Advances in high-resolution ultrasound-modulated optical tomography in biological tissues

We present an extension of our work on implementation of high-resolution ultrasound-modulated optical tomography that, based on optical contrast, can image several millimeters deep into soft biological tissues. A long-cavity confocal Fabry-Perot interferometer, which provides a large etendue and a short response time, was used to detect the ultrasound-modulated coherent light that traversed the scattering biological tissue. Using 15-MHz ultrasound, light absorbing structures placed > 3 mm below the surface of chicken breast tissue were imaged with high contrast. The resolutions along the axial and lateral directions with respect to the ultrasound propagation direction were better than 70 mu m and 120 mu m, respectively. The resolutions can be scaled down further by using higher ultrasound frequencies. This technology is complementary to other imaging technologies, such as confocal microscopy and optical-coherence tomography, and has potential for broad biomedical applications.