FIGURE 46-4 This woman in her third trimester was involved in a high-speed motor vehicle accident. A. Maximum intensity projection acquired for maternal indications readily identifies fetal skull fractures (arrows). B.3-D reformatted CT image in a bone algorithm demonstrates the fetal skeleton from data acquired during the maternal examination. Again, the arrow marks one fracture site. (Reproduced with permission from Bailey AA, Twickler OM: Perioperative imaging. In Yeomans ER, Hoffman BL, Gilstrap LC III, et al (eds): Cunningham and Gilstrap'S Operative Obstetrics 3rd ed. New York: McGraw-Hili Education; 201o7. Photo contributor: Dr. Travis Browning.)
Figure 46-4, abdominal tomography is performed if indicated in the pregnant woman with severe trauma (Matzon, 2015; Shakerian, 2015).
Most experience with chest CT scanning is with suspected pulmonary embolism. The most recent recommendations for its use in pregnancy from the Prospective Investigation of Pulmonary Embolism Diagnosis-PIOPED-II investigators were summarized by Stein and associates (2007). They found that pulmonary scintigraphy-the V/Q scan-was recommended at that time for pregnant women by 70 percent of radiologists and chest CT angiography by 30 percent. Indeed, scintigraphy is still recommended by the American Thoracic Society for gravidas with a normal chest x-ray (Leung, 2012). hat said, most agree that multidetector-CT angiography has improved accuracy because of increasingly faster acquisition times (Brown, 2014). Others have reported a higher use rate for CT angiography and emphasize that dosimetry is similar to that with V/Q scintigraphy (Brenner, 2007; Greer, 2015; Hurwitz, 2006). Controversies on this topic continue, recognizing that fetal radiation doses are lower with CT angiography compared with the V/Q scan, but maternal chest radiation doses are substantially higher with CT scanning (van Mens, 2017). We prefer MDCT scanning initially for suspected pulmonary embolism (Chap. 52, p. 1016).
CT pelvimetry is used by some before attempting breech vaginal delivery (Chap. 28, p. 542). he fetal dose approaches 0.015 Gyor 1.5 rad, but use of a low-exposure technique may reduce this to 0.0025 Gy or 0.25 rad.
hese can be given intravenously or taken orally. Intravenous contrast agents are considered category B by the FDA. The types of intravenous contrast employed for imaging today are iodinated and low osmolality, thus, they cross the placenta to the fetus. With water-soluble iodinated contrast, no cases of neonatal hypothyroidism or other adverse efects have been documented (American College of Radiology, 2015). Oral contrast preparations, typically containing iodine or barium, have minimal systemic absorption and are unlikely to afect the fetus.