Ultrasonic Modulation Of Scattered Light In Scattering Media: Principle, Simulations And Experiments

Ultrasound-modulated optical tomography is a promising and noninvasive method for biomedical imaging. This hybrid technique that combines optical and ultrasonic wave and takes advantage of both optical contrast and ultrasonic resolution has been explored.There are two important and unresolved problems in ultrasound-modulated optical tomography. Firstly, the propagation of light in the tissue which an ultrasonic wave is focused into remains a mystery. Secondly, the spatial resolution of this technique is always limited by ultrasound waist size, so that the poor resolution doesn't fit the requirement of clinic. In this thesis, some new views and means for these problems are presented as follows:1. An analytic model about the propagation of light through the tissue in which an ultrasonic wave is focused based on the diffuse theory is presented.2. Two new ultrasound modulate models are presented. One is based on the ultrasonic grating mechanism, the other is based on the absorption mechanism.3. Based on the Monte Carlo simulation, the relations to the modulation light intensity and modulation depth contributed by the tissue thickness and optical properties are figured out and supported by an equivalent experiment and an extended condition also agrees with the diffuse theory.4. A new method using deconvolution algorithm was suggested to process ultrasound modulated optical signals before the modulated optical signals were used for image reconstruction. Both theory analysis and numerical calculation results have shown that the spatial resolution could be greatly improved and image quality became better. This method requires no modification of optical geometry and detection system, only appropriate mathematical processing was needed. It is believed to be a simple, practical and effective way in realizing super resolution in ultrasound modulated optical tomography.