Fetal MRI: Is it safe?

Abstract

Since the introduction of prenatal magnetic resonance imaging in 1980s, safety issues have been discussed in numerous publications. The examination is contraindicated in certain circumstances, as in the general population. Available fast magnetic resonance imaging (MRI) techniques make sedation of the mother (and fetus) unnecessary. Proper positioning of the patient is important to avoid compression of the inferior vena cava by the pregnant uterus. Static magnetic field, radiofrequency pulses and magnetic field gradients constitute the three hazards to the fetus examined in the MRI scanner. High static magnetic fields are only responsible for sensory effects: vertigo, metallic taste and magnetophosphenes. Electromagnetic radiofrequency pulses result in energy deposition and are responsible for tissue heating during MRI. Increased temperature is especially harmful to the fetal central nervous system. Temperature rise of 2 °C lasting for 24 h may cause neural tube and cranio-facial abnormalities. The amount of energy deposited in a patient over time is reflected by specific absorption rate (SAR). In a study using SAR of 4.0 W/kg (the upper limit in general clinical MRI imaging) no maternal temperature changes were detected. MRI is unlikely to result in significant temperature changes provided that temperature and humidity in the MRI suite are kept within the recommended limits: of less than 24 degrees °C and below 60%, respectively. MRI generates noise. Water – the main component of the amniotic fluid – reduces sound intensity of approximately 30 dB. It is unlikely that the MRI scan would harm the fetus hearing and such harmful effects have not been observed in follow-up studies. The mother is protected by headphones with music, which also has a calming effect in case of claustrophobia and general anxiety. Harmful influence of MRI on organogenesis in the first trimester of pregnancy has not been described at the clinically used magnetic field strengths. In most centers, gadolinium is not used for fetal imaging. If it is used, it is for maternal reasons, if the benefits outweigh the potential risk. Last but not least, it is important to perform fetal MRI in specialized centers. Staff experience both in performing and interpreting the study is crucial to make the examination as short and conclusive as possible.

Keywords

MRI - fetus - safety