Serial noninvasive photoacoustic imaging of neovascularization in tumor angiogenesis.

We present photoacoustic images of tumor neovascularization obtained over a 10-day period after subcutaneous inoculation of pancreatic tumor cells in a rat. The images were obtained from ultrasound generated by absorption in hemoglobin of short laser pulses at a wavelength of 1064 nm. The ultrasound signals were measured in reflection mode using a single scanning piezodetector, and images were reconstructed with a weighted delay-and-sum algorithm. Three-dimensional data visualize the development and quantify the extent of individual blood vessels around the growing tumor, blood concentration changes inside the tumor and growth in depth of the neovascularized region.