A filtered backprojection algorithm with ray-by-ray noise weighting.

PURPOSE This paper derives a ray-by-ray weighted filtered backprojection (rFBP) algorithm, based on our recently developed view-by-view weighted, filtered backprojection (vFBP) algorithm. METHODS The rFBP algorithm directly extends the vFBP algorithm by letting the noise weighting vary from channel to channel within each view. The projection data can be weighted in inverse proportion to their noise variances. Also, an edge-preserving bilateral filter is suggested to perform post filtering to further reduce the noise. The proposed algorithm has been implemented for the circular-orbit cone-beam geometry based on Feldkamp's algorithm. RESULTS Image reconstructions with computer simulations and clinical cadaver data are presented to illustrate the effectiveness and feasibility of the proposed algorithm. The new FBP-type algorithm is able to significantly reduce or remove the noise texture, which the conventional FBP is unable to do. The computation time of the proposed rFBP algorithm is approximately the same as the conventional FBP algorithm. CONCLUSIONS A ray-based noise-weighting scheme is introduced to the FBP algorithm. This new FBP-type algorithm significantly reduces or removes the streaking artifacts in low-dose CT.