Method for estimating microbubble concentration with ultrasound in vitro

Abstract

Sonoporation is a method for transferring small bioactive molecules into the cell with the aid of ultrasound and contrast agents. Gas-filled microbubbles (MBs) are used as contrast agents, and their concentration plays a pivotal role in sonoporation effectiveness. Either by counting microbubbles manually with the light microscope or using B-scan mode takes much time, and the measurements could not be performed during the experiment. We propose a novel method for MB concentration measurement. Transducer sends ultrasound signal, which is reflected from reference reflector, and the echo is recorded with the same transducer. The cuvette with microbubble solution is placed in between transducer and reference reflector. If there are no bubbles in the solution, 100% of initial signal returns. When microbubble concentration is increasing, the echo is decreasing gradually. In such a way the calibrated curve allows to determine absolute values of MB concentration. The method also allows distinguishing different type of MB. If the echo is recorded for 2 min or longer, microbubble decay kinetics could be seen, which is different for different types of MB.