An Exploration of a Phased-Array RF Coil for Very Low-Field Brain MRI

Very low magnetic field (VLF) magnetic resonance imaging (MRI) presents an affordable and easily deployable solution, facilitating MRI usage within inpatient wards, intensive care units (ICUs), ambulances, and resource-limited areas. In spite of the advantages, VLF MRI encounters challenges like a reduced signal-to-noise ratio (SNR). While high-field MRIs have employed phased-array RF coils to enhance SNR and expedite imaging, leveraging phased-array RF coils to improve imaging SNR and reduce scan time in VLF MRI has been highly expected. Compared to high-field MRI, the dramatically reduced working frequency has a significant impact on the performance of the phased-array RF coil for VLF MRI. In this study, we attempted to evaluate the performance of phased-array RF coils for VLF MRI. Specifically, we built a phased-array RF coil system, which consists of an optimized eight-channel head RF coil and a custom-made low input impedance (LII) preamplifier. We optimized the system based on impedance analysis and evaluated its performance by bench test, phantom imaging, and healthy volunteer imaging. This article presents the first attempt to develop a phased-array RF coil for VLF MRI and reveals the advantage of improving SNR by RF coil structure optimization and the challenge of phased-array decoupling in VLF MRI.