JPH0685052B2 - Laminate used for energy subtraction method of X-ray image - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to the energy of X-ray images.
X-ray film used in the subtraction method
It relates to a fluorescent intensifying screen-filter laminate. More specifically, an X-ray film and an intensifying screen are used to record an X-ray image on the X-ray film, and then the X-ray film on which the X-ray image is recorded is optically scanned. X-ray image in an X-ray image recording / reproducing system in which an X-ray image is photoelectrically read by a photodetector in the form of transmitted light or reflected light, the obtained image signal is subjected to signal processing and then reproduced as a visible image. The present invention relates to a radiographic film-fluorescent intensifying screen-filter laminate used in the energy subtraction method.

[0002]

2. Description of the Related Art The same subject is irradiated with X-rays having different energy distributions, and a specific structure (eg, organ, bone, blood vessel) of the subject has a characteristic X-ray energy absorption characteristic. We can obtain two X-ray images in which a specific structure is visualized differently, and then use these two X-ray images.
A so-called energy subtraction method in which a line image is appropriately weighted and then an image of a specific structure is extracted by performing subtraction (subtraction) between the two images is called a digital subtraction method (also referred to as digital radiography. It is known as one form. Here, as the DR, the existing I.D. I. Digital Fluoroscopy (Digital Flu) which digitally processes the output of the X-ray fluoroscopy camera consisting of a tube and a TV camera.
oroscopy) and a scanned projection system that uses the X-ray detection system used for CT such as Xe-detector.
Radiography (Scanned Projection Radiography)
What is called is known.

More specifically, the following various methods are known as conventional energy subtraction methods.

(I) X having different energy distributions
The subject is irradiated with a line intermittently at short time intervals, and X-rays transmitted through the subject are synchronized with the I.D. I. Tube and T.S.
V. A method of obtaining a subtraction image from two or more X-ray images obtained by detecting with an X-ray fluoroscopic camera including a camera or an X-ray detector such as a Xe-detector.
Here, as a method of irradiating X-rays having different energy distributions, i) modifying the X-ray source so as to be capable of emitting X-rays having such different energy distributions, ii)
Two or more X-ray sources that emit X-rays having different energy distributions are brought close to each other so that the X-rays emitted from them do not interfere with each other. Iii) X between the X-ray source and the subject
There is a method of inserting and removing a filter that changes the energy distribution of the line.

(II) X having different energy distributions
Two X-ray sources capable of simultaneously radiating rays are arranged close to each other, and a large number of fine slits or fine holes (for example, circles or square holes arranged in a checkered pattern) are arranged. A filter made of an X-ray shielding material such as lead having a structure in which the area ratio between the X-ray shielding portion and the void portion is 1: 1 is provided on one side of the light receiving surface of the X-ray detector. From the X-ray from the other X-ray source
X-rays are inserted between the X-ray source and the subject so that the X-rays do not interfere with each other, and the X-rays are simultaneously emitted from the two X-ray sources to the subject in such a state, whereby different energy distributions are obtained. X on the light receiving surface of the X-ray detector by the X-ray having
A method of forming a line image, detecting the X-ray images by an X-ray detector, separating the detected X-ray images at the time of reading or after reading, and then obtaining a subtraction image from the separated images.

(III) While moving the subject relative to the X-ray source and the X-ray detector, fan-shaped X-rays having different energy distributions are continuously generated from the X-ray source alternately for a certain period of time, Fan-shaped X-rays transmitted through the subject are detected by an X-ray detector installed behind the subject, X-ray images corresponding to X-rays having different energy distributions are obtained from the obtained image signals, and then those X-ray images are obtained. How to get the subtraction image from. As a method of generating X-rays having different energy distributions, the same method as (I) can be considered.

(IV) A filter having the same shape as the filter used in the method (II) is formed of a metal such as copper that absorbs low energy components of X-rays, and this filter is used as one X-ray source and an object. X-rays having different energy distributions which are inserted between the X-rays to generate X-rays having different energy distributions that do not interfere with each other on the light receiving surface of the X-ray detector from the X-rays emitted from the X-ray source. X-ray image is formed on the light receiving surface of the X-ray detector by the X-ray detector, the X-ray image is detected by the X-ray detector, and the detected X-ray image is separated at the time of reading or after the reading, and then the separated image. How to get the subtraction image from.

The energy subtraction method can separate and extract images of structures of the subject having different energy absorption characteristics, and can form an image of only soft tissue excluding bones. For example, it is possible to separate and extract an image of a structure such as a bronchus existing in the mediastinum, which has been difficult to be diagnosed by overlapping with a bone in the related art, from the image of the bone. Further, when time subtraction is performed in imaging such as abdominal angiography, an artifact due to an abdominal gas image becomes a problem, but the energy subtraction method can erase information on soft tissue and a bone without a gas image. It is possible to form only a contrast image. Therefore, the energy subtraction method can obtain diagnostic information that could not be obtained by the conventional method, and is a method that is attracting attention in the medical diagnostic field in principle as a very outstanding method.

[0009]

However, the above-mentioned conventional energy subtraction method has an essential drawback related to DR. That is, the spatial resolution of the subtraction image obtained by DR is generally I.S.
I. Tube and T.S. V. It is determined by the resolution of an X-ray fluoroscopic camera including a camera or an X-ray detector such as a Xe-detector, but the resolution of the X-ray detector used in such a conventional DR is not so high, and The conventional energy subtraction method has a problem that it is impossible to make a fine diagnosis for a specific structure. Further, since the imaging range in the DR is limited by the light receiving area of the X-ray detector, the conventional energy subtraction method has a problem that it is not possible to simultaneously obtain a subtraction image for a wide range of structures of an object.

Further, the above-mentioned conventional energy subtraction methods (I), (II), (III) and (IV) have the following drawbacks.

1. A special X-ray source is required [method (I) and method (II)].

2. Misalignment occurs between corresponding pixels of two X-ray images [method when using two X-ray sources]
(I), method (II), method (III) and method (IV)].

3. Only half the resolution can be obtained as compared with the usual X-ray image forming method [method (II) and method (I
V)].

4. Since each X-ray image by X-rays having different energy distributions is formed on the same plane, it is difficult to separate the X-ray images at the time of reading or after the reading [Method (II)]. And method (IV)].

5. Since X-rays having different energy distributions are intermittently applied to the subject, muscle movement of the subject,
A positional deviation occurs between the images due to respiratory motion, peristalsis, etc., and as a result, a good subtraction image cannot be obtained [Method (I)].

6. Since the subject is scanned by the fan-shaped X-ray, it takes time to form one image, and there is a time difference between the beginning and the end of the scanning, and each image is caused by the subject's muscular movement, respiratory movement, peristalsis, etc. As a result, a good subtraction image cannot be obtained, which is unsuitable for extracting an angiographic image [Method (III)].

Therefore, the object of the present invention does not have the drawbacks of the above-mentioned conventional energy subtraction methods, and is used for an X-ray image energy subtraction method capable of obtaining a good subtraction image. It is to provide a laminated body.

By the way, an X-ray image is once recorded on an X-ray film, and the X-ray image on which the X-ray image is recorded is optically scanned to form the X-ray image in the form of transmitted light or reflected light. The present applicant has already proposed an X-ray photographic recording / reproducing system that records and reproduces an X-ray image by photoelectrically detecting it, performing signal processing on the image signal obtained by this detection, and then reproducing it as a visible image. (Japanese Patent Laid-Open No. 54-121043).

Generally, an X-ray photographic film is required to have high sensitivity suitable for X-ray photography and a wide exposure range, and to have high contrast, high sharpness and fine graininess suitable for observation and interpretation. However, these characteristics are often inconsistent with each other, and it is difficult to produce an X-ray photo film satisfying all the characteristics, and the film was designed at the sacrifice of photographing suitability and observation and interpretation suitability. However, the use of the above X-ray image recording / reproducing system can improve the contrast, sharpness, and graininess, and thereby improve the diagnostic performance of the X-ray image. Therefore, a lot of diagnostic information can be obtained, and at the same time, the X-ray photographic film can be provided with a better imaging suitability.

[0020]

The laminate used in the energy subtraction method for X-ray images of the present invention is used in the above X-ray image recording system. That is, in the laminate used in the energy subtraction method for X-ray images of the present invention, a plurality of X-ray photographic films were arranged in a laminated state together with a fluorescent intensifying screen and a filter made of a low energy component absorbing substance for X-rays. An X-ray film-fluorescent intensifying screen-filter laminate, which is obtained by irradiating an X-ray transmitted through an object including a specific structure having a different X-ray energy absorption characteristic to the laminate. At least two X-ray images having different image information of the portion corresponding to the above-mentioned specific structure are recorded, and then a subtraction image is obtained from each X-ray image read from each film constituting the laminated body. It is what

That is, the X-ray photographic film-fluorescent intensifying screen-filter laminate used in the X-ray image energy subtraction method of the present invention is a) i) phosphor layers arranged in a laminated state face each other. X-ray photographic film-fluorescent intensifying screen assembly consisting of a pair of fluorescent intensifying screens arranged in this manner, and ii) an X-ray photographic film interposed between the phosphor layers facing each other of these fluorescent intensifying screens. It is characterized by comprising a plurality of combinations and b) a filter made of a substance absorbing a low energy component of X-rays which is interposed at least at one place between the respective combinations.

The X-ray photographic film-fluorescent intensifying screen-filter laminate of the present invention is used in an X-ray image energy subtraction method as described below. That is, by irradiating the X-ray photographic film-fluorescent intensifying screen-filter laminate of the present invention with X-rays transmitted through a subject including a specific structure having a different X-ray energy absorption characteristic, The low energy component of X-rays is present in the portion corresponding to the specific structure in the X-ray photo film located on the side opposite to the subject with respect to the intervening part, as compared to the X-ray photo film located on the subject side. The X-ray images recorded with X-ray images are optically scanned to record the more absorbed image information, and the X-ray images recorded on each film are transmitted or reflected in the form of light. It is photoelectrically read by and converted into a digital image signal, and it is divided into (the number of the places where the filter is inserted + 1) blocks by the places where the filter is inserted. For each block of the X-ray film-fluorescent intensifying screen-filter laminate, one X-ray to be subtracted from the X-ray image converted to the digital image signal obtained from the X-ray film existing in the block By obtaining an image (the number of locations where the filter is interposed + 1) X-ray images to be subtracted are obtained, and the digital image signal is subtracted between the corresponding pixels of the X-ray images to be subtracted. It is used in an energy subtraction method characterized by extracting an image of a specific structure.

In the above-mentioned present invention, the X-ray film-fluorescent intensifying screen-filter laminate is composed of two or three X-ray films.
It is preferably composed of a radiographic film. 2 stacks
When it is composed of one X-ray photographic film, two X-ray images obtained from the respective films are directly two images to be subtracted. In the energy subtraction method for an X-ray film-fluorescent intensifying screen-filter laminate of the present invention, subtracting a digital image signal between corresponding pixels of an X-ray image corresponds to that of an X-ray image. This means obtaining a new image signal by multiplying a digital image signal of a pixel by a weighting coefficient and performing subtraction. Further, the X-ray low energy component absorbing substance means a substance which absorbs the low energy component more than the high energy component of the X ray.

The X-ray film-fluorescent intensifying screen combination forming the laminate used in the energy subtraction method of the present invention does not necessarily have to be separable in combination units. That is, of the fluorescent intensifying screens constituting the laminate, one intensifying screen is placed at the position closest to the subject and the other intensifying screen is placed at the position farthest from the subject. Having the function of substantially two intensifying screens capable of sensitizing both of the X-ray film arranged in (1) (that is, four intensifying screens constituting two consecutive combinations of intensifying screens). One of them may have the function of two intensifying screens arranged between two X-ray film). Of course, such an intensifying screen must have a phosphor layer on both sides (the side facing each X-ray film), and such an intensifying screen must have a phosphor layer on both sides of the support. An intensifying screen provided with, a self-supporting intensifying screen consisting only of a phosphor layer, and the like are used.
As described above, the number of fluorescent intensifying screens constituting the laminated body does not necessarily have to be twice the number of X-ray photographic films constituting the laminated body. However, the energy of the present invention
X-ray film used in the subtraction method
In the fluorescent intensifying screen-filter laminate, the intensifying screen having the function of the two intensifying screens as described above is not used at the place where the filter is interposed, and the filter is always two intensifying screens. It is placed between the sheets of paper.

[0025]

In the X-ray photo film-fluorescent intensifying screen-filter laminate used in the X-ray image energy subtraction method of the present invention, a plurality of sets of X-ray photo films arranged in a laminated state are used. X is provided by interposing a filter made of a substance absorbing low energy components of X-rays in at least one place of each combination of fluorescent intensifying screens, and absorbing low energy components of X-rays transmitted through an object by this filter. A line image is recorded. In this case, the filter made of the X-ray low energy component absorbing substance may be made of only the X-ray low energy component absorbing substance, or the X-ray low energy component absorbing substance and this substance are dispersed. It may be composed of another substance contained in.

In the laminated body used in the energy subtraction method for the X-ray image of the present invention, the absorption of the low energy component of the X-rays transmitted through the subject is absorbed by the filter provided separately from the fluorescent intensifying screen. Since this is performed, it is possible to efficiently absorb the low energy component of X-rays, and the fluorescent intensifying screen used for simple photographing can be diverted as it is.

As described above, the X-ray low energy component absorbing substance means a substance that absorbs the low energy component more than the high energy component of the X-ray, and a specific example thereof is a metal. , Especially Cu, W, Mo, Ni,
Pb, Au, Ag, Ba, Ta, Fe, Al, Zn, C
It is preferably at least one of d, Ti, Zr, V, Nd, Cr, Co and Sn.

The X-ray photographic film of the present invention-fluorescent intensifying screen-
In the energy subtraction method using the filter laminate, the spot diameter of the light beam scanning on the X-ray photographic film at the time of reading can be made small, and the number of pixels per unit area can be increased, and the subtraction processing can be performed. Also, since the final output of the image data after various signal processing can be directly recorded on the photosensitive material such as silver salt, it is possible to obtain a subtraction image having a remarkably high spatial resolution as compared with the conventional DR. In principle, it is possible to obtain a clear subtraction image having a spatial resolution equal to or lower than the discrimination resolution of human vision. At the same time, there is no technical problem in enlarging the area of the X-ray photographic film or the fluorescent intensifying screen, so that a subtraction image can be obtained at a time for a large area covering a wide range of structures of the human body. Thus, the X of the present invention
The use of the energy subtraction method for the radiographic film-fluorescent intensifying screen-filter stack eliminates the essential problems associated with X-ray detectors in DR.

Further, in the X-ray film-fluorescent intensifying screen-filter laminate used in the energy subtraction method of the present invention, X-rays emitted from the X-ray source and transmitted through the subject are transferred to the X-ray film-fluorescent film. Since the X-ray film forming the screen-filter laminate is irradiated at the same time, there is no time difference between the formation of at least two X-ray images to be subtracted, and therefore, the human body which changes from moment to moment is identified. The subtraction image of the structure can also be obtained as a good image. Furthermore, in the X-ray photo film-fluorescent intensifying screen-filter laminate of the present invention, since a single X-ray source can be used, there is no displacement between corresponding pixels of at least two X-ray images. . Further, in the X-ray photographic film-fluorescent intensifying screen-filter laminate of the present invention, the conventional general-purpose X-ray generator and photographing apparatus can be used as they are. Further, in the X-ray photographic film-fluorescent intensifying screen-filter laminate of the present invention, X-ray images for X-rays having different energy distributions are recorded in separate X-ray photographic films. The problem of having to separate the images later does not occur, and the resolution is not halved by obtaining the subtraction image. As described above, by using the X-ray film-fluorescent intensifying screen-filter laminate of the present invention for the energy subtraction method, the problems of the conventional energy subtraction method can be solved at once.

The X-ray photographic film of the present invention-fluorescent intensifying screen-
In the X-ray image energy subtraction method in which a filter stack is used, subtraction is performed between corresponding pixels of the X-ray image to be subtracted in order to obtain a subtraction image. This subtraction is as described above. Means that a new image signal is obtained by multiplying the image signal of the corresponding pixel of the X-ray image to be subtracted by multiplying it by a weighting coefficient. For example, when there are two images to be subtracted, this subtraction is expressed by an equation: L = mP-nQ (where P and Q are digital image signals of the X-ray image to be subtracted, m and n are weighting factors, and L is a new Image signal). To get the subtraction image,
In order to erase the image information other than the image information related to the specific structure to be extracted, it is preferable to match the intensity distributions of the image signals of the portions to be deleted between the images to be subtracted. It is convenient to match the gradations of the parts. In order to realize this, it is preferable that the weighting factors m and n are selected so that the gradations of the portions to be erased of both images match and the subtraction is performed. Depending on the shooting conditions, m = n and further m = n = 1.
Also, in the image to be subtracted, various structures are complicatedly overlapped and recorded as an integral image, so the above weighting coefficient is not necessarily a constant, and in some cases it becomes a function of the thickness of the structure. , It may have non-linearity.

As a concrete method of the subtraction, the structure to be erased (for example, soft tissue such as lung in a chest image)
Choose the weighting factors so that the intensity distributions in
There is a method of multiplying the image signals of all pixels of the image to be subtracted by the weighting coefficient. According to this method, the region of the soft tissue only in each image to be subtracted has a constant intensity, and when subtraction is performed between the images to be subtracted, the image information relating to the soft tissue is lost and only the bone is extracted. The image information is rendered as a difference. Therefore, it is preferable to practice such a simple method.

In the X-ray photographic film-fluorescent intensifying screen-filter laminate used in the X-ray image energy subtraction method of the present invention, a plurality of sets of X-ray photographic film-fluorescent intensifying screens constituting the laminate are used. A filter made of a substance absorbing a low energy component of X-rays is interposed at least at one position between the combinations, and the number of the positions where the filter is interposed is (the number of the positions where the filter is interposed + 1). An X-ray image to be subtracted is obtained for each block of the laminated body divided into blocks, and when the blocks are composed of two or more sets of X-ray film-fluorescent intensifying screens, they are consecutive. One X to be subtracted from the X-ray images obtained from the X-ray film that constitutes each combination
A line image is obtained. X constituting each of a plurality of consecutive X-ray film-fluorescent intensifying screen combinations as described above.
In order to obtain one X-ray image to be subtracted from the X-ray image obtained from the radiographic film, it is preferable to use the superposition processing. That is, the X-ray images obtained from the X-ray film forming each of a plurality of sets of continuous X-ray film-fluorescent intensifying screen combinations were obtained from the X-ray film located farther from the subject. The X-ray image contains more noise, but each X-ray image is multiplied by an appropriate weighting factor, and then the plurality of X-ray images are superposed on each other to obtain one of the X-ray images before the processing. An X-ray image having an improved S / N ratio (that is, an X-ray image to be subtracted) can be obtained.

In the X-ray film-fluorescent intensifying screen-filter laminate used in the X-ray image energy subtraction method of the present invention, the following I), II) and II are used.
It is preferred to use any of the radiographic film of I) -fluorescent intensifying screen-filter laminate.

I) X-ray film-fluorescent intensifying screen-composed of two sets of X-ray film-fluorescent intensifying screen and a filter interposed between the two sets.
Filter laminate.

II) Three sets of X-ray film-fluorescent intensifying screen combinations, and a filter interposed between the combination of these combinations located on the subject side and the combination located in the middle. X-ray film-Fluorescent intensifying screen-
Filter laminate.

III) X-ray film-fluorescent intensifying screen-filter stack consisting of three sets of X-ray film-fluorescent intensifying screen combinations and a filter interposed between each of these combinations. body.

X-ray photographic film of the above I) or III)
In the case of a fluorescent intensifying screen-filter laminate, two or three X-ray images obtained from the X-ray film forming each X-ray film-fluorescent intensifying screen combination are directly two or three. It becomes an X-ray image to be subtracted. In the case of the X-ray photo film-fluorescent intensifying screen-filter laminate of the above II), X obtained from the X-ray photo film forming the X-ray photo film-fluorescent intensifying screen combination located on the subject side. The X-ray image becomes one X-ray image to be subtracted, and the remaining two sets of X-ray film-
An X-ray image obtained by, for example, a superimposing process from two X-ray images obtained from the X-ray photographic film forming each of the fluorescent intensifying screen combinations becomes another X-ray image to be subtracted.

The X-ray photographic film of the present invention-fluorescent intensifying screen-
In an energy subtraction method for an X-ray image using a filter laminate, when used as an X-ray for irradiating a subject with X-rays separated into a high energy band and a low energy band by a specific filter in advance, an X-ray photograph is obtained. This is preferable because the separation of the high energy component and the low energy component of the X-ray in the film-fluorescent intensifying screen-filter laminate becomes easier.

Further, in the X-ray film-fluorescent intensifying screen-filter laminate used in the X-ray image energy subtraction method of the present invention, the thickness of the fluorescent intensifying screen placed closer to the subject can be further improved. The thinning is effective in preventing the reduction of the X-ray dose reaching the fluorescent intensifying screen placed at a position farther from the subject.

In the present invention, X from a radiographic film is used.
As a means for optically scanning the X-ray photographic film for reading out the line image, a means for two-dimensionally scanning the light beam on the X-ray photographic film, a fixed drum and a rotating drum for the X-ray photographic film. It is possible to use various means such as electronic scanning, such as a flying spot scanner, or a means for moving by moving in a direction parallel to the rotation axis. Here, various light beams such as those obtained by condensing light emitted from a point light source with a condensing lens and laser beams can be used. For reading, the reflected or transmitted light (X-ray) from the X-ray image when the X-ray photographic film is optically scanned.
(When the line film is transparent) can be detected by the light detecting means.

The X-ray film of the present invention-fluorescent intensifying screen-
In the X-ray image energy subtraction method in which the filter laminate is used, various signal processing can be performed on the X-ray image before or after the subtraction, and the signal processing used is Japanese Patent Laid-Open No. 56-1103.
No. 5, No. 56-75136, No. 56-75138, No. 56-75140
Nos. 56-91735 and the like, and frequency processing disclosed in JP-A-55-116338 and JP-A-55-88741.

[0042]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic sectional view showing an embodiment of an X-ray photographic film-fluorescent intensifying screen-filter laminate used in the X-ray image energy subtraction method of the present invention. This X-ray photographic film-fluorescent intensifying screen-filter laminate is composed of two sets of X-ray photographic films arranged in a laminated state.
It is composed of a fluorescent intensifying screen combination and a filter 3 made of a substance absorbing a low energy component of X-rays interposed between the two combinations. The X-ray film-fluorescent intensifying screen combination on the subject side with respect to the filter 3 is a pair of fluorescent intensifying screens a and b arranged so that the phosphor layers 1a and 1b face each other, and these fluorescent intensifying screens. It consists of an X-ray photographic film A interposed between the facing phosphor layers of papers a and b. Similarly, the X-ray film-fluorescent intensifying screen combination on the side opposite to the subject with respect to the filter 3 includes a pair of fluorescent intensifying screens c and d arranged so that the phosphor layers 1c and 1d face each other. , These fluorescent intensifying screens c
And an x-ray photographic film B interposed between the phosphor layers facing each other. The fluorescent intensifying screens a, b,
The phosphor layers 1a, 1b, 1c and 1d of c and d are physically or chemically protected on the surface (the surface opposite to the side of the supports 2a, 2b, 2c and 2d). A protective film such as polyethylene terephthalate film may be provided (the same applies to the laminated body shown in FIGS. 5 and 6 below). Further, the fluorescent intensifying screens a, b, c and d are the supports 2a, 2b, 2c, respectively.
And 2d, the fluorescent intensifying screens may be self-supporting without a support. The filter 3 may be composed of an X-ray low energy component absorbing substance and another substance containing this substance in a dispersed state, or may be composed only of an X-ray low energy component absorbing substance. The filter 3 may absorb the low energy component of the X-ray transmitted through the subject.

FIG. 2 shows the radiographic film shown in FIG.
It is a schematic diagram explaining a mode that an X-ray image is recorded on an X-ray photographic film by an energy subtraction method of an X-ray image using a fluorescent intensifying screen-filter laminate. A single X-ray source 4 that emits X-rays 6 is arranged in the upper part of the figure, and the X-ray film-fluorescent intensifying screen laminate shown in FIG. It is stored and arranged.

When X-rays 6 are emitted from the X-ray source 4, the X-rays 6 pass through the subject 7 including a specific structure having an X-ray energy absorption characteristic different from the others, and first, the fluorescent intensifying screen a. And b and an X-ray film-fluorescent intensifying screen combination consisting of X-ray film A is reached. Here, the X-ray image of the subject 7 is recorded on the X-ray photographic film A. Next, the X-rays transmitted through the combination of the X-ray film-fluorescent intensifying screen pass through the filter 3 and are composed of the fluorescent intensifying screens c and d and the X-ray photographic film B. When the combination is reached, the X-ray image of the subject 7 is recorded on the X-ray photographic film B. Since the filter 3 absorbs the low energy component of the X-ray more, the X-ray transmitted through the filter 3 has the low energy component reduced and the high energy component emphasized. Therefore, the X-ray photographic film is In B, an X-ray image of the subject 7 in which the image information related to the low energy component of X-ray is reduced is recorded. In this way, two X-ray images having different image information in the portion corresponding to the specific structure of the subject 7 are simultaneously recorded on the two X-ray photographic films A and B.

An X-ray image is read from the thus obtained two X-ray photographic films A and B by a reading system as shown in FIG. 3 to obtain a digital image signal representing the image. First, while moving the X-ray photographic film A in the direction of the arrow Y for sub-scanning, the laser light 11 from the laser light source 10 is mainly scanned in the X-direction by the scanning mirror 12, and the X-ray photographic film A is moved to the film. Recorded in X
The line image is read out as the reflected light 13. The reflected light 13 enters the inside of the condenser plate 14 from one end surface of the condenser plate 14 formed by molding a transparent acrylic plate and reaches the photo-maru 15 while repeating total reflection in the condenser plate 14, and the amount of light is the image signal S. Is output as. The output image signal S is converted into a logarithmic value (logS) digital image signal logS _A by a logarithmic converter 16 including an amplifier and an A / D converter. This digital image signal l
The ogS _A is input to the digital calculator 17 and recorded therein. Next, in exactly the same manner, another recorded image of the X-ray photographic film B is read out, and its digital image signal lo
g S _B is stored in the digital calculator 17. In the digital calculator 17, the digital image signal logS _{A is} output between the corresponding pixels.
Image signal of a specific structure is obtained to be more digital image signal log S _B is subtracted extracted. At this time, each of the digital image signals logS _A and logS _B is multiplied by an appropriate weighting coefficient, but the two weighting coefficients are preferably selected so that the gradations of the portions to be erased of both images match.
The digital image signal is treated as a logarithmic value here because the image data is band-compressed and unnecessary image information can be completely removed. It is possible to do the same.

In this way, the signal obtained by performing the digital subtraction processing is subjected to image processing such as spatial frequency processing, gradation processing, and averaging processing, if necessary, and then displayed on a CRT or the like. It is reproduced directly on the apparatus or reproduced and recorded on a recording material such as a photosensitive film as described below.

FIG. 4 shows an example of image scanning recording for reproduction. The photosensitive film 20 is moved in the sub-scanning direction of arrow Y, and the laser beam 21 is moved to the photosensitive film 20.
The main scanning is performed in the X direction, and the laser beam 21 is modulated by the A / O modulator 22 by the image signal from the image signal supplier 23 to form a visible image on the photosensitive film 20. If the output of the digital calculator 17 is used as this image signal, the image of the desired specific structure subjected to the digital subtraction processing can be reproduced and recorded on the photosensitive film 20.

In the case where the energy subtraction is carried out using the X-ray photo film-fluorescent intensifying screen-filter laminate shown in FIGS. 5 and 6, the subtraction process is performed in the same manner as described above. .

FIG. 5 is a schematic sectional view showing another embodiment of an X-ray film-fluorescent intensifying screen-filter laminate used in the X-ray image energy subtraction method of the present invention. This X-ray film-fluorescent intensifying screen-filter laminate is composed of three sets of X-ray film-fluorescent intensifying screens arranged in a laminated state, and a combination of these combinations located on the subject side and an intermediate position. And a filter 3 made of a substance absorbing a low energy component of X-rays, which is interposed between the filter 3 and the combination. The fluorescent intensifying screens a, b, c, d, e and f constituting the laminated body are respectively the support 2
Although they have a, 2b, 2c, 2d, 2e and 2f, these fluorescent intensifying screens may be self-supporting ones having no support. Further, the filter 3 may be made of an X-ray low energy component absorbing substance and another substance containing this substance in a dispersed state, or may be made of only an X-ray low energy component absorbing substance. It may be one.

In order to obtain a subtraction image using the X-ray photo film-fluorescent intensifying screen-filter laminate having the above-mentioned structure, the laminate is irradiated with X-rays that have passed through the subject, and then the above-mentioned is followed. In this way, the X-ray images are read out from the respective films A, B and B ', and the X-ray images obtained from the films B and B'are superposed to make 1
One X-ray image to be subtracted is obtained, the X-ray image obtained from the film A is directly used as the other X-ray image to be subtracted, and the same subtraction as described above can be performed between the X-ray images to be subtracted. Good.

FIG. 6 is a schematic sectional view showing still another embodiment of the X-ray film-fluorescent intensifying screen-filter laminate used in the X-ray image energy subtraction method of the present invention. This laminated body is a filter composed of three sets of X-ray film-fluorescent intensifying screens arranged in a laminated state, and an X-ray low energy component absorbing substance interposed between each combination of these combinations. 3 and 3 '. The fluorescent intensifying screens a, b, and
c, d, e and f are supports 2a, 2b, 2 respectively
Although the fluorescent intensifying screens have c, 2d, 2e and 2f, they may be self-supporting ones having no support. Further, the filters 3 and 3'may be made of an X-ray low energy component absorbing substance and another substance containing this substance in a dispersed state, or an X-ray low energy component absorbing substance. It may consist of only one.

In order to obtain a subtraction image by using the X-ray film-fluorescent intensifying screen-filter laminate having the above-mentioned structure, the X-ray transmitted through the subject is passed through the laminate.
After irradiating the X-ray, the X-ray images obtained from the films A, B and C may be subtracted.

As described in detail above, the X-ray image energy subtraction method of the present invention has extremely excellent characteristics, and it greatly contributes to the field of medical diagnosis.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an example of an X-ray film-fluorescent intensifying screen-filter laminate of the present invention.

FIG. 2 is a schematic view for explaining a manner of recording an X-ray image of a subject on the X-ray photographic film-fluorescent intensifying screen-filter laminate of the present invention.

FIG. 3 is a schematic diagram illustrating steps of photoelectrically converting an X-ray image recorded from an X-ray photographic film in the form of reflected light to obtain a digital signal and performing subtraction processing on the digital signal.

FIG. 4 is a schematic diagram illustrating steps for reproducing and recording an image subjected to subtraction processing on a photosensitive film by using a signal obtained by the subtraction processing.

FIG. 5 is a schematic sectional view showing another embodiment of the X-ray film-fluorescent intensifying screen-filter laminate of the present invention.

FIG. 6 is a schematic sectional view showing still another embodiment of the radiographic film-fluorescent intensifying screen-filter laminate of the present invention.

[Explanation of symbols]

 A, B, B ', C X-ray film a, b, c, d, e, f Fluorescent intensifying screen 1a, 1b, 1c, 1d, 1e, 1f Phosphor layer 2a, 2b, 2c, 2d, 2e , 2f Support 3,3 'Filter 4 X-ray source 6 X-ray 7 Subject 10 Laser light source 11 Laser light 12 Scanning mirror 13 Reflected light 14 Condenser plate 15 Photomul 16 Logarithmic converter 17 Digital calculator 20 Photosensitive film 21 Laser light 22 A / O modulator 23 Image signal supplier

Claims (8)

[Claims] 1. A) a) a pair of fluorescent intensifying screens arranged in a laminated state so that the phosphor layers are opposed to each other, and ii) between the opposing phosphor layers of these fluorescent intensifying screens. A plurality of radiographic film-fluorescent intensifying screen combinations consisting of an intervening X-ray film, and b) low energy of the intervening X-rays in at least one place between each combination of these combinations. An X-ray film-fluorescent intensifying screen-filter laminate for use in an X-ray image energy subtraction method, which comprises a filter made of a component-absorbing substance. 2. An X-ray film-fluorescent intensifying screen-filter laminate comprising two sets of said X-ray film-fluorescent intensifying screen combination, and said filter interposed between these combinations. The X-ray film-fluorescent intensifying screen-filter laminate according to claim 1, which comprises: 3. An X-ray film-fluorescent intensifying screen-filter laminate having three sets of the X-ray film-fluorescent intensifying screen, and a combination of these combinations located on the object side and an intermediate portion. 2. The filter, which is interposed between the filter and the combination located at 1.
The described X-ray film-fluorescent intensifying screen-filter laminate. 4. The X-ray film-fluorescent intensifying screen-filter laminate is interposed between three sets of the X-ray film-fluorescent intensifying screen and each of these combinations. The radiographic film-fluorescent intensifying screen-filter laminate according to claim 1, which comprises the filter. 5. The filter according to claim 1, wherein the filter is composed of a substance absorbing the low energy component of the X-ray and another substance containing the substance in a dispersed state. The described X-ray film-fluorescent intensifying screen-filter laminate. 6. The X-ray photographic film-fluorescent intensifying screen-filter laminate according to any one of claims 1 to 4, wherein the filter is composed only of a substance absorbing the low energy component of the X-rays. . 7. The X-ray film-fluorescent intensifying screen-filter laminate according to claim 1, wherein the X-ray low energy component absorbing substance is a metal. 8. The metal is Cu, W, Mo, Ni, P
b, Au, Ag, Ba, Ta, Fe, Al, Zn, C
The radiographic film-fluorescent intensifying screen-filter laminate according to claim 7, which is at least one of d, Ti, Zr, V, Nb, Cr, Co and Sn.