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IMAGING TECHNIQUES

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Imaging modalities that are used as adjuncts for diagnosis and therapy during pregnancy include sonography, radiography, and magnetic resonance (MR) imaging. Given rapid changes in imaging technology, this chapter is not exhaustive but serves as a guide for imaging obstetric patients with perioperative needs. The focus is on safety, especially with regard to radiation exposure. Thus, detailed dosimetry is provided to help direct examination selection and patient counseling.

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SONOGRAPHY

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Safety

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Of all the major advances in obstetrics, the development of sonography for study of both fetus and mother certainly is one of the greater achievements. The technique has become virtually indispensable in everyday practice (Figs. 5-1, 5-2, 5-3).

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FIGURE 5-1

A 22-year-old gravida at 9 weeks' gestation. A. Transvaginal sonography in a sagittal view demonstrates mild inhomogeneity of the endometrium and no gestational sac. B. With evaluation of the adnexa, a normal appearing right ovary (RO) is noted and contains a corpus luteum cyst (arrowheads). C. With color Doppler imaging, characteristic peripheral vascularity, often called a "ring of fire," is seen. D. With gentle pressure from the transducer, the intraovarian position of the corpus luteum cyst is documented.

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FIGURE 5-2

A 23-year-old gravida at 12 weeks' gestation complained of lower abdominal pain. A. Transabdominal sonography in a sagittal view shows an enlarged right ovary containing a multiseptate cyst (calipers). B. Color Doppler images demonstrate minimal vascularity within the right ovary. Importantly, absent vascular flow within an ovary is not necessary for the diagnosis of torsion. Given her compelling symptoms, diagnostic laparoscopy was performed, adnexal torsion was identified, and a right salpingo-oophorectomy was completed. Histologic evaluation revealed an ovarian serous cystadenoma.

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FIGURE 5-3

A 27-year-old gravida at 15 weeks' gestation complained of vaginal bleeding. This longitudinal image taken during transvaginal sonography shows cystic and solid heterogeneous tissue filling the endometrial cavity (calipers), and no fetal parts are identified. A complete hydatidiform mole was diagnosed histologically from a dilation and curettage specimen.

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Diagnostic sonography uses sound wave transmission at certain frequencies. Recall that ultrasound is a form of nonionizing radiation that transmits energy. Studies involving prolonged ultrasound exposure of animal fetuses suggest that it is possible to induce cellular alterations. For example, with at least 30 minutes of ultrasound exposure to embryonic mouse neurons, a statistically significant number of neurons were impeded from their expected migration (Ang, 2007). At this time, however, the American Institute of Ultrasound in Medicine (2010) and other organizations agree that these findings should not alter the use of ultrasound in pregnant women. Moreover, Naumburg and associates (2000) ...

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