Radiography

Claim 1

A scanning structure for scanning a source of radiation around a patient during a radiographic examination of the patient, the structure comprising: a static main frame having an annular portion surrounding an aperture in which the patient's body is disposed; a frame member having an annular flange coaxial with, and of smaller radius than, said annular portion, a first lockable bearing disposed between said flange and said annular portion of said main frame, an annular ring member coaxial with, and of smaller diameter than, said annular flange, a second lockable bearing disposed between said ring member and said flange, the axes of said ring member, said flange and said annular portion of said main frame extending longitudinally of said patient's body, an outer tilt frame of annular form pivotally mounted to said ring member, an inner tilt frame, also of annular form, disposed within said outer tilt frame and supporting said source, a third lockable bearing disposed between said inner and outer tilt frames and a drive link extensible in the direction of said axes but substantially rigid in a direction tangential of the scanning movement coupling said inner tilt frame to said ring member; the inner tilt frame encircling the patient's body, means for causing said ring member to rotate, about its axis, around the patient's body, causing said inner tilt frame to rotate therewith by means of said drive link at an attitude dependent upon the pivotal position, relative to said frame member, adopted by said outer tilt frame, and means for selectively locking one or more of said lockable bearings, in dependence upon the motion, relative to the patient, required of said source.