A novel method to measure the zero-frequency DQE of a non-linear imaging system

Abstract

A new method of measuring the zero-frequency value of the detective quantum efficiency (DQE) of x-ray detectors is described. The method is unique in that it uses what we call a "simulated neutral-attenuator" method to determine the system gain derived from image-based measurements of x-ray transmission through a thin copper foil of known thickness. Since this method uses only low-contrast image structure, it is a true measure of the "small-signal" system gain which is assumed piece-wise linear. A theoretical expression is derived for the linearized pixel value which is the pixel value that a linear system would have for the test conditions. Combining this with the measured detector exposure and zero-frequency value of the Wiener noise power spectrum provides the DQE. It is shown this method gives a DQE value that is in agreement with conventional test methods on a linear flat-panel detector, and that the same DQE value is obtained when using both raw (linear) and processed (non-linear) images.