1. A method of performing of an iterative reconstruction process, forming part of a method for reconstructing an image of an examined object using a spiral computed tomographic scanner, is carried out by a procedure comprising of: performing of a 2D FFT of a reconstructed image μ i,j t ; a resulting matrix M k,l t is a frequency representation of the reconstructed image μ i,j t ; performing multiplication of elements of the resulting matrix M k,l t which is obtained in a previous step of the iterative reconstruction process by corresponding elements of a matrix H k,l ; a resulting matrix A k,l t is a frequency representation of a referential image a k,l t for an image {tilde over (μ)} i,j t obtained after a back-projection operation; performing of a 2D IFFT of the matrix A k,l t obtained in a previous step of the iterative reconstruction process; a resulting matrix represents the referential image a k,l t for the image {tilde over (μ)} i,j t obtained after the back-projection operation; transforming, by a nonlinear function, of differences between corresponding pixels of a referential image a k,l t obtained as a result of a previous step of the iterative reconstruction process and pixels of the image {tilde over (μ)} i,j t obtained after the back-projection operation; a resulting matrix is a matrix b k,l t ; performing of the 2D FFT of the matrix b k,l t obtained in a previous step of the iterative reconstruction process; a resulting matrix B k,l t is a frequency representation of the matrix b k,l t ; performing multiplication of elements of the matrix B k,l t obtained in a previous step of the iterative reconstruction process by corresponding elements of a matrix H k,l ; a resulting matrix C k,l t is a frequency representation of a matrix of corrections for the reconstructed image μ i,j t ; performing of the 2D IFFT of the matrix C k,l t obtained in a previous step of the iterative reconstruction process; a resulting matrix c k,l t represents a matrix of corrections for the reconstructed image μ i,j t ; performing a correction of the reconstructed image μ i,j t ; using of a criterion of an iterative process for stopping.