DOI: 10.1148/rg.243035133
AAPM/RSNA Tutorial on Equipment Selection: PACS Equipment Overview
Display Systems1
Aldo Badano, PhD
1 From the Office of Science and Technology, Center for Devices and Radiological Health, Food and Drug Administration, 12720 Twinbrook Pkwy, HFZ-142, Rockville, MD 20857. From the AAPM/RSNA Tutorial on Equipment Selection at the 2002 RSNA scientific assembly. Received May 13, 2003; revision requested July 14 and received August 7; accepted August 21. Address correspondence to the author (e-mail: agb@cdrh.fda.gov).
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Figure 1a. (a, b) Photographs of 30-mm-square regions of P104 (a) and P45 (b) CRT screens show the different appearances of noise due to phosphor granularity. (c) Photograph of the screen of a monochrome medical AMLCD, obtained at the same magnification, shows a fixed regular pattern due to the subpixel structure.
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Figure 1b. (a, b) Photographs of 30-mm-square regions of P104 (a) and P45 (b) CRT screens show the different appearances of noise due to phosphor granularity. (c) Photograph of the screen of a monochrome medical AMLCD, obtained at the same magnification, shows a fixed regular pattern due to the subpixel structure.
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Figure 1c. (a, b) Photographs of 30-mm-square regions of P104 (a) and P45 (b) CRT screens show the different appearances of noise due to phosphor granularity. (c) Photograph of the screen of a monochrome medical AMLCD, obtained at the same magnification, shows a fixed regular pattern due to the subpixel structure.
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Figure 2. Pixel structure for a dual-domain AMLCD. Individual display pixels consist of six subpixel regions in a chevron arrangement, which is determined by the dual domain and three color stripes. The simplified equivalent circuit shows one thin-film transistor (TFT) per color subpixel. C = capacitor. (Adapted and reprinted, with permission, from reference 13.)
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Figure 3. Schematic of the three sources of veiling glare in CRTs: light diffusion, light leakage, and electron backscattering. AR = antireflective coating.
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Figure 4. Specular and diffuse reflections for a CRT. The thick lines indicate the position of the electron beam and the luminance that it generates when it impinges on the phosphor layer. The specular reflections occur mostly at the front surface of the faceplate. The reflective coating, which is designed primarily to increase the light output of the phosphor, also increases the diffuse component of the display reflections.
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Figure 5. To reduce reflections from ambient light, transmission through the faceplate of a medical monitor is typically 0.2-0.5. If a transmission of 0.3 is assumed, diffuse reflections are reduced to at least 0.09, resulting in improved black levels. The display brightness diminishes only to 0.3. Absorption also reduces veiling glare by dampening the scattering within the faceplate.
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Figure 6. Contrast ratio (CR) measurements for CRTs and AMLCDs as a function of the dark spot size. Dashed lines = monochrome CRTs, dotted line = color CRT. (Adapted and reprinted, with permission, from reference 27.)
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Figure 7. The light transmission and intensity modulation that occur in an AMLCD result in a non-Lambertian luminous emission from the screen. The electro-optic effect in the liquid crystal cell that determines the pixel luminance is highly dependent on the relative orientation of the input light (from the backlight) and the liquid crystal molecules and polarizer films in the liquid crystal display stack, as well as the path length associated with each direction of emission. I = intensity.
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Figure 8. Contrast ratio measurements for a medical AMLCD. In this case, the contrast ratio is the ratio of maximum to minimum luminance for a 20% region in the midgray background.
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Figure 9a. Changes in luminance (a) and contrast (b) for a medical AMLCD at different angles along a diagonal direction of viewing (29). The data points labeled "0" correspond to perpendicular viewing. JND = just noticeable difference, L = luminance.
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Figure 9b. Changes in luminance (a) and contrast (b) for a medical AMLCD at different angles along a diagonal direction of viewing (29). The data points labeled "0" correspond to perpendicular viewing. JND = just noticeable difference, L = luminance.
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Figure 10a. Effect of viewing angle on white noise images. (a) Image shows the pattern as seen in the perpendicular direction. (b, c) Corresponding images obtained with the technique described in the text show the changes in the gray scale-luminance relationship due to a viewing angle of 45° in the horizontal plane (b) and in one of the diagonal planes (c).
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Figure 10b. Effect of viewing angle on white noise images. (a) Image shows the pattern as seen in the perpendicular direction. (b, c) Corresponding images obtained with the technique described in the text show the changes in the gray scale-luminance relationship due to a viewing angle of 45° in the horizontal plane (b) and in one of the diagonal planes (c).
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Figure 10c. Effect of viewing angle on white noise images. (a) Image shows the pattern as seen in the perpendicular direction. (b, c) Corresponding images obtained with the technique described in the text show the changes in the gray scale-luminance relationship due to a viewing angle of 45° in the horizontal plane (b) and in one of the diagonal planes (c).
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Figure 11. Effect of viewing angle on the luminance calibration functions of AMLCDs for a fixed centered observer. The luminance output for perpendicular viewing (right graph) is distorted at the corners and the edge of the display screen (left graphs). If a lesion were present in these screen locations, its detectability would be different than if it were in the center.
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Copyright © 2004 by the Radiological Society of North America.
