Scanning radiographic apparatus

Radiographic apparatus including means defining a patient position, a source of penetrating radiation, such as X-radiation, arranged to project said radiation through said patient position along at least one beam path, scanning means for scanning the source of said radiation angularly and laterally relative to the patient position so as to project said radiation therethrough along further beam paths displaced angularly and/or laterally from said at least one beam path, a sensing arrangement for sensing the progress of said lateral scanning and for providing timing signals indicative thereof, detecting means including at least one detector device for detecting the amount of said radiation emergent from said patient position along each of said beam paths and for producing output signals indicative of said amounts, circuit means connected to receive said timing signals and said output signals and adapted to utilise said timing signals to determine, at least in part, the effective widths of said beam paths to which said output signals relate, and means for varying a characteristic of said timing signals to change the effective widths of said paths.