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.
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