Radiation imagery chemistry: process – composition – or product th – Luminescent imaging
Reexamination Certificate
2003-03-26
2004-02-03
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Luminescent imaging
C430S434000, C430S502000, C430S567000, C430S569000, C430S611000, C430S642000, C430S966000, C430S967000
Reexamination Certificate
active
06686115
ABSTRACT:
FIELD OF THE INVENTION
This invention is directed to radiography. In particular, it is directed to blue light-sensitive, radiographic silver halide films that provide improved medical diagnostic images with higher contrast, desired image tone, and have improved processing characteristics. This invention also provides an imaging assembly and a method of radiographic imaging using these improved radiographic films.
BACKGROUND OF THE INVENTION
The use of radiation-sensitive silver halide emulsions for medical diagnostic imaging can be traced to Roentgen's discovery of X-radiation by the inadvertent exposure of a silver halide film. Eastman Kodak Company then introduced its first product specifically that was intended to be exposed by X-radiation in 1913. The discovery of X-rays in 1895 provided the beginning of a new way of providing medical evaluation and diagnosis. Prior to that time, medical examination comprised predominantly manual probing and consideration of symptoms. Such examinations would obviously be incomplete and inconclusive in most instances, and incorrect in some instances. In some cultures, there was a prohibition of touching the female anatomy, further limiting the effectiveness of medical examination. Thus, the discovery that X-radiation could pass through the body with relatively little harm and provide useful images provided a powerful tool in medical diagnosis and treatment.
In conventional medical diagnostic imaging the object is to obtain an image of a patient's internal anatomy with as little X-radiation exposure as possible. The fastest imaging speeds are realized by mounting a dual-coated radiographic element between a pair of fluorescent intensifying screens for imagewise exposure. About 5% or less of the exposing X-radiation passing through the patient is adsorbed directly by the latent image forming silver halide emulsion layers within the dual-coated radiographic element. Most of the X-radiation that participates in image formation is absorbed by phosphor particles within the fluorescent screens. This stimulates light emission that is more readily absorbed by the silver halide emulsion layers of the radiographic element.
Examples of radiographic element constructions for medical diagnostic purposes are provided by U.S. Pat. No. 4,425,425 (Abbott et al.) and U.S. Pat. No. 4,425,426 (Abbott et al.), U.S. Pat. No. 4,414,310 (Dickerson), U.S. Pat. No. 4,803,150 (Dickerson et al.), U.S. Pat. No. 4,900,652 (Dickerson et al.), U.S. Pat. No. 5,252,442 (Tsaur et al.), and
Research Disclosure,
Vol. 184, August 1979, Item 18431.
Problem to be Solved
Some commercial radiographic films that are available from Eastman Kodak Company and Agfa-Gevaert are sensitive to blue light and designed to be used in combination with blue-emitting fluorescent intensifying screens such as those containing calcium tungstate as the phosphor. Those films generally contain high silver coverage in the form of grains having cubic or other 3-dimensional morphology. The emulsion layers in those films are relatively “soft” meaning that relatively low levels of film hardener are used, in order to maximize covering power and to reduce drying time after processing with wet chemistries. However, the higher silver coverage contributed to longer processing times.
In addition, the silver halide emulsions in such films are generally “internally fogged” meaning that the emulsion grains have internal latent image sensitivity. Such emulsions, when coated in combination with high silver iodide emulsions sufficient to release iodide upon development to render the internally fogged emulsion developable, results in higher covering power than would be possible with the silver iodide emulsions. This property can provide the advantage of lower silver coverage and improved processing compared to higher silver-containing films, but it is also disadvantageous in that if the developer is contaminated with photographic fixers from the fixing tank, the internally fogged emulsion is developer prematurely and provided high fogging (D
min
).
Early radiographic films were processed manually in trays before automatic processors were available. Manual processing is still used to day in some parts of the world. This process generally requires the operator to visually determine if the processed film is “dark” enough and thus if development has proceeded for a sufficient period of time. Obviously, this process is prone to errors in image formation and varying sensitometric properties such as image tone.
Images can be identified as “cold” or “warm” depending upon where they fall within the noted color scale as defined by a* and b* values. A “cold” image would be one that is on the bluish side of neutral (that is, a negative b* value) and a “warm” image would be one that is the yellowish of positive b* side of neutral, both measured at a density of 1.0 (for dual-coated films). The a* value is a measure of redness (positive a* value) or greenness (negative a* value). Such measurements can be obtained using known techniques, for example as described by Billmeyer et al.,
Principles of Color Technology,
2
nd
Ed., Wiley & Sons, New York, 1981, Chapter 3.
For medical diagnostic films, it is generally desired that the film exhibit a sufficiently cold image tone to provide a b* value more negative than −6.0 and preferably more negative than −7.0. This requires more than merely adding specific tinting dyes to the film support or silver halide emulsion layers, and when other components of the film are changed to acquire desirable sensitometric results, the image tone can also be changed in an undesirable fashion. For example, while known medical radiographic films exhibit the desired b* values (bluish tone), it has been found that when silver coverage is reduced, some of them exhibit an unacceptable green tint, particularly at high densities.
U.S. Pat. No. 5,876,913 (Dickerson et al.) describes radiographic films having reduced hydrophilic colloid in tabular grain emulsions to provide colder image tone. In addition, the patent describes the use of various “covering power enhancing” compounds such as various mercapto-substituted heterocycles such as 2-mercaptobenzothiazole. Additional compounds of this type are described in U.S. Pat. No. 4,013,470 (Landon, Jr.) for use in combination with quaternary ammonium salts in photographic prints to provide “warmer” image ones.
There is a desire in the industry to have “blue-sensitive” or “blue-light sensitive” radiographic films that have reduced silver coverage and improved processability without significant loss of desired sensitometric properties. In addition, it is desired to provide “colder” image tone in these films despite variations in process conditions and reduction in silver coverage.
SUMMARY OF THE INVENTION
The present invention provides a blue-sensitive, radiographic silver halide film comprising a support having first and second major surfaces,
the radiographic silver halide film having disposed on the first major support surface, one or more hydrophilic colloid layers including a first silver halide emulsion layer, and on the second major support surface, one or more hydrophilic colloid layers including a second silver halide emulsion layer,
the first silver halide emulsion layer comprising predominantly tabular silver halide grains that have an aspect ratio of at least 15, a grain thickness of at least 0.1 &mgr;m, and comprise at least 90 mol % bromide and from about 0.5 to about 2.75 mol % iodide, based on total silver halide, substantially all of the iodide being present in an internal localized portion of the tabular silver halide grains that excludes the surface of the grains,
wherein the tabular silver halide grains in the first silver halide emulsion layer are dispersed in a hydrophilic polymeric vehicle mixture comprising at least 0.5% of oxidized gelatin, based on the total dry weight of the polymeric vehicle mixture, and
wherein the first silver halide emulsion layer further comprises a mercapto-substituted benzothiazole, benzoxazole, or
Davis Richard F.
Dickerson Robert E.
Mroczek Susan K.
Eastman Kodak Company
Schilling Richard L.
Tucker J. Lanny
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