1. A method of adjusting values for sensitivities of X-ray detectors comprised in a CT-imager that generate signals responsive to X-rays from an X-ray source in the imager, comprising: acquiring signals generated by X-ray detectors in the CT-imager responsive to X-rays incident thereon from the X-ray source for views taken during a scanning procedure performed by the CT-imager to image a patient when only air is present in a space between the X-ray source and the detectors; and using the signals to adjust the values of the sensitivities.