Heterogeneity of contrast effect during intermittent second harmonic myocardial contrast echocardiography in healthy...

Intermittent harmonic imaging with contrast is increasingly used to detect perfusion defects in patients with coronary disease. To achieve this, image homogeneity and the ability to visualize segments on the lateral and distal portions of the imaging field are important. The objective of this study was to evaluate whether the use of specific postprocessing algorithms, such as background subtraction with color coding and parametric display, allows for improved image homogeneity compared with conventional intermittent second harmonic imaging. For this purpose, 20 participants who were free of cardiac abnormalities and in whom myocardial perfusion should by definition be homogeneously distributed, underwent contrast echocardiography during the constant intravenous infusion of 1.0 +/- 0.3 mL/min of perfluorocarbon-enhanced sonicated dextrose albumin. End-systolic ECG-triggered images were obtained from the apical 4-chamber view at pulsing intervals of 300-ms 1, 3, 5, and 8 cardiac cycles. For analysis, each set of images was aligned, averaged, background subtracted, and color coded. Pulsing intervals versus videointensity plots were then generated for each pixel in the images and fitted to an exponential function to produce parametric images of beta (an index of microbubble velocity) and A (a measure of myocardial blood volume). The heterogeneity of the contrast effect was evaluated by computing the coefficients of variation in each image. Contrast heterogeneity was >20% with all 4 methods. However, it was greater in gray-scale second harmonic (39 +/- 13%) and color-coded (47 +/- 16%) images than in parametric images of beta and A (24 +/- 14 and 24 +/- 8%, respectively; both P <.05 vs gray-scale second harmonic and color-coded images). With all 4 methods, basal- and apical-lateral segments contributed most to image heterogeneity, albeit significantly less so with parametric imaging. In conclusion, our data indicate that myocardial opacification is frequently heterogeneous in healthy participants, particularly when using gray-scale second harmonic and background-subtracted with color-coding imaging. Parametric imaging allows reduction, albeit incomplete, of the heterogeneity of the contrast effect and therefore improves image quality.