Image enhancement by noncontrast harmonic echocardiography. Part II. Quantitative assessment with use of contrast-to-speckle ratio

Objective: To ascertain whether 'harmonic imaging' - use of ultrasound signals with the frequency twice that of the transmitted signal for ultrasound image generation - can improve image contrast while reducing noise. Methods: Technically difficult echocardiograms (nonvisualization of 2 or more endocardial segments in a 16-segment model) from 25 patients were analyzed. Corresponding fundamental and harmonic images of the left ventricle in the apical four-chamber, two-chamber, and long-axis views were divided into basal, mid, and apical regions. The difference in image quality between fundamental and harmonic scans was assessed by using the muscle-to-cavity contrast-to-speckle ratio (CSR(mc)). Results: The mean CSR(mc) values of pooled data revealed significant image enhancement by harmonic scanning (CSR(mc) increased from 0.84 to 1.06; P<0.0001). Regression analysis showed that harmonic imaging im proved the CSR(mc) values in 68% of all scans. Regional analysis indicated the most enhancement in basal regions (CSR(mc) increased from 0.96 to 1.34; P<0.0001), followed by the mid (CSR(mc) increased from 0.84 to 1.04; P<0.0001) and apical (CSR(mc) increased from 0.68 to 0.74; P = 0.0138) left ventricular regions. Conclusion: Noncontrast harmonic imaging significantly enhances suboptimal echocardiographic images, particularly in the regions distant from the transducer.