Evaluation of a 16-Channel Transceiver Loop + Dipole Antenna Array for Human Head Imaging at 10.5 Tesla

Abstract

We evaluated a 16-channel loop + dipole (LD) transceiver antenna array with improved specific absorption rate (SAR) efficiency for 10.5 Tesla (T) human head imaging applications. Three different array designs with equal inner dimensions were considered: an 8-channel dipole antenna, an 8channel loop, and a 16-channel LD antenna arrays. Signal-to-noise ratio (SNR) and B1 + efficiency (in units of µT per √W) were simulated and measured in 10.5 T magnetic resonance imaging (MRI) experiments. For the safety validation, 10 g SAR and SAR efficiency (defined as the B1 + over √ (peak 10 g SAR)) were calculated through simulation. Finally, high resolution porcine brain images were acquired with the 16channel LD antenna array, including a fast turbo-spin echo (TSE) sequence incorporating B1 shimming techniques. Both the simulation and experiments demonstrated that the combined 16-channel LD antenna array showed similar B1 + efficiency compared to the 8-channel dipole antenna and the 8-channel loop arrays in a circular polarized (CP) mode. In a central 2 mm × 2 mm region of the phantom, however, the 16-channel LD antenna array showed an improvement in peak 10 g SAR of 27.5 % and 32.5 % over the 8channel dipole antenna and the 8-channel loop arrays, respectively. We conclude that the proposed 16channel head LD antenna array design is capable of achieving ~7% higher SAR efficiency at 10.5 T compared to either the 8-channel loop-only or the 8-channel dipole-only antenna arrays of the same dimensions. INDEX TERMS dipole antenna array, human head array, loop array, magnetic resonance imaging, RF coil, ultra-high field

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

“…Eight quarter-wave (~13 cm at 10.5 T) monopole antennas were connected to a 35 cm × 36 cm dimension copper ground plate, which was segmented and reconnected with 330 pF capacitors to reduce eddy currents. As shown in our previous research [ 6 , 8 , 17 , 19 ], all arrays were operated without an intra-element decoupling circuit.…”

“…Compared to other coil types, such as loop [ 13 , 14 ] or microstrip antennas [ 15 , 16 ], dipole antennas have the additional advantage of symmetric B 1 + field (defined as the transmit magnetic field generated by an RF coil) patterns, as well as a favorable direction of energy propagation (Poynting vector), which results in greater penetration depth. Consequently, both dipole antennas and the combination of loops with dipole antennas have been successfully used for UHF human imaging applications with high penetration, efficiency, and SNR [ 17 , 18 , 19 ]. However, for realistic head array housings, the coaxial feed cables for dipole antennas have to be routed in close proximity to one leg of the dipole and they interact with the antenna elements.…”

A nine‐channel transmit/receive array for spine imaging at 10.5 T: Introduction to a nonuniform dielectric substrate antenna

“…A single-element comparison was performed between the NODES antenna, fractionated dipole (FD), 3 and loop coil, 54 as shown in Figure 4A. For this purpose, a max l,w,h, r1 , r2 , r3 Mean r;l, w, h, r1 , r2 , r3 at depth of 50 to 100mm…”

“…The optimization parameters included permittivity variation of the substrate, substrate thickness, antenna length, and conductor geometry. We evaluated the ‐ power efficiency and ‐ SAR efficiency of the proposed design and compared it to the fractionated dipole 3 and loop 54 in EM simulations. We also conducted phantom imaging experiments at 10.5 T and compared the power efficiencies and 10g‐averaged SAR distributions of the same elements, thereby validating our EM simulations.…”

“…10.5 Tesla, MRI, NODES, RF safety, spine imaging, ultrahigh-field design and compared it to the fractionated dipole 3 and loop 54 in EM simulations. We also conducted phantom imaging experiments at 10.5 T and compared the power efficiencies and 10g-averaged SAR distributions of the same elements, thereby validating our EM simulations.…”