Computerized radio-frequency analysis of concentration and `decay´ of echo-contrast agents

The linear relationship between dose of contrast agent and radio-frequency (RF) signal constitutes a means of noninvasive evaluation of intracardiac flows by contrast echocardiography. To assess the concentration of echo-contrast agents by ultrasound, a commercially available echocardiographic instrument was modified. The RF signal (unprocessed backscattered signal) corresponding to a region of interest inside the 2-D echo image was sampled in real time and transferred online to a personal computer. The relationship between different doses of contrast agent and RF signal was tested in an in vitro system of circulation. In the range of doses between 0.25 and 1.5 ml of contrast a linear correlation was found between dose and RF (r=0.92). At higher doses (1.75-2.0) ml, the dynamic converter used in this modified echo instrument produced a significant distortion of the signal. The system also made it possible to study the spontaneous decay of the echo contrast agent. The spontaneous T_1/2 (68 s) is long enough to allow flow evaluation