Combination of photoacoustic and fluorescence in-vivo imaging using bioavailable nanoparticles containing a fluorescent dye

We have developed fluorescent dye-encapsulating nanoparticle reagents that can be administered to animal model, enabling both photoacoustic and fluorescence imaging. Two types of in vivo photoacoustic imaging systems were developed to visualize the imaging reagents administrated to tumor model mouse. Of the two imaging systems, one used a high frequency linear array ultrasound transducer and the other used a low frequency concave array ultrasound transducer. We also used an IVIS system for fluorescence imaging of the reagents administered to tumor model mouse. IVIS allows us to easily obtain the fluorescence distribution of the reagent on a two-dimensional plane of the whole body of mouse. We successfully obtained photoacoustic images of the distribution of reagents after intravenous administration. The photoacoustic image, as well as the fluorescence image, was able to visualize the tumor accumulation of the reagents due to the EPR (Enhanced Permeation and Retention) effect. Our fluorescent dye-encapsulated nanoparticle reagents can be used for the evaluation in vivo localization and accumulation over time. The reason for this success is that we took advantage of the ability of the reagents to simultaneously generate photoacoustic and fluorescence signals. This means that the measuring conditions for photoacoustic imaging could be determined based on the fluorescence data acquired with IVIS. In the case of in vivo photoacoustic imaging of the administered reagents such as the nanoparticle reagents developed in this study, whose distribution changes over time and has not previously been used as imaging targets, the simultaneous fluorescence signals must be effective in detecting photoacoustic signals of the reagents.