Image analysis – Applications – Biomedical applications
Reexamination Certificate
1998-03-31
2002-03-12
Boudreau, Leo (Department: 2721)
Image analysis
Applications
Biomedical applications
C128S922000
Reexamination Certificate
active
06356651
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of recognizing an irradiation field on a radiation image, and an apparatus for carrying out the method. This invention also relates to a blackening processing method, and an apparatus for carrying out the blackening processing method.
2. Description of the Prior Art
Techniques for reading out a recorded radiation image in order to obtain an image signal, carrying out appropriate image processing on the image signal, and then reproducing a visible image having good image quality by use of the processed image signal have heretofore been known in various fields. For example, as such techniques, the applicant proposed various radiation image recording and reproducing systems which use stimulable phosphor sheets.
When a radiation image of an object, such as a living body, is recorded on a recording medium, such as X-ray film or a stimulable phosphor sheet, it is desirable that adverse effects of radiation upon the living body can be kept as small as possible. Also, if object portions not related to a diagnosis, or the like, are exposed to radiation, the radiation will be scattered by such portions to the portion that is related to a diagnosis, or the like, and the image quality will be adversely affected by the scattered radiation. Therefore, when a radiation image is recorded on the recording medium, a collimation plate made from lead, or the like, is often used in order to limit the irradiation field to an area smaller than the overall recording region of the recording medium, such that radiation may be irradiated only to that portion of the object, the image of which is to be used.
In cases where a radiation image is recorded on a recording medium, such as a stimulable phosphor sheet, by using a collimation plate, an image of an object, or the like, is recorded in a region (i.e., an irradiation field) inward from the aperture contour of the irradiation field stop. Also, a region outward from the aperture contour of the irradiation field stop (i.e., a region outside of the irradiation field) is not exposed to the radiation. Therefore, an irradiation field contour on the image, which contour corresponds to the aperture contour of the irradiation field stop, constitutes edge lines in the image.
In cases where an image signal is detected from the recording medium, on which an image has been recorded within only the irradiation field, and image processing is carried out on the image signal, the image processing, such as gradation processing, may be carried out on only the image signal components of the image signal, which correspond to the region inside of the irradiation field. In this manner, the amount of the processing can be reduced markedly, the load of the processing can be kept small, and the processing speed can be kept high.
The region outside of the irradiation field is not exposed to the radiation. Therefore, in cases where the image is a negative image recorded on medical X-ray film, the image density of the region outside of the irradiation field becomes approximately lowest on the image. By way of example, when the medical X-ray film is set on a viewing screen and the transmission image with light produced by a fluorescent lamp is seen, the region having the lowest level of image density becomes the very bright region. Therefore, in particular, the portion of the irradiation field, which portion is close to the region outside of the irradiation field, cannot be seen clearly due to dazzling effects of the bright region outside of the irradiation field. Also, in cases where an electric image signal is detected from the recording medium, on which an image has been recorded within only the irradiation field, and a visible image is reproduced from the image signal and displayed on an image displaying device, such as a cathode ray tube (CRT) display device, the region outside of the irradiation field has the highest level of luminance, and therefore the image within the irradiation field cannot be seen clearly.
Accordingly, in the radiation image recording and reproducing systems, a process for forcibly replacing the image signal values, which correspond to the region outside of the irradiation field, by image signal values representing the highest level of image density (or the lowest level of luminance) is carried out. The process is ordinarily referred to as the blackening process. It is important that the irradiation field contour, which serves as the spatial reference for the blackening process, can be recognized accurately.
Specifically, if a contour, which is smaller than the correct irradiation field contour (i.e., which is positioned more inward than the correct irradiation field contour), is recognized as the irradiation field contour by mistake, the image portion, which is to be used as the one within the irradiation field, will be subjected to the blackening process as being the one outside of the irradiation field, and therefore the image information at the image portion cannot be seen on the image obtained from the blackening process. Also, if a contour, which is larger than the correct irradiation field contour (i.e., which is positioned more outward than the correct irradiation field contour), is recognized as the irradiation field contour by mistake, the image portion, which has the lowest level of image density (or the highest level of luminance), will remain unblackened, and the effects to be obtained from the blackening process cannot be obtained.
Accordingly, various techniques for accurately carrying out the process for recognizing the irradiation field (contour) have been proposed.
For example, techniques have been proposed, wherein an irradiation field contour is determined by utilizing the characteristics in that the irradiation field contour constitutes the edge lines in the image, at which the image density changes sharply, and finding a portion, at which the value of the image signal changes sharply. One of such techniques for determining the edge lines has been proposed in U.S. Pat. No. 4,967,079. With the technique proposed in U.S. Pat. No. 4,967,079, the edge lines are determined by (a) setting a plurality of radial straight lines, which extend from a predetermined point in the image (e.g., a center point in the image) toward ends of the image, (b) detecting an edge candidate point, at which the different in image signal value is large, from the image signal values corresponding to positions along each of the radial straight lines, a plurality of edge candidate points being thereby detected with respect to the plurality of the radial straight lines, and (c) determining the edge lines in accordance with the thus detected edge candidate points.
However, with the aforesaid technique for recognizing the edge lines, i.e. the irradiation field contour, in accordance with the edge candidate points having been obtained with respect to the radial directions, an irradiation field contour, which coincides with the actual irradiation field contour, cannot necessarily be obtained. In such cases, the problems occur in that an image portion, which is to be used, is blackened with the blackening process, or in that an image portion, which has the lowest level of image density and is to be blackened, remains unblackened.
SUMMARY OF THE INVENTION
The primary object of the present invention is to provide a method of recognizing an irradiation field on a radiation image, wherein the accuracy, with which the irradiation field is recognized, is kept to be higher than the accuracy of a conventional technique for recognizing an irradiation field.
Another object of the present invention is to provide an apparatus for carrying out the method of recognizing an irradiation field on a radiation image.
A further object of the present invention is to provide a blackening processing method for a radiation image, wherein the accuracy, with which a blackening process is carried out, is kept to be higher than the accuracy of a conventional technique for the blackening process.
A still furth
Boudreau Leo
Fuji Photo Film Co. , Ltd.
Tabutabai Abolfazl
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