On reduction of Moire pattern distortion in digital diagnostic X-ray imaging

Sampling analog signals will cause aliasing interference if the signal has frequency components higher than the folding frequency, i.e. half the sampling frequency. This distortion originates in the folding of these higher frequency components into the lower signal frequency spectrum with interference as a result. Usually aliasing artefacts are avoided by analog low-pass filtering of the signal prior to digitization. However, in the area of digitizing video signals from a CCD based sensor such anti-alias filter is not feasible. The problem grows in importance due to increasing resolution requirements in many imaging applications urging for CCD technology. The paper reports the development of image restoration algorithms for the reduction of Moire interference arising from anti-scatter grids applied in digital diagnostic X-ray imaging. The approach followed is to remove the alias distortion by means of inverse filtering. Results are discussed, including simulation results with acquired images