Study of pressure dependence of signals from ultrasound contrast agents

Noninvasive pressure estimation within the heart cavities or coronary arteries is essential for providing information on blood perfusion and viability of the organ. Some ultrasound contrast agents (UCA) are particularly well suited for pressure measurements because pressure changes affect the reflectivity of the microbubbles after their injection. In-vitro experiments were conducted with UCA (Optison) using 2.0 MHz ultrasound pulses. Preliminary results indicate that, over the pressure range of 0-210 mmHg, the rate (slope) of decline as a function of time, of the amplitudes of the. first and second harmonics and that of the sub-harmonic, may be a suitable parameter for estimation of the hydrostatic pressure changes. The difference between the amplitude of the first harmonic and that of the sub-harmonic stays almost constant throughout specific time window, thus demonstrating a good and stable correlation with the hydrostatic pressure.