Metamaterial inspired wireless coil for clinical breast imaging

Detunable wireless Litzcage coil for human head MRI at 1.5 T

Inductively coupled radiofrequency (RF) coils are an inexpensive and simple method to realize wireless RF coils in magnetic resonance imaging (MRI), which can significantly ease the MRI scan setup and improve patient comfort because they do not require bulky components such as cables, baluns, preamplifiers, and connectors. However, volume-type wireless coils are typically operated in transmit/receive mode because detuning such coils is much more challenging due to their complex structure and multiple resonant modes. Meanwhile, adding too many detuning circuits to a wireless coil would decrease the coil's quality factor, impair the signal-to-noise ratio, and increase the cost. In this work, we proposed, constructed, and tested a novel wireless volume coil based on the Litzcage design for 1.5-T head imaging. Being an inductively coupled coil, it has a much simpler structure, resulting in a lighter weight and less bulky design. Despite its simpler structure, it exhibits comparable imaging performance with a commercial receive array, providing an alternative to conventional wired coils with a high cost and complex structure. The unique figure-of-8 conductor pattern within the rungs ensures that the proposed wireless Litzcage can be efficiently detuned with minimal detuning circuits.

A detunable wireless resonator insert for high-resolution TMJ MRI at 1.5 T

MRI is essential for evaluating and diagnosing various conditions affecting the temporomandibular joint (TMJ) and surrounding structures, as it provides highly detailed images that enable healthcare professionals to assess the joints and surroundings in great detail. While commercial MRI scanners typically come equipped with basic receive coils, such as the head receive array, RF coils tailored for specialized applications like TMJ MRI must be obtained separately. Consequently, TMJ MRI scans are often conducted using the head receive array, yet this configuration proves suboptimal due to the lack of specialized coils. In this study, we introduce a simple, low-cost, and easy-to-reproduce wireless resonator insert to enhance the quality of TMJ MRI at 1.5 T. The wireless resonator shows a significant improvement in signal-to-noise ratio (SNR) and noticeably better imaging quality than the head array alone configuration in both phantom and in vivo images.

Volumetric wireless coils for breast MRI: A comparative analysis of metamaterial-inspired coil, Helmholtz coil, ceramic coil, and solenoid

This study comprehensively assesses radiofrequency (RF) volumetric wireless coils utilizing artificial materials for clinical breast MRI. In particular, we evaluated the transmit efficiency, RF safety, and homogeneity of magnetic field amplitude distribution for four structures electromagnetically coupled with a whole-body birdcage coil: extremely high permittivity ceramic coil, solenoid coil, Helmholtz coil, and metamaterial-inspired coil based on periodically coupled split-loop resonators. These coils exhibit favorable attributes, including lightweight construction, compactness, cost-effectiveness, and ease of manufacturing. The results of this study demonstrated that the metamaterial-inspired coil outperforms other wireless coils considered for addressing a specific problem in terms of the set of characteristics. In particular, the metamaterial-inspired coil achieved 85% and 88% homogeneity in magnetic field amplitude distribution at 3 T and 1.5 T MRI, respectively. Also, the 1.5 T metamaterial-inspired coil demonstrated the best performance, increasing the efficiency gain of the birdcage coil by 4.93 times and improving RF safety by 2.96 times. This research explains the limitations and peculiarity of utilizing the volumetric wireless coils in 1.5 and 3 T MRI systems.

In vivo MRI of knee using a metasurface-inspired wireless coil

PURPOSE

To investigate the application of a metasurface-inspired wireless coil and evaluate its performance in clinical knee MRI.

METHODS

A metasurface surface coil is designed for knee MRI at 1.5T. The image SNR and uniformity are assessed using a water phantom. In vivo studies are performed on 10 healthy volunteers (age range, 24-30 y; three males) and two patients (ages 31 and 76 y; two males) with knee conditions. A commercial 4-channel flexible coil and a 12-channel knee coil are used for comparison. The SNRs of different tissues on knee MRI images are evaluated and compared. The image quality is evaluated using a five-point Likert scale.

RESULTS

The SNRs of the images acquired by the metasurface coil with spine coil as receiving coil are similar to the 12-channel knee coil, whereas the uniformity from groups where the metasurface coil was used is higher than that acquired by conventional coils in phantom studies. For in vivo knee MRI, the SNRs of the images acquired by the metasurface coil with spine coil as receiving coil are between that of the 4- and 12-channel phased-array coils. The image quality scores evaluated by radiologists are higher when metasurface is used.

CONCLUSION

The metasurface-inspired wireless coil is applicable to clinical knee MRI. When used in conjunction with the spine coil, it provides a favorable SNR between that of the 4- and 12-channel phased-array coil at 1.5T MRI system. The metasurface coil improves image uniformity regardless of which coil is used as the receiving coil.

Quadrature transceive wireless coil: Design concept and application for bilateral breast MRI at 1.5 T

PURPOSE

Development of a novel quadrature inductively driven transceive wireless coil for breast MRI at 1.5 T.

METHODS

A quadrature wireless coil (HHMM-coil) design has been developed as a combination of two linearly polarized coils: a pair of 'metasolenoid' coils (MM-coil) and a pair of Helmholtz-type coils (HH-coil). The MM-coil consisted of an array of split-loop resonators. The HH-coil design included two electrically connected flat spirals. All the wireless coils were coupled to a whole-body birdcage coil. The HHMM-coil was studied and compared to the linear coils in terms of transmit and SAR efficiencies via numerical simulations. A prototype of HHMM-coil was built and tested on a 1.5 T scanner in a phantom and healthy volunteer. We also proposed an extended design of the HHMM-coil and compared its performance to a dedicated breast array.

RESULTS

Numerical simulations of the HHMM-coil with a female voxel model have shown more than a 2.5-fold increase in transmit efficiency and a 1.7-fold enhancement of SAR efficiency compared to the linearly polarized coils. Phantom and in vivo imaging showed good agreement with the numerical simulations. Moreover, the HHMM-coil provided good image quality, visualizing all areas of interest similar to a multichannel breast array with a 32% reduction in signal-to-noise ratio.

CONCLUSION

The proposed quadrature HHMM-coil allows the B 1 + $$ {\mathrm{B}}_1^{+} $$ -field to be significantly better focused in the region-of-interest compared to the linearly polarized coils. Thus, the HHMM-coil provides high-quality breast imaging on a 1.5 T scanner using a whole-body birdcage coil for transmit and receive.

Imaging Capabilities of the ¹H-X-Nucleus Metamaterial-Inspired Multinuclear RF-Coil

In this paper, we present the initial experimental investigation of a two-coil receive/transmit design for small animals imaging at 7T MRI. The system uses a butterfly-type coil tuned to 300 MHz for scanning the ¹H nuclei and a non-resonant loop antenna with a metamaterial-inspired resonator with the ability to tune over a wide frequency range for X-nuclei. ¹H, ³¹P, ²³Na and ¹³C, which are of particular interest in biomedical MRI, were selected as test nuclei in this work. Coil simulations show the two parts of the radiofrequency (RF) assembly to be decoupled and operating independently due to the orthogonality of the excited RF transverse magnetic fields. Simulations and phantom experimental imaging show sufficiently homogeneous transverse transmit RF fields and tuning capabilities for the pilot multiheteronuclear experiments.

Recent Advances in Radio-Frequency Coil Technologies: Flexible, Wireless, and Integrated Coil Arrays

Radio-frequency (RF) coils are to magnetic resonance imaging (MRI) scanners what eyes are to the human body. Because of their critical importance, there have been constant innovations driving the rapid development of RF coil technologies. Over the past four decades, the breadth and depth of the RF coil technology evolution have far exceeded the space allowed for this review article. However, these past developments have laid the very foundation on which some of the recent technical breakthroughs are built upon. Here, we narrow our focus on some of the most recent RF coil advances, specifically, on flexible, wireless, and integrated coil arrays. To provide a detailed review, we discuss the theoretical underpinnings, experimental implementations, promising results, as well as future outlooks covering these exciting topics. These recent innovations have greatly improved patient comfort and ease of scan, while also increasing the signal-to-noise ratio, image resolution, temporal throughput, and diagnostic and treatment accuracy. Together with advances in other MRI subfields, they will undoubtedly continue to drive the field forward and lead us to an ever more exciting future. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY: Stage 1.