A three-dimensional (3D) finite-element optical tomographic reconstruction algorithm based on a diffusion equation approximation is presented. The algorithm uses a regularized Newton method to update an initial (guess) optical property distribution iteratively in order to minimize an object function composed of a weighted sum of the squared difference between computed and measured data, and reconstructs the spatial distribution of the absorption and scattering coefficients of turbid media/tissues using DC data. Considering the memory requirements and computational cost for 3D reconstruction, the algorithm has been parallelized with Message-Passing Interface. We have conducted both phantom and in vivo clinical experiments to evaluate our parallelized three-dimensional reconstruction algorithm. The results show that 3D volumetric images of turbid media and in vivo tissues can be successfully reconstructed.
The reconstruction of fluorescence lifetime distributions in heterogeneous turbid media and tumor-bearing animals are experimentally demonstrated by frequency-domain measurements. A set of coupled diffusion equations are used to describe the propagation of excitation and fluorescent emission light in multiply scattering media. A finite element based reconstruction algorithm combined with Marquardt and Tikhonov regularization methods are used to obtain the fluorescence images. The experimental set-up is an automatic multi-channel frequency-domain system. 16 sources and 16 detectors are used. Experiments are performed using indocyanine green (ICG) and 3,3'-diethylthiatricarbocyanine iodide (DTTCI) in tissue-like phantoms of both single- and multi-target configurations with considerations of perfect and imperfect uptake of fluorescence dyes in the scattering media. ICG are used in tumor-bearing animal studies. Our results show that the fluorescence lifetime image of the heterogeneities within a circular surrounding medium and in-vivo tissue can be reconstructed successfully.
A pilot clinical study on ten female volunteers is reported using our multi-channel frequency-domain optical imager. Seven of these patients were previously identified with tumors or microcalcifications by x-ray and/or ultrasound mammography. These tumors had a size between 5 and 38 mm. Using our optical imager and reconstruction methods we were able to detect all tumors that had been identified by x-ray and/or ultrasound mammography. The quantification of our improved scattering images shows a clear differentiation between benign and malignant tumors. A comparison between our results and x-ray/ultrasound results is also given.