A CT scanner according to the present invention is particularly adapted for scanning the extremities of a patient. The CT scanner includes an x-ray source and x-ray detector mounted for rotation and translation along an axis parallel to a table for supporting the patient's extremity. The source and detector are mounted opposite one another on an inner circumference of an inner ring. The inner ring is rotatable about the axis within an outer ring mounted on at least one carriage. The carriage is movable parallel to the axis. During scanning, the inner ring rotates within the outer ring while the rings and carriage move along the axis, thereby producing a helical scan of the extremity.