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Yueqi Qiu¹, Haoran Bai¹, Hao Chen¹, and Zhiyong Zhang^1
1School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai Jiao Tong University, Shanghai, China

Keywords: Low-Field MRI, Low-Field MRI

Low-field MRI systems have seen a renaissance recently due to improvements in technology and its low costs. However, properties like SNR, T1 and T2 values of low fields have caused a lot of concern because they always change with field strengths. This study conducted the SNR comparison based on phantom and fitted the quantitative mapping of human brains at 0.11T, 0.25T, 1.5T and 3T to design a set of protocols enabling similar contrasts of the typical clinical images at different fields. The impacts of lowered magnetic field strengths on imaging quality were shown in this study.

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Anja Samardzija¹, Kartiga Selvaganesan¹, Younghyun Ha², Zhehong Zhang¹, Chenhao Sun², Heng Sun¹, Gigi Galiana², and Todd Constable^2
1Biomedical 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, RF Arrays & Systems

We developed a stop-motion imaging technique in which a 3x3 radiofrequency coil that transmits Bloch-Siegert encodings is placed in a different position within the field-of-view for each MR signal acquisition. This study is performed using a non-linear gradient-free low-field MRI system. High spatial resolution is achieved through stop-motion imaging. We show that stop-motion imaging done with a total of 200 encodings (20 imaging positions and 10 encodings per position) outperformed stationary imaging performed with 200 encodings (1 imaging position and 200 encodings per position). 

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MEENA RAJENDRAN¹ and SHAOYING HUANG^1
1Engineering Product Developement, Singapore University of Technology and Design, Singapore, Singapore

Keywords: Low-Field MRI, Low-Field MRI, RF coil

A widened-bandwidth RF volume coil using crossed elliptical winding pattern (symmetric in azimuthal direction) is proposed for Halbach-array-based portable MRI knee scanner. The fractional bandwidth (FBW) is 0.51% centered at 2.84 MHz (B₀ = 67mT) with a high B₁ field strength (57µT) and a high homogeneity (94%) within a cylindrical volume of diameter and  length of both 95mm. Compared to solenoid coils of comparable dimensions, it is an increase of 18% in FBW,  an improvement in homogeneity by 6.1%, and only a compromise of 1.9% in the field strength, which is the best combination.

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Anupama Ramachandran¹, Hero Hussain¹, Mishal Mendiratta Lala², Jacob Richardson³, Nancy Dudek², Joel Morehouse², Katherine Wright⁴, Vikas Gulani³, and Nicole Seiberlich^3
1Radiology, University of Michigan, Ann Arbor, MI, United States, ²University of michigan, Ann arbor, MI, United States, ³Radiology, University of michigan, Ann arbor, MI, United States, ⁴University of Michigan, Ann arbor, MI, United States

Keywords: Low-Field MRI, Body, Abdomen

Abdominal MRI including MRCP was performed in 15 healthy subjects on both a 0.55T and a 1.5T MR system. Image quality (IQ) was rated by two radiologists (22 and 17 yrs experience). All sequences were rated acceptable at 0.55T. In comparison to 1.5T, IQ scores at 0.55T were higher for DWI and 3D MRCP, and lower for the other sequences. Acquisition times were longer at 0.55T for all sequences except 3D MRCP. Thus, acceptable quality abdominal images can be obtained on a commercial 0.55T system with slightly lower IQ ratings of some of the sequences compared to 1.5T.

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Fernando Vega^1,2,3, Abdoljalil Addeh^1,2,3, and M. Ethan MacDonald^1,2,3,4
1Biomedical Engineering, University of Calgary, Calgary, AB, Canada, ²Electrical & Software Engineering, University of Calgary, Calgary, AB, Canada, ³Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada, ⁴Department of Radiology, University of Calgary, Calgary, AB, Canada

Keywords: Low-Field MRI, Machine Learning/Artificial Intelligence, MRI, Unpaired Image Translation

In this work, a denoising Cycle-GAN is implemented to yield high-field, high resolution, high signal-to-noise ratio MRI images from simulated low-field, low resolution, low signal-to-noise MRI images.  Resampling and additive Rician noise were used to simulate low-field MRI.   Images were utilized to train a DAE and Cycle-GAN, with paired and unpaired cases, respectively.  Both networks were evaluated using SSIM and PSNR image quality metrics.   This work demonstrates the use of advanced machine learning to improve low-field MRI images that can outperform classical denoising autoencoders and does not require image pairs.

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José Miguel Algarín^1,2, Teresa Guallart-Naval^2,3, Ana Ferri-Caruana⁴, Rubén Bosch³, Francisco Juan-Lloris⁵, Eduardo Pallás^1,2, Juan Pablo Rigla³, Pablo Martínez⁵, José Borreguero³, José María Benlloch^1,2, Fernando Galve^1,2, and Joseba Alonso^1,2
1Institute for Instrumentation in Molecular Imaging (i3M), CSIC, Valencia, Spain, ²Institute for Instrumentation in Molecular Imaging (i3M), Universitat Politècnica de València, Valencia, Spain, ³Tesoro Imaging SL, Valencia, Spain, ⁴Educación Física y Deportiva, Universitàt de València, Valencia, Spain, ⁵Physio MRI SL, Valencia, Spain

Keywords: Low-Field MRI, Low-Field MRI, Sport MRI

Here we show the results of the first systematic study performed in our low-field 72 mT MRI scanner. Calf images were acquired from 35 volunteers whose performance was measured during different physical activities before the scan. We segmented the images to determine the cross-sectional area and volume of the gastrocnemius muscles and correlated the results with the muscular activity measurements of the volunteers. We found that the medial gastrocnemius muscle volume correlates significantly with participants weight and unilateral jump capacity.

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Keerthi Sravan Ravi^1,2, Kunal Aggarwal³, John Thomas Vaughan Jr.², Yun Soung Kim⁴, and Sairam Geethanath^5
1Biomedical Engineering, Columbia University, New York, NY, United States, ²Columbia Magnetic Resonance Research Center, Columbia University, New York, NY, United States, ³Accessible MR Lab, BMEII, Diagnostic, molecular and interventional radiology, Icahn School of Medicine at Mt. Sinai, New York City, NY, United States, ⁴Biomedical Engineering and Imaging Institute, Dept. of Diagnostic, Molecular and Interventional Radiology,, Mt.Sinai, New York, NY, United States, ⁵Accessible MR Laboratory, Biomedical Engineering and Imaging Institute, Dept. of Diagnostic, Molecular and Interventional Radiology,, Mt. Sinai, New York, NY, United States

Keywords: Low-Field MRI, Low-Field MRI

These artifacts degrade image quality, often causing misdiagnosis. A 6-axis motion tracking sensor (ICM-20649, TDK-InvenSense) with a full-scale range of +-4000 degrees per second for the gyroscope and +-30g for the accelerometer was integrated with a 50mT scanner. The sensor’s readings can successfully be processed to detect motion. However, it resulted in zipper artifacts and degraded image quality in a phantom experiment. Still, the sensor’s placement on the forehead or the temples or the chin might not significantly impact brain data when coupled with slab-wise shimming.

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Jessica Schäper^1,2 and Oliver Bieri^1,2
1Department of Biomedical Engineering, University of Basel, Basel, Switzerland, ²Division of Radiological Physics, Department of Radiology, University Hospital Basel, Basel, Switzerland

Keywords: Low-Field MRI, Brain, MP-RAGE, low-field, white matter, gray matter

The MP-RAGE is the most commonly used sequence for structural brain imaging in clinical routine. Consequently, the optimization of imaging parameters for maximum contrast and signal is an important task. In this work, we implemented a previously developed computation and calculated optimal parameters for 0.55T. Additionally, the obtained images were compared with a gray-white matter contrast-optimized FLASH. Computing the contrast-to-noise ratio revealed a clear benefit for MP-RAGE over FLASH at mid to low resolutions, while a trend towards similar or even higher contrast-to-noise ratios for FLASH as compared to MP-RAGE at high resolutions was observed.

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Jordina Aviles Verdera^1,2, David Leitao^1,2, Daniel West^1,2, Joseph V Hajnal ^1,2, Shaihan Malik^1,2, Raphael Tomi-Tricot^1,2,3, and Jana Hutter^1,2
1Center for the Developing Brain, School of Biomedical Engineering & Imaging Sciences, King's College London, London, United Kingdom, ²Biomedical Engineering Department, School of Biomedical Engineering & Imaging Sciences, King's College London, London, United Kingdom, ³MR Research Collaborations, Siemens Healthcare Limited, Frimley, United Kingdom

Keywords: Low-Field MRI, Data Acquisition

Fetal MRI is an important complementary technique to ultrasound to monitor fetal health. Low-field MRI benefits from reduced distortion, increased B1 homogeneity, wider bore sizes for maintained field homogeneity and longer T2*. The latter is particularly beneficial for single-shot techniques as it allows more flexible and longer read-out strategies. This abstract explores, for the first time, spiral read-out for fetal brain T2* relaxometry and offers preliminary quantitative fetal brain T2* results. Next steps include further exploration of flexible read-out strategies such as undersampled interleaved spirals to work towards higher temporal resolution and motion robustness.

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Marko Havu¹, Koos Zevenhoven¹, Antti Mäkinen¹, and Risto J Ilmoniemi^1
1Department of Neuroscience and Biomedical Engineering, Aalto University, Espoo, Finland

Keywords: Low-Field MRI, Image Reconstruction

In low-field and ultra-low-field MRI, concomitant fields can cause severe blurring and distortion in traditional Fourier reconstruction. We have developed an improved image reconstruction framework based on our previously published method that uses a frequency–space formulation. It provides more accurate reconstruction results with the cost of increased computation time. Known inhomogeneity and other field nonidealities can be incorporated into the model to improve the quality of the reconstruction. The framework will be published as open source.
 

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Bart de Vos¹, Rob Remis², and Andrew Webb^1,2
1C.J. Gorter MRI Center, Leiden University Medical Center, Leiden, Netherlands, ²Circuits and Systems, Delft University of Technology, Delft, Netherlands

Keywords: Low-Field MRI, Artifacts, Concomitant fields

Low field Halbach systems are susceptible to concomitant gradient effects. The associated fields are significantly different from clinical systems and are presented here for the first time. The corresponding equations and associated effects are verified using a spin echo sequence on a 46 mT Halbach system where a gradient strength of 10 mT/m on a phantom with maximum dimension of 200 mm is observed to create distortions. These are most evident in the transverse plane, where the phase encoding gradient causes blurring and overlapping the other transverse gradient lobe results in an additional warping effect.

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MEENA RAJENDRAN¹ and SHAOYING HUANG^1
1Engineering Product Developement, Singapore University of Technology and Design, Singapore, Singapore

Keywords: Low-Field MRI, Low-Field MRI

The lightweight frequency selective surface(FSS) using high-pass inductive mesh grids is proposed as shielding of RF solenoids at 2.84MHz for an MRI system using a Halbach array(average B₀=67mT). Its effects on the coil B₁-sensitivity and the shielding effectiveness are examined. A solenoid(diameter=60mm) was used as an example and the shielding of 5-25mm away was examined. The 5mm-away-FSS-shielded coil has 50.1% (in simulation) and 91.3% (in measurements) higher B₁-sensitivity and comparable shielding effectiveness within a defined FoV compared to the copper-shielded coil of the same dimensions. The measured data agree with the simulated ones.

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Torben P.P Hornung^1,2,3, Neha Koonjoo^1,2, Susu Yan^3,4, Matthew S Rosen^1,2,5, and Thomas R Bortfeld^3,4
1Department of Radiology, A.A Martinos Center for Biomedical Imaging / MGH, Charlestown, MA, United States, ²Harvard Medical School, Boston, MA, United States, ³Department of Physics, ETH Zürich, Zürich, Switzerland, ⁴Department of Radiation Oncology, MGH, Boston, MA, United States, ⁵Department of Physics, Harvard University, Cambridge, MA, United States

Keywords: Low-Field MRI, Breast, Hybrid & Novel System Technology

MRI guidance in Proton Therapy can improve breast cancer targeting accuracy during treatment planning. This study focuses on RF coil optimization for breast imaging at ultra-low field where proton beam deflection is minimal. Our previous optimization algorithm was further improved to adapt to any breast-shaped coil and any anatomical region. It was also developed for organs-at-risk imaging with a deep view into the chest. This new optimization method was tested for a single-channel conical-shaped coil and validated with imaging. The optimized coil showed a more homogenous B-field compared to its unoptimized evenly spaced wound coil in agreement with the simulations.

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Samson Lecurieux Lafayette¹, Francesco Padormo², Paul Cawley¹, Emil Ljunberg^3,4, Rui Teixeira², David Edwards¹, Mary Rutherford¹, Tomoki Arichi¹, and Joseph Hajnal^1
1Perinatal Imaging & Health, King's College, London, United Kingdom, ²Hyperfine, London, United Kingdom, ³Department of Neuroimaging, King's College, London, United Kingdom, ⁴Department of Medical Radiation Physics, Lund University, Lund, Sweden

Keywords: Low-Field MRI, Brain

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Olivier E Mougin¹, Paul Glover¹, Richard Bowtell¹, and Penny A Gowland^1
1SPMIC, University of Nottingham, Nottingham, United Kingdom

Keywords: Low-Field MRI, Gradients

Open magnet provide advantageous facility for imaging the human body in a natural way. However field inhomogeneities can reduce the utilisable imaging field-of-view. We present a simple way to map the static field inhomogeneity and the non-linear gradient inhomogeneity in order to correct them during the image reconstruction.

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Liliana Edmonds¹, Irene Kuang¹, Elfar Adalsteinsson^1,2, and Jacob White^1
1Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, United States, ²Institute for Medical Engineering and Science, Massachusetts Institute of Technology, Cambridge, MA, United States

Keywords: Low-Field MRI, Low-Field MRI

The easily constructed Aubert ring-inspired “spokes-and-hub” magnets show promise as a topology for handheld MR imaging, particularly for educational purposes. In this paper we show the scalability of the spokes-and-hub design, and associated tools and RF signal processing, by scaling up the magnet. Constructing a 2x larger magnet yields a volume large enough to potentially image a finger (with which we hope to inspire students). We used our simulator to design and optimize the magnet topology, then constructed it from off-the-shelf small bar magnets, and verified its fields by direct Hall-effect measurements as well as indirectly through spin echoes. 

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Yonghyun Ha¹, Kartiga Selvaganesan², Chenhao Sun¹, Zhehong Zhang², Anja Samardzija², Heng Sun², Gigi Galiana¹, and Todd Constable^1
1Radiology and Biomedical Imaging, Yale University, New Haven, CT, United States, ²Biomedical Engineering, Yale University, New Haven, CT, United States

Keywords: RF Arrays & Systems, RF Arrays & Systems

We introduced a new RF coil made with Moebius cable and RF shield bowl that can be tuned with relatively low capacitance and has good isolation between the coils at low field. B1 amplitude, isolation between the coils, and SNR of the NMR signal of the proposed coil were compared with reference coils (made with copper wire and Moebius cable without an RF shield). Both bench measurements and MR experiments have demonstrated that this coil performs well as part of a low field coil array.

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Mikah Mellors¹ and Rebecca Feldman^2
1University of Toronto, Toronto, ON, Canada, ²University of British Columbia, Kelowna, BC, Canada

Keywords: Low-Field MRI, Magnets (B0)

A low-field tabletop spoke-and-hub permanent magnet array was constructed and assessed for homogeneity as a B0 field. Spatial encoding in the x and y directions was achieved by tilting the hubs relative to one other to generate a linearly increasing field in the tilt direction. A non-array RF coil was designed and optimized for low field strengths, where the signal-to-noise ratio is limited by the weak signal from the sample. The optimized coil design was tuned and matched to the resonant frequency of the spoke-and-hub magnet.