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  • 1
    ISSN: 1613-9674
    Keywords: Radiography ; Dental ; Signal processing ; Computer-assisted ; Dosimetry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The exposure required to obtain optimal image quality was determined using conventional intraoral x-ray film (Eastman Kodak, Rochester, NY) and the RVG-S Radio VisioGraphy-S: Trophy Radiology, Vincennes, France) CCD-based intraoral radiographic imaging system. The RVG-S permitted dose reductions of 50 to 65% for individual exposures in comparison with Ektaspeed film, and 73 to 76% when compared to Ultraspeed film. The dose dynamic for the RVG-S was 8.6 times narrower than that for conventional film. Perception of low contrast details was not significantly different between either type of x-ray film and the RVG-S.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1613-9674
    Keywords: Radiography ; dental ; X-ray film ; Visual perception
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Eastman Kodak Company has developed a new E-speed dental X-ray film called Ektaspeed plus. The sensitometric properties, and information yield of this film were compared with those of other conventional direct emulsion dental X-ray films produced by Eastman Kodak, Ektaspeed EP-22 and Ultra-Speed DF-57. The contrast of Ektaspeed plus is close to that of Ultra-Speed, whilst the speed of Ektaspeed plus is similar to that of Ektaspeed. The latitude of the new film is narrower than that both Ektaspeed and Ultra-Speed.
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  • 3
    ISSN: 1613-9674
    Keywords: Dental radiography ; Digital image processing ; CCD-based intraoral radiographic system
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Purpose Current CCD-based intraoral radiographic systems permit the use of any dental X-ray generator. As a consequence, beam quality can be altered. This study was carried out to investigate studied the effects of varying beam quality on the VIXA-2 image contrast (Gendex Dental Systems srl Milan, Italy). Methods Images were made of a standard aluminum stepwedge and the pixel value of each step was measured. An optical bench was used to standardize geometric projection. Soft-tissue equivalent attenuation was effected using 1.75 cm plexiglass. Exposures were made at 2–48 impulses using 50–90 kVp settings at 10 kVp intervals. Exposures (μC/kg) were determined using a beryllium-windowed ionization chamber. Results The pixel values for each step decreased both with increased exposure (μC/kg) and with increased kVp. The relationship between exposure and pixel value was not linear. The longest scale of contrast was obtained at 17.3, 15.2, 13.5, 11.7, and 11.3 μC/kg respectively at 50, 60, 70, 80, and 90 kVp. The gradient for pixel values along the steps was steeper at lower kVp settings than at higher kVp settings. Conclusions The VIXA-2 can be operated at a wide range of kVp settings. Gamma conversion inherent in the VIXA-2 creates wide variations in the pixel values for different stepwedge thicknesses.
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  • 4
    ISSN: 1613-9674
    Keywords: Dental Radiography ; CCD-based intraoral imaging system ; Signal-to-noise ratio
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The signal-to-noise ratio (SNR) describes the ability of a detector to differentiate a signal from random fluctuations in signal intensity or noise in an image. The dose-response curves and the SNRs were measured and compared between Computed Dental Radiography (CDR) and Sens-A-Ray. The dose-response curves at 60, 70 and 80 kVp of both systems indicated that the pixel values increased in proportion to the radiation exposure. The pixel value gradient was slightly steeper for the CDR than for the Sens-A-Ray. Sensitivity increased slightly at the higher kVp setting with the CDR only. All SNRs increased with increased exposure for both systems. The SNR for the CDR was superior to that for the Sens-A-Ray, even with low exposures. The SNR for CDR increased steeply as exposure and average pixel values increased. On the other hand, the SNR for the Sens-A-Ray showed only a relatively slight increase with exposure. In conclusion, due to the high SNR in the lower exposure range, the CDR has the capability of substantially reducing the level of exposure in comparison with the Sens-A-Ray.
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  • 5
    ISSN: 1613-9674
    Keywords: Dental Radiography ; Digital image processing ; CCD-based intraoral radiographic system
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The RVG-4 permits automatic exposure compensation (AEC). The purpose of this investigation was to determine the effects of AEC on image contrast. Images were made either with or without a dental QA jaw phantom using a fixed image projection geometry. Exposures were 6.3 through 27.3 μC/kg using an X-ray generator operated at 70 kVp. Region of interest pixel value distributions were measured at tissue thicknesses in this phantom, and the average pixel values and signal-to-noise ratios (SNR) were calculated. The use of AEC without an object in place resulted in a disproportionate relationship between pixel value and exposure with a marked reduction in SNR. The use of AEC on under- and over-exposed images of the phantom simultaneously enhanced image contrast and reduced SNR. Thus, AEC provides a convenient and quick method for achieving high-contrast images with sub-optimal exposures, however, this could lead to inappropriate patient dosages if the function is used for over-exposed images. AEC reduces the SNR and produces disproportionate pixel values relative to exposure.
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  • 6
    ISSN: 1613-9674
    Keywords: Radiography, dental ; Radiography, panoramic ; Radiation dosage ; Screen-film
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Absorbed doses modified by the use of rare-earth intensifying screens were measured with rotational panoramic radiography. Equipments with the constant potential, Veraview (J.Morita) and PM 2002 CC (Planmeca) was utilized. The optimum exposure settings at each tube voltage were determined by radiography of a Rando® phantom. Absorbed doses to parotid and thyroid glands were measured under the optimum exposure settings by using the Rando® phantom and thermoluminescence dosimeters. The sensitivity of the rare-earth intesifying screen system increased as the tube voltage bacame higher. Absorbed doses decreased steeply as the tube voltage became higher. The highly sensitive system of the LANEX REGULAR and T-Mat G (Eastman Kodak) reduced the thyroid gland dose to a half at 70 kV in comparison with the regular system of the PX-III (Kasei Optonics) and X-Omat S (Eastman Kodak). This high sensitivity, however, made it impossible to set the optimum tube current at above 70 kV. The another rare-earth system, the TRIMAX 16 and TRIMAX XUD (3M) had a lower sensitivity than the regular system of the PX-III and X-Omat S at below 80 kV. But they had equal sensitivity at the highest tube voltage of 80 kV.
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  • 7
    ISSN: 1613-9674
    Keywords: Radiography ; Cephalometric ; Filtration ; Radiation dose
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effect of added niobum filtration 30 μm and 50μm on constant potential and conventional full-wave rectified cephalometric units was explored in terms of radiation dose. Water was used to simulate soft tissues to attenuate the X-ray beam. The addition of niobium 30μm and 50μm for each unit caused a reduction in the surface dose, but resulted in an increase in the dose deep to 8 cm of water. The more heavily filtered beam reduced the surface dose most for each operating potential, while, providing the highest deep dose through 8cm of water in each case. There was a comparatively strong linear association between half-value layer (HVL) and relative dose at both the zero and the 8cm thicknesses of water. The coefficients of determination (r2) and the significant probabilities of correlation coefficient (p) were 0.82 (p〈0.0001) at the surface and 0.89 (p〈0.0001) with 8cm of water.
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