Radiation imagery chemistry: process – composition – or product th – Luminescent imaging
Reexamination Certificate
2000-11-06
2002-03-26
Letscher, Geraldine (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Luminescent imaging
C430S496000, C430S508000, C430S966000, C430S567000, C430S963000, C430S502000
Reexamination Certificate
active
06361918
ABSTRACT:
FIELD OF THE INVENTION
This invention is directed to a high speed and high contrast radiographic film that can be rapidly processed and directly viewed. This invention also provides a film/screen imaging assembly for radiographic purposes, and a method of processing the film to obtain a high contrast 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).
Radiographic films that can be rapidly wet processed (that is, processed in an automatic processor within 90 seconds and preferably less than 45 seconds) are also described in the noted U.S. Pat. No. 5,576,156. Typical processing cycles include contacting with a black-and-white developing composition, desilvering with a fixing composition, and rinsing and drying. Films processed in this fashion are then ready for image viewing. In recent years, there has been an emphasis in the industry for more rapidly processing such films to increase equipment productivity and to enable medical professionals to make faster and better medical decisions.
As could be expected, image quality and workflow productivity (that is processing time) are of paramount importance in choosing a radiographic imaging system [radiographic film and intensifying screen(s)]. One problem encountered using known systems is that these requirements are not necessarily mutually inclusive. Some film/screen combinations provide excellent image quality but cannot be rapidly processed. Other combinations can be rapidly processed but image quality may be diminished. Both features are not readily provided at the same time. Still again, some films have high contrast but lack sufficient photographic speed.
Rhodium-doped emulsions have been used in the graphic arts industry as well as radiography in recent years to provide films for radiation therapy imaging. Such emulsions are generally useful for obtaining high contrast images. Generally, higher contrast is achieved as a result of a significant loss in photographic speed as the rhodium dopant preferentially slows down the largest and fastest silver halide grains in the emulsion. As a result of the loss in speed, rhodium dopants are used generally only in the slower speed films.
In radiology, X-radiation exposure is very important as excessive X-radiation is potentially harmful and a design of a very slow speed film would be impractical. With these constraints in mind, the industry has been looking for a radiation therapy film and film/screen combination that has the desired image quality, rapid processability, high contrast and high speed.
SUMMARY OF THE INVENTION
The present invention provides a solution to the noted problems with a high speed radiographic silver halide film comprising a support having first and second major surfaces and that is capable of transmitting X-radiation,
the film having disposed on the first major support surface, one or more hydrophilic colloid layers including a silver halide emulsion layer, and on the second major support surface, one or more hydrophilic colloid layers including a 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, (c) have an average thickness of from about 0.09 to about 0.11 &mgr;m, and (d) have an average aspect ratio of greater than 5,
all hydrophilic layers of the film being fully forehardened and wet processing solution permeable for image formation within 45 seconds, and
one or more of the silver halide emulsion layers also comprising a rhodium dopant for the tabular silver halide grains, the rhodium dopant being present independently, in an amount of from about 1×10
−5
to about 5×10
−5
mole per mole of silver.
This invention also provides a radiographic imaging assembly comprising the radiographic film described above provided in combination with an intensifying screen on either side of the film.
Further, this invention provides a method comprising contacting the radiographic film described above, sequentially, with a black-and-white developing composition and a fixing composition, the method being carried out within 90 seconds to provide a black-and-white image.
The films of this invention have high speed and can provide high contrast black-and-white image using specific amounts of rhodium dopants and silver halide grains having a specific average thickness. Particulate microcrystalline dyes that are often used to provide crossover control are not present in the films of this invention.
In addition, all other desirable sensitometric properties are maintained, crossover is desirably low, and the films can be rapidly processed in conventional processing equipment and compositions.
DETAILED DESCRIPTION OF THE INVENTION
The term “contrast” as herein employed indicates the average contrast (also referred to as &ggr;) derived from a characteristic curve of a radiographic element using as a first reference point (1) a density (D
1
) of 0.25 above minimum density and as a second reference point (2) a density (D
2
) of 2.0 above minimum density, where contrast is &Dgr;D (i.e. 1.75)÷&Dgr;log
10
E (log
10
E
2
−log
10
E
1
), E
1
and E
2
being the exposure levels at the reference points (1) and (2).
“Lower scale contrast” is the slope of the characteristic curve measured between of a density of 0.85 to the density achieved by shifting −0.3 log E units.
“Upper scale contrast” is the slope of the characteristic curve measured between a density of 1.5 above D
min
to 2.5 above D
min
.
“Mid-scale contrast” is the slope of the characteristic curve measured between a density of 0.25 above D
min
to 2.0 above D
min
Photographic “speed” refers to the exposure necessary to obtain a density of at least 1.0 plus D
min
.
“Dynamic range” refers to the range of exposures over which useful images can be obtained.
The term “fully forehardened” is employed to indicate the forehardening of hydrophilic colloid layers to a level that limits the weight gain of a radi
Dickerson Robert E.
Preddy Carl R.
Eastman Kodak Company
Letscher Geraldine
Tucker J. Lanny
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