English: Principle of CT scanner: This figure indicates　a schematic configuration of a CT scanner for the purpose of mathematical modeling and examination of the principle of tomography utilizing the parallel beam irradiation optical system. The numbers in the figure (see the numbers within the parentheses) respectively indicate: (1) = an object; (2) = the parallel beam light source; (3) = the screen; (4) = transmission beam; (5) = the datum circle; (6) = the origin; and (7) = a fluoroscopic image (a one-dimensional image; p (s, θ)). Two datum coordinate systems xy and ts are also imagined in order to explain the positional relations and movements of features (0) - (7) in the figure. In addition, a virtual circle centered at the abovementioned origin (6) is set on the datum plane (it will be called “the datum circle” henceforth). This datum circle (6) will be represents the orbit of the parallel beam irradiation optical system.