Sep 22, 2011

Local SAR Enhancements in Anatomically Correct Children and Adult Models as a Function of Position within 1.5T MR Body Coil

Manuel Murbach, Eugenia Cabot, Esra Neufeld, Marie-Christine Gosselin, Andreas Christ, Klaas Prüssmann, and Niels Kuster, Progress in Biophysics and Molecular Biology, Volume 107, Issue 3, pp. 428–433, December, 2011. Online September 22

Usage of magnetic resonance imaging (MRI) is continuously increasing due to its excellent soft-tissue contrast and improving diagnostic values. MRI also has the advantage that it operates without ionizing radiation. The main safety concerns are torque, acceleration by the static field, nerve stimulation by the gradient fields, and tissue heating by the radio-frequency (RF) fields. This paper investigates if children and fetuses are at higher risks than adults when the current RF regulations are applied. We analyzed and compared local absorption hotspots, i.e., the peak spatial specific absorption rate averaged over any 10g (psSAR10g) for five adults, three children of ages 5, 11 and 14 years, and 1 pregnant female (36 weeks' gestation) in 10 different Z-positions (head to calves). In the FIRST LEVEL OPERATING MODE (4 W/kg whole-body averaged exposure), the psSAR10g values found for adults were as large as 60 W/kg in the trunk and 104 W/kg in the extremities.

The results suggest that local exposure for children and fetuses is smaller than for adults (15-75%), i.e., no special considerations for children and the unborn child are needed regarding psSAR10g due to RF. However, the local thermal load of the unborn may be significantly increased due to the high exposure average (up to 4 W/kg) of the non-perfused amniotic fluid.

The scientific and technical impact of the study can be summarized as:

  • For the first time, the maximum local RF exposure has been systematically evaluated for a wide range of anatomies and landmark positions for the exposure  conditions accepted by the product standard [IEC 2010].
  • The study indicates that exposure of children is not higher than that of adults but further investigations are suggested for the evaluation of the thermal load of unborn children.