1. A method for reconstructing an image of an examined object of a spiral computed tomographic scan comprising establishing a radiation source; establishing a detector array; calculating coefficients h Δi,Δj ; performing a scanning of an examined object by using a spiral computed tomographic imaging system to obtain a projection dataset; performing of a back-projection operation for a fixed cross-section of an examined object wherein projections are used in the back-projection operation in a direct way; calculating coefficients g i,j ; calculating of an initial image for an iterative reconstruction process; performing of the iterative reconstruction process.