Computational assessment of radiofrequency energy absorption of fetus during an MRI scan

This study presents a systematic analysis of specific energy absorption rate (SAR) in computational models of a pregnant woman and the fetus at three different gestation ages (3rd, 6th, and 9th month). Numerical simulations were performed at two frequencies (i.e., 64 and 128 MHz), for two coil diameters (i.e., 750 and 650 mm), and for seven landmarks, namely shoulder, heart, sternum, abdomen (i.e., fetus head), pelvis (i.e., fetus body), thigh, and knee. The effect of additional features on the SAR, such as input source locations and y-position of the pregnant woman model in the birdcage coil was evaluated. The highest values of 10g-average SAR (SARpeak-10g) in the fetus occurred for the abdomen, pelvis, and thigh landmarks. Notably, the simulations showed that the highest increase of 10g-average SAR in the fetus occurred when the model abdomen was near the rings of the coil (i.e., pelvis landmark with a shift in y-axis closer to the coil rings) and when the RF sources were also placed near the same end-ring. When the position of the fetus was shifted closer to the coil, the average whole body SAR in the fetus was 5 W kg−1, exceeding the maximum average SAR allowed in First Level Control Operating Mode (i.e., 4 W kg−1), while the average whole body SAR of the mother was normalized to 2 W kg−1.