Skull, face, and neck
Other abnormalities with potential airway obstruction
Evaluation of pulmonary hypoplasia secondary to diaphragmatic hernia, oligohydramnios, chest mass, or ske!etal dysplasia
Abdomen, pelvis, and retroperitoneum
Abdominopelvic cystic mass evaluation Tumor evaluation (sacrococcygeal teratoma, neuroblastoma, hemangioma, suprarenal or renal masses) Complex genitourinary anomalies (bladder outlet obstruction syndromes, bladder exstrophy, cloacal exstrophy)
Assess rena! anomalies with oligohydramnios
Diagnose bowel anomalies (anorectal malformations,
Complications of monochorionic twins
Determine vascular anatomy prior to laser treatment Assess morbidity ater death of a monochorionic co-twin
Fetal brain anatomy before and after surgical intervention Anomalies for which fetal surgery is planned aln some cases, magnetic resonance (MR) imaging is indicated only if the anomaly is ed but cannot be adequately characterized sonographically, vvhich is assessed on a case-by case basis.
Data from American College of Radiology, 2015.
field is measured in tesLa (), and most imaging studies during pregnancy are performed using 1.5 T. A few preliminary studies advocate the use of 3 T for fetal imaging to potentially improve signal-to-noise ratios and thus image clarity (Victoria, 2016). For safety, all clinical examinations must adhere to the speciic absorption rate, which is regulated by the Food and Drug Administration, and the ALARA principle should be followed. Thus, for routine clinical examinations, the lower ield strength of 1.5 T is recommended (Prayer, 2017).
Human and tissue studies support the safety of fetal MR imaging. Repetitive exposure of human lung fibroblasts to a static 1.5-T magnetic ield does not afect cellular proliferation (Wiskirchen, 1999). Fetal heart rate patterns have been evaluated before and during MR imaging, and no signiicant diferences were observed (Vadeyar, 2000). Children exposed to MR as fetuses do not show a greater incidence of disease or disability when tested at age 9 months or 3 years (Baker, 1994; Clements, 2000).
Glover and associates (1995) attempted to mimic the sound level experienced by the fetal ear by having an adult volunteer swallow a microphone while the stomach was illed with a liter of luid to represent the amnionic sac. Sound intensity was attenuated at least 30-dB from the body surface to the fluidfilled stomach and reduced the sound pressure from 120 dB to below 90 dB. This level is considerably less than the 135 dB experienced from vibroacoustic stimulation used in antepartum well-being assessments (Chap. 17, p. 337). Cochlear function testing in infants exposed to 1.5-T MR imaging as fetuses showed no hearing impairment (Reeves, 2010).
he American College of Radiology (2013) concludes that based on available evidence, MR imaging has no documented deleterious efects on the developing fetus. Therefore, MR imaging can be performed in pregnancy if data are needed to care for the fetus or mother. Health-care providers who are pregnant may work in and around an MR unit, but it is recommended that they not remain in the MR scanner magnet room-known as Zone IV-while an examination is in progress.