Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2001-06-08
2003-04-01
Bennett, Henry (Department: 3743)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C382S132000, C382S128000
Reexamination Certificate
active
06542771
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of and a system for detecting a prospective abnormal shadow in a radiation image and a method of reproducing a radiation image.
2. Description of the Related Art
Conventionally, disease or injury of a patient has been sometimes diagnosed by reading an X-ray film on which a radiation image of the patient is recorded. Recently, there has been developed a system in which a radiation image of a patient is once stored on a stimulable phosphor sheet (or a radiation image conversion panel) by exposing the stimulable phosphor sheet to radiation through the object (patient) to have the stimulable phosphor sheet store radiation energy, and stimulated emission which is emitted from each part of the stimulable phosphor sheet upon exposure to stimulating light in proportion to the radiation energy stored thereon is digitally read, thereby obtaining a digital image signal representing the radiation image stored on the stimulable phosphor sheet, and the digital image signal is reproduced as a visible image on a recording medium such as a photographic film or on an image display system such as those using a CRT. (A radiation image recording and read-out apparatus: computed radiography, see, for instance, Japanese Unexamined Patent Publication Nos. 55(1975)-12429, 56(1976)-11395 and 56(1976)-11397)
In accordance with such a radiation image recording and read-out apparatus, by carrying out image processing on the digital image signal in various ways, the tone properties and the frequency properties of the output visible image can be improved so that the visible image becomes more suitable for reading and diagnose through the visible image can be made more correctly.
Further, there has been developed a system in which the digital image signal is analyzed by a computer to automatically detect an abnormal shadow representing a growth, a micro calcification or the like, whereby a certain detecting level can be ensured irrespective of the skillfulness of the reader. (Prospective abnormal shadow detecting system: see, for instance, Japanese Unexamined Patent Publication Nos. 8(1996)-294479)
In this system, the degree of convergence of density (signal value) gradient vectors is evaluated in a digital image signal of a breast (a mammogram) mainly obtained by breast cancer examination, thereby automatically detecting a prospective growth shadow in the radiation image, or a prospective micro calcification shadow is automatically detected by carrying out morphology operation (e.g., dilation processing, erosion processing, opening processing, and closing processing). The prospective abnormal shadow thus detected is marked with a ROI frame or the like on a visible image reproduced on a display such as of a CRT or a liquid crystal display or on a print. Then the display or the print is used for diagnosis.
Though being substantially high in detecting accuracy, the prospective abnormal shadow detecting system cannot detect an abnormal shadow at one-hundred percent accuracy at present. That is, the conventional prospective abnormal shadow detecting system cannot perfectly remove noise of radiation and/or other noise generated at random and sometimes mistakes such noise for a prospective abnormal shadow. Further it sometimes mistakes normal tissues or normal structures such as the mammary glands for a prospective abnormal shadow. Accordingly, there has been a strong demand for a prospective abnormal shadow detecting system which can detect a prospective abnormal shadow at a higher accuracy.
SUMMARY OF THE INVENTION
In view of the foregoing observations and description, the primary object of the present invention is to provide a prospective abnormal shadow detecting method and a prospective abnormal shadow detecting system which can detect a prospective abnormal shadow more accurately.
Another object of the present invention is to provide a radiation image reproducing method which can reproduce a radiation image with a prospective abnormal shadow clearly separated from a normal shadow.
In accordance with the present invention, at least two radiation images of an object are taken in different directions, prospective abnormal shadows are detected in the respective radiation images, and when prospective abnormal shadows detected in the respective radiation images are in substantially the same position on the object, the prospective abnormal shadows detected in the respective radiation images are taken as one final prospective abnormal shadow.
That is, when a tumor or the like which is observed as an abnormal shadow on a radiation image really exists on the object, an abnormal shadow should be detected in the same position in each of radiation images taken in different directions, whereas there is little probability that noise or the like which is generated at random is detected in the same position in each of radiation images taken in different directions. In the case of a normal tissue or a normal structure such as the mammary glands which really exists in the object, there is little probability that such a normal tissue is mistaken for an abnormal shadow in all the radiation images taken in different directions since such a normal tissue is viewed in different shapes according to the direction of taking a radiation image.
This invention has been made on the basis of such a recognition, and in accordance with a first aspect of the present invention, there is provided a prospective abnormal shadow detecting method for detecting a prospective abnormal shadow in a radiation image, characterized by the steps of
detecting a prospective abnormal shadow in each of at least two radiation images of an object taken in different directions,
determining correspondence of positions on the object between the radiation images, and
taking, as a final prospective abnormal shadow, only prospective abnormal shadows which are detected in the respective radiation images and are in substantially the same position on the object.
Preferably a prospective abnormal shadow in each radiation image is detected by a method disclosed, for instance, in Japanese Unexamined Patent Publication Nos. 8(1996)-294479) in which the degree of convergence of density (signal value) gradient vectors is evaluated in a digital image signal, thereby automatically detecting a prospective growth shadow in the radiation image, or a prospective micro calcification shadow is automatically detected by carrying out morphology operation (e.g., dilation processing, erosion processing, opening processing, and closing processing).
The final prospective abnormal shadow is a prospective abnormal shadow which is more probable than that detected in only one of the radiation images.
“Determining correspondence of positions on the object between the radiation images” need not be effected three-dimensionally. That is, since the radiation image is only a projection of a three-dimensional object on a two-dimensional plane, positions in the direction of taking the radiation image (in the direction of depth of the radiation image) cannot be obtained from each radiation image. Accordingly, correspondence of positions on the object between the radiation images can be determined only with respect to a direction perpendicular to the planes on which the radiation images are projected. Thus, correspondence of positions on the object between the radiation images may be determined only in one-dimension.
That is, “the expression that the prospective abnormal shadows are in the same position on the object” need not be interpreted that the positions of the prospective abnormal shadows are three-dimensionally the same as each other but should be interpreted to include the case where the positions of the prospective abnormal shadows are the same as each other only in a predetermined direction but the direction of depth of the radiation image. Further, the expression “in substantially the same position” means that the prospective abnormal shadows need not be strictly in the same position but they are conside
Ohkubo Takeshi
Saotome Shigeru
Shimura Kazuo
Bennett Henry
Dagostino Sabrina
Fuji Photo Film Co. , Ltd.
Sughrue & Mion, PLLC
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