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Image enhancement by noncontrast harmonic echocardiography. Part I. Qualitative assessment of endocardial visualization.

OBJECTIVE
To determine whether harmonic imaging--use of signals with frequencies twice that of the transmitted ultrasound to produce ultrasound images--can improve endocardial border definition in patients who have technically difficult echocardiograms.


METHODS
We studied 29 patients with technically difficult echocardiograms (nonvisualization of 2 or more endocardial segments in a 16-segment model). Apical long-axis, four-chamber, and two-chamber images were acquired during fundamental imaging (at 2.0 and 3.5 MHz) and second harmonic imaging (3.5-MHz receive mode) in random order. Images were digitally stored and subsequently reviewed blindly for endocardial segment score (0 = not visualized; 1 = adequate; or 2 = excellent) and overall ranking of image quality (1 [best] to 3 [worst]).


RESULTS
Mean endocardial segment score was significantly better (P < 0.0001) for harmonic imaging (1.02 +/- 0.36) than for either fundamental mode (0.49 +/- 0.21 and 0.57 +/- 0.27 for the 2.0- and 3.5-MHz images, respectively). The harmonic images were ranked as better (P < 0.0001) than those of either fundamental mode: harmonic mean rank was 1.07 in comparison with 2.67 and 2.26 for the 2.0- and 3.5-MHz fundamental images, respectively.


CONCLUSION
Noncontrast harmonic imaging appreciably enhances endocardial definition in patients with technically difficult echocardiographic studies and significantly improves overall image quality.