3-D ultrasound: gimmick or preferred method? (Only as Good as the 2-D Information).

BOSTON -- It is fun to do, it thrills parents-to-be, and it has equipment marketing teams working overtime. But is 3-D obstetrical ultrasound really necessary?

"I can't answer that completely, but I will tell you that eventually, most ultrasound machines will have 3-D Capability much like they now have Doppler. You won't use it in all cases, but it will be there when you want it," Dr. Beryl Benacerraf said at an ultrasound meeting sponsored by Harvard Medical School and the Brigham and Women's Hospital.

Three-dimensional sonography is actually an extrapolation of standard 2-D scanning. The image processing algorithms combine 2-D images taken from the transverse, longitudinal, and horizontal planes into a single composite 3-D image. Once the 3-D view has been constructed, it can be rotated and flipped in any direction, enabling one to visualize the precise location of a point within the image volume in any of the 3 planes.

Obstetrical 3-D sonography has gotten considerable attention simply because it can produce astonishing fetal images. "They [patients] are coming in now and asking for in utero 3-D 'portraits' of their children," said Dr. Benacerraf of Brigham and Women's Hospital, Boston.

What the patients don't know is that those dramatic portrait shots they've seen in media reports on 3-D ultrasound are possible in only about 10% of cases. "It depends on the baby's actual position," not to mention the sonographer's skill and the time available to a technician for sitting at the computer and manipulating the image processing system. For the moment, in utero portraiture is far from routine.

This underscores an important point about 3-D: It is only as good as the 2-D information from which the 3-D image is composed. "Any defects in the 2-D are going to be amplified and compounded in 3-D, not attenuated. If you don't get good 2-D views, you're not going to magically make a good 3-D image," Dr. Benacerraf said.

The real question, though, is whether 3-D adds anything more significant than oohs and aahs.