Technology gives rise to diagnostic breakthroughs (Part – IV)

Several technologies are being combined in novel ways to address previously intractable problems
By: GREG FREIHERR
Echocardiography presents the ultimate challenge and promises the greatest patient benefits for volumetric sonography. Instantaneously capturing the beating heart at stop-action speeds would dramatically reduce exam time and improve the diagnostic value of the data. The Model One-and still experimental-V360 Real-time Volumetric Ultrasound system from Volumetrics Medical Imaging incorporate many features found in conventional 2-D imaging, as well as real-time volumetric acquisition. Interactive capabilities allow retrospective multi-view analysis of the heart. A work-in-progress shown at the 1999 annual meeting of the American Heart Association featured on-the-fly viewing of 3-D volumes of the heart.
"Based on our market research, within three to five years every company will have to offer 3-D capability," said Jim Mundell, general manager at Volumetrics.
3D echocardiography is especially suited to imaging the fetal heart, which for obvious reasons is not a candidate for nuclear medicine . Researchers at the University of California, San Diego, evaluated 10 human fetuses in-utero, four of whom had congenital heart disease. They performed freehand trans-abdominal scanning, using a real-time, 3-D echocardiography system from Volumetrics.
Four scans, lasting just 1.5 seconds and acquiring 20 volumes per second, were obtained for each fetal heart and stored for off-line analysis. Two-dimensional images displayed simultaneously in four planes were reconstructed in real-time during the acquisition, providing the operator with enough feedback to ensure that an adequate 3-D volume was being captured. Off-line reconstructions allowed the heart to be slowed, stopped, or viewed at its original speed.
The researchers consistently visualized most structures and views, as well as cardiac function and they could readily detect abnormal structures.
Yet the current of clinical medicine is hampered by clinical and economic realities. While the technologies necessary to make volumetric imaging a reality are almost at hand, the perceived clinical value of volumetric imaging has not resulted in widespread adoption of the technology. Some kinks remain to be worked out, such as exactly demonstrating blood flow.
Despite the perception of 3-D as leading-edge technology, 2-D imaging is serving as the pathfinder for new types of data acquisition and processing, both qualitative and quantitative. Researchers at Thomas Jefferson University in Philadelphia have been exploring ways to get around some of the limitations of harmonic imaging, especially the problems caused by second harmonic generation and harmonic frequency accumulation within the tissue itself. They are attempting to create sub-harmonic images by transmitting at the fundamental frequency and receiving at half that frequency.8 This technique brings better lateral resolution as well as improved scanning of deep-lying structures. The latter are better visualized with the higher transmit frequency and smaller attenuation of scattered sub-harmonic signals.