Detective quantum efficiency

The detective quantum efficiency (often abbreviated as DQE) is a measure of the combined effects of the signal (related to image contrast) and noise performance of an imaging system, generally expressed as a function of spatial frequency. This value is used primarily to describe imaging detectors in optical imaging and medical radiography. The detective quantum efficiency (often abbreviated as DQE) is a measure of the combined effects of the signal (related to image contrast) and noise performance of an imaging system, generally expressed as a function of spatial frequency. This value is used primarily to describe imaging detectors in optical imaging and medical radiography. In medical radiography, the DQE describes how effectively an x-ray imaging system can produce an image with a high signal-to-noise ratio (SNR) relative to an ideal detector. It is sometimes viewed to be a surrogate measure of the radiation dose efficiency of a detector since the required radiation exposure to a patient (and therefore the biological risk from that radiation exposure) decreases as the DQE is increased for the same image SNR and exposure conditions. The DQE is also an important consideration for CCDs, especially those used for low-level imaging in light and electron microscopy, because it affects the SNR of the images. It is also similar to the noise factor used to describe some electronic devices. The concept has been extended to chemical sensors, in which case the alternative term detectivity is more appropriate. Starting in the 1940s, there was much scientific interest in classifying the signal and noise performance of various optical detectors such as television cameras and photoconductive devices. It was shown, for example, that image quality is limited by the number of quanta used to produce an image. The quantum efficiency of a detector is a primary metric of performance because it describes the fraction of incident quanta that interact and therefore affected image quality. However, other physical processes may also degrade image quality, and in 1946, Albert Rose proposed the concept of a useful quantum efficiency or equivalent quantum efficiency to describe the performance of those systems, which we now call the detective quantum efficiency. Early reviews of the importance and application of the DQE were given by Zweig and Jones. The DQE was introduced to the medical-imaging community by Shaw for the description of x-ray film-screen systems. He showed how image quality with these systems (in terms of the signal-to-noise ratio) could be expressed in terms of the noise-equivalent quanta (NEQ). The NEQ describes the minimum number of x-ray quanta required to produce a specified SNR. Thus, the NEQ is a measure of image quality and, in a very fundamental sense, describes how many x-ray quanta an image is worth. It also has an important physical meaning as it describes how well a low-contrast structure can be detected in a uniform noise-limited image by the ideal observer which is an indication of what can be visualized by a human observer under specified conditions. If we also know how many x-ray quanta were used to produce the image (the number of x-ray quanta incident on a detector), q, we know the cost of the image in terms of a number of x-ray quanta. The DQE is the ratio of what an image is worth to what it cost in terms of numbers of Poisson-distributed quanta: