WO1990006520A2 - Electrographic process for generating an electrical image signal - Google Patents
Electrographic process for generating an electrical image signal Download PDFInfo
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- WO1990006520A2 WO1990006520A2 PCT/US1989/005396 US8905396W WO9006520A2 WO 1990006520 A2 WO1990006520 A2 WO 1990006520A2 US 8905396 W US8905396 W US 8905396W WO 9006520 A2 WO9006520 A2 WO 9006520A2
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- image
- photoconductor
- toner
- radiation
- exciting
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/26—Testing of individual semiconductor devices
- G01R31/265—Contactless testing
- G01R31/2656—Contactless testing using non-ionising electromagnetic radiation, e.g. optical radiation
Definitions
- the present invention relates to electrography, and in particular to a process for generating an electrical image signal from an electrographic image.
- Background of the Invention The conventional electrophotographic process has an inherently lower gain than the silver halide photographic process. A low exposure in an electrophotographic process results in a small amplitude differential voltage pattern on a photoconductor, and when developed with conventional toner, the resulting image is of low density. It has been a longstanding goal to increase the gain of the electrophotographic process so that higher density images may be produced from low exposures.
- Electrographic processes are processes in which differential patterns of voltage, charge, current or conductivity are developed with toner. Electrographic processes include, for example, dielectric recording, photoconductography, electrophotography, photoelectrophoresis , ionography, stylus recording, and ion projection.
- the presence of a small coverage of toner is detected as the difference in two large signals: the reflectance signal from a clean photoconductor, and the slightly different reflectance signal from a photoconductor with a small coverage of toner.
- the resulting difference signal will be noisy.
- the method is sensitive to slight scratches or imperfections on the surface of the photoconductor.
- the use of a Fresnel type lens to collect the specular light over a large scanning area as taught in col 6, pp 47-55 of U.S. 4,624,543, will introduce unwanted ripples in the output signal which may interfere with the detection of small modulations in the toner coverage, thereby making the signal difficult to interpret.
- the primary object of the present invention to provide a method of generating an electrical image signal from a low exposure in an electrophotographic process that is free from the shortcomings noted above. It is a further object of the invention to provide means of detecting very low coverages of toner produced imagewise by other electrographic methods such as ionography, stylus recording, ion projection and photoelectrophoresis , or any related process in which a weak differential pattern of voltage, charge, current or conductivity is toned.
- the object of amplifying an image in an electrographic process is achieved according to the present invention by forming a differential voltage pattern and developing with a toner containing luminescent material.
- a material is termed luminescent if, when excited by radiation of a first wavelength, it emits radiation of a second different wavelength.
- Luminescent materials include phosphors, fluorescent compounds, scintillating compounds, etc.
- the imagewise luminescent toner deposit is excited to produce emitted radiation.
- the emitted radiation is photoelectrically detected to produce an electrical image signal which, after electronic processing, can be used to create either a video image or a hardcopy output image.
- the small amplitude differential voltage pattern or charge pattern is formed on a selenium photoconductor by small exposure to X-rays.
- the small amplitude differential voltage pattern or charge pattern is developed with a liquid luminescent toner, employing a development electrode.
- the luminescent toner image is excited by raster scanning with a laser beam or with a collimated light beam, and the emitted radiation is collected by a light collector and directed to a photomultiplier tube, photodiode, or other detector, where it is detected to produce the image signal.
- the exciting radiation can be blocked by a filter from reaching the detector, and only the emitted radiation sensed, the modulation of the resulting image signal is much improved over that produced by the prior art methods.
- the emitted radiation coming as it does only from the toner, does not involve the substrate, so that the resulting electrical image signal is inherently much easier to interpret than signals produced by the method of Young et al.
- the signal modulations need not be extracted from a difference of large values, nor are they combined with unwanted signal modulations due to use of a Fresnel lens, as in the detection method of U.S. Patent No. 4,624,543.
- the toner particles have a size distribution between 0.4 and 1 ⁇ m in diameter, and the toner charge is such that at least 1 to 2 toner particles are deposited for each X-ray photon that is absorbed by the photoconductor.
- an image sensor such as a charge coupled device (CCD) image sensor can be used to capture the luminescence from the entire toned image, or from a portion of it, after or during blanket excitation by the exciting wavelength, using suitable filtration as necessary to block the exciting light.
- CCD charge coupled device
- the luminescent emission pattern may be altered in size by optical imaging means prior to its detection.
- Said optical imaging means include fiber optics, conventional lenses, holographic lenses, mirrors, and combinations thereof, and may also include filters in the optical train to block, for example, the excitation spectrum producing the luminescence. Image magnification by a factor greater, equal to or less than unity may be achieved by said optical imaging means.
- a portion of the luminescent radiation image is expanded (magnification factor greater than unity) prior to detection by the CCD, thereby providing a zoom feature. Since a CCD has a finite number per unit area or per unit length of sensitive elements or pixels, this zoom feature provides a means of increasing the detective resolution.
- Fig 1. is a flow diagram showing the steps of the electrophotographic process according to the present invention.
- Fig 2. is a schematic diagram showing the steps employed in the preferred mode of practicing the invention
- Fig. 3 is a flow diagram showing the steps of a further extension of the process shown in Fig. 1;
- Fig. 4 is a schematic diagram illustrating the extra steps shown in Fig. 3.
- Fig. 5 is a schematic diagram illustrating the use of an image sensor to produce the electrical image signal according to the present invention. Description of the Invention
- a voltage differential image is formed (10) by an electrographic process such as electrophotography, photoconductography or dielectric recording.
- the photoconductor may comprise, for example, any photoconductor known in the art.
- Typical photoconductor films that can be used are made from sensitized organic dyes in polymeric binders, or from inorganic photoconductive particles such as zinc oxide or cadmium sulfide in organic binders.
- Photoconductive plates such as those made from selenium on a rigid support may also be used.
- photoconductors containing the heavier elements including selenium, selenium—tellurium alloys, lead oxide, mercury iodide, bismuth oxide mixed with other oxides, and the like.
- Single layer or composite, multilayer photoconductive elements may be used.
- the electrostatic latent image may be formed by charging and exposing the photoconductor to an image-wise pattern of radiation as is known in the art.
- the photoconductor may be charged to conventional voltage levels for the particular photoconductor or process, or to lower than normal charging levels for certain photoconductors to avoid the problems of dark decay noise or dielectric breakdown that occur in some photoconductors.
- the photoconductor may be exposed to normal or lower than normal intensities of radiation to produce the latent image.
- Preferably a low amplitude differential voltage latent image is formed, in order to maximize the sensitivity or detectivity of the system by making use of the amplification provided by the readout process.
- the term "low amplitude differential voltage image” refers to a latent electrostatic image having a voltage differential that is lower than that considered in the prior art to be sufficient to produce a satisfactory image.
- the average entrance exposure for ma mography as practiced in the prior art using xeroradiography was found to be about 2.58 x 10 — C/Kg, using an x—ray beam with a half— alue layer (HVL) of 1.1 mm of aluminium.
- HVL half— alue layer
- a latent image may be formed with an x—ray entrance exposure of 0.31 x 10 —4 C/Kg which results in a final output image of excellent contrast.
- the X—ray exposure employed to produce the low voltage differential image may be from one half to one tenth the exposure normally required to produce a diagnostically useful image in the particular photoconductor.
- the low voltage differential image may also be produced as a result of charging the photoconductor to a lower than normal level to avoid artifacts caused by excessive dark decay noise or by dielectric breakdown.
- Low voltage differential images may also be produced by normal level exposures of organic photoconductors, where the amount of organic photoconductor in a binder is reduced below that which is conventionally employed.
- photoconductors which are not optimally responsive to particular wavelengths of exposing radiation may be employed with these wavelengths to produce a low amplitude differential voltage image.
- the low amplitude differential voltage image is developed (12) with a luminescent toner.
- the image may be developed using any of the known electrophotographic development techniques such as liquid, dry magnetic brush or cloud development; however, for xeroradiography, liquid development with a development electrode is the presently preferred method.
- the luminescent toner material may comprise, for example, luminescent pi ments, dyed latices in which the dyes are luminescent or optical brighteners, luminescent metal chelates , or fluorescent polymers such as polymers containing fluorescing anthracene or other fluorescing units.
- the developed luminescent toned image is excited (14) to produce emitted light.
- the manner in which the image is excited depends on the manner in which the emitted light is to be detected in the following step (16). If the emitted fluorescent image is detected with a line or area image sensor, comprising a line or area arrangement of detector elements (pixels), it is excited with a line or area illumination, respectively.
- the presently preferred mode is to stimulate and detect the image pixel by pixel by scanning the image in a raster fashion with a beam of exciting radiation.
- the scanning may be effected by any of the well known techniques for scanning an image with a beam of radiation.
- the emitted luminescence is detected (16) to produce the electrical image signal.
- the detection means can be any of the known photoelectric image sensing transducers such as linear or area array image sensors.
- the image is excited pixel by pixel, and the emitted light is collected over a large solid angle and directed to a non-imagewise photoelectric sensor such as a photomultiplier tube, or photodiode.
- the detected signal may be electronically amplified as is well known in the art to produce a final electrical image signal. Amplification in detection may also be obtained by increasing the intensity of the scanning beam, or by scanning more slowly in order to increase the luminescent counts per pixel detected. As shown in Figure 1, the image signal may then be digitized (17) and processed (18) for example by adjusting the tone scale, enhancing edges, removing noise, or compressing the digital image. The processed image may be stored (19) or displayed in known ways such as printing 20 or video display 21. In the present method, modulations in toner coverage corresponding to voltage contrasts of less than 57 ⁇ are easily detected and may be electronically enhanced, whereas in the prior art method U.S. 4,624,543 the sensitivity cannot be much greater than the artifact ripple in the signal itself, which is claimed to be 10% or less.
- a photoconductor generally designated 22 comprising a selenium layer 24 on an aluminum support 26 is charged (10) to a positive potential by a corona charger 28.
- Selenium plates were obtained from Noranda Research Center, Quebec Canada. Plates are prepared by vacuum evaporation of selenium on to an aluminum support that has been provided with a barrier layer to prevent electron injection from the aluminum into the selenium when the plate is positively charged by a corona charger.
- An X—ray source 30 is employed to expose
- the amount of x—ray exposure required is not determined by the need to achieve a high level of toner density, but only by the need to produce a detectable electrical signal having sufficient signal—to-noise ratio (SNR), the exposure may be greatly reduced.
- the low amplitude differential voltage image on the photoconductor 22 is developed (12) with a liquid developer 36 employing a development electrode 38 as shown in above referenced U.S. Patent 4,624,543.
- the development electrode is connected to one terminal of a voltage source 42.
- the other terminal of the voltage source is connected to an electrode 44 that contacts the aluminum support 26 which serves as a backside electrode of the photoconductor 22.
- the liquid toner comprises fluorescent toner particles suspended in a carrier liquid, having a preferred size distribution of between 0.4 and 1 ⁇ m and having a charge such that at least 1 to 2 toner particles are deposited on the image per absorbed X-ray photon.
- the toner was prepared as described below in example 2.
- the small particle size and a development efficiency of at least 1—2 particles per photon are important to provide the highest possible resolution, and to provide the ability to detect threshold x-ray exposures with a high degree of statistical certainty.
- the toned image may be rinsed (not shown) with an inert hydrocarbon liquid such as the toner carrier liquid to remove toner from background areas of the image. After rinsing, the toned image is dried (not shown) as is known in the prior art.
- the toned image 46 is excited (14) by scanning with a beam of stimulating light 48 generated by a laser 50.
- the laser beam is deflected by a mirror or polygon 52, while the photoconductor is moved in the direction of arrow A to effect a raster scan of the luminescent toned image 46.
- Light emitted from the image is collected and detected (16) by a light collector of the type comprising a mirror box 54 to collect the emitted light and direct it to a photomultiplier tube (PMT) 56 or photodiode.
- a filter 57 over the face of the PMT blocks exciting radiation and passes emitted radiation. Examples of such a light collector/detector useful with the present invention are shown in U.S. patent no. 4,743,758 issued May 10, 1988 to Chan et al. and U.S. 4,743,759 issued May 10, 1988 to John C. Boutet.
- the electrical image signal S produced by the photomultiplier tube may be amplified by an amplifier 58, and digitized (17) by an analog to digital convertor 60 and digital image processing electronics 62.
- the digital image processing electronics 62 may implement any of the known digital image processing operations on the digital image signal, such as tone scale adjustment, edge enhancement, and noise reduction.
- the above described scanning method can also be employed to detect electrical noise due to non-uniform corona charging of a photoconductor caused by a permanent non—uniform dark decay pattern over the surface of the photoconductor, and characteristic of a given photoconductor film sample or plate. This is done by charging photoconductor 22, for example, by corona charger 28 and then bias-developing, without exposure of the photo— conductor, a thin layer of toner by means of the development electrode 38 the potential of which is set at a convenient offset voltage from the corona—charged surface potential of the photoconductor.
- the dark decay pattern now decorated by toner is scanned, allowing electronic storage of the locations and amplitudes of noise fluctuations due to the dark decay pattern of the given photoconductor.
- This pattern in electronic digitized form, can be manipulated electronically, e.g. its amplitude adjusted, and then subtracted from subsequent images made by imagewise exposures, thereby reducing the noise in the output images created from the stored electrical images.
- the above scanning method can also be used to prescan a toned image in order to optimally adjust the gain in the detector, in order to avoid the loss of any image information due to clipping, e.g., in a subsequent main scan.
- the processed image signal may be either stored for future use, or displayed for example by a laser film printer 64.
- the luminescent image is amplified by a luminescent amplification process prior to being excited and detected.
- the luminescent amplification process which is the subject of copending U.S. Patent Application No. 236,411 entitled "Electrophotographic Luminescent Amplification Process" filed on August 25, 1988 by J. May and R. Young, comprises the steps of forming a low amplitude differential voltage image in a photoconductor; developing the low amplitude differential voltage image with a luminescent toner, exciting the luminescent toner to produce emitted radiation; exposing a photoconductor to the emitted radiation to produce a high amplitude differential voltage image on the exposed photoconductor; and developing the high amplitude differential voltage image.
- This amplification process can be employed with the present invention to imagewise increase the toner coverage of the luminescent toned image prior to generating the electrical image signal.
- the toner image on the plate may be cleaned off so that the photoconductor can be reused.
- Any suitable cleaning method can be employed, including the use of solvents, agitation (including ultrasonic agitation), or mechanical methods such as using a brush, skive, or wiper, or any other method known in the art.
- the scanning method can also be used to advantage prescan the cleaned photoconductor and subsequently to subtract electrically, analogously to the method described above for dark decay noise, the signal corresponding to any toner residue left from a previous image.
- Fig. 3 is a flow diagram showing the steps of the process according to the present invention, including the luminescent amplification step.
- the steps shown in Fig. 3 that correspond with similar steps in Fig. 1 are similarly numbered.
- the added steps include: exciting (70) the luminescent toner image formed in step (12); exposing (72) a photoconductor with the emitted radiation to form a high amplitude differential voltage image; and developing (74) the high amplitude differential voltage image with a luminescent toner.
- the added luminescent ampli ication steps are illustrated in Fig. 4.
- the photoconductor is provided with a filter 76 that blocks stimulating radiation and passes emitted radiation.
- the luminescent toner image is stimulated by flooding with stimulating radiation 78.
- the filter 76 blocks the stimulating radiation 78, and passes the emitted radiation 80.
- the emitted radiation further discharges the photoconductor layer 24 to form a high amplitude differential voltage image in the photoconductor.
- the high amplitude differential voltage image is developed (74), employing the same development apparatus and luminescent toner that was used to develop the low amplitude differential voltage image.
- the resulting toned image on the photoconductor comprises the toner 82 resulting from development of the high amplitude differential voltage image, overlying the toner 46 resulting from development of the low amplitude differential voltage image.
- the luminescent toned image may be detected with a line or area array image sensor to produce the electrical image signal S.
- Figure 5 illustrates such a sensing arrangement.
- the luminescent toned image 46 is excited by light sources 100, 102.
- the emitted fluorescent light is directed by a lens 104 onto an image sensor 106, such as a line or area array CCD image sensor.
- a filter 108 blocks the exciting light from the light sources 100, 102, and passes the emitted light.
- lens 104 can comprise a zoom lens for providing variable resolution of the image signal S produced by the sensor. Examples:
- Example 1 Samples of photoconductor film containing an organic photoconductive dye in a polyester binder, and available from the Eastman Kodak Company as photoconductive film type SO-101, were positively charged and exposed to a test pattern simulating a standard x—ray mask test target with sets of lines ranging in frequency from 0.05 to 3.7 cycles per mm, to simulate low intensity X—ray exposures, and to form low amplitude differential voltage images in the photoconducto . The images were toned with a liquid developer containing Rhodamine 6G dye dissolved in a cellulose acetate-co—cyclohexene orthodicarboxylic acid polymeric binder (CAP—6).
- CAP cellulose acetate-co—cyclohexene orthodicarboxylic acid polymeric binder
- the dye was chosen for excitation by an Argon ion laser at a wavelength of 488 nm.
- the toner was prepared as follows: A 64% by weight solution containing 0.2 g of Rhodamine 6G plus 5.8 g of said binder was added to heptane to yield a precipitate comprising a solid solution of dye in binder.
- the heptane contained a dispersent which aided formation of small particles but which remained in solution and did not coprecipitate.
- Equivalent ⁇ V values that would be produced by the same ⁇ Q values on a selenium plate, typically 320 ⁇ m thick, are 530, 195, and 184 volts (corresponding to 34, 13, and 12 volts on SO-101, respectively).
- corresponding percentage discharges are 17, 6, and 6, respectively, showing that sufficient sensitivity was obtained to provide more than adequate detection of contrast in xeroradiographic mammography, insofar as the image 62—14, which had optical density too low to measure, was nevertheless easily visible by eye without any amplification.
- Image 62—10 was scanned using an argon ion laser of beam width 100 ⁇ 5 ⁇ m in a laser scanner having a light collector comprising an integrating cylinder with filters, and photomultiplier tubes arranged at the two ends of the cylinder.
- the luminescent signal was sampled at 100 ⁇ m spatial intervals, filtered electronically to remove high frequency noise, and digitized using a 12—bit analog—to—digital converter.
- the resulting video image was displayed on a CRT.
- the digitized image was also sent to a drum scanner/printer, and printed on silver halide film having hlue tinted support, to simulate a conventional medical radiograph.
- the print from image 62—10 was made at unit magnification, and showed an excellent rendition of the original.
- the 3.7 cycles/mm bars (135 ⁇ m bars and 135 ⁇ m spaces) were cleanly separated and sharp.
- Example 2 An improved toner was made using Rhodamine 6G as the fluorescent material.
- Rhodamine 6G (0.6 g) and CAP-6 binder (11.4 g) were precipi ⁇ tated by the method of Example 1 to produce a pigment (solid solution of dye in binder). This was melt—compounded with 20 g of a polyester binder and 10 g of a 1:1 mixture of low molecular weight polyethelene wax/ELVAX [poly(ethelene—co— vinylacetate) from Dupont Company], coarsely pulverized, and then milled with stabilizer polymers to produce a developer concentrate.
- a developer was produced by dilution with purified ISOPAR G. The new developer had much improved shelf—life.
- Example 1 Images were made on SO—101 film using the same test pattern as Example 1. The procedure was similar to that of Example 1, namely, charging the film positively to potential V volts with a corona charger, exposing with white light through the test pattern, and developing in N/P mode in a liquid developer station having a development electrode at potential V, . In all images with the new toner, the bar patterns were sharply resolved down to 3.7 cycles/mm. After scanning and forming silver halide hardcopy output, the output prints were examined, and in all cases showed similar sharpness and resolution at 1:1 reproduction. The low frequency bars (or • patches) showed good fill—in and large area uniformity.
- the small developed ⁇ V of the image bars was calculated accurately by measuring the magenta transmission density of the low frequency bars, and using a calibration curve of density versus developed voltage measured separately (see Table II).
- magenta optical densities of toner are small, corresponding to very small developed ⁇ V value that are approximately 10 times lower than are normally used to form conventional xerographic images.
- Electronic tone scale adjustment was used to produce output printout densities close to 5 times the input densities in all cases, with a linear relationship between the magenta toner densities (proportional to toner laydown coverage) and the output silver developed in the hard copy film. Different electronic gain would have produced proportionately different output silver densities from the same toner images .
- Example 3 This example demonstrates that dry luminescent toner can be useful in the practice of this invention, especially for non—radiological imaging purposes .
- a two—component developer was prepared, consisting of oxidized iron core particles (diameter approximately 150 ⁇ m) mixed with ground polyester fluorescent toner particles (diameter approximately 15 ⁇ m) at 8% w/w toner concentra ⁇ tion.
- the toner formulation consisted of VITEL 10038A polyester binder from Dupont Company, containing 0.2% w/w of the methyl ester of Rhodamine B trifluoromethanesulfonate and 1.0% w/w of charge agent.
- the charge agent is disclosed in co—pending U.S. Patent Application 134,344 by D. Bugner et al. , filed Dec.
- image 153-1 was incompletely developed, so that low frequency bars showed enhanced edge development as well as directionality effects associated with transport through the developer station. Nevertheless, solid area laydown was judged to be fairly good. Increasing the development time for image 153-2 resulted in complete development. The much weaker toning fields in image 153-3 were close to threshold for solid area development to occur, resulting in very fringy incomplete development of low frequency bars, with full bar development occurring only at frequencies higher than 1.4 cycles/mm. At the higher frequencies, all images showed sharp resolution and clean edged lines.
- Example 4 A selenium plate, 0.15 mm thick, obtained-from Noranda Research Centre, Quebec, Canada was charged to a potential of +2250 volts and placed in a light—tight box. An x-ray beam from a Picker single-phase, W anode x-ray machine, operated at 30 kVp with a measured half—value layer thickness of -0.55 mm AL, was used to expose the plate after transmission through a standard KODAK-PATHE radiographic test phantom. The test phantom consisted of a plastic disk 1.3 cm thick, in which were embedded various objects such as wire meshes, plastic balls, and fine fibers.
- Rhodamine dye was used, namely the methyl ester of Rhodamine B trifluoromethanesulfonate.
- the preparation procedure was identical to Example 2, except that the following ingredients and proportions were used: 0.4 g dye, 19.6 g CAP-6, 30 grams polyester binder, and 16 g of 1:1 wax/ELVAX.
- This toner was improved over that of Example 2 by having brighter fluorescence.
- the development electrode bias was set at 160 volts above the average plate surface potential in the region where the plate had been exposed through the test phantom. The plate was dried, and a clear but low density toner image was on the plate.
- the toned plate was then scanned with an Ar ion laser (Spectra-Physics Model 162-03) at 488 nm in a scanner equipped with a rotating polygon to deflect the laser beam, a translation stage to move the plate, a reflective light collector as described in U.S. 4,743,759, two PMT's (Hammamatsu type R1512) with colored glass filters (Schott OG—530), and a high-speed data acquisition system with a 12-bit A/D converter to digitize the signals and a magnetic disk to store the image data.
- the pixel size in both directions was 100 ⁇ m, and the l/e**2 diameter of the scan beam was 100 ⁇ m.
- the power in the beam at the sample plane was 0.27 milliwatt, and the polygon rotated at 429 rpm.
- the number of lines scanned was 1500, the number of pixels/line was 1500, and the time to scan the image area was about 6 seconds.
- the digital image data were processed in several ways, to enhance the appearance of the output images. These included tone scale processing to enhance the contrast in the output image; remapping to display the output image with reversed tone polarity (i.e., "black-bone” vs. "white-bone”), and pixel interpolation to display a magnified output.
- the processed image data were sent to a laser film printer, and output prints were created on blue-tinted film, which were viewed in transmission on a light box.
- the processed images were also displayed and viewed on a CRT screen.
- the images may also be written on photographic paper and viewed in reflection, or some other form of hard copy display may also be used including electrophotographic, thermal transfer, ink jet, or the like.
- the output images were of high contrast, and all the various types of objects in the test phantom including wire meshes, plastic balls, and fine fibers were clearly visible.
- the output image contrast was adjustable by tone scale processing and could be made equal to or higher than that in a comparison image made by conventional film—screen radiographic technique. In addition, the visibility of fine details could be enhanced in the output image by magnification.
- the present invention is advantageous with respect to conventional film—screen radiography, particularly for applications such as ma mography, in that: electronic image data are generated which may be conveniently processed, stored, or transmitted; the latitude for x—ray exposure is greatly increased over that of conventional screen—film systems, since the steps of exposing the photoconductor with x—rays and exposing the output film with light are separated, thus reducing misexposures; conventional W anode x—ray sources rather than dedicated Mo x—ray sources may be used; and the spatial resolution loss in the x—ray detecting layer can be less since the lateral spreading of charges moving in a charged photoconductor is less than the lateral spreading of photons diffusing through a radiographic phosphor screen.
- the present invention is advantageous with respect to conventional xeroradiography in that: it has all the advantages of an electronic detector mentioned above; it requires less x-ray exposure and dose to the patient since the exposure is not determined by the need to achieve a high toner density; it has improved image quality since no transfer of the toned image is required; and it achieves both high spatial resolution and high solid area development through the use of liquid developer and a development electrode.
- the present invention is advantageous over other electronic radiography methods known in the art such as storage phosphors in that whereas in the case of storage phosphors the amount of light exposure required to scan out the stored image is very large, being determined by the optical cross section of the electronic storage states which is very small; the corresponding amount of light in the present invention is very small being determined only by the requirement for sufficient SNR in the scanning photodetector. Also, whereas the lifetime of the stimulated luminescence in a storage phosphor material is typically on the order of 1 microsecond, the luminescent lifetime of the dye used in the present invention is much shorter, on the order of 1 nanosecond or less. Thus the scanning process in the present invention may be carried out much more rapidly and with less intense and less expensive light sources than in the prior art.
- the scanning process was destructive; i.e. the image was erased while being scanned
- the scanning is nondestructive, which is advantageous in that artifacts such as banding due to nonuniform motion of the scanning spot are much reduced.
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Abstract
Description
Claims
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
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US28079388A | 1988-12-07 | 1988-12-07 | |
US280,793 | 1988-12-07 |
Publications (2)
Publication Number | Publication Date |
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WO1990006520A2 true WO1990006520A2 (en) | 1990-06-14 |
WO1990006520A3 WO1990006520A3 (en) | 1990-09-07 |
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Application Number | Title | Priority Date | Filing Date |
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PCT/US1989/005396 WO1990006520A2 (en) | 1988-12-07 | 1989-12-04 | Electrographic process for generating an electrical image signal |
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EP (1) | EP0397846A1 (en) |
JP (1) | JPH03502498A (en) |
WO (1) | WO1990006520A2 (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US8936897B2 (en) * | 2012-05-02 | 2015-01-20 | Eastman Kodak Company | Enhancing color toner images with fluorescing magenta toners |
Citations (4)
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US4070577A (en) * | 1976-09-10 | 1978-01-24 | Xonics, Inc. | Imaging systems with fluorescent and phosphorescent toner |
GB2015142A (en) * | 1978-02-24 | 1979-09-05 | Mpd Technology | Hydride Container |
GB2034075A (en) * | 1978-11-09 | 1980-05-29 | Savin Corp | Method and apparatus for xeroradiography |
EP0252327A1 (en) * | 1986-06-13 | 1988-01-13 | Fuji Photo Film Co., Ltd. | Radiation image read-out method and apparatus |
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1989
- 1989-12-04 JP JP50089090A patent/JPH03502498A/en active Pending
- 1989-12-04 WO PCT/US1989/005396 patent/WO1990006520A2/en not_active Application Discontinuation
- 1989-12-04 EP EP19900900606 patent/EP0397846A1/en not_active Withdrawn
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
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US4070577A (en) * | 1976-09-10 | 1978-01-24 | Xonics, Inc. | Imaging systems with fluorescent and phosphorescent toner |
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Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US8936897B2 (en) * | 2012-05-02 | 2015-01-20 | Eastman Kodak Company | Enhancing color toner images with fluorescing magenta toners |
US9057978B2 (en) | 2012-05-02 | 2015-06-16 | Eastman Kodak Company | Enhanced color toner images using fluorescing magenta toners |
Also Published As
Publication number | Publication date |
---|---|
WO1990006520A3 (en) | 1990-09-07 |
EP0397846A1 (en) | 1990-11-22 |
JPH03502498A (en) | 1991-06-06 |
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