Multislice B1 Mapping Method Using Magnetic Resonance Composite Spin Echo Sequences and Simultaneous Echo Refocusing

Abstract

Radiofrequency (RF) transmit field (B₁) mapping is a promising method in mitigating the B₁ inhomogeneity in various magnetic resonance imaging (MRI) applications. Although several phase- or magnitude-based B₁ mapping methods have been proposed, these methods often require complex modeling, long acquisition time, or specialized MRI sequences. A recently introduced simultaneous echo refocusing (SER) technique can be applied in the B₁ mapping method to extend the three-dimensional (3D) spatial coverage only without long data acquisition. Therefore, in this study, a multislice B₁ mapping method using composite spin echo sequences and SER techniques is proposed to obtain more accurate B₁ mapping with short data acquisition time. To evaluate the performance of the proposed B₁ mapping method, computational simulations were performed and compared with Morrell’s method, double angle method, and Yarnykh’s method. These results showed that the angle-to-noise ratio of the proposed B₁ mapping method has wider B₁ range compared to that of other B₁ mapping methods. In addition, the proposed B₁ mapping methods were compared to the multislice iterative signal intensity mapping method in both phantom and in vivo human experiments, and there was no remarkable difference between the two methods regarding the flip angle distribution in these experiments. Based on these results, this study demonstrated that the proposed B₁ mapping method is suitable for accurately measuring B₁ propagation under the condition providing reduced scan time and wider 3D coverage of B₁ mapping by applying composite RF pulse and SER techniques into the phase-sensitive method.