Received July 5, 1995; accepted after revision October 24, 1995. I University of Catifomia, San Francisco, Department of Radiology, Box 0628, L-308, 505 Pamassus Ave., San Francisco, CA 94143-0628. Address correspon- dence to H. Hnicak. 1139 AJR 1996;166:1139-1144 036i-803X/96/1665-1i39 ©American Roentgen Ray Society Pictorial Essay Abdominopelvic MR Imaging in the Nonobstetric Evaluation of Pregnant Patients Rosemarie Forstner1 , Carl L. Kalbhen, Roy A. Filly, Hedvig Hricak Managing a pregnant patient with a suspected nonobstetric abdominopelvic disorder is challenging. Information from imaging affects the treatment options, which range from oper- ating emergently and risking miscarriage to terminating the pregnancy or delaying treatment until after delivery. The most common indications for MR Imaging during pregnancy are dis- orders of the central nervous and cardiovascular systems. In the evaluation of the abdomen and pelvis, sonography plays the pivotal role; however, sonography may be Inconclusive because of Its limited specificity in tissue characterization and technical difficulties caused by the enlarged uterus. For these reasons MR imaging has emerged as a valuable adjunct to sonography. In this pictorial essay we describe a variety of nonobstetric abdominopelvic disorders during pregnancy in which MR imaging contributed to patient management. Biosafety Although no adverse effects of MR imaging toward the fetus have been documented, Food and Drug Administration guidelines require labeling of MR imaging devices to indicate that the safety of MR imaging with respect to the fetus has not been established [1]. The potential risks of MR imaging should be weighed against the expected diagnostic benefits and the known hazards of ionizing radiation from other imag- ing techniques [1]. Therefore, abdominopelvic MR imaging is indicated during pregnancy only if sonography is nondiag- nostic or as an alternative to an examination that requires ionizing radiation. Whenever possible, MR imaging should be delayed until the second or third trimester [2]. A safety concern during all MR examinations is tissue heat- ing caused by the radiofrequency pulses; these effects are greatest at the body surface and approach zero near the body center [3]. The Food and Drug Administration requires that the radiofrequency pulses result in a core temperature increase of less than 1 #{176}C and that the deposited energy, as measured by the specific absorption rate, be less than 0.4 W/kg [1]. Technique Informed consent for MR imaging during pregnancy is not mandatory but is still recommended. Informed consent helps ensure that the patient receives a detailed explanation and understands the procedure. The examination time and number of sequences should be minimized. Imaging of the abdomen and pelvis requires axial Ti- and T2-weighted sequences. Sag- thaI T2-weighted images also should be obtained when evalu- ating the pelvis. Additional sequences, such as other planes of section or fat suppression, may be necessary in some patients. IV contrast media, that is, gadolinium chelates, are not recom- mended. These paramagnetic agents cross the placenta, and the long-term effects are not known [3]. Indeterminate Abdominal Masses on Sonography Abdominal masses are uncommon in women of childbear- ing age. In a pregnant patient with a suspected abdominal mass, sonography should be the initial diagnostic study. Sono- graphically detected renal masses in pregnant women are usually benign. However, in atypical cases, MR imaging may provide valuable information by further characterizing lesions without the use of ionizing radiation (Fig. 1). Toward the end of gestation, masses in the upper abdomen may mimic parauter-