Method for estimation and correction of grid pattern due to scatter

An X-ray imager that calibrates a pattern of an anti-scatter grid induced by X-ray scatter, the X-ray imager comprising:

• an imaging system including
• an X-ray source, and
• a detector array arranged across from the X-ray source, and acquire projection images representing an intensity of X-ray radiation detected by the detector array, the projections images acquired by the detector array including a first calibration image and a second calibration image, wherein
• each of the first calibration image and second calibration image is a projection image in which a uniform phantom is fixed at a respective position between the detector array and an X-ray source of the X-ray imager, the position of the uniform phantom being spaced from the detector array by a respective patient-to-detector distance (PDD), which is different for the first projection image and the second projection image, respectively, the PDD of the first projection image corresponding to a position at which an object to be imaged is to be arranged during X-ray imaging using the X-ray imager;
• and
• circuitry configured to
• generate a ratio image between the first calibration image and a second calibration image, and using the ratio image to estimate a background-scatter image due to scatter,
• perform a spatial-frequency transformation on the background-scatter image, and
• store, as a calibration result, in a memory (i) non-zero frequency components of the spatial-frequency transformation as a zero-mean scatter pattern, and (ii) a zero frequency component of the spatial-frequency transformation as a scaling factor.