The technique of tomography has long been used in radiography and in nuclear medicine to sharpen images of objects on the tomographic plane and to blur images of objects on the off-planes. The method is illustrated in Figure 1. Suppose one is interested in examining the plane T in the object. The x-ray source and the film are moved parallel to each other in the opposite directions with the plane of interest as the fulcrum. This is achieved by choosing the velocity v 1 of the x-ray source and the velocity v 2 of the film such that the ratio v 1/v 2 is equal to d 1/d 2, where dl is the source-to-plane distance, and d 2 is the plane-to-film distance. The objects on the plane of interest are in focus, whereas the objects on the other planes are out of focus and blurred. However, the blurrings could become quite serious in some cases and interfere with the objects of interest.