Inductively Coupled Wireless Coils for Magnetic Resonance Imaging: A Review

Magnetic Resonance Imaging (MRI) is indispensable in clinical diagnosis and biomedical research due to its advantages such as non-ionizing radiation and high soft tissue resolution. As a core component of the MRI system, the performance of radiofrequency (RF) coils directly affects imaging quality. Wired RF coils are the standard configuration in clinical practice, but they have several limitations including cable constraints and high costs. Active wireless coils face technical challenges such as high system complexity, difficult clock signal synchronization and data throughput limitation. As a passive wireless signal transmission solution, the inductively coupled wireless coil (ICWC), serving as a complementary RF component, achieves signal and energy transmission through near-field magnetic coupling with the wired coil. They possess numerous advantages including localized reception unique advantages of non-ionizing radiation, high soft-tissue resolution, multi-parametric analysis, and metabolic information monitoring. Since the 1970s [1, 2], MRI has not only revolutionized the traditional medical understanding of human anatomy and pathological changes but also achieved groundbreaking advancements in numerous specialized subfields, such as neuroscience [3-5] and oncology [6-8]. sensitivity enhancement, cross-tissue/species transplantability, adaptability to different main magnetic fields, reduction of the g-factor, B1 + field shaping, cable-free advantages in special scenarios, design scalability, and cross-manufacturer compatibility. This review elaborates on the inductive coupling mechanism of ICWCs, the derivation of the SNR formula, potential causes of g-factor reduction, and recommendations for fabrication methods. Additionally, it systematically summarizes the application progress in scenarios such as invasive imaging, multi-site human imaging, animal imaging, and applications in special scenarios. Finally, it discusses the development prospects ICWCs in fields including neuroimaging, ultra-high/ultra-low field MRI, and X-nucleus MRI/MRS, as well as ICWCs' advantages and limitations, providing a reference for the innovation of MRI RF coil technology and the clinical translation of ICWCs.