Evaluations of specific absorption rate and temperature increase within pregnant female models in magnetic resonance imaging birdcage coils

This paper presents a detailed numerical study of specific absorption rate (SAR) and temperature increase calculations within pregnant female models exposed to magnetic resonance imaging (MRI). Nine pregnant female models, representing different pregnant stages, were used for this study. SAR and temperature increase within and around fetuses at different pregnancy stages were calculated for two MRI operating modes (normal mode and first-level controlled mode) at 64 and 128 MHz. Local fetus energy deposition exceeds the International Electrotechnical Commission limit of 10 W/kg in the first-level controlled mode at 64 MHz. Fetus temperature exceeds or approaches 38 C for both frequencies in the first-level controlled mode at later stages of pregnancy. The core temperature limits for both modes and both frequencies are not exceeded. The results show higher maximum SAR and higher temperature at 64 MHz and during later pregnancy stages with a significant increase starting with the fifth month of pregnancy. Based on the results of this study, radiologists can minimize local fetus heating, especially late in pregnancy, by using normal mode sequences, which minimize the whole body SAR in the mother.