Ultrasound-mediated drug delivery has been proposed as a safe and non-invasive method to achieve localized drug release. Drug-loaded microbubbles are injected in the vascular system and ultrasound waves are then used to localize and burst the microbubbles at a specific targeted area. The relatively large size of microbubbles however limits both their lifetime and their reach in the human body.

Phase-change liquid droplets can extend the use of ultrasound contrast agents for localized drug delivery. Their smaller size provides several advantages. The droplets can reach smaller capillaries, such as those in tumors vasculature. Their lifetime is also considerably prolonged.

Through the phenomenon of Acoustic Droplet Vaporization (ADV), triggered by ultrasound stimulation, the liquid-filled droplets experience a phase change and are converted into gas-filled microbubbles. The newly created microbubbles can then be disrupted by further stimulation and release their drug load in the tumor tissue.

In this project, a protocol to image and burst perfluoropentane-based micro-sized droplets using a single transducer is developed using the Verasonics Ultrasound System.

The pulse sequences are developed to allow close monitoring of the drug delivery by capturing a series of images before and after the vaporization or destruction of the droplets.

The droplets response was assessed for different pulse voltages and durations. Mean pixel value was calculated for the regions of interest, using the images captured before and after delivery of the ultrasound pulse.

Vaporization of the droplets can be achieved with low voltage (10V), whereas high voltage (50V) triggers their destruction.

Combined with high voltage, pulse duration affects the rate at which droplets can be destructed.