The need for investigating the optical transfer functions in several field orientations for nonisotropic radiographic...

In this paper, it is demonstrated that obtaining OTF's for only two directions, parallel and perpendicular to the x-ray tube axis, is insufficient to completely describe the performance of nonisotropic radiographic systems. By performing experiments with three radiological systems in which slit images were obtained for ten different directions, we confirmed that OTF's vary in a nonlinear fashion for directions that are intermediate to the parallel and perpendicular ones. Moreover, we have also identified for each system a range of field orientations--referred to as "Optimum Region"--where sharper images can be obtained. These experimental results can be accounted for by the transfer functions theory.