32-Channel self-grounded bow-tie transceiver array for cardiac MR at 7.0T

Abstract

Purpose: Design, implementation, evaluation, and application of a 32-channel Self-Grounded Bow-Tie (SGBT) transceiver array for cardiac MR (CMR) at 7.0T.

Methods: The array consists of 32 compact SGBT building blocks. Transmission field ( $B_1^{+}$ ) shimming and radiofrequency safety assessment were performed with numerical simulations and benchmarked against phantom experiments. In vivo $B_1^{+}$ efficiency mapping was conducted with actual flip angle imaging. The array's applicability for accelerated high spatial resolution 2D FLASH CINE imaging of the heart was examined in a volunteer study (n = 7).

Results: $B_1^{+}$ shimming provided a uniform field distribution suitable for female and male subjects. Phantom studies demonstrated an excellent agreement between simulated and measured $B_1^{+}$ efficiency maps (7% mean difference). The SGBT array afforded a spatial resolution of (0.8 × 0.8 × 2.5) mm³ for 2D CINE FLASH which is by a factor of 12 superior to standardized cardiovascular MR (CMR) protocols. The density of the SGBT array supports 1D acceleration of up to R = 4 (mean signal-to-noise ratio (whole heart) ≥ 16.7, mean contrast-to-noise ratio ≥ 13.5) without impairing image quality significantly.

Conclusion: The compact SGBT building block facilitates a modular high-density array that supports accelerated and high spatial resolution CMR at 7.0T. The array provides a technological basis for future clinical assessment of parallel transmission techniques.

Keywords: RF coil; cardiovascular MRI; electrical dipole; parallel imaging; transceiver array; ultrahigh field MRI.