RF Exposure and Resulting Temperature in the Fetus During MRI

Jeff W. Hand¹, Yan Li¹, Jo V. Hajnal¹

SAR and temperature in a 26 week pregnant woman within a 64 MHz birdcage coil are predicted numerically. Heat transfer from fetus to placenta via the umbilical vein and arteries as well as that across the fetal skin/amniotic fluid /uterine wall boundaries is modelled. Fetal SAR and average temperature comply with international limits when maternal whole body SAR ≤2 W kg^-1, although maximum fetal temperature > 38^oC may result from continuous exposure over periods ≥7.5 minutes. However, assessment of risk posed by the maximum temperature predicted in a static model is difficult in view of frequent fetal movement.