Anti-scatter grids are well established in the field of X-ray projection imaging. In general these grids consist of a large
number of parallel lead lamellae separated by X-ray-transparent material. This regular structure defines the characteristic
grid frequency. Modern X-ray imaging systems apply digital receptors, i.e. image intensifiers coupled to a CCD camera
or solid state flat-panel detector. Combining a digital detector and an anti-scatter grid may lead to Moire artifacts. This
results from sampling an analog X-ray image with signal components higher than half the sampling frequency. Especially
in high dose DSA images (Digital Subtraction Angiography) these irritating artifacts may be visible to the user.
In this paper we present a concept for minimizing these grid artifacts: Signal propagation in the detector is modeled by
three steps, scintillator MTF, aperture MTF, and sampling. Since the scintillator MTF is irrelevant for the grid optimization
process, we focus on aperture MTF and sampling. From the given geometry of the detector elements the corresponding
2D Fourier transform is calculated. An evaluation for typical grid frequencies, i.e. arcs around the origin of the 2D
Fourier transform, results in profiles exhibiting pronounced minima. From the respective angle values for these minima,
grid orientation can be optimized for minimum Moire disturbances.
Simulation results for typical detector pixel geometries and for grid frequencies used in practice are validated by measurement
for two different anti-scatter grids on a Siemens angiographic system with a digital flat-panel detector.