A hierarchical algorithm for fast backprojection in helical cone-beam tomography

Existing algorithms for exact helical cone beam (HCB) tomographic reconstruction involve a 3-D backprojection step, which dominates the computational cost of the algorithm. We present a fast hierarchical 3-D backprojection algorithm, generalizing fast 2-D parallel beam and fan beam algorithms, which reduces the complexity of this step from O(N/sup 4/) to O(N/sup 3/log N), greatly accelerating the reconstruction process.