Harmonic Imaging in Echocardiography
ABSTRACT & COMMENTARY
Synopsis: Native tissue harmonic imaging significantly improves echocardiographic wall motion analysis at rest.
Source: Kornbluth M, et al. J Soc Echocardiogr 1998; 11:693-701.
Harmonic imaging techniques were developed to augment the ultrasound differentiation of contrast bubbles from tissue. However, the ultrasound scanner can be tuned to selectively receive harmonic frequencies from tissue and since harmonic echocardiograms are stronger than fundamental echocardiograms, endocardial border detection should be improved. To test this hypothesis, Kornbluth and colleagues from Stanford University evaluated 60 consecutive patients by both echocardiographic techniques. Wall segment visualization was improved in 64% of segments, with 26% improving from poor to excellent. Of those rated poor, 70% improved to good or excellent. Most of the improvement involved the anterior and lateral walls in the apical views. Wall motion scoring was changed in 16% of segments by harmonic imaging. Kornbluth et al conclude that native tissue harmonic imaging significantly improves echocardiographic wall motion analysis at rest.
COMMENT BY MICHAEL H. CRAWFORD, MD
Although this study used the Acuson Sequoia C256 system, most ultrasound manufacturers now offer this option. A new ultrasound machine with this feature costs about $300,000, and, if your old machine is suitable, an upgrade to harmonic imaging costs about $100,000. Thus, many echocardiography laboratory employees are wondering if it is worth the investment. Now that new intravenous contrast agents are available that can opacify the left heart, contrast echocardiography is another rationale for this equipment upgrade. Cavity contrast echocardiography is also useful for helping to define the endocardial border. Perhaps with native tissue harmonic imaging and cavity contrast, no patient will have a poor study for wall motion.
The real test for both these technologies and the new equipment that is required will be exercised echocardiography. The anterior and lateral walls in the apical views are particularly difficult with exercise echocardiography. Thus, tissue harmonic imaging holds great promise for better stress echocardiograms without the need for intravenous access.
The major limitation of this study was that the readers were not blinded to the imaging modality and may have been biased toward the new technique. Of interest, inter-observer differences in the scoring of wall motion with harmonic imaging were 10%, which is close to the difference in scoring results of 16% going from fundamental to harmonic imaging. Kornbluth et al did not report whether inter-observer differences were lessened with harmonic imaging. However, one would expect better imaging to reduce disagreements in scoring wall segments.
Our own limited experience with harmonic tissue imaging with exercise echocardiography suggests that there are still difficult patients who are hard to image immediately after treadmill exercise. The results of this study also suggest that not all patients' images are improved. Clearly, if you are contemplating a new purchase, this option is probably worth the extra cost. Upgrading to this technology is a more difficult decision, which may depend on your experience with this technology. Request a demonstration in your facility with your patients.