Among other things, one or more techniques and/or systems for correcting projection data representative of an object under examination to account for drift in a radiation system are provided. System drift is measured by performing a drift calibration on the radiation system. During the drift calibration, a temperature of the radiation system is measured and one or more calibration tables, such as an air table and/or offset table, are corrected based upon the measured temperature to derive a theoretical projection (e.g., indicative of measurements that are expected to be acquired from the radiation system during the drift calibration). The theoretical projection is compared to an actual projection acquired during the drift calibration to measure a degree of drift. Based upon the measured degree of drift, one or more correction factors are determined to correct and/or otherwise adjust for system drift in a projection respective of the object.
