Organic nanoparticle-doped microdroplets as dual-modality contrast agents for ultrasound microvascular flow and photoacoustic imaging (Conference Presentation)

Tumor blood vessels have been known as being heterogeneous because of their chaotic and abundant distribution. Thus, imaging techniques which reveal hemodynamic information of tumor vasculature play significant roles in tumor studies. Photoacoustic (PA) imaging could acquire hemodynamic information based on the intrinsic characteristics of hemoglobin, while ultrasound (US) imaging provides information of structure and blood flow. Therefore, an integrated system was developed for both US microvascular imaging and PA imaging of the tumor region. To further improve the imaging performance, a liquid filled dual-modality microdroplets was designed for both ultrasound flow and PA imaging. The microdroplets were manufactured using the microfluidics technique to produce consistent microbubble with diameters between 23 µm to 25 µm, determining the vascular size for imaging. Additionally, the microdroplets were filled with saline diluted organic nanoparticles as contrast agents for PA imaging, while commercial microbubbles are filled with inert gas. Both in vitro and in vivo studies have been conducted for evaluating the designed contrast agent and system. Results of in vitro experiments, which performed with microtubes submerged in a scattering medium, demonstrated different flow speeds and directions of the designed phantom. Subcutaneous tumor was next tested during in vivo studies. Based on the organic nanoparticle-doped droplet, we were able to obtain the information of total hemoglobin concentration, oxygen saturation and blood flow speed of the tumor angiogenesis region with a higher sensitivity. In the future, our microdroplets could be applied to more applications, such as slow drug release based on its specific structure.