Radiation imagery chemistry: process – composition – or product th – Luminescent imaging
Reexamination Certificate
2001-11-26
2003-02-11
Letscher, Geraldine (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Luminescent imaging
C430S502000, C430S567000, C430S966000, C430S517000
Reexamination Certificate
active
06517986
ABSTRACT:
FIELD OF THE INVENTION
This invention is directed to a low silver radiographic film that can be rapidly processed and directly viewed. This film has an improved visual appearance. This invention also provides a film/screen imaging assembly for radiographic purposes, and a method of processing the film to obtain a black-and-white image.
BACKGROUND OF THE INVENTION
Over one hundred years ago, W. C. Roentgen discovered X-radiation by the inadvertent exposure of a silver halide photographic element. In 1913, Eastman Kodak Company introduced its first product specifically intended to be exposed by X-radiation (X-rays). Today, radiographic silver halide films account for the overwhelming majority of medical diagnostic images. Such films provide viewable black-and-white images upon imagewise exposure followed by processing with the suitable wet developing and fixing photochemicals.
In medical radiography an image of a patient's anatomy is produced by exposing the patient to X-rays and recording the pattern of penetrating X-radiation using a radiographic film containing at least one radiation-sensitive silver halide emulsion layer coated on a transparent support. X-radiation can be directly recorded by the emulsion layer where only low levels of exposure are required. Because of the potential harm of exposure to the patient, an efficient approach to reducing patient exposure is to employ one or more phosphor-containing intensifying screens in combination with the radiographic film (usually both in the front and back of the film). An intensifying screen absorbs X-rays and emits longer wavelength electromagnetic radiation that the 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 “dual coated” radiographic film so the film can provide suitable images with less exposure. Of course, a number of commercial products provide assemblies of both dual coated films in combination with two intensifying screens to allow the lowest possible patient exposure to X-rays. Typical arrangements of film and screens are described in considerable detail for example in U.S. Pat. No. 4,803,150 (Dickerson et al.), U.S. Pat. No. 5,021,327 (Bunch et al.), and U.S. Pat. No. 5,576,156 (Dickerson).
Medical radiographic X-radiation films are currently manufactured with several different contrasts in order to meet the diverse radiographic imaging needs. These include high contrast films such as commercially available KODAK TMAT-G Film and low contrast films such as KODAK TMAT-L Film. High contrast films are designed to image anatomy parts that exhibit a narrow range of X-radiation absorbance (such as bones). Medium and low contrast films are designed to image simultaneously several different types of anatomy having different X-radiation absorbance. Radiography of the thoracic cavity (chest) is an example of this need where radiologists need to image the relatively radio-opaque mediastinal area (behind the vertebral column, heart and diaphragm). These areas are quite dense and require greater amounts of X-radiation for desired penetration and imaging on a film. However, it is also desired to image the more radio-transparent lungs. Such imaging requires less X-radiation. KODAK InSight™. IT Film and KODAK InSight™ VHC Film, and the appropriate intensifying screens, are low crossover systems designed to record this wide range of tissue densities with high imaging quality and varying exposure latitude.
During recent years as radiographic films were designed to have high resolution, similar improvements were being achieved in the reduction of processing time. Only a few years ago, processing cycles (“dry to dry”) of 90 seconds were the standard in the industry. More recent processing systems such as Eastman Kodak's Rapid Access (RA) system that include forehardened films, special processing chemistry and rapid processing equipment, has reduced the processing cycle to 40 seconds. Because of this trend to faster processing, great demands are placed on the drying of radiographic films since the other processing steps (development, fixing, and washing) are being shortened.
In view of today's needs to reduce health costs, to provide rapid processing, and to minimize the impact of discarded processing chemicals to the environment, even greater demands are placed on medical radiographic films. One approach to meeting those needs is to reduce the level of silver in the films while optimizing the “covering power” of the coated silver halide emulsions.
Previous discoveries have led to useful radiographic films containing reduced amounts of silver as described for example in U.S. Pat. No. 5,876,913 (Dickerson et al.) and U.S. Pat. No. 5,800,976 (Dickerson et al.). The films described in these patents exhibit acceptable image tone as measured using the conventional CIELAB (Commission Internationale de l'Eclairage) color scale.
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.
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. It is to this problem that the present invention is addressed. Thus, there is a need to improve visual appearance by reducing or eliminating the undesirable green tint (change in a* value) while maintaining or improving image tone (b* value) in radiographic films having minimal silver.
SUMMARY OF THE INVENTION
The present invention provides a solution to the noted problems with a radiographic silver halide film comprising a transparent support, the film having disposed on each side of the support, one or more hydrophilic colloid layers including at least one silver halide emulsion layer,
each of the silver halide emulsion layers comprising silver halide tabular grains that (a) have the same or different composition in each silver halide emulsion layer, (b) account for at least 50% of the total grain projected area within each silver halide emulsion layer, and (c) have an average aspect ratio of greater than 5,
the silver coverage on each side of the support being from about 10 to about 14 mg/dm
2
,
each silver halide emulsion layer comprising one or more hydrophilic polymer vehicles at a total coverage of from about 7 to about 20 mg/dm
2
,
the level of hardener on each side of the support being from about 0.3 to about 1 weight % based on total polymer vehicles on that side,
the radiographic silver halide film further comprising in one or more of the silver halide emulsion layers, a colorant that is present in an amount sufficient to provide a film a* value of from about −3.2 to about −2.0 at a film b* value of −7.
In preferred embodiments, the present invention provides a radiographic silver halide film comprising a transparent polymeric support, the film having disposed on each side of the support, two or three hydrophilic colloid layers including a single silver halide emulsion layer on each side of the support,
each of the silver halide emulsion layers comprising silver halide tabular grains that (a) have the same or different composition in each silver halide emulsion layer, (b) account for at least 80% of the total grain projected area within each silver halide emulsion layer, and (c) have an average aspect ratio of greater than 8, each silver halide emulsion layer being
Eastman Kodak Company
Letscher Geraldine
Tucker J. Lanny
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