High spatial resolution computed tomography of chemiluminescence with densely sampled parallel projections.

Computed tomography of chemiluminescence (CTC) is an effective tool for combustion diagnostics by using optical detectors to capture the projections of luminescence from multiple views and realizing the three-dimensional (3D) reconstruction by computed tomography (CT) theories. In the existing CTC, ordinary commodity lenses were employed in the system for imaging, the imaging effects complicate the projection model and the low sampling rate decreases the spatial resolution and reconstruction accuracy. In classical CT techniques, parallel projection based on 2D Radon transform is the simplest model, which has been widely used in CT applications. In this work, double telecentric lens is introduced in CTC to realize the acquisition of parallel projection with high sampling rate. Despite the parallel projection CT theories have been well studied, there are still a few theoretical and technological drawbacks need to be solved when utilizing double telecentric lens in CTC. Firstly, a simple method based on bilinear interpolation is studied to improve the calculation accuracy of the weight matrix. Secondly, the exact reconstruction condition for parallel projections is studied based on the discrete Radon transform theory. It establishes the theoretical relationship of the reconstruction quality and the sampling rate of the projections, the number of views, the range and the spatial resolution of the reconstructed region. In experiment, camera calibration technique for double telecentric lens is studied, and the results of which are used for projection correction. The tomographic reconstructions of an axisymmetric flame demonstrate the feasibility and accuracy of the studies.