Ultrasound-assisted optical reflectometry in highly scattering media

We have developed an optical reflectometry system to investigate the inside of a scattering medium by using focused ultrasound wave to specify the measuring point. The reflected light is generated by the variation of the refractive indices induced by a focused ultrasound wave, The optical reflectometry technique enables us to observe an internal structure such as a human tissue noninvasively for biomedical applications. We have observed samples which consist of an agarose block with a cubic piece of agarose stained with a dye as an absorptive material, The intensity of the light reflected from the focal region of the ultrasound is decreased when the measuring point was in the stained agarose section because of absorption by the dye. Furthermore, we have observed a sample with a weak scattering object made of agarose surrounded by strong scattering agarose that contains poly(methyl methacrylate) (PMMA) particles.