This should be replaced~

Please see our publication in IEEE Transactions on Nuclear Science, October, 2004.

Establishing penalized weighted least-squares cost function with known variance-mean relationship and spatial correlation in the sinogram domain is one fundamental issue in our approach. Reducing the high dimensions and considering the spatial correlation by K-L transform is another fundamental point in our approach. Utilizing the well-established FBP (filtered backprojection) to invert exactly the Radon transform is a big benefit for so large data volume in CT applications.