Noninvasive pressure measurement using microbubble contrast agent and wavelet transforms

Indirect noninvasive pressure measurement using ultrasound contrast agent (UCA) has been previously described. The UCA containing encapsulated gas bubbles was used as a vehicle to transport free-gas microbubbles to the region of interest. The encapsulated gas bubbles are ruptured upon exposure to a high acoustic US burst and small free-gas microbubbles are released. The released microbubbles persist in the medium for only a few ms and then dissolve. The disappearance time of the microbubbles showed to be significantly dependent on the surrounding pressure, resulting in a quicker disappearance for higher values of overpressure. This method showed sensitivity for pressures down to 50 mmHg. However, in clinical situations pressure differences of 5 to 20 mmHg are of importance. We propose in this study a technique to improve the sensitivity using wavelet processing. The results obtained using wavelet processing showed that the sensitivity is increased. Moreover further improvements in the sensitivity might be achieved by choosing an appropriate wavelet that describes more accurately the acoustic response of the bubbles.