Repeatable vaporization of optically vaporizable perfluorocarbon droplets for photoacoustic contrast enhanced imaging

Perflurorocarbon droplets that can be vaporized optically over multiple laser pulse applications are formulated. Photoacoustic contrast agents (PCAs) are important in visualizing molecular targets, deeply seated lesions, and vasculature. A novel PCA consisting of optically vaporizable perfluorocarbon droplets (OPDs) was investigated in this study. It has been reported that OPDs vaporize and emit a unique acoustic signal stronger than that from a light absorber alone, but that it only happened once at the time of vaporization. Our goal is to obtain repeatable vaporization of OPDs in order to sustain a high photoacoustic signal caused by vaporization over multiple laser pulse applications. By changing the contents of droplets to a compound with a higher boiling point, repeatable vaporization was successfully accomplished. Three times higher photoacoustic signals were produced repeatedly by droplets that exhibit transient vaporization behavior, namely PFH droplets within the size range of 0.2-1 μm.