Ultrasound versus magnetic resonance imaging in fetal evaluation.

Ultrasound is the screening modality of choice for fetal imaging. However, there are circumstances in which an alternate imaging modality is needed for additional information regarding fetal anatomy or pathology. Fast magnetic resonance imaging (MRI) is increasingly being used as a correlative imaging modality in pregnancy because it uses no ionizing radiation, provides excellent soft-tissue contrast, and has multiple planes for reconstruction and a large field of view. However, sonographic evaluation of the fetus still is important to select the appropriate fetuses for magnetic resonance (MR) examination and to guide the protocol of the examination. Performance of high-quality sonographic and MR examinations as well as interpretation by individuals familiar with prenatal diagnosis are important factors for optimal parental counseling. MRI frequently adds additional information beyond that available with ultrasound. This information commonly changes patient counseling and, at times, patient management.