Abstract

In radiography a pointlike x-ray source is used to generate the picture of an object. This simple shadow projection suffers from radiation being diffusely scattered by the object itself since it reduces considerably the contrast of the picture. To avoid this drawback it is proposed in this paper to introduce a grating between source and object of an incoherent shadow projection. The primary picture is modulated by this grating while scattered radiation is essentially not, thus being nearly invariant against a shifting of the grating. After electronic scanning the primary picture can be reconstructed by electronic demodulation. A projection of the grating with the object removed serves as the carrier frequency for the demodulation. In addition to the suppression of scattered radiation the application of gratings leads to enhanced spatial resolution. Taking multiple pictures with a shifted grating, the modulation transfer function is repeated several times within the frequency plane. A detailed mathematical treatment for a point source is given.

© 1976 Optical Society of America

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