A method of mounting a CT imager on a gantry: determining a center of rotation of a rotor of the gantry; siting a plurality of mounting elements at predetermined positions with respect to the center of rotation; and attaching the mounting elements to the rotor while keeping the mounting elements at the predetermined positions. An opening is formed near the smaller end of the tube. These linear cuts reach the air bubble cells such that the air bubble cells communicate with the exterior through the linear cuts.