Photoacoustic studies of tissue-like phantoms with scattering and absorbing properties

We studied the nature of photoacoustic signals that were generated under a variety of conditions from vessel-mimicking polyethylene tubes. The vessels, filled with a range of contrast agents, were buried in tissue-like phantoms that possessed low to high optical absorption and scattering properties. In a photoacoustic image, we observed that either a single spot or two distinct spots could represent a single vessel depending on the strength of the infused contrast agent and on the size of the vessels. We typically found linear increase of the photoacoustic intensity with laser excitation power as well as with absorption coefficient of the contrast agent. However, we found that there is an optimum excitation power for achieving the best photoacoustic signal. If a vessel is buried in a highly absorbing background, increasing the laser power beyond a certain limit reversibly reduces the photoacoustic signal from the vessel, eventually decreasing it to zero. We also studied the blood-to-tissue absorption contrast requirement for observing the photoacoustic signal from a vessel buried in an absorbing and scattering tissue. We find that, in order to distinguish the photoacoustic signal from its background, the absorption coefficient of contrast agent in the vessel must be at least 2.5 times larger than that of the surroundings.© (2008) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.