FIGURE 2.

Average and coefficient of variation (CV) of the transmit field magnitude $\left(\left|{\text{B}}_1^{+}\right|\right)$ inside the fetus for different RF shim settings, where the relative amplitude and relative phase of the two channels are varied from 0 to 2 (vertical axis) and −90° to 270° (horizontal axis), respectively. All shim settings are normalized to a maternal whole-body average SAR (wbSAR) of 2 W/kg. CP mode: circularly polarized birdcage mode, improved imaging performance: both average $\left|{\text{B}}_1^{+}\right|$ and $\left|{\text{B}}_1^{+}\right|$ CV are improved compared with CP mode, improved SAR: all three SAR metrics (maternal pSAR10g, fetal pSAR10g, and fetal aveSAR) are less than CP mode values of the corresponding body model