May 17, 2016

Pregnant women models analyzed for RF exposure and temperature increase in 3T RF shimmed birdcages

Manuel Murbach, Esra Neufeld, Theodoros Samaras, Juan Córcoles, Fraser J. Robb, Wolfgang Kainz, and Niels Kuster, Magnetic Resonance in Medicine, Early View, May 2016, online May 17, 2016

Magnetic resonance imaging (MRI) is increasingly used to scan pregnant patients. RF shimming improves  B1+ uniformity, but may at the same time significantly alter the induced current distribution and result in large changes in both the level and location of the absorbed RF energy. In this study, we evaluated the electrothermal exposure of pregnant women in the 3rd, 7th, and 9th months of gestation at various imaging landmarks in RF body coils. While RF shimming typically is beneficial for the exposure level of the mother, it may significantly increase exposure of the fetus. Factors influencing the exposure have been investigated systematically: stage of gestation, RF coil dimensions, imaging landmarks, and RF shimming excitation, which allowed us to describe typical worst-case scenarios. We discuss the shortcomings of the current standard and confirm that pregnant patients should not be scanned outside of the normal operating mode.

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

  • The electrothermal exposure of numerical model pregnant patients undergoing MRI at 3T was systematically evaluated by means of Sim4Life and SEMCAD X simulations
  • Worst-case exposure scenarios have been identified for the fetus that are fundamentally different from those of the mother