the principle of linear tomography is pretty simple. During linear tomography, the x-ray tube is attached mechanically to the image receptor and moves in one direction, while the image receptor moves in the opposite direction. An imaginary pivot point called the fulcrum is the point where the tube and the image receptor move. The position of the fulcrum determines the object plane, and only those anatomical structures lying within this plane are clearly imaged, thus blurring out every other another anatomy below or above the object plane.