SU‐D‐301‐04: Development of a Simple Method for Measuring the DQE of An X‐Ray Imaging System with Unspecified Characteristic Response

Abstract

Purpose: To develop a method of measuring the detective quantum efficiency (DQE) of an x‐ray imaging system with unspecified characteristic response for use in a hospital quality assurance program. Methods: Measurement of the DQE of radiographic systems in a hospital setting is made difficult by the fact that many systems have a non‐linear or unspecified characteristic response curve. This makes it difficult to determine the detector signal as a function of a number of incident x‐ray quanta as required to linearize the system response. We solve this problem with what we call a “neutral attenuator” method that uses a copper stepwedge to attenuate the beam and incorporate a theoretical correction for spectral beam hardening effects. Using a standardized spectrum (IEC 61267 RQA‐5, 7.1mm hvl), a copper stepwedge consisting of 5 steps with transmissions ranging from 0.94 to 0.01 was placed in the beam to determine the characteristic curve. The method was validated by comparing a conventional (IEC 62220‐1) DQE assessment with the DQE obtained using our method based on both raw (linear) and processed (non‐linear) image data from a General Electric Revolution Xrd Q/i detector. Results: The DQE obtained using the conventional method had a zero‐frequency value of 0.49 with an estimated uncertainty of 0.03. Our new method generated a value of 0.50 using raw image data and 0.47 using processed image data. Conclusions: A simple method has been developed to determine the DQE of an x‐ray system that can be used on both linear image data and non‐linear image data. While not IEC 62220‐1 compliant, it is simple enough to be incorporated into a hospital quality assurance program.