Title

Diffuse optical tomography and fluorescence diffuse optical tomography

Date of Completion

January 2006

Keywords

Engineering, Biomedical|Health Sciences, Radiology|Biophysics, Medical

Degree

Ph.D.

Abstract

Diffuse optical tomography (DOT) and fluorescence diffuse optical tomography (FDOT) provide not only structural information, but also the functional information for a heterogeneous target. However, conventional DOT and FDOT suffer from low reconstruction accuracy. In this study, we focused on improving the reconstruction accuracy. Also, a new fluorescence imaging technique was proposed to improve the resolution of diffuse optical imaging techniques while maintaining appropriate penetration depth. ^ In DOT, a hybrid imaging method, combing optical with ultrasonic techniques, has been proposed for many years as a way to improve the reconstruction accuracy. However, this technique failed to image an absorbing target when the target was close to the boundary between air and tissue. In this study, we found that the imaging qualities of a shallow target could be significantly improved if a reflecting boundary, rather than an absorbing boundary, was employed between the imaging probe and the medium. ^ In order to improve the reconstruction accuracy of FDOT, a new reconstruction technique was proposed in this study. Unlike conventional FDOT, the new reconstruction process was divided into two steps. In the first step, the structural parameters of the target were estimated by using the ratios of the fluorescence signals measured at different positions. Secondly, based on the estimated structural parameters, the target was limited to a small region, and the measured fluorescence signals were used to reconstruct the functional parameters. Simulated and experimental results showed that the reconstruction accuracy of both the structural and functional parameters was significantly improved by this technique. ^ Additionally, a novel fluorescence imaging technique, called ultrasound-modulated fluorescence imaging technique (UFIT), was theoretically studied. In this technique, a focused ultrasound beam was used to modulate the fluorophore concentration only within the focal zone of the ultrasound beam. The modulated fluorophore concentration could be converted into modulated fluorescence signals that could be used to extract the concentration and lifetime of the fluorophore. The spatial resolution of this hybrid technique depends only on the resolution of the ultrasound. The penetration depth is determined by the diffused photons, and is much deeper than those of techniques employing ballistic photons for imaging.^