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High-Fidelity Electronic Display of Digital Radiographs¹

¹ From the Department of Diagnostic Radiology, Henry Ford Health System, 1 Ford Place, Detroit, MI 48202 (M.J.F., A.B., W.R.E.); and the Center for Integrated Microsystems, University of Michigan, Ann Arbor (J.K., A.B.). Recipient of a Certificate of Merit award for a scientific exhibit at the 1997 RSNA scientific assembly. Received December 4, 1998; revision requested February 9, 1999, and received May 7; accepted May 17. Supported in part by breast cancer research grant DAMD 17-96-1-6283 from the U.S. Army. Address reprint requests to M.J.F.

View larger version (23K): [in a new window]   Figure 1.   Stimulus response relationship and light adaptation. Graph shows the measured rate of neuronal signals for different adaptation states with illustrative numeric values. The profile of the response function was approximated with the expression P = L/(L + S) (6). Similar incremental changes in stimulus cause a different response according to the adaptation state.

View larger version (15K): [in a new window]   Figure 2.   Biologic contrast response of the human visual system. The curve was obtained by differentiating the photoreceptor response. The perception of contrast deteriorates rapidly as the intensity of the stimulus is increased or decreased with respect to the optimum response coordinate.

View larger version (18K): [in a new window]   Figure 3.   Contrast threshold of the human visual system plotted as a function of luminance for a particular spatial frequency in the signal. Although constant at higher luminance values, the threshold deteriorates at low luminance, a property known as the Weber-Fechner law (12).

View larger version (12K): [in a new window]   Figure 4.   Standard display function curve shown as luminance versus display pixel value (DV) (15,16). A unit change in display pixel value causes a luminance change equal to the contrast threshold at the indicated luminance level. The upper curve shows the effect of diffuse ambient light reflection for a display device with a diffuse reflection coefficient of 0.01 cd/m2 per lux in a room producing 100 lux. The difference between the standard curve and the modified curve becomes small for regions where the luminance is greater than 5 cd/m2.

View larger version (15K): [in a new window]   Figure 5.   Cross-sectional diagram shows the relative dimensions of a typical CRT bulb.

View larger version (161K): [in a new window]   Figure 6.   Scanning electron microscope image of a CRT faceplate sample. The phosphor layers were exposed by using a scalpel scratch. The width of the image corresponds to 50 µm. Debris from the sample preparation process can be seen on top of the aluminum layer.

View larger version (130K): [in a new window]   Figure 7.   Photograph of the inner surface of a CRT faceplate core after removal of the aluminum and phosphor layers. The roughness causes internal reflections at the interior surface to have a diffuse angular distribution.

View larger version (13K): [in a new window]   Figure 8.   Simulated luminance point-spread functions (PSF) for two CRT emissive structure designs with a 16-mm-thick faceplate. r is the radial distance from a point source of emitted light. Curve a represents a typical monochrome CRT with no faceplate glass absorption. When a black matrix is combined with an absorption of 0.2 cm-1 (curve b), the magnitude of the tails of the point-spread function is reduced significantly, thus increasing the available display contrast.

View larger version (43K): [in a new window]   Figure 9.   Effect of contrast degradation on glare test patterns. The curves below the images depict a center data row from the images, thus showing the diffuse background component that reduces the glare ratio (defined as Lmax/Lmin [31]).

View larger version (20K): [in a new window]   Figure 10.   Cross-sectional diagram of typical CRT emissive structure. Light generated in the phosphor layer by electron impact scatters in the different components until its fate is determined. The processes can be described by three efficiencies. First, the incident electron beam deposits energy in the phosphor with an efficiency ee, which relates the energy of the incoming electrons to the deposited energy in the phosphor. Second, the energy deposited by the electrons in the phosphor is converted into light photons in the luminescence sites with a quantum efficiency ep. Once the light is generated, it diffuses and eventually reaches the viewer by escaping the structure with an efficiency eg, which depends on the characteristics of light emission, the spatial distribution of the emitted photons, and the relative dimensions of the components of the emissive structure. The complex light transport that takes place may consist of several possible processes, which include reflection and refraction at the surfaces and scattering and absorption in the medium.

View larger version (181K): [in a new window]   Figure 11a.   Highly magnified recordings of uniform gray regions (5 mm in diameter) from CRT devices with high-brightness P-104 phosphors (a); P-45 phosphors that emit a broad spectrum (b); and red, green, and blue phosphors in a black matrix (c).

View larger version (221K): [in a new window]   Figure 11b.   Highly magnified recordings of uniform gray regions (5 mm in diameter) from CRT devices with high-brightness P-104 phosphors (a); P-45 phosphors that emit a broad spectrum (b); and red, green, and blue phosphors in a black matrix (c).

View larger version (212K): [in a new window]   Figure 11c.   Highly magnified recordings of uniform gray regions (5 mm in diameter) from CRT devices with high-brightness P-104 phosphors (a); P-45 phosphors that emit a broad spectrum (b); and red, green, and blue phosphors in a black matrix (c).

View larger version (40K): [in a new window]   Figure 12.   Cross-sectional diagram of an active-matrix LCD. The liquid crystal (LC) cell modulates light intensity according to the driving voltages and is confined by multilayer structures. ITO = indium tin oxide, TFT = thin-film transistor.

View larger version (20K): [in a new window]   Figure 13.   Diagram shows that light is transmitted through several layers in an LCD. AR = anti-reflective, LC = liquid crystal, T = transmission, TFT = thin-film transistor.

View larger version (17K): [in a new window]   Figure 14.   Typical improvement in viewing angle for a multidomain LCD (39,40). Because anisotropies in the configuration of the liquid crystal are averaged over all domains, the angular distribution of light emission is enhanced. Ideally, emitted light should have a near-Lambertian distribution. AMLCD = active-matrix LCD, T = transmission.

View larger version (43K): [in a new window]   Figure 15.   Diagram of pixel structure shows the transmissive area (aperture) of a thin-film transistor (TFT) high-aperture-ratio design for an active-matrix LCD. ITO = indium tin oxide.

View larger version (9K): [in a new window]   Figure 16.   Thin-film transistor (TFT) design for an active-matrix LCD with overlap between the indium tin oxide (ITO) and bus line for a higher pixel aperture ratio.

View larger version (28K): [in a new window]   Figure 17.   Cross-sectional diagram of a typical field-emission display shows the sharp emitters and the structures that confine the microvacuum cell. ITO = indium tin oxide.

View larger version (12K): [in a new window]   Figure 18.   Cross-sectional diagram of a typical electroluminescent (EL) display shows the film arrangement needed for a display device, although layers for specific designs may differ. ITO = indium tin oxide.

View larger version (14K): [in a new window]   Figure 19.   Attained luminance versus driving voltage for organic and inorganic electroluminescent (EL) devices (52,53).