| Computer # |
| 4072.
 | 49 | A Low-cost, Small-footprint Gradient Amplifier for Low Field MRI Based on GaN FETs N Reid Bolding1, Varun Gosula2, Andrew Dupuis2, Jessie Sun3, and Mark Griswold3
1Physics, Case Western Reserve University, Cleveland, OH, United States, 2Biomedical Engineering, Case Western Reserve University, Cleveland, OH, United States, 3Radiology, Case Western Reserve University, Cleveland, OH, United States Keywords: Gradients, Gradients Motivation: The gradient system can be the most expensive part of a low field MRI system with minimal construction costs. Current solutions have linear amplifiers which may not reach power requirements, requiring pricey off-the-shelf amplifiers. Goal(s): Reduce the cost of the gradient drivers by taking amplifier efficiency into consideration to enable better low field MRI system creations. Approach: Uses an amplifier topology more commonly used at higher power, an H-bridge, but a high switching frequency reduces filtering requirements. A modular design eases construction. Results: The amplifier we created attains an increased efficiency, a smaller size, and a lower cost to attain useful power. Impact: Gradient drivers can dominate the overall cost of low-field MRI scanners. Our amplifier costs under 80USD and is capable of a 120V 15A DC output with a bandwidth of 150kHz. It contributes to cost reduction of gradient drivers significantly. |
| 4073.
 | 50 | Comparison at 7T of the Impulse head gradient and whole-body SC72 gradient transfer functions. Caroline Le Ster1, Franck Mauconduit1, An T. Vu2,3, Sajjad Feizollah4, Christine Lucas Tardif4, Alexander Beckett5,6, David Feinberg5,6, and Nicolas Boulant1
1CEA, CNRS, BAOBAB, NeuroSpin, University of Paris-Saclay, Saclay, France, 2University of California, San Francisco, CA, United States, 3San Francisco VA Health Care System, San Francisco, CA, United States, 4McGill University, Montreal Neurological Institute-Hospital, Montreal, QC, Canada, 5Brain imaging center and Helen Wills Neuroscience institute, Berkeley, CA, United States, 6Advanced MRI technologies, Sebastopol, CA, United States Keywords: System Imperfections, System Imperfections: Measurement & Correction Motivation: Ultra-high field MRI requires high performance and accurate gradients to push forward the spatio-temporal resolution, especially for fMRI scans. Goal(s): Compare two commercial gradient coils (whole-body SC72 and head-only Impulse) available on 7T scanners. Approach: Characterization of the gradient transfer function (GTF) and measurement of field perturbations following a spoiler gradient using a field camera. Results: The Impulse gradient coil revealed a smooth GTF profile while the SC72 gradient coil exhibited strong resonances. Field oscillations following a spoiler gradient were greatly reduced with the Impulse gradient. Disconnecting the 3rd order shim coils on the SC72 gradient coil improved the quality of its response. Impact: The GTF of the head-only Impulse gradient coil yields interesting prospects. It remains to be determined whether the apparent benefits versus the SC72 are due to the absence of third order shim coils. |
| 4074.
 | 51 | Eliminating banding artifacts in bSSFP using Parallel Transmission in vivo Chia-Yin Wu1,2,3, Jin Jin1,2,3,4, Markus Barth1,2,3, and Martijn Cloos1,2
1Centre for Advanced Imaging, University of Queensland, Brisbane, Australia, 2ARC Training Centre for Innovation in Biomedical Imaging Technology, University of Queensland, Brisbane, Australia, 3School of Electrical Engineering and Computer Science, University of Queensland, Brisbane, Australia, 4Siemens Healthcare Pty Ltd, Brisbane, Australia Keywords: Parallel Transmit & Multiband, Parallel Transmit & Multiband, RF Pulse Design Motivation: The bSSFP sequence is a highly efficient acquisition strategy that provides high SNR. At ultra-high field it becomes more susceptible to B0 inhomogeneities which leads to banding artifacts and signal loss. Goal(s): To eliminate banding artifacts without SNR loss or time penalty. Approach: A pair of parallel transmit (pTx) pulses was designed to compensate for the off-resonance dephasing accumulated over the duration of one TR in the human brain at 7T. Results: With a tailored pair of pTx pulses it was possible to compensate for off-resonance effects which lead to banding artifacts whilst also providing a uniform excitation in a single bSSFP acquisition. Impact: Parallel transmit is well known for efficient radiofrequency pulse designs that produce uniform excitations. We showed that pTx pulses can simultaneously address other off-resonance effects accumulated over the duration of one TR in the human brain at 7 Tesla. |
| 4075.
 | 52 | Open-Source, High-Efficiency, Easily-Reconfigurable Switch-mode Current Driver for B0 Shimming and Local Field Control Ishaan Govindarajan1, Donald Straney2, Juan Rivas-Davilla3, Kawin Setsompop4, Hong En Chew3, Thomas Witzel5, Lawrence Wald6, Yulin Chang7, and Jason P Stockmann2
1Massachusetts Institute of Technology, Cambridge, MA, United States, 2Athinoula A. Martinos Center for Biomedical Imaging, Cambridge, MA, United States, 3Electrical Engineering, Stanford University, Stanford, CA, United States, 4Radiological Sciences Laboratory, Stanford University, Stanford, CA, United States, 5Q Bio, Inc., San Carlos, CA, United States, 6Massachusetts General Hospital, Charlestown, MA, United States, 7Siemens Healthcare, Charlestown, MA, United States Keywords: New Devices, New Devices Motivation: Multi-coil arrays have demonstrated utility for higher-order B0 shimming, spatial encoding, and local field control. However, existing amplifiers used to drive these coils typically trade off efficiency and imaging noise. Goal(s): Demonstrate a proof-of-concept amplifier with both high efficiency and low imaging noise, while being easily reconfigurable for different loads impedances. Approach: A switch-mode amplifier with highly-integrated power stages, 6th-order LC filtering, and fully-digital control was developed. Its thermal performance, dynamic performance, and impact on imaging noise was tested. Results: Our amplifier demonstrated heatsink-free 10ADC drive capability, <25μs step response rise-times with multiple loads, acceptable disturbance rejection, all while minimally impacting image quality. Impact: We have demonstrated an open-source, proof-of-concept amplifier
achieving power efficiencies of switch-mode designs while maintaining imaging
noise levels akin to linear designs. Such an amplifier unblocks novel spatial
encoding techniques and local field control applications. Development is active
and ongoing. |
| 4076.
 | 53 | Movable Linear Gradients Optimized on Non-Planar B0 Slice Profiles Used for Improving Spatial Encoding in a Non-Linear Low-Field MRI Anja Samardzija1, Yonghyun Ha2, Chenhao Sun2, Heng Sun1, Ryan Gross2, Gigi Galiana1,2, and R. Todd Constable1,2
1Department of Biomedical Engineering, Yale University, New Haven, CT, United States, 2Department of Radiology and Biomedical Imaging, Yale School of Medicine, New Haven, CT, United States Keywords: Low-Field MRI, Low-Field MRI Motivation: Spatial resolution in an open low-field MRI that uses surface RF coils for B1-encoding can be improved by repositioning the RF coils within FOV for each TR. However, this approach is limited by space constraints in the left-right dimension. Linear gradients, especially movable ones optimized for a slab, effectively supplement encoding in that direction. Goal(s): To improve spatial resolution in the left-right direction of an open low-field MRI. Approach: A linear gradient optimized on B0 slice volume is moved in the anterior-posterior direction dependent on readout slice location. Results: Movable gradients improve spatial encoding. Impact: There is an unmet need for open low-field MRIs that can accommodate patients of all sizes and disabilities: this approach to generating high spatial resolution images without the use of volume-encompassing gradients makes open MRI viable. |
| 4077.
 | 54 | A comparison study of different eddy current measurements at low field portable MRI Suen Chen1,2, Yunhao Xie3, Yueqi Qiu1,2, Hao Chen1,2, Hai Luo3, and Zhiyong Zhang1,2
1School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai, China, 2National Engineering Research Center of Advanced Magnetic Resonance Technologies for Diagnosis and Therapy (NERC-AMRT), Shanghai Jiao Tong University, Shanghai, China, 3Wuxi Marvel Stone Healthcare Co. Ltd., Wuxi, China Keywords: Low-Field MRI, Low-Field MRI, eddy current measurement, field probe Motivation: Eddy current results in resolution degradation and unwanted phase variations. However, there have been relatively few eddy-current related studies carried out in low field recently. Goal(s): Our goal was to introduce and compare image-phase based and FID-phase based eddy current measurement techniques in a 64mT MRI system and reduced eddy-current effects. Approach: We employed a large phantom or six field probes to measure eddy-current-induced gradients shift. And we modeled them as sums of exponentially decaying components to compensate the gradient unit. Results: Eddy-current-induced field shift was initially about 350ppm, and reduced to 240ppm and 20ppm by these two methods. Impact: This work develops two methods for measuring eddy
current in low-field MRI, especially for portable scanner, which help reducing
eddy-current-induced effects and improving the image quality of clinical
sequence (e.g. DWI, DTI) in low field scanner. |
| 4078.
 | 55 | Design of a segmented RF shield to minimize eddy currents on low-field Halbach MRI systems Bart de Vos1, Thomas O'Reilly1, Rob Remis2, and Andrew Webb1
1Radiology, C.J. Gorter MRI Center, Leiden University Medical Center, Leiden, Netherlands, 2Microelectronics, Terahertz Sensing, Delft University of Technology, Delft, Netherlands Keywords: Low-Field MRI, Low-Field MRI, Shielding, Eddy-currents Motivation: Eddy-currents induced in the shielding layer placed between the gradient coils and RF transmit coil can create artefacts and lead to longer echo times. Reducing these currents by segmenting the shield while keeping the noise-reduction properties is important for low-field point-of-care systems. Goal(s): Minimizing eddy currents for transverse B0 magnets while maintaining shielding effectiveness. Approach: The segmentation locations are chosen by taking into account the wire pattern of the RF coil and gradient-induced eddy current simulations. Results: The suggested shield results in a decrease in the measured eddy current effects by a factor of 15, with only a noise increase of 4%. Impact: The
proposed shield reduces eddy current effects by a factor of 15, giving the
opportunity to achieve shorter echo-times and higher slew rates with fewer distortions
on point-of-care low-field systems. |
| 4079.
 | 56 | Halbach Magnet Design for Low-Field MRI using Higher-Order Halbach Shimming and Layer-independent Segmentation. Natnael A. Anjulo1, Reid Bolding2, Jessie E.P Sun3, Sai Abitha Srinivas1, Michael Martens2, and Mark A. Griswold1,3
1Biomedical Engineering, Case Western Reserve University, Cleveland, OH, United States, 2Physics, Case Western Reserve University, Cleveland, OH, United States, 3Radiology, Case Western Reserve University, Cleveland, OH, United States Keywords: Magnets (B0), Magnets (B0) Motivation: Existing low-field magnet designs are too heavy. They often have small usable imaging regions and inconvenient bore diameters.
Goal(s): To design a compact, lightweight, and portable low-field magnet system with a large usable imaging region and a small length-to-bore aspect ratio. Approach: Our approach includes data-driven higher-order Halbach-based shim design. We also employed Mu-metal to enhance the shimming. We further improved the homogeneity by discretizing the multilayered Halbach into segments. We used COMSOL multiphysics for simulation. Results: In COMSOL-based magnetostatic simulation, we achieved a compact, lightweight magnet design with an imaging region spanning over half the magnet's bore. Impact: The improvement of the low-field MRI design with a lightweight and inexpensive magnet system with a potential benefit in resource-constrained and point-of-care settings. |
| 4080.
 | 57 | MRI4ALL Hackathon: Under a Week Build of Open-Source Gradient Coils for a Low-Field MRI Anja Samardzija1, Yun Shang2, Andrew Mao3, Karthik Lakshmanan3, Heng Sun1, Bernhard Gruber4,5, Kalina V Jordanova6, Jeff Short4, Vito Ciancia7, Philipp Amrein8, Sebastian Littin8, Leeor Alon3,9, and Jason Stockmann4
1Department of Biomedical Engineering, Yale University, New Haven, CT, United States, 2Department of Biomedical Engineering, Columbia University in the City of New York, New York City, NY, United States, 3Bernard and Irene Schwartz Center for Biomedical Imaging, New York University Grossman School of Medicine, New York City, NY, United States, 4Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA, United States, 5BARNLabs, Muenzkirchen, Austria, 6NIST: National Institutes of standards and Technology, Boulder, CO, United States, 7LaGuardia Studio, New York University, New York City, NY, United States, 8Division of Medical Physics, Department of Diagnostic and Interventional Radiology, University Medical Center Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany, 9Center for Advanced Imaging Innovation and Research (CAI2R), Department of Radiology, New York University Grossman School of Medicine, New York City, NY, United States Keywords: Low-Field MRI, Low-Field MRI Motivation: High production costs limit the accessibility of MRI. To break this accessibility and cost barrier, we demonstrate that affordable gradients can be designed and built in less than two weeks using open-source software and conventional 3D printing. Goal(s): To develop X, Y, and Z gradients for an ultra low-field Halbach MRI. Approach: We used open-source software to design the gradients. The casing was 3D printed, and the coils were manually wound. The fields were measured using an open-source field-mapping probe. Results: We constructed gradients that generated magnetic fields with great correspondence to simulated fields. 2D images were acquired with a fast spin-echo sequence. Impact: Open-source software can be used to design, build, and test MRI gradient coils in a quick and affordable manner. This demonstrates that open-source software for design of MRI hardware can lead to more accessible MRI. |
| 4081.
 | 58 | A 64-channel ex-vivo brain coil array for temperature-controlled diffusion imaging with the Connectome 2.0 MRI scanner Alina Scholz1, Mirsad Mahmutovic1, Gabriel Ramos-Llordén2, Chiara Maffei2, Jason Stockman2, John E Kirsch2, Lawrence L Wald2, Choukri Mekkaoui2, Anastasia Yendiki2, Susie Y Huang2, and Boris Keil1
1Institute of Medical Physics and Radiation Protection, Mittelhessen University of Applied Sciences, Giessen, Germany, 2Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital and Harvard Medical School, Charlstown, MA, United States Keywords: RF Arrays & Systems, RF Arrays & Systems Motivation: Ex-vivo brain DWI with long scan times poses the problem of temperature-related drift of diffusion measurement results. Goal(s): The construction of a 64-channel ex-vivo brain coil with time-course temperature stabilization for obtaining accurate DWI measurements. Approach: Combining a newly developed high-density ex-vivo brain coil array with a forced-air cooling system and a multi-channel temperature recording. Results: The air circulation system was able to maintain the ambient temperature of the coil and, thus, stabilizing the mean diffusivity values over repeated lengthy scans. Without cooling, a drift of the mean diffusivity was overserved, peaking at a 35%-offset at approximately 11 hours. Impact: Temperature-stabilized post-mortem brain samples for diffusion MRI
in combination with a dedicated large channel count ex-vivo brain coil improves
image quality in terms of achievable SNR and greatly reduced
temperature-induced diffusivity shifts. |
| 4082.
 | 59 | MRI in-bore wireless link fidelity investigation with integrated ultra-wide-band antennas Wonje Lee1, Shreyas Vasanawala1, John Pauly1, and Greig Scott1
1Stanford University, Stanford, CA, United States Keywords: RF Arrays & Systems, MR Fingerprinting Motivation: Optimum antenna allocation within the MRI bore is essential for reliable wireless link establishment. Goal(s): Our goal was to identify a sweet spot for in-bore antenna integration. Approach: We utilized time domain pulse distortion metric to evaluate various link fidelities. Results: Study results suggest that the antenna allocation at the middle of the birdcage circumference may produce the minimum pulse distortion and interference. Impact: A time domain pulse distortion metric may provide useful design information to system engineers for reliable in-bore wireless link establishment over a desired bandwidth. |
| 4083.
 | 60 | Detailed Investigations into Inward-Outward Ring for Portable MRI Tingou Liang1, Wenwei Yu2, Erping Li3, Bing Keong Li4, and Shao Ying Huang1
1Singapore University of Technology and Design, Singapore, Singapore, 2Chiba University, Chiba, Japan, 3Zhejiang University, Hangzhou, China, 4Jiangsu LiCi Medical Device Co. Ltd, Lianyungang, China Keywords: Low-Field MRI, Magnets (B0) Motivation: Halbach arrays that supplies transversal magnetic fields are widely used in portable magnetic resonance imaging (MRI), while the Inward-Outward ring (IO-ring) array that supplies longitudinal magnetic fields has great unrevealed potential yet remains under studied. Goal(s): We aim to inspect the potential of IO-ring to widen its range of applications in portable MRI. Approach: By identifying the key geometric parameters and examining their effects on field strength and pattern. Analyses were conducted and the potential applications were discussed. Results: IO-ring is shown to be a promising candidate for providing flexible magnetic field patterns for portable MRI in different application scenarios. Impact: The relationship between all design parameters of IO-ring and the
corresponding field pattern, as well as some intuitive variants of IO-ring
design has been explored, providing new insight to PMA design for portable MRI. |
| 4084.
 | 61 | Design and application of a 16-channel field-probe insert for a 16Tx/32 Rx coil at 9.4 Tesla Jonas Bause1, Praveen Iyyappan Valsala1,2, Dario Bosch1, Philipp Ehses3, Nikolai Avdievich1, and Klaus Scheffler1,2
1High Field Magnetic Resonance, Max-Planck Institute for Biological Cybernetics, Tübingen, Germany, 2Department of Biomedical Magnetic Resonance, Eberhard Karls University Tübingen, Tübingen, Germany, 3German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany Keywords: System Imperfections, System Imperfections: Measurement & Correction, field camera, gradients, spiral, rf coils, physiological, fluctuations Motivation: Gradient imperfections and significant field fluctuations due to physiology at higher field can degrade the image quality and thus limit the use of certain readout trajectories. Goal(s): To perform concurrent monitoring of the encoding gradients and other spatio-temporal field variations during imaging at 9.4 Tesla. Approach: We optimized, designed and manufactured a highly customizable field-probe insert for a 16Tx/32Rx RF array and performed an initial in-vivo experiment. Results: The locations of the probes yield good conditioning for measuring field up to second order spherical harmonics and showed an acceptable reduction in decay time. We demonstrated concurrent field monitoring with a 2D spiral experiment. Impact: Correction of trajectory and field deviations due to system imperfections and physiological effects is important for measurements with long readouts and echo times at ultra-high fields. We present a coil insert that allows simultaneous field monitoring at 9.4 T. |
| 4085.
 | 62 | An open source tool for design and construction of Halbach array based low field magnets, passive shims and a robotic field mapper: MRI4ALL Sai Abitha Srinivas1, Fernando E Boada2, Vito Ciancia3, Clarissa Cooley4,5, Bernhard Gruber5,6, Dinank Gupta7, Kalina V Jordanova8, Aaron R Purchase4,5, Thiago I Rubio9, Jason P Stockmann4,5, Florin Teleanu 9, Chengtong Zhang9, and Leeor Alon10,11
1Biomedical Engineering, Case Western Reserve University, Cleveland, OH, United States, 2Radiology, Stanford University, Palo Alto, CA, United States, 3LaGuardia Studio, New York University, New York, NY, United States, 4Radiology, Massachusetts General Hospital, Boston, MA, United States, 5A.A. Martinos Center for Biomedical Imaging, Charlestown, MA, United States, 6BARNLabs, Muenzkirchen, Austria, 7Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States, 8NIST: National Institutes of standards and Technology, Boulder, CO, United States, 9Chemistry, New york university, New York, NY, United States, 10Radiology, Bernard and Irene Schwartz center for Biomedical Imaging, New York University Grossman school of medicine, New York, NY, United States, 11Radiology, Center for Advanced Imaging Innovation and Research (CAI2R), New York University Grossman school of Medicine, New York, NY, United States Keywords: Low-Field MRI, Low-Field MRI, Open source, magnet design , passive shim, field map Motivation: A comprehensive open-source toolbox for both design and development of low-field MRI magnets, passive shims and a robotic field mapper can accelerate democratization of low field MRIs. Goal(s): Develop an open-source tool for optimization and construction of Halbach array magnets and passive shims. Additionally, develop and build open-source field mapper.
Approach: A simple python-based workflow was used for magnet and passive shim design, and an automated CAD model export and ring former development for the optimized geometry.
Results: A 43mT Halbach array was developed with our approach in a week at the MRI4ALL Hackathon. Compact passive shims improved homogeneity in simulation and measurements. Impact: We have built an easy-to-use open source framework for magnet and passive shim design for low-field MRI with a capability to extract a CAD-file for easy building. Additionally an open source field mapper is developed and is used for validation. |
| 4086. | 63 | Experimental validation of simulated SNR loss due to noise coupling Christian Findeklee1, Peter Vernickel1, and Christoph Leussler1
1Philips Research Hamburg, Philips GmbH Innovative Technologies, Hamburg, Germany Keywords: RF Arrays & Systems, Simulations, SNR, Noise Coupling Motivation: The aim of our study was to analyze the SNR loss due to noise coupling during reception with MRI coil arrays. Goal(s): In particular, we wanted to experimentally confirm the existing calculation methods. Approach: We compared the simulation predicted SNR loss due receiver noise against measurements for a single as well as for three coil elements. Results: A nice agreement was shown between theory and experiment. Impact: With our study, we also show how decisively noise coupling affects the
SNR of an array. |