A method for operating an X-ray computed tomography (CT) apparatus includes obtaining a first projection data set by scanning an area of interest with X-rays at a first time obtaining a second projection data set by scanning the area of interest with X-rays at a second time obtaining at least one item of difference data which includes a difference between a first item of projection data from among the first projection data set and a corresponding item of projection data from among the second projection data set and determining a rescanning of the area of interest by using X-rays based on information relating to the difference data.
