Image reconstruction from minimum helical cone-beam projections

We proposed a new reconstruction algorithm for image reconstruction from helical cone-beam data only within the Tam-Danielsson window, thus allowing the potential reduction of radiation dose to patients. The new algorithm can be expressed as two terms. The first term dominates the contribution to the reconstructed image, and the second term provides only a small correction. In fact. such a correction is generally negligible as compared to that from the first term and introduces a detectable DC-type shift to the reconstructed images only in the situations where the ratio between the size of field of view and the helical radius approaches to 0.625, which is the limit to the validity of the first term. Based on the Grangeat formula. we have developed an algorithm to calculate the correction (i.e., the second) term from the data within the window.