Time-resolved measurement of bubble cavitation by combination of ultrasound power Doppler image and delayed US irradiation

Abstract

Microbubble cavitation is key dynamics of ultrasound assisted drug delivery system (US-DDS). However, its mechanism is too complicated to control due to bubble cloud formation under US irradiation. In US-DDS, a feed-back system which monitors bubble cavitation in-situ and optimizes the US irradiation sequence according to the bubble characteristics, such as the sensitivity of bubble to US wave and temporal response which leads to bubble destruction, is needed to improve the efficiency of DDS. In this study, a novel measurement method of secondary US wave irradiated by bubble cavitation is proposed. High intensity US(h-US), which produces bubble cavitation, is irradiated with a fixed time delay after introducing an imaging US(i-US) wave whose frequency is different with that of h-US. Frequency component of bubble cavitation signal: BCS, whose frequency range is the same with that of i-US, is detected by the signal processing unit of ultrasound power Doppler imaging instrument. In power Doppler image, two images (S-image and T-image) are appeared. By this method, both spatial resolved bubble image and temporal transition of BCS are monitored simultaneously. Feature is the method is BCS is observed in-situ by sub-micro second time resolution. Although relative value of BCS is monitored by this method, US wave which is introduced to simulate BCS is measured with the maximum error of 9.15%. This method is applied to measure BCS of ultrasound contrast agent microbubble. Inherent temporal transition of BCS, which changed depending on the sound pressured of h-US was observed.