Validity of the Modulation Transfer Function of Radiographic Screen-Film Systems Measured by the Slit Method

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Abstract
At present, the line spread-function (LSF) and modulation transfer function (MTF) of radiographic screen-film systems containing double-coated film are often determined from slit exposures. The measurement procedure involves conversion of the density distribution in the slit image to the corresponding effective illuminance distribution in the film sandwich by means of large-area sensitometry of the film as a whole. With several screen-film systems of different optical and sensitometric properties as examples, it is shown experimentally that the present method yields LSF''s which permit prediction of outputs from known inputs to the systems. These results and consideration of some theoretical aspects of the transfer theory of linear systems indicate that present LSF''s and MTF''s form a self-consistent, valid description of the transfer characteristics of present screen-film systems. Other, equally valid descriptions may be found, depending on the manner in which outputs are measured.