In some cases diagnostic ultrasound scans are complemented by magnetic resonance imaging (MRI) of the developing child. MRI is always valuable when ultrasound comes up against its limits, e.g. in maternal overweight, absence of amniotic fluid, or unfavorable fetal lie. The fetal brain can be visualized particularly well. Unlike with ultrasound, the whole child is always imaged. The images become somewhat blurred if the mother or child makes any brisk movement. Like ultrasound, MRI is completely harmless to the fetus.