Abstract: A driving and positioning arrangement for radiography includes a patient support which can be driven, in a direction longitudinally of the patient, through an aperture in a housing which contains the active elements of a computerised tomographic apparatus. A scale member comprises a part which is supported by the housing and a part which is supported by the patient support. Once the patient is correctly positioned for examination, one of the parts of the scale member is moved relative to its respective support so that the two parts can be caused to assume a selected relative position.

Abstract: 3. Automatic target following apparatus comprisingA. sensing means for deriving a video signal representing a target,B. means for storing signal elements from a frame of said video signal,C. means for comparing signal elements from a subsequent frame of said video signal with the stored signal elements with different relative phase shifts to detect deviation from a desired point of view of the target,D. said comparing means including means for deriving a plurality of correlation signals dependent on the correlations of the signal elements from said subsequent frame and said stored signal elements with different relative phase shifts,E. means for deriving a guidance signal for the apparatus responsive to the largest of said correlation signals,F. means for detecting a decline in the correlation of signal elements from said subsequent frame with said stored signal elements, andG.