A radiographic system comprising a source of penetrative radiation (10) and a detector (14) having a plurality of energy sensitive detector elements for producting electrical signals in repsonse to the radiation. Means are provided for actuating the source (10) so as to direct radiation through a subject (P) onto the detector (14). Means are also provided for moving the detector (14) relative to the subject (P) whilst exposing a number of detector elements to the radiation passing through the subject (P). Time delay and integrate circuitry is associated with the detector elements so as to operate on the signals produced by the elements so as to improve their signal to noise ratio. Imaging circuitry is provided for producing a representation of the internal structure of the subject corresponding to the pattern of radiation incident on the detector elements.