Optically-triggered nanodroplets for enhanced ultrasound and photoacoustic imaging
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Medical ultrasound imaging is ubiquitous in clinics due to its safety, low cost, portability, and imaging depth. The development of technologies to assist ultrasound in the diagnosis of diseases thus have a potentially broad clinical impact. More recently, photoacoustics has emerged as a complementary, high contrast modality for imaging optical absorption. Injectable dyes and nanoparticles locally amplify ultrasound and photoacoustic signal, helping to identify disease markers and track its progression. We have constructed a dual ultrasound and photoacoustic contrast agent that can be activated using an external optical trigger. In response to pulsed laser irradiation, the particle undergoes a liquid to gas phase change, or vaporization, which emits a strong acoustic wave and results in an echogenic microbubble, simultaneously enhancing contrast for both modalities. We designed and developed several iterations of particles, altering parameters to optimize biocompatibility, cost, and image contrast enhancement, and we then characterized key traits of the particles. Next, we imaged the contrast agents in phantom, ex vivo, and in vivo models to validate the image enhancement, developing image process algorithms to maximize image quality. These optically triggered contrast agents are a valuable tool for minimally invasive, highly specific, early identification of cancer.