EP0384634A2 - Assemblages radiographiques écran/film à rendement de détection quantique modifié - Google Patents

Assemblages radiographiques écran/film à rendement de détection quantique modifié Download PDF

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Publication number
EP0384634A2
EP0384634A2 EP90301550A EP90301550A EP0384634A2 EP 0384634 A2 EP0384634 A2 EP 0384634A2 EP 90301550 A EP90301550 A EP 90301550A EP 90301550 A EP90301550 A EP 90301550A EP 0384634 A2 EP0384634 A2 EP 0384634A2
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Prior art keywords
emulsion layer
screen
crossover
assembly according
layer unit
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German (de)
English (en)
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EP0384634A3 (fr
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Phillip Carter C/O Eastman Kodak Company Bunch
Robert Edward C/O Eastman Kodak Comp. Dickerson
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Eastman Kodak Co
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Eastman Kodak Co
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Priority claimed from US07/456,889 external-priority patent/US5021327A/en
Application filed by Eastman Kodak Co filed Critical Eastman Kodak Co
Publication of EP0384634A2 publication Critical patent/EP0384634A2/fr
Publication of EP0384634A3 publication Critical patent/EP0384634A3/fr
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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03C—PHOTOSENSITIVE MATERIALS FOR PHOTOGRAPHIC PURPOSES; PHOTOGRAPHIC PROCESSES, e.g. CINE, X-RAY, COLOUR, STEREO-PHOTOGRAPHIC PROCESSES; AUXILIARY PROCESSES IN PHOTOGRAPHY
    • G03C5/00—Photographic processes or agents therefor; Regeneration of such processing agents
    • G03C5/16—X-ray, infrared, or ultraviolet ray processes
    • G03C5/17—X-ray, infrared, or ultraviolet ray processes using screens to intensify X-ray images

Definitions

  • the invention relates to radiographic imaging. More specifically, the invention relates to assemblies of double coated silver halide radiographic elements and intensifying screen pairs.
  • an image of a patient's tissue and bone structure is produced by exposing the patient to X-radiation and recording the pattern of penetrating X-radiation using a radiographic element containing at least one radiation-sensitive silver halide emulsion layer coated on a transparent (usually blue tinted) film support.
  • the X-radiation can be directly recorded by the emulsion layer where only low levels of exposure are required, as in dental imaging and the imaging of body extremities.
  • a more efficient approach which greatly reduces X-radiation levels required, is to employ an intensifying screen in combination with the radiographic element.
  • the intensifying screen absorbs X-radiation and emits longer wavelength electromagnetic radiation which silver halide emulsions more readily absorb.
  • Another technique for reducing patient exposure is to coat two silver halide emulsion layers on opposite sides of the film support to form a "double coated" radiographic element.
  • Diagnostic needs can be satisfied at the lowest patient X-radiation exposure levels by employing a double coated radiographic element in combination with a pair of intensifying screens.
  • the silver halide emulsion layer unit on each side of the support directly absorbs about 1 to 2 percent of incident X-radiation.
  • the front screen, the screen nearest the X-radiation source absorbs a much higher percentage of X-radiation, but still transmits sufficient X-radiation to expose the back screen, the screen farthest from the X-radiation source.
  • the front and back screens are balanced so that each absorbs about the same proportion of the total X-radiation.
  • a few variations have been reported from time to time.
  • An imagewise exposed double coated radiographic element contains a latent image in each of the two silver halide emulsion units on opposite sides of the film support. Processing converts the latent images to silver images and concurrently fixes out undeveloped silver halide, rendering the film light insensitive. When the film is mounted on a view box, the two superimposed silver images on opposite sides of the support are seen as a single image against a white, illuminated background.
  • An art recognized difficulty with employing double coated radiographic elements in combination with intensifying screens as described above is that some light emitted by each screen passes through the transparent film support to expose the silver halide emulsion layer unit on the opposite side of the support to light.
  • the light emitted by a screen that exposes the emulsion layer unit on the opposite side of the support reduces image sharpness. The effect is referred to in the art as crossover.
  • hydrophilic colloid coating coverages in the emulsion and dye containing layers to allow the "zero" crossover radiographic elements to emerge dry to the touch from a conventional rapid access processor in less than 90 seconds with the crossover reducing microcrystalline dye decolorized.
  • DQE detective quantum efficiency
  • the DQE of a radiographic element can be determined by making two direct noise measurements, measurement of the input noise power spectrum (NPSi) and measurement of the output noise power spectrum (NPSo), and by making a mathematical adjustment to account for the influence of system gain (image contrast) and image sharpness as a function of its spatial frequency (modulation transfer factor or MTF).
  • DQE can be expressed mathematically by the following equation;
  • DQE is a dimensionless ratio of the input and output noise power spectra with adjustments for MTF and contrast, the latter being the ratio of density change (AD) per log unit of exposure change (A log E, where E is exposure in meter-candle-seconds).
  • AD density change
  • a log E where E is exposure in meter-candle-seconds.
  • contrast 1.0
  • contrast ceases to be a significant factor in DQE.
  • MTF is always a significant factor reducing DQE, since MTF is always less than unity when any degree of imaging detail is being considered.
  • MTF is unity only when the spatial frequency of the image is 0-i.e. , there is no image detail present.
  • MTF typically declines from unity to a small fraction over the image spatial frequency range of 0 to 10 cycles/mm. Stated qualitatively, the image noise introduced by the radiographic element increases progressively as finer imaging detail is considered.
  • an imaging assembly comprised of a transparent film support, front and back silver halide emulsion layer units coated on opposite sides of the film support, a front and back pair of intensifying screens adjacent the front and back emulsion layer units, respectively, for absorbing exposures to X-radiation and emitting electromagnetic radiation having a wavelength longer than 300 nm to imagewise expose the front and back silver halide emulsion layer units, and means for reducing to less than 10 percent crossover of the longer than 300 nm wavelength electromagnetic radiation emitted from the front screen to the back emulsion layer unit and from the back screen to the front emulsion layer unit, the crossover reducing means being decolorized in less than 90 seconds during processing of the emulsion layers.
  • the assembly is characterized in that the back screen and back emulsion layer unit in combination exhibit a photicity at least twice that of the front screen and the front emulsion layer unit in combination and the front screen is chosen to exhibit modulation transfer factors greater than those of reference curve A in Figure 2.
  • the radiographic imaging assemblies of the present invention are comprised of a transparent film support, front and back silver halide emulsion layer units coated on opposite sides of the film support, a front and back pair of intensifying screens adjacent the front and back emulsion layer units, respectively, for absorbing exposures to X-radiation and emitting electromagnetic radiation having a wavelength longer than 300 nm to imagewise expose the front and back silver halide emulsion layer units, and processing solution decolorizable means for reducing to less than 10 percent crossover of the longer than 300 nm wavelength electromagnetic radiation emitted from the front screen to the back emulsion layer unit and from the back screen to the front emulsion layer unit.
  • the intensifying screens can take any convenient conventional form, provided certain specific criteria are met.
  • the front screen (the screen nearest the source of X-radiation during imaging) must exhibit modulation transfer factors (MTF) greater than those of reference curve A in Figure 2.
  • MTF modulation transfer factors
  • Modulation transfer factor measurement for screen-film radiographic systems is described by Kunio Doi et al, "MTF and Wiener Spectra of Radiographic Screen-Film Systems", U.S. Department of Health and Human Services, pamphlet FDA 82-8187.
  • the profile of the individual modulation transfer factors over a range of cycles per mm constitutes a modulation transfer function.
  • the front and back screens In addition to containing at least a front intensifying screen which exceeds an objectively measureable MTF criterion, the front and back screens must satisfy a specific emission relationship on exposure.
  • the back screen upon imagewise exposure of the assembly to X-radiation emits at least twice the longer than 300 nm electromagnetic radiation to which the emulsion layer units are responsive as compared to the front screen. While the emissions of the front and back screens can differ widely, depending upon the imaging application to be served and the specific choices of emulsion layer units, it is generally preferred that the back screen emission exceed that of the front screen by 2 to 10 times, optimally from about 2 to 4 times.
  • the assemblies of the present invention embrace those that contain either symmetrical or unsymmetrical low crossover double coated radiographic elements.
  • Symmetrical radiographic elements are those in which the emulsion layer units on opposite sides of the support art identical.
  • Unsymmetrical radiographic elements embrace those in which the emulsion layer units on opposites sides of the support differ in their sensitometric characteristics. For example, unsymmetrical radiographic elements in which the emulsion layer units on opposite sides of the support exhibiting are differentiated in speed can be used to adjust imaging contrast effectively.
  • low crossover double coated radiographic elements containing front and back emulsion layer units that differ in contrast can also be used to advantage.
  • an assembly containing a front emulsion layer unit exhibiting a contrast of ⁇ 2 and a back emulsion layer unit exhibiting a contrast of at least 2.5 proeuces superior levels of contrast over a 1.0 log E exposure range, which is sufficient to obtain both heart and lung image detail in a single radiograph. It is specifically contemplated to form assemblies satisfying the requirements of this invention which include unsymmetrical radiographic elements of these types.
  • the general relationship of interest is the relationship of the photicity of the back screen back emulsion layer unit combination to the photicity of the front screen front emulsion layer unit combination.
  • the photicity of each screen and the emulsion layer unit it exposes is the integrated product of (1) the total emission of the screen over the wavelength range to which the emulsion layer is responsive, (2) the sensitivity of the emulsion layer unit over this emission range, and (3) the transmittance of radiation between the screen and its adjacent emulsion layer unit over this emission range. Transmittance is typically near unity and can in this instance be ignored. Photicity is discussed in greater detail in Mees, The Theory of the Photographic Process, 3rd Ed., Macmillan, 1966, at page 462.
  • the assemblies of this invention require the photicity of the back screen in combination with the back emulsion layer unit of the double coated radiographic element to be at least twice the photicity of the front screen in combination with the front emulsion layer unit.
  • the back screen in combination with the back emulsion layer unit exhibits a photicity which is in the range of from 2 to 10 times, optimally from about 2 to 4 times, that of the front screen in combination with the front emulsion layer unit. Since in most instances the double coated radiographic element is symmetrical (i.e., the speeds of the front and back emulsion layer units are identical), the relative photicities of the front and back combinations are the same as the relative emissions of the front and back screens. Therefore, the invention is discussed below in terms of relative front and back screen emissions, but it is to be understood that these emission comparisons are in reality photicity comparisons for symmetrical double coated radiographic elements.
  • Assemblies according to the present invention can contain front and back emulsion layer units that exhibit the same contrast or differ in contrast.
  • the front emulsion layer unit exhibit the lower contrast.
  • the front emulsion layer unit exhibit a contrast of ⁇ 2.0 and that the back emulsion layer unit exhibit a contrast of at least 2.5.
  • the front and back emulsion layer units exhibit a contrast differing by 0.5 to 2.0, optimally from 1.0 to 1.5.
  • Customarily sensitometric characterizations of double coated radiographic elements generate characteristic (density vs. log exposure) curves that are the sum of two identical emulsion layer units, one coated on each of the two sides of the transparent support. Therefore, to keep speed and other sensitometric measurements (minimum density, contrast, maximum density, etc.) as compatible with customary practices as possible, the speed and other sensitometric characteristics of the front silver halide emulsion layer unit are determined with the front silver halide emulsion unit replacing the back silver halide emulsion unit to provide an arrangement with the front silver halide emulsion unit present on both sides of the transparent support.
  • the speed and other sensitometric characteristics of the back silver halide emulsion layer unit are similarly determined with the back silver halide emulsion unit replacing the front silver halide emulsion unit to provide an arrangement with the back silver halide emulsion unit present on both sides of the transparent support. While speed is measured at 1.0 above minimum density, it is recognized that this is an arbitrary selection point, chosen simply because it is typical of art speed measurements. For nontypical characteristic curves (e.g., direct positive imaging or unusual curve shapes) another speed reference point can be selected.
  • the double coated radiographic elements of this invention offer the capability of producing superimposed silver images capable of transmission viewing which can satisfy the highest standards of the art in terms of speed and sharpness.
  • the radiographic elements are capable of producing a wide range of contrasts merely by altering the choice of intensifying screens employed in combination with the radiographic elements.
  • the radiographic element is achieved by constructing the radiographic element with a transparent film support and front and back emulsion layer units coated on opposite sides of the support. This allows transmission viewing of the silver images on opposite sides of the support after exposure and processing.
  • means are provided for reducing to less than 10 percent crossover of electromagnetic radiation of wavelengths longer than 300 nm capable of forming a latent image in the silver halide emulsion layer units.
  • the crossover reducing means In addition to having the capability of absorbing longer wavelength radiation during imagewise exposure of the emulsion layer units the crossover reducing means must also have the capability of being decolorized in less than 90 seconds during processing, so that no visual hindrance is presented to viewing the superimposed silver images.
  • the crossover reducing means decreases crossover to less than 10 percent, preferably to less than 5 percent, and optimally to less than 3 percent.
  • the crossover percent being referred to also includes "false crossover", apparent crossover that is actually the product of direct X-radiation absorption. That is, even when crossover of longer wavelength radiation is entirely eliminated, measured crossover will still be in the range of 1 to 2 percent, attributable to the X-radiation that is directly absorbed by the emulsion farthest from the intensifying screen.
  • Crossover percentages are determined by the procedures set forth in Abbott et al U.S. Patents 4,425,425 and 4,425,426.
  • T-GrainTM emulsions tabular grain emulsions as disclosed by Abbott et al U.S. Patents 4,425,425 and 4,425,426, cited above, hereinafter referred to as T-GrainTM emulsions; (2) sharpness levels attributable to crossover levels of less than 10 percent, (3) crossover reduction without emulsion desensitization or residual stain, and (4) the capability of rapid access processing, are realized in addition to the advantages discussed above.
  • a radiographic element 100 is positioned between a pair of light emitting intensifying screens 201 and 202.
  • the radiographic element support is comprised of a transparent radiographic support element 101, typically blue tinted, capable of transmitting light to which it is exposed and optionally, similarly transmissive under layer units 103 and 105.
  • On the first and second opposed major faces 107 and 109 of the support formed by the under layer units are crossover reducing hydrophilic colloid layers 111 and 113, respectively.
  • Overlying the crossover reducing layers 111 and 113 are light recording latent image forming silver halide emulsion layer units 115 and 117, respectively.
  • Each of the emulsion layer units is formed of one or more hydrophilic colloid layers including at least one silver halide emulsion layer. Overlying the emulsion layer units 115 and 117 are optional hydrophilic colloid protective overcoat layers 119 and 121, respectively. All of the hydrophilic colloid layers are permeable to processing solutions.
  • the assembly is imagewise exposed to X radiation.
  • the X radiation is principally absorbed by the intensifying screens 201 and 202, which promptly emit light as a direct function of X ray exposure.
  • the intensifying screens 201 and 202 which promptly emit light as a direct function of X ray exposure.
  • the light recording latent image forming emulsion layer unit 115 is positioned adjacent this screen to receive the light which it emits. Because of the proximity of the screen 201 to the emulsion layer unit 115 only minimal light scattering occurs before latent image forming absorption occurs in this layer unit. Hence light emission from screen 201 forms a sharp image in emulsion layer unit 115.
  • crossover reducing layers 111 and 113 are interposed between the screen 201 and the remote emulsion layer unit and are capable of intercepting and attenuating this remaining light. Both of these layers thereby contribute to reducing crossover exposure of emulsion layer unit 117 by the screen 201.
  • the screen 202 produces a sharp image in emulsion layer unit 117, and the light absorbing layers 111 and 113 similarly reduce crossover exposure of the emulsion layer unit 115 by the screen 202.
  • the radiographic element 100 is removed from association with the intensifying screens 210 and 202 and processed in a rapid access processor-that is, a processor, such as an RP-X-OmatTM processor, which is capable of producing a image bearing radiographic element dry to the touch in less than 90 seconds.
  • a rapid access processor that is, a processor, such as an RP-X-OmatTM processor, which is capable of producing a image bearing radiographic element dry to the touch in less than 90 seconds.
  • Rapid access processors are illustrated by Barnes et al U.S. Patent 3,545,971 and Akio et al published European Patent Application 248,390.
  • radiographic elements satisfying the requirements of the present invention are specifically identified as being those that are capable of emerging dry to the touch when processed in 90 seconds according to the following reference conditions:
  • the preferred radiographic elements of the present invention make possible the unique combination of advantages set forth above by employing (1) substantially optimally spectrally sensitized tabular grain emulsions in the emulsion layer units to reach low crossover levels while achieving the high covering power and other known advantages of tabular grain emulsions, (2) one or more particulate dyes in the interlayer units to further reduce crossover to less than 10 percent without emulsion desensitization and minimal or no residual dye stain, and (3) hydrophilic colloid swell and coverage levels compatible with obtaining uniform coatings, rapid access processing, and reduced or eliminated wet pressure sensitivity.
  • particulate dye optical densities of 1.00 are effective to reduce crossover to less than 10 percent
  • particulate dye densities can be increased until radiographic element crossover is effectively eliminated. For example, by increasing the particulate dye concentration so that it imparts a density of 2.0 to the radiographic element, crossover is reduced to only 1 percent.
  • the size of the dye particles is chosen to facilitate coating and rapid decolorization of the dye. In general smaller dye particles lend themselves to more uniform coatings and more rapid decolorization.
  • the dye particles employed in all instances have a mean diameter of less than 10.0 nm and preferably less than 1.0 u.m. There is no theoretical limit on the minimum sizes the dye particles can take.
  • the dye particles can be most conveniently formed by crystallization from solution in sizes ranging down to about 0.01 I lm or less. Where the dyes are initially crystallized in the form of particles larger than desired for use, conventional techniques for achieving smaller particle sizes can be employed, such as ball milling, roller milling, sand milling, and the like.
  • hydrophilic colloid layers can take any of various conventional forms, such as any of the forms set forth in Research Disclosure, Vol. 176, December 1978, Item 17643, Section IX, Vehicles and vehicle extenders the hydrophilic colloid layers are most commonly gelatin and gelatin derivatives (e.g., acetylated or phthalated gelatin). To achieve adequate coating uniformity the hydrophilic colloid must be coated at a layer coverage of at least 10 mg/dm 2 . Any convenient higher coating coverage can be employed, provided the total hydrophilic colloid coverage per side of the radiographic element does not exceed that compatible with rapid access processing.
  • Hydrophilic colloids are typically coated as aqueous solutions in the pH range of from about 5 to 6, most typically from 5.5 to 6.0, to form radiographic element layers.
  • the dyes which are selected for use in the practice of this invention are those which are capable of remaining in particulate form at those pH levels in aqueous solutions.
  • Dyes which by reason of their chromophoric make up are inherently ionic, such as cyanine dyes, as well as dyes which contain substituents which are ionically dissociated in the above-noted pH ranges of coating may in individual instances be sufficiently insoluble to satisfy the requirements of this invention, but do not in general constitute preferred classes of dyes for use in the practice of the invention.
  • dyes with sulfonic acid substituents are normally too soluble to satisfy the requirements of the invention.
  • nonionic dyes with carboxylic acid groups (depending in some instances on the specific substitution location of the carboxylic acid group) are in general insoluble under aqueous acid coating conditions. Specific dye selections can be made from known dye characteristics or by observing solubilities in the pH range of from 5.5 to 6.0 at normal layer coating temperatures-e.g., at a reference temperature of 40. C.
  • Preferred particulate dyes are nonionic polymethine dyes, which include the merocyanine, oxonol, hemioxonol, styryl, and arylidene dyes.
  • the merocyanine dyes include, joined by a methine linkage, at least one basic heterocyclic nucleus and at least one acidic nucleus.
  • the nuclei can be joined by an even number or methine groups or in so- called "zero methine" merocyanine dyes, the methine linkage takes the form of a double bond between methine groups incorporated in the nuclei.
  • Basic nuclei such as azolium or azinium nuclei, for example, include those derived from pyridinium, quinolinium, isoquinolinium, oxazolium, pyrazolium, pyrrolium, indolium, oxadiazolium, 3H- or 1 H-benzoindolium, pyrrolopyridinium, phenanthrothiazolium, and acenaph- thothiazolium quaternary salts.
  • Exemplary of the basic heterocyclic nuclei are those satisfying Formulae I and II. where
  • Merocyanine dyes link one of the basic heterocyclic nuclei described above to an acidic keto methylene nucleus through a methine linkage as described above.
  • Exemplary acidic nuclei are those which satisfy Formula III.
  • Useful hemioxonol dyes exhibit a keto methylene nucleus as shown in Formula III and a nucleus as shown in Formula IV.
  • Exemplary oxonol dyes exhibit two keto methylene nuclei as shown in Formula III joined through one or higher uneven number of methine groups.
  • Useful arylidene dyes exhibit a keto methylene nucleus as shown in Formula III and a nucleus as shown in Formula V joined by a methine linkage as described above containing one or a higher uneven number of methine groups.
  • a specifically preferred class of oxonol dyes for use in the practice of the invention are the oxonol dyes disclosed in Factor and Diehl European published patent application 299,435. These oxonol dyes satisfy Formula VI. wherein
  • arylidene dyes for use in the practice of the invention are the arylidene dyes disclosed in Diehl and Factor European published patent applications 274,723 and 294,461. These arylidene dyes satisfy Formula VII. wherein
  • Oxazole and oxazoline pyrazolone merocyanine particulate dyes are also contemplated. These particulate dyes can be represented by Formula VIII.
  • R, and R 2 are each independently substituted or unsubstituted alkyl or substituted or unsubstituted aryl, or together represent the atoms necessary to complete a substituted or unsubstituted 5-or 6-membered ring.
  • R 3 and R4 each independently represents H, substituted or unsubstituted alkyl, substituted or unsubstituted aryl, C0 2 H, or NHS0 2 R 6 .
  • R s is H, substituted or unsubstituted alkyl, substituted or unsubstituted aryl, carboxylate (i.e., COOR where R is substituted or unsubstituted alkyl), or substituted or unsubstituted acyl
  • R 6 and R 7 are each independently substituted or unsubstituted alkyl or substituted or unsubstituted aryl
  • n is 1 or 2.
  • R 8 is either substituted or unsubstituted alkyl, or is part of a double bond between the ring carbon atoms to which R 1 and R 2 are attached. At least one of the aryl rings of the dye molecule must have at least one substituent that is CO 2 H or NHSO 2 R 6 .
  • Oxazole and oxazoline benzoylacetonitrile merocyanine particulate dyes are also contemplated. These particulate dyes can be represented by Formula IX.
  • R 1 , R 2 , R 3 , R 4 , R 5 , and R 6 may each be substituted or unsubstituted alkyl or substituted or unsubstituted aryl, preferably substituted or unsubstituted alkyl of 1 to 6 carbon atoms or substituted or unsubstituted aryl of 6 to 12 carbon atoms.
  • R 7 may be substituted or unsubstituted alkyl of from 1 to 6 carbon atoms.
  • alkyl or aryl groups may be substituted with any of a number of substituents as is known in the art, other than those, such as sulfo substituents, that would tend to increase the solubility of the dye so much as to cause it to become soluble at coating pH's.
  • substituents include halogen, alkoxy, ester groups, amido, acyl, and alkylamino.
  • alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, n-pentyl, n-hexyl, or isohexyl.
  • aryl groups include phenyl, naphthyl, anthracenyl, pyridyl, and styryl.
  • R 1 and R 2 may also together represent the atoms necessary to complete a substituted or unsubstituted 5- or 6-membered ring, such as phenyl, naphthyl, pyridyl, cyclohexyl, dihydronaphthyl, or acenaphthyl.
  • This ring may be substituted with substituents, other than those, such as sulfo substituents, that would tend to increase the solubility of the dye so much as to cause it to become soluble at coating pH's.
  • substituents include halogen, alkyl, alkoxy, ester, amido, acyl, and alkylamino.
  • Useful bleachable particulate dyes can be found among a wide range of cyanine, merocyanine, oxonol, arylidene (i.e., merostyryl), anthraquinone, triphenylmethine, azo, azomethine, and other dyes of the type identified in published European patent applications 274,723 and 294,461. Such dyes satisfy Formula X.
  • D is a chromophoric light-absorbing compound, which may or may not comprise an aromatic ring if y is not 0 and which comprises an aromatic ring if y is 0,
  • A is an aromatic ring bonded directly or indirectly to D
  • X is a substituent, either on A or on an aromatic ring portion of D, with an ionizable proton
  • y is 0 to 4
  • n is 1 to 7, where the dye is substantially aqueous insoluble at a pH of 6 or below and substantially aqueous soluble at a pH of 8 or above.
  • Synthesis of the particulate dyes can be achieved by procedures known in the art for the synthesis of dyes of the same classes. For example, those familiar with techniques for dye synthesis disclosed in "The Cyanine Dyes and Related Compounds", Frances Hamer, Interscience Publishers, 1964, could readily synthesize the cyanine, merocyanine, merostyryl, and other polymethine dyes.
  • the oxonol, anthraquinone, triphenylmethane, azo, and azomethine dyes are either known dyes or substituent variants of known dyes of these classes and can be synthesized by known or obvious variants of known synthetic techniques forming dyes of these classes. Specific illustrations of dye preparations are provided by Dickerson et al U.S. Patent 4,803,150.
  • particulate bleachable dyes useful in the practice of this invention include the following:
  • the dye can be added directly to the hydrophilic colloid as a particulate solid or can be converted to a particulate solid after it is added to the hydrophilic colloid.
  • One example of the latter technique is to dissolve a dye which is not water soluble in a solvent which is water soluble.
  • the dye solution is mixed with an aqueous hydrophilic colloid, followed by noodling and washing of the hydrophilic colloid (see Research Disclosure, Item 17643, cited above, Section II), the dye solvent is removed, leaving particulate dye dispersed within the hydrophilic colloid.
  • any water insoluble dye which that is soluble in a water miscible organic solvent can be employed as a particulate dye in the practice of the invention, provided the dye is susceptible to bleaching under processing conditions-e.g., at alkaline pH levels.
  • contemplated water miscible organic solvents are methanol, ethyl acetate, cyclohexanone, methyl ethyl ketone, 2-(2-butoxyethoxy)ethyl acetate, triethyl phosphate, methylacetate, acetone, ethanol, and dimethylformamide.
  • Dyes preferred for use with these solvents are sulfonamide substituted arylidene dyes, specifically preferred examples of which are set forth about in Tables IIA and III.
  • the dyes employed in the under layer units must be substantially decolorized on processing.
  • substantially decolorized is employed to mean that the dye in the under layer units raises the minimum density of the radiographic element when fully processed under the reference processing conditions, stated above, by no more than 0.1, preferably no more than 0.05, within the visible spectrum. As shown in the examples below the preferred particulate dyes produce no significant increase in the optical density of fully processed radiographic elements of the invention.
  • UV absorber preferably blended with the dye in each of crossover reducing layers 111 and 113.
  • Any conventional UV absorber can be employed for this purpose.
  • Illustrative useful UV absorbers are those disclosed in Research Disclosure, Item 18431, cited above, Section V, or Research Disclosure, Item 17643, cited above, Section VIII(C).
  • Preferred UV absorbers are those which either exhibit minimal absorption in the visible portion of the spectrum or are decolorized on processing similarly as the crossover reducing dyes.
  • At least one additional hydrophilic colloid layer specifically at one halide emulsion layer unit comprised of a spectrally sensitized silver bromide or bromoiodide tabular grain emulsion layer. At least 50 percent (preferably at least 70 percent and optimally at least 90 percent) of the total grain projected area of the tabular grain emulsion is accounted for by tabular grains having a thickness less than 0.3 u.m (preferably less than 0.2 I Lm) and an average aspect ratio of greater than 5:1 (preferably greater than 8:1 and optimally at least 12:1).
  • Preferred tabular grain silver bromide and bromoiodide emulsions are those disclosed by Wilgus et al U.S. Patent 4,434,226; Kofron et al U.S. Patent 4,439,530; Abbott et al U.S. Patents 4,425,425 and 4,425,426; Dickerson U.S. Patent 4,414,304; Maskasky U.S. Patent 4,425,501; and Dickerson U.S. Patent 4,520,098.
  • the tabular grain emulsions are substantially optimally spectrally sensitized. That is, sufficient spectral sensitizing dye is adsorbed to the emulsion grain surfaces to achieve at least 60 percent of the maximum speed attainable from the emulsions under the contemplated conditions of exposure. It is known that optimum spectral sensitization is achieved at about 25 to 100 percent or more of monolayer coverage of the total available surface area presented by the grains.
  • the preferred dyes for spectral sensitization are polymethine dyes, such as cyanine, merocyanine, hemicyanine, hemioxonol, and merostyryl dyes. Specific examples of spectral sensitizing dyes and their use to sensitize tabular grain emulsions are provided by Kofron et al U.S. Patent 4,439,520.
  • the tabular grain emulsions are rarely put to practical use without chemical sensitization. Any convenient chemical sensitization of the tabular grain emulsions can be undertaken.
  • the tabular grain emulsions are preferably substantially optimally (as defined above) chemically and spectrally sensitized.
  • Useful chemical sensitizations including noble metal (e.g., gold) and chalcogen (e.g., sulfur and/or selenium) sensitizations as well as selected site epitaxial sensitizations, are disclosed by the patents cited above relating to tabular grain emulsions, particularly Kofron et al and Maskasky.
  • the emulsion layers can include as vehicles any one or combination of various conventional hardenable hydrophilic colloids alone or in combination with vehicle extenders, such as latices and the like.
  • vehicle extenders such as latices and the like.
  • the vehicles and vehicle extenders of the emulsion layer units can be identical to those of the interlayer units.
  • the vehicles and vehicle extenders can be selected from among those disclosed by Research Disclosure, Item 17643, cited above, Section IX.
  • Specifically preferred hydrophilic colloids are gelatin and gelatin derivatives.
  • each emulsion layer unit should contain a silver coverage from about 18 to 30 mg/dm 2 , preferably 21 to 27 mg/dm 2 .
  • overcoat layers can be formed of the same vehicles and vehicle extenders disclosed above in connection with the emulsion layers.
  • the overcoat layers are most commonly gelatin or a gelatin derivative.
  • the total hydrophilic colloid coverage on each major surface of the support must be at least 35 mg/dm 2. It is an observation of this invention that it is the total hydrophilic colloid coverage on each surface of the support and not, as has been generally believed, simply the hydrophilic colloid coverage in each silver halide emulsion layer that controls its wet pressure sensitivity.
  • the emulsion layer can contain as little as 20 mg/dm 2 of hydrophilic colloid.
  • the total hydrophilic coating coverage on each major surface of the support must be less than 65 mg/dm 2 , preferably less than 55 mg/dm 2 and the hydrophilic colloid layers must be substantially fully forehardened.
  • substantially fully forehardened it is meant that the processing solution permeable hydrophilic colloid layers are forehardened in an amount sufficient to reduce swelling of these layers to less than 300 percent, percent swelling being determined by the following reference swell determination procedure: (a) incubating said radiographic element at 38° C for 3 days at 50 percent relative humidity, (b) measuring layer thickness, (c) immersing said radiographic element in distilled water at 21 ° C for 3 minutes, and (d) determining the percent change in layer thickness as compared to the layer thickness measured in step (b).
  • This reference procedure for measuring forehardening is disclosed by Dickerson U.S. Patent 4,414,304. Employing this reference procedure, it is preferred that the hydrophilic colloid layers be sufficiently forehardened that swelling is reduced to less than 200
  • Transparent film supports such as any of those disclosed in Research Disclosure, Item 17643, cited above, Section XIV, are all contemplated. Due to their superior dimensional stability the transparent film supports preferred are polyester supports. Poly(ethylene terephthalate) is a specifically preferred polyester film support. The support is typically tinted blue to aid in the examination of image patterns. Blue anthracene dyes are typically employed for this purpose. In addition to the film itself, the support is usually formed with a subbing layer on the major surface intended to receive the under layer units. For further details of support construction, including exemplary incorporated anthracene dyes and subbing layers, refer to Research Disclosure, Item 18431, cited above, Section XII.
  • the radiographic elements can and in most practical applications will contain additional conventional features.
  • the emulsion layer units can contain stabilizers, antifoggants, and antikinking agents of the type set forth in Section II, and the overcoat layers can contain any of variety of conventional addenda of the type set forth in Section IV.
  • the outermost layers of the radiographic element can also contain matting agents of the type set out in Research Disclosure, Item 17643, cited above, Section XVI. Referring further to Research Disclosure, Item 17643, incorporation of the coating aids of Section XI, the plasticizers and lubricants of Section XII, and the antistatic layers of Section XIII, are each contemplated.
  • the intensifying screens can be selected from among various conventional intensifying screens, such as those disclosed in Research Disclosure, Item 18431, cited above, Section IX.
  • Intensifying screens typically consist of a support, which can be transparent, light absorbing, or reflective, depending upon the speed and sharpness required for the specific imaging application.
  • a fluorescent layer is coated on the support containing a phosphor and a binder.
  • Light absorbers such as carbon or dyes, light scattering materials, such as titania, and sometimes combinations of both can be employed to tailor the speed and/or sharpness of screen emission to match the requirements of a specific imaging application.
  • preferred phosphors include calcium tungstate (CaWO 4 .); niobium and/or rare earth activated yttrium, lutetium, and gadolinium tantalates; and rare earth activated rare earth oxychalcogenides and halides.
  • employed rare earths are elements having an atomic number of 39 or 57 through 71.
  • the rare earth oxychalcogenide and halide phosphors are preferably chosen from among those of the Formula XI. wherein:
  • the optimum assembly performance is realized when the optimum level of front screen X radiation absorption is achieved with the thinnest possible front screen phosphor layer. This requires use of phosphors with the highest absorption efficiencies known.
  • the optimum phosphors for construction of the front screen are calcium tungstate and niobium-activated or thulium-activated yttrium tantalate for ultraviolet and blue light emissions and terbium-activated gadolinium or lutetium oxysulfide for green light emissions.
  • the phosphors can be used in any conventional particle size range and distribution. It is generally appreciated that sharper images are realized with smaller mean particle sizes, but light emission efficiency declines with decreasing particle size. Thus, the optimum mean particle size for a given application is a reflection of the balance between imaging speed and image sharpness desired. Conventional phosphor particle size ranges and distributions are illustrated in the phosphor teachings cited above.
  • the same order of preference applies for phosphors used in the back screen as indicated above for the front screen.
  • the lower permissible MTF's and greater thicknesses of the back screen permit phosphors of somewhat lower efficiencies of absorption and/or emission to be employed while still satisfying acceptable imaging characteristics.
  • the phosphor layers need not contain a separate binder, in most applications the phosphor layers contain sufficient binder to give structural coherence to the phosphor layer.
  • the binders useful in the practice of the invention are those conventionally employed in the art. Binders are generally chosen from a wide variety of known organic polymers which are transparent to X radiation and emitted light.
  • Binders commonly employed in the art include sodium o-sulfobenzaldehye acetal of poly(vinyl alcohol); chlorosulfonated poly(ethylene); a mixture of macromolecular bisphenol poly(carbonates) and copolymers comprising bisphenol carbonates and poly(alkylene oxides); aqueous ethanol soluble nylons; poly(alkyl acrylates and methacrylates) and copolymers of poly(alkyl acrylates and methacrylates with acrylic and methacrylic acid); poly(vinyl butyral); and poly(urethane) elastomers. These and other useful binders are disclosed in U.S.
  • any conventional ratio of phosphor to binder can be employed. Generally thinner phosphor layers and sharper images are realized when a high weight ratio of phosphor to binder is employed. Preferred phosphor to binder ratios are in the range of from about 10:1 to 25:1 for screen constructions intended to equal commercial screen exposure repetitions without loss of structural integrity. For limited or single exposure applications it is, of course, appreciated that any minimal amount of binder consistent with structural integrity is satisfactory.
  • the phosphor layer is modified to impart a small, but significant degree of light absorption. If the binder is chosen to exhibit the desired degree of light absorption, then no other ingredient of the phosphor layer is required to perform the light attenuation function. For example, a slightly yellow transparent polymer will absorb a significant fraction of phosphor emitted blue light. Ultraviolet absorption can be similarly achieved. It is specifically noted that the less structurally complex chromophores for ultraviolet absorption particularly lend themselves to incorporation in polymers.
  • a separate absorber is incorporated in the phosphor layer to reduce its effective thickness.
  • the absorber can be a dye or pigment capable of absorbing light within the spectrum emitted by the phosphor. Yellow dye or pigment selectively absorbs blue light emissions and is particularly useful with a blue emitting phosphor. On the other hand, a green emitting phosphor is better used in combination with magenta dyes or pigments.
  • Ultraviolet emitting phosphors can be used with known ultraviolet absorbers. Black dyes and pigments are, of course, generally useful with phosphors, because of their broad absorption spectra. Carbon black is a preferred light absorber for incorporation in the phosphor layers. Luckey and Cleare U.S. Patent 4,259,588 teaches that increased sharpness (primarily attributable to reduced crossover, discussed below) can be achieved by incorporating a yellow dye in a terbium-activated gadolinium oxysulfide phosphor layer.
  • the patents cited above for phosphor teachings also disclose typical screen constructions.
  • the screen supports are most commonly film supports of high dimensional integrity, such as poly(ethylene terephthalate) film supports.
  • the phosphor layer contains an absorber or a black surface is positioned adjacent the anticurl layer during exposure.
  • a black poly(vinyl chloride) or paper sheet can be positioned adjacent the anticurl layer.
  • the adjacent interior surface of the cassette in which the assembly is mounted is a black polyurethane (or similar polymeric) foam layer, which can be relied upon for light absorption contributing to image sharpness.
  • the screen supports are not themselves black, best sharpness levels are realized when a black film or paper is interposed between the cassette and each screen of the image recording assembly.
  • the front screen support and/or its subbing and anticurl layers can be black or suitably colored to absorb emitted light, thereby minimizing light reflection and image sharpness degradation.
  • the back screen support as well as its subbing and anticurl layers can be of the same form as described for the front screen. If desired to increase speed, either or both of the front and back screen supports and/or their subbing and anticurl layers can be reflective of emitted light.
  • a blue or white back screen support can be chosen to reflect light emitted by calcium tungstate or rare earth-activated yttrium tantalate or a green or white support can be chosen to reflect light emitted from a rare earth-activated lutetium or gadolinium oxysulfide phosphor.
  • Titania is preferably coated on or incorporated in the front and back screen supports to maximize reflection of green light.
  • Metal layers, such as aluminum, can be used to enhance reflection.
  • Paper supports, though less common for intensifying screens than film supports, are known and can be used for specific applications. Dyes and pigments are commonly loaded into supports to enhance absorption or reflection of light. Air can be trapped in supports to reflect ultraviolet light.
  • Intensifying screen supports and the subbing layers used to improve coating adhesion can be chosen from among those employed for silver halide photographic and radiographic elements, as illustrated by Research Disclosure, Item 17643, cited above, Section XVII, and Research Disclosure, Item 18431, cited above, Section I.
  • overcoat though not required, is commonly located over the phosphor layer for humidity and wear protection.
  • the overcoat can be chosen using the criteria described above for the binder.
  • the overcoat can be chosen from among the same polymers used to form either the screen binder or the support, with the requirements of toughness and scratch resistance usually favoring polymers conventionally employed for film supports.
  • cellulose acetate is a preferred overcoat used with the preferred poly(urethane) binders.
  • Overcoat polymers are often used also to seal the edges of the phosphor layer.
  • anticurl layers are not required for the screens, they are generally preferred for inclusion.
  • the function of the anticurl layer is to balance the forces exerted by the layers coated on the opposite major surface of the screen support which, if left unchecked, cause the screen to assume a non-planar configuration-e.g., to curl or roll up on itself.
  • Materials forming the anticurl layers can be chosen from among those identified above for use as binders and overcoats.
  • an anticurl layer is formed of the same polymer as the overcoat on the opposite side of the support. For example, cellulose acetate is preferred for both overcoat and anticurl layers.
  • the overcoats of the phosphor layers can include a matting agent, although matting agents are more commonly included in radiographic elements than in screens.
  • matting agents can be chosen from among those cited by Research Disclosure, Item 17643, cited above, Section XVI.
  • a variety of other optional materials can be included in the surface coatings of the intensifying screens, such as materials to reduce static electrical charge accumulation, plasticizers, lubricants, and the like, but such materials are more commonly included in the radiographic elements which come into contact with the intensifying screens.
  • the assemblies of this invention consist of two intensifying screens and a separate low crossover radiographic element positioned between the intensifying screens. It is, however, recognized that the three elements can, if desired, be integrated into one or two elements merely by integrating one or both of the intensifying screens with the radiographic element.
  • the assembly can take the form of a double coated radiographic element having intensifying screens optically coupled on opposite sides that are peeled away for processing after imagewise exposure.
  • one or more of the intensifying screens take the form of a fluorescent layer positioned between the support and the emulsion layer unit it is intended to expose.
  • This screen has a composition and structure corresponding to that of a commercial, medium to high resolution screen. It consists of a terbium activated gadolinium oxysulfide phosphor having a median particle size of 5 to 6 ⁇ m coated on a blue dyed polyester support in a PermuthaneTM polyurethane binder at a total phosphor coverage of 3.1 g/dm 2 at a phosphor to binder ratio of 19:1.
  • This screen has a composition and structure corresponding to that of a commercial, high speed screen. It consists of a terbium activated gadolinium oxysulfide phosphor having a median particle size of 8 to 9 ⁇ m coated on a white pigmented polyester support in a PermuthaneTM polyurethane binder at a total phosphor coverage of 13.3 g/dm 2 at a phosphor to binder ratio of 19:1.
  • This screen has a composition and structure corresponding to that of a commercial, general purpose screen. It consists of a terbium activated gadolinium oxysulfide phosphor having a median particle size of 7 u.m coated on a white pigmented polyester support in a PermuthaneTM polyurethane binder at a total phosphor coverage of 7.0 g/dm 2 at a phosphor to binder ratio of 15:1.
  • This screen has a composition and structure corresponding to that of a commercial, medium resolution screen. It consists of a terbium activated gadolinium oxysulfide phosphor having a median particle size of 7 ⁇ m coated on a white pigmented polyester support in a PermuthaneTM polyurethane binder at a total phosphor coverage of 5.9 g/dm 2 at a phosphor to binder ratio of 15:1 and containing 0.017535% by weight of a 100:1 weight ratio of a yellow dye and carbon.
  • This screen has a composition and structure corresponding to that of a commercial, high resolution screen. It consists of a terbium activated gadolinium oxysulfide phosphor having a median particle size of 5 u.m coated on a blue tinted clear polyester support in a PermuthaneTM polyurethane binder at a total phosphor coverage of 3.4 g/dm 2 at a phosphor to binder ratio of 21:1 and containing 0.0015% carbon.
  • the relative emissions of electromagnetic radiation longer than 370 nm in wavelength of the intensifying screens were determined as follows:
  • the X-radiation response of each screen was obtained using a tungsten target X-ray source in an XRD 6TM generator.
  • the X-ray tube was operated at 70 kVp and 30 mA, and the X-radiation from the tube was filtered through 0.5 mm Cu and 1 mm AI filters before reaching the screen.
  • the emitted light was detected by a Princeton Applied Research model 1422/01 TM intensified diode array detector coupled to an Instruments SA model HR-320TM grating spectrograph. This instrument was calibrated to within ⁇ 0.5 nm with a resolution of better than 2 nm (full width at half maximum). The intensity calibration was performed using two traceable National Bureau of Standards sources, which yielded an arbitrary intensity scale proportional to Watts/nm/cm2. The total integrated emission intensity from 250 to 700 nm was calculated on a Princeton Applied Research model 1460 OMA IIITM optical multichannel analyzer by adding all data points within this region and multiplying by the bandwidth of the region.
  • Radiographic element A was a double coated radiographic element exhibiting near zero crossover.
  • Radiographic element A was constructed of a blue-tinted polyester support. On each side of the support a crossover reducing layer consisting of gelatin (1.6g/m z ) containing 320 mg/m 2 of a 1:1 weight ratio mixture of Dyes 56 and 59.
  • the same emulsion was identically coated over the crossover reducing layers on opposite sides of the support.
  • the emulsion was a green-sensitized high aspect ratio tabular grain silver bromide emulsion, where the term "high aspect ratio" is employed as defined by Abbott et al U.S. Patent 4,425,425 to require that at least 50 percent of the total grain projected area be accounted for by tabular grains having a thickness of less than 0.3 nm and having an average aspect ratio of greater than 8:1.
  • the emulsion exhibited an average grain diameter of 1.7 ⁇ m and an average grain thickness of 0.13 ⁇ m.
  • the emulsion was spectrally sensitized with 400 mg/Ag mol of anhydro-5,5-dichloro-9-ethyl-3,3'-bis(3-sulfopropyl)-oxacarbocyanine hydroxide, followed by 300 mg/Ag mol of potassium iodide.
  • the emulsion layers were each coated with a silver-coverage of 2.48 g/m 2 and a gelatin coverage of 2.85 g/m 2 .
  • Protective gelatin layers (0.89 g/m 2 ) were coated over the emulsion layers.
  • Each of the gelatin containing layers were hardened with bis(vinylsulfonylmethyl) ether at 1 % of the total gelatin.
  • Radiographic element B was a conventional double coated radiographic element exhibiting higher crossover levels.
  • the same emulsion was identically coated on opposite sides of the support.
  • the emulsion was a green-sensitized high aspect ratio tabular grain silver bromide emulsion.
  • the emulsion exhibited an average grain diameter of 2.1 ⁇ m and an average grain thickness of 0.10 ⁇ m.
  • the emulsion was spectrally sensitized with 800 mg/Ag mol of anhydro-5,5-dichloro-9-ethyl-3,3'-bis(3-sulfopropyl)oxacarbocyanine hydroxide, followed by 400 mg/Ag mol of potassium iodide.
  • the emulsion layers were each coated with a silver coverage of 2.10 g/m 2 and a gelatin coverage of 2.85 g/m 2 .
  • Protective gelatin layers (0.89 g/m 2 ) were coated over the emulsion layers.
  • Each of the gelatin containing layers were hardened with bis(vinylsulfonylmethyl) ether at 1 % of the total gelatin.
  • Radiographic element C was a conventional double coated radiographic element exhibiting extended exposure latitude.
  • Radiographic element C was constructed of a blue-tinted polyester support. Identical emulsion layers were coated on opposite sides of the support.
  • the emulsion employed was a green-sensitized polydispersed silver bromide emulsion.
  • the emulsion was a blend of two high aspect ratio tabular grain silver bromide emulsions having mean grain diameters of 2.1 and 1.2 ⁇ m and each having a mean grain thickness of about 0.1 um.
  • the emulsion was spectrally sensitized with 800 mg/Ag mol of anhydro-5,5-dichloro-9-ethyl-3,3'-bis(3-sulfopropyl)oxacarbocyanine hydroxide, followed by 400 mg/Ag mol of potassium iodide.
  • the emulsion layers were each coated with a silver coverage of 1.98 g/m 2.
  • Protective gelatin layers (0.89 g/m 2 ) were coated over the emulsion layers.
  • Each of the gelatin containing layers were hardened with bis-(vinylsulfonylmethyl) ether at 1 % of the total gelatin.
  • Radiographic element D was a double coated radiographic element exhibiting near zero crossover.
  • Radiographic element D was constructed of a low crossover support composite (LXO) identical to that of element A, described above.
  • LXO low crossover support composite
  • FLC Fast low contrast
  • SHC slow high contrast
  • Emulsion FLC When coated symmetrically, with Emulsion FLC coated on both sides of the support and Emulsion SHC omitted, using a Screen X pair, Emulsion FLC exhibited a relative log speed of 113 and an average contrast of 1.98. Similarly, Emulsion SHC when coated symmetrically with Emulsion FLC omitted exhibited a relative log speed of 69 and an average contrast of 2.61. The emulsions thus differed in average contrast by 0.63 while differing in speed by 44 relative log speed units (or 0.44 log E).
  • the Element D was oriented with the slower, higher contrast emulsion layer unit adjacent the front screen and the faster, lower contrast emulsion layer unit adjacent the back screen.
  • Optical densities are expressed in terms of diffuse density as measured by an X-rite Model 310TM densitometer, which was calibrated to ANSI standard PH 2.19 and was traceable to a National Bureau of Standards calibration step tablet.
  • the characteristic curve (density vs. log E) was plotted for each radiographic element processed. Speed, reported in relative log units, was measured at 1.0 above minimum density.
  • X-radiation noise power spectrum (NPSi) exposures were performed using a tungsten target X-ray tube (12 target angle) driven by a three phase, twelve pulse generator operated at 70kVp with 0.5 mm copper and 1 mm aluminum added filtration with a calculated half-value layer of 6.4 mm aluminum.
  • X-ray exposure values were measured using calibrated air ionization chambers (RADCALTM models 10X5-60; 20X5-60, 20X5-6M). These exposure values were converted to incident quantum fluence using a conversion factor determined from the half value layer and the calculated relationship between quantum fluence per unit exposure and half value layer for appropriate published X-ray spectra (R. Birch, M. Marshall, and G.M.
  • a low pass, 4 pole ButterworthTM electronic filter with the 3dB point set to the Nyquist frequency for the scan was inserted into the analog signal line of the microdensitometer. From these data, an effective scanning slit, 12.16 mm by 0.02 mm, was synthesized. The resulting 128 slit synthesized 256 point blocks were used to estimate the output noise power spectrum (NPSo).
  • the algorithm used is summared in a recent publication, P.C. Bunch, K.E. Huff, and R. VanMetter, "Analysis of the Detective Quantum Efficiency of a Radiographic Screen-Film Combination", J. Opt. Soc. Am. A, 4, 902-909 (1987).
  • Control Assembly Y/C/Y The inferiority of Control Assembly Y/C/Y is attributed to two factors. First, the radiographic film, Element C, exhibits crossover levels of greater than 10 percent, and second, the front and back screens are symmetrical, providing approximately the same light emissions to the radiographic element.
  • Control Assembly Z/B/X is next presented for comparison to Example Assembly Z/A/X. Note that the sole difference between these assemblies is the radiographic element.
  • the radiographic film, Element B exhibits a crossover of greater than 10 percent while the radiographic film, Element A, exhibits a crossover well below 10 percent.
  • Example Assembly Z/A/X over Control Assembly Z/B/X is confirmed in Figure 8, wherein contours have been provided which are the ratio of The contours greater than 1.0 confirm the superiority of Example Assembly Z/A/X over Control Assembly Z/B/X. Note that the highest improvements in DQE from about 2.0 to 7.5 and higher are realized at the higher log relative Q levels plotted, above about 1.23.
  • Example Assemblies Z/A/W and V/A/W demonstrate the invention using varied screen constructions.
  • the DQE contours produced by Example Assembly Z/A/W are shown in Figure 9.
  • the DQE contours produced by Example Assembly V/A/W are shown in Figure 10. Both figures demonstrate the advantageous features of the invention.
  • Figure 11 was generated similarly as Figure 4, except that Control Assembly Z/A/Z was substituted for Example Assembly Z/A/X.
  • the superiority of Example Assembly Z/A/X over Control Assembly Z/A/Z is confirmed in Figure 12, wherein contours have been provided which are the ratio of The contours greater than 1.0 confirm the superiority of Example Assembly Z/A/X over Control Assembly Z/A/Z.
  • the assymetrical screen assembly of the invention produces log Q advantages at lower relative frequencies.
  • Example Assembly Z/A/W produces improved image definition at lower spatial frequencies, making it superior for chest and adominal imaging applications were relatively large organ features are commonly viewed.
  • Figure 13 was generated similarly as Figure 4, except that Control Assembly X/A/X was substituted for Example Assembly Z/A/X.
  • the superiority of Example Assembly Z/A/X over Control Assembly X/A/X at higher spatial frequencies is confirmed in Figure 14, wherein contours have been provided which are the ratio of The contours greater than 1.0 confirm the superiority of Example Assembly Z/A/X over Control Assembly X/A/X.
  • Example Assembly Z/D/X the DQE levels of Example Assembly Z/D/X appear as contours in the plot of log Q vs. Spatial Frequency.
  • Figure 16 a similar plot is provided for Example Assembly Z/D/Z, which differs solely from Example Assembly Z/D/X in that identical front and back screens are employed. Even though the front and back screens are identical, the back emulsion layer unit-screen combination exhibits a photicity that is more than twice that of the front emulsion layer unit-screen combination.
  • Example Assembly Z/D/X which adds a screen imparted photicity difference to that imparted by the difference in emulsion layer units speeds, over Example Assembly Z/D/Z is demonstrated in Figure 17, wherein contours have been provided which are the ratio of The contours greater than 1.0 confirm the superiority of Example Assembly Z/D/X over Example Assembly Z/D/Z at lower spatial frequencies and lower exposure levels.
  • Example Assembly Z/D/X is therefore superior to Control Assembly Z/D/Z is viewing larger anatomical features that receive lower exposure levels, such as the portion of the spinal column that lies behind the heart.
  • Example Assembly Z/A/W provides superior DQE's at lower spatial frequencies, independent of the exposure level, and superior DQE's at higher exposure levels at all spatial frequencies.
  • Example Assembly Z/A/W is superior to Control Assembly Z/A/Z for producing radiographs of the chest cavity where the object is to obtain a sharp view of larger chest features and, additionally, a sharp view of detailed lung features. Since the lungs contain air, they have a restricted ability to attenuate X-radiation and therefore receive relatively large exposures.
  • Example Assembly Z/A/W for Control Assembly improves not only the view of the spinal column behind the heart (a lower exposure, lower spatial frequency feature), but also the view of the lungs (a less dense organ receiving a higher exposure level and having both lower and higher spatial frequency features of potential interest).

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WO1993011458A1 (fr) * 1991-11-27 1993-06-10 E.I. Du Pont De Nemours And Company Colorants de sensibilisation a l'arylidene pour grains tabulaires
WO1995021402A1 (fr) * 1994-02-04 1995-08-10 Eastman Kodak Company Systeme radiographique destine a l'imagerie orthopedique

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JP2784702B2 (ja) * 1991-11-26 1998-08-06 富士写真フイルム株式会社 エネルギーサブトラクション方法
JP2770207B2 (ja) * 1991-11-15 1998-06-25 富士写真フイルム株式会社 Ｘ線画像読取方法

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GB466249A (en) * 1935-10-09 1937-05-25 Kali Chemie Ag X-ray film assembly
DE1472865A1 (de) * 1964-10-23 1969-01-23 Eastman Kodak Co Radiographisches Material
DE2449149A1 (de) * 1973-10-17 1975-04-24 Du Pont Roentgenographisches aufzeichnungsmaterial
AT357031B (de) * 1977-04-08 1980-06-10 Bernhardt Karl Heinz Verfahren zur herstellung einer fotografischen kopie von einer transparenten vorlage
EP0065877A1 (fr) * 1981-05-26 1982-12-01 Minnesota Mining And Manufacturing Company Système industriel à rayons X
US4425426A (en) * 1982-09-30 1984-01-10 Eastman Kodak Company Radiographic elements exhibiting reduced crossover
EP0276566A1 (fr) * 1986-12-23 1988-08-03 EASTMAN KODAK COMPANY (a New Jersey corporation) Elément radiographique à effet interimage réduit

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GB466249A (en) * 1935-10-09 1937-05-25 Kali Chemie Ag X-ray film assembly
DE1472865A1 (de) * 1964-10-23 1969-01-23 Eastman Kodak Co Radiographisches Material
DE2449149A1 (de) * 1973-10-17 1975-04-24 Du Pont Roentgenographisches aufzeichnungsmaterial
AT357031B (de) * 1977-04-08 1980-06-10 Bernhardt Karl Heinz Verfahren zur herstellung einer fotografischen kopie von einer transparenten vorlage
EP0065877A1 (fr) * 1981-05-26 1982-12-01 Minnesota Mining And Manufacturing Company Système industriel à rayons X
US4425426A (en) * 1982-09-30 1984-01-10 Eastman Kodak Company Radiographic elements exhibiting reduced crossover
US4425426B1 (fr) * 1982-09-30 1988-08-09
EP0276566A1 (fr) * 1986-12-23 1988-08-03 EASTMAN KODAK COMPANY (a New Jersey corporation) Elément radiographique à effet interimage réduit

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1993011458A1 (fr) * 1991-11-27 1993-06-10 E.I. Du Pont De Nemours And Company Colorants de sensibilisation a l'arylidene pour grains tabulaires
US5275928A (en) * 1991-11-27 1994-01-04 E. I. Du Pont De Nemours And Company Arylidene sensitizing dyes for tabular grains
WO1995021402A1 (fr) * 1994-02-04 1995-08-10 Eastman Kodak Company Systeme radiographique destine a l'imagerie orthopedique

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EP0384634A3 (fr) 1990-11-07

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