Time-resolved opto-acoustic diagnostics of tissue

Opto-acoustic investigations of copper chloride water solution, milk, suspension of graphite particles in water and milk, and biological tissues were carried out with Q-switched Nd-YAG laser. The pressure course of the leading edge of acoustic pulse is determined by the distribution of the intensity of light in the absorbing medium. The registration of the acoustic transients both at front and rare surfaces of investigated medium was carried out. The distribution of absorption for homogeneously absorbing and micro-inhomogeneous media was reconstructed. The experimental arrangement allows the user to measure the light absorption coefficient in the range of 10 - 300 l/cm with the spatial resolution of the order of 10 microns. Absorbing particles in transparent, homogeneously absorbing and scattering media were detected. The proposed method of time-resolved opto-acoustic diagnostics possess the ability to investigate z-axial distribution of light absorption averaged in lateral directions over the laser spot. For biological tissues it is most promising to use front surface registration of acoustic transients that are well established to detect boundaries of absorbing layers.