-the-art room temperature RF coils, while facilitating the acquisition of better spatially-resolved images within shorter scan times.