Subject‐loaded quadrifilar helical‐antenna RF coil with high B₁⁺ field uniformity and large FOV for 3‐T MRI

Abstract

A novel method for excitation of RF B1 field in high‐field (3‐T) magnetic resonance imaging (MRI) systems using a subject‐loaded quadrifilar helical antenna as an RF coil is proposed, evaluated, and demonstrated. Design, analysis, characterization, and evaluation of the novel coil when situated in a 3‐T MRI bore and loaded with different phantoms are performed and cross‐validated by extensive numerical simulations using multiple computational electromagnetics techniques. The results for the quadrifilar helical‐antenna RF body coil show (a) strong field penetration in the entire phantoms; (b) excellent right‐hand circular polarization (RCP); (c) high spatial uniformity of RCP RF magnetic field, B1+, throughout the phantoms; (d) large field of view (FOV); (e) good transmit efficiency; and (f) low local specific absorption rate (SAR). The examples show that the new RF coil provides substantially better B1+‐field uniformity and much larger FOV than any of the previously reported numerical and experimental results for the existing RF coil designs at 3 T in literature that enable comparison. In addition, helical RF body coils of different lengths can, for instance, easily provide an excellent RCP and highly uniform B1+‐field within the MRI maximum FOV length of 50 cm, and even 100 cm. The proposed MRI RF coil yields a remarkable improvement in the field uniformity in the longitudinal direction, for various phantoms, with comparable efficiency and SAR levels.

External waveguide magnetic resonance imaging for lower limbs at 3 T

“…also published similar patterns of , obtained with a patched antenna at 9.4 T 64 . The simulations shown in Figure 3 corroborate the numerical results obtained with the methods of moments (MoM) for a quadrifilar helical antenna at 3 T 65 . While the electric field, E, remained constant between 50 and 100 cm, reached its maximum value around ; after this, started decreasing.…”

“…The patterns observed for both E and B 1 were similar to those reported by Ayadin and Sevgi using a virtual tool 62 ; further, their magnitudes lay in the interval calculated by Zhou et al for current dipole excitation on PPWG with a dielectric discontinuity. 63 Brenner et al also published similar patterns of B 1 , obtained with a patched antenna at 9.4 T. 64 The B 1 simulations shown in Figure 3 corroborate the numerical results obtained with the methods of moments (MoM) for a quadrifilar helical antenna at 3 T. 65 While the electric field, E, remained constant between 50 and 100 cm, B 1 reached its maximum value around 𝜆∕4; after this, B 1 started decreasing. Figure 3(d) shows an increase in the electric field between 130 cm and 200 cm, until it reached its previous values obtained from 33 cm up to 100 cm.…”

Multi‐channel helical‐antenna inner‐volume RF coils for ultra‐high field MR scanners

“…[43][44][45][46] A novel method for excitation of RF B 1 field in high-field MRI systems at B 0 = 3 T using a subject-loaded quadrifilar (4-channel) helical antenna as an RF coil is proposed, evaluated, and demonstrated, by numerical simulations, in Ref. 47 with respect to the UHF-MR helical-antenna RF coils, at B 0 = 7 T (f 0 = 300 MHz) and B 0 = 10.5 T (f 0 = 443 MHz), are as follows. 47 with respect to the UHF-MR helical-antenna RF coils, at B 0 = 7 T (f 0 = 300 MHz) and B 0 = 10.5 T (f 0 = 443 MHz), are as follows.…”

“…47 The main differences of the 3-T coil in Ref. 47 with respect to the UHF-MR helical-antenna RF coils, at B 0 = 7 T (f 0 = 300 MHz) and B 0 = 10.5 T (f 0 = 443 MHz), are as follows. The helical antenna in a 3-T MR bore, at an operating frequency of f 0 = 127.8 MHz, is not a traveling-wave antenna, and the helix RF coil at 3 T is not a TW coil.…”