Non-invasive, high-resolution, 3D imaging and sensing through highly scattering materials

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

This project explores and develops techniques to enable high-fidelity imaging and light focusing inside and through turbid media such as biological tissue. The methods investigated are non-invasive and combine optics and acoustics. State-of-the-art high-resolution three-dimensional optical microscopy techniques have already generated a strong impact in biological and biomedical applications. Current commercial modalities include mature technologies such as confocal microscopy, two-photon microscopy, and optical coherence tomography. Unfortunately, a common shortcoming is the limited penetration into biological tissue beyond a fraction of 1 mm, the problem at the core of this proposal. High-resolution deep imaging in tissue would enable numerous biomedical research and diagnosis tools such as imaging of blood oxygenation or improving photodynamic therapy. The research will create opportunities for undergraduate and graduate students to join in collaborative interdisciplinary projects associated with this proposal. The project will also enable broad educational activities in biomedical optical imaging. Recent advances in adaptive wavefront shaping have made imaging through scattering environments a possibility. By pre-compensating the optical wavefront, light propagation can be controlled through and beyond scattering materials. Most existing techniques, however, are limited by their need to generate a feedback signal from behind or inside the scattering media with direct invasive access, something not possible in the majority of biomedical imaging scenarios. This project emphasizes fundamental developments that address the need for deep, high-resolution imaging and focusing to tackle emerging applications. The photoacoustic effect, where acoustic waves are generated in response to an optical field, offers a new feedback mechanism for wavefront optimization because acoustic waves propagate in tissue with little scattering. Hence by detecting the acoustic waves at the surface of the scattering media, an effective and noninvasive feedback signal is obtained to guide wavefront compensation. Furthermore, the spatially nonuniform sensitivity of the acoustic transducer can be used to guide the light to a point that is substantially smaller than the acoustic focal region. Nevertheless, optical focusing and imaging through and within real biological materials remains a challenge due to the fast rate of change of the speckle field from blood flow and physiological motion and the fact that the speckle size deep in biological tissue is on the order of a wavelength. In this project, fundamental and experimental limitations on focusing in scattering media will be explored, algorithms for wavefront compensation will be optimized for focusing speed and fluence enhancement, and hardware developments for implementing wavefront compensation at speeds sufficient to overcome speckle decorrelation in biological media will be investigated.