Development of a direct-mapping tomography method to solve confined space problems with enhanced calculation efficiency

This work reports an improved tomography method to solve three-dimensional (3D) reconstructions in confined space with enhanced calculation efficiency and accuracy compared to other similar approaches. Confined-space tomography methods are designed to correct the image distortion on recorded target images caused by light refraction through optical walls, such as optical engine cylinders. However, past confined space tomography methods have shortcomings in reconstruction accuracy and time efficiency, since they usually involve time-consuming iterations or numerical interpolation during calculating the mapping relationship from 3D measurement domain to 2D imaging planes. Therefore, based on the improvement and innovation of our existing confined space tomography methods, the present method developed in this work directly calculates the mapping relationship by performing reverse ray-tracings originated from imaging planes, then decides the intersection volumes with the discretized measurement domain. Numerical and experimental demonstrations of present method are, respectively, performed based on multiple simulated phantoms and a two-branch laminar flame contained inside an optical cylinder. Compared to past confined space tomography algorithms, the present method consumes ~ 40% of the computational time under the voxel size of 0.5 mm, along with slightly enhanced accuracy. Moreover, the present method becomes more efficient under smaller voxel sizes. The robustness of present method and its endurance on measurement errors are then systematically analyzed and demonstrated.