TIME-RESOLVED LASER OPTOACOUSTIC TOMOGRAPHY OF INHOMOGENEOUS-MEDIA

The methods of time-resolved laser optoacoustic tomography of inhomoge neous media and related problems are reviewed. Time-resolved laser opt oacoustic tomography allows one to measure the distribution of light a bsorption in turbid media with depth resolution up to several microns in real time. The theory of laser excitation of acoustic waves by abso rbing of light in particles, dispersed in transparent, light-absorbing or scattering media, is developed. The distribution of light absorpti on can be obtained from the temporal course of acoustic pressure. Two schemes of acoustic wave detection - in the medium under testing (dire ct detection) and in transparent medium, coupled to the investigated o ne (indirect detection) - are discussed. In both cases the reconstruct ion of light absorption can be made by simple calculations. Test exper iments with homogeneous and layered media confirm the proposed theoret ical models and the possibility of using the proposed experimental sch emes. Light absorption in homogeneous, inhomogeneous media and in abso rbing particles dispersed in turbid media was investigated. The experi mental setup allows one to measure the absorption coefficients over th e range 1-500 cm(-1) with the depth resolution 10-15 mu m over the dep th 1-1.5 mm.