Ultrasound-modulated optical tomography in soft biological tissues

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Title: Ultrasound-modulated optical tomography in soft biological tissues
Author: Sakadzic, Sava
Abstract: Optical imaging of soft biological tissues is highly desirable since it is nonionizing and provides sensitive contrast information which enables detection of physiological functions and abnormalities , including potentially early cancer detection . However , due to the diffusion of light , it is dificult to achieve simultaneously both good spatial resolution and good imaging depth with the pure optical imaging modalities . This work focuses on the ultrasound -modulated optical tomography - a hybrid technique which combines advantages of ultrasonic resolution and optical contrast . In this technique , focused ultrasound and optical radiation of high temporal co -herence are simultaneously applied to soft biological tissue , and the intensity of the ultrasound -modulated light is measured . This provides information about the optical properties of the tissue , spatially localized at the interaction region of the ultrasonic and electromagnetic waves . In experimental part of this work we present a novel 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 was used to detect the ultrasound -modulated coherent light that traversed the scattering biological tissue . Using 15 -MHz ultrasound , we imaged with high contrast light absorbing structures placed 3 mm below the surface of chicken breast tissue . The resolution along the axial and the lateral directions with respect to the ultrasound propagation direction was better than 70 and 120 ? ? ? ?m , respectively . This technology is complementary to other imaging technologies , such as confocal microscopy and optical -coherence tomography , and has potential for broad biomedical applications . In the theoretical part we present various methods to model interaction be -tween the ultrasonic and electromagnetic waves in optically scattering media . We first extend the existing theoretical model based on the diffusing -wave spectroscopy approach to account for anisotropic optical scattering , Brownian motion , pulsed ul -trasound , and strong correlations between the ultrasound -induced optical phase in -crements . Based on the Bethe -Salpeter equation , we further develop a more general correlation transfer equation , and subsequently a correlation diffusion equation , for ultrasound -modulated multiply scattered light . We expect these equations to be applicable to a wide spectrum of conditions in the ultrasound -modulated optical tomography of soft biological tissues .
URI: http : / /hdl .handle .net /1969 .1 /5875
Date: 2007-09-17

Citation

Ultrasound-modulated optical tomography in soft biological tissues. Available electronically from http : / /hdl .handle .net /1969 .1 /5875 .

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