A method for operating a measurement arrangement for a computer tomograph. The measurement arrangement has a radiation source of invasive radiation and a flat image detector with scintillation layer and a photocell array of photocells for detection of radiation from the radiation source. A calibration object is arranged between the radiation source and the flat image detector, and at least one radiation image of the calibration object is recorded with the flat image detector. From known dimensions of the calibration object and from the at least one radiation image, a distortion error, which occurred as a result of a distortion of the flat image detector, is determined as a function of the location in the photocell array (device 6). In particular, a radiation image of an object to be measured, recorded with the flat image detector, is corrected on the basis of the determined distortion error.
