Performance of Digital Radiographic Detectors: Quantification and Assessment Methods

Digital radiographic systems are gaining widespread use in many clinical applications. Digital radiographic detectors vary dramatically with respect to the technologies that they use and the particular implementation. Their performance thus varies from system to system. It is often necessary to characterize the performance of a digital radiographic or mammographic detector for optimization, design, comparison, or quality assurance purposes. To do so, it is most useful to measure the performance of the detector in terms of common performance metrics, so that meaningful comparisons can be made. The performance of a digital radiographic detector can be described in terms of a number of performance factors. Among them, sharpness and noise are two key characteristics that describe the intrinsic image quality performance of digital radiographic systems (1,2). Together, these two, along with an associated characteristic, the signal-to-noise ratio (SNR), define the intrinsic ability of an imaging system to faithfully represent the anatomic features of the body part being imaged. This chapter first focuses on the quantification of sharpness, noise, and SNR in radiographic systems in terms of common performance metrics of the modulation transfer function (MTF), the noise power spectrum (NPS), and the detective quantum efficiency (DQE). Methods for measuring the MTF, the NPS, and the DQE are then described. The chapter ends with an outline of detector performance factors that may be considered in a comprehensive evaluation of the performance of a detector. The next chapter in the syllabus focuses on the factors that influence the sharpness and noise performance of a digital radiographic detector.