Tingou Liang¹, Tie Qiu¹, and Shaoying Huang^1
1Singapore University of Technology and Design, Singapore, Singapore

We propose a magnet simulator (named “MagTetris”) for fast calculation of both magnetic field and magnetic force generated by multiple cuboid magnets in arbitrary configurations. The accuracy of “MagTetris” is examined by comparing the calculated results to the FEM-based simulations and the experimental results through a 2-magnet experiment. The average differences between the FEM-based simulations and the “MagTetris” calculations are within 6% for field and 2% for force, while those between the measurements and the “MagTetris” are within 10% for field and 4.5% for force. For the calculation speed, “MagTetris” is 123 times faster compared to the FEM-based commercial software.

Shiwei Yang¹, Xiao Chen², Shuen Chen¹, Hai Luo², Yue Zhao², Ziyue Wu², and Zhiyong Zhang^1
1School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai, China, Shanghai, China, ²Wuxi Marvel Stone Healthcare Co. Ltd., Wuxi, Jiangsu, China, Wuxi, China

Earlier diagnosis of non-alcoholic fatty liver disease (NAFLD) becomes important to prevent the disease progression. Recently, a low-cost portable MR system was developed as a point-of-care screening tool for in vivo liver fat quantification. However, the subcutaneous fat may confound the live fat quantification, particularly in the NAFLD susceptible population. In this work, we propose a novel RF coil design composed of a main target coil sandwiching a set of “saturation” coil to improve human liver fat quantification. We demonstrate the capability and effectiveness of the novel RF design in phantom experiments as well as in-vivo liver scans.

Weiman Jiang¹, Fan Yang¹, and Kun Wang^1
1GE Healthcare, Beijing, China

In this study, electromagnetic simulation was used to calculate RF heating for the patients with metallic gamma knife stereotaxic headframe in MRI. The relationship between headframe structure parameters and patient SAR was investigated. Two effective SAR derating methods of adjusting the headframe structure parameters were proposed, which can significantly decrease 10 g local SAR from 253 W/kg to 68 W/kg and head SAR from 4.2 W/kg to 2.0 W/kg. This study provides the efficient and reliable methods to ensure safety of the patients with metallic gamma knife headframe in MRI.

Alex T. L. Leong^1,2, Yilong Liu^1,2, Yujiao Zhao^1,2, Linfang Xiao^1,2, Henry K. F. Mak³, Tsang Anderson⁴, Gary K. K. Lau⁵, Gilberto K. K. Leung⁴, and Ed X. Wu^1,2,6
1Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Hong Kong SAR, China, ²Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong SAR, China, ³Department of Diagnostic Radiology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China, ⁴Department of Surgery, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China, ⁵Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China, ⁶School of Biomedical Sciences, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China

Magnetic resonance imaging is a key diagnostic tool in modern healthcare, yet its accessibility is low with the vast majority of clinical MRI scanners being placed in highly specialized radiology departments, large centralized imaging centers, and housed on ground floors of hospitals and clinics. In this study, we deployed our recently developed 0.055T brain ultra-low-field MRI scanner to demonstrate preliminary feasibility in diagnosing tumor and stroke cases with direct comparisons to 3T clinical MRI results. The development of such ULF MRI technologies will enable patient-centric and site-agnostic MRI scanners to fulfill the unmet clinical needs across various global healthcare sites.

Ed X. Wu^1,2,3, Yilong Liu^1,2, Alex T. L. Leong^1,2, Yujiao Zhao^1,2, Linfang Xiao^1,2, Henry K. F. Mak⁴, Tsang Anderson⁵, Gary K. K. Lau⁶, and Gilberto K. K. Leung^5
1Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Hong Kong SAR, China, ²Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong SAR, China, ³School of Biomedical Sciences, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China, ⁴Department of Diagnostic Radiology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China, ⁵Department of Surgery, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China, ⁶Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China

In this study, we describe an ultra-low-field brain MRI scanner that operates using a standard AC power outlet and is low cost to build. Using a permanent 0.055 Tesla Samarium-cobalt magnet and deep learning for cancellation of electromagnetic interference, it requires neither magnetic nor radiofrequency shielding cages. We also successfully implement four standard clinical neuroimaging protocols (T1W, T2W, FLAIR like, and DWI) and demonstrate human brain imaging on this system. This proof-of-concept work will advance the development of a new class of MRI technologies to democratize MRI for low and middle income countries and increase MRI accessibility in healthcare.

Fangfang Tang¹, Luca Giaccone², Fabio Freschi^1,2, Stuart Crozier¹, and Feng Liu^1
1School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, Australia, ²Department of Energy, Politecnico di Torino, Torino, Italy

In pediatric magnetic resonance imaging, infants are exposed to rapid, time-varying gradient magnetic fields, leading to electric fields induced in the body of infants and potential safety risks (e.g., peripheral nerve stimulation). In this work, the induced electric fields by the small x, y, z gradient coils in an infant model were numerically evaluated at different model positions. It was found that the induced electric fields in most tissues exceeded the basic restrictions of the ICNIRP 2010 guidelines. 

Aiping Yao¹, Minjuan Ma¹, Yunfeng Pei¹, and Longjun Tang^2
1Lanzhou University, Lanzhou, China, ²Shanghai NeuraZing Co., Ltd, Shanghai, China

This work intends to provide a preliminary evaluation of the uncertainty produced by current Tier 3 approach during the assessment of subcutaneous and partially implanted devices. The transfer function of a 600 mm long DBS and guidance wire for Interventional MRI are derived under homogeneous and heterogeneous tissue environments, respectively. The resulting power deposition using different transfer function are evaluated and compared. The results show that using current Tier 3 approach may lead to potential large underestimation of the power deposition for subcutaneous and partially implanted devices, methods which can overcome or reduce these uncertainty are needed.

Ziming Huang^1,2, Alex T. L. Leong^1,2, and Ed X. Wu^1,2
1Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Hong Kong, China, ²Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong, China

Halbach permanent magnet array offers lightweight and mobility but its field is sensitive to temperature, thus hindering its robust point-of-care MRI applications. This work presents a temperature-insensitive Halbach magnet array design for ultra-low-field MRI. The proposed array is of adequate bore diameter and reasonable weight (~50kg), and provides a 30 mT B0 within a 20 cm imaging field of view (FOV). Numerical simulation is conducted to test the proposed design, demonstrating a drastic reduction in temperature-induced B0 drifting and inhomogeneity.