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 monkeyin 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 7Tin 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.