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.

Background and Objectives: The ability to correctly visualize the architectural arrangement of microvasculature is valuable to many diverse fields in medicine. In this study, we applied photoacoustics (PA) to obtain highresolution images of submillimeter blood vessels. Study Design/Materials and Methods: Short laser pulses are used to generate ultrasound from superficial blood vessels in several animal models. From these ultrasound waves the interior of blood vessels can be reconstructed. Results: We present results from a novel approach based on the PA principle that allows specific in vivo visualization of dermal blood vessels without the use of contrast agents or ionizing radiation. Conclusions: We show PA images of externalized blood vessels and demonstrate in vivo PA imaging of vasculature through layers of skin varying in thickness. Lasers Surg.

Photoacoustic ͑PA͒ signal generation can be used as the basis for a new medical tomographic technique. In this article, we present results, which have been obtained by applying the PA technique on animals and more specifically on Wistar rats. The primary goal was to investigate the possibility of using PA for monitoring the changes in the blood circulation. This was achieved by tracking the vessel position with one-dimensional scans and by monitoring the changes in the signal due to artificially induced changes in the blood circulation.

Photoacoustic imaging is a hybrid imaging modality that is based on the detection of acoustic waves generated by absorption of pulsed light by tissue chromophores such as hemoglobin in blood. Serial photoacoustic imaging has been performed 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 double-ring photoacoustic detector. A correction algorithm has been developed to correct for scanning and movement artifacts during the measurements. 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.

Photoacoustic imaging is demonstrated in imaging blood vessels of a chicken embryo. Using a weighted sumand-delay beamforming algorithm we were able to reconstruct two-and three-dimensional images of these blood vessels.