arXiv subjects

Komlan Payne

Publications and source records attributed to Komlan Payne.

7 recordsLinked to original sources

arXiv2025

A coupled planar transmit RF array for ultrahigh field spine MR imaging

Ultrahigh-field MRI, such as those operating at 7 Tesla, enhances diagnostic capabilities but also presents unique challenges, including the need for advanced RF coil designs to achieve an optimal signal-to-noise ratio and transmit efficiency, particularly when imaging large samples. In this work, we introduce the coupled planar array, a novel technique for high-frequency, large-size RF coil design with enhanced the RF magnetic field (B1) efficiency and transmit performance for ultrahigh-field spine imaging applications. This array comprises multiple resonators that are electromagnetically coupled to function as a single multimodal resonator. The field distribution of its highest frequency mode is suitable for spine imaging applications. Based on the numerical modeling and calculation, a prototype of the coupled planar array was constructed and its performance was evaluated through comprehensive numerical simulations, rigorous RF measurements, empirical tests, and a comparison against a conventional surface coil with the same size and geometry. The results of this study demonstrate that the proposed coupled planar array exhibits superior performance compared to conventional surface coils in terms of B1 efficiency for both transmit (B1+) and receive (B1-) fields, specific absorption rate (SAR), and the ability to operate at high frequencies. This study suggests a promising and efficient approach to the design of high-frequency, large-size RF coils for spine MR imaging at ultrahigh magnetic fields.

physics.med-ph↗

arXiv2025

Discrete Dielectric Coatings for Length Control and Tunability of Half-Wave Dipole Antennas at 300 MHz Magnetic Resonance Imaging Applications

This study presents a novel discretely dielectric material-coated (DDMC) dipole antenna design for ultra-high-field (UHF) MRI applications. This design improves frequency tuning, lowers electric field intensity, and reduces SAR by including discrete high-permittivity dielectric coatings at both ends of the dipole. The DDMC dipole's performance was compared to that of a fractionated dipole design using metrics such as inter-element coupling, B1 field distribution, and SNR. Simulations and experimental results showed that the DDMC dipole provided superior B1 field uniformity with significantly reduced B1 variation along the dipole conductor while reducing SAR, making it a safer and more efficient option for MR signal excitation and reception in UHF MR imaging. Furthermore, with its improved electromagnetic decoupling performance, the multichannel array made from the proposed DDMC dipoles shows promise for improving parallel imaging and imaging quality in UHF MRI, with future work focusing on material optimization and scalability for multi-channel arrays.

physics.med-ph↗

arXiv2024

Superconducting and low temperature RF Coils for Ultra-Low-Field MRI: A Study on SNR Performance

This study incorporates electromagnetic simulations to assess the performance of multi-turn solenoid coils for ultra-low field MR imaging with various conductor materials (superconducting material, low-temperature copper, and room-temperature copper) across different human samples (elbow, knee, and brain). At 70 mT, superconducting materials performed significantly better than both room-temperature and low-temperature copper. The high Q-factor of the superconducting material indicates lower energy loss, which is useful for MR imaging. Furthermore, B1+ field efficiency increased significantly with superconducting materials, indicating superior performance. SNR evaluations revealed that materials with higher conductivity significantly improve SNR, which is critical for producing high-quality MR images. These results show that superconducting and low-temperature copper materials can significantly improve MR imaging quality at ultra-low fields, which has important implications for coil design and optimization.

physics.med-ph↗

arXiv2023

Dual-tuned Coaxial-transmission-line RF coils for Hyperpolarized 13C and Deuterium 2H Metabolic MRS Imaging at Ultrahigh Fields

$Objective:$ Information on the metabolism of tissues in both healthy and diseased states plays a significant role in the detection and understanding of tumors, neurodegenerative diseases, diabetes, and other metabolic disorders. Hyperpolarized carbon-13 magnetic resonance imaging ($^{13}$C-HPMRI) and deuterium metabolic imaging ($^2$H-DMI) are two emerging X-nuclei used as practical imaging tools to investigate tissue metabolism. However due to their low gyromagnetic ratios ($γ_{13C}$ = 10.7 MHz/T; $γ_{2H}$ = 6.5 MHz/T) and natural abundance, such method required a sophisticated dual-tuned radiofrequency (RF) coil. $ Methods:$ Here, we report a dual-tuned coaxial transmission line (CTL) RF coil agile for metabolite information operating at 7T with independent tuning capability. The design analysis has demonstrated how both resonant frequencies can be individually controlled by simply varying the constituent of the design parameters. $Results:$ Numerical results have demonstrated a broadband tuning range capability, covering most of the X-nucleus signal, especially the $^{13}$C and $^2$H spectra at 7T. Furthermore, in order to validate the feasibility of the proposed design, both dual-tuned $^1$H/$^{13}$C and $^1$H/$^2$H RF coils are fabricated using a semi-flexible RG-405 .086" coaxial cable and bench test results (scattering parameters and magnetic field efficiency/distribution) are successfully obtained. $Conclusion:$ The proposed dual-tuned RF coils reveal highly effective magnetic field obtained from both proton and heteronuclear signal which is crucial for accurate and detailed imaging. $Significance:$ The successful development of this new dual-tuned RF coil technique would provide a tangible and efficient tool for ultrahigh field metabolic MR imaging.

physics.med-ph↗

arXiv2022

Double Cross Magnetic Wall Decoupling for Quadrature Transceiver RF Array Coils using Common-Mode Differential-mode Resonators

In contrast to linearly polarized RF coil arrays, quadrature transceiver coil arrays are capable of improving signal-to-noise ratio (SNR), spatial resolution and parallel imaging performance. Owing to a reduced excitation power, low specific absorption rate can be also obtained using quadrature RF coils. However, due to the complex nature of their structure and their electromagnetic proprieties, it is challenging to achieve sufficient electromagnetic decoupling while designing multichannel quadrature RF coil arrays, particularly at ultrahigh fields. In this work, we proposed a double cross magnetic wall decoupling for quadrature transceiver RF arrays and implemented the decoupling method on common-mode differential mode quadrature (CMDM) quadrature transceiver arrays at ultrahigh field of 7T. The proposed magnetic decoupling wall comprised of two intrinsic decoupled loops is used to reduce the mutual coupling between all the multi-mode current present in the quadrature CMDM array. The decoupling network has no physical connection with the CMDMs' coils giving leverage over size adjustable RF arrays. In order to validate the feasibility of the proposed cross magnetic decoupling wall, systematic studies on the decoupling performance based on the impedance of two intrinsic loops are numerically performed. A pair of quadrature transceiver CMDMs is constructed along with the proposed decoupling network and their scattering matrix is characterized using a network analyzer. The measured results show all the current modes coupling are concurrently suppressed using the proposed cross magnetic wall. Moreover, field distribution, and SNR intensity are numerically obtained for a well-decoupled 8-channel quadrature knee-coil array.

physics.med-ph↗

arXiv2022

Low-Profile Dual Band-pass Frequency Selective Surface with independent bands of operation

A low-profile, modified Complementary Frequency Selective Surface (CFSS) with dual band-pass characteristic is presented. This technique adds independent control of the operation bands, which was a limitation from previous FSSs design based on CFSS concept. The FSS structure utilizes resonant elements and interaction between the layers to deliverer the first operating bandpass response at a low frequency. It is demonstrated that the first order response can achieved miniaturized periodic dimensions of about $λ_l/15$ and ultra-thin overall thickness compressed down to $λ_l/200$, where $λ_l$ is the free space wavelength at the lowest band of operation. An equivalent circuit model (ECM) is presented to explain the working principles of the proposed FSS. This investigation is further supported by parametric studies based on full wave simulation showing how this simple approach allows decoupling of the two bands of operation. A prototype, simultaneously operating at S and C bands is fabricated and tested in a free space environment for validation purpose.

eess.SY↗

arXiv2022

Hairpin RF Resonators for Transceiver Arrays with High Inter-channel Isolation and B1 Efficiency at Ultrahigh Field 7T MR Imaging

Electromagnetic decoupling among a close-fitting or high-density transceiver RF array elements is required to maintain the integrity of the magnetic flux density from individual channel for enhanced performance in detection sensitivity and parallel imaging. High-impedance RF coils have demonstrated to be a prominent design method to circumvent these coupling issues. Yet, inherent characteristics of these coils have ramification on the B1 field efficiency and SNR. In this work, we propose a hairpin high impedance RF resonator design for highly decoupled multichannel transceiver arrays at ultrahigh magnetic fields. Due to the high impedance property of the hairpin resonators, the proposed transceiver array can provide high decoupling performance without using any dedicated decoupling circuit among the resonant elements. Because of elimination of lumped inductors in the resonator circuit, higher B1 field efficiency in imaging subjects can be expected. In order to validate the feasibility of the proposed hairpin RF coils, systematical studies on decoupling performance, field distribution, and SNR are performed, and the results are compared with those obtained from existing high-impedance RF coil, e.g., "self-decoupled RF coil". To further investigate its performance, an 8-channel head coil array using the proposed hairpin resonators loaded with a cylindrical phantom is designed, demonstrating a 19 % increase of the B1+ field intensity compared to the "self-decoupled" coils at 7T. Furthermore, the characteristics of the hairpin RF coils are evaluated using a more realistic human head voxel model numerically. The proposed hairpin RF coil provides excellent decoupling performance and superior RF magnetic field efficiency compared to the self-decoupled high impedance coils. Bench test of a pair of fabricated hairpin coils prove to be in good accordance with numerical results.

physics.med-ph↗