Kazuya Sakaguchi¹ and Yasuhiko Terada^1
1Institute of Applied Physics, University of Tsukuba, Tsukuba, Japan

 Most of gradients coils are cylindrical or planar, but deformed gradients that fit an object shape should have superior performance. A truncated singular value decomposition (SVD) is a design method for arbitrary shaped gradients, but the design process is time-consuming, especially for shielded gradients. Moreover, coil performance, such as coil inductance and power dissipation cannot be optimized. In this study, we proposed a new strategy that combines the SVD method with a meta-heuristic method for automatically optimizing desired performance for shielded gradients.

Reza Babaloo^1,2, Soheil Taraghinia¹, Volkan Acikel³, Manoochehr Takrimi¹, and Ergin Atalar^1,2
1National Magnetic Resonance Resarch Center (UMRAM), Bilkent University, Ankara, Turkey, ²Department of Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey, ³Aselsan, REHIS Power Amplifier Technologies, Ankara, Turkey

Gradient array systems can produce highly flexible spatial encoding magnetic fields. In the array structure, time fidelity of gradient current waveforms decreases due to high mutual coupling between gradient coils. Here we propose a closed-loop feedback in combination with feedforward to compensate for errors in the gradient current waveforms. A real-time digital PID controller is designed by considering the transfer function of the array system. The controller updates the applied voltage on the gradient coil by changing the duty cycle of pulse-width modulated (PWM) signals to decrease the error between desired and measured currents.

Yihe Hua¹, Desmond T.B. Yeo¹, and Thomas K.F. Foo^1
1GE Global Research, Niskayuna, NY, United States

Head-only gradient coil is not only more power efficient than the whole body system for high quality MR neuroimaging, but also reduces risk of peripheral nerve stimulation. In this abstract we compared two different head-only transverse gradient coil designs -- a non-folded design and a patient-end folded design, pointed out that the current turns on the connection region of the folded design that close to human body is more efficient to induce electric field and eddy current than the non-folded design in the neck, shoulder, chest and back. A connection-region turn-constrained folded coil design confirmed the observation.

Niklas Wehkamp¹, Philipp Rovedo¹, Elmar Fischer¹, Jürgen Hennig¹, and Maxim Zaitsev^1
1Radiology - Medical Physics, Medical Center - University Hospital Freiburg, Freiburg, Germany

Manipulating the Larmor frequency of a frequency-adjustable 1H field probe provides interesting new possibilities to excite and record the probe’s signal. Here, we present first proof-of-concept experiments that demonstrate the feasibility of selective off-resonant excitation of the probe. Free induction decays with the applied resonance offset current were recorded and characterized.

Martin Sandrink^1,2, Ruben Pellicer-Guridi¹, Jiasheng Su¹, Viktor Vegh¹, and David C. Reutens^1
1University of Queensland, Centre for Advanced Imaging, Brisbane, Australia, ²Departement of Engineering Physics, FH Muenster University of Applied Sciences, Muenster, Germany

The construction of a permanent magnet based 3D encoding system for an Ultra-Low field MR is presented and its initial characterization is presented. Proposed system moves a single permanent magnet along a prescribed helical path as proposed in our previous numerical study. This initial prototype is built to fit an existing ULF-MRI human extremity system. Preliminary results are in good agreement with the simulations. However, further studies are needed to identify the sources of error and improve the precision of the field estimations towards a practical encoding system.

Huan Hu¹, Juan A Sabate¹, and Ruxi Wang^2
1GE Global Research, Niskayuna, NY, United States, ²GE Aviation, Dayton, OH, United States

MRI gradient amplifier needs to provide current with extremely high fidelity to the commanded values of any arbitrary shape. Therefore, the control requires very accurate compensations of nonlinearities. One of the major sources is the deadtime among the power semiconductor devices. The existing deadtime compensation was to pre-test the specific system with different current commands and summarize a look-up table for use, which required lots of time and effort and cannot be used for different systems. This abstract demonstrates an adaptive deadtime compensation method which works well under different current commands and different systems without additional hardware cost.

Manuela B. Rösler¹, Roger Luechinger¹, David O. Brunner¹, Markus Weiger¹, and Klaas P. Pruessmann^1
1Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland

Gradient induced heating is relevant for RF coils used in recent high-performance gradient coils. In this abstract, we investigate the predictability of gradient induced heating on the basis of theoretical gradient field data. Furthermore, the heating of components usually used for coil construction e.g. different plugs, cables and shielding materials under intense gradient usage (EPI readout with 100 mT/m and 1200 mT/m/s at almost 100% duty cycle for 1 min) was measured. Depending on the position and orientation we observe temperature increases up to 67°C for an N-plug and 12°C for a coaxial cable.

Sheng Shen^1,2, Zheng Xu¹, Neha Koonjoo^2,3,4, and Matthew S. Rosen^2,3,4
1Chongqing University, Chongqing, China, ²MGH/A.A. Martinos Center for Biomedical Imaging, Cambridge, MA, United States, ³Department of Physics, Harvard University, Cambridge, MA, United States, ⁴Harvard Medical School, Boston, MA, United States

The gradient subsystem is an essential part of an MRI system. Figures of merit for these systems include slew rate and the gradient field linearity. Our previously described 6.5 mT ultra-low-field MRI scanner has marginal gradient performance with low slew rates (minimal rise time of 750µs) and low efficiency (around 10µT/m/A). We describe here the optimization of a new gradient coil system with improved slew rate and efficiency. We introduce the equivalent magnetic dipole method  to design biplanar gradient coils, and our design study of the geometric parameters of the gradient coil (including the coil pattern, its size and density). 

Manouchehr Takrimi¹ and Ergin Atalar^1,2
1National Magnetic Resonance Research Center, Bilkent University, Ankara, Turkey, ²Department of Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey

A novel programmable set of z-gradient array equipped with an active-shield array is introduced and simulated for diverse applications in magnetic resonance imaging (MRI).  The proposed active-shield array can dynamically provide a proper shield for the main array in which its magnetic profile can be programmed based on the required scenario. This is achieved by using a set of independently tunable power amplifiers that feed both array elements individually or in a cluster. As a proof of concept, two sets of arrays are simulated: one for a double-gradient z-coil array and another one possessing a large field of view (FOV).

Juan Sabate¹, Huan Hu¹, Ruxi Wang², and Logan Snow^1
1GE Global Research, Niskayuna, NY, United States, ²GE Aviation, Dayton, OH, United States

The gradient driver was implemented with SiC MOSFETs. The amplifier has less losses and is more compact, however switching has higher high frequency contents. The new amplifier was tested in an EMI shielded room. The results show the effectiveness of the double shielding method at reducing the radiated noise generated by a gradient driver system. The tests confirmed the correlation between the conducted and radiated noise. The double shielding method proposed reduced the radiated noise caused by the CM circulating current between cables. The measurements showed up to 35dB radiated noise reduction with this method.
 

Patrick Fuchs¹, Bart de Vos¹, Thomas O'Reilly², Andrew Webb², and Rob Remis^1
1Circuits and Systems, Delft University of Technology, Delft, Netherlands, ²C.J. Gorter Center for High Field MRI, Leiden University Medical Center, Leiden, Netherlands

We describe the application of the target field method for designing three-axes gradients for the transverse magnetic field produced by a Halbach array, as well as verify this method by constructing a set of 3 gradient coils and using it for 3D imaging. Additionally an open-source tool is described which allows for easy gradient design using this method.

Sebastian Theilenberg¹, Ben John Parkinson², and Christoph Juchem^1,3
1Department of Biomedical Engineering, Columbia University in the City of New York, New York, NY, United States, ²Robinson Research Institute, Victoria University of Wellington, Wellington, New Zealand, ³Department of Radiology, Columbia University in the City of New York, New York, NY, United States

As part of a collaborative effort to create a novel compact high-temperature superconductor 1.5 T head-only scanner for improved accessibility of MRI and advanced motor coordination studies, we are developing a 31-coil Multi-Coil (MC) array for linear and non-linear image encoding and concomitant B₀ shimming. Here we present a preliminary characterization of the expected eddy currents generated by the unshielded MC array in the unusual scanner assembly at hand based on finite element based electromagnetic simulations.

Feng Jia¹, Sebastian Littin¹, Philipp Amrein¹, Huijun Yu¹, Arthur Magill², Tristan Kuder², Sebastian Bickelhaupt³, Frederik Laun⁴, Mark E. Ladd², and Maxim Zaitsev^1
1Dept.of Radiology, Medical Physics, Medical Center University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany, ²Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Germany, ³Junior Group Medical Imaging and Radiology – Cancer Prevention, German Cancer Research Center (DKFZ), Heidelberg, Germany, ⁴Department of Radiology, MR Physics, University Medical Center Erlangen, Erlangen, Germany

A nonlinear human-breast coil for diffusion weighting with a high performance 1T/m is designed.

Eric J Lessard^1,2, William B Handler², and Blaine A Chronik^1,2
1Department of Medical Biophysics, Western University, London, ON, Canada, ²Department of Physics, Western University, London, ON, Canada

In this work a design study of a shoulder cut-out gradient coil for use in a head-only MRI platform was performed. Specifically, based on previous work, it explored the effect of rotating the gradient axes on performance. This was due to the imbalance of gradient performance degradation due to the presence of cut-outs on conducting surfaces next to the patient's shoulders. This proof-of-concept exploration is the first demonstration of the feasibility of rotating the gradient axes during the design process to design a shoulder cut-out gradient coil.

Yun Shang¹, Sebastian Theilenberg¹, Jalal Ghazouani^1,2, and Christoph Juchem^1,3
1Department of Biomedical Engineering, Columbia University, New York, NY, United States, ²Hamburg University of Technology, Hamburg, Germany, ³Department of Radiology, Columbia University, New York, NY, United States

The development of advanced Multi-Coil (MC) setups for the generation of MRI encoding fields necessitates the manufacture of wire wound coil fixated with epoxy resin. Common winding techniques, however, are not suitable for the required geometries. As a remedy, we developed an automated coil winding machine capable of winding coils with a large number of turns in irregular curved shapes whilst impregnating them with epoxy resin. 

Magdoom Kulam Najmudeen¹, Malisa Sarntinoranont², and Thomas H Mareci^2
1SQITS/NICHD, National Institute of Health, Bethesda, MD, United States, ²University of Florida, Gainesville, FL, United States

A new gradient pattern is introduced for performing pre-emphasis by uniform bandlimited excitation of eddy current and mechanical eigenmodes of the gradient system. The presented pattern is shown to be more effective in eliciting the gradient response than the energy equivalent trapezoidal pulse.  This approach may allow the design of gradient waveforms that reduce artifacts in PFG experiments, e.g. measuring very slow diffusion and flow.

Ming Lu^1,2,3, William A. Grissom^1,2,4, John C. Gore^1,2,4, and Xinqiang Yan^1,2
1Vanderbilt University Institute of Imaging Science, Nashville, TN, United States, ²Department of Radiology, Vanderbilt University Medical Center, Nashville, TN, United States, ³College of Nuclear Equipment and Nuclear Engineering, Yantai University, Yantai, China, ⁴Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, United States

At ultrahigh fields, to achieve ultimate receive performance, the optimal current patterns go beyond the uniform current of loops. A dipole-like current is desired and can be realized by directly adding dipole antennas or by inducing dipole-mode in loops. In this work, we investigated the receive performance of different kinds of arrays with self-decoupled loops (SDLs) or/and self-decoupled folded dipoles (SDFDs). These coils have dipole-like as well as loop-like patterns and are highly isolated. We found that the combination of SDL and SDFD exhibits considerable improvement for both peripheral/central SNR and parallel imaging, even compared to mixed loop+dipole arrays.

Amer Ajanovic¹, Joseph V Hajnal^1,2, and Shaihan Malik^1,2
1Biomedical Engineering Department, School of Biomedical Engineering & Imaging Sciences, King's College London, London, United Kingdom, ²Centre for the Developing Brain, School of Biomedical Engineering & Imaging Sciences, King's College London, London, United Kingdom

One of the main problems at UHF resonance frequencies is the significant spatial variation in radiofrequency electromagnetic fields. Mitigating this problem has been one of the goals of the parallel transmission MRI, but it causes greater local SAR variability, which has led to more rigorous safety restrictions. We have used MARIE with an MRGF implementation to study position sensitivity of SAR estimation at 7T by performing multiple simulations in which the coil is moved with respect to the head. We observe higher positional variability in rotational perturbations than in translational ones with solutions obtained in 7.5 min per body-coil configuration.

J. Nuno Teixeira¹, Shaihan Malik^1,2, and Joseph V Hajnal^1,2
1Biomedical Engineering Department, School of Biomedical Engineering & Imaging Sciences, King's College London, London, United Kingdom, ²Centre for the Developing Brain, School of Biomedical Engineering & Imaging Sciences, King's College London, London, United Kingdom

Several MRI scenarios can be studied by using electromagnetic simulation tools. The most common EM simulation software requires spatial discretization which can, for narrow objects like elongated conductors, become computationally heavy and time consuming. To avoid that, such objects are typically discretized suboptimally. Here, using FDTD simulations, we explore how these practices can often lead to errors which are not trivial to track and how simple changes in modelling can lead to significatively different results.

Viacheslav Ivanov¹, Anna Hurshkainen¹, Georgiy Solomakha¹, and Mikhail Zubkov^1
1Faculty of Physics and Engineering, ITMO University, Saint-Petersburg, Russian Federation

We propose a double-coil setup for broad-range heteronuclear MRI. The system designed for an 11.7T scanner comprises two independent coils, one of them tuned to ¹H frequency to perform anatomical imaging, and another one, wire-array coil, tuned to the X-nucleus (including ²H, ¹¹B, ¹³C, ²³Na,  ⁷Li and ³¹P) frequency. In order to tune the X-coil over such a wide range, both structural capacitance and inductance of the coil are made variable; narrow range tuning of the ¹H coil is achieved via conventional tuning-matching circuit. The design principle and setup tunability are investigated in simulations and experimentally.

Lei Guo¹, Aurelien Destruel¹, Mingyan Li¹, Haiwei Chen¹, Ewald Weber¹, Feng Liu¹, and Stuart Crozier^1
1School of ITEE, The University of Queensland, Brisbane, Australia

At ultra-high field (UHF) MRI, dipole-based antennas have deeper field penetration but increased specific absorption rate (SAR) levels than loop-type coils. In this work, a novel RF coil is proposed based on layer-configured dipole and multiple radiating elements. The designed RF coil is compared with a conventional dipole antenna in electromagnetic simulations and it is observed that more than 30% SAR reduction can be achieved with improved B₁⁺ efficiency.

Qiaoyan Chen¹, Zidong Wei², Nan Li¹, Feng Du¹, Qiang He², Xiaoliang Zhang³, Dong Liang¹, Xin Liu¹, Hairong Zheng¹, and Ye Li^1
1Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China, ²Shanghai United Imaging Healthcare, Shanghai, China, ³Department of Biomedical Engineering, State University of New York, Buffalo, NY, United States

 To achieve high SNR and high contrast for human MRI, ultra-high field can be applied. Considering the safety issues and the inhomogeneity of images at high fields, we aim to build a 5 T whole body MRI system. Based on this system, a transmit coil system for human head and neck imaging is designed and simulated. This work shows the preliminary studies with B1+ field and SAR assessments at 5 T.

Yubin Cai¹, John Stager¹, Hsin-Jung Yang¹, Debiao Li¹, and Hui Han^1
1Biomedical Imaging Research Institute, Cedars-Sinai Medical Center, Los Angeles, CA, United States

Arthur W. Magill^1
1Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany

Virtual Observation Point (VOP) sets generated using the spectral and Frobenius norm are compared. It is found that while the spectral norm produces less VOPs for a certain over-estimation factor, the Frobenius norm actually produces more accurate VOPs. When compared in terms of sets containing (approximately) equal numbers of VOPs, the Frobenius norm performs better.

Wyger Brink¹, Jeroen van Gemert², Andrew Webb¹, and Rob Remis^2
1C.J. Gorter Center for High Field MRI, dept. Radiology, Leiden University Medical Center, Leiden, Netherlands, ²Circuits and Systems, Delft University of Technology, Delft, Netherlands

An efficient approach to local SAR prediction is presented based on anatomical differences and model order reduction, which substantially reduces the memory footprint of this framework. The reduced order model can be solved using a direct inverse, which allows solving for the RF fields for multiple transmit channels simultaneously, which significantly improves the scalability in view of upcoming high field systems with an increasing number of RF transmit channels.

Mingyan Li¹, Jin Jin^1,2,3,4, Aurelien Destruel¹, Lei Guo¹, Ewald Weber¹, Feng Liu¹, and Stuart Crozier^1
1School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, Australia, ²Siemens Healthineers, Brisbane, Australia, ³4. Mark and Mary Stevens Neuroimaging and Informatics Institute, University of Southern California, Los Angeles, CA, United States, ⁴ARC Training Centre for Innovation in Biomedical Imaging Technology, The University of Queensland, Brisbane, Australia

An 8-element rotating radiofrequency coil array (RRFCA) consisting of loop and dipole pairs is proposed. By placing the dipole coil along the central axis of the loop coil, they are naturally decoupled due to the orthogonality of their polarised fields. Compared with a traditional 8-element static dipole coil array, the RRFCA is designed to provide better B₁ shimming and SAR control performance benefited from the physical rotation. In addition, with eight coil elements, SNR will be improved compared to the previously developed 4-element RRFCA.

Mingyan Li¹, Ewald Weber¹, Aurelien Destruel¹, Feng Liu¹, and Stuart Crozier^1
1School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, Australia

The whole-body coil of the Australian MRI-Linac system can produce images without interfering with the Linac beam during radiotherapy. However, the whole-body coil is distant from the patient, causing lower SNR and is not parallel imaging capable. According to the radiotherapy treatment requirement, an 8-element surface coil array was designed to be radio-transparent and the corresponding imaging algorithms were developed for this coil array. The simulation results showed that the proposed coil array has improved SNR compared to the whole-body coil, and a reduction rate of three can be achieved in parallel imaging without prominent aliasing artefacts.

Carel Costijn van Leeuwen¹, Cornelis A.T. van den Berg¹, Dennis Klomp¹, and Alexander J.E. Raaijmakers^1,2
1Department of radiology, University Medical Center Utrecht, Utrecht, Netherlands, ²Eindhoven University of Technology, Eindhoven, Netherlands

Typical transmit arrays for the head use dipole or loop antennas within an RF shield. However, for certain applications an unshielded head coil array is required. This study explores different designs for unshielded head coil arrays using simulations. Using L-curves, the tradeoff which exists between power efficiency, homogeneity and SAR is evaluated for arrays consisting of loops and dipoles of various dimensions. Loops are found to be superior to dipoles. Small loops yield the highest power efficiency, while larger loops improve homogeneity and SAR efficiency.

Jose EC Serralles¹, Elfar Adalsteinsson¹, Lawrence L Wald², and Luca Daniel^1
1Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, United States, ²A. A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, United States

In this paper we efficiently combine a coil optimization process with an electromagnetic field solver and show preliminary proof of concept on simple systems leading to 22% to 45% improvement in Signal to Noise Ratios.

M. Arcan Erturk¹, Russell L Lagore¹, Gregor Adriany¹, and Gregory J Metzger^1
1Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States

A novel combined shielded-loop-resonator (SLR) and dipole antenna 16-channel transceiver body imaging array (16-SLR-D) is designed by combining eight pairs of dipole antennae and 10x20cm2 SLRs. Performance of the 16-SLR-D is compared against a 16-channel loop-dipole (16-L-D) array through finite-difference-time-domain simulations. Despite the larger loops size and closer placement of the elements, 16-SLR-D design has significantly improved coupling performance with less than 6% power coupled to other channels on average, compared to ~16% of average power coupling of 16-L-D. The combined SLR-dipole array(16-SLR-D) demonstrated ~+15% in transmit efficiency(mT/W0.5), ~+9% in transmit SAR efficiency  (mT/SAR0.5) and ~+6% SNR inside the prostate.

Zhengshi Yang¹, Xiaowei Zhuang¹, Karthik Sreenivasan¹, Virendra Mishra¹, and Dietmar Cordes^1,2
1Cleveland Clinic Lou Ruvo Center for Brain Health, Las Vegas, NV, United States, ²Department of Psychology and Neuroscience, University of Colorado, Boulder, CO, United States

The segmentation of human hippocampal subfields on in vivo MRI has gained great interest in the last decade, because these anatomic subregions were found to be highly specialized in recent studies and are potentially affected differentially by normal aging, Alzheimer’s disease, schizophrenia, epilepsy, major depressive disorder, and posttraumatic stress disorder. However, manually segmenting hippocampal subfields is labor-intensive and time-consuming, which limits the study to a small sample size. We developed a multi-scale Convolutional neural network based Automated hippocampal subfield Segmentation Toolbox (CAST) for automated segmentation, which can be easily trained and output segmented images in one minute.

Kiyoi Okamoto¹, Minghui Tang², and Toru Yamamoto^2
1Graduate School of Health Sciences, Hokkaido University, Sapporo, Japan, ²Faculty of Health Sciences, Hokkaido University, Sapporo, Japan

It is commonly believed that forming of a conductive loop in an MRI scanner is dangerous because a loop induces a large electric current by the RF excitation and causes RF burn injuries. To verify this belief, we modeled an RF burn injury case, which was caused by an ECG lead, on an electromagnetic analysis software, and simulated SAR and electric field.  A large SAR that causes RF burns was confirmed with and without looping that induced small electric field not to cause RF burns. It was suggested that loop formation is not a major cause of RF heating.

Ria Forner¹, Janot P. Tokaya², Alexander Raaijmakers^2,3, and Dennis Klomp^2
1Radiology, UMC Utrecht, Utrecht, Netherlands, ²UMC Utrecht, Utrecht, Netherlands, ³Biomedical Engineering, Eindhoven University of Technology, Utrecht, Netherlands

This work is presenting a simulation study on X-nuclei imaging at 7T with a birdcage body coil for sodium, carbon and phosphorous. Three models and four imaging targets have been investigated. Although B₁⁺ efficiency generally decreases with frequency, we show that the SAR efficiency, ( B₁⁺/√SAR ) stays more or less constant over the investigated frequencies. Furthermore, it is shown that although every model and every imaging target has one optimal relative phase setting between the birdcage ports, for each frequency there exists one generic phase setting that provides only a minimal drop in performance over all imaging targets and models.

Andreas Georg Berg¹ and Martin Börner^2
1Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria, ²Karlsruhe Nano Micro Facility (KNMF), Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Germany

Quality control for systematic improvements in spatial resolution up to the microscopy range becomes increasingly relevant not only for preclinical imaging but also for High Field MR human scanners. The design, manufacturing technology, a prototype phantom and an exemplary evaluation for qualitative and quantitative measurement of the spatial resolution of MR-scanners claimed to offer spatial resolutions better than 100µm is presented. The spatial resolution for 2D-FT anisotropic imaging can be checked qualitatively and quantitatively by interpolation of the Modulation-Transfer-Function in two different spatial encoding directions at the same time with slice-thickness below 120µm up to 64 line-pairs/mm (pixel-size: 8µm).

Limin Li¹ and Alice M. Wyrwicz^1,2
1Center for Basic MR Research, Northshore University HealthSystem, Evanston, IL, United States, ²Department of Biomedical Engineering, Northwestern University, Evanston, IL, United States

We report the early development of a multifunctional digital transceiver built on a Field-Programmable Gate Array (FPGA). The multifunctional transceiver not only offers the functionalities of a conventional transceiver and pulse sequencer, but also is capable of combining frequency detection and compensation, inline data correction and image reconstruction. We describe the design and implementation of the multifunctional transceiver and demonstrate its capabilities of image acquisition and reconstruction with real-time frequency and phase compensation.

Manuel Chapa^1,2,3, Hernán Valenzuela⁴, Nestor Muñoz^1,2,3, Mathias Lambert^1,2,3, Marisleydis García^1,2,3, Flavia Zacconi⁴, and Cristian Tejos^1,2,3
1Biomedical Imaging Center, Pontificia Universidad Católica de Chile, Santiago, Chile, ²Millennium Nucleus for Cardiovascular Magnetic Resonance, Santiago, Chile, ³Department of Electrical Engineering, Pontificia Universidad Católica de Chile, Santiago, Chile, ⁴Faculty of Chemistry, Pontificia Universidad Católica de Chile, Santiago, Chile

In this work, we present a realistic phantom made of a solid material that we developed, which can mimic the human brain anatomy, including grey and white matter. Our new material also allows us to modulate T2 and susceptibility values by changing the ratios of a 4 component mix wich can result in T2 times from 100ms to 250ms and susceptibility values close to the human brain.
 

Hanna Maria Hanson¹, Marcel van Herk¹, David Cobben^1,2, and Benjamin C Rowland^1
1University of Manchester, Manchester, United Kingdom, ²The Christie NHS Trust, Manchester, United Kingdom

We present a digital phantom intended for MR-guided radiotherapy imaging sequence design and testing. The framework uses existing phantom generating software to provide the anatomical shape and movement, while the MRI simulation is handled by a modified version of a Bloch simulator. The accuracy of the phantom framework was demonstrated by simulating a 4D image of a single respiratory cycle and also by reproducing motion-related artefacts in a 2D image.

Ryan T Oglesby^1,2, Wendy Oakden², Wilfred W Lam², Agata Chudzik³, Katarzyna Kochalska³, Radoslaw Rola³, and Greg J Stanisz^1,2,3
1Medical Biophysics, University of Toronto, Toronto, ON, Canada, ²Sunnybrook Research Institute, Toronto, ON, Canada, ³Neurosurgery and Paediatric Neurosurgery, Medical University of Lublin, Lublin, Poland

The development of quantitative MRI sequences at ultra-high field (UHF) (7 T or higher) is difficult due to non-uniform RF fields, enhanced susceptibility artifacts, and increased SAR. Phantoms are required in order to test quantitative pulse sequences, and it becomes increasingly important that artifacts in phantoms be as similar as possible to those observed in vivo. In this study, a 3D printed three-compartment spherical phantom was designed to evaluate chemical exchange saturation transfer (CEST), magnetization transfer (MT), and T₁ mapping sequences on UHF MRI systems. 

Lena Nohava^1,2, Raphaela Czerny², Michael Obermann^1,2, Jacques Felblinger³, Roberta Frass-Kriegl², Jean-Christophe Ginefri¹, and Elmar Laistler^2
1IR4M (Imagerie par Résonance Magnétique et Multi-Modalités), UMR8081, Université Paris-Sud/CNRS, Université Paris-Saclay, Orsay, France, ²Division MR Physics, Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria, ³Université de Lorraine, Inserm, IADI, Nancy, France

We propose flexible multi-gap transmit/receive coaxial coils for 7 T MRI with 4, 7, 10 and 15 cm loop diameters, targeting different anatomies with large inter-subject variability and the need for close-fitting coil design. On the bench and in MRI, we evaluate the coaxial coils’ robustness upon bending, compare their performance to standard copper wire coils and demonstrate a significant SNR gain when using form-fitted coaxial coils instead of flat standard coils.

Jana Vincent^1,2 and Joseph Rispoli^1,3
1Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN, United States, ²Basic Medical Sciences, Purdue University, West Lafayette, IN, United States, ³School of Electrical & Computer Engineering, Purdue University, West Lafayette, IN, United States

Undesired common-mode currents traveling along the shield of cabling can affect radiofrequency coil performance and cause patient burns. Cable traps are necessary to suppress these common-mode currents in Magnetic Resonance environments. Floating cable traps, which allow for repositioning and reuse and eliminate the need to solder directly to cabling, have previously been reported as custom-manufactured apparatuses¹. To streamline the manufacturing of floating cable traps and reduce manufacturing cost, we have designed 3D-printable versions that only require the addition of copper circuitry (e.g., tape/PCB) and lumped elements.      

Jana Vincent^1,2 and Joseph Rispoli^1,3
1Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN, United States, ²Basic Medical Sciences, Purdue University, West Lafayette, IN, United States, ³School of Electrical & Computer Engineering, Purdue University, West Lafayette, IN, United States

Given the decrease in mammography sensitivity for those with denser breast tissue, MRI is often utilized for supplemental screening. Here we present a stretchable, flexible, two-channel breast RF coil array that allows for a customized fit to the breast and closest possible positioning to the skin. This coil array was created by utilizing conductive thread, stitched onto polyester/spandex blend fabric. Clear images of both the phantom and in-vivo were obtained. Omnidirectional stretching provided increased patient comfort and customized fit. With this close proximity, greater sensitivity can be achieved when compared to traditional breast coils.

Belinda Ding¹, Christopher Wickens¹, Iulius Dragonu², Catarina Rua¹, Saba Shirvani¹, Patrick Liebig³, Robin Heidemann³, Guy B Williams¹, and Christopher T Rodgers^1
1Wolfson Brain Imaging Centre, University of Cambridge, Cambridge, United Kingdom, ²Siemens Healthcare Limited, Firmley, United Kingdom, ³Siemens Healthcare Limited, Erlangen, Germany

We compare performance of two approaches for magnetisation inversion on a Siemens 7T Terra scanner, with 8Tx32Rx Nova head coil. We compared 3D non-selective pTx pulses designed in the scanner’s online pulse design tool, against traditional adiabatic pulses in both phantoms and the brain of a volunteer. We observe that spiral pTx pulses have substantially lower SAR burden than adiabatic hyperbolic secant pulses, but using the default parameter sets, the spiral inversion is less homogeneous. Thus, spiral pTx pulses are advantageous in SAR limited sequences, and further optimisation is likely to improve the inversion efficiency of these pulses.

Eulalia Serés Roig¹ and Rolf Gruetter^1,2,3
1Laboratory of Functional and Metabolic Imaging (LIFMET) - Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland, ²Centre d'Imagerie BioMédicale - Animal and Imaging Technology (CIBM-AIT) - Ecole Polytechnique de Lausanne (EPFL), Lausanne, Switzerland, ³Department of Radiology, Universities of Lausanne (UNIL) and Geneva (UNIGE), Lausanne, Switzerland

The quantification of metabolite signals in the ¹H-spectrum of the human brain in vivo is complicated by an extensive spectral overlap of resonances, due to the restricted chemical shift dispersion of the ¹H-nucleus. For instance, the myo-Inositol peaks observable in the ¹H-spectrum at 7T are close the water resonance and overlap with that of glycine. In contrast, the high resolution of the ¹³C-MR spectrum aids in the interpretation of the highly sensitive but poorly resolved ¹H-MR spectrum. In this study, we demonstrate the advantage of ¹³C-MRS at 7T by measuring high resolved myo-Inositol C₁-C₆ resonances in the human brain.      

Liyuan Jin¹, Yaan Ge¹, Qilin Lu¹, Qingyu Dai¹, and Kun Wang^1
1GE Healthcare, Beijing, China

This abstract investigated the method for quantitatively predicting B0 variation induced by human body. Magnetic field simulation was performed, with human phantom positioned in different strength’s B0 fields, and revealed the linear relationship between patient-induced B0 inhomogeneity and the background B0 field. The linear relationship was proved in clinical experiment, which used the relationship to predict B0 field map and compared the predicted B0 field map with the real B0 field map. The clinical experiment shows that 95% voxels has a prediction accuracy within 50Hz. The finding could further benefit image quality and improve scan workflow.

Niraj Shalikram Yadav¹, Miheer Pradeep Mayekar¹, Rajesh Harsh¹, and Vishal Dinesh Boricha^1
1TID, Society For Applied Microwave Electronics Engineering & Research, Mumbai, India

Volume coils such as the Birdcage Coil possess homogeneous magnetic fields due to circularly polarized fields assisted by the Hybrid Coupler. To perform the complete operation of the birdcage coil for imaging, the Transmit power must be well isolated from the receive front end which is done by introducing RF switches in the receive path. However, Reflective switches cause impedance mismatch at the ports of the coupler. This work demonstrates an absorptive switch due to which the impedance mismatch problem is solved. Also, comparative analysis were done for both the type of RF switches.

Rohit Apurva¹, Niraj Yadav¹, Miheer Mayekar¹, Bhaskara Naik¹, Tapas Bhuiya¹, and Rajesh Harsh^1
1Technology Innovation Department, Society for Applied Microwave Electronics Engineering and Research, Mumbai, India

To improve the homogeneity of magnetic field and SNR of the Image by a factor of , quadrature feeding is required. For Quadrature Feeding, Hybrid coupler is an essential microwave circuit, but at RF range the size of hybrid coupler is large. To make it miniaturized and to overcome the problem of power handling capacity (compared to lumped element) we have proposed coaxial cable with inductive loading. This technique minimizes the size of hybrid by 75% and has a coupling of 3dB and phase difference of 90⁰ at 63.87MHz.

Nicole Wake^1,2, Maggie Fung³, Stephen Dashnaw⁴, J. Thomas Vaughan Jr.⁴, and Fraser Robb^5
1Department of Radiology, Montefiore Medical Center, Albert Einstein College of Medicine, Bronx, NY, United States, ²Center for Advanced Imaging Innovation and Research, Department of Radiology, NYU School of Medicine, New York, NY, United States, ³GE Healthcare, New York, NY, United States, ⁴Columbia University, New York, NY, United States, ⁵GE Healthcare, Aurora, OH, United States

An approach to 3D capture a life-sized MRI machine using 3D surface scanning is described. The 3D files generated can be used for 3D printing, augmented or virtual reality, or simulation studies.

Yonghyun Ha¹, Kartiga Selvaganesan¹, Baosong Wu¹, Charles Rogers III¹, Sajad Hosseinnezhadian¹, Gigi Galiana¹, and R. Todd Constable^1
1Department of Radiology and Biomedical Imaging, Yale School of Medicine, New Haven, CT, United States

To achieve frequency encoding using Bloch-Siegert shift, the off-resonance pulse and signal reception would need to take place simultaneously. In this work we describe two methods to get rid of applied off-resonance signal from the receive signal. Both Tx cancelling and RF filter methods can be integrated into the RF chain to reduce the power of the off-resonance signal. It was found that using an RF filter was more effective for both blocking off-resonance signal and keeping receive signal. It was also demonstrated that the combination of two methods is promising in terms of reducing the off-resonance signal.

Jonathan K. Stelter¹, Andreas K. Bitz^1,2, Mark E. Ladd^1,3,4, and Thomas M. Fiedler^1
1Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany, ²Electromagnetic Theory and Applied Mathematics, Faculty of Electrical Engineering and Information Technology, FH Aachen – University of Applied Sciences, Aachen, Germany, ³Erwin L. Hahn Institute for MRI, University Duisburg-Essen, Essen, Germany, ⁴Faculty of Physics and Astronomy and Faculty of Medicine, University of Heidelberg, Heidelberg, Germany

The transmit and receive performance of 8-channel array configurations of microstrip antennas with meander structures and fractionated dipoles was evaluated at 7T using numerical simulations. Simulations with a homogenous phantom and an anatomical body model use similar parameters to facilitate direct comparison. The microstrip antenna array configuration provides higher SNR than the fractionated dipole array configurations and shows superior RF shimming performance for large-FOV transverse and coronal slices, whereas single-element simulations estimate similar SAR efficiencies. The RF shimming performance of the array configurations does not differ significantly for smaller ROIs as evaluated for prostate imaging.

Hankyeol Lee¹, Jeongtaek Lee^1,2, Jang-Yeon Park^1,2, and Seung-Kyun Lee^1,2,3
1Center for Neuroscience Imaging Research, Institute for Basic Science, Suwon, Republic of Korea, ²Dept. of Biomedical Engineering, Sungkyunkwan University, Suwon, Korea, Republic of, ³Dept. of Physics, Sungkyunkwan University, Suwon, Korea, Republic of

Imaging fluid motion in MRI is possible with high temporal resolution and reliable motion-inducing mechanism. In this study, line-scanning with 5.5 ms temporal resolution was used to image fluid motion inside quail eggs which were periodically driven by an MR actuator. Resulting time-course images captured accurate displacements of the eggs and the internal fluid motion over time.

Takafumi Ohishi^1
1Advanced Technology Department, Research and Development Center, Canon Medical Systems Corporation, Kawasaki, Japan

This paper investigates the appropriate frequency band and antenna used for a non-contact heart and respiratory rate monitoring system applying an antenna. As a result of measurements with different resonant frequency antennas, it is found that the appropriate frequency band is around 600 MHz. Furthermore, an antenna having multi resonance elements reduces the influence of abdominal motion in breathing at detecting heart rate.

Md Shahadat Hossain Akram¹, Takayuki Obata², Fumihiko Nishikido¹, and Taiga Yamaya^1
1Advance Nuclear Medicine Sciences, National Institute of Radiological Sciences (NIRS-QST), Chiba, Japan, ²Molecular Imaging and Theranostics, National Institute of Radiological Sciences (NIRS-QST), Chiba, Japan

We used shielded RF coil in combination with unshielded PET detector. A microstrip coil and a head-size birdcage coil was used. For microstrip coil, the ground conductor acted as the shield, while for the birdcage coil a cylindrical RF shield was implemented. A PET detector with front-end electronics was implemented 40 mm far from the RF shields. Phantom studies revealed no RF pickup noise in any of these cases. A maximum 16% reduction in SNR was seen for the microstrip coil between PET detector powered OFF and ON conditions. However, the SNR reduction for the birdcage coil was negligible. 

Qiong Zhang¹, Yong Xiao Zhang², and Yulong Liu^3
1DL, Siemens, Shenzhen, China, ²MR Collaborations, Siemens Healthcare Ltd., Shenzhen, China, ³Beijing Institute of Technology, BeiJing, China

In this work, we provided a component-projection algorithm for Pilot Tone (PT) signal anti-jamming. The interference of a PT signal induced by the MR measurement can be effectively mitigated with the following procedure: the original PT signals received by the array coil are orthogonally transformed into the Eigen Space of interference signal, and the principle component of interference Eigen Space is subsequently discarded to maximally suppress the interference before the remaining components are projected into a predefined direction to combine the final PT navigator signal. Phantom and volunteer experiments demonstrated that the technique can effectively reduce the interference during scanning.

Saba Shirvani*¹, Belinda Ding*¹, Iulius Dragonu², Patrick Liebig³, Catarina Rua¹, Jabrane Karkouri¹, Dennis Klomp⁴, Aaron T. Hess⁵, and Christopher T. Rodgers^1
1Wolfson Brain Imaging Centre, Department of Clinical Neurosciences, University of Cambridge, Cambridge, United Kingdom, ²Siemens Healthcare Ltd, Research and Collaboration UK, Frimley, United Kingdom, ³Siemens Healthcare Limited, Erlangen, Germany, ⁴UMC Utrecht, Utrecht, Netherlands, ⁵Oxford Centre for Magnetic Resonance, University of Oxford, Oxford, United Kingdom

Abdominal 7T MRI is technically demanding, but has great potential due to the improved signal-to-noise-ratio and altered image contrast. We describe our initial experience of abdominal imaging on a 7T Terra scanner (Siemens), using an 8-channel TEM coil that was previously used on a Magnetom 7T scanner. First, we describe how we adapted the RF power limits from the VB17 format to the VE12U format, including an experimental validation. Then, we show our first human in vivo liver images from the 7T Terra, including B0 and B1+ maps, and FLASH images (radial and Cartesian), for two RF shim settings.

Kyung Min Nam¹, Cezar Alborahal¹, Kaizad Rustomji², Tryfon Antonakakis³, Catalina Arteaga de Castro⁴, Jannie P. Wijnen¹, and Dennis W.J. Klomp^1
1Imaging and Oncology, UMC Utrecht, Utrecht, Netherlands, ²Multiwave Innovation, Marseille, France, ³Multiwave Innovation, Geneva, Switzerland, ⁴Tesla Dynamic Coils, Zaltbommel, Netherlands

High-quality MRI uses arrays of local receiver coils positioned close to the region of interest to maximize acceleration performance and SNR in the images. This comes at the expense of patient comfort, particularly when considering surgical interventions under close to real-time MRI guidance. Here we demonstrate that when the tissue dominates the noise source over the electronic noise, the distance of the coil array to the tissue can be increased beyond the head to the bore liner of a head MR system without substantially decreasing the acceleration performance and intrinsic signal to noise compared to commercially available head coils.

Mingyan Li¹, Aurelien Destruel¹, Ewald Weber¹, Aiman Al-Najjar², Shekhar Chandra¹, Feng Liu¹, Craig Engstrom³, and Stuart Crozier^1
1School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, Australia, ²Centre for Advanced Imaging, The University of Queensland, Brisbane, Australia, ³School of Human Movement and Nutrition Sciences, The University of Queensland, Brisbane, Australia

High-resolution prostate imaging for both 3T and 7T MRI are challenging, given the deep location of this exocrine gland which accentuates technical issues related to the reduced electromagnetic penetration and B₁ inhomogeneity.  In this work, high-resolution (0.3 x 0.3mm in-plane) non-interpolated T2w-TSE prostate images from a healthy volunteer were acquired at 3T using a commercial 18-channel body matrix and 32-channel spine coil and an 8-channel prototype coil at 7T at 15 slices and 11 slices, respectively. Compared with standard clinical prostate imaging at 3T, the 7T prostate images provided higher SNR and better differentiation of various zones of the prostate.

Bixia Chen^1,2, Taku Sato^2,3, Oliver Gembruch^1,2, Michael Forsting⁴, Alexander Radbruch⁴, Jan Rodemerk², Shiqing He², Stefan Maderwald¹, Harald H. Quick^1,5, Mark E. Ladd^1,6, Ulrich Sure², and Karsten H. Wrede^1,2
1Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany, ²Department of Neurosurgery, University Hospital Essen, University Duisburg-Essen, Essen, Germany, ³Department of Neurosurgery, Fukushima Medical University, Fukushima, Japan, ⁴Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, University Duisburg-Essen, Essen, Germany, ⁵High Field and Hybrid MR Imaging, University Hospital Essen, University Duisburg-Essen, Essen, Germany, ⁶Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany

This in-vivo study aimed to investigate the relationship between thrombus characteristics and the aneurysm wall (AW) in partially thrombosed intracranial aneurysms (pTIAs) using MPRAGE at 7T MRI. The AWs with the highest signal intensity ratio of thrombus were significantly thicker. In the histopathological examinations, three cases with hypointensity of the thrombus showed only a few macrophages in the thrombus and a thin AW. Three cases with hyperintensity of the thrombus in the MPRAGE showed abundant macrophages in the thrombus. In 7T MPRAGE, the signal intensity ratio of thrombus in pTIAs correlates with AW thickness and histologic features indicating wall instability.

Robin Navest^1,2, Stefano Mandija^1,2, Stefan Zijlema^1,2, Luca van Dijk¹, Bjorn Stemkens¹, Jan Lagendijk¹, Anna Andreychenko^1,3, and Cornelis van den Berg^1,2
1Radiotherapy, UMC Utrecht, Utrecht, Netherlands, ²Computational Imaging Group for MRI Diagnostics & Therapy, Center for Image Sciences, UMC Utrecht, Utrecht, Netherlands, ³Research and Practical Clinical Center of Diagnostics and Telemedicine Technologies of the Moscow Department of Healthcare, Moscow, Russian Federation

The ECG signal can be disturbed by the magnetohydrodynamic effect and requires placement of ECG electrodes. The latter adds extra workload in the patient setup. Moreover, for MRI-guided radiotherapy, ECG skin electrodes will interfere with dose delivery and thus cannot be used. We propose to use the noise navigator, a passive self-navigation method based on the physiological motion-induced modulation of the thermal noise variance measured by an RF receive coil, which does not require additional hardware and is inherently synchronized with MR acquisition.

Christoph Michael Schildknecht¹, David Otto Brunner¹, Thomas Schmid¹, and Klaas Paul Pruessmann^1
1Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland

RF short-wave based motion tracking offers interesting prospects by allowing to  localize markers without line of site, minimal interaction with the MRI scanner, very short latency and high precision. The design of the employed antenna arrays is however determinant for the performance of the entire system and subject to various requirements. The design criteria and parameters have hence been analyzed and used for optimization of the receiver array geometry. The resulting arrays have then been evaluated using signal simulations as well implemented and verified by bench measurements using a robotic positioning system as reference.

Jinyoung Kim¹, Rémi Patriat¹, Oren Rosenberg¹, and Noam Harel^1
1Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States

In this study, we leverage 7T MR multi-modality and deep neural networks for accurate and efficient segmentation of the thalamus. Our contributions are 1) to build a dual-pathway and feature pyramid scheme to simultaneously encode global contextual information and local details within an encoder-decoder network; 2) to learn the optimal combination of global and local attentions to increase the feature representation power by adaptively recalibrating feature maps in an end-to-end manner. The proposed framework shows state-of-the-art performance on segmentation of the thalamus with 7T multi-modal MRI in an automatic and efficient way.

Theresa Reiter^1,2, David Lohr², Michael Hock², Markus Johannes Ankenbrand², Maria Roxana Stefanescu², Maxim Terekhov², and Laura Maria Schreiber^2
1Department of Internal Medicine, University Hospital Wuerzburg, Wuerzburg, Germany, ²Chair of Cellular and Molecular Imaging, Comprehensive Heart Failure Centre (CHCF), University Hospital Wuerzburg, Wuerzburg, Germany

The establishment of human cardiac MRI in the setting of ultra highfield MRI puts high demands on hardware, sequences and handling of the examinees. Practical and safety relevant limitations are set for extensive modifications regarding hardware and sequence. As a consequence, human based factors play a paramount role in the success of a routinely used cardiac imaging study at 7T. We report our experiences from 71 volunteers with cardiac MRI scans with the aim to increase the understanding of the practical implementation of cardiac MRI and factors that influence and do not influence image quality in this specific setting.

Said Aldemir¹, Fatima tu Zahra², Redi Poni³, and Ergin Atalar^4
1Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey, ²-, Ankara, Turkey, ³ETH Zurich, Zurich, Sweden, ⁴Electrical Electronics Engineering, Bilkent University, Ankara, Turkey

In this work, performance of coupled Class-E amplifiers in a transmit array system is investigated. Conditions for these nonlinear amplifiers to work efficiently with desired output power are determined. Also a tuning procedure mitigating undesired effects of coupling on the performance of these nonlinear amplifiers is explained. Simulations are performed in ADS 2016 with 2 Class-E amplifiers and different coupling levels are tested. MRI experiment is performed in order to observe the effects of coupling on amplifier performance. With contour plots, how overall performance of the system is affected by phase and amplitude of an amplifier channel is investigated.