In order to reduce the grid artifacts, which are caused by using the
antiscatter grid in obtaining x-ray digital images, we analyze the
grid artifacts based on the multiplicative image formation model
instead of the traditional additive model, and apply filters to
suppress the artifact terms. The artifact terms are aliases of the
modulated terms from the harmonics of the grid frequency. Hence,
several filters are required to efficiently suppress the grid
artifacts. However, applying filters also distort the original image
that will be recovered. If the distance between the origin and the
center frequency of the artifact term is relatively large, then we
can suppress the artifact term less distorting the original image.
In this paper, by increasing the distances for a given sampling
frequency of the image detector, we design antiscatter grids, which
are good in terms of efficient grid artifact reduction. In order to
design optimal grids, we formulate min-max optimization problems and
provide optimal grid frequencies for a fixed grid angle with respect
to the sampling direction of the image detector and optimal grid
angles for a fixed grid frequency. We then propose using rotated
grids with the optimal grid angles in digital radiography imaging.
By applying band-rejection filters to the artifact, we can
considerably reduce the grid artifacts when comparing to the
traditional non-rotated grid case for real x-ray images.