Enhanced methods for visualizing myocardial perfusion with peripheral venous injection of levovist: application of triggered harmonic imaging and triggered harmonic power Doppler imaging techniques.

Abstract

The purpose of this study was to determine whether triggered harmonic imaging (THI) or triggered harmonic power Doppler imaging (THPDI) could obtain the myocardial contrast enhancement using peripheral venous injection of a first generation echocardiographic contrast agent, Levovist. In a phantom model, we examined the influence of an acoustic power, harmonic filters, transmitted frequencies and focus positions of transducer on Levovist. Then fundamental, harmonic or harmonic power Doppler imaging were performed with ECG-triggered imaging in eight closed-chest dogs using bolus injection of Levovist. In a phantom model, the highest transmission power (Mechanical index 1.6), a medium harmonic filter and a focus position (6 cm) resulted in the best enhanced contrast in both THI and THPDI. Furthermore, higher pulse repetition frequency (5500 Hz) of harmonic power Doppler made clearer enhancement. In animal models, we could not observe the apparent myocardial contrast using triggered fundamental imaging, and the intensity of each region of interest (ROI) of myocardium had not changed significantly. However, homogeneous myocardial contrast could be obtained using THI, which was conditioned on the highest transmission power, a medium harmonic filter same as the phantom model, at a lower transmitted frequency (1.8 MHz) and a focus position, which were located in the middle portion of the left ventricle. The peak intensity of each ROI increased significantly in a gray level. Furthermore, THPDI caused emphasized myocardial contrast visually. These results indicate that THI and THPDI produce obvious MCE using peripheral venous injection of Levovist.