Focusing on mathematical methods in computer tomography, this book introduces novel approaches to help solve the problem of image reconstruction on the Cartesian lattice. Specifically, it discusses methods of image processing along parallel rays to more accurately reconstruct images from a finite number of projections and avoid overradiating the body during a CT scan. The book presents several new concepts and methods, including methods of transferring the geometry of rays from the plane to the Cartesian lattice, the point map of projections, the particle and its field function, and the statistical model of averaging.