The present disclosure relates to systems and methods for image data processing. A first correction coefficient corresponding to a first collimation width of a collimator of a scanner may be obtained. The collimator may have a collimation width being adjustable. A relationship between scattered radiation intensities and collimation widths may be obtained. A relationship between correction coefficients and collimation widths may be determined based on the first correction coefficient, the first collimation width, and the relationship between scattered radiation intensities and collimation widths. A target collimation width of the collimator may be obtained. A target correction coefficient may be determined based on the target collimation width and the relationship between correction coefficients and collimation widths.