Photoacoustic determination of tissue optical properties and structure by use of an optical parametric oscillator

摘要

Abstract: Measurement of photoacoustic transients excited by absorption of short (ns-) laser pulses yields information about the optical properties and the layer structure of tissue. The method is based on the generation of thermoplastic stress in the irradiated tissue volume, which acts as the source of the photoacoustic wave. Interpretation of the experimental results is strongly facilitated if the influence of acoustic diffraction at the boundaries of the spatially limited source is minimized. In our study this was achieved by using a special optical technique for the recording of stress waves. By combining this detector with an optical parametric oscillator (OPO) and a fiberoptic delivery system, we could obtain wavelength dependent values of the effective attenuation coefficient of tissue samples. First measurements in living tissue have shown the capability to resolve the layer structure of human skin. As it was also demonstrated on a simple two-layered phantom, wavelength tuning offers the possibility to achieve maximum contrast in the photoacoustic distinction between layers with different optical properties. !15