![]() The digital images were acquired using bitewing projection geometry. The original Al filter from the X-ray machine was removed since it has a thickness of 2.5 mm which is greater than required by the law governing the sector 9 that states an X-ray machine up to 70 kVp requires an Al filter with a thickness of 1.5 mm. The tested filters were individually attached in a GE 1000 X-ray machine (General Electric Co., Milwaukee, WI), which operated at 65 kVp, 10 mA, 40 cm focus-receptor distance, using three different exposure times: 0.05 s, 0.16 s and 0.35 s. G1, 97% aluminium (Al) and 3% copper (Cu) with 1.47 mm thickness G2, 96% Al and 4% Cu with 1.53 mm thickness G3, 95% Al and 5% zinc (Zn) with 1.56 mm thickness G4, 98% Al and 2% Zn with 1.5 mm thickness G5, 95% Cu and 5% Zn with 1.6 mm thickness. The aim of this study was to evaluate the effect of the modulation of the radiation spectrum with the use of alternative X-ray filters on the quality of intra-oral digital images from SPPs. 7 Shibuya et al 8 evaluated alternative filters to be used with digital systems of solid-state sensors, in this case a charge-coupled device (CCD), and observed that the KEY filter, an alloy of aluminum (Al), copper (Cu) and tin, reduced the exposure to radiation and enhanced the diagnostic information. The low-energy photons would be absorbed by the soft tissue of the patient without affecting useful diagnostic information. 3- 7 The X-ray filters can decrease the exposure dose to radiation by removing those low-energy photons from the X-ray beam. Other factors, such as current, voltage of the tube and filtration of the X-ray beam, can also modify the number of photons in the X-ray beam, causing a modulation of the radiation spectrum that affects exposure dose and image quality. However, storage phosphor plates (SPPs) have a much larger dynamic range, enabling the selection of a broad scale of exposure times without causing saturation of the final image. ![]() As the dynamic range of solid-state sensors is small, it requires careful selection of the exposure time. In accordance with the fundamental principle of radiation protection known as ALARA (as low as reasonably achievable), the desired amount of diagnostic information should be obtained with minimum possible radiation exposure. In these systems, the exposure time is automatically standardized according to individual characteristics of the patients, independently of the control of operator. However, there has been little investment in replacing the X-ray machine for use with intra-oral digital imaging systems, despite the current introduction of X-ray machines with automatic exposure control (AEC) systems in direct digital techniques. This is the result of both innovations in image acquisition systems and in programs for image manipulation. ![]() Digital imaging systems are gradually replacing conventional analogue film in dentistry.
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