Abstract：Magnetic resonance imaging (MRI) plays an irreplaceable role in modern clinical practice especially for brain diseases due to its excellent soft tissue imaging resolution, radiation-free nature, and rich imaging parameters. The ultra-low-field (ULF) MRI technology (<0.1 T) is characterized by its small size, light weightmaking it more suitable for mobile imaging scenarios and enables rapid imaging examinations for emergency patients. But the weaker background field results in a lower signal-to-noise ratio (SNR) in ULF MRI images. To enhance the signal-to-noise ratio (SNR), it is crucial for the radio frequency (RF) coil to be positioned close to the imaging area while maintaining excellent performance. To ensure that the RF coil conforms closely to the shape of the sample, an optimization algorithm is required, which should consider the conditions and requirements of wiring and the imaging target area, thus enabling the design of a distributed winding method. In this study, the indirect boundary element method was employed to determine the coil current distribution from an inverse problem perspective. The term of indirect means that a density function needs to be introduced as an intermediate variable to bridge the gap between magnetic induction intensity of the target area and the current stream function on the wiring surface. Then, linear programming is used to obtain the optimal layout of RF coil conductors that closely resemble the simulated current distribution. To validate the effectiveness of ULF MRI in diagnosing cranial diseases, above-mentioned method was applied to design a dual-channel RF receive coil for the head-brain geometric shape of the rat at 54 mT. The performance of proposed RF receive coil was then evaluated by CuSO4 solution phantom sample imaging tests and the signal-noise-ratio of the dual-channel coil images increased by 15.0% and 21.4% compared to the single-channel images, while the homogeneity remained unchanged. Imaging experiments were conducted on rat models with ischemic stroke, hemorrhagic stroke, and traumatic brain injury (TBI) including T1 weighted, T2 weighted, and T2 star-weighted imaging sequences. The experiments demonstrated that 54 mT MRI can detect edema and hemorrhagic lesions, aligning with pathological slices or clinical 3.0 T MRI images. Furthermore, a 7-day medium-term follow-up study on TBI model rats was conducted. The results suggest that both 54 mT and 3.0 T MRI can effectively demonstrate the pathological changes in acute and subacute phases of TBI, consistent on the progression and outcome cycles of brain contusions. Moreover, the 54 mT MRI can show better performance in detecting scalp injuries compared to brain contusions that only manifested as mild edema. This paper adopts a method combining indirect boundary element inverse problem technique with linear programming to design RF receive coils suitable for rats under a 54 mT B0 field. Then, the images obtained from the coils of the two channels are superimposed to achieve high signal-to-noise ratio ultra-low field magnetic resonance images. The experiments with the rat model demonstrated the potential and value of ULF MRI technology in the clinical diagnosis of acute stroke and long-term radiological follow-up of patients with traumatic brain injury.
孟凡钦, 郭轶, 何为, 徐征. 基于边界元逆问题法的超低场磁共鼠脑部成像双通道射频线圈优化设计[J]. 电工技术学报, 2025, 40(1): 25-35.
Meng Fanqin, Guo Yi, He Wei, Xu Zheng. Optimal Design of Rat Brain Dual-Channel RF Coils for Ultra-Low-Field Magnetic Resonance Imaging Based on Boundary Element Inverse Problem Method. Transactions of China Electrotechnical Society, 2025, 40(1): 25-35.
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