A 5‐channel local B₀ shimming coil combined with a 3‐channel RF receiver coil for rat brain imaging at 3 T

Abstract

Purpose We aimed to improve B0 magnetic field homogeneity and minimize the interference between RF coils and local B0 shimming coils with few channel numbers. Methods To design and construct the prototype for B0 shimming of the rat brain, we first evaluated the interferences of single shimming loops on RF receiver loops. Then, B0 shimming of the whole rat brain was implemented using an optimization procedure. The positions and currents of the local shimming coils with channel numbers from 3 to 6 were optimized to improve shimming performance. Based on the simulation results, a 5‐channel local shimming coil, combined with a 3‐channel RF receiver coil, was constructed and evaluated by animal experiments. Results There was marginal SNR loss within 5% after integrating the local shimming coil into the RF receiver coil. With respect to the Siemens standard shims up to second order, the B0 inhomogeneity in one whole rat brain was reduced from 39.6 Hz to 24.7 Hz by using the local shimming coil. A large portion of the EPI distortions was recovered after using the 5‐channel local shimming coil. The temporal SNR using the local shimming coil was higher than that using the Siemens standard shims up to second order, with an improvement of more than 24%. Conclusions The local shimming coil can improve B0 magnetic field homogeneity despite minor effects on the RF coil and can benefit a variety of applications that are sensitive to B0 inhomogeneity. Nevertheless, EPI for rat brain is still very challenging.

Reliable Off-Resonance Correction in High-Field Cardiac MRI Using Autonomous Cardiac B0 Segmentation with Dual-Modality Deep Neural Networks

“…Our data demonstrated that the model’s ability to produce accurate, motion-robust contours on cardiac field maps quickly could significantly enhance the homogeneity with the standard clinical shimming hardware. Furthermore, it is worth noting that the shim volume accuracy is particularly important for the fast-developing multi-coil shimming hardware and combined shim-RF coils [ 24 , 25 , 65 , 66 , 67 ]. Because of the increased flexibility of the shimming fields, an erroneous shimming ROI can lead to strong overfitting to the false field and corrupt the overall robustness of the procedure.…”