Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
2000-03-22
2001-03-13
Le, Hoa Van (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C430S581000
Reexamination Certificate
active
06200743
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a light-sensitive silver halide photographic emulsion, a material comprising said emulsion and a screen-film combination of a radiographic intensifying phosphor screen and said material.
BACKGROUND OF THE INVENTION
Tabular silver halide grains are grains possessing two parallel crystal faces with an aspect ratio of two or more. Said aspect ratio is defined as the ratio between the diameter of a circle having an equivalent surface area as one of these crystal faces, and the thickness, being the distance between the two major faces.
Tabular grains are known in the photographic art for quite some time. As early as 1961 Berry et al. described the preparation and growth of tabular silver bromoiodide grains in Photographic Science and Engineering, Vol 5, No 6. A discussion of tabular grains appeared in Duffin, Photographic Emulsion Chemistry, Focal Press, 1966,p.66-72.
Early patent literature includes Bogg U.S. Pat. No. 4,063,951, Lewis U.S. Pat. No. 4,067,739 and Maternaghan U.S. Pat. Nos. 4,150,994; 4,184,877 and 4,184,878. However the tabular grains described herein cannot be regarded as showing a high diameter to thickness ratio, commonly termed aspect ratio. In a number of U.S. patents filed in 1981 and issued in 1984 tabular grains with high aspect ratio and their advantages in photographic applications are described as e.g. U.S. Pat. Nos. 4,434,226; 4,439,520; 4,425,425 and 4,425,426 and in Research Disclosure, Volume 225, January 1983, Item 22534.
Anisotropic growth characteristics for the said tabular grains are known to be due to the formation of parallel twin planes in the nucleation step of the precipitation. However for the said {111} tabular silver halide grains rich in silver chloride use of a crystal habit modifier in relatively high amounts is therefore required, as has been illustrated in U.S. Pat. Nos. 4,713,323; 4,804,621; 5,176,692; 5,183,732; 5,185,239; 5,252,452; 5,286,621; 5,298,385 and 5,298,388. Treatment with iodide of tabular grain emulsions having {111} crystals rich in silver chloride in order to get an enhanced morphological stability and enhanced photographic performance has been disclosed in EP-A 0 678 772 and in Research Disclosure 388046, published Aug. 1, 1996.
However as a global result fairly heterogeneous emulsion crystal distributions are obtained: a common variability coefficient (defined as a ratio between average standard deviation on equivalent circular diameter and the said average equivalent circular diameter) of 0.30 to 0.60 is calculated, partly due to the presence of quite a large number of non-tabular grains having a sphere equivalent diameter of less than 0.3 &mgr;m. Moreover differences in thickness growth are observed, said differences leading to unevenness as a consequence of observed differences in image tone.
Heterodispersity of grain morphology further leads to e.g. uncontrolled chemical and spectral sensitization, lower contrast and lower covering power, thereby losing typical advantages of the said grains as referred to hereinbefore.
Until now efforts in order to get more monodisperse tabular silver halide crystal distributions in emulsion preparation have been directed towards silver halide crystals rich in silver bromide as has e.g. been described in U.S. Pat. Nos. 4,797,354; 5,147,771; 5,147,772; 5,147,773; 5,171,659; 5,248,587; 5,204,235; 5,210,013; 5,215,879; 5,250,403; 5,252,442, 5,252,453; 5,254,453; 5,318,888; 5,439,787; 5,472,837; 5,482,826 and 5,484,697 and in Research Disclosure No. 391, p. 713-723 (1996).
Many attempts have been made in order to improve the degree of homogeneity of the size and shape of the crystals but the majority of them is related with tabular grains rich in silver bromide. So radiographic materials comprising emulsions having monodisperse tabular silver brom(oiod)ide crystals have e.g. been described in U.S. Pat. Nos. 5,252,442 and 5,508,158. The same preparation methods as for the forementioned tabular grains rich in silver bromide can however not be applied as such in preparing tabular grains rich in silver chloride, especially due to the presence of crystal habit modifiers or stabilizers, usually adenine or more generally aminoazaindenes, as this leads to the disadvantages set forth hereinbefore. Stabilization of the crystal habit of anisotropically grown crystals having flat parallel twins however remains an ever lasting demand.
Combinations of intensifying screens provided with luminescent phosphors and light-sensitive silver halide photographic materials are conventionally used for medical diagnosis. By X-ray radiation the luminescent phosphors in the screen panel or panels are converting X-rays into visible radiation, thereby exposing the film material in contact with the said panel (for single-side coated materials as e.g. in mammography) or panels (for duplitized materials as e.g. in chest imaging).
In mammography e.g. the compressed breast is irradiated with soft X-rays emitted from an X-ray generating device and the modulated X-rays are detected with a radiographic X-ray conversion screen, also called intensifying screen, fluorescent screen or phosphor screen. The X-ray conversion screen comprises a luminescent phosphor which converts the absorbed X-rays into visible light and the emitted visible light exposes a silver halide film that is brought into contact with said X-ray conversion screen. After film processing, comprising the steps of developing, fixing, rinsing and drying, a mammogram is obtained which can be read on a light box. No other field of medical radiology demands such a high level of image quality as mammography and the ability of the mammogram to portray relevant diagnostic information is highly determined by the image quality of the screen-film system. Image quality is manifested by a number of features in the image including sharpness, noise, contrast, silver image colour and skin line perceptibility. Conventional mammography films can roughly be classified in low and high contrast types according to the value of their average gradation as defined above. The low contrast type can be characterized by a relatively low average gradation ranging from 2.0 to 2.5 whereas the average gradation of the high contrast type may range higher than 3.0. Often, high contrast films are preferred because of the higher ability to detect tiny cancers deep in the glandular tissue of the breast. If the contrast is too high, however, it may preclude visualization of both thin (i.e. the skin line) and thick tissues (i.e. the inside of the breast) in the same image due to lack of exposure latitude. Therefore, some radiologists prefer low contrast mammography films. When the contrast is low, skin line perceptibility is excellent, but then the chance of missing possibly malignant breast lesions is high. Thus a balance has to be found between contrast and exposure latitude and an example of this approach has been described in U.S. Pat. No. 5,290,655.
Maintaining the image quality constant is becoming another requirement of facilities performing mammography. Accordingly, quality control tests are executed on a regular basis in order to monitor the consistency of the performance of the X-ray equipment, the image receptors and the film processor. In order to minimize the influence of varying film processing time, temperature, chemistry and replenishment, a preferred mammography film requires a stable speed and contrast with regard to these processing parameters. As in addition, there is a general trend in the field of radiology to shorten the film processing time and likewise in the field of mammography, being driven by intensified screening programs, the interest has focused on rapid access of mammograms. As a consequence, mammography films are preferred which comprise silver halide crystals that can be processed rapidly and consistently in a dry-to-dry processing cycle of 90 seconds or less and therefore, most mammography films today comprise good developable cubic silver halide crystals. As described in EP-A 0 712
Callant Paul
Elst Kathy
Verbeeck Ann
Agfa-Gevaert N.V.
Breiner & Breiner
Le Hoa Van
LandOfFree
Radiation-sensitive emulsion, light-sensitive silver halide... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Radiation-sensitive emulsion, light-sensitive silver halide..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Radiation-sensitive emulsion, light-sensitive silver halide... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2546505