Direct backprojection-filtration formula for region-of-interest imaging with few additional projections

This paper provides a backprojection-filtration method for image reconstruction in divergent circular fan-beam and cone-beam geometries with flat detectors. It is based on a splitting of the acquisition angular range into angular sectors admitting filtering orientations in the image space where a simple, mono-directional Fourier-based filtering is possible. The new workflow is used for region-of-interest (ROI) reconstruction from dual-rotation acquisitions, consisting of a truncated, densely sampled acquisition and of a few additional non-truncated views. Results show that the reconstructed images using our new approach are similar to what FBP would achieve in the non- truncated case, and demonstrate the feasibility of an accurate direct reconstruction method for dual-rotation ROI imaging with very few non-truncated views.