JP2011036407A - Radiographic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray radiographing device 1 which obtains a tomogram D suitable for diagnosis by removing a false image appearing in the tomogram D wherein the numbers of superimposed perspective images are different depending on the portion. <P>SOLUTION: According to an embodiment 1, a superimposed image C is generated by superimposing a series of perspective images P, and a luminance correction part 13 divides the superimposed image C by a luminance correction coefficient K which is the number of the superimposed perspective images P to obtain the tomogram D. Then, in the superimposed image C, supposing an area wherein the end of a subject M in the moving direction of an X-ray tube 3 and an FPD 4 is reflected to be a circumferential area and the other area to be a center area, the luminance correction coefficient K in circumferential area is smaller than that in the center area. Accordingly, the luminance of the tomogram C is suitably corrected depending on the portion, and the tomogram of the subject M is reflected with similar luminance in all the areas of the tomogram D. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The configuration of the present invention relates to a radiation imaging apparatus including a radiation source and an FPD. In particular, a series of fluoroscopic images are taken while the radiation source and the FPD are synchronously moved in opposite directions, and based on this, a series of fluoroscopic images is taken. The present invention relates to a radiographic apparatus that acquires tomographic images.

  In the medical institution, a radiation imaging apparatus 51 that acquires a tomographic image of the subject M is provided. In such a radiation imaging apparatus 51, a series of fluoroscopic images are continuously shot while a radiation source 53 for irradiating radiation and an FPD 54 for detecting radiation move synchronously, and the series of fluoroscopic images are overlapped to obtain a tomographic image. Some are configured to acquire images (see FIG. 12). In such a radiation imaging apparatus 51, during the imaging of a series of fluoroscopic images, the radiation source 53 and the FPD 54 move so as to approach each other along the body axis direction A of the subject M, and the radiation source 53 and the FPD 54 After the positions in the body axis direction A coincide with each other, the radiation source 53 and the FPD 54 move away from each other along the body axis direction A. Such a radiation imaging apparatus is described in, for example, cited document 1.

  An operation when the radiation imaging apparatus 51 captures a tomographic image as described above will be described. First, the radiation source 53 emits radiation intermittently while moving. That is, every time one irradiation is completed, the radiation source 53 moves along the body axis direction of the subject M, and again performs radiation irradiation. In this way, 74 perspective images are acquired, and these are superimposed. The completed image is a tomographic image in which a tomographic image obtained by cutting the subject with a certain cut surface is reflected.

JP 2002-263092 A

However, the conventional configuration as described above has the following problems.
That is, according to the conventional configuration, the end portion of the obtained tomographic image becomes dark. This problem will be described with reference to FIG. In FIG. 12A, the tomographic image moves from the initial state when the X-ray tube 53 and the FPD 54 are at the solid line position to the end state when the X-ray tube 53 and the FPD 54 are at the broken line position. Meanwhile, 74 fluoroscopic images are acquired. The moving direction of the X-ray tube 53 and the FPD 54 is along the body axis direction A of the subject M. At this time, what is always reflected in the 74 fluoroscopic images is limited to the portion of the subject existing in the pentagonal region R.

  The radiation imaging apparatus can acquire tomographic images when the subject is cut at various heights. When acquiring a tomographic image at the reference cut section S1 where the region R is the widest in the body axis direction A, the entire area of the tomographic image is within the region R. Therefore, if 74 perspective images are superimposed, A tomographic image suitable for diagnosis can be acquired.

  However, when acquiring a tomographic image at the cut surface S2 in which the width of the region R is narrower in the body axis direction A, a part of the tomographic image protrudes from the region R. The cut surface S2 is divided into a central region CC that fits in the region R and a peripheral region CS that protrudes from the region R.

  Since the central region CC is generated by superimposing 74 fluoroscopic images, the manner in which the fluoroscopic images are superimposed is the same as the tomographic image in the reference cut surface S1. However, when the peripheral area CS is generated, the fluoroscopic images to be superimposed are fewer than 74 images. This is because the portion of the subject M existing in the peripheral area CS is not always reflected in 74 fluoroscopic images. However, the number of fluoroscopic images superimposed in the peripheral area CS is sufficient to generate a tomographic image. For simplicity, it is assumed that the peripheral region CS is generated by superimposing 37 perspective images.

  When generating a tomographic image, if the number of fluoroscopic images to be partially overlapped is different, there are the following problems. That is, in the tomographic image obtained at the cut surface S2, the peripheral area CS becomes dark as shown in FIG. This is a luminance unevenness caused by a conventional tomographic image generation method. According to the conventional configuration, the tomographic image is generated through a process of superimposing radiographic images and dividing by the number of acquired fluoroscopic images. In this case, the tomographic image is generated by dividing the superimposed fluoroscopic image by 74. When a tomographic image is generated in this way, luminance unevenness as shown in FIG. 13 occurs.

  The cause of the occurrence of uneven brightness will be described. Since the peripheral area CS is generated by superimposing 37 perspective images, it should be divided by 37 originally. In practice, however, it is divided by 74. Then, the brightness of the peripheral area CS is half of the brightness of the central area CC. This is the reason why the peripheral area CS becomes darker than the central area CC.

  Actually, the number of fluoroscopic images to be overlaid in the peripheral area CS is not fixed at 37, but differs depending on the part of the peripheral area CS. Specifically, the number of fluoroscopic images to be superimposed gradually decreases as the distance from the central region CC increases in the peripheral region CS. Accordingly, the peripheral area CS appearing in the tomographic image becomes gradually darker as the distance from the central area CC increases, as shown in FIG.

  The configuration of the present invention has been made in view of such circumstances, and its purpose is to remove unevenness in luminance that appears in a tomographic image due to the difference in the number of fluoroscopic images to be superimposed depending on the portion. An object of the present invention is to provide a radiation imaging apparatus capable of acquiring a tomographic image suitable for diagnosis.

The configuration of the present invention has the following configuration in order to achieve the above object.
That is, a radiation imaging apparatus according to the present invention includes a radiation source that irradiates a subject with radiation, a top plate on which the subject is placed, a radiation detection unit that detects radiation on the subject, and a radiation source and radiation detection unit. Moving means moving in the direction opposite to each other in the moving direction, image generating means for generating a fluoroscopic image based on a detection signal output from the radiation detecting means, a radiation source, and the radiation detecting means A superimposing unit that superimposes a series of fluoroscopic images continuously taken to generate a superposed image, and a luminance correction coefficient to normalize unevenness in luminance superimposed on the superposed image, thereby allowing the subject to have an arbitrary height. Luminance correction means for acquiring a tomographic image in which a tomographic image when cut on a horizontal plane is reflected, and the luminance correction means uses a different luminance correction coefficient depending on the portion of the superimposed image, When the area where the end of the subject in the moving direction is reflected is the peripheral area, and the area where the central area of the subject is reflected in the superimposed image is the central area, the luminance correction in the peripheral area The coefficient is different from the luminance correction coefficient in the central region.

  [Operation / Effect] According to the configuration of the present invention, a series of fluoroscopic images are overlapped to generate a superimposed image, and a luminance correction coefficient is applied to this to generate a tomographic image. The superposed image is simply a superposition of the fluoroscopic images, and the visibility is not excellent. Therefore, a tomographic image is generated by correcting the luminance of the superimposed image. Specifically, the luminance correction unit applies a luminance correction coefficient to the superimposed image, thereby normalizing unevenness in luminance superimposed on the superimposed image, thereby obtaining a tomographic image. As a result, the luminance of the tomographic image is adjusted to the level of the luminance of the fluoroscopic image.

  However, the number of fluoroscopic images to be superimposed differs depending on the overlapped image portion. Therefore, when the same luminance correction coefficient is used in the entire area of the superimposed image, the normalization action may be too strong depending on the portion of the superimposed image. In such a peripheral area of the superimposed image, the number of fluoroscopic images to be superimposed is small, and a smaller value should be selected as a luminance correction coefficient used for normalization.

  Therefore, according to the configuration of the present invention, a region in which the end of the subject in the moving direction, which is the direction in which the radiation source and the radiation detecting unit move, is included in the superposed image as a peripheral region. When the region where the central region of the subject in the moving direction is reflected is the central region, the luminance correction coefficient in the peripheral region is different from the luminance correction coefficient in the central region. The number of fluoroscopic images superimposed in the peripheral area in the moving direction of the superimposed image is smaller than that in the central area. According to the configuration of the present invention, it is possible to make the luminance correction coefficient acting on the peripheral region different from that acting on the central region in accordance with this characteristic. Thereby, the luminance of the tomographic image is optimally corrected according to the portion, and the tomographic image of the subject is captured with the same luminance over the entire area of the tomographic image.

  Further, it is more preferable that the above-described luminance correction unit divides the luminance correction coefficient with respect to the superimposed image while gradually decreasing the luminance correction coefficient in the peripheral region as the distance from the central region increases.

  [Operation / Effect] According to the above-described configuration, the brightness correction means can perform more precise brightness correction. The number of fluoroscopic images (luminance correction coefficient) superimposed on the superimposed image gradually decreases from the central region toward the end in the moving direction. According to the above-described configuration, the luminance correction unit performs division on the superimposed image while gradually decreasing the luminance correction coefficient as the distance from the central region increases in the peripheral region, so that the number of fluoroscopic images superimposed on the superimposed image is obtained. In addition, division is performed, and the luminance correction means can perform more accurate luminance correction.

  In addition, it is more preferable that the above-described luminance correction unit multiply the superimposed image by the luminance correction coefficient while gradually increasing the luminance correction coefficient in the peripheral region as the distance from the central region increases.

  [Operation / Effect] According to the above-described configuration, the brightness correction means can perform more precise brightness correction. The number of fluoroscopic images to be superimposed on the superimposed image (luminance correction coefficient) gradually increases from the central region toward the end in the moving direction. According to the above-described configuration, the luminance correction unit performs multiplication on the superimposed image while gradually increasing the luminance correction coefficient as the distance from the central region increases in the peripheral region, so that the number of fluoroscopic images superimposed on the superimposed image is increased. In addition, multiplication is performed, and the luminance correction means can perform more accurate luminance correction.

  Further, it is more desirable that the luminance correction coefficient acting on a certain portion of the above-described superimposed image is the number of fluoroscopic images superimposed on that portion.

  [Operation / Effect] According to the above-described configuration, the luminance can be corrected more reliably. If a uniform luminance correction coefficient is applied to the entire overlapped image, the division effect is too strong in a part of the overlapped image. Since the entire area of the superimposed image is overlapped by the number of the series of fluoroscopic images, the luminance correction coefficient is collectively applied to the entire area of the superimposed image. The effect appears stronger than expected. According to the above-described configuration, the luminance correction coefficient that acts on a part of the superimposed image is the number of superimposed fluoroscopic images in that part. Therefore, the strength of the division is constant over the entire area of the superimposed image. It can be.

  Further, the radiation source tilting means for tilting the radiation source in synchronization with the movement of the radiation source and the radiation detecting means along the moving direction, and a coefficient acquisition means for acquiring a luminance correction coefficient are further provided. The means controls the radiation source so that the central axis of the radiation beam irradiated by the radiation source passes through the center point of the radiation detection means in synchronization with the movement of the radiation source and the radiation detection means along the movement direction. When the cutting position in which the tomographic image of the subject is reflected at the same position in the series of fluoroscopic images is set as the reference cutting position, the coefficient acquisition unit is configured to superimpose the peripheral area of the superposed image at the center in the moving direction of the superposed image. (B) the vertical distance from the radiation source to the radiation detection means; (B) how many fluoroscopic images are divided in accordance with the distance to the center of the image; From radiation sources Vertical distance to the cutting position, (C) Vertical distance from the cut surface that cuts the subject to the reference cut surface, (D) Distance from each section to the center of the superimposed image, (E) Perspective It is more desirable if it is obtained from the inclination angle of the radiation source when the image is acquired and (F) the width of the detection surface for detecting the radiation of the radiation detection means in the moving direction.

  [Operation / Effect] The above-described configuration shows a specific method for obtaining the luminance correction coefficient. The coefficient acquisition means divides the superposition image, and the vertical distance from the radiation source to the radiation detection means, the vertical distance from the radiation source to the reference cutting position, the height of the cut surface for cutting the subject, Using the six parameters of the distance from the section to the center of the superimposed image, the inclination angle of the radiation source, and the width of the radiation detection means, the luminance correction coefficient used for each section is obtained. Any parameter can be easily obtained as long as the shooting conditions are determined. Therefore, according to the above-described configuration, it is possible to provide a radiation imaging apparatus that can easily obtain a luminance correction coefficient.

  In the above-mentioned radiation detection means, the radiation detection elements for detecting radiation are arranged vertically and horizontally at a predetermined pitch, and the longitudinal direction of the array coincides with the moving direction. It is more desirable to divide the peripheral area of the superimposed image into a plurality of sections based on the vertical pitch of the elements and to apply a luminance correction coefficient for each section.

  Further, it is more preferable that the above-described coefficient acquisition unit divides the peripheral region into a plurality of sections for each width of one radiation detection element reflected in the peripheral region of the superimposed image.

  [Operation / Effect] The above-described configuration shows a specific configuration of the division of the superposed image by the coefficient acquisition means. In the radiation detection means, radiation detection elements for detecting radiation are arranged vertically and horizontally at a predetermined pitch. The division of the superposed image is meaningless even if it is finer than one radiation detection element. Therefore, according to the above-described configuration, the coefficient acquisition unit is configured to divide the peripheral region of the superimposed image into a plurality of sections based on the vertical pitch of the radiation detection elements, and more preferably, the coefficient acquisition unit. In this case, the peripheral region is divided into a plurality of sections for each width of one radiation detection element reflected in the superimposed image. In this way, a brightness correction coefficient is generated individually for each radiation detection element (exactly, a detection element array in which the radiation detection elements are arranged in the horizontal direction) reflected in the superimposed image. The correction coefficient can be acquired efficiently.

  According to the configuration of the present invention, a series of fluoroscopic images are superimposed to generate a superposed image, and the luminance correction unit divides a luminance correction coefficient, which is the number of fluoroscopic images superimposed from the superposed image, to obtain a tomographic image. To be acquired. As a result, the luminance of the tomographic image is adjusted to the level of the luminance of the fluoroscopic image. However, the number of fluoroscopic images to be superimposed differs depending on the overlapped image portion. According to the configuration of the present invention, a region in which the end of the subject is reflected in the movement direction, which is a direction in which the radiation source and the radiation detection unit move, is set as a peripheral region, and When the region where the central region of the subject in the direction is reflected is defined as the central region, the luminance correction coefficient in the peripheral region is smaller than the luminance correction coefficient in the central region. Thereby, the luminance of the tomographic image is optimally corrected according to the portion, and the tomographic image of the subject is captured with the same luminance over the entire area of the tomographic image.

It is a functional block diagram explaining the structure of the X-ray imaging apparatus which concerns on this invention. It is a schematic diagram explaining the structure of FPD which concerns on this invention. It is a schematic diagram explaining the structure of the brightness | luminance correction coefficient table which concerns on this invention. It is a schematic diagram explaining the acquisition method of the tomographic image which concerns on this invention. It is a flowchart explaining operation | movement of the X-ray imaging apparatus which concerns on this invention. It is a schematic diagram explaining the acquisition method of the luminance correction coefficient based on this invention. It is a schematic diagram explaining the acquisition method of the luminance correction coefficient based on this invention. It is a schematic diagram explaining the acquisition method of the luminance correction coefficient based on this invention. It is a schematic diagram explaining the acquisition method of the luminance correction coefficient based on this invention. It is a schematic diagram explaining the acquisition method of the luminance correction coefficient based on this invention. It is a mimetic diagram explaining one modification of the present invention. It is a schematic diagram explaining the structure of the conventional X-ray imaging apparatus. It is a schematic diagram of the tomographic image acquired with the conventional X-ray imaging apparatus.

  Next, embodiments of the radiation imaging apparatus according to Embodiment 1 will be described with reference to the drawings. In addition, the X-ray in each Example is equivalent to the radiation of the structure of Example 1.

  FIG. 1 is a functional block diagram illustrating the configuration of the radiation imaging apparatus according to the first embodiment. As shown in FIG. 1, an X-ray imaging apparatus 1 according to the first embodiment includes a top plate 2 on which a subject M that is a target of X-ray tomography is placed, and a subject provided above the top plate 2. An X-ray tube 3 that irradiates M with a cone-shaped X-ray beam, and a sheet-like flat panel X-ray detector that is provided below the top plate 2 and detects a transmission X-ray image of the subject M ( (Hereinafter abbreviated as FPD) 4, and the X-ray tube 3 and the FPD 4 are connected to each other across the region of interest of the subject M in a state where the central axis of the cone-shaped X-ray beam and the center point of the FPD 4 always coincide with each other. An X-ray grid that absorbs scattered X-rays provided so as to cover an X-ray detection surface that detects X-rays of the FPD 4 and a synchronous movement control unit 8 that controls the synchronous movement mechanism 7 that moves synchronously in the opposite direction. And 5. Thus, the X-ray tube 3, the top plate 2, and the FPD 4 are arranged in the vertical direction in this order. The X-ray imaging apparatus 1 corresponds to the radiation imaging apparatus of the present invention, and the X-ray tube 3 corresponds to the radiation source of the present invention. The FPD 4 corresponds to the radiation detection means of the present invention.

  The X-ray tube 3 is configured to repeatedly irradiate the subject M with a cone-shaped and pulsed X-ray beam according to the control of the X-ray tube control unit 6. The X-ray tube 3 is provided with a collimator that collimates the X-ray beam into a cone shape that is a pyramid. The X-ray tube 3 and the FPD 4 generate imaging systems 3 and 4 that capture X-ray fluoroscopic images.

  The X-ray imaging apparatus 1 according to the first embodiment further includes a main control unit 25 that comprehensively controls the control units 6 and 8 and a display unit 22 that displays an X-ray tomographic image. The main control unit 25 is constituted by a CPU, and by executing various programs, the control units 6 and 8, an image generation unit 11, a superimposition unit 12, a luminance correction unit 13, and a coefficient acquisition unit 14 described later are provided. Realized. The luminance correction unit 13 corresponds to the luminance correction unit of the present invention, and the superimposing unit 12 corresponds to the superimposing unit of the present invention. The coefficient acquisition unit 14 corresponds to the coefficient acquisition unit of the present invention, and the image generation unit 11 corresponds to the image generation unit of the present invention.

  The synchronous movement mechanism 7 is configured to move the X-ray tube 3 and the FPD 4 in synchronization. The synchronous movement mechanism 7 linearly moves the X-ray tube 3 along a linear trajectory parallel to the body axis direction A of the subject M according to the control of the synchronous movement control unit 8. Moreover, during the examination, the cone-shaped X-ray beam irradiated by the X-ray tube 3 is always irradiated toward the region of interest of the subject M. The X-ray irradiation angle is determined by the X-ray tube 3. Is changed from, for example, an initial angle of −20 ° to a final angle of 20 °. Such an X-ray irradiation angle change is performed by the X-ray tube tilting mechanism 9. The synchronous movement control unit 8 controls the synchronous movement mechanism 7 and the X-ray tube tilt mechanism 9 synchronously. The body axis direction A corresponds to the moving direction of the present invention, and the X-ray tube tilting mechanism 9 corresponds to the radiation source tilting means of the present invention.

  In addition, the synchronous movement mechanism 7 moves the FPD 4 provided below the top plate 2 linearly along the body axis direction A of the subject M in synchronization with the linear movement of the X-ray tube 3 described above. The moving direction is opposite to the moving direction of the X-ray tube 3. That is, the cone-shaped X-ray beam whose irradiation source position and irradiation direction change as the X-ray tube 3 moves is always received by the entire surface of the X-ray detection surface of the FPD 4. As described above, in one inspection, the FPD 4 acquires, for example, 74 fluoroscopic images P while moving in synchronization with the X-ray tube 3 in the opposite directions. Specifically, the imaging systems 3 and 4 are opposed to the position indicated by the alternate long and short dash line illustrated in FIG. 1 through the position indicated by the broken line with the position of the solid line as the initial position. That is, a plurality of fluoroscopic images are taken while changing the positions of the X-ray tube 3 and the FPD 4. Incidentally, since the cone-shaped X-ray beam 19 is always received by the entire surface of the X-ray detection surface of the FPD 4, the central axis of the cone-shaped X-ray beam 19 is always coincident with the center point of the FPD 4 during imaging. During imaging, the center of the FPD 4 moves straight, but this movement is in the direction opposite to the movement of the X-ray tube 3. That is, the X-ray tube 3 and the FPD 4 are moved synchronously and in opposite directions along the body axis direction A.

  A configuration of the FPD 4 will be described. On the detection surface for detecting the X-rays of the FDP 4, as shown in FIG. 2, X-ray detection elements 4a for detecting the X-rays are arranged vertically and horizontally. For example, 1,024 X-ray detection elements 4a are arranged in the body axis direction A of the subject, and 1,024 are arranged in the body side direction S of the subject. The arrangement pitch is 300 μm in both the body axis direction A and the body side direction S.

  Further, an image generation unit 11 that generates an X-ray fluoroscopic image based on a detection signal output from the FPD 4 is provided (see FIG. 1), and further downstream of the image generation unit 11. , A superimposing unit 12 that superimposes a plurality of images to generate a superimposed image C, and a luminance correcting unit 13 to be described later are provided.

  The coefficient acquisition unit 14 generates a luminance correction coefficient table T1 that the luminance correction unit 13 refers to. The luminance correction coefficient table T1 is a mapping of the luminance correction coefficient K corresponding to the portion of the superimposed image C, and the luminance correction unit 13 responds to the portion of the superimposed image C based on the luminance correction coefficient table T1. Different luminance correction coefficients K are applied to the superimposed image C.

  The configuration of the brightness correction coefficient table T1 will be described. As shown in FIG. 3, the luminance correction coefficient table T1 is table data in which integers are arranged in order from serial numbers 1 to n. The luminance correction coefficient K corresponding to No. 1 in the luminance correction coefficient table T1 is 37, for example, and the luminance correction coefficient K increases as the serial number increases. The luminance correction coefficient K reaches 74, which is the total number of fluoroscopic images P acquired. After that, even if the serial number of the luminance correction coefficient table T1 increases, the value of the luminance correction coefficient K does not change for a while, but as it approaches the maximum nth, the luminance correction coefficient K gradually decreases, and the luminance at the nth The correction coefficient K is 37. In the luminance correction coefficient table T1, an area that is 74, which is the total number of fluoroscopic images P from which the luminance correction coefficient K is acquired, is referred to as a central area TC, and other areas are referred to as a peripheral area TS. The peripheral area TS of the luminance correction coefficient table T1 corresponds to the peripheral area CS of the superimposed image C, and the central area TC of the luminance correction coefficient table T1 corresponds to the central area CC of the superimposed image C. The brightness correction coefficient table T1 is stored in the storage unit 23.

  Note that the number of fluoroscopic images P need not be used for the luminance correction coefficient K. For example, the correction coefficient K in FIG. 3 may be divided in advance by the number of fluoroscopic images P (74). In this case, for example, the first luminance correction coefficient K in the luminance correction coefficient table T1 is 37/74. In this case, the overlapping unit 12 is configured to previously divide 74 by 74 with respect to the entire area of the superimposed image C when generating the superimposed image C.

  Each image generated by the image generation unit 11, the overlay unit 12, and the luminance correction unit 13 is stored in the storage unit 23. The storage unit 23 stores all set values (for example, luminance correction coefficient table T1, array pitches p, q and SID, SOD, which will be described later) that are referred to when each unit operates.

  Next, the principle of obtaining a tomographic image of the X-ray imaging apparatus 1 according to the first embodiment will be described. FIG. 4 is a diagram illustrating a tomographic image acquisition method of the X-ray imaging apparatus according to the first embodiment. For example, a reference cutting surface MA parallel to the top plate 2 (horizontal with respect to the vertical direction) will be described. As shown in FIG. 4, points P and Q positioned on the reference cutting surface MA are always X-rays of the FPD 4. A series of FPDs 4 are synchronously moved in the opposite direction of the X-ray tube 3 in accordance with the irradiation direction of the cone-shaped X-ray beam 19 by the X-ray tube 3 so as to be projected onto the fixed points p and q of the detection surface. The subject image is generated by the image generation unit 11. In the series of subject images Pm, the projected images of the subject are reflected while changing the position. Then, when this series of subject images Pm is superimposed by the superimposing unit 12, images (for example, fixed points p and q) positioned on the reference cut surface MA are accumulated and imaged as an X-ray tomographic image. become. On the other hand, the point I that is not located on the reference cut surface MA is reflected as a point i in a series of subject images while changing the projection position on the FPD 4. Unlike the fixed points p and q, such a point i is blurred without forming an image when the superimposing unit 12 superimposes the fluoroscopic images. Thus, by superimposing a series of subject images Pm, an X-ray tomographic image in which only an image of the subject M located on the reference cut surface MA is reflected is obtained. In this way, when the X-ray fluoroscopic images are simply superimposed, an X-ray tomographic image at the reference cut surface MA is obtained. The position in the vertical direction of the reference cutting section MA is the reference cutting position of the present invention.

  Furthermore, by changing the setting of the overlapping portion 12, a similar tomographic image can be obtained at any cutting position horizontal to the reference cut surface MA. During shooting, the projection position of the point i moves in the FPD 4, but this moving speed increases as the separation distance between the point I before projection and the reference cut surface MA increases. By using this to superimpose a series of acquired subject images while shifting in the body axis direction A at a predetermined pitch, an X-ray tomographic image at a cutting position parallel to the reference cut surface MA is obtained. The superimposing unit 12 performs superimposition of such a series of subject images. A method for acquiring a tomographic image in this way is called filter back projection.

<Operation of X-ray imaging apparatus>
Next, the operation of the X-ray imaging apparatus according to Embodiment 1 will be described. As shown in FIG. 5, the acquisition operation of the tomographic image of the subject M using the X-ray imaging apparatus according to the first embodiment is a table acquisition step S1 for acquiring the luminance correction coefficient table T1, and the subject M is copied. Each of the fluoroscopic image acquisition step S2 for acquiring the 74 fluoroscopic images P, the superimposing step S3 for superimposing the fluoroscopic images P, and the dividing step S4 for performing a predetermined division according to the part of the superposed images. It is executed according to the steps. Details of these steps will be described in order with reference to the drawings.

<Table acquisition step S1>
First, the luminance acquisition coefficient table T1 is acquired by the coefficient acquisition unit 14. The coefficient acquisition unit 14 reads the width of the SID, SOD, and FPD 4 in FIG. 6 (actually, the distance Δ from one end of the FPD 4 in the body axis direction A to the center point of the FPD 4: see FIG. 10) from the storage unit 23. . This SID is the distance in the Z direction (vertical direction) from the focal point that is the radiation source of the radiation beam emitted by the X-ray tube 3 to the center point of the FPD 4. SOD is the distance in the Z direction from the focal point of the X-ray tube 3 to the reference cut surface MA. The distance Δ is half the width of the detection surface of the FPD 4 in the subject body axis direction A.

  The origin O in the schematic diagram of FIG. 6 will be described. The origin O is a point where the line segment connecting the focal point of the X-ray tube 3 and the center point of the FPD 4 and the reference cut surface MA intersect.

  When acquiring a tomographic image at the reference cut surface MA, the luminance correction coefficients K in the luminance correction coefficient table T1 are all 74 over the serial numbers 1 to n. 74 is the total number of fluoroscopic images P to be acquired. Therefore, in this case, it is not necessary to obtain the luminance correction coefficient table T1 by calculation. Therefore, in the present embodiment, an operation in the case of generating a tomographic image D in the cut surface MB (see FIG. 6) positioned above the reference cut surface MA will be described. In this case, the luminance correction coefficient table T1 includes a value other than 74, which is the total number of fluoroscopic images P to be acquired, and needs to be newly generated. The range of the field of view in which the tomographic image is generated at the cut surface MB is the same size as the reference cut surface MA. In FIG. 6, the cut section MB is a portion indicated by a thick line, and will be simply referred to as a photographing range hereinafter.

  Next, the division pitch q obtained by the coefficient acquisition unit 14 will be described. As shown in FIG. 7, it is assumed that the cut surface MB is covered with a virtual two-dimensional grid composed of a plurality of points. When this virtual two-dimensional grid is projected onto the FPD 4 by the cone-shaped X-ray beam 19, each point just overlaps each X-ray detection element 4a included in the FPD 4. The arrangement pitch of each point of the cut surface MB at this time is the division pitch q.

  The coefficient acquisition unit 14 reads the arrangement pitch p in the body axis direction A of the X-ray detection element 4a of the FPD 4 from the storage unit 23, and obtains the division pitch q in the A direction of the virtual two-dimensional grid. The division pitch q can be obtained geometrically from SOD, SID, arrangement pitch p, and the distance z in the Z direction from the position of the reference cut surface MA to the position of the cut surface MB shown in FIG.

  The coefficient acquisition unit 14 divides the photographing range along the body axis direction A for each division pitch q, and calculates a luminance correction coefficient K for each divided section. The luminance correction coefficient K indicates how many sections of the 74 fluoroscopic images P acquired from now are reflected in the fluoroscopic image P, and the value differs for each section. The calculation method will be described. First, as shown in FIG. 9, the luminance correction coefficient K of the section constituting the central area CC of the superimposed image C is 74 without calculation. This is because the area inside the central area CC is reflected in all the fluoroscopic images P.

  Since the section existing in the peripheral region CS of the photographing range is reflected only in a part of the acquired fluoroscopic image P, the luminance correction coefficient K is lower than 74, which is the total number of the fluoroscopic images P acquired. A method for calculating the luminance correction coefficient K in the peripheral area CS will be described. Therefore, as shown in FIG. 10, it is assumed that how many fluoroscopic images P are superimposed on a certain section d belonging to the peripheral area CS. The section d is assumed to be separated from the origin O by a distance y in the A direction. That is, the position of the section d can be expressed as (y, z) as coordinates.

  As shown in FIG. 10, the inclination angle of the X-ray tube 3 is θ. More precisely, θ is an angle formed by the Z axis in the vertical direction and the central axis of the X-ray beam 19.

  The coefficient acquisition unit 14 calculates which range the inclination angle θ of the X-ray tube 3 is in and the section d is reflected in the fluoroscopic image P. The distance from the center point of the FPD 4 to one end of the FPD 4 is Δ, the mapping κ when the section d is projected on the virtual plane obtained by extending the detection surface of the FPD 4, and the distance to the center point of the FPD 4 is δ (FIG. 10).

  Here, the distance δ, the inclination angle θ, the distance SID, the distance SOD, the distance y, and the relationship between the distance z and θ are represented by equations. The position of κ shown in FIG. 10 can be expressed by the following vector equation using the positions of the focal point p, the section d, and the origin O of the X-ray tube 3.

By the way, since the coordinates of the section d are (y, z) and the coordinates of the focal point p are (SOD tan θ, SOD), if the coordinates of the mapping κ are (a, b), Various relationships can be derived.
(A, b) = t (y, z) + (1-t) (SOD tan θ, SOD) (2)

The equation (2) is decomposed into components a and b as follows.
a = ty + (1-t) SOD tan θ (3)
b = tz + (1-t) SOD (4)

  FIG. 10 shows that b = − (SID−SOD). Therefore, from equation (4), t = −SID / (z−SOD). Substituting this t into equation (3), a can be expressed by the following equation.

  Since the coordinates of the center point Q of the FPD 4 in FIG. 10 are (− (SID−SOD) tan θ, − (SID−SOD)), using equation (5), the distance δ from κ to the center point Q is It can be expressed as follows.

Solving equation (6) gives the following.
δ = | (ztanθ-y) SID / (z-SOD) | (7)

If Δ ≧ δ, the mapping κ of the section d is projected on the detection surface of the FPD 4, and the section d is reflected in the fluoroscopic image P. When δ is greater than or equal to Δ, the range that θ can take can be expressed as follows based on Equation (7).
(Y− | Δ · H |) / z ≦ tan θ ≦ (y + | Δ · H |) / z (8)
However, H = (z-SOD) / SID.

That is, in the section d, the inclination angle θ of the X-ray tube 3 is tan ⁻¹ {(y− | Δ · H |) / z} or more and tan ⁻¹ {(y + | Δ · H |) / z} or less. Sometimes it appears in the fluoroscopic image P. This range represents the maximum value / minimum value of the inclination angle of the X-ray tube 3 allowed for the section d to appear in the fluoroscopic image P. Note that z is constant when one tomographic image is generated, and therefore, the range (allowable range) that the inclination angle of the X-ray tube 3 allowed for the section d to appear in the fluoroscopic image P can be taken. ) Is determined only by the position of the section d in the y direction. Therefore, this allowable range is different for each section d.

  If a permissible range for a certain section d is equal to or larger than the range in which the angle at which the X-ray tube 3 is tilted in tomographic image change (change range) is larger than the change range, 74 sections are acquired. It is reflected in all of the fluoroscopic images P.

  On the other hand, if the allowable range does not cover the entire change range in another section d that is separated from the previous section d in the y direction, a perspective image P that does not include the section d is captured. come. This is because the X-ray tube 3 is tilted beyond the tilt angle of the X-ray tube 3 allowed for the section d to appear in the fluoroscopic image P, and photographing may be performed.

  The coefficient acquisition unit 14 calculates an allowable range for each section d while changing y based on the equation (8), and compares the allowable range with a change range of the inclination angle of the X-ray tube. The section d is reflected in the fluoroscopic image P photographed by tilting the X-ray tube 3 at an inclination angle in a range where the change range of the X-ray tube 3 and the allowable range of a certain section d overlap. In addition, the section d is not reflected in the fluoroscopic image P photographed at a tilt angle in a non-overlapping range.

  Acquisition of the luminance correction coefficient K will be described. The coefficient acquisition unit 14 reads the change range from the storage unit 23 and obtains an overlap range where the change range and the partition range overlap. The luminance correction coefficient K constituting the luminance correction coefficient table T1 is obtained by multiplying the ratio of the overlapping range in the change range by the total number (74) of the fluoroscopic images P. The coefficient acquisition unit 14 repeatedly acquires the luminance correction coefficient K for each section d of the superimposed image C, and associates the serial number representing the position in the A direction of each section with the brightness correction coefficient K in each section d imaging range. Thus, the brightness correction coefficient table T1 is generated. The brightness correction coefficient table T1 is stored in the storage unit 23.

<Transparent Image Acquisition Step S2>
Next, the subject M is placed on the top 2. Then, when the surgeon gives an instruction to acquire the fluoroscopic image P through the console 21, the synchronous movement control unit 8 moves the X-ray tube 3 and the FPD 4 to a predetermined initial position. The imaging systems 3 and 4 at this time are arranged as shown by a solid line in FIG. That is, the X-ray tube 3 in the initial position is located in the front stage in the body axis direction A (longitudinal direction of the top plate 2), and the FPD 4 is located in the rear stage in the body axis direction A. At this time, the X-ray tube 3 is inclined to an initial angle of −20 degrees.

  The X-ray tube control unit 6 controls the X-ray tube 3, and the X-ray tube 3 irradiates the X-ray beam 19 toward the FPD 4 with a predetermined pulse width, tube voltage, and tube current. The X-ray beam 19 passes through the top plate 2 and then enters the FPD 4. The image generation unit 11 assembles the detection signal output by the FPD 4 into an air image (an image in which the subject is not transferred).

  Thereafter, the synchronous movement control unit 8 moves the X-ray tube 3 and the FPD 4 synchronously and in directions opposite to each other. The X-ray tube control unit 6 intermittently irradiates the X-ray beam 19 during the movement, and the image generation unit 11 generates a fluoroscopic image P each time. In this way, a series of perspective images P are generated. At this time, the synchronous movement control unit 8 moves the X-ray tube 3 to the rear stage side in the body axis direction A, and moves the FPD 4 to the front stage side in the body axis direction A.

  Then, the synchronous movement control unit 8 moves the X-ray tube 3 and the FPD 4 to a predetermined final position. The imaging systems 3 and 4 at this time are arranged as shown by a one-dot chain line in FIG. That is, the X-ray tube 3 at the final position is located at the rear stage of the body axis direction A (longitudinal direction of the top plate 2), and the FPD 4 is located at the front stage of the body axis direction A. At this time, the X-ray tube 3 is inclined to a final angle of 20 degrees. In this state, the last fluoroscopic image P is acquired, and acquisition of a series of fluoroscopic images P ends. In the first embodiment, 74 fluoroscopic images P are acquired.

<Superposition step S3>
A series of fluoroscopic images P is sent to the overlapping unit 12. The superimposing unit 12 superimposes a series of fluoroscopic images P while shifting in the body axis direction of the subject M, and generates a superposed image C in which a tomographic image of the subject M in the cut surface MB is reflected. Since the superposed image C is simply overlaid, it is necessary to improve the visibility by performing luminance correction on the superposed image C.

<Division step S4>
The superimposed image C is sent to the luminance correction unit 13. The luminance correction unit 13 reads the luminance correction coefficient table T1 stored in the storage unit 23, divides the superposed image C into n regions along the body axis direction of the subject M, and the body of the subject M The luminance data of the first region in which the end portion in the axial direction is reflected is divided by the first luminance correction coefficient (specifically, 37) in the luminance correction coefficient table T1. Thereafter, the luminance correction unit 13 generates the tomographic image D by dividing the luminance data of each area of the superimposed image C by the luminance correction coefficient K corresponding to this area while referring to the luminance correction coefficient table T1. In this way, the luminance correction unit 13 reflects the superposed image C in the body axis direction A at the pitch of one X-ray detection element 4a reflected in the superposed image C (more precisely, the superposed image C is reflected in the superposed image C). The superposed image C is divided along the body axis direction of the subject image, and an individual luminance correction coefficient is applied to each of the divided sections. It is sufficient that the operation of the luminance correction unit 13 is performed at least for the peripheral region CS of the superimposed image C.

  A specific operation of the luminance correction unit 13 will be described. In the portion corresponding to the central region of the superimposed image C, 74 perspective images P are superimposed, and the luminance data in this portion is the sum of the luminance data of the 74 perspective images P. On the other hand, in the peripheral portion corresponding to the end portion of the subject M in the body axis direction of the superposed image C, 37 perspective images P are superimposed, and only the luminance data of the 37 perspective images P are added. Therefore, the luminance data in the peripheral portion of the superimposed image C is smaller than the luminance data in the central area. If the brightness of the superposed image C is corrected and the entire area of the superposed image C is divided by 74, the division is performed at the peripheral portion by a number equal to or larger than the number of the fluoroscopic images P superimposed. Therefore, the brightness is darker than that in the central area. However, according to the configuration of the first embodiment, the luminance correction unit 13 changes the luminance correction coefficient K in accordance with the portion of the superimposed image C, and the superimposed image in which the number of the superimposed fluoroscopic images P is partially different. C brightness correction is performed. Specifically, the luminance correction coefficient K in a certain part of the superimposed image C is equal to the number of fluoroscopic images P superimposed on that part. Accordingly, the luminance unevenness described in FIG. 13 does not appear in the tomographic image D. The luminance correction coefficient table T1 needs to be obtained again every time the cutting position is reset. A table corresponding to each cutting position may be stored in the storage unit 23, and the luminance correction unit 13 may be configured to select a table suitable for correction.

  The tomographic image D is displayed on the display unit 22, and the operation of the X-ray imaging apparatus 1 is completed.

  As described above, according to the configuration of the first embodiment, a superimposed image C is generated by superimposing a series of fluoroscopic images P, and a tomographic image D is generated by applying a luminance correction coefficient K thereto. Yes. The superposed image C is obtained by simply superimposing the fluoroscopic images P, and the visibility is not excellent. Therefore, the tomographic image D is generated by correcting the luminance of the superimposed image C. Specifically, the tomographic image D is acquired by the luminance correction unit 13 dividing the luminance correction coefficient K, which is the number of fluoroscopic images P superimposed from the superimposed image C. As a result, the luminance of the tomographic image D is adjusted to the level of the luminance of the fluoroscopic image P.

  However, the number of fluoroscopic images P to be overlaid differs depending on the overlapped image C portion. Therefore, if the same luminance correction coefficient K is used in the entire area of the superimposed image C, the division effect may be too strong depending on the portion of the superimposed image C. In such a superposed image C portion, the number of fluoroscopic images P to be superimposed is small, and a smaller value should be selected as the luminance correction coefficient K used for division.

  Therefore, according to the configuration of the first embodiment, the luminance correction coefficient K in the peripheral area CS of the superimposed image C is smaller than the luminance correction coefficient K in the central area CC of the superimposed image C. In the configuration of the first embodiment, it is noted that the number of fluoroscopic images P superimposed in the peripheral region CS in the body axis direction A of the superimposed image C is smaller than that in the central region CC. Set K. Specifically, the luminance correction coefficient K in the peripheral area CS is smaller than that in the central area CC. That is, the luminance correction coefficient K acting on the peripheral area CS of the superimposed image C belongs to the peripheral area CS of the luminance correction coefficient table T1, and its value is an integer from 37 to 73. The luminance correction coefficient K acting on the central area CC of the superimposed image C belongs to the central area CC of the luminance correction coefficient table T1, and its value is 74. In this way, the luminance of the tomographic image D is optimally corrected according to the portion, and the tomographic image of the subject M is copied with the same luminance over the entire area of the tomographic image D.

  According to the configuration of the first embodiment, the luminance correction unit 13 can perform accurate luminance correction. The number of fluoroscopic images P superimposed on the superimposed image C gradually decreases from the central region CC toward the end in the body axis direction A. Therefore, in the configuration of the first embodiment, the luminance correction unit 13 performs division on the superimposed image C while gradually decreasing the luminance correction coefficient K as the distance from the central region CC increases in the peripheral region CS. Thereby, the brightness correction unit 13 can perform more precise brightness correction.

  Further, according to the configuration of the first embodiment, the luminance can be corrected more reliably. If a uniform luminance correction coefficient K is applied to the entire area of the superimposed image C, the division operation becomes too strong in a part of the superimposed image C. Since the entire area of the superposed image C is overlapped by the number of the series of fluoroscopic images P, the uniform brightness correction coefficient K is applied to the entire area of the superposed image C, so that the fluoroscopic image P is overlapped. The smaller the number, the stronger the effect of division. According to the configuration of the first embodiment, the luminance correction coefficient K acting on a portion of the superimposed image C is the number of the fluoroscopic images P superimposed on the portion, so that the division is performed in the entire region of the superimposed image C. The strength of the action can be made constant.

  A specific method for obtaining the luminance correction coefficient K is as follows. That is, the coefficient acquisition unit 14 divides the superimposed image C, and uses the six parameters of the distance y, the inclination angle θ, the distance SID, the distance SOD, the distance z, and the width Δ, and the luminance correction coefficient used for each section. Find K. Any parameter can be easily obtained as long as the shooting conditions are determined. Therefore, according to the configuration of the first embodiment, the X-ray imaging apparatus 1 that can easily obtain the luminance correction coefficient K can be provided.

  The division of the superposition image C by the coefficient acquisition unit 14 is performed with reference to the X-ray detection element 4a of the FPD 4. This is because the division of the superposed image C is meaningless even if it is finer than that of one X-ray detection element 4a. According to the configuration of the first embodiment, the coefficient acquisition unit 14 is configured to divide the peripheral region CS of the superimposed image C into a plurality of sections based on the vertical pitch of the X-ray detection element 4a, which is more desirable. That is, the coefficient acquisition unit 14 divides the peripheral region CS into a plurality of sections for each width of one X-ray detection element 4a reflected in the superimposed image C. In this way, an individual luminance correction coefficient K is generated for each X-ray detection element 4a (exactly, a detection element array in which the X-ray detection elements 4a are arranged in the body side direction S) reflected in the superimposed image C. Therefore, the luminance correction coefficient K suitable for correction can be acquired efficiently.

  The present invention is not limited to the configuration of the above-described embodiment, and the following modified implementation is possible.

  (1) Although the embodiment described above is a medical device, the present invention can also be applied to industrial and nuclear devices.

  (2) X-rays referred to in the above-described embodiments are an example of radiation in the present invention. Therefore, the present invention can be applied to radiation other than X-rays.

  (3) Although the luminance correction unit 13 of the above-described embodiment performs the division process, the present invention is not limited to this. A multiplication process may be used instead of the division process. In this case, the luminance correction coefficient is the reciprocal of the luminance correction coefficient of the first embodiment. The configuration of the luminance correction coefficient table T1 in this case will be described. As shown in FIG. 11, the luminance correction coefficient table T1 is table data in which integers are arranged in order from serial numbers 1 to n. The brightness correction coefficient K corresponding to No. 1 in the brightness correction coefficient table T1 is, for example, 1/37, and the brightness correction coefficient K decreases as the serial number increases. The luminance correction coefficient K reaches 1/74 which is the reciprocal of the total number of fluoroscopic images P to be acquired. Thereafter, even if the serial number of the luminance correction coefficient table T1 increases, the value of the luminance correction coefficient K does not change for a while, but the luminance correction coefficient K gradually increases as it approaches the maximum nth, The luminance correction coefficient K is 1/37. The brightness correction coefficient table T1 is stored in the storage unit 23.

  In addition, the luminance correction unit 13 can employ an operation that cancels out uneven luminance that varies depending on the portion of the superimposed image C other than division processing / multiplication processing.

A Body axis direction (moving direction)
C superposition image D tomographic image CS peripheral area CC central area K luminance correction coefficient 1 X-ray imaging apparatus (radiation imaging apparatus)
2 Top plate 3 X-ray tube (radiation source)
4 FPD (radiation detection means)
4a X-ray detector (radiation detector)
9 X-ray tube tilting mechanism (radiation source tilting means)
11 Image generation unit (image generation means)
12 Superposition part (superposition means)
13 Luminance correction unit (luminance correction means)
14 Coefficient acquisition unit (coefficient acquisition means)

Claims (7)

A radiation source for irradiating the subject with radiation;
A top plate on which the subject is placed;
Radiation detecting means for detecting radiation on the subject;
Moving means for moving the radiation source and the radiation detecting means synchronously and in opposite directions along the moving direction;
Image generating means for generating a fluoroscopic image based on a detection signal output by the radiation detecting means;
A superimposing unit that superimposes a series of fluoroscopic images continuously taken while the radiation source and the radiation detecting unit are moved to generate a superimposed image;
Luminance correction means for correcting a luminance unevenness superimposed on the superposed image using a luminance correction coefficient and acquiring a tomographic image in which a tomographic image is obtained when the subject is cut at a horizontal plane of an arbitrary height. Means and
The luminance correction means uses a different luminance correction coefficient depending on the portion of the superimposed image,
A region in which the end of the subject in the moving direction is reflected in the superimposed image is a peripheral region, and a region in which the central region of the subject in the moving direction is reflected in the superimposed image is a central region. When
A radiation imaging apparatus, wherein a brightness correction coefficient in the peripheral region and a brightness correction coefficient in the central region are different. The radiographic apparatus according to claim 1,
The radiographic apparatus according to claim 1, wherein the luminance correction unit divides the luminance correction coefficient with respect to the superimposed image while gradually decreasing the luminance correction coefficient in the peripheral region as the distance from the central region increases. The radiographic apparatus according to claim 1,
The radiography apparatus, wherein the brightness correction unit multiplies the superimposed image by the brightness correction coefficient while gradually increasing the brightness correction coefficient in the peripheral area as the distance from the center area increases. The radiographic apparatus according to any one of claims 1 to 3,
The radiation tomography apparatus according to claim 1, wherein the luminance correction coefficient acting on a portion of the superimposed image is a number of the fluoroscopic images superimposed on the portion. The radiation imaging apparatus according to any one of claims 1 to 4,
Radiation source tilting means for tilting the radiation source in synchronization with movement of the radiation source and the radiation detection means along the moving direction;
Coefficient acquisition means for acquiring the luminance correction coefficient is further provided,
The radiation source tilting means is configured such that a central axis of a radiation beam irradiated by the radiation source is set to a center of the radiation detection means in synchronization with the movement of the radiation source and the radiation detection means along the movement direction. Tilt the radiation source to pass the point,
When the cutting position where the tomographic image of the subject is reflected at the same position in a series of fluoroscopic images is the reference cutting position,
The coefficient acquisition unit divides the peripheral region of the superposed image according to a distance to the center of the superposed image that is the center in the moving direction of the superposed image, and superimposes a number of fluoroscopic images on each of the divided sections. (A) the vertical distance from the radiation source to the radiation detection means,
(B) Vertical distance from the radiation source to the cutting position,
(C) The vertical distance from the cut surface that cuts the subject to the reference cut surface,
(D) distance from each section to the center of the superimposed image,
(E) An inclination angle of a radiation source when each fluoroscopic image is acquired, and (F) a radiation imaging apparatus, which is obtained from a width in a moving direction of a detection surface for detecting radiation included in the radiation detection means. The radiographic apparatus according to claim 5,
In the radiation detection means, radiation detection elements for detecting radiation are arranged vertically and horizontally at a predetermined pitch, and the longitudinal direction of the array coincides with the moving direction,
The coefficient acquisition means divides the peripheral area of the superposed image into a plurality of sections based on a vertical pitch of the radiation detection elements, and applies a luminance correction coefficient for each section. apparatus. The radiographic apparatus according to claim 6,
The radiographic apparatus according to claim 1, wherein the coefficient acquisition unit divides the peripheral region into a plurality of sections for each width of the radiation detecting element reflected in the peripheral region of the superimposed image.

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