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Daniel Papp¹, Nicolas Boulant², Aurelien Massire³, Frank Mauconduit², Vincent Gras², and Julien Cohen-Adad^1,4,5,6
1NeuroPoly Lab, Institute of Biomedical Engineering, Polytechnique Montreal, Montreal, QC, Canada, ²University of Paris-Saclay, CEA, NeuroSpin, CNRS, BAOBAB, Gif sur Yvette, France, ³Siemens Healthcare SAS, Saint-Denis, France, ⁴Mila - Quebec AI Institute, Montreal, QC, Canada, ⁵Functional Neuroimaging Unit, Centre de recherche de l'Institut universitaire de gériatrie de Montréal, Montreal, QC, Canada, ⁶Centre de recherche du CHU Sainte-Justine, Université de Montréal, Montreal, QC, Canada

Keywords: Parallel Transmit & Multiband, Spinal Cord

While the Universal Pulse approach to mitigate the RF field inhomogeneity effect has been successfully deployed in brain imaging, adoption in spinal cord imaging is lacking. Here, we demonstrate the feasibility of designing Universal Pulses for the cervical spinal cord at 7T, and show a marked improvement for signal intensity in the upper thoracic cord.

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Jiayao Yang¹, Jon-Fredrik Nielsen², and Yun Jiang^2,3
1Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI, United States, ²Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States, ³Department of Radiology, University of Michigan, Ann Arbor, MI, United States

Keywords: RF Pulse Design & Fields, RF Pulse Design & Fields

This study proposed a novel algorithm for designing multidimensional RF in spin-domain using auto-differentiation in PyTorch. Our algorithm uses spin-domain description of rotations to formulate the RF pulse design into optimization problems. We designed 3D refocusing pulses and verified the performance using spin-echo based sequences in phantom at 1.5T and in vivo in the brain at 3T.

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zheng zhong¹, Congyu Liao², Janhavi Singhal³, Frank Ong², Shreyas S. Vasanawala², and John M. Pauly^4
1Radiology, Stanford University, Palo Alto, CA, United States, ²Radiology, Stanford University, Stanford, CA, United States, ³University of California Santa Barbara, Santa Barbara, CA, United States, ⁴Electrical Engineering, Stanford University, Stanford, CA, United States

Keywords: RF Pulse Design & Fields, RF Pulse Design & Fields

SLfRank is a novel RF pulse design framework proposed to improve upon the well-established Shinnar Le-Roux (SLR) design algorithm. Numerical experiments demonstrated promising effectiveness of SLfRank, prompting a need to validate its experimental feasibility. An experimental comparison of SLR and SLfRank is achieved by measuring slice profiles, multiband excitation, and spin-echo pulses on phantom and human brain. SLfRank produced images of comparable quality to the SLR algorithm, but with reduced RF energy and greater control over RF pulse phase. SLfRank’s numerical feasibility aligned closely with its effectiveness experimentally thus proving its technical feasibility for applications in this work and beyond.

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Dario Bosch^1,2, Jonas Bause¹, and Klaus Scheffler^1,2
1High Field MR Center, MPI for Biological Cybernetics, Tuebingen, Germany, ²Department for Biomedical Magnetic Resonance, University Hospital Tübingen, Tuebingen, Germany

Keywords: Parallel Transmit & Multiband, RF Pulse Design & Fields, Python, PyTorch, Optimization

Traditional pTx pulse design focuses on optimizing RF pulses with a fixed or parametrized gradient waveform. Utilizing fast GPUs for autodifferentiation, the optimization process becomes sufficiently efficient that RF pulses and the underlying gradient waveforms can be freely optimized concurrently within short time. This allows for the time-efficient creation of pTx pulses without prior knowledge about suitable gradient trajectories. Still, restrictions e.g. due to hardware limitations may be included into the optimization process.
We provide a pulse design toolbox and demonstrate its ability to generate universal small-FA excitation pulses as well as large-FA pulses.

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Xin Shao¹, Xiaodong Ma², Hua Guo¹, Kamil Ugurbil³, and Xiaoping Wu^3
1Center for Biomedical Imaging Research, Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing, China, ²Department of Radiology and Imaging Sciences, University of Utah, Salt Lake City, UT, United States, ³Center for Magnetic Resonance Research, Radiology, Medical School, University of Minnesota, Minneapolis, MN, United States

Keywords: Parallel Transmit & Multiband, RF Pulse Design & Fields

There has been an increasing interest in designing parallel transmit spatial spectral (pTx SPSP) RF pulses for reducing transmit B1 inhomogeneity while achieving water selective excitation. In this study, we propose a new pTx SPSP pulse design method with explicit SAR control with nearly complete fat suppression. Our results based on human calibration data acquired at 7T suggest that our method is equally applicable to both kT-point and SPINS pulse design, outperforming an existing method based on combining pTx with binomial pulse design approach. We believe our method will have a utility for high-resolution, whole-brain functional MRI at ultrahigh field.

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David Leitão¹, Raphael Tomi-Tricot^2,3, Pip Bridgen¹, Patrick Liebig⁴, Rene Gumbrecht⁴, Dieter Ritter⁴, Jo Hajnal^1,3, and Shaihan Malik^1,3
1Biomedical Engineering & Imaging Sciences, King's College London, London, United Kingdom, ²MR Research Collaborations, Siemens Healthcare, Frimley, United Kingdom, ³Centre for the Developing Brain, King's College London, London, United Kingdom, ⁴Siemens Healthcare GmbH, Erlangen, Germany

Keywords: RF Pulse Design & Fields, Magnetization transfer

While standard pulse design methods control the rotation of magnetization (i.e. flip angle), the recently proposed PUSH method aims to control the root-mean-squared B1, to control magnetization transfer (MT) effects. General RF pulses create both effects simultaneously: this is important in T1 mapping, where incidental MT effects introduce bias. We show that using standard pulse design methods to improve flip angle uniformity can actually worsen the bias in T1 measurement by producing uncontrolled spatially variable MT effects. We propose a ‘hybrid-PUSH’ method optimizing both flip angle and B1rms, and demonstrate this improves quality of T1 estimation in-vivo at 7T.

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Matthijs H.S. de Buck¹, Aaron T. Hess¹, and Peter Jezzard^1
1Wellcome Centre for Integrative Neuroimaging, FMRIB, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom

Keywords: Parallel Transmit & Multiband, High-Field MRI, Neurovascular

Cerebrovascular imaging methods suffer from a rapid drop in B1⁺ into the neck when using typical transmit head coils at 7T. Custom RF shims on regular pTx head coils could improve the B1⁺ magnitude in the major feeding arteries in the neck region over standard CP transmit mode. We found that this can improve the B1⁺ magnitude in the carotid arteries by 36% while also improving the RF homogeneity. This can be achieved using universal, phase-only RF shims, facilitating easy implementation in existing sequences and without requiring custom hardware.

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Chia-Yin Wu^1,2,3, Jin Jin^2,4, Markus Barth^1,2,3, and Martijn Cloos^1,2
1Centre for Advanced Imaging, University of Queensland, St Lucia, Australia, ²ARC Training Centre for Innovation in Biomedical Imaging Technology, University of Queensland, St Lucia, Australia, ³School of Information Technology and Electrical Engineering, University of Queensland, St Lucia, Australia, ⁴Siemens Healthcare Pty Ltd, Brisbane, Australia

Keywords: Parallel Transmit & Multiband, RF Pulse Design & Fields

In this work, we demonstrate a parallel transmit implementation of the bSSFP sequence at 7 Tesla. The bSSFP sequence is one of the most efficient acquisition strategies however highly sensitive to B0 inhomogeneity which creates undesirable banding artefacts. A tailored pair of pTx pulses can be used to induce the desired steady-state magnetisation behaviour at all spatial locations regardless of the off-resonance frequency due to B0 inhomogeneity. Shown through simulation and experimental validation, we were able to capture signal in one acquisition with significant mitigation of banding artifacts and improvement in signal uniformity without SNR loss and time penalty.

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Sydney Nicole Williams¹, Paul McElhinney¹, Belinda Ding^1,2, Sarah Allwood-Spiers³, David A. Porter¹, Shajan Gunamony^1,4, and Wyger Brink^5
1Imaging Centre of Excellence, University of Glasgow, Glasgow, Scotland, ²Siemens Healthcare Ltd., Frimley, United Kingdom, ³NHS GGC MRI Physics, NHS Greater Glasgow & Clyde, Glasgow, Scotland, ⁴MR CoilTech Ltd., Glasgow, Scotland, ⁵Magnetic Detection & Imaging Group, University of Twente, TechMed Centre, Netherlands

Keywords: Parallel Transmit & Multiband, Safety, RF Pulse Design, RF Coils

Previous simulation studies of motion in parallel transmission (pTx) have identified large increases in specific absorption rate (SAR) and pulse performance error. This abstract extends this by evaluating the effects of motion on RF shimming and dynamic pTx in vivo at 7T. The T1w image of a healthy volunteer was segmented to create a body model for electromagnetic simulation in a custom pTx coil. The model was simulated at six head positions matched to experimental measurements. Motion had a detrimental effect on pTx pulse performance and also caused local SAR changes, though not as severe as seen previously in simulation.

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Minghao Zhang¹ and Christopher T. Rodgers^1
1Wolfson Brain Imaging Centre, University of Cambridge, Cambridge, United Kingdom

Keywords: Parallel Transmit & Multiband, Parallel Transmit & Multiband

Spokes parallel transmit pulses improve the homogeneity of ultra-high field imaging. Typically the gradient trajectory (i.e. spoke k_t-space positions) is determined using the iterative Fourier transform approach (FTA). We introduce “BOGAT” (Bayesian Optimisation of GrAdient Trajectory) to efficiently determine globally optimal gradient trajectories.

 

We evaluated BOGAT in phantoms for single-band and multi-band excitation, and retrospectively in 9 volunteers using existing B₀ and B₁⁺ maps.

 

BOGAT improves flip angle homogeneity (by 12.8% vs FTA, P<0.001) and reduces SAR (17.2%, P<0.001). Calculations take ~10s extra for a set of multiband pulses, making it feasible to use for online per-subject optimisation.

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Ali Caglar Özen¹, Serhat Ilbey¹, Feng Jia¹, and Michael Bock^1
1Division of Medical Physics, Department of Radiology, University Medical Center Freiburg, Freiburg, Germany

Keywords: Non-Array RF Coils, Antennas & Waveguides, New Devices, dental MRI

MRI can simultaneously image soft and hard tissues such as glands, teeth, gum, nerves and bone, thus could be valuable for diagnosis of dental pathologies and implant planning. Intraoral coils have been proved essential to dental MRI due to superior sensitivity compared to external coils. In this study, we introduce a modified transverse loop coil design, which provides improved sensitivity, homogeneity, comfort and safety. We also introduce a bio-compatible, artefact-free and MR-silent coating for intraoral coils. Phantom and in vivo dental MR images demonstrate the advantages of the new intraoral coil design.

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Sayim Gokyar¹, Chenyang Zhao¹, Shajan Gunamony^2,3, Jiaruo Yan², Jonathan West⁴, Niels Kokot⁴, and Danny JJ Wang^1,5
1USC Stevens Neuroimaging and Informatics Institute, Los Angeles, CA, United States, ²MR Coiltech Limited, Glasgow, UK, Glasgow, United Kingdom, ³Imaging Centre of Excellence, University of Glasgow, Glasgow, United Kingdom, ⁴Department of Otolaryngology - Head and Neck Surgery, LAC+USC Medical Center, Keck Medicine of USC, Los Angeles, CA, United States, ⁵Department of Neurology, Keck School of Medicine, University of Southern California, Los Angeles, CA, United States

Keywords: New Devices, Neuro

Parotid salivary gland neoplasms occur in conspicuous locations near the facial nerve and have a risk for malignant transformation – making early diagnosis and treatment essential. Here we present a novel three-dimensional surface coil (3D Coil) architecture and a deep learning-based noise reduction method that offers twice higher signal to noise ratio compared to single channel surface coil for parotid gland imaging at 7T.

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Matt Waks¹, Russell Lagore¹, Edward Auerbach¹, Andrea Grant¹, Lance DelaBarre¹, Steve Jungst¹, Nader Tavaf¹, Jerahmie Radder¹, Pierre-Francois Van de Moortele¹, Alireza Sadeghi-Tarakameh¹, Yigitcan Eryaman¹, Gregor Adriany¹, and Kamil Ugurbil^1
1Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States

Keywords: RF Arrays & Systems, RF Arrays & Systems

We present a splittable 16-channel self-decoupled (SD)¹ transmit/receive (Tx/Rx) loop array combined with a 64-channel receive-only (Rx) loop array to generate a 80Rx/16Tx array for human head imaging at 10.5 Tesla. Compared to the previously presented SD transmitter, we designed, miniaturized, and integrated the MR system interface, including custom transmit/receive switches and preamplifiers, into the coil housing. We also implemented our new custom 128 receiver system, which supported this combined 80 channel receive configuration. Experimental MR results demonstrate advantages over our previous 16-channel transmit-only SD array and substantially increased central SNR with the 80-channel compared to the 64-Rx only configuration.

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Felix Glang¹, Anton V. Nikulin^1,2, Nikolai Avdievich¹, Dario Bosch^1,2, Theodor Steffen¹, and Klaus Scheffler^1,2
1High-field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany, ²Department of Biomedical Magnetic Resonance, Eberhard Karls University Tübingen, Tübingen, Germany

Keywords: RF Arrays & Systems, High-Field MRI

Parallel imaging with electronically modulated time-varying receive sensitivities is a novel concept for improved reconstruction quality and reduced noise amplification. Previously, it was demonstrated for 2D imaging using reconfigurable surface loop receive elements. In the present work, we extend the approach to 3D imaging and for that introduce a reconfigurable single-row dipole receive array. By using PIN diodes to switch between capacitive and inductive impedance in the dipole arms, spatially distinct sensitivity profiles are formed that can be rapidly modulated. This is shown to enable parallel imaging acceleration along the dipole’s axis and improve reconstruction quality compared to static sensitivities.

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Lyanne M I Budé^1,2, Bart R Steensma³, Irena Zivkovic¹, and Alexander J E Raaijmakers^2,3
1Electrical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands, ²Biomedical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands, ³Division of Imaging and Oncology, UMC Utrecht, Utrecht, Netherlands

Keywords: RF Arrays & Systems, High-Field MRI

This work introduces the coax monopole antenna. The antenna consists of a continuation of the feeding cable and uses only one inductor at the distal side of the antenna to achieve matching. Creating a radiative antenna is done by introducing one interruption in the shield of the coaxial cable, and the antenna length is enforced using a cable trap. Simulations and measurements show that the performance of this antenna is comparable to the fractionated dipole antenna, while introducing many advantages like easy cable routing, proper loading of the coil due to its flexibility, and easy construction.

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Jan Paska^1,2, Bili Wang^1,2, Anna Chen^1,2, Guillame Madelin^1,2, and Ryan Brown^1,2
1Center for Advanced Imaging Innovation and Research (CAI2R), NYU School of Medicine, New York, NY, United States, ²Center for Biomedical Imaging, Department of Radiology, NYU School of Medicine, New York, NY, United States

Keywords: RF Arrays & Systems, RF Arrays & Systems

One method to achieve multiple coil resonances involves the use of diode or microelectromechanical system (MEMS) switches to toggle between resonances at proton and x-nuclei frequencies. While this approach provides a straightforward means to activate or deactivate coils corresponding to the desired nucleus, it does not allow simultaneous multinuclear data acquisition hat is required to eliminate temporal disparities. In this work we present a triple tuned birdcage for truly simultaneous imaging of X-nuclei combined with a proton dipole array at 7T. We show initial phantom imaging experiments and compare SNR with existing RF coils.

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Alina Scholz¹, Mirsad Mahmutovic¹, Mona Alem¹, Roland Müller², Torsten Schlumm², Harald E Möller², Anastasia Yendiki^3,4, Gabriel Ramos-Llorden^3,4, Lawrence L Wald^3,4,5, Susie Y Huang^3,4,5, and Boris Keil^1,6
1Institute of Medical Physics and Radiation Protection (IMPS), TH-Mittelhessen University of Applied Sciences, Giessen, Germany, ²Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, ³A. A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlstown, MA, United States, ⁴Harvard Medical School, Boston, MA, United States, ⁵Harvard-MIT Division of Health Sciences and Technology, Cambridge, MA, United States, ⁶Center for Mind, Brain and Behavior (CMBB), Marburg, Germany

Keywords: RF Arrays & Systems, Brain

Long-durational diffusion weighted MRI scans with high gradient strength and high slew rate experiences in addition to the generally low signal-to-noise-ratio several problems, such as image artifacts due to eddy currents and the gradual increase of the sample temperature. Combining a high-density anatomically shaped receive coil with field monitoring and temperature control can overcome these limitations. Therefore, we designed and constructed a 64-channel whole human ex vivo brain Rx coil with integrated field monitoring and temperature control system. First SNR measurements confirm the receive capability with high SNR.

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Daniel Wenz^1,2, Thomas Dardano^1,2, Mark Widmaier^1,3, Songi Lim^1,2, Zhiwei Huang^1,2, and Lijing Xin^1,2
1CIBM Center for Biomedical Imaging, Lausanne, Switzerland, ²Animal Imaging and Technology, Ecole Polytechnique Federale de Lausanne (EPFL), Lausanne, Switzerland, ³Laboratory of functional and metabolic imaging, Ecole Polytechnique Federale de Lausanne (EPFL), Lausanne, Switzerland

Keywords: RF Arrays & Systems, RF Arrays & Systems

Dipole antennas can be combined with loop elements to increase a central SNR in human brain MRI at 7T (300MHz). However, this approach was not investigated at lower frequencies. In this study a degenerate birdcage coil was combined with a pair of bent dipole antennas to increase a central SNR for phosphorus MRS of human brain at 7T (120MHz). Simulations showed that this approach could provide a 1.6-fold central SNR gain vs. degenerate birdcage-only. The RF coil was constructed and successfully tested at the bench. In the next step, an experimental validation of the proposed strategy will be performed.

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Sadri Güler^1,2, Vitaliy Zhurbenko^1,3, Irena Zivkovic^1,4, Hanne Christensen⁵, Sverre Rosenbaum⁵, Inger Birgitte Havsteen⁶, and Esben Thade Petersen^1,2
1Section for Magnetic Resonance, DTU Health Tech, Technical University of Denmark, Kgs Lyngby, Denmark, ²Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital - Amager and Hvidovre, Copenhagen, Denmark, ³Department of Electrical Engineering, Technical University of Denmark, Kgs Lyngby, Denmark, ⁴Electrical Engineering Department, Technical University of Eindhoven, Eindhoven, Netherlands, ⁵Department of Neurology, Copenhagen University Hospital - Bispebjerg and Frederiksberg, Copenhagen, Denmark, ⁶Department of Radiology, Copenhagen University Hospital - Bispebjerg and Frederiksberg, Copenhagen, Denmark

Keywords: RF Arrays & Systems, RF Arrays & Systems

The advantage of low coupling ratios of shielded-coaxial-cable coils (SCCs) are used to obtain an eight-channel head-neck transmit array for 7T-MRI. The six SCCs are combined with the two-channel Nova coil by taking the advantage of low coupling between SCCs and the Nova coil. Low inter element coupling along with the independent radiation regions of the SCCs and the Nova coil made it possible to do a straightforward B1-shimming resulting in a relatively homogeneous magnetic field in both head and neck region. Structural images are acquired with large coverage down to the bifurcation while high SNR is preserved.

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Leo Rémillard¹, Adam Mitchell Maunder¹, Fraser Robb², Ashwin K. Iyer³, and Nicola De Zanche^1
1Oncology, Medical Physics, University of Alberta, Edmonton, AB, Canada, ²GE Healthcare, Aurora, OH, United States, ³Electrical and Computer Engineering, University of Alberta, Edmonton, AB, Canada

Keywords: Hybrid & Novel Systems Technology, Body, metamaterial

The transmit field suffers from standing wave inhomogeneities at field strengths ≥3T, which degrade image quality and create specific absorption rate (SAR) hotspots. We present the first experimental demonstration of a whole-body metamaterial liner (metaliner) that enables traveling wave excitation at a lower frequency than achievable otherwise. The simulated transmit efficiencies for a comparable birdcage and metaliner were 2.43μT⁄√kW±23.8% and 1.80μT⁄√kW±25.5% respectively, and the maximum 10g local SAR was reduced by 18% with the metaliner. This shows that the metaliner is an attractive alternative to the BC with greater safety thanks to the lower localized SAR.