POCS-based restoration algorithm for beam modulation CT acquisition

Region-of-interest (ROI) imaging is considered an effective method to reduce the exposure dose. We propose ROI-based beam modulation acquisition to restore the information outside of the ROI. The CT system and 3D voxelized abdominal phantom were simulated using the MATLAB R2017b program. A total of 360 projections were obtained and used for CT reconstruction with a filtered back projection (FBP) algorithm. Beam modulation CT images were reconstructed using 288 truncated and 72 full projections. An interpolation method and our proposed method based on a projection onto convex sets (POCS) algorithm corrected the truncated projections. The image quality of three ROIs was evaluated using the structural similarity index measure (SSIM). The reconstructed image obtained by beam modulation acquisition resulted in a much higher SSIM value for the external information than that obtained by the ROI scan. The proposed method based on a POCS algorithm provides the best image quality in beam modulation acquisition. In conclusion, we have verified the possibility of restoring the ROI external information using beam modulation acquisition.