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, providing a reference for the innovation of MRI RF coil technology and the clinical translation of ICWCs.
Abstract
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.
This work presents an open-source, optimized solenoid head coil tailored for the 50 mT open-source scanner (OSII ONE v2.1), set the basis for a fully reliable and reproducible component for the open-source OSII ONE MRI scanner.
Umberto Zanovello, Julia Pfitzer, Ariane Ernst et al.· 1 citation
High-performance breast magnetic resonance imaging (MRI) remains limited by the availability, geometry, and cost of dedicated receive coils. In contrast, spine coils are widely installed in MR scanners globally but provide insufficient sensitivity for anterior breast tissue. Here, we report a wireless volumetric metamaterial resonator (VMR) that converts a standard built-in spine coil into a scalable breast MRI receiver platform without modifying the scanner hardware. The VMR consists of axially stacked coaxial resonant rings that support a co-rotating collective mode, producing a centrally concentrated RF magnetic field within the enclosed imaging volume. Leveraging distributed capacitance in the coaxial cable, gap-engineered geometric tuning, and PIN-diode-based self-detuning, the VMR enables size scalability, electric-field confinement, and transmit-receive compatibility, as validated through bench measurements and 3.0 T MRI experiments. Three VMR prototypes spanning small, medium, and large breast-equivalent volumes were designed and evaluated using electromagnetic simulations, bench measurements, and phantom MRI experiments. Compared with a commercial 16-channel breast coil, the VMR-augmented spine coil achieved more than 4-fold higher central SNR and reduced spatial non-uniformity from approximately 70% to 20% within the target imaging region. Under SENSE parallel imaging at acceleration factors of 2-4, the VMR-augmented spine coil maintained an average 4-fold higher central SNR than the commercial coil for three sizes. These results establish the VMR as a passive, scalable hardware strategy for improving breast MRI performance using existing clinical scanner infrastructure.
Yuhang Liu, Xia Zhu, C. LeBedis et al.· 0 citations
Magnetic resonance imaging (MRI) scanning remains largely restricted to specific modalities, typically involving low radiofrequency (RF) power levels and stringent protocols for patients with deep brain stimulation (DBS) implants, due to safety concerns related to RF-induced heating of the implants. A 6-channel dual-role head coil array capable of modulating the electric-field (E-field) distribution was designed and evaluated using electromagnetic (EM) simulations. By optimizing the resonant frequency of each coil element during RF transmission, the transmit field was reshaped, leading to a significant reduction in RF-induced heating near the DBS lead tip. The proposed method was validated across two scenarios of increasing complexity: 1) a simple straight conductive wire for concept validation and 2) four realistic DBS leads representing complex real-world scenarios. The coil settings can be optimized either to suppress the E-field at a specific location, such as the DBS lead tip, or to suppress the peak specific absorption rate (SAR) across the entire human head. For location-specific E-field suppression, the simplified predefined-state control scheme and the fine-tuning genetic algorithm (GA)-based framework were implemented, achieving E-field reductions of 45.9% and 68.3%, respectively. For whole-head peak SAR suppression, the annealed Log-Sum-Exp (LSE)–Adaptive Moment Estimation (Adam) framework (LSE–Adam) was implemented, achieving an average 1 g SAR reduction of 72.09% across four realistic DBS lead models. The dual-role coil demonstrated a high degree of flexibility in controlling the transmit field and reducing RF-induced heating at DBS implants, offering a novel approach to mitigate RF-induced heating of the implants in MRI.
Zhonghao Zhang, Ming Lu, Zhengyi Lu et al.· IEEE Access· 0 citations
The use of ultra-high magnetic fields, such as 11.74 T in magnetic resonance imaging (MRI), offers great potential for achieving superior image quality and enabling advanced imaging applications. The development of new field-strength systems requires an investigation into the performance of radiofrequency transmitters and receivers. Loop coils are a popular choice for MRI scanners up to 7 T, with better performance exhibited at 3 T, whereas volume coils such as birdcage coils are preferred for 1.5 T scanners. On this basis, the field strength of 11.74 T raises the question of which resonator design will provide superior performance. Dipole antennas have been proposed for many applications involving different field strengths and target organs. One of the limitations of dipole antennas is the relationship between the resonance and the length. At 11.74 T, the dipole frequency of operation is 500 MHz, which provides a dipole antenna length of approximately 28 cm, which is acceptable for an MRI scanner. This study analyzed the transmission and reception performances of dipole arrays with different radii in terms of field intensity, uniformity, SAR, effectiveness, g-factor, and field optimization.
D. Hernández, Taewoo Nam, Yeji Han et al.· Applied Sciences· 0 citations
Improving the signal-to-noise ratio (SNR) is crucial for enhancing image quality and diagnostic reliability in magnetic resonance imaging (MRI). However, traditional methods that rely on increasing the number of coil channels are approaching their physical and engineering optimization limits. In recent years, wireless, passive metamaterials have been explored for local magnetic field enhancement via radiofrequency field modulation, offering a new pathway to improve SNR. However, the regular configurations of most existing metamaterial structures hinder their conformance to anatomical contours, thereby limiting the spatial filling factor and preventing further SNR enhancement, while anatomically conformal designs often result in nondegenerate orthogonal modes. This study presents a conformal elliptical cylindrical metamaterial designed to achieve uniform magnetic-field enhancement and restore orthogonal-mode degeneracy in a non-axisymmetric geometric configuration. This is achieved through cross-sectional gradient impedance design and end-ring impedance tuning. Additionally, nonlinear response control is introduced to eliminate interference with the radiofrequency transmit field. Experimental results show that, when used in various clinical imaging sequences, the metamaterial yields wrist MR images with an SNR more than 4 times that obtained with a commercial flexible coil. This work provides a general design methodology for the synergistic regulation of field distributions and modal characteristics in asymmetric electromagnetic structures, establishing a robust technical foundation for the development of high-performance, anatomically conformal clinical MRI hardware.
Yingyi Qi, Zhonghai Chi, Xinxin Li et al.· ACS Applied Materials and In...· 0 citations
The recent developments in ultra-low-field brain MRI are reviewed, which enable imaging in open environments and demonstrate initial clinical applicability in point-of-care settings, and future developments are envisioned to address the current limitations of image quality and contrast in ultra-low-field brain MRI systems.
Ed X. Wu, Yujiao Zhao, Yilong Liu et al.· Stroke· 1 citation
