B1-control receive array coil (B-RAC) for reducing B1+ inhomogeneity in abdominal imaging at 3T-MRI

• Published in: Journal of magnetic resonance (1997) 2018-02, Vol.287, p.25-32
• Main Authors: Kaneko, Yukio, Soutome, Yoshihisa, Habara, Hideta, Bito, Yoshitaka, Ochi, Hisaaki
• Format: Article
• Language: English
• Subjects: B1+ inhomogeneity; B1-control receive array coil; Local SAR; Magnetic Resonance Imaging (MRI); RF shimming
• ISSN: 1090-7807; 1096-0856
• DOI: 10.1016/j.jmr.2017.12.011

[Display omitted] •B1-control receive array coil (B-RAC) was developed for B1+ homogenization.•B1+ homogenization effect was analyzed by simulation and 3T-MRI experiment.•B-RAC was demonstrated to be able to control the spatial distribution of B1+.•B-RAC can reduce B1+ inhomogeneity without increasing the maximum local SAR.•B-RAC can reduce B1+ inhomogeneity while maintaining the receive sensitivity. B1+ inhomogeneity in the human body increases as the nuclear magnetic resonance (NMR) frequency increases. Various methods have thus been developed to reduce B1+ inhomogeneity, such as a dielectric pad, a coupling coil, parallel transmit, and radio-frequency (RF) shimming. However, B1+ inhomogeneity still remains in some cases of abdominal imaging. In this study, we developed a B1-control receive array coil (B-RAC). Unlike the conventional receive array coil, B-RAC reduces B1+ inhomogeneity by using additional PIN diodes to generate the inductive loop during the RF transmit period. The inductive loop can generate dense and sparse regions of the magnetic flux, which can be used to compensate for B1+ inhomogeneity. First, B-RAC is modeled in the numerical simulation, and the spatial distributions of B1+ in a phantom and a human model were analyzed. Next, we fabricated a 12-channel B-RAC and measured receive sensitivity and B1+ maps in a 3T-MRI experiment. It was demonstrated that B-RAC can reduce B1+ inhomogeneity in the phantom and human model without increasing the maximum local specific absorption rate (SAR) in the body. B-RAC was also found to have almost the same the receive sensitivity as the conventional receive coil. Using RF shimming combined with B-RAC was revealed to more effectively reduce B1+ inhomogeneity than using only RF shimming. Therefore, B-RAC can reduce B1+ inhomogeneity while maintaining the receive sensitivity.