Random noise, such as read noise, dark current, and photon shot noise.Noise on scientific cameras is error that has a number of sources, but can largely be categorized into two categories: While the former is dependent mostly on QE and pixel size, the latter is a much larger subject. At Teledyne Photometrics sensitivity is paramount and is our approach to highly sensitive cameras is twofold: maximize signal collection, and minimize noise levels. Also, with more than needed images being taken, the X-ray suite will age and deteriorate more quickly.The sensitivity of a scientific camera is vital, with insufficient sensitivity it may not even be possible to acquire clear images of your sample. Even if, fortunately, the misrepresentation is identified right away, a repeat will be requested which would increase the radiation exposure to the patient. Too much noise on the diagnostic images can either lead to a misdiagnosis of the pathology and this would furthermore impact treatment plan. If more than standardized amount of noise is not corrected in time, certain undesired situations could happen. If the EI value exceeds the standard demonstrated above, a corrective action needs to be conducted in order to maintain the proper functioning of the CR system, ensuring that the best possible image quality could be provided. Another example can be that the CR system is not properly quality controlled. There are some sources of error which can lead to a failure of the dark noise test, such as little damages to the imaging plate. Since the obtained EI value fell into the standard set by the manufacturer, the CR system in the lab passed the quantitative criteria. In this lab, an EI value of 20 was obtained. Since a general purpose imaging plate was tested in the lab, an EI value of 80 or less is the acceptance criteria that should be looked for. The dark noise test CR lab was conducted in X-ray room 5, B114 of the Institute of Applied Health Sciences on the McMaster University Campus. The window width and window level were manipulated in order to visualize the cassette under different viewing conditions of contrast and brightness, which further would show any artifacts the cassette might have. The uniformity of appearance was checked visually and the exposure index (EI) value was recorded. Without any exposure, the cassette was reloaded into the CR reader in order to go through the reading process, and the “Pattern” was set on the CR reader for it. To perform this test, a 10” × 12” CR cassette was erased first using the Kodak CR reading system. The procedure for this lab was fairly simple. In general, this test is recommended to be performed quarterly (Desai & Valentino, 2011). Thus, the purpose of dark noise test is to assess the level of noise inherent in the system since excessive noise in the plates can compromise image quality (Muhogora, Bonutti, Kazema, Padovani, & Msaki, 2011). The dark noise test measures the erasure efficiency of the imaging plate and the CR system (Desai & Valentino, 2011). Therefore, the less the dark noise is, the better the image quality will be. During the reading process of an image, a certain amount of noise would be unavoidably produced. In the imaging plate, with attenuated X-ray photons first converted into light by the crystals, a radiographic image could be created. CR employs phosphorous crystals to produce an image. Similar to the “snow” on the television screens which is inherent in the design of a video system, dark noise is also inherent in a computed radiography (CR) system. Dark noise is the noise produced in a photo-detector when the photo-cathode is shielded from all external optical radiation and operating voltages are applied (Desai & Valentino, 2011).
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