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Optical cross-sectional imaging of a scattering medium with the aid of a pulse ultrasound wave

We have developed an optical cross sectional imaging method for scattering media with the aid of a pulse ultrasound wave. A converging pulse ultrasound wave and a He-Ne laser beam, which are set on the same axis and same direction, are irradiated simultaneously to a sample. As the pulse ultrasound wave travels into the sample, the instantaneous position of the wave changes the optical properties of a localized region of the sample and modulates the scattered intensity of the incident laser light. We detected the modulation of the scattered light that is transmitted through the sample to observe the absorptive features inside a thick sample. Depth resolving capability is achieved from the time-dependent measurement of the scattered light intensity. This system achieves 3D resolution determined by the focal spot of the focused ultrasound wave. The resolution of our system is measured at 1.5 mm in the axial direction and 0.3 mm in the transverse direction. We verify the system by observing an absorptive object, which is a silk thread stained with Victoria blue dye, that is embedded in silicone rubber. We also obtained a cross-sectional image of an absorbing object that is surrounded by a 10-mm thick highly scattering medium.