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

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.