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, Volume 77, Issue 5, Pages C1–C1, 1729–2086; Early View: 13 May 2016; Online: 18 April 2017; doi: 10.1002/mrm.26268.

MRI is increasingly used to scan pregnant patients. We investigated the effect of 3 Tesla (T) two-port radiofrequency (RF) shimming in anatomical pregnant women models. 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 third, seventh, and ninth month of gestation at various imaging landmarks in RF body coils, including modes with RF shimming. Although RF shimmed configurations may lower the local RF exposure for the mother, they can increase the thermal load on the fetus. In worst-case configurations, whole-body exposure and local peak temperatures – up to 40.8°C – are equal in fetus and mother. Conclusions

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

• Two-port RF shimming can significantly increase the fetal exposure in pregnant women
• Restriction to circular polarization mode, – which, compared with linear-horizontal polarization modes, reduces fetal exposure – may be advisable
• The scanning of pregnant patients at above the normal operating mode is not supported by the study results
• Further research to derive a very robust safety management protocol is required

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This paper was featured on the May 2017 cover of Magnetic Resonance in Medicine