Diagnostic Imaging
September 2003

TECH WATCH

Real-time 3D Doppler imaging impresses early clinical users

New Philips system generates volumetric images as soon as the transducer touches the patient

Few technologies have been so long awaited and elusive as clinically viable 3D ultrasound. The first such reconstructions appeared nearly 20 years ago, but only after painstakingly gathered 2D data underwent hours of offline manipulation. By the mid-1990s, processing time had shrunk from hours to minutes, and optimism ran high that a real-time 3D system was near at hand.

"In 1994, I predicted we would have real-time in two years," said Dr. Natesa Pandian, director of the cardiovascular imaging and hemodynamic laboratory at Tufts-New England Medical Center. "Finally, we have it."

Live 3D Echo generates volumetric images as soon as the transducer is placed on the patient. Data are acquired at 25 to 28 frames per second. The benefits of the product, commercially released in October by Philips Medical Systems, are self-evident, according to Pandian.

"Every structure in the heart-every facet of function, any pathology-is three dimensional in time and space," he said. "The ideal technique to look at the heart and cardiac pathology is a 3D technique."

Live 3D Echo did not, however, include an essential part of the echo exam: 3D color flow. Philips announced the release of that piece in spring 2003. Integrated with Live 3D Echo and running on Philips' Sonos 7500 flagship echo system, 3D color Doppler depicts blood flow inside the heart. Doppler data are processed into 3D color flow images, showing red, blue, green, and yellow flashes in a wedge of gray tissue. These images are now being generated routinely at Oregon Health and Sciences University in Portland, where live 3D echo and 3D color flow have been used together to document congestive heart failure, coronary artery disease, and valvular pathologies.

"You can tell exactly where the regurgitant orifice is in 3D," said Dr. David J. Sahn, a professor of pediatrics, diagnostic radiology, and ob/gyn at OHSU. "In one patient, we found a hole in the mitral valve, called an isolated cleft, that wasn't seen in four years of 2D exams. Now we know what she has."

Quantitative analyses may also be useful. Preliminary studies by Philips luminaries indicate that it may be possible to calculate stroke volume using measurements generated with Live 3D Echo. It may even be possible to calculate an index of regurgitation and correlate this index to the health of the patient by imaging the volume of the atrium and the regurgitation within.

Patient throughput may increase because the volume of data obtained over several heartbeats can be reexamined for specific information from different perspectives, eliminating the need to recall patients for additional scans. Equipped with both 3D technologies, Philips Sonos 7500 is priced between $200,000 and $225,000.

Images acquired using Live 3D Echo are instantaneous, meeting a criterion for true real-time 3D ultrasound. Color Doppler images, however, are not. The data set is so large that, even though processing occurs on the fly, images take a few seconds to appear, according to Kevin Appareti, market development manager for high-end cardiovascular ultrasound at Philips.

"Color flow needs more data obtained through more frequent sampling than black-and-white imaging to calculate the Doppler shift-the velocity, amplitude, and direction of blood flow," he said.

Modern 3D eventually will displace 2D as the preferred method of echocardiography, according to Pandian. There may be some resistance, as there is to the adoption of any new technology, but it will pass, he added.

"When 2D echo came along almost three decades ago, some argued that it was not needed because we had M-mode," Pandian said. "Now if you look at that argument, you see how stupid it was. It will be the same thing with 2D and 3D. I am hoping all (echo) instruments will have 3D in the future so all exams can be done in 3D."

Sahn concurs, describing the new technology as fundamental to a complete system, rather than simply an elective upgrade.