MRI Shimming via Field Intensity Shaping

The high frequency of the radiofrequency (RF) fields used in high field magnetic resonance imaging (MRI) causes electromagnetic field variations which increase the specific absorption rate (SAR) local level and also imaging artifacts degrading the quality of MRI images. For this reason, different approaches have been proposed in literature, which aim at simultaneously improving the B1+ homogeneity and reduce the SAR level in the body. However, most of them do not involve the determination of the complex excitation currents pertaining to the RF coil of MRI systems. In this contribution, starting from a recently introduced field intensity shaping technique, we propose a novel procedure for B1+ shimming which is also able to control the purity of polarization of the total RF field as well as to limit the SAR level within the biological tissues. This procedure is based on convex optimization and is assessed in the following in case of brain imaging.