Hybrid Monopole/Loop Coil Array for Human Head MR Imaging at 7 T

The monopole coil and loop coil have orthogonal radiofrequency (RF) fields and thus are intrinsically decoupled electromagnetically if they are laid out appropriately. In this study, we proposed a hybrid monopole/loop technique which could combine the advantages of both loop arrays and monopole arrays. To investigate this technique, a hybrid RF coil array containing four monopole channels and four loop channels was developed for human head magnetic resonance (MR) imaging at 7 T. In vivo MR imaging and g-factor results using monopole-only channels, loop-only channels and all channels of the hybrid array were acquired and evaluated. Compared with the monopole-only and loop-only channels, the proposed hybrid array has the higher signal-to-noise ratio (SNR) and better parallel imaging performance. Sufficient electromagnetic decoupling and diverse RF magnetic field (B₁) distributions of monopole channels and loop channels may contribute to this performance improvement. From experimental results, the hybrid monopole/loop array has low g-factor and excellent SNR at both periphery and center of the brain, which is valuable for human head imaging at ultrahigh fields.