Accurate Evaluation of Modulation Transfer Function Using the Fourier Shift Theorem

Abstract

Accurate determination of the line spread function (LSF) on the basis of the edge processing algorithm in X-ray imaging systems is one of the most basic procedures for evaluating the performance of such systems. Extensive research has been focused on algorithms for the precise or fast measurement of the LSF in digital X-ray systems. Most of the standard methods for evaluating the performance of an imaging system are based on a fully digitalized radiographic system or a film-based system. However, images obtained by computed radiography (CR), which converts a captured analog signal into a digital image through an analog-to-digital converting scanner, show the combined characteristics of analog and digital imaging systems. Fundamentally, the characteristics of digital imaging systems differ substantially from those of film imaging systems because of their different methods of acquiring and displaying image data. In addition, a system with both analog and digital component has characteristics that differ from those of both digital and analog systems. In this research, we present a new modulation transfer function (MTF) that mimics the existing MTF in terms of measurement but satisfies existing standard protocols through modification of the hypothesis contents. In the case of the LSF and the point spread function measured with a CR system, the developed edge algorithm shows better performance than the conventional methods. We also demonstrate the usefulness of this method in an actual measurement with a CR digital X-ray imaging system.