Radiation imagery chemistry: process – composition – or product th – Luminescent imaging
Reexamination Certificate
2002-03-18
2003-06-03
Chea, Thorl (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Luminescent imaging
C430S502000, C430S507000, C430S567000, C430S966000
Reexamination Certificate
active
06573019
ABSTRACT:
BACKGROUND OF THE INVENTION
The incidence of breast cancer carcinoma among women continues to increase, posing a serious health problem throughout the world. The mortality rate from breast cancer can be decreased significantly by early detection using the radiological mammography technique. With this technique the compressed breast is irradiated with soft X-rays emitted from an X-ray generating device and 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 color and skin line perceptibility. It is common practice to set the amount of X-ray exposure so that the tissues on the inside of the breast are depicted at medium optical density values, i.e. in the optical density range from [Dmin+1.0] to [Dmin+2.5], Dmin being defined as the [base+fog]-density obtained after processing the unexposed film, and the diagnostic perceptibility of small, potentially malignant lesions in these tissues is highly determined by the contrast of the mammography film within said density range. A quantitative measure of the film contrast is the so-called average gradation, defined as the slope of the line drawn by connecting both points of the sensitometric curve of optical density vs. logarithmic exposure at which the optical density is equal to [Dmin+1.0] and [Dmin+2.5].
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 from 3.0 to 3.5. 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 is described in U.S. Pat. No. 5,290,665.
In order to extend the exposure latitude some manufacturers have introduced high contrast mammography films characterized by a higher maximum density (hereinafter referred to as Dmax) than conventional high contrast films, e.g. a Dmax equal to at least 3.7, preferably even higher than 4.0. However, a film characterized by a higher “Dmax” is only a minor improvement with regard to better skin line perceptibility, since the background density is too high for the skin line to be clearly visible. Indeed at optical density values above 3.5, the local gradient, i.e. the slope of the sensitometric curve, must be very high in order to guarantee a reasonable perceptibility as described in the well-known article titled “Determination of optimum film density range for röntgenograms from visual effect” by H. Kanamori (Acta Radiol. Diagn. Vol.4, p. 463, 1966). Nevertheless, processed mammography films showing a higher maxmum density are appreciated by a growing number of radiologists because of the wider dynamic range, i.e., the density range [Dmax-Dmin] of the mammogram.
To summarize: it remains difficult to obtain mammograms with high contrast and high maximum density, moreover clearly depicting thin tissue such as the skin line of the breast. Some improvements have been obtained by modifying the X-ray generating device, such as the scanning mammography system described in U.S. Pat. No. 5,164,976. These solutions however require the replacement of the conventional X-ray apparatus by a completely new system with a much higher technical complexity. 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. To minimize the influence of varying film processing time, temperature, chemistry and replenishment, a preferred mammography film requires a stable speed and contrast with respect to these processing parameters.
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, 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 0 712 036, such cubic crystals show a stable speed and contrast upon varying processing parameters. Cubic emulsions however are characterized by a very high contrast, resulting in a poor skin line perceptibility. On the other hand tabular silver halide emulsion crystals, also being rapidly processable, are characterized by a much lower contrast than cubic silver halide emulsions and thus are only applicable for manufacturing low contrast mammography films. Another drawback of these tabular emulsions is the residual color after processing: due to the larger specific area of the tabular grains compared e.g. with cubic crystals having the same crystal volume, these tabular grains require higher amounts of spectrally sensitizing dye(s), which may leave dye stain after the short processing cycle. Also the brownish color of the developed silver image of thin tabular grains, resulting in an undesired image tone, is a disadvantage for mammography making use of the said tabular grains.
Nowadays most of the single-side coated film materials for mammography have an amount of coated silver halide, expressed as an equivalent amount of silver nitrate, in the range from 6.0 up to less than 8.5 g/m
2
. A disadvantage related with such high coating amounts is the presence of high amounts of coated gelatin, present as protective colloid of the silver halide crystals and as hydrophilic binder of the coated layers, which results in absorption of high amounts of water at one side of the support and long drying times in the processing. A high pressure sensitivity as coated minimum amounts of hydrophilic colloidal binder are envisaged on one hand and questionable archivability as a consequence of long fixing times, shortened in order to provide ending processing within shortened rapid processing cycles at the other hand, clearly lay burden on the most critical feature in mammography, being “image quality”, and more particularly “sharpness”.
As mammographic and similar soft tissue imaging medical diagnostic films are coated in a single-sided format in order to maximize image sharpness and uniformity, higher rates of rapid access processing finding increasing use in processing dual-coated radiographic films are questionable. A first attempt has been made by Luckey et al, U.S. Pat. No. 4,710,637 in order to pr
den Zegel Marc Van
Vanhoudt Francis
Agfa-Gevaert
Chea Thorl
Guy Joseph T.
Nexsen Pruet Jacobs & Pollard LLC
LandOfFree
Photographic silver halide photographic material 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 Photographic silver halide photographic material for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Photographic silver halide photographic material for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3113413