Fetal MRI imaging protocols: current standards, optimization strategies and emerging techniques

Prenatal Magnetic resonance imaging helps to assess the fetus and the pregnancy structures. Maternal obesity, fetal position, or oligohydramnios do not significantly affect MRI image visibility of the fetus, and the ossified skull does not interfere with visualisation of the brain. Many authors have mentioned practical approaches and imaging applications for diagnosis, but there is a lack of a complete standardised imaging protocol for fetal MRI. Different diagnostic centres or hospitals use different sequences, slice thickness, field strength or motion correction methods. This variability in protocol reduces reproducibility and comparison across studies. Thus, there is a need for a standardised fetal MRI protocol. The objective of this review is to provide an overview of fetal Magnetic resonance imaging sequences (SSFSE, SSFP, IVIM, DWI), their applications and parameters, limitations, and safety of fetal magnetic resonance imaging. Magnetic resonance imaging using a T2-weighted sequence of a gravid uterus shows the fetus and pregnancy structures (umbilical cord, placenta and amniotic fluid). T1-weighted sequences are mostly used to demonstrate haemorrhage, calcification, and obesity. The assessment is done in a system-oriented approach that involves the fetal brain, spine, face, neck, chest, abdomen, pelvis, extremities and pregnancy structures. It is an interesting choice of investigation for indications such as congenital anomalies (holoprosencephaly, encephalocele), vascular anomalies (malformations, infarction, twin pregnancy complications), mass (hemangioma, teratoma), etc. Fetal Magnetic resonance imaging is said to be completed when the evaluation of the fetus, placenta, umbilical cord and amniotic cavity is carefully completed.