Enhanced Ultrasound and Photoacoustic Imaging Using Photoacoustic Nanodroplets

date March 7, 2014
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Friday, March 7, 2014 4:00 p.m. ETC 4.150

Alexander S. Hannah
Department of Biomedical Engineering
The University of Texas at Austin

Disease detection by noninvasive imaging requires contrast against the surrounding healthy tissue, which is insufficient using many available techniques, including clinical ultrasound (US) and recently emerging photoacoustics (PA). The introduction of exogenous contrast agents highlights selected regions, but these formulations have several shortcomings. Microbubbles used for US contrast are too large to reach tumor neovasculature, and their instability limits the time window for imaging. Contrast agents for PA are also flawed; dyes offer only a modest increase in signal, and metal nanoparticles must undergo regulatory approval before clinical translation. We have developed a dual contrast agent, named photoacoustic nanodroplets (PAnDs), which resolve these issues. These perfluorocarbon droplets are small enough to reach and extravasate from tumor neovasculature, and stable enough to allow for accumulation over several hours. The droplets can be optically triggered to induce particle vaporization, which emits a stronger PA signal than from thermal expansion of metal particles. The resulting gaseous microbubbles are a source of high US contrast as well. We have constructed a dye-loaded droplet comprised of biocompatible materials ready for clinical translation, as well as a droplet which can be triggered using an inexpensive 1064 nm laser source. We characterize the various properties of these nanodroplets and quantify image enhancement from remote triggering of the droplets, while investigating mechanisms of optical droplet vaporization. Additionally, we explore the use of high and low boiling point droplets for specific applications. Lastly we explore droplet formulations to molecularly target specific disease. These PAnDs improve image quality for US and PA modalities, and may encapsulate drugs for image-guided, controlled release of therapeutics.