  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.
