WO2016103427A1

WO2016103427A1 - Radiation imaging apparatus

Info

Publication number: WO2016103427A1
Application number: PCT/JP2014/084425
Authority: WO
Inventors: 歩馬場
Original assignee: 株式会社島津製作所
Priority date: 2014-12-25
Filing date: 2014-12-25
Publication date: 2016-06-30

Abstract

Provided is an X-ray tomography apparatus such that artifacts do not occur in a tomographic image. In this X-ray tomography apparatus 1, the speed of a FPD 4 changes when imaging a series of X-ray images P while an X-ray tube 3 and the FPD 4 is moved in opposite directions. As a result, the imaged positions of a reference point on a transverse section change among the series of X-ray images P. Because the positions of the imaged artifacts are the same among the series of X-ray images P, generating a tomographic image D on the basis of a series of X-ray images Pa that have been subjected to an image shifting process prevents artifacts from being included in the tomographic image D.

Description

Radiography equipment

The present invention relates to a radiographic apparatus that generates a tomographic image based on radiographic images taken continuously while changing the imaging direction.

Medical institutions are equipped with radiation imaging devices that acquire images of subjects with radiation. As shown in FIG. 24, such a conventional radiographic apparatus includes a bed that supports a top plate 52 on which a subject is placed, a radiation source 53, and a radiation detector that detects radiation provided inside the bed. 54.

Some apparatuses as shown in FIG. 24 are configured such that the radiation source 53 and the radiation detector 54 can move synchronously so that a tomographic image by tomosynthesis can be acquired. Imaging by tomosynthesis is a specific method in which the radiation source 53 and the radiation detector 54 are moved in opposite directions with respect to the subject M on the top plate 52, and the radiographic images continuously taken between them are superimposed. This is a method of obtaining a tomographic image when the subject M is cut in a plane (see, for example, Patent Document 1).

JP-A-57-203430

However, the conventional radiation tomography apparatus has the following problems.
That is, in the conventional radiation tomography apparatus, the tomographic image may become unclear.

A false image that is not related to the subject image may appear in the radiation image that is the basis of the tomographic image. Among such false images, there are those that do not appear in the tomographic image because they fade as the radiographic images are superimposed. However, some radiographic images become increasingly clear as they are superimposed. Such a false image appears on the tomographic image in the form of being superimposed on the subject image, causing a reduction in visibility.

Among the false images that appear in the radiation image, what appears on the tomographic image is, for example, the shadow of the radiation grid. A radiation grid 55 is attached to the radiation detector 54 for scattered radiation generated in the subject. The radiation grid 55 has a structure like a window blind in which strip-shaped absorbers that absorb scattered radiation are arranged. Since the absorber is made of a material that absorbs radiation, when an attempt is made to capture a radiation image, the shadow of the radiation grid 55 appears thinly in the radiation image.

The shadow of the radiation grid 55 is reflected in the same pattern in a series of radiation images. Therefore, when a series of radiographic images are overlapped in order to obtain a tomographic image, the shadows of the radiation grids 55 strengthen each other as shown in FIG. 25 and an image is formed on the tomographic image. In order to suppress the occurrence of such a false image on the tomographic image, it is necessary to take a series of radiation images so that the positions where the shadow of the radiation grid 55 is reflected are different from each other. Conventionally, a mechanism for suppressing a false image on a tomographic image by taking a series of radiation images while swinging the radiation grid 55 with respect to the radiation detector 54 has been devised.

However, the false image that appears in the same pattern in a series of radiation images is not limited to the shadow of the radiation grid 55. The above-described rocking method cannot be expected to suppress false images except for the shadow of the radiation grid 55. Therefore, a new configuration is desired in which a false image of the same pattern does not appear in a series of radiation images more reliably.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a tomographic image in a radiography apparatus that generates a tomographic image based on radiographic images continuously shot while changing the imaging direction. The purpose is to prevent the image from forming.

The present invention has the following configuration in order to solve the above-described problems.
That is, a radiation tomography apparatus according to the present invention includes a radiation source that irradiates a subject with radiation, a detection unit that detects radiation transmitted through the subject, a radiation source moving unit that moves the radiation source relative to the subject, A radiation source movement control means for controlling the movement of the radiation source, a detector moving means for moving the detection means relative to the subject, and a radiation image in which a false image is reflected together with the subject image based on the output of the detection means The detector moving means is controlled so that the speed of the detecting means is changed when a series of radiographic images taken while the image generating means, the radiation source and the detecting means are moved in opposite directions. Detector movement control means, and image processing for shifting the image to a series of radiation images in which a false image of the same pattern is captured, so that the positions to be captured are a series of Shift image processing means that shifts the reference point inside the subject, which differs depending on the ray image, to the same position on the image, and a reference point based on a series of radiation images in which the appearance positions of false images are shifted from each other by shift image processing And a tomographic image generating means for generating a tomographic image of a subject in a cut surface including

[Operation / Effect] According to the present invention, a radiation tomography apparatus in which a false image is not formed on a tomographic image can be provided. That is, the radiation tomography apparatus according to the present invention changes the speed of the detection means when taking a series of radiation images while the radiation source and the detection means are moved in opposite directions. As a result, the position of the reference point on the cut surface changes between a series of radiation images. On the other hand, the position where the false image appears is the same between the series of radiation images. If a tomographic image is generated based on a series of radiographic images that have been subjected to image processing that shifts so that the reference point is at the same position on the image, the tomographic image of the subject at the cutting plane that reliably includes the reference point is included in the tomographic image. Is reflected. On the other hand, no false image appears in the tomographic image. This is because the appearance positions of the false images reflected in the series of radiographic images are shifted by the image processing and are canceled out when generating the tomographic image.

In the above-mentioned radiation tomography apparatus, the detector movement control means is more desirable if the detector movement means is controlled so that the detection means repeats acceleration and deceleration.

[Operation / Effect] The above-described configuration represents a more desirable form of the apparatus according to the present invention. If the detection means is moved so that the detection means repeats acceleration and deceleration, a series of radiographic images necessary for generating a tomographic image can be reliably executed while changing the speed of the detection means. This is because the average speed of the detection means can be set to the speed of the detection means in the conventional device related to the detection means constant speed movement.

Further, in the above-described radiation tomography apparatus, the detector movement control means includes detector movement means so that the positions at which the reference points are reflected are different between the radiographic images taken when the detection means changes from acceleration to deceleration. It is more desirable to control.

Further, in the above-mentioned radiation tomography apparatus, the detector movement control means includes detector movement means so that the positions at which the reference points are reflected are different between the radiographic images taken when the detection means changes from deceleration to acceleration. It is more desirable to control.

[Operation / Effect] The above-described configuration represents a more desirable form of the apparatus according to the present invention. The position at which the reference point is reflected between the radiographic images tends to be particularly similar between the images taken when the detection unit changes from acceleration to deceleration. If such a state is left as it is, it may not be possible to reliably suppress the appearance of a false image on the tomographic image. Such a problem also occurs when the detecting means changes from deceleration to acceleration. Therefore, the above configuration pays attention to this problem, and the movement mode of the detection means is selected so that the positions where the reference points are reflected are different between the radiographic images taken when the detection means changes from acceleration to deceleration. The Similarly, the movement mode of the detection means is selected so that the positions where the reference points are reflected are different between the radiographic images taken when the detection means changes from deceleration to acceleration. Thereby, it can suppress reliably that a false image appears on a tomographic image.

In the above-mentioned radiation tomography apparatus, the detector movement control means recognizes the speed corresponding to each of the radiographic images based on a composite function obtained by adding two periodic functions having different periods and a constant, and detects the detector. It is more desirable to control the moving means.

[Operation / Effect] The above-described configuration represents a more desirable form of the apparatus according to the present invention. If the detection means is moved at a speed based on a combined function obtained by adding two periodic functions having different periods and a constant, between the radiographic images taken when the detection means changes from acceleration to deceleration (or from deceleration to acceleration). As a result, the positions where the reference points are reflected are surely different from each other.

In the above-described radiation tomography apparatus, the detector movement control means recognizes the speed corresponding to each of the radiographic images based on a composite function in which the speed of the detection means adds a constant to a periodic function, and moves the detector. It is more desirable to control the means.

[Operation / Effect] The above-described configuration represents a more desirable form of the apparatus according to the present invention. If the detection means is moved at a speed based on a composite function in which the speed of the detection means is a constant added to a periodic function, acceleration and deceleration of the detection means are reliably repeated.

In the above-mentioned radiation tomography apparatus, the detector movement control means is more preferably controlled by controlling the detector movement means so that the detection means continues to accelerate.

[Operation / Effect] The above-described configuration represents a more desirable form of the apparatus according to the present invention. If the detection means is moved so as to continue to accelerate, the detection means will not rattle during imaging, and a tomography apparatus that is safe and less burdensome on the subject and the apparatus itself can be provided.

According to the present invention, it is possible to provide a radiation tomography apparatus in which a false image is not formed on a tomographic image. That is, the radiation tomography apparatus according to the present invention changes the speed of the detection means when taking a series of radiation images while the radiation source and the detection means are moved in opposite directions. As a result, the position of the reference point on the cut surface changes between a series of radiation images. On the other hand, since the position where the false image is reflected is the same between the series of radiographic images, if the tomographic image is generated based on the series of radiographic images subjected to the image shift process, the false image is reflected in the tomographic image. There is nothing.

1 is a functional block diagram illustrating an overall configuration of an X-ray tomography apparatus according to Embodiment 1. FIG. FIG. 3 is a schematic diagram illustrating the principle of obtaining a tomographic image according to the first embodiment. It is a schematic diagram explaining the shadow of the X grid which becomes a problem in the apparatus according to the first embodiment. FIG. 6 is a schematic diagram illustrating a complementary mark of a defective pixel that is a problem in the apparatus according to the first embodiment. FIG. 5 is a schematic diagram for explaining calibration overcorrection which is a problem in the apparatus according to the first embodiment. FIG. 5 is a schematic diagram for explaining calibration overcorrection which is a problem in the apparatus according to the first embodiment. FIG. 6 is a schematic diagram illustrating the principle that a false image that becomes a problem in the apparatus according to the first embodiment appears in a tomographic image. FIG. 6 is a schematic diagram illustrating the principle that a false image that becomes a problem in the apparatus according to the first embodiment appears in a tomographic image. FIG. 6 is a schematic diagram illustrating the principle that a false image that becomes a problem in the apparatus according to the first embodiment appears in a tomographic image. FIG. 4 is a schematic diagram for explaining the importance of a reference cross section according to the first embodiment. FIG. 5 is a schematic diagram illustrating the speed of the FPD according to the first embodiment. 6 is a schematic diagram illustrating movement of an FPD according to Embodiment 1. FIG. 6 is a schematic diagram illustrating movement of an FPD according to Embodiment 1. FIG. FIG. 6 is a schematic diagram for explaining the operation of the FPD movement control unit according to the first embodiment. FIG. 6 is a schematic diagram for explaining the operation of the FPD movement control unit according to the first embodiment. FIG. 6 is a schematic diagram illustrating an operation of the image processing unit according to the first embodiment. FIG. 6 is a schematic diagram illustrating an operation of the image processing unit according to the first embodiment. FIG. 6 is a schematic diagram illustrating optimization of FPD movement according to the first embodiment. FIG. 6 is a schematic diagram illustrating optimization of FPD movement according to the first embodiment. FIG. 6 is a schematic diagram illustrating optimization of FPD movement according to the first embodiment. FIG. 6 is a schematic diagram illustrating optimization of FPD movement according to the first embodiment. FIG. 6 is a schematic diagram illustrating optimization of FPD movement according to the first embodiment. FIG. 6 is a schematic diagram illustrating optimization of FPD movement according to the first embodiment. It is a schematic diagram explaining the structure of the conventional apparatus. It is a schematic diagram explaining the problem of a conventional apparatus.

The configuration of the X-ray imaging apparatus according to the present invention will be described. X-rays correspond to the radiation of the present invention. FPD is an abbreviation for flat panel detector. In addition, the X-ray imaging apparatus according to the present invention can capture tomographic images based on the principles of tomosynthesis reconstruction methods such as shift addition, filter back projection, and successive approximation. The subject M corresponds to the subject of the present invention.

<Overall configuration of X-ray imaging apparatus>
As shown in FIG. 1, the X-ray tomography apparatus 1 according to the first embodiment uses a top plate 2 on which a subject M in a supine position is placed, and X-rays provided on the upper side (one surface side) of the top plate 2. An X-ray tube 3 that irradiates the subject M, and a device that is placed on the top 2 and disposed below the subject M, detects X-rays transmitted through the subject M, and detects signals Is provided. The FPD 4 is a rectangle having four sides along either the body axis direction A or the body side direction S of the subject M. One of the FPDs 4 is used at the time of imaging, and is arranged between the subject M and the top board 2 in the case of imaging related to the supine position. The detection surface for detecting X-rays of the FPD 4 faces the X-ray tube 3 and the subject M side. The X-ray tube 3 irradiates the quadrangular pyramid-shaped X-rays toward the FPD 4. Therefore, the FPD 4 receives X-rays on the entire detection surface. The X-ray tube 3 corresponds to the radiation source of the present invention, and the FPD 4 corresponds to the detection means of the present invention.

The X-ray grid 5 is provided so as to cover the detection surface of the FPD 4. The X-ray grid 5 is configured to absorb scattered X-rays that are secondarily generated when the X-ray beam passes through the subject M. The X-ray grid 5 suppresses the scattered X-rays from being detected by the FPD 4 and prevents the image quality from being deteriorated by the scattered X-rays. The X-ray grid 5 moves following the movement of the FPD 4.

The X-ray tube controller 6 shown in FIG. 1 is provided for the purpose of controlling the X-ray tube 3 with a predetermined tube current, tube voltage, and pulse width. The X-ray tube control unit 6 controls the X-ray tube 3 so that an X-ray beam is irradiated toward the subject M every time a predetermined time elapses. By this control, the imaging of the X-ray image P is repeated every elapse of a predetermined time, and a series of imaging of the X-ray image P in the apparatus according to the present invention is executed.

The X-ray tube moving mechanism 7 a is configured to move the X-ray tube 3 relative to the top plate 2. The X-ray tube moving mechanism 7 a can move the X-ray tube 3 along the body axis of the subject M. Thus, the X-ray tube 3 can be moved with respect to the subject M on the top 2 by the X-ray tube moving mechanism 7a. The X-ray tube movement control unit 8a is provided for the purpose of controlling the X-ray tube movement mechanism 7a. The X-ray tube movement control unit 8a controls the movement of the X-ray tube 3 through the X-ray tube moving mechanism 7a. The X-ray tube movement mechanism 7a corresponds to the radiation source movement means of the present invention, and the X-ray tube movement control unit 8a corresponds to the radiation source movement control means of the present invention.

The FPD moving mechanism 7 b is configured to move the FPD 4 relative to the top plate 2 below the top plate 2. The FPD moving mechanism 7b can move the FPD 4 along the body axis of the subject M. In this way, the FPD 4 can move relative to the subject M on the top 2 by the FPD moving mechanism 7b. The FPD movement control unit 8b is provided for the purpose of controlling the FPD movement mechanism 7b. The FPD movement mechanism 7b corresponds to the detector movement means of the present invention, and the FPD movement control unit 8b corresponds to the detector movement control means of the present invention.

The FPD movement control unit 8b plays an important role for the present invention. In other words, the FPD movement control unit 8b allows the FPD 4 to change the speed of the FPD 4 when the X-ray tube 3 and the FPD 4 are taken in a series of X-ray images P while being moved in opposite directions. The moving mechanism 7b is controlled. More specifically, the FPD movement control unit 8b is configured to control the FPD movement mechanism 7b so that the FPD 4 repeats acceleration and deceleration. Details of the control performed by the FPD movement control unit 8b will be described later.

The X-ray tube moving mechanism 7a and the FPD moving mechanism 7b are configured to move the X-ray tube 3 and the FPD 4 in synchronization with the subject M. The X-ray tube moving mechanism 7a and the FPD moving mechanism 7b are linear trajectories (longitudinal of the top plate 2) parallel to the body axis direction A of the subject M according to the control of the X-ray tube moving control unit 8a and the FPD moving control unit 8b. The X-ray tube 3 is moved straight along (direction). The moving direction of the X-ray tube 3 and the FPD 4 coincides with the longitudinal direction of the top 2. The directions of the synchronous movement of the X-ray tube 3 and the FPD 4 realized by the X-ray tube moving mechanism 7a and the FPD moving mechanism 7b are opposite to each other. Therefore, when the X-ray tube 3 moves from the head of the subject M toward the toes, the FPD 4 moves from the toes of the subject M toward the head.

During the synchronous movement of the X-ray tube 3 and the FPD 4, 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. That is, the irradiation angle of the X-ray beam is changed from, for example, an initial angle of −20 ° to a final angle of 20 ° by changing the angle of the X-ray tube 3. In other words, the apparatus according to the present invention is devised so that the X-ray tube 3 is inclined so that the X-ray beam irradiated by the X-ray tube 3 is always received by the entire surface of the X-ray detection surface of the FPD 4. . Such an X-ray irradiation angle change is performed by the X-ray tube tilting mechanism 9. The X-ray tube tilt control unit 10 is provided for the purpose of controlling the X-ray tube tilt mechanism 9.

When the X-ray imaging apparatus according to the present invention generates a tomographic image, the X-ray tube 3 and the FPD 4 are indicated by an alternate long and short dash line through a position indicated by a broken line with the position of the solid line shown in FIG. 1 as an initial position. Move counter to position. At this time, the X-ray tube 3 irradiates the pulsed X-ray beam 74 times while moving synchronously with the FPD 4.

The image generation unit 11 acquires an X-ray detection signal output by the FPD 4 every time X-ray irradiation is performed, and generates 74 X-ray images P1, P2, P3,. The generated image is sent to the image processing unit 12. The image generation unit 11 corresponds to the image generation unit of the present invention, and the image processing unit 12 corresponds to the shift image processing unit of the present invention.

The image processing unit 12 performs image processing for individually shifting the images in the body axis direction A on the 74 X-ray images P1, P2, P3,... P74, and generates 74 X-ray images P1a, P2a, P3a,... P74a is generated. The generated image is sent to the tomographic image generation unit 13. The tomographic image generation unit 13 corresponds to the tomographic image generation means of the present invention.

The tomographic image generation unit 13 shifts and adds a series of X-ray images P1a, P2a, P3a,... P74a continuously shot while the X-ray tube 3 and the FPD 4 are moved in opposite directions to each other. A tomographic image D obtained when the subject M is cut along a certain cut surface is generated by superimposing them on the basis of the approximation method.

The main control unit 25 is provided for the purpose of comprehensively controlling the

units

6, 8 a, 8 b, 10, 11, 12, and 13. This main control part is comprised by CPU, and implement | achieves each part by running various programs. In addition, each of these units may be executed by being divided into an arithmetic device in charge of them. Each unit can access the storage unit 23 as necessary. The console 26 is provided for the purpose of inputting an operator's instruction. The display unit 27 is provided for the purpose of displaying the tomographic image D.

<Principle of the filter back projection method>
FIG. 2 illustrates the principle of the filter back projection method used by the tomographic image generation unit 13. For example, a virtual plane (reference cut section MA) parallel to the top plate 2 (horizontal with respect to the vertical direction) will be described. As shown in FIG. The FPD 4 is synchronized with the opposite direction of the X-ray tube 3 in accordance with the irradiation direction of the cone-shaped X-ray beam B by the X-ray tube 3 so as to be projected onto the fixed points p and q of the X-ray detection surface of the FPD 4. A series of X-ray images Pa are generated by the image generation unit 11 and the image processing unit 12 while being moved.

In the series of X-ray images Pa, the projected image of the subject M is reflected while changing the position. Then, when this series of X-ray images Pa is reconstructed by the tomographic image generation unit 13, images (for example, fixed points p and q) positioned on the reference cut surface MA are accumulated and imaged as X-ray tomographic images. Will be.

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 M 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 tomographic image generation unit 13 superimposes the X-ray projection images. In this way, by superimposing a series of projection images, an X-ray tomographic image in which only an image positioned on the reference cut surface MA of the subject M is reflected is obtained. In this way, when the projected images are simply superimposed, a tomographic image at the reference cut surface MA is obtained.

Furthermore, the tomographic image generation unit 13 can obtain a similar tomographic image even at an arbitrary cut surface 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 utilizing this, reconstruction is performed while shifting the acquired series of subject M images in the body axis direction A at a predetermined pitch, and a tomographic image at a cutting plane parallel to the reference cutting plane MA is obtained. That is why.

The 74 X-ray images P1a, P2a, P3a,... P74a are subjected to image shift processing by the image processing unit 12. Accordingly, the question arises that the subject image on the reference cut surface MA may not be formed even if the 74 X-ray images P1a, P2a, P3a,. In fact, in the 74 X-ray images P1, P2, P3,... P74 generated by the image generation unit 11 of the present invention, the position of the image reflected in the image is deviated from the ideal position. Therefore, even if 74 X-ray images P1, P2, P3,... P74 are superposed by a normal filter back projection method, only a blurred image can be obtained. The image processing unit 12 is configured to perform image processing for returning an image generated in each X-ray image P1, P2, P3,... P74 to an ideal position. Therefore, the X-ray images P1a, P2a, P3a,... P74a after the shift processing can be considered to be the same as a series of X-ray images assumed by the normal filter back projection method.

The reason for providing such an image processing unit 12 is to prevent a false image that appears in common in any of the 74 X-ray images P1, P2, P3,. It is in. This situation will be described later.

<Example of false image to be removed by the present invention>
The false image to be removed by the present invention is a false image of the same pattern that appears in the same position in a series of X-ray images P1, P2, P3,. Such a false image includes, for example, the shadow of the X-ray grid 5, the corrected image of the defective pixel, and the shadow of the top 2 reflected in the calibration image. Hereinafter, these false images will be specifically described.

FIG. 3 illustrates the shadow of the X-ray grid 5 reflected in a series of X-ray images P1, P2, P3,... P74. The X-ray grid 5 is provided so as to cover the FPD 4 and has a configuration in which absorption foils extending in the body side direction S of the subject M are arranged in the body axis direction A of the subject M as shown on the left side of FIG. is doing. Absorption foil is comprised with the member which is hard to permeate | transmit strip-shaped X-ray | X_line. Direct X-rays directly from the X-ray tube 3 toward the FPD 4 can pass through the X-ray grid 5 by passing between the absorbing foils. On the other hand, although the scattered X-rays are the same X-rays, the angle incident on the absorbing foil is different from the direct X-rays. Scattered X-rays enter the absorbing foil in an attempt to penetrate the absorbing foil. Scattered X-rays are absorbed by the absorbing foil and cannot enter the FPD 4.

Ideally, it is desirable that the X-ray grid 5 does not absorb X-rays directly. However, the absorbing foil of the X-ray grid 5 is not without any thickness. Some of the direct X-rays are incident on the absorbing foil and cannot be transmitted through the X-ray grid 5.

Such uneven transmission of direct X-rays appears on the FPD 4 behind the stripe pattern. This shadow is the shadow of the X-ray grid 5, and as shown on the right side of FIG. 3, it is also thinly reflected in a series of X-ray images P1, P2, P3,. The shadow of the X-ray grid 5 appears as the same pattern at the same position between the series of X-ray images P1, P2, P3,. This is because the positional relationship between the FPD 4 and the X-ray grid 5 does not change during continuous shooting of X-ray images.
Even when the image processing for removing the X-ray grid shadow is performed by removing the specific frequency component from the image, the trace after the shadow removal is located at the same position as the pattern in the same manner as the shadow of the X-ray grid 5. Move in.

FIG. 4 illustrates a corrected image of a defective pixel. On the detection surface of the FPD 4, detection elements for detecting X-rays are arranged vertically and horizontally. Ideally, it is desirable that all of these detection elements operate normally. However, some detection elements may not be able to operate normally. Such a detection element has lost the ability to detect X-rays. Such a detection element is represented by the symbol d on the left side of FIG.

When a series of X-ray images P are photographed using the FPD 4 having a detection element that cannot operate, a defect image appears as a dark spot or a bright spot in the same place in the X-ray images P. This defective pixel appears on the tomographic image D and impairs the visibility of the image. Therefore, the image generation unit 11 performs processing for removing the defective pixel from the X-ray image P. This process is realized by averaging the pixel values of surrounding pixels surrounding the defective pixel and setting the average value to the pixel value of the defective pixel. As a result, the location where the defective pixel indicated by □ is present melts into surrounding pixels surrounded by a dotted line as shown on the right side of FIG.

The corrected pixel left after correcting the defective pixel cannot be said to be the same as the surrounding pixels just because it is not noticeable on the X-ray image P. That is, the corrected pixel is slightly darker than the surrounding pixels due to the influence of the fraction processing when calculating the average value. The corrected pixels left after correcting the missing pixels appear in the same position between the series of X-ray images P1, P2, P3,. This is because the detection element that causes the defective pixel always exists at the same position in the FPD 4 during the continuous shooting of the X-ray images.

FIG. 5 illustrates the shade of the top 2 reflected in the calibration image. On the detection surface of the FPD 4, detection elements for detecting X-rays are arranged vertically and horizontally. Ideally, it is desirable that these detection elements detect X-rays with the same sensitivity. However, the detection sensitivity is uneven among the detection elements as shown on the left side of FIG. Therefore, as shown on the right side of FIG. 5, this detection sensitivity non-uniformity is imaged in advance without the subject M being placed on the top 2. This shooting is called calibration shooting.

Thereafter, when a series of X-ray images P1, P2, P3,... P74 are taken with the subject M placed on the top board, the sensitivity unevenness of the detection element is reflected in these X-ray images P. Since this unevenness has the same pattern as the previously measured unevenness of detection sensitivity, if image processing for subtracting the unevenness of detection sensitivity from a series of X-ray images P1, P2, P3,. Can be removed. The operation for removing such unevenness is called calibration and is executed by the image generation unit 11.

Referring to the right side of FIG. 5, it can be seen that the calibration shooting is being performed with the top 2 placed on. In the radiation imaging apparatus according to the first embodiment, the top plate 2 cannot be easily removed, so that the calibration imaging must be performed while the top plate 2 is being copied. Although the top plate 2 transmits almost X-rays, it still does not absorb X-rays at all. Therefore, the shadow of the top 2 is superimposed on the calibration image obtained by the calibration photographing.

The left side of FIG. 6 represents a calibration image. In the calibration image, the detection unevenness of the FPD 4 and the shade of the top 2 represented by a grid pattern are superimposed.

If an attempt is made to subtract unevenness in detection sensitivity from a series of X-ray images P1, P2, P3,... P74, the shadow of the top plate 2 included in the calibration image is subtracted. This appears as a false image in a series of X-ray images P1, P2, P3,. As shown on the right side of FIG. 6, the shadow of the top 2 is reflected in the same position between a series of X-ray images P1, P2, P3,... P74. This is because the calibration image used in the calibration is common among the X-ray images P1, P2, P3,.

The shade of the X-ray grid 5, the corrected image of the defective pixel, and the shade of the top 2 reflected in the calibration image are all faint false images in the series of X-ray images P1, P2, P3,. Therefore, even if a series of X-ray images P1, P2, P3,... P74 are viewed, it does not seem that these false images significantly deteriorate the visibility of the entire image. However, there is a problem that these false images are reflected as the same pattern at the same position in a series of X-ray images P1, P2, P3,.

A state in which a false image on the X-ray image P appears conspicuously in the tomographic image D will be described. As shown in FIG. 7, consider a case where a tomographic image D on the reference cut surface MA is captured for a rectangle that looks like an organ in a subject. A series of continuously shot X-ray images P1, P2, P3,... P74 are superimposed without being shifted to generate a tomographic image D.

When the same operation is performed on the X-ray images P1, P2, P3,... P74 in which the false image related to the shadow of the X-ray grid 5 is reflected, the X-ray image is also displayed on the tomographic image D as shown in FIG. The same false image as P appears. In addition, the false image on the tomographic image D appears more clearly than the false image on the X-ray image P. This is because when the X-ray images P1, P2, P3,... P74 are superimposed, the false images having the same pattern are superimposed many times.

FIG. 9 particularly shows a state in which the shadow of the X-ray grid 5 is clearly reflected in the tomographic image D. The subject image represented by a rectangle is obstructed by the shadow of the X-ray grid 5 and is difficult to view.

Such an imaging of the shadow of the X-ray grid 5 should occur on the reference cut surface MA. This is because the tomographic image D on the reference cut surface MA should be generated by superimposing the X-ray images P1, P2, P3,. The fact that the X-ray images P1, P2, P3,... P74 are not shifted at the time of superimposing means that the false images are superimposed without being shifted and formed on the tomographic image D. According to the apparatus of the conventional configuration, this is as expected.

The standard cutting surface MA is useful for diagnosis. FIG. 10 explains the circumstances. The visual field of the tomographic image D is limited. The tomographic image D is generated by superimposing the images on the cut surface of the subject M that appear in the series of X-ray images P1, P2, P3,. The image of the subject M that can be imaged on the tomographic image D is limited to that reflected in all of the series of X-ray images P1, P2, P3,. Since a series of X-ray images P1, P2, P3,... P74 are taken while moving the X-ray tube 3 and the FPD 4, the region of the subject M that is reflected in all of these X-ray images P is limited.

If it is desired to acquire a tomographic image D with a large field of view, it is better to generate a tomographic image D on the reference cut surface MA. This is because a tomographic image D having a visual field corresponding to the entire surface of the FPD 4 is obtained as shown in FIG. The cut surface MB, which is different from the reference cut surface MA, is located on the FPD4 side of the reference cut surface MA, and has a narrow range of reflection in a series of X-ray images P1, P2, P3,. Therefore, the field of view of the tomographic image D on the cut surface MB is narrow.

If the shadow imaging of the X-ray grid 5 occurs on the reference cut surface MA, the tomographic image D may be generated with a cut surface other than the reference cut surface MA. According to the explanation of FIG. 2, the tomographic image D in the cut surface other than the reference cut surface MA should be generated by superimposing the X-ray images P1, P2, P3,. When the X-ray images P1, P2, P3,... P74 are shifted at the time of superimposing, the false images are also shifted and superimposed, and the tomographic image D is not formed. This expectation is correct.

However, the reference cut surface MA is a special cut surface from which the tomographic image D having the maximum field of view can be acquired. Even if there is a problem that the false image is easily reflected, the other cut surface does not always replace the reference cut surface MA.

Therefore, according to the present invention, a configuration is adopted in which a false image is not reflected in the tomographic image D of the reference cut surface MA. Such tomography that cannot be considered in the conventional apparatus is realized by the FPD movement control unit 8b and the image processing unit 12.

<Operation of FPD Movement Control Unit 8b and its Effect>
First, the operation of the FPD movement control unit 8b will be described. The FPD movement control unit 8b controls the FPD movement mechanism 7b so that the speed of the FPD 4 varies during shooting. An example of the fluctuation of the speed of the FPD 4 at this time is shown in FIG. In FIG. 11, a dotted line indicates the moving speed of the FPD 4 when the conventional configuration continuously captures the X-ray image P. Although the FPD 4 of the present invention is slower or faster than the FPD 4 in the conventional photographing method, the distance that the FPD 4 moves from the start to the end of the photographing is the same as that of the conventional photographing method (or the image processing unit 12 is conventional). The X-ray image P74 obtained by this imaging method is set to be substantially the same to the extent that it can be reproduced). The function shown in FIG. 11 is obtained by adding a constant to a trigonometric function. The FPD movement control unit 8b controls the FPD movement mechanism 7b by recognizing the speed corresponding to each of the X-ray images P based on the composite function as shown in FIG. 11 in which the speed of the FPD 4 is obtained by adding a constant to the periodic function. Configured to do.

FIG. 12 visually represents the movement of the FPD 4 of the present invention. The upper side of FIG. 12 shows the movement of the FPD 4 according to the conventional apparatus, and the FPD 4 moves at a constant speed during continuous shooting of a series of X-ray images P. The lower side of FIG. 12 shows the movement of the FPD 4 of the apparatus according to the present invention. In the configuration of the first embodiment, the FPD 4 repeats speeding up and down during continuous shooting of a series of X-ray images P.

FIG. 13 shows the relationship between the numbers 1 to 74 of the X-ray image P and the position of the FPD 4 when the X-ray image P is imaged in the imaging method according to the present invention. In this relationship diagram, it is assumed that the FPD 4 when the X-ray image P1 is taken is at the 0 position. The position of the FPD 4 is defined similarly in the following FIGS. 18, 20, and 22. The FPD 4 being imaged moves in the body axis direction A of the subject M while passing or overtaking the FPD 4 related to conventional imaging indicated by the dotted line.

The effect of the configuration for changing the speed of the FPD 4 will be described. FIG. 14 shows a case where a series of X-ray images P are captured by the movement method of the FPD 4 of the conventional apparatus. A rectangle indicated by a broken line on the series of X-ray images P1, P2, P3,... P74 represents a subject image on the reference cut surface MA. The image on the reference cut surface MA is always reflected at the same position in a series of X-ray images P1, P2, P3,. However, in reality, it is difficult to visually recognize it in the X-ray image P.

In the series of X-ray images P1, P2, P3,... P74, the shadow of the X-ray grid 5 having the same pattern is also reflected at the same position. There is no change in the relative positional relationship between the image on the reference cut surface MA and the shadow of the X-ray grid 5 through the series of X-ray images P1, P2, P3,. Accordingly, the tomographic image D on the reference cut surface MA includes the shadow of the X-ray grid 5 together with the tomographic image of the subject M. This is because, when a series of X-ray images P1, P2, P3,... P74 are overlapped in order to obtain an image on the reference cut surface MA, the shadow of the X-ray grid 5 is also overlapped at the same position in the tomographic image D.

On the other hand, when the moving speed of the FPD 4 is changed as in the present invention, the relative positional relationship between the image on the reference cut surface MA and the shadow of the X-ray grid 5 through a series of X-ray images P1, P2, P3,. Changes. FIG. 15 shows a case where a series of X-ray images P are captured by the method of moving the FPD 4 of the apparatus according to the present invention. A rectangle indicated by a broken line on the series of X-ray images P1, P2, P3,... P74 represents a subject image on the reference cut surface MA.

Each of the X-ray images P1, P2, P3,... P74 of the present invention corresponds to each of 74 X-ray images P obtained by a conventional imaging method. Among these, the X-ray image P2 of the present invention has the image on the reference cut surface MA shifted to the right as compared with the X-ray image P2 obtained by the conventional imaging method. This deviation is caused by the acceleration of the FPD 4. If the X-ray image P2 is taken while the FPD 4 is moved at a constant speed as in conventional photography, the image on the reference cut surface MA should appear at the same position as the X-ray image P1. However, in the imaging method of the present invention, the X-ray image P2 is captured with the FPD 4 sufficiently accelerated. The X-ray image P2 in the present invention is taken under the condition that the movement amount of the FPD 4 is larger than that in the conventional imaging method.

Further, in the X-ray image P30 of the present invention, the image on the reference cut surface MA is shifted to the left as compared with the X-ray image P30 of the conventional imaging method. This shift is caused by the FPD 4 being decelerated. If the X-ray image P30 is taken while the FPD 4 is moved at a constant speed as in conventional photography, the image on the reference cut surface MA should appear at the same position as the X-ray image P1. However, in the imaging method of the present invention, the X-ray image P30 is captured with the FPD 4 sufficiently decelerated. The X-ray image P30 in the present invention is taken under the condition that the movement amount of the FPD 4 is small as compared with the conventional imaging method.

Thus, in the series of X-ray images P1, P2, P3,... P74 obtained by the imaging method of the present invention, the image on the reference cut surface MA is not reflected at the same position. However, X-ray grid images are not. The X-ray grid image is reflected in the same pattern in the same position in a series of X-ray images P1, P2, P3,. In this way, the FPD movement control unit 8b controls the FPD movement mechanism 7b so that the speed of the FPD 4 changes during imaging, so that the X-ray image P is changed while changing the positions of the X-ray grid image and the subject image. Can be taken continuously.

Therefore, even if a series of X-ray images P1, P2, P3,... P74 obtained by the imaging method of the present invention is simply superimposed, the tomographic image D is generated on the tomographic image D on the reference cut surface MA. The subject image is not formed. This is because the position at which the subject image on the reference cut surface MA appears in the image is not constant between the series of X-ray images P1, P2, P3,. On the other hand, the X-ray grid image clearly appears on the tomographic image D by superimposing a series of X-ray images P1, P2, P3,. This is because the position at which the X-ray grid image appears in the image is constant between a series of X-ray images P1, P2, P3,.

From these explanations, it can be seen that further ingenuity is necessary to obtain a tomographic image of the subject M. According to the present invention, the tomographic image D on which the subject image is formed is obtained by providing the image processing unit 12.

<Operation of Image Processing Unit 12>
A series of X-ray images P1, P2, P3,... P74 are sent from the image generation unit 11 to the image processing unit 12. The image processing unit 12 converts an image reflected in each of the X-ray images P based on a table formed by associating each of the X-ray images P with the data indicating the shift amount and the shift direction corresponding thereto. Image processing that shifts in the direction A (the movement direction of the FPD 4) is performed, and each of the X-ray images Pa is generated. The table is stored in the storage unit 23.

The image processing unit 12 performs image processing so that the images on the reference cut surface MA that are shifted and displayed in the series of X-ray images P1, P2, P3,. A certain point on the reference cut surface MA in FIG. In the conventional X-ray images P1, P2, P3,... P74 that are continuously shot by moving the FPD 4 at a constant speed, all the images of the reference point s appear in the center of the image.

As shown in FIG. 16, the image processing unit 12 has an image of the reference point s on the reference cut surface MA that is reflected while changing the position between a series of X-ray images P1, P2, P3,. The image shift process is performed. Since the shift direction and the amount of shift of the image of the reference point s differ between the series of X-ray images P1, P2, P3,... P74, in order to realize such shift processing, different shift processing is applied to the X-ray image P. Need to be done for each. The image processing unit 12 performs individual shift processing on the X-ray image P by referring to the table stored in the storage unit 23.

The FPD movement control unit 8b controls the FPD movement mechanism 7b so that the speed of the FPD 4 varies during continuous shooting of the X-ray image P. Accordingly, the FPD 4 moves while shifting. However, the speed change method is not changed every time the image is taken. If the continuous shooting of the X-ray image P is repeated, the speed of the FPD 4 will fluctuate as shown in FIG. 11, for example. Therefore, the position of the FPD 4 when the X-ray images P1, P2, P3,. Accordingly, in what direction and how much the position of the FPD 4 at the time of photographing the X-ray image P2 according to the present invention is deviated from the position of the FPD 4 at the time of photographing of the X-ray image P2 according to the conventional FPD constant velocity moving method. I understand.

The distance between the X-ray tube 3 and the reference cut surface MA and the distance from the reference cut surface MA to the FPD 4 are known. Therefore, the reference cutting of the subject M reflected in the X-ray image P2 according to the present invention with respect to the image on the reference cutting plane MA of the subject M reflected in the X-ray image P2 according to the conventional FPD constant velocity moving method. It can be calculated by geometric calculation how much the image on the surface MA is shifted in which direction. Such a situation is the same for the other X-ray images P. The table can be calculated by executing such a geometric calculation for each X-ray image P1, P2, P3,.

FIG. 17 shows a state in which the image processing unit 12 performs shift processing on the X-ray images P1, P2, P3,... P74 in which the X-ray grid image and the subject image are reflected. The image processing unit 12 performs a shift process on each of the X-ray images P1, P2, P3,... P74, thereby shifting the subject image on the reference cut surface MA indicated by the dashed rectangle to the center of the image. Images P1a, P2a, P3a,... P74a are generated. In these X-ray images P1a, P2a, P3a,... P74a, the subject image on the reference cut surface MA is reflected at the same position. The image processing unit 12 performs image processing for shifting an image on a series of X-ray images P on which a false image of the same pattern is captured, so that the positions to be captured vary depending on the series of X-ray images P. Are shifted so that the reference point s is at the same position on the image.

The X-ray grid images reflected in the X-ray images P1, P2, P3,... P74 are also reflected in the X-ray images P1a, P2a, P3a,. It should be noted here that the X-ray images P1, P2, P3,... P74 show that the X-ray grid images are reflected at the same position in the same direction, and that the X-ray images P1, P2, P3,. The shift processing performed is different for each image. For example, in the X-ray image P2 in FIG. 17, the subject image is shifted to the right as a result of the acceleration of the FPD 4. This shift is corrected by the image processing unit 12, and as a result, the subject image moves to a central position in the X-ray image P2a. At this time, the X-ray grid on the X-ray image P2 also moves following the subject image. Similarly, in the X-ray image P30, the subject image is shifted to the left as a result of the deceleration of the FPD 4. This shift is corrected by the image processing unit 12, and as a result, the subject image moves to the center position in the X-ray image P30a. At this time, the X-ray grid on the X-ray image P30 also moves following the subject image.

Therefore, even if a series of X-ray images P1a, P2a, P3a,... P74a obtained by the imaging method of the present invention is superimposed to generate a tomographic image D, an X-ray grid image is formed on the tomographic image D. do not do. This is because the position at which the X-ray grid image appears in the image is not constant among the series of X-ray images P1a, P2a, P3a,. On the other hand, the subject image on the reference cut surface MA clearly appears on the tomographic image D by superimposing a series of X-ray images P1a, P2a, P3a,. This is because the position at which the subject image on the reference cut surface MA appears in the image is constant among the series of X-ray images P1a, P2a, P3a,.

A series of X-ray images P1a, P2a, P3a,... P74a generated by the image processing unit 12 as described above are reproduced from X-ray images obtained when the FPD 4 moves at a constant speed as usual without shifting. It has become.

As described above, in the apparatus of the present invention, the FPD movement control unit 8b and the image processing unit 12 function in cooperation to form an X-ray grid image even in the tomographic image D on the reference cut surface MA. Can be suppressed. Such a situation is not limited to the X-ray grid image, and the same applies to the other false images described with reference to FIGS. 4 to 6 reflected in the same series of X-ray images P1, P2, P3,. .

<Operation of Tomographic Image Generation Unit 13>
A series of X-ray images P1a, P2a, P3a,... P74a is sent to the tomographic image generation unit 13. The tomographic image generation unit 13 generates a tomographic image D by superimposing these X-ray images Pa. Since the X-ray grid images reflected in the X-ray image Pa are different from each other in the positions reflected in the images, they cancel each other out when they are superimposed, and do not appear in the tomographic image D. The tomographic image generation unit 13 can use the one provided in the conventional apparatus related to the FPD constant speed movement method. A series of X-ray images P1a, P2a, P3a,... P74a are reproductions of X-ray images obtained when the FPD 4 moves at a constant speed as usual without shifting. The tomographic image generation unit 13 generates a tomographic image D of the subject M on the cut surface including the reference point s based on a series of X-ray images Pa in which the appearance positions of the false images are shifted from each other by the shift image processing.

<Optimization of FPD4 transmission system>
By devising the speed change method of the FPD 4, it is possible to prevent the false image from being imprinted on the tomographic image D, so this point will be described. FIG. 18 shows a case where a series of X-ray images P are continuously shot while the FPD 4 is moved at a constant speed as usual. The solid line in FIG. 18 represents the conventional imaging method, and the value indicating the position of the FPD 4 at the time of imaging is proportional to the number of the X-ray image P. In the X-ray image P taken when the relationship between the image number and the position of the FPD 4 is on the solid line, it is assumed that the subject image of the reference cross section MA is reflected in the center of the image.

18 also shows the case where the FPD 4 is moved at the same speed as the conventional photographing method. However, the departure timing of the FPD 4 is earlier than the conventional photographing method. When the relationship between the image number and the position of the FPD 4 is on this broken line, the subject image of the reference cut surface MA is shifted to the right side of the X-ray image P. The shift amount does not change as long as the relationship between the image number and the position of the FPD 4 is on the broken line. The image reflected on the X-ray image P at this time will be referred to as a shift image Fa.

18 also shows the case where the FPD 4 is moved at the same speed as the conventional imaging method. However, the departure timing of the FPD 4 is later than the conventional photographing method. When the relationship between the image number and the position of the FPD 4 is on this one-dot chain line, the subject image of the reference cut surface MA is shifted to the left side of the X-ray image P. The amount of deviation does not change as long as the relationship between the image number and the position of the FPD 4 is on this one-dot chain line. The image reflected on the X-ray image P at this time is referred to as a shift image Da.

Consider a case where the image processing unit 12 performs a shift process on the X-ray image P in which the image of the shift image Fa is captured. Since the image processing unit 12 performs a shift process for moving the subject image of the reference cut surface MA to the center, the image of the shift image Fa is moved to the left as shown in the left side of FIG. Become. Similarly, consider a case where the image processing unit 12 performs shift processing on the X-ray image P in which the image of the shift image Da is captured. Since the image processing unit 12 performs a shift process for moving the subject image of the reference cut surface MA to the center, the image of the shift image Da is moved to the right as a whole as shown on the right side of FIG. Become. The method of shifting the image performed by the image processing unit 12 on the X-ray image P in which the image of the shift image Fa is captured is referred to as shift method Fb, and the image processing unit 12 applies to the X-ray image P in which the image of the shift image Da is captured. The method of shifting the image to be applied will be referred to as shifting method Db.

When the shift of the FPD 4 is as shown in FIG. 11, the relationship between the position of the FPD 4 and time is as shown in FIG. That is, when the FPD 4 of the present invention repeats acceleration and deceleration, the relationship between the image number and the position of the FPD 4 can be reciprocated between the point on the broken line and the point on the alternate long and short dash line described in FIG.

Here, consider the point in time when the FPD 4 switches from acceleration to deceleration. At this point, the speed change needs to be small. Otherwise, the movement of the FPD 4 will not be smooth, causing vibration of the apparatus. Such vibrations are not desirable when aiming for a shooting method that is safe, free of camera shake, and reduced damage to the apparatus body. Therefore, it is necessary to moderate the speed change when the FPD 4 changes from acceleration to deceleration. This situation is the same when the FPD 4 changes from deceleration to acceleration.

Here, assuming that the X-ray image P is captured when the FPD 4 changes from acceleration to deceleration, the relationship between the image number of the X-ray image P and the position of the FPD 4 is further shown in the coordinate system shown in FIG. The coordinates are on the broken line. Then, the deviation image Fa described in FIG. 19 is reflected in the X-ray image P. Similarly, assuming that the X-ray image P is captured when the FPD 4 changes from deceleration to acceleration, the relationship between the image number of the X-ray image P and the position of the FPD 4 is further shown in the coordinate system shown in FIG. It is assumed that the coordinates are on a one-dot chain line. Then, the deviation image Da described in FIG. 19 is reflected in the X-ray image P.

Actually, the series of X-ray images P1, P2, P3,... P74 that are the basis of the tomographic image D include many images in which the shift image Fa is reflected. Before and after the FPD 4 changes from acceleration to deceleration, the shift of the FPD 4 is gentle, and the relationship between the image number and the position of the FPD 4 is close to the broken line for a long period indicated by hatching in FIG. Therefore, when the X-ray images P are continuously shot, many X-ray images P on which the shift image Fa or an image similar to that is copied can be obtained. Similarly, the continuously shot X-ray image P includes many images in which the shift image Da is reflected. Before and after the FPD 4 changes from deceleration to acceleration, the speed of the FPD 4 is gentle, and the relationship between the image number and the position of the FPD 4 is close to the alternate long and short dash line for a long period of time indicated by the oblique lines in FIG. Therefore, when the X-ray images P are continuously shot, many X-ray images P on which the shift image Da or an image similar thereto is copied can be obtained.

FIG. 21 shows only a portion of the series of X-ray images P on which a shift image Fa or an image similar thereto is extracted. The image processing unit 12 generates a X-ray image Pa by performing a shift process for shifting a plurality of X-ray images P in which the misalignment image Fa appears in the same shifting method Fb. The essence of the present invention is to prevent the X-ray grid image from being formed on the tomographic image D by changing the shifting method of the X-ray grid image for each X-ray image P. Nevertheless, the image processing unit 12 has executed the shift process by shifting different X-ray images P in the same way. With such a configuration, an X-ray grid image reflected on the misalignment image Fa is formed on the generated tomographic image D. The X-ray grid image of the X-ray image Pa is formed at the destination. Such a situation is the same for the displacement image Da.

FIG. 22 has a configuration in which the FPD 4 is moved in consideration of this point. That is, the relationship between the image number and the position of the FPD 4 according to the photographing of the present invention is shown by the thick line in FIG. According to this method of moving the FPD 4, the point at which the FPD 4 changes from acceleration to deceleration corresponds to the speed of the conventional FPD related to constant speed movement (the speed of the FPD 4 related to the movement method of the FPD 4 reproduced by the image processing unit 12). Adjustments are made so that they are not arranged on a straight line having an inclination. By doing so, it is possible to prevent as much as possible that the same X-ray grid image appears in a series of X-ray images P, and to prevent the X-ray grid image from appearing in the tomographic image D. Can do.

In order to realize such a method of moving the FPD 4, the image number and the speed of the FPD 4 may be set as shown in FIG. The function shown in FIG. 23 can be generated by further adding a constant to a composite function of two trigonometric functions having different frequencies. Even in such a case, the FPD 4 of the present invention is slower or faster than the FPD 4 in the conventional photographing method, but the distance that the FPD 4 moves from the start to the end of the photographing is the same as the conventional photographing method (or The image processing unit 12 is set so that the X-ray image P74 obtained by the conventional imaging method can be reproduced.

The movement of the FPD 4 is realized by the FPD movement control unit 8b. The FPD movement control unit 8b controls the FPD moving mechanism 7b so that the FPD 4 moves in the manner described with reference to FIGS. 22 and 23, so that the X-ray image taken when the FPD 4 changes from acceleration to deceleration. The positions where the reference point s is reflected between P are different from each other. Similarly, the FPD movement control unit 8b makes the positions at which the reference point s is reflected between the X-ray images P captured when the FPD 4 changes from deceleration to acceleration. The FPD movement control unit 8b controls the FPD movement mechanism 7b by recognizing the speed corresponding to each of the X-ray images P based on a composite function as shown in FIG. 23 in which the speed of the FPD 4 adds a constant to a periodic function. Configured to do.

As described above, according to the present invention, it is possible to provide the X-ray tomography apparatus 1 in which a false image is not formed on the tomographic image D. That is, when the X-ray tomography apparatus 1 according to the present invention captures a series of X-ray images P taken while the X-ray tube 3 and the FPD 4 are moved in opposite directions, the speed of the FPD 4 changes. Is done. As a result, the position of the reference point on the cut surface changes between a series of X-ray images P. On the other hand, the position where the false image appears is the same between the series of X-ray images P. If the tomographic image D is generated on the basis of a series of X-ray images P subjected to image processing for shifting so that the reference point comes to the same position on the image, the tomographic image D is surely in the cut surface including the reference point. A tomographic image of the subject M is reflected. On the other hand, no false image appears in the tomographic image D. This is because the appearance positions of the false images that appear in the series of X-ray images P are shifted by image processing and cancel each other out when generating the tomographic image.

Further, if the FPD 4 is moved so that the FPD 4 repeats acceleration and deceleration, a series of X-ray images P necessary for generating the tomographic image D can be reliably executed while the speed of the FPD 4 is changed. This is because the average speed of the FPD 4 can be made the speed of the FPD 4 in the conventional apparatus related to the detection means constant speed movement.

The position where the reference point is reflected between the X-ray images P tends to be particularly similar between images taken when the FPD 4 changes from acceleration to deceleration. If such a state is left as it is, it may not be possible to reliably suppress the appearance of a false image on the tomographic image. This problem also occurs when the FPD 4 changes from deceleration to acceleration. Therefore, the above configuration pays attention to this problem, and the movement mode of the FPD 4 is selected so that the positions where the reference points are reflected are different between the X-ray images P taken when the FPD 4 changes from acceleration to deceleration. The Similarly, the movement mode of the FPD 4 is selected so that the positions at which the reference points are captured differ between the X-ray images P taken when the FPD 4 changes from deceleration to acceleration. Thereby, it can suppress reliably that a false image appears on a tomographic image.

As shown in FIG. 11, if the FPD 4 is moved at a speed based on a composite function in which the speed of the FPD 4 is obtained by adding a constant to a periodic function, acceleration and deceleration of the FPD 4 are reliably repeated.

As shown in FIG. 23, if the FPD 4 is moved at a speed based on a combined function obtained by adding two periodic functions having different periods and a constant, the FPD 4 is photographed when the FPD 4 changes from acceleration to deceleration (or from deceleration to acceleration). In addition, the positions where the reference points are reflected between the X-ray images P are surely different from each other.

The configuration of the present invention is not limited to the above-described configuration, and can be modified as follows.

(1) Although the speed of the FPD 4 of the first embodiment has a configuration represented by a function as shown in FIG. 11 or FIG. 23, the present invention is not limited to this configuration. You may make it determine the speed of FPD4 using functions other than these.

(2) Although the method of shifting the FPD 4 of the first embodiment is one type, the present invention is not limited to this configuration. The method of shifting the FPD 4 may be selected from a plurality of modes. The image processing unit 12 of this modification can be configured to change the table to be referred to in accordance with the selection of this mode.

(3) The shifting method of the FPD 4 shown in FIG. 23 is only an example of the present invention. The FPD movement control unit 8b may recognize the speed of the FPD 4 by a function other than that shown in FIG.

(4) Although the speed of the FPD 4 of the first embodiment is calculated based on a trigonometric function, the present invention is not limited to this configuration. An arbitrary periodic function can be used for the calculation instead of the trigonometric function. As a function to be used, a function having no non-differentiable singularity is desirable. This is because if there is such a singular point, the FPD 4 will rattle due to movement.

(5) In the above-described configuration, the filtered back projection method in which a series of X-ray images are superimposed is used as a tomographic reconstruction method. However, a well-known shift addition method or successive approximation method may be used.

(6) Although the method of shifting the FPD 4 in the first embodiment repeats acceleration and deceleration, the present invention is not limited to this configuration. During imaging of a series of X-ray images P, the FPD 4 may be moved so as to continue to accelerate. In this way, the FPD 4 does not rattle during imaging and vibrations can be prevented, and the X-ray tomography apparatus 1 that is safe and less burdensome on the subject M and the apparatus itself can be provided. Note that such movement of the FPD 4 is realized by the FPD movement control unit 8b executing control of the FPD movement mechanism 7b so as to continuously accelerate the FPD 4.

(7) Although the reference point s in Example 1 was on the reference section, the present invention is not limited to this configuration. The reference point s can be set on a cut surface other than the reference cut surface.

The present invention is suitable for the medical field as described above.

3 X-ray tube (radiation source)
4 FPD (detection means)
7a X-ray tube moving mechanism (radiation source moving means)
7b FPD moving mechanism (detector moving means)
8a X-ray tube movement control unit (radiation source movement control means)
8b FPD movement control unit (detector movement control means)
11 Image generation unit (image generation means)
12 Image processing unit (shifted image processing means)
13 Tomographic image generating unit (tomographic image generating means)

Claims

A radiation source for irradiating the subject with radiation;
Detecting means for detecting radiation transmitted through the subject;
Radiation source moving means for moving the radiation source relative to the subject;
Radiation source movement control means for controlling movement of the radiation source;
Detector moving means for moving the detection means relative to the subject;
Image generating means for generating a radiographic image in which a false image is reflected together with the subject image based on the output of the detecting means;
Detection that controls the detector moving means so that the speed of the detecting means is changed when taking a series of radiographic images continuously taken while the radiation source and the detecting means are moved in opposite directions. Movement control means,
By applying image processing that shifts the image to a series of radiographic images that contain the same pattern of false images, the reference points inside the subject that are different depending on the series of radiographic images are located at the same position on the image. Shifted image processing means for shifting
Radiation comprising: a tomographic image generation means for generating a tomographic image of the subject in a cut plane including the reference point based on a series of radiation images in which the appearance positions of false images are shifted from each other by shift image processing Tomography equipment.
The radiation tomography apparatus according to claim 1,
The radiation tomography apparatus according to claim 1, wherein the detector movement control means controls the detector movement means so that the detection means repeats acceleration and deceleration.
The radiation tomography apparatus according to claim 2,
The detector movement control means controls the detector movement means so that the positions at which the reference points are reflected differ between the radiographic images taken when the detection means changes from acceleration to deceleration. Radiation tomography equipment.
The radiation tomography apparatus according to claim 2 or 3,
The detector movement control means controls the detector movement means so that positions where the reference points are reflected are different between radiographic images taken when the detection means changes from deceleration to acceleration. Radiation tomography equipment.
The radiation tomography apparatus according to any one of claims 2 to 4,
The detector movement control means controls the detector movement means by recognizing a speed corresponding to each of the radiographic images based on a composite function obtained by adding two periodic functions having different periods and a constant. Radiation tomography equipment.
The radiation tomography apparatus according to claim 1,
The detector movement control means controls the detector movement means by recognizing the speed corresponding to each of the radiographic images based on a composite function in which the speed of the detection means is a periodic function plus a constant. Radiation tomography equipment.
The radiation tomography apparatus according to claim 1,
The radiation tomography apparatus according to claim 1, wherein the detector movement control means controls the detector movement means so that the detection means continues to accelerate.