Arthur C. Fleischer
Three-dimensional (3D) sonography has become a clinically useful problem-solving technique that can also expedite sonographic examinations in certain obstetric and gynecologic disorders. Improved instrumentation has afforded its incorporation into clinical practice and provides interesting new areas for future applications. This is an illustrative overview of the important points of 3D sonography for the sonographer and sonologist. The reader is encouraged to read the articles that describe new, ever-expanding applications of this technique.1–5
Three-dimensional acquisitions can be obtained with freehand sweeps of an area of interest or with automated transducers that interrogate a specified area of interest. Three-dimensional automated transducers consist of an imaging array mounted on a gimbal. These transducers can be as small as the transvaginal probe or as large as a large handheld probe. The scanning section axis can be selected from 30° to more than 120° (Figs. 8–1 and 8–2). The patient must suspend respiration and remain motionless when the images are obtained in order to avoid scan artefacts.
FIGURE 8–1. Three-dimensional obstetrical probe showing sectored volume. (Courtesy of Philips Healthcare.)
FIGURE 8–2. Four-dimensional matrix array probe. (Courtesy of Philips Healthcare.)
For freehand scanning, the scanner memory is filled with two-dimensional (2D) images that are reprocessed into a 3D volume. Although adequate 3D sonography can be obtained this way, its resolution is not as great as with images obtained with an automatically sectored probe.
Automated 3D transducer probes contain an array of transducer elements that are swept in a selectable arc through an area of interest. The images are displayed in a multiplanar format with the long-axis, short-axis, and coronal planes, as well as the volumetric image. The multiplanar images are usually displayed with the long-axis view on the top left, followed by the short-axis images obtained at 90° or orthogonal to the long axis displayed in top right, followed by the coronal image scan plane (Fig. 8–3, bottom left). The combined volume is shown, within which (Fig. 8–3 bottom right) the scan plane can be maneuvered.
FIGURE 8–3. Multiplanar imaging format. (Courtesy of Philips Healthcare.): Top left: long-axis plane; Top right: short-axis plane; Bottom left: coronal plane; Bottom right: 3D volume.
This layout of multiplanar reconstructed images can be varied to emphasize the volumetric images as the largest one displayed. Three-dimensional images can be manipulated to emphasize the surface (surface rendering) or the entire volume (volume rendering). The ability to visualize the structure from a selectable scan plane is particularly helpful when such planes cannot be readably obtainable from a 2D image. This is particularly true in the evaluation of the fetal heart when obtaining an optimal image of the outflow tracts, this may not be possible on 2D acquisition but quite possible with 3D. Another new feature is the ability to display multiple tomographic images (Philips’ iSlice) obtained in selectable intervals and slice thicknesses.
OBSTETRICAL 3D SONOGRAPHY
Three-dimensional sonography offers a detailed depiction of the fetal face, extremities, outer contours, and certain organs such as the fetal heart, brain, liver, kidneys, and spine (Figs. 8–4 through 8–27). Depiction of the fetus with 3D sonography has gained widespread and universal demand. However, there should be clinical indication for such studies since any unnecessary exposure to ultrasound (see the American Institute of Ultrasound in Medicine statement regarding use of 3D ultrasound for “entertainment”) should be avoided.
FIGURE 8–4. Normal uterus and endometrium as shown in multiplanar images. (Courtesy of Philips Healthcare.): Top left: short-axis uterus; Top right: long-axis uterus; Bottom left: coronal; Bottom right: surface rendered volume.
FIGURE 8–5. Three-dimensional sonogram of 10-week intrauterine pregnancy. (Courtesy of Philips Healthcare.): Top left: long axis showing fetal heart and trunk; Top right: short axis through bottom of left hand; Bottom left: coronal plane; Bottom right: 3D volume with surface rendering showing the entire fetus and umbilical cord.
FIGURE 8–6. Three-dimensional image of twins at 11-weeks’ gestation. (Courtesy of Philips Healthcare.)
FIGURE 8–7. Three-dimensional sonogram of 12-week fetus showing normal umbilical cord fetal abdominal insertion. The physiologic herniation of bowel into the base of the cord that can be seen between 8 and 12 weeks should be completed by 12 weeks. (Courtesy of Philips Healthcare.)
FIGURE 8–8. Three-dimensional sonogram of a 17-week fetus showing unfused cranial sutures. (Courtesy of Philips Healthcare.)
FIGURE 8–9. Three-dimensional sonogram of face of 20-week fetus. (Courtesy of Philips Healthcare.)
FIGURE 8–10. iSlice 3D showing normal fetal palate. (Courtesy of Philips Healthcare.)
FIGURE 8–11. iSlice 3D showing normal fetal palate and mandible. (Courtesy of Philips Healthcare.)
FIGURE 8–12. Three-dimensional sonogram showing bilateral cleft palate. (Courtesy of Philips Healthcare.)
FIGURE 8–13. Three-dimensional sonogram of cleft lip and palate. (Courtesy of Philips Healthcare.)
FIGURE 8–14. 3D sonogram of an encephalic fetus. (Courtesy of Philips Healthcare.)
FIGURE 8–15. Multiplanar image and 3D reconstruction of the brain of a fetus at 25-weeks’ gestation. The corpus callosum is clearly depicted on the volumetric image (4). (Courtesy of Philips Healthcare.)
FIGURE 8–16. Spatial, temporal image correlation (STIC) of normal fetal ventricles/atria and outflow tracts. (Courtesy of Philips Healthcare.)
FIGURE 8–17. Multiplanar image of normal fetal spine. (Courtesy of Philips Healthcare.)
FIGURE 8–18. Multiplanar image of normal sacrum of a fetus at 26-weeks’ gestation. (Courtesy of Philips Healthcare.)
FIGURE 8–19. Multiplanar reconstructed image of normal kidneys. (Courtesy of Philips Healthcare.)
FIGURE 8–20. Three dimensional sonogram of normal umbilical cord showing two (paired) arteries coiled around umbilical vein. (Courtesy of Philips Healthcare.)
FIGURE 8–21. Three-dimensional sonogram of a fetus 26-weeks’ gestation with a large omphalocele. (Courtesy of Philips Healthcare.)
FIGURE 8–22. Three-dimensional sonogram of the scrotum and penis of a fetus at 31 -weeks’ gestation. (Courtesy of Philips Healthcare.)
FIGURE 8–23. Three-dimensional sonogram of labia majora of a female fetus at 30-weeks’ gestation. (Courtesy of Philips Healthcare.)
FIGURE 8–24. Three-dimensional sonogram of hand of a fetus at 29-weeks’ gestation. (Courtesy of Philips Healthcare.)
FIGURE 8–25. Three-dimensional sonogram of fingers of a fetus at 30-weeks’ gestation. (Courtesy of Philips Healthcare.)
FIGURE 8–26. Three-dimensional sonogram of fetal feet and toes. (Courtesy of Philips Healthcare.)
FIGURE 8–27. Three-dimensional sonogram showing bilateral club feet. (Courtesy of Philips Healthcare.)
Fetal facial malformations such as cleft lip or cleft palate are readily seen on 3D. It is important to determine whether a cleft lip defect extends into the hard palate. Fetal facial anomalies have a higher association with brain malformations and 3D may be used to evaluate intracranial anomalies.
Three-dimensional sonography is particularly useful in the evaluation of the fetal heart. This is due to the ability to depict selected scan planes that may not be obtainable on 2D. The heart volume can be obtained with special software that affords spatial, temporal image correlation (STIC). This technique allows for systematic evaluation of cardiac structures regardless of fetal position.
Three-dimensional sonography may be useful in depicting complete anomalies involving an abnormal abdominal wall such as omphalocele or internal disruptions such as congenital diaphragmatic hernia. Using 3D, the actual volume of the remaining lungs of a fetus with congenital diaphragmatic hernia can be estimated.
Other applications of 3D in obstetrics include evaluation of placental vascular bed or umbilical cord insertion or coiling anomalies. Umbilical cord knots and nuchal cords are readily depicted on 3D.
Three-dimensional color Doppler sonography can provide the arrangement of intraplacental vessels as well as focal areas of retroplacental hemorrhage. Three-dimensional sonography can depict abnormal umbilical cord placental insertion such as velamentous cord insertions onto the membrane rather than the placental surface chorionic plate.
Other applications may include using 3D sonography to depict ectopic pregnancies and their spatial relationship to the ovary, as well as to assess internal organ malformations. As 3D sonography is used more, sonographers will undoubtedly discover new and expanded clinical applications of this technique.
GYNECOLOGIC 3D SONOGRAPHY
Three-dimensional sonography has many clinical applications in gynecologic disorders (Figs. 8–28 through 8–37). As in obstetrical 3D, gynecologic 3D affords depiction of the uterus and ovaries in any selectable scan plane, including those not readily obtained with 2D. These include improved depiction of endometrial masses such as polyps or submucosal fibroids, improved localization and calculation of changes in fibroid volume, enhanced depiction of tubal masses, intrauterine device localization, and uterine malformations. Three-dimensional depiction of tumor morphology and vascularity within ovarian masses has important implications in distinguishing benign from malignant masses.
FIGURE 8–28. Normal endometrium as shown in coronal plane 3D. (Courtesy of Philips Healthcare.)
FIGURE 8–29. Two separate endometrial cavities and uterine horns. (Courtesy of Philips Healthcare.)
FIGURE 8–30. Endometrial polyp as shown in coronal plane 3D surface rendering pedunculated. (Courtesy of Philips Healthcare.)
FIGURE 8–31. Submucosal fibroid that is intraluminal as depicted in coronal 3D. (Courtesy of Philips Healthcare.)
FIGURE 8–32. Three-dimensional surface-rendered image obtained during sonohysterography showing polyp (arrow). (Courtesy of Philips Healthcare.)
FIGURE 8–33. Multiplanar image showing centrally located intrauterine contraceptive device. (Courtesy of Philips Healthcare.)
FIGURE 8–34. Three-dimensional image of ovarian cyst containing fibrin strands. (Courtesy of Philips Healthcare.)
FIGURE 8–35. Three-dimensional image of hemorrhagic ovarian mass containing formed clot. (Courtesy of Philips Healthcare.)
FIGURE 8–36. Three-dimensional image of ovarian tumor containing a papillary excrescence. (Courtesy of Philips Healthcare.)
FIGURE 8–37. Three-dimensional images of ovarian cancer showing clusters of abnormal vessel (top right) in area of papillary excrescence. (Courtesy of Philips Healthcare.)
Three-dimensional sonography affords depiction of the configuration of the uterine fundus. With a septated uterus, the fundal contour is smooth, whereas with bicornuate and didelphys, a sharp cleft is seen.
Fibroids have a peripheral rim of vascularity and this is seen readily with 3D color Doppler sonography. Any collaterals such as those arising from the ovarian vessels can be seen. Marked changes in the vascularity fibroids such as that occurring post-uterine artery embolization can be documented accurately with 3D sonography.
Because of its ability to display in the coronal plane, 3D sonography is accurate in depicting intraluminal masses such as polyps or fibroids. The location of an intrauterine contraceptive device (IUCD) within the endometrium is readily depicted with 3D sonography. Three-dimensional sonography obtained in the transverse plane of the uterus fundus is also useful in identifying tubal masses since their origins can be traced to the cornual area of the uterus.
Three-dimensional sonography can depict focal wall irregularities within mostly cystic adnexal lesions. Three-dimensional color Doppler sonography can depict vessel density and branching pattern. The vessels within a tumor typically are clustered and show differences in their caliber.
Acquisition of large sample volumes affords later evaluation of organs in selected scan planes. Some advocate that volumetric acquisition in obstetrics and gynecology can expedite the examinations, making them quicker to obtain and complete.3 Additional time is needed to obtain the required scan plans from the 3D volume set.
It is clear that 3D sonography has a role in the evaluation of certain obstetric and gynecologic disorders. Live 3D or “4D” can depict fetal behavior and also will have many applications for guided procedures.4 Undoubtedly, future applications of this technique will evolve within its greater use.5
1. Merz E. 3D Ultrasound in Obstetrics/Gynecology. New York: Lippincott Publishers; 1998.
2. Fleischer AC, Black AS, Grippo RJ, Pham T. 3D pelvic sonography: current use and potential applications. J Women’s Imaging. 2003; 5(2):52–59.
3. Benacerraf BR. Tomographic sonography of the fetus: is it accurate enough to be a frontline screen for fetal malformation? J Ultrasound Med. 2006; 25:687–689.
4. Goncalves LF, Espinoza J, Kusanovic JP, et al. Applications of 2-dimensional matrix array for 3- and 4-dimensional examination of the fetus: a pictorial essay. J Ultrasound Med. 2006; 25:745–755.
5. Goncalves LF, Nien JK, Espinoza J, et al. What does 2-dimensional imaging add to 3- and 4-dimensional obstetric ultrasonography? J Ultrasound Med. 2006; 25:691–699.