Incorporating realistic fetal motion into RF safety assessment of fetal MRI

Motivation: Recent simulation studies using static fetus models show possible fetal heating concerns and the potential for fetal motion to mitigate tissue heating is unknown. Goal(s): To demonstrate the effect of realistic fetal motion on fetal SAR estimations. Approach: We used automatic and manual segmentation, and registration approaches to generate 4 body models of a pregnant subject with different fetal positions. Fetal SAR was simulated in each model. Results: Fetal average and peak SAR changed by up to 23% and 9% respectively and fetal peak SAR was located at different regions in the fetus including the back and left arm. Impact: We demonstrated a pipeline to incorporate realistic fetal motion into SAR estimations for the first time, enhancing RF safety assessment of fetal MRI. Our results show fetal motion is critical for accurate tissue heating estimations in the fetus.