1. A method for reconstructing CT image data, comprising: providing measured CT projection data p; reconstructing first CT image data f k=1 based on the provided CT projection data p; and iteratively generating, on the basis of the reconstructed first CT image data f k=1 , k+1-th CT image data according to the formula: 
 f k+1 =f k −α( Q ( Pf k −p )+β R ( f k )) provided the standard ∥f k+1 −f k ∥ 2 is ≦n with f k representing the CT image data after the k'th iteration, Q representing a reconstruction operator, P representing a reprojection operator, α,β representing constants, R(f k ) representing a regularization operator, and n representing a predefinable constant, with the reconstruction operator Q containing a noise weighting: 
 Q=B·W statist. ·H, with B back projection operator, W statist. weighting operator, and H ramp filter.