The design and evaluation of single-channel loopole coils at 7T MRI.

Objective . Improving the local uniformity ofB1+field for awake monkey brain magnetic resonance imaging (MRI) at ultra-high fields while facilitating convenient placement and fixation of MRI-compatible multimodal devices for neuroscience study, can eventually advance our understanding of the primate's brain organization. Approach . A group of single-channel RF coils including conventional loop coils and loopole coils sharing the same size and shape were designed for comparison; their performance as the transmit coil was quantitatively evaluated through a series of numerical electromagnetic (EM) simulations, and further verified by using 7T MRI over a saline phantom and a monkey in vivo. Main results . Compared to conventional loop coils, the optimized loopole coil brought up to 23.5%B1+uniformity improvement for monkey brain imaging in EM simulations, and this performance was further verified over monkey brain imaging at 7T in vivo . Importantly, we have systematically explored the underlying mechanism regarding the relationship between loopole coils' current density distribution andB1+uniformity, observing that it can be approximated as a sinusoidal curve. Significance . The proposed loopole coil design can improve the imaging quality in awake and behaving monkeys, thus benefiting advanced brain research at UHF.