Application of Rotating RF Coil Array in B1 Shimming with Strict Local SAR Constraints
Introduction: The most challenging radiofrequency (RF)-related issues at high fields are the inhomogeneous excitation and high RF energy absorption, quantified as specific absorption rate (SAR). The former can lead to image intensity variation and regional signal drop-offs, while the latter raises concerns towards the safe use of high-field system. To date, B1-shimming is one of the most promising techniques to circumvent these issues. However, it has been demonstrated that the number of independently controlled transmit elements necessary for applications at 7 T and above is potentially very large [1]. Massive parallel transmit arrays face challenges such as shallow RF penetration and difficulties in managing coil-coil couplings. Moreover, increasing the number of coils and individual power amplifiers escalates the operational cost and system complexity. Herein, we propose using a low channel-count rotating RF coil array [2, 3] to perform B1shimming, while the maximum 10-gram averaged SAR is strictly controlled.