Developing a stochastic model for acousto-optic tissue imaging

Direct optical measurements in scattering media offer poor resolution due to the high scattering. Ultrasound is scattered orders of magnitude less in tissue compared with light and therefore offers good resolution. Photoacoustics and acoustooptics are both relatively new hybrid techniques that enable measurements of optical properties in scattering media by combining ultrasound and light. Quantified measurements of the fluence and absorption coefficient however are desired and can not be performed by these separate techniques. A new approach to achieve this goal is to combine both hybrid techniques. By combining photoacoustic and acousto-optic measurements there is sufficient information to calculate the absorption coefficient and fluence at the ultrasound focus used for the acousto-optics. We require knowledge on the interaction of light and sound inside tissue, so the size of the so called tagging volume can be determined. This tagging volume is defined by the size and shape of the ultrasound focus used in the acousto-optic measurements. A stochastic model for acousto-optics is under development that used existing knowledge on the in the interaction between light and sound. By separating light transport and the interactions of light and sound and writing this interaction as a probability density function it is possible to find the effective geometrical properties of the tagging volume. At the moment multiple interaction mechanisms of sound and light are added to this model. In the future this model will be validated in phantoms and biological tissue.