JP2932022B2 - Radiation image alignment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of correcting the positional deviation of a plurality of images to be subjected to a superposition process or a subtraction process of a radiographic image and performing the positioning of the images. The present invention relates to a method of aligning images without using a marker for printing.

[0002]

2. Description of the Related Art In recent years, using a stimulable phosphor, radiation image information of a subject such as a human body is temporarily recorded on a stimulable phosphor sheet (hereinafter referred to as a stimulable phosphor sheet) and excited. A method has been proposed in which scanning is performed with light to emit stimulating light, the stimulating light is read photoelectrically to obtain an image signal, and this image signal is processed to obtain a radiation image of a subject having good diagnostic suitability ( For example, JP-A-55-12429, 55-116340
No. 55-163472, No. 56-11395, No. 56-104645). This final image can be played back as a hard copy or on a CRT.

On the other hand, superposition processing of radiation images has been conventionally known (see, for example, JP-A-56-11399).
Generally, a radiographic image is used for diagnosis and other purposes, and in using the radiographic image, it is required to detect a minute radiation absorption difference of a subject satisfactorily. The degree of this detection in a radiographic image is referred to as contrast detectability or simply detectability, and the higher the detectability, the higher the diagnostic performance,
It can be said that the radiation image has a high practical value. Therefore, in order to enhance the diagnostic performance, it is desired to increase the detectability, but the biggest obstacle is various noises. The superposition process is a method of greatly reducing the various noises, making it possible to clearly observe even a slight radiation absorption difference of the subject in the final image, and greatly improving the detectability. That is, a radiation image is captured (stored and recorded) on a plurality of stimulable phosphor sheets, and a plurality of image signals obtained by subjecting the plurality of sheets to a reading process are added. Decrease.

Conventionally, in order to actually perform this superposition processing, for example, two stimulable phosphor sheets are placed in a cassette in a superimposed state, and an object is photographed. A method of sequentially performing normal reading processing to obtain two sets of image signals and adding the two sets of image signals is used.

On the other hand, subtraction processing of a radiation image has been conventionally known. This subtraction of a radiation image means that two radiation images captured under different conditions are photoelectrically read out to obtain digital image signals, and then these digital image signals are subjected to subtraction processing in correspondence with each pixel of both images. This is a method of obtaining a difference signal for extracting a specific structure in a radiation image. By using the difference signal thus obtained, a radiation image in which only the specific structure is extracted can be reproduced.

There are basically the following two methods for this subtraction processing. That is, (1) a specific structure is extracted by subtracting (subtracting) an image signal of a radiographic image to which a contrast agent is not injected from an image signal of a radiological image in which a specific structure is enhanced by injection of a contrast agent. So-called time subtraction processing, and (2) irradiating the same subject with radiation having different energy distributions, or irradiating the radiation after passing through the subject to two radiation detecting means by changing the energy distribution state, As a result, an image in which a specific structure is different exists between the two radiographic images, and after subtraction is performed after appropriately weighting the image signals of the two radiographic images, a subtraction is performed. This is a so-called energy subtraction process for extracting an image.

Since this subtraction processing is a particularly effective method for medical diagnosis, it has attracted much attention in recent years, and its research and development have been actively promoted by making full use of electronic engineering technology.

[0008] However, the following problems occur in the method of superimposing and subtracting radiation images using the stimulable phosphor sheet as described above.

That is, in each of the above-described processing methods using the stimulable phosphor sheets, two (or three or more) stimulable phosphor sheets are sequentially or simultaneously inserted into the photographing table and overlapped or overlapped. A radiation image to be subtracted is taken, and then the stimulable phosphor sheet is individually inserted into the reader, and each time the stimulable phosphor sheet is irradiated with excitation light to detect the stimulated emission light. The radiation image is read out, and in this process, even if the mechanical accuracy of all devices related to imaging and reading is increased, a positional deviation and a rotational deviation occur between the images to be superimposed or subtracted. It will be. As a result, in the superimposition process, although various noises are averaged and reduced by this process, blurring occurs in the entire image including the edges of the structures in the image, and the image to be observed is not suitable for observation, Further, in the subtraction processing, an image to be erased is not erased, or an image to be extracted is erased, and a false image is generated, so that an accurate subtraction image cannot be obtained. As described above, it has been found that the positional deviation and the rotational deviation described above cause serious problems in diagnosis.

If such a deviation occurs between the radiation image information stored and recorded on the stimulable phosphor sheet, the radiation image is stored and recorded in the stimulable phosphor as a latent image.
Unlike the case of an X-ray film capable of capturing an X-ray image as a visible image, it is not possible to visually match two X-ray photographs, and it is extremely difficult to correct the displacement.

Further, even if a positional deviation and a rotational deviation occurring between two radiation images can be detected by some means, a conventionally known arithmetic processing for correcting data of the read radiation image is performed. A great deal of time is spent on correction, which is a very serious problem in practical use.

The present applicant has proposed in Japanese Patent Application Laid-Open No. 58-163338 a method of subtracting a radiographic image using a marker having a shape that provides a reference point or a reference line. In this method, the marker is recorded on two stimulable phosphor sheets at a fixed position with respect to the radiographic image, the marker is detected at the time of reading the radiographic image, and a positional shift and a rotational shift are calculated. One of the radiographic images to be subtracted is rotated and / or moved on the digital data, and the image data is subtracted between the corresponding pixels of the radiographic image. The positioning process in the subtraction processing method of the radiological image using the marker can also be applied to the above-described superposition processing method. In this case, the image data may be added between the corresponding pixels of the radiation image after the alignment.

[0013]

However, in this method, each time a radiographic image is taken, the above-described marker must be accumulated and recorded together with the subject on the stimulable phosphor sheet. Then, there is a problem that image information of the subject cannot be obtained from a portion overlapping the position of the marker of the accumulated and recorded radiographic image.

In view of the above circumstances, it is an object of the present invention to provide a radiographic image positioning method capable of performing quick and highly accurate positioning without recording a marker or the like with a subject for positioning. It is intended for.

[0015]

SUMMARY OF THE INVENTION An image registration method according to the present invention is a method of registering a plurality of radiation images for superposition processing or subtraction processing of radiation images. Setting at least two regions of interest substantially common to the plurality of images, setting each of the regions of interest of a reference image among the plurality of images as a reference region, and defining the regions of interest of other images as templates. Region, define orthogonal coordinates for each of the plurality of images, perform template matching to match the template region to the reference region, determine coordinate values of at least two corresponding points of the plurality of images that correspond to each other, The coordinate values of the image including the template area are converted to the coordinate values of the image including the reference area so that the corresponding points match. Formula,

[0016]

(Equation 2)

(Where u and v are the coordinates of the reference area, x and y are the coordinates of the specific area, a, b, c and d are the coefficients indicating the rotational movement correction and the enlargement or reduction rate correction, and e and f are the parallel movements. A coefficient of an affine transformation represented by a correction coefficient) is obtained, and a first affine transformation for performing at least rotational movement correction and enlargement or reduction ratio correction on a plurality of images including the template region is performed using the coefficient. The template matching is performed again on the plurality of images on which the first affine transformation has been performed, coefficients of the affine transformation represented by the above equation are obtained, and using these coefficients, rotational movement correction and enlargement of the plurality of images including the template region are performed. Alternatively, a second affine transformation for performing reduction ratio correction and parallel movement correction is performed.

In the image registration method according to the present invention, the first affine transformation is repeated a plurality of times.
It is more preferable in that the accuracy of the alignment is improved. Note that this accuracy increases as the number of affine transformations is increased, but the time required for completing the alignment also increases.Accordingly, the number of affine transformations is set in consideration of the time, It is preferable to perform alignment with desired accuracy.

Here, the template matching is a process in which, when the template region and the reference region are set as described above, the template region is moved on an image including the reference region to search for the best matching place. The point representing the location gives the coordinates of the corresponding point.

In such template matching, an evaluation scale representing the degree of matching includes a correlation method and an SSDA (Sequential Similarity Detection Algorithm).
lithms).

In the correlation method, a product is calculated for each corresponding pixel, and a value obtained by standardizing the sum of the products (hereinafter referred to as a standardized value) is used as a measure of superposition. In this standardization, the sum of the product (square) of the pixel itself is calculated in each region, the product of each sum is further calculated, and the square root of this product is calculated as the sum of the products of the corresponding pixels. This is done by using the denominator. When the superposition is complete, all products of the numerator do not become the sum of the squares due to noise or the like. Therefore, it is considered that the standardized value does not become 1, but becomes the maximum value closest to 1. Therefore, it is considered that the superposition has been achieved by moving the template region variously on the image including the standard region and moving the template region to the maximum standardized value. However, the movement with the maximum standardized value cannot be determined unless all the movements are completed. For details of this method, see, for example, Smith et al., “Automated cloud tracking using precisely align
eddigital ATS pictures "ibid. , July 1972 c-21
Volume, pages 715-729.

SSDA uses the sum of the absolute values of the differences (residuals) for each pixel as a measure of superposition.
When the superposition is complete, it is considered that the residual is minimized even if it does not become 0 due to noise or the like. Therefore, it is considered that the superposition has been achieved by moving the template region variously on the image including the reference region and moving the template region to minimize the residual. At this time, if the superposition is displaced, the residual increases rapidly when the pixels are sequentially added. Therefore, the SSDA is a method in which if the residual exceeds a certain threshold value during the addition, the addition is stopped immediately and the next movement is performed. The calculation to be used is only addition, and in many cases is terminated halfway, so that the calculation time is greatly reduced. Details of this method are described in, for example, "A class of algorithms for fast digital image reg" by Barnea et al.
istration "IEEE. Trans. , February 1972 c-21, 179-
It is described on page 186.

In the present invention, after obtaining a complete superimposed area by these methods, affine transformation represented by the above equation is performed to perform at least rotational movement correction and enlargement or reduction rate correction on the image including the template area. . That is, the affine transformation is performed using the coefficients a, b, c, and d indicating the rotational movement correction and the enlargement or reduction ratio correction.

Next, the above-described template matching is performed again on the image subjected to the affine transformation. Since the second template matching is performed on the image on which the rotational movement correction and the enlargement or reduction ratio correction have been performed, more accurate matching is performed as compared with the template matching performed first.

Rotational movement correction, enlargement or reduction ratio correction, and parallel movement correction are performed on the image including the template region by affine transformation based on the corresponding points obtained by the template matching. That is, the affine transformation is performed using the coefficients a, b, c, and d indicating the rotational movement correction and the enlargement or reduction ratio correction, and the coefficients e and f indicating the parallel movement correction.

[0026]

According to the radiographic image positioning method of the present invention, a specific region is set in a radiographic image instead of recording a marker for positioning with a subject, and the specific region is rotated and moved. Since the affine transformation for enlarging or reducing is performed at least twice, it is possible to obtain radiation image information of a portion that has been overlapped with a marker in the related art, and it is also possible to improve alignment accuracy.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

FIG. 1 is a schematic diagram of an X-ray photographing apparatus which is an embodiment of the apparatus for recording a radiation image used in the present invention. The X-ray image obtained by this imaging is used for energy subtraction processing.

The stimulable phosphor sheets 5 and 7 are stacked with the filter 6 interposed therebetween, with the sheets 7 facing down. Above this, an X-ray tube 2 that emits X-rays 3 via a subject 4 is arranged. The X-ray imaging apparatus 1 is configured as described above.

An object 4 is irradiated with X-rays 3 emitted from the X-ray tube 2. The X-rays 3a transmitted through the subject 4 are applied to the first stimulable phosphor sheet 5, and a part of the energy of the X-rays 3a is recorded on the first stimulable phosphor sheet 5, whereby the sheet 5 An X-ray image of the subject 4 is stored and recorded in the storage area. The X-rays 3b transmitted through the sheet 5 further pass through the filter 6, and the X-rays 3c transmitted through the filter 6 are applied to the second stimulable phosphor sheet 7. Thus, the X-ray image of the subject 4 is also stored and recorded on the sheet 7.

FIG. 2 shows each of the stimulable phosphor sheets 5 and 7.
FIG. 3 is a diagram schematically illustrating an X-ray image stored and recorded in FIG. The X-ray images 4a and 4b of the subject 4 are stored and recorded on almost the entire surface of each of the stimulable phosphor sheets 5 and 7.

FIG. 3 is an embodiment of an X-ray image reading apparatus which is an embodiment of a reading unit for reading a radiation image used in the present invention, and an arithmetic unit which executes a positioning method of the present invention and performs a subtraction process. It is a perspective view of a certain image processing display.

After the image is taken by the X-ray imaging apparatus 1 shown in FIG. 1, the first and second stimulable phosphor sheets 5, 7 are set one by one at a predetermined position of the X-ray image reading apparatus 10. You. Here, the case of reading the first X-ray image stored and recorded on the first stimulable phosphor sheet 5 will be described.

The stimulable phosphor sheet 5 set at a predetermined position and on which the first X-ray image is stored is recorded by a sheet conveying means 15 such as an endless belt driven by a driving means (not shown) in the direction of arrow Y. (Sub-scan). On the other hand, a light beam 17 emitted from a laser light source 16 is reflected and deflected by a rotary polygon mirror 19 driven by a motor 18 and rotated at a high speed in the direction of arrow Z, and transmitted through a focusing lens 20 such as an fθ lens. In the direction of sub-scan (arrow Y direction)
The main scanning is performed in the direction of arrow X, which is substantially vertical. From the place where the light beam 17 of the stimulable phosphor sheet 5 is irradiated, a stimulable luminescent light 22 of an amount corresponding to the stored and recorded X-ray image information is emitted. It is guided by 23 and is detected photoelectrically by a photomultiplier (photomultiplier) 24. The light guide 23 is formed by molding a light-guiding material such as an acrylic plate. The light guide 23 is arranged such that a linear incident end face 23a extends along the main scanning line on the stimulable phosphor sheet 5. The injection end face 23 formed in an annular shape
The light receiving surface of the photomultiplier 24 is connected to b. The stimulated emission light 22 that has entered the light guide 23 from the incident end face 23a travels inside the light guide 23 by repeating total reflection, exits from the emission end face 23b, and exits from the photomultiplier 24.
The photostimulated luminescence light 22 representing the radiation image is converted by the photomultiplier 24 into an electric signal. The analog signal S output from the photo multiplier 24 is
After being logarithmically amplified by the log amplifier 25, the A / D converter 26
, Sampled and digital image signal S
O is obtained. This image signal SO represents the first X-ray image stored and recorded on the first stimulable phosphor sheet 5, and is referred to as a _first image signal SO1. This first image signal SO ₁ is temporarily recorded in an internal memory in the image processing display device 30.

The image processing display device 30 includes a keyboard 31 for inputting various instructions, a CRT display 32 for displaying auxiliary information for instructions and a visible image based on image signals,
Floppy disk drive 33 loaded with and driven by a floppy disk as an auxiliary storage medium, and CPU
And a main unit 34 having a built-in internal memory.

Next, in the same manner as described above, a second image signal SO ₂ representing the second X-ray image stored and recorded on the second stimulable phosphor sheet 7 is obtained. SO
_{2 is} also temporarily stored in the internal memory in the image processing display device 30.

When the two image signals SO ₁ and SO ₂ to be subjected to the subtraction operation are stored in the internal memory as described above, these two image signals SO ₁ and SO ₂ are read out, and these two image signals SO ₁ and SO ₂ are read out. Image positioning is performed so that the corresponding subtraction operation is performed between each pixel of each X-ray image carried by the signals SO ₁ and SO ₂ .

Here, the image signal SO in this embodiment is
_A method of aligning two X-ray images represented by ₁ , SO ₂ will be described.

In the radiographic image registration method of the present invention, at least two characteristic regions of interest (complex portions having a structure such as a cross edge) are included in each of the X-ray images 4a and 4b shown in FIG. It is important to set more than one place. Therefore, the region of interest is set as template regions 8 and 8 'in the X-ray image 4a, and the regions of interest are set as reference regions 9 and 9' in the X-ray image 4b. Here, it is assumed that an operation is performed to match the template regions 8 and 8 'with the reference regions 9 and 9', respectively. At the same time, the coordinate system of the x-axis and the y-axis is set for the sheet 5 and the coordinate system of the u-axis and the v-axis is set for the sheet 7 as common rectangular coordinates.
The u axis is the left-right direction on the paper surface of FIG. 1, and the y axis and the v axis are
This is a direction perpendicular to the paper surface of FIG.

Here, template matching for matching the template region with the reference region is performed using the correlation method or SSDA as described above. In the correlation method, the point at which the standardized value is the maximum gives the coordinates of the corresponding point (sampling point) described below, as described above. Alternatively, in SSDA, as described above, the point at which the sum of the residuals is minimum gives the coordinates of the corresponding point.

The first X carried by the first image signal SO ₁
The coordinates of each sampling point of the template area on the line image are (X ₁ , Y ₁ ), and the coordinates of each sampling point of the reference area on the second X-ray image carried by the second image signal SO ₂ are (X ₂ , Y ₂ ), a, b, c, d,
When e and f are coefficients, affine transformation

[0042]

(Equation 3)

By transforming the coordinates of the first X-ray image according to the above, the first X-ray image and the second X-ray image are superimposed. Here, in the coordinate transformation based on the expression (1), the entire first X-ray image is enlarged or reduced independently of each other in the X direction and the Y direction, and the entire first X-ray image is rotationally moved. And moving the first X-ray image in the X and Y directions in parallel. However, in the radiographic image alignment method of the present invention, the alignment is not performed only by one affine transformation, so that the first affine transformation involves rotation and conversion of the enlargement or reduction ratio. I do. In other words, even if the translation is performed here, since the rotation and the enlargement or reduction are performed again, the relatively easy translation may be performed by the second or final affine transformation.

Next, the coefficients a, b, c,
A method for obtaining d, e, and f will be described.

Equation (1) is:

[0046]

(Equation 4)

[0047]

(Equation 5)

[0048] Wherein the first mark 11a on the X-ray image, 12a, 13a respectively the coordinates of (X _{11,
Y 11), (X 12,} Y 12), (X 13, Y 13) and then, the mark 11a on the second X-ray image ', 12a', respectively each coordinate of _{13a '(X 21, Y 21} ) , (X ₂₂ , Y ₂₂ ), (X ₂₃ , Y ₂₃ )
And At this time, from Eqs. (2) and (3),

[0049]

(Equation 6)

[0050]

(Equation 7)

[0051]

(Equation 8)

[0052]

(Equation 9)

[0053]

(Equation 10)

[0054]

[Equation 11]

Is as follows. The coefficients to be obtained here are a, b,
Since there are six of c, d, e, and f, the above (2a), (2b), (2
c); can be obtained based on the six equations (3a), (3b) and (3c),

[0056]

(Equation 12)

[0057]

(Equation 13)

[0058]

[Equation 14]

[0059]

(Equation 15)

[0060]

(Equation 16)

[0061]

[Equation 17]

Is obtained.

However, as described above, in the first affine transformation, only the rotational movement and the transformation of enlargement or reduction need only be performed, so that e and f need not be obtained here, but are necessary in the final affine transformation. So e,
The method for obtaining f is described here.

Using the coefficients a, b, c, and d obtained in accordance with the equations (4) to (7) in this way, and performing coordinate transformation in accordance with the equation (1), the first X-ray image is obtained. The inclination can be made substantially equal to the second X-ray image.

In the registration method of the present invention, the affine transformation is performed one or more times after the first affine transformation in order to further increase the accuracy. 2
The affine transformation after the first time is performed in the template regions 8 and 8 ′ in the first X-ray image subjected to the first affine transformation.
Then, template matching is performed again, and each coefficient of the affine transformation shown in the equation (1) is obtained. If the affine transformation is completed twice, the coefficients a, b, c,
d, e, and f are obtained. When affine transformation is further performed, (4)
The coefficients a, b, c, and d may be obtained in accordance with Equations (7) to (7). In this case, when performing the last affine transformation, (4)
The six coefficients a, b, c, d, e, and f may be obtained from Equations (9) to (9).

In the first affine transformation of the above embodiment, only the rotational movement and the transformation of the enlargement or reduction ratio are performed, but the translation may be performed simultaneously in this transformation.

Here, the principle of improving the positioning accuracy by repeating the affine transformation a plurality of times will be described with reference to FIGS.

FIG. 4 is a graph showing the relationship between the relative inclination between a plurality of images, the position of the corresponding point obtained by template matching, and the error of the position of the true corresponding point. This graph shows that the smaller the inclination of the image is, the smaller the positional deviation of the corresponding points is. Also,
For example, when the relative inclination of the image is 2 °, it indicates that the error between the corresponding point obtained by the template matching as described above and the true corresponding point is about one pixel. The actual deviation between the images is within ± 3 ° because it occurs within the cassette, the photographing device, and the reading device, but the relationship shown in FIG. 4 has been confirmed to be effective over a range of approximately ± 5 °. ing.

FIG. 5 shows that the corresponding points are 100 in the X and Y directions.
FIG. 9 is a diagram showing a true corresponding point when the pixel is located at a distance from each pixel and the position of the corresponding point obtained by template matching. FIG. 5A shows a true corresponding point, and FIG.
Indicates the corresponding points obtained. The corresponding point shown in FIG. 5B shows a state where the relative inclination of the image is 2 ° as described above and the position is shifted by one pixel from the true corresponding point.

Here, in FIG. 5A, the inclination of the straight line connecting the true corresponding points is θr = tan ⁻¹ (100/100) = 45 °. On the other hand, in FIG. 5B, even in the worst case, the inclination of the straight line connecting the corresponding points estimated by template matching is θm = tan ⁻¹ (101/99) = 45.6 °, which is true. Indicates that the deviation from the inclination of the straight line connecting the corresponding points is 0.6 ° at the maximum. In other words, it is shown that the relative inclination of the image was originally 2 °, but was improved to 0.6 ° by one affine transformation. Next, when the template matching is performed again by the method of the present invention and the second affine transformation is performed, it can be seen from FIG. 4 that the shift of the corresponding point can be kept within 0.3 pixel. The inclination of the straight line connecting the corresponding points estimated by template matching at this time is, at worst, θm ′ = tan ⁻¹ (100.3 / 99.7) = 45.2 °, which is the straight line connecting the true corresponding points. This shows that the deviation from the inclination is at most 0.2 °. That is, 2
This indicates that the degree of affine transformation has improved to 0.2 °. Therefore, it will be understood that by repeating the affine transformation a plurality of times as described above, the relative displacement related to the rotational movement of the image is gradually reduced, that is, the accuracy of the registration is gradually improved.

Here, the corresponding points are set in the X and Y directions.
Although an example has been shown where the pixels are separated by 100 pixels, the present invention is not limited to this. As another example, a case will be described in which the corresponding point is located at a distance of 1000 pixels in the X and Y directions and the relative inclination of the image is 2 °. The slope of the line connecting the true corresponding points
45 °. On the other hand, the inclination of the straight line connecting the corresponding points estimated by the template matching is, at worst, θm = tan ⁻¹ (1001/999) = 45.06 °, which is equal to the inclination of the straight line connecting the true corresponding points. The maximum deviation is 0.06 °. In other words, this indicates that the image whose relative inclination was 2 ° was improved to 0.06 ° by one affine transformation. From this, it can be seen that the greater the distance between the corresponding points, the higher the accuracy of alignment.

[0072]

According to the radiographic image registration method of the present invention, a region of interest is set for each of a plurality of images to be registered, and the affine transformation is performed on those regions of interest at least twice. Quick and accurate positioning can be performed without recording a marker or the like together with the subject for positioning.

[Brief description of the drawings]

FIG. 1 is an example of an apparatus for recording a radiation image, X
Schematic diagram of X-ray equipment

FIG. 2 is a diagram schematically showing an X-ray image stored and recorded on each stimulable phosphor sheet.

FIG. 3 is an X-ray image reading apparatus that is an embodiment of a reading unit that reads a radiation image used in the present invention, and image processing that is an embodiment of an arithmetic unit that performs the alignment method of the present invention and performs subtraction processing. Perspective view of display device

FIG. 4 is a graph showing a relationship between a relative inclination between a plurality of images, a position of a corresponding point obtained by template matching, and an error of a position of a true corresponding point.

FIG. 5 is a diagram showing a position of a true corresponding point and a position of a corresponding point obtained by template matching when the corresponding point is located at a position separated by 100 pixels in the X direction and the Y direction.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 X-ray imaging apparatus 2 X-ray tube 3 X-ray 4 subject 5 first stimulable phosphor sheet 6 filter 7 second stimulable phosphor sheet 8 template area 9 reference area 10 X-ray image reading device 15 sheet conveying means 16 Laser light source 17 Light beam 18 Motor 19 Rotating polygon mirror 20 Focusing lens 21 Mirror 22 Stimulated emission light 23 Light guide 24 Photomultiplier 25 Log amplifier 26 A / D converter 30 Image processing display 31 Keyboard 32 CRT display 33 Floppy Disk drive 34 Main unit

Claims (2)

(57) [Claims] 1. A method of aligning a plurality of radiation images for a superposition process or a subtraction process of the radiation images, wherein at least two of the plurality of images to be aligned are substantially common to the plurality of images. Setting a region of interest, defining each of the regions of interest of a reference image among the plurality of images as a reference region, the region of interest of another image as a template region, and defining orthogonal coordinates for each of the plurality of images. Performing template matching for matching the template region with the reference region, obtaining coordinate values of at least two corresponding points of the plurality of images, the image including the template region such that the corresponding points match. To convert the coordinate values of the image into the coordinate values of the image including the reference area, (Where u and v are the coordinates of the reference area, x and y are the coordinates of the specific area, a, b, c, and d are the coefficients indicating the rotational movement correction and the enlargement or reduction rate correction, and e and f indicate the parallel movement correction. A coefficient of an affine transformation represented by a coefficient) is obtained, and a first affine transformation for performing at least rotational movement correction and enlargement or reduction ratio correction on a plurality of images including the template region is performed using the coefficient. For multiple images subjected to affine transformation,
Performing template matching again to obtain a coefficient of the affine transformation represented by the above equation, and using this coefficient to perform rotational movement correction, enlargement or reduction rate correction, and parallel movement correction on a plurality of images including the template area A method for positioning a radiographic image, comprising performing affine transformation. 2. The method according to claim 1, wherein the first affine transformation is repeated a plurality of times.