3-D ultrasound reveals 'tremendous detail'.(Obstetrics)

NEW YORK -- Three-dimensional ultrasound represents an emerging advance in imaging with important applications in obstetrics, Alfred Z. Abuhamad, M.D., said at an obstetrics symposium that was sponsored by Columbia University and New York Presbyterian Hospital.

The ability to rotate images, change planes, and manipulate displays according to signal strength makes it possible to visualize skeletal and vascular structures and fluid spaces, in addition to providing detailed views of fetal appearance, according to Dr. Abuhamad, who is professor and chair of obstetrics and gynecology and the director of the division of maternal-fetal medicine at Eastern Virginia Medical School, Norfolk.

The term "3-D" is something of a misnomer in that the image is displayed on a 2-D monitor.

"[Instead of '3-D'] the term should be volume sonography that gives the appearance of depth," Dr. Abuhamad said.

The volume image is created by the summation of 2-D slices from multiple planes, as the probe is steered from side to side.

The size of the acquired image is determined by the angle across which the probe is moved. Since fetal movement makes the speed of volume acquisition highly important, "we use the smallest angle [needed for evaluation of the structure of interest] in the smallest box," Dr. Abuhamad said.

With a multiplanar display, an image constructed from sagittal, coronal, and transverse planes can be rotated along the x-, y-, and z-axis to visualize the same structure from different angles. To maintain orientation, it is helpful to determine a reference point, and it may be necessary to use 2-D ultrasound to locate key structures.