Laser opto-acoustic tomography for medical diagnostics: experiments with biological tissues

Feasibility of laser optoacoustic tomography to detect turbid tissues with different optical properties was experimentally investigated using real biological tissues. The following abilities of this technique were quantitatively studied: maximal depth of optoacoustic signal detection, acoustic attenuation of laser-induced pressure waves, and limit of resolution. Two types of biological tissues were used for the experiments: chicken breast muscle as a tissue with low absorption coefficient and bovine liver as a tissue with higher absorption coefficient. Tissue samples were irradiated by Q-switched Nd:YAG-laser pulses to satisfy stress-confined irradiation conditions. Laser-induced pressure waves generated in the liver samples were detected by a wide-band acoustic transducer. Pressure wave amplitude, duration, and propagation time were analyzed after the experiments. The results and theoretical calculations have demonstrated that laser-induced optoacoustic signals from biological tissues with higher absorption coefficient are measurable at depth 5 times higher than penetration depth of radiation. Low acoustic attenuation (0.006 cm^-1) for laser-induced pressure waves was detected. Feasibility of the proposed imaging to detect 3 mm³ liver sample (tumor model) placed inside 80 mm-muscle tissue is demonstrated.