A Dedicated Tomographic Image Reconstruction Algorithm for Integration-Mode Detector Configuration in Ion Imaging

摘要

A dedicated tomographic image reconstruction algorithm for integration-mode detector configuration is proposed and investigated. The algorithm makes use of the stopping power and the model of the scattering power for the entire histogram of Water Equivalent Thickness (WET) components. Therefore, compared to conventional tomographic image reconstruction of the WET component with maximum occurrence along straight trajectories, this algorithm is expected to provide better image quality. An anthropomorphic phantom, adopted as ground truth, is used to simulate the proton trajectories. The system matrix of the proposed algorithm is based on the statistical estimation of the integral scattering power for each WET as a 2D Gaussian distribution according to a multiple Coulomb scattering model. The 2D Gaussian distributions are normalized to the unit, thus forming a 3D distribution, namely the "cone", for each WET. The cones are interpolated to each integration line, thus matching the image. The updating formula of the simultaneous algebraic reconstruction technique is modified to account for the entire histogram of the WET components. For computational reasons, the tomographic image reconstruction is implemented relying on ordered subsets of projection angles. In general, better convergence is obtained for the dedicated algorithm, thus showing extremely reduced noise break-up. The results indicate the potential of the proposed algorithm to provide better image quality than conventional tomographic image reconstruction. Future studies will include the application of the proposed algorithm to Monte Carlo simulations of clinical ion imaging and a deeper image quality assessment.