One example method to improve image quality of projection image data may include obtaining projection image data and channel offset data associated with the projection image data. The channel offset data may be acquired using the flat panel detector and include at least one set of channel offset data values associated with respective channels of the flat panel detector. The method may also include generating channel offset drift data representing one or more variations of the channel offset data from a reference channel offset data. The method may further include generating offset-compensated projection image data by modifying the projection image data based on the channel offset drift data to compensate for the one or more variations of the channel offset data.