  The reconstruction problem of voxels with individual weightings can be
modeled a position- and angle- dependent function in the forward-projection.
This changes the system matrix and prohibits to use standard filtered
backprojection. In this work we first formulate this reconstruction problem in
terms of a system matrix and weighting part. We compute the pseudoinverse and
show that the solution is rank-deficient and hence very ill posed. This is a
fundamental limitation for reconstruction. We then derive an iterative solution
and experimentally show its uperiority to any closed-form solution.
