Detection Of Nanoparticles In Mice Using An Integrated Photoacoustic Micro-Ultrasound System

VisualSonics have recently developed a photoacoustic imaging system (VevoLAZR, Toronto, Canada) that combines the sensitivity of optical imaging modalities and the high resolution of micro‐ultrasound. The high sensitivity enables detection of nano‐scaled contrast agents. Due to their small size, nanoparticles likely can cross the leaky tumor microvasculature and deposit in the extra‐ and intracellular space. This presents countless potential benefits in cancer therapy. Using VevoLAZR we investigated the use of various gold nanoparticles and common optical fluorescent dyes as photoacoustic contrast agents in a vessel phantom study. We also injected gold nanorods intravenously in mice bearing tumors and investigated the preferential accumulation of these nanoparticles in the tumor tissue. Tumor perfusion was also quantified using ultrasound contrast imaging. Gold nanorods showed the greatest photoacoustic intensity amongst the nanoparticles tested. Optical fluorescent dyes used were also readily detectable in photoacoustic imaging. In the tumor study, preferential accumulation of gold nanorods was observed in the tumor relative to mammary tissue. Interestingly, tumor perfusion appeared to be inversely correlated with amount of gold nanorod accumulation. Collectively, we have demonstrated photoacoustics as a novel and powerful tool to detect and quantify nanoparticles in mice tumors.