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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,〔S. Manghani and J.J. Ramsden, The efficiency of chemical detectors, J Biol Phys Chem 3:11-17, 2003〕 in which case the alternative term detectivity〔R.C. Jones, Detectivity: The reciprocal of noise equivalent input of radiation, Nature (London) 170:937-938, 1952〕 is more appropriate. == History == 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 image quality. However, other physical processes may also degrade image quality, and in 1946, Albert Rose〔A. Rose, A unified approach to the performance of photographic film, television pick-up tubes, and the human eye, J Soc Motion Pict Telev Eng 47:273-294, 1946〕 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〔H.J. Zweig, Performance criteria for photo-detectors -- concepts in evolution, Photogr Sci Engng 8:305-311, 1964〕 and Jones.〔R.C. Jones, Scientific American 219:110, 1968〕 The DQE was introduced to the medical-imaging community by Shaw〔R. Shaw, The equivalent quantum efficiency of the photographic process, J Photogr Sci 11:199-204, 1963〕〔J.C. Dainty and R. Shaw, Image Science, Academic Press, New York, 1974〕 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.〔H.H. Barrett, J. Yao, J.P. Rolland and K.J. Myers, Model observers for assessment of image quality, Proc Natl Acad Sci USA 90:9758-9765, 1993〕〔Medical Imaging -- The Assessment of Image Quality, Int Comm Rad Units and Meas, ICRU Report 54, 1995〕 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: :. In this sense the DQE describes how effectively an imaging system captures the information content available in an x-ray image relative to an ideal detector. This is critically important in x-ray medical imaging as it tells us that radiation exposures to patients can only be kept as low as possible if the DQE is made as close to unity as possible. For this reason, the DQE is widely accepted in regulatory, commercial, scientific and medical communities as a fundamental measure of detector performance. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Detective quantum efficiency」の詳細全文を読む スポンサード リンク
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