Experimental Study on CW Diffuse Reflective Optical CT

点击翻译按钮获取中文摘要

This project is a feasibility study on diffuse optical tomography which has 3-D spatial resolution using 2-dimensional CW source-detector arrays on the body surface, aiming at real time imaging of the brain activation minimally contaminated by skin circulation fluctuation. We formulated the forward problem based on the Rytov approximation for the small perturbation of the absorption coefficients in the diffusion equation approximation of the photon migration, and formulated the 3-D tomographic reconstruction using simple regularized Moore-Penrose pseudo inverse. We analyzed the dependencies of the reconstruction error and the spatial resolution on the regularization parameter, the target depth and the reconstruction voxel size. The study showed that the trade-off between the reconstruction error and the spatial resolution does not depend on the voxel size. The simple regularized inverse, however, was found to have strong depth dependencies of the reconstruction sensitivity so that the … More target brain signal in the depth would be easily masked by the unwanted skin circulation signal in the shallow range. We devised the depth-adaptive voxel size method and the depth-adaptive regularization, both of which were shown to be effective to overcome this serious problem. Based on these extensive simulation studies, we clarified trade-offs between spatial resolution, reconstruction noise, reconstruction region of interest and the uniformity of the reconstruction sensitivity etc. To assess the feasibility experimentally, we modified a existing commercial optical topograph, enabling digital data acquisition for the reconstruction, and checked the performance by phantom study. Finally, we designed a practical imaging system with the source-detector system of the existing topograph. The system would visualize the brain activity with the spatial resolution of 1cm in the 4cm X 4cm area of the cerebral cortex assumed at the 1cm depth from the skin surface with the 20 dB suppression of the unwanted skin circulation signal. Less