Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Two or more radiation-sensitive layers containing other than...
Reexamination Certificate
2000-11-06
2002-05-21
Le, Hoa Van (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Two or more radiation-sensitive layers containing other than...
C430S139000
Reexamination Certificate
active
06391531
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 is particularly useful for thoracic imaging. In addition, the radiographic film of this invention also has excellent exposure latitude. 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 differing X-radiation absorbance. Radiography of the thoracic cavity (chest) is an example of this need there radiologists need to image the relatively radioopaque 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 radiotransparent 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.
Control of intensifying screen light crossover has been very important for providing high-resolution medical X-radiation films. “Crossover” refers to exposure of an emulsion from light emitted by an intensifying screen on the opposite of the film and results in reduced image sharpness. Approaches to achieve crossover control include the use of high aspect ratio tabular silver halide emulsions containing spectral sensitizing dyes. This approach can reduce crossover from 30% to 18%. Further reduction in crossover below 10% has been achieved using microcrystalline dyes in the silver halide emulsion or antihalation layer. These microcrystalline dyes are readily decolorized during the wet processing cycle so they are not visible in the resulting image.
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, greater demands are placed on the drying of radiographic films since the other processing steps (development, fixing, and washing) are being shortened.
The greatest problem has been to quickly process low crossover radiographic films that include particulate filter dyes in a separate layer because that feature adds additional film thickness that must be dried.
With these constraints in mind, the industry has been looking for a thoracic radiographic film that would provide good lung field information while also providing information in more radiopaque areas such as the mediastinum and retrocardiac regions. It is also desirable to have a radiographic film/screen combination that has the desired image quality, rapid processability, and high resolution.
SUMMARY OF THE INVENTION
The present invention provides a solution to the noted problems with a 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, two or more hydrophilic colloid layers including first and second silver halide emulsion layers, and on the second major support surface, two or more hydrophilic colloid layers including third and fourth silver halide emulsion layers, the first and third silver halide emulsion layers being closer to the support than the second and fourth silver halide emulsion layers,
each of the first, second, third and fourth 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 less than 0.3 &mgr;m, and (d) have an average aspect ratio of greater than 5,
the silver coverage on each side of the support being from about 15 to about 20 mg/dm
2
,
all hydrophilic layers of the film being fully forehardened and wet processing solution permeable for image formation within 45 seconds,
the first and third silver halide emulsion layers comprising at least one particulate dye that is (a) capable of absorbing radiation to which the silver halide emulsions are sensitive, (b) present in an amount sufficient to reduce crossover to less than 15%, and (c) capable of being substantially decolorized during wet processing,
the first and third silver halide emulsion layers also comprising a rhodium dopant for the tabular silver halide grains, the rhodium dopant being present in each silver halide emulsion layer in an amount, independently, of from about 1×10
−5
to about 5×10
−5
mole per mole of silver in each emulsion layer,
the ratio of photographic speed of the first silver halide emulsion layer to the second silver halide emulsion layer and the ratio of the third silver halide emulsion layer to the fourth silver halide emulsion layer being independently greater than 0.3 log E.
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
Eastman Kodak Company
Le Hoa Van
Tucker J. Lanny
LandOfFree
Low silver radiographic film and imaging assembly for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Low silver radiographic film and imaging assembly for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Low silver radiographic film and imaging assembly for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2905290