Evaluation of 8-Channel Radiative Antenna Arrays for Human Head Imaging at 10.5 Tesla.

Myung Kyun Woo,Lance Delabarre,Young Woo Park,Matt Thomas Waks,Se-Hong Oh,Gregor Adriany,Yigitcan Eryaman,Steve Jungst,Kamil Ugurbil,Russell Luke Lagore

doi:10.3390/s21186000

Abstract

For human head magnetic resonance imaging at 10.5 tesla (T), we built an 8-channel transceiver dipole antenna array and evaluated the influence of coaxial feed cables. The influence of coaxial feed cables was evaluated in simulation and compared against a physically constructed array in terms of transmit magnetic field (B1+) and specific absorption rate (SAR) efficiency. A substantial drop (23.1% in simulation and 20.7% in experiment) in B1+ efficiency was observed with a tight coaxial feed cable setup. For the investigation of the feed location, the center-fed dipole antenna array was compared to two 8-channel end-fed arrays: monopole and sleeve antenna arrays. The simulation results with a phantom indicate that these arrays achieved ~24% higher SAR efficiency compared to the dipole antenna array. For a human head model, we observed 30.8% lower SAR efficiency with the 8-channel monopole antenna array compared to the phantom. Importantly, our simulation with the human model indicates that the sleeve antenna arrays can achieve 23.8% and 21% higher SAR efficiency compared to the dipole and monopole antenna arrays, respectively. Finally, we obtained high-resolution human cadaver images at 10.5 T with the 8-channel sleeve antenna array.

Highlights

Published: 8 September 2021Fundamentally, the physics of magnetic resonance imaging (MRI) dictates that the achievable signal-to-noise ratio (SNR) increases with magnetic field strength [1,2,3,4]
B1 + efficiency compared to the dipole antenna array with coaxial cables (Figure 1d)
We evaluated three types of 8-channel radiative antenna arrays for ultra-high field (UHF) MRI

Summary

Introduction

Published: 8 September 2021Fundamentally, the physics of magnetic resonance imaging (MRI) dictates that the achievable signal-to-noise ratio (SNR) increases with magnetic field strength [1,2,3,4]. Since the wavelength at 447 MHz (in the presence of human tissue) is within the dimension of the imaging subject, unique challenges, related to overall field homogeneity, arise at UHF, and the design of radiofrequency (RF) coil arrays for MRI applications benefits from serious consideration of antenna concepts [9,10]. This is a significant change from the strict near-field regime-dominated RF coil arrays operating at clinical MRI frequencies below 3 T/128 MHz. At UHF frequencies, radiative-type antennas, dipole antennas, have been suggested as excellent building blocks for transmit arrays and have, shown promising performance [11,12]. Compared to other coil types, such as loop [13,14] or microstrip antennas [15,16], dipole antennas have the additional advantage of symmetric B1 + field

Methods

Results

Discussion

Conclusion