The Impact of Vendor-Specific Ultrasound Beam-Forming and Processing Techniques on the Visualization of In Vitro Experimental “Scar”: Implications for Myocardial Scar Imaging Using Two-Dimensional and Three-Dimensional Echocardiography

Abstract

Myocardial scar appears brighter compared with normal myocardium on echocardiography because of differences in tissue characteristics. The aim of this study was to test how different ultrasound pulse characteristics affect the brightness contrast (i.e., contrast ratio [CR]) between tissues of different acoustic properties, as well as the accuracy of assessing tissue volume. An experimental invitro "scar" model was created using overheated and raw pieces of commercially available bovine muscle. Two-dimensional and three-dimensional ultrasound scanning of the model was performed using combinations of ultrasound pulse characteristics: ultrasound frequency, harmonics, pulse amplitude, steady pulse (SP) emission, power modulation (PM), and pulse inversion modalities. On both two-dimensional and three-dimensional imaging, the CR between the "scar" and its adjacent tissue was higher when PM was used. PM, as well as SP ultrasound imaging, provided good "scar" volume quantification. When tested on 10 "scars" of different size and shape, PM resulted in lower bias (-9.7 vs 54.2mm3) and narrower limits of agreement (-168.6 to 149.2mm3 vs -296.0 to 404.4mm3, P=.03). The interobserver variability for "scar" volume was better with PM (intraclass correlation coefficient=0.901 vs 0.815). Two-dimensional and three-dimensional echocardiography with PM and SP was performed on 15 individuals with myocardial scar secondary to infarction. The CR was higher on PM imaging. Using cardiac magnetic resonance as a reference, quantification of myocardial scar volume showed better agreement when PM was used (bias, -645mm3; limits of agreement, -3,158 to 1,868mm3) as opposed to SP (bias, -1,138mm3; limits of agreement, -5,510 to 3,233mm3). The PM modality increased the CR between tissues with different acoustic properties in an experimental invitro "scar" model while allowing accurate quantification of "scar" volume. By applying the invitro findings to humans, PM resulted in higher CR between scarred and healthy myocardium, providing better scar volume quantification than SP compared with cardiac magnetic resonance.