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