JP4770594B2 - Tomography equipment - Google Patents

Description

  The present invention relates to a tomographic apparatus used in the medical field, industrial fields such as non-destructive inspection, RI (Radio isotope) inspection, and optical inspection.

  An example of this type of conventional apparatus is shown in FIG. As shown in the figure, an X-ray tube 81 and a flat panel X-ray detector (hereinafter referred to as “FPD” where appropriate) 83 are held by a C-shaped arm 84 at positions facing each other. The C-shaped arm 84 is supported to be rotatable about the rotation axis B. As the C-shaped arm 84 rotates, the X-ray tube 81 and the FPD 83 rotate together. The subject M1 is positioned so that its body axis C1 is the rotation axis B of the X-ray tube 81 and the FPD 83. Thereby, when the X-ray tube 81 and the FPD 83 are rotationally moved, the body axis C1 of the subject M1 is always projected onto the center of the FPD 83.

Between the X-ray tube 81 and the subject M1, two wedge filters 85 and 86 for attenuating X-rays are provided. The wedge filters 85 and 86 are installed to be able to advance and retreat with respect to the irradiation axis A in synchronization with each other so as to be always symmetrical about the X-ray irradiation axis A. The interval between the wedge filters 85 and 86 is defined as a separation distance d. The positions of the wedge filters 85 and 86 are controlled so that the overall shape of the wedge filters 85 and 86 and the shape of the subject M1 are complementary when viewed from the direction of X-ray irradiation. Therefore, the X-rays are attenuated to the same extent, and the intensity of the X-rays is made uniform over the detection surface of the FPD 83 (referred to as a compensation effect). Therefore, the X-ray intensity does not exceed the dynamic range of the FPD 83, and an appropriate captured image can be obtained from the FPD 83. In addition, an appropriate tomographic image can be acquired by reconstructing an appropriate captured image (see, for example, Patent Documents 1 and 2).
JP 55-40531 A JP-A-8-605

However, the conventional example having such a configuration has the following problems.
That is, the FPD 83 is as small as about 40 cm even at the maximum size. When the distance between the X-ray tube 81 and the subject M1 is 70 cm and the distance between the X-ray tube 81 and the FPD 13 is 110 cm, the entire subject M1 is not projected unless the diameter of the subject M1 is about 25 cm or less. For this reason, it may be difficult to acquire a tomographic image of the human abdomen.

  Therefore, when obtaining a tomographic image of a specific organ (for example, the liver) of the human body, it is necessary to place the human body eccentric so that the organ is the center. In FIG. 7, the subject M2 is an example of an eccentric arrangement.

  As apparent from FIG. 7, since the body axis C2 of the subject M2 is decentered from the rotation axis B, the subject M2 may deviate from the irradiation axis A in some cases. In this case, the compensation effect is reduced no matter how the wedge filters 85 and 86 are moved. That is, there is a possibility that X-rays with extremely high X-ray intensity may enter any position on the detection surface of the FPD 83. As a result, when the X-ray intensity exceeds the dynamic range of the FPD 83, the FPD 83 cannot properly detect X-rays.

  Please refer to FIG. FIG. 8A shows a virtual X-ray intensity profile obtained after passing through only the subject M2, and FIG. 8B shows a virtual X-ray obtained after passing through only the wedge filters 85 and 86. FIG. 8C shows a profile of the actual X-ray intensity transmitted through the wedge filters 85 and 86 and the subject M2. The vertical axis of each figure is a logarithmic display of the signal value proportional to the X-ray intensity, and the lower the X-ray intensity, the lower the X-ray intensity (the X-rays are attenuated). In FIG. 8C, the upper limit value and the lower limit value of the dynamic range of the FPD 83 are clearly shown.

  The X-ray intensity profile in FIG. 8A is a valley-like curved curve, but the entire curve is shifted to the left. This is because the body axis C2 of the subject M2 is displaced from the irradiation axis A. The profile of the X-ray intensity in FIG. 8B is a mountain-shaped curved curve, but is symmetrical left and right. This is because the wedge filters 85 and 86 are symmetric with respect to the X-ray irradiation axis A. As a result, as shown in FIG. 8C, the intensity of a part of the X-rays incident on the FPD 83 exceeds the upper limit value of the dynamic range of the FPD 83.

  The conventional example also has another problem as follows. The intensity of the X-rays passing near the edges 85a and 86a of the wedge filters 85 and 86 changes abruptly. Since the edges 85a and 86a are projected onto the FPD 83, the projection image and the tomographic image obtained from the FPD 83 have a disadvantage that the image quality deteriorates due to the influence. In addition, it is necessary to provide separate drive mechanisms for moving the two wedge filters 85 and 86, respectively, and there is a disadvantage that the configuration becomes complicated.

  The present invention has been made in view of such circumstances, and the irradiation means and detection means, or when the subject's body axis is not on the irradiation axis when the subject is rotated around the rotation axis Even so, an object of the present invention is to provide a tomographic apparatus capable of suppressing the intensity of the electromagnetic wave incident on the detection means from exceeding the dynamic range of the detection means.

In order to achieve such an object, the present invention has the following configuration.
That is, the invention according to claim 1 acquires a tomographic image based on data detected by the detection unit by irradiating the subject with the electromagnetic wave irradiated from the irradiation unit through an attenuation body having a high attenuation at the end. In the tomography apparatus, the irradiation means and the detection means, or a rotation means for rotating the subject around the rotation axis intersecting the irradiation axis of the electromagnetic wave emitted from the irradiation means, and the rotational movement by the rotation means A moving means for moving the attenuation body relative to the irradiating means within the tomographic plane formed by the method, and the intensity of the electromagnetic wave detected by the detecting means accompanying the rotational movement is less than a predetermined value, and a control means for moving said control moving means and said attenuator based on the relative position information between the rotary shaft and the illumination axis and the body axis of the subject, the body and the tomographic plane The position where the electromagnetic wave is emitted on the irradiation axis is the emission source point, and the control means is configured such that the portion where the attenuation of the electromagnetic wave in the attenuation body is low Control is performed so as to be positioned on a straight line connecting the body axis points, and the moving means translates the attenuating body along a circle or an ellipse in the tomographic plane .

[Operation / Effect] According to the first aspect of the present invention, the moving means moves the attenuator relative to the irradiation means by the control of the control means. Even when the deviation is, the intensity of the electromagnetic wave incident on the detection means can be set to a predetermined value or less. The predetermined value is an upper limit value of a dynamic range that is an intensity range of electromagnetic waves that can be appropriately detected by the detecting means. Therefore, the detection unit can appropriately detect the electromagnetic wave, and can acquire an appropriate tomographic image based on the data obtained from the detection unit.
In addition, the intensity of the electromagnetic wave can be effectively reduced to a predetermined value or less.
The moving means moves the attenuation body in the direction of fluctuation of the subject in the electromagnetic field of view and attenuates from the emission source point in response to the change of the size of the subject in the electromagnetic field of view. Since it moves so that the distance to a body may be changed, it can suppress more effectively that the intensity | strength of electromagnetic waves shall be below a predetermined value.

In the present invention, it is preferable that the position information includes a rotation angle formed by the irradiation axis and a straight line connecting the intersection of the irradiation axis and the rotation axis and the body axis point ( Claim 2 ). By including a rotation angle that varies with rotational movement as the position information, the control means can appropriately control.

In the present invention, the irradiation means by the rotational movement, or a measurement means for measuring the rotational movement amount of the subject, and a position information acquisition means for calculating the rotation angle based on the measurement result of the measurement means. ( Claim 3 ). Position information can be acquired reliably and appropriately.

In the present invention, a rotation control unit that controls the rotational movement by operating the rotation unit, and a position information acquisition unit that calculates the rotation angle based on an operation amount of the rotation control unit. Preferred ( claim 4 ). Position information can be acquired easily and appropriately.

  The present specification also discloses an invention relating to the following cross-sectional image reconstruction apparatus.

  (1) In the tomography apparatus according to claim 1, the control means performs control so that the thin portion of the attenuation body is positioned on a straight line connecting the emission source point and the body axis point. A tomography apparatus characterized by:

  According to the invention described in (1) above, the intensity of electromagnetic waves can be effectively reduced to a predetermined value or less.

  (2) In the tomography apparatus according to claim 1 or 2, the position information includes a second rotation angle formed by a straight line connecting the emission source point and the body axis point and the irradiation axis. A tomography apparatus characterized by this.

  By including the second rotation angle that varies with the rotational movement as the position information, the control means can appropriately control.

  (3) In the tomography apparatus for irradiating the subject with the electromagnetic wave irradiated from the irradiation unit through an attenuation body having a high attenuation at the end and acquiring a tomographic image based on data detected by the detection unit, the irradiation unit In the tomographic plane created by the rotational movement of the irradiation means and the detection means, or the rotation means for rotating the subject around the rotation axis intersecting the irradiation axis of the electromagnetic wave emitted from the rotation means, A moving means for moving the attenuating body relative to the irradiating means; and the tomographic plane and the body of the subject so that the intensity of the electromagnetic wave detected by the detecting means as the rotational movement becomes a predetermined value or less. Based on relative positional information between the body axis point and the emission source point, the intersection point with the axis is a body axis point, and the position where the electromagnetic wave is emitted on the irradiation axis is the emission source point. Tomography apparatus characterized by comprising a control means for moving the attenuation body Gyoshi.

  By the control by the control means, the moving means moves the attenuation body relative to the irradiation means, so that even if the body axis of the subject is deviated from the irradiation axis of the electromagnetic wave, the electromagnetic waves incident on the detection means The strength of can be set to a predetermined value or less. The predetermined value is an upper limit value of a dynamic range that is an intensity range of electromagnetic waves that can be appropriately detected by the detecting means. Therefore, the detection unit can appropriately detect the electromagnetic wave, and an appropriate tomographic image can be acquired by reconstructing a captured image obtained from the detection unit.

  According to the tomography apparatus according to the present invention, the moving means moves the attenuation body relative to the irradiation means by the control of the control means, so that the body axis of the subject is deviated from the irradiation axis of the electromagnetic wave. Even so, the intensity of the electromagnetic wave incident on the detection means can be set to a predetermined value or less. The predetermined value is an upper limit value of a dynamic range that is an intensity range of electromagnetic waves that can be appropriately detected by the detecting means. Therefore, the detection unit can appropriately detect the electromagnetic wave, and can acquire an appropriate tomographic image based on the data obtained from the detection unit.

Embodiment 1 of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram illustrating a schematic configuration of the tomography apparatus according to the first embodiment, and FIG. 2 is a cross-sectional view of a main part of the tomography apparatus cut along a tomographic plane.

  The tomography apparatus according to the first embodiment includes an X-ray tube 1 that irradiates a subject M with X-rays, and a flat panel X-ray detector (hereinafter referred to as an X-ray detector that is disposed opposite to the X-ray tube 1 and detects X-rays). , 3 (abbreviated as “FPD”). The X-ray tube 1 and the FPD 3 are respectively held at both ends of the C-shaped arm 5. The rotation mechanism 7 holds the C-shaped arm 5 and slides the C-shaped arm 5. As the C-shaped arm 5 slides, the X-ray tube 1 and the FPD 3 rotate around the rotation axis B intersecting the X-ray irradiation axis A. Here, a plane formed by the rotational movement of the X-ray tube 1 and the FPD 3 is referred to as a tomographic plane H. The rotation mechanism 7 is fixedly provided on the floor by a base (not shown). The rotation sensor 11 indirectly measures the amount of rotational movement of the X-ray tube 1 by detecting the amount of rotation of the C-shaped arm 5. An example of the rotation sensor 11 is a rotary encoder. The X-ray tube 1, the FPD 3 and the rotation sensor 11 correspond to the irradiation means, detection means and measurement means in this invention, respectively. The C-shaped arm 5 and the rotation mechanism 7 correspond to the rotation means in the present invention.

  The subject M is placed on a top plate (not shown). The top plate is disposed between the X-ray tube 1 and the FPD 3 so that the body axis C of the subject M deviates from the rotation axis B.

  A single wedge filter 13 that attenuates X-rays is provided between the X-ray tube 1 and the subject M. The wedge filter 13 has a higher degree of attenuation toward the end. More specifically, the wedge filter 13 is so large that the end thereof does not enter the X-ray irradiation field, has a shape complementary to the shape of the subject M, and the front and back surfaces thereof are smoothly formed. Yes. 1 and 2, the surface on the X-ray tube 1 side is a flat surface, and the surface on the opposite side is recessed in a curve. In the present embodiment, the wedge filter 13 has the thinnest central portion in a cross-sectional view and the smallest attenuation (attenuation degree). The moving mechanism 15 is fixedly supported by the C-shaped arm 5 and is connected to the wedge filter 13 via the holding member 17. Then, the wedge filter 13 is linearly moved in the one-axis u direction orthogonal to the irradiation axis A in the tomographic plane H. The wedge filter 13 and the moving mechanism 15 correspond to the attenuator and moving means in the present invention, respectively.

  The filter control unit 19 controls the moving mechanism 15 to move the wedge filter 13. The position information acquisition unit 21 calculates relative position information of the irradiation axis A, the rotation axis B, and the body axis C based on the detection result from the rotation sensor 11 described above, and outputs the relative position information to the filter control unit 19. The filter control unit 19 calculates a moving amount for moving the wedge filter 13 based on the relative position information, and controls the moving mechanism 15 based on the calculated moving amount. The filter control unit 19 and the position information acquisition unit 21 are a central processing unit (CPU) that reads out and executes a predetermined program, a RAM (Random-Access Memory) that stores various information, a storage medium such as a fixed disk, and the like. Realized. The filter control unit 19 and the position information acquisition unit 21 correspond to the control unit and the position information acquisition unit in the present invention, respectively.

  The position information acquisition unit 21 and the filter control unit 19 will be described in more detail. The rotation axis B and the body axis C are naturally determined from the structures and dimensions of the X-ray tube 1, the FPD 3, the C-shaped arm 5, the top plate, and the like. Therefore, the position of the tomographic plane H and the body axis point c which is the intersection of the tomographic plane H and the body axis C are also known. In the storage unit included in the position information acquisition unit 21, known position information such as the rotation axis B and the body axis point c is set in advance.

The position information acquisition unit 21 obtains position information of the irradiation axis A based on the rotational movement amount of the X-ray tube 1 obtained from the rotation sensor 11 when the X-ray tube 1 rotates. Then, with reference to the known position information, the rotation between the irradiation axis A and the straight line connecting the intersection of the irradiation axis A and the rotation axis B (hereinafter simply referred to as “intersection point a”) and the body axis point c. The angle θ ₁ is calculated. This rotation angle θ ₁ corresponds to the relative position information described above.

  Also in the storage unit of the filter control unit 19, the following known position information is set in advance. That is, the position at which X-rays are emitted from the X-ray tube 1 is defined as an emission source point e, the first distance D1 between the emission source point e and the intersection point a, and the emission when the wedge filter 13 is positioned on the irradiation axis A. The second distance D2 between the origin e and the wedge filter 13 and the eccentric distance r between the intersection point a and the body axis point c.

  When the X-ray tube 1 rotates, the filter control unit 19 calculates the displacement in the one-axis u direction with respect to the intersection of the irradiation axis A and the one axis u as the movement amount F of the wedge filter 13. Specifically, it is given by Equation (1).

Here, first, because the eccentricity r and the second distance D1, D2 are both constant, the movement amount F changes depending only on the rotation angle theta _1. The amount of movement F is a region where the attenuation amount (attenuation degree) of the wedge filter 13 is the smallest (low), which is the center of the wedge filter 13 in the first embodiment, and the source point e and the body axis point c. It is a value to be positioned on the connecting straight line.

  The image processing unit 31 collects data (captured images) detected by the FPD 3 and reconstructs a plurality of captured images to generate a tomographic image. The monitor 33 displays the generated tomographic image. The image processing unit 31 is realized by a central processing unit (CPU) that reads and executes a predetermined program, a RAM (Random-Access Memory) that stores various information, a storage medium such as a fixed disk, and the like.

  Next, the operation of the tomography apparatus according to Embodiment 1 will be described.

The rotating mechanism 7 slides the C-shaped arm 5 in a state where the subject M is placed on a top plate (not shown). At this time, the rotation sensor 11 detects the movement amount of the C-shaped arm 5 and outputs it to the position information acquisition unit 21. The position information acquisition unit 21 calculates the rotation angle θ ₁ based on the rotational movement amount of the X-ray tube 1 according to the detection result of the rotation sensor 11. The filter control unit 19 calculates a moving amount F for moving the wedge filter 13 based on the rotation angle θ ₁ and controls the moving mechanism 15. The moving mechanism 15 moves the wedge filter 13 forward and backward in the direction of one axis u by a distance of the moving amount.

  As the C-arm 5 slides, the X-ray tube 1 and the FPD 3 rotate. At this time, the X-ray tube 1 irradiates the subject M with X-rays from various angles. The irradiated X-ray is attenuated by passing through the wedge filter 13 and the subject M. The FPD 3 detects attenuated X-rays.

  With reference to FIG. 3, the profile of the X-ray intensity incident on the FPD 3 at a certain imaging angle will be described. FIG. 3A shows a virtual X-ray intensity profile obtained after passing through only the subject M, and FIG. 3B shows a virtual X-ray intensity obtained after passing through the wedge filter 13 only. FIG. 3C shows a profile of the actual X-ray intensity transmitted through the wedge filter 13 and the subject M. The vertical axis of each figure is a logarithmic display of the signal value proportional to the X-ray intensity, and the lower the X-ray intensity, the lower the X-ray intensity (the X-rays are attenuated). In FIG. 3C, the upper limit value and the lower limit value of the X-ray intensity at which the FPD 3 can detect X-rays appropriately are clearly shown. In this specification, a range from the lower limit value to the upper limit value is referred to as a dynamic range.

  The X-ray intensity profile in FIG. 3A is a valley-like curved curve, but the entire curve is shifted to the left. This indicates that the body axis C of the subject M is displaced from the irradiation axis A.

  At this time, the profile of the X-ray intensity in FIG. 3B is a mountain-shaped curve, but the entire curve is shifted to a position shifted to the left. This indicates that the portion where the thickness of the wedge filter 13 is the smallest is displaced from the irradiation axis A as a result of the movement of the wedge filter 13 relative to the X-ray tube 1 under the control of the filter control unit 19.

  As a result, as shown in FIG. 3C, the profile of the X-ray intensity incident on the FPD 3 is equivalent to the sum of the X-ray intensity profiles shown in FIGS. 3A and 3B. To do. Thus, the incident X-ray intensity is distributed within the dynamic range of the FPD 3. Therefore, the FPD 3 can detect X-rays appropriately.

  The image processing unit 31 collects a plurality of captured images from the FPD 3 and performs a predetermined reconstruction process to create a tomographic image. Examples of the reconstruction process include a process of performing convolution integration using an appropriate reconstruction function and backprojecting the result of convolution integration. Then, a tomographic image is appropriately output to the monitor 33 based on an operator's instruction or the like.

As described above, according to the tomography apparatus according to the first embodiment, the body axis C of the subject M is separated from the irradiation axis A by including the moving mechanism 15 that linearly moves the wedge filter 13 in the uniaxial u direction. Even if it shifts, the wedge filter 13 can be moved in that direction. Further, by providing the filter control unit 19 that calculates the movement amount F of the wedge filter 13 according to the rotation angle θ ₁ and controls the movement mechanism 15, the attenuation amount (attenuation degree) of the wedge filter 13 is the smallest (low). ) The part can be positioned on a straight line connecting the emission origin e and the body axis point c. Therefore, it is possible to effectively prevent the intensity of X-rays incident on the FPD 3 from exceeding the upper limit value of the dynamic range of the FPD 3.

  The maximum size of the FPD 13 is 40 cm. For example, when the first distance D1 is 70 cm and the distance between the emission source point e and the FPD 13 is 110 cm, the effective visual field is only 25 cm. In this case, when the subject M is a human body and the X-ray tube 1 and the FPD 3 are rotationally moved, the body axis C of the subject M is set to the rotation axis B in order to keep an organ such as the liver in the abdomen within the irradiation field. However, according to the first embodiment, an appropriate captured image of the region of interest can always be obtained.

  Moreover, since the wedge filter 13 is single, the edge part of the wedge filter 13 is not projected on FPD3, and it can prevent that the X-ray intensity detected by FPD3 changes abruptly. Further, a single moving mechanism 15 for moving the wedge filter 13 is sufficient, and the apparatus configuration can be simplified as compared with the conventional one.

  Further, by providing the rotation sensor 11, the rotational movement amount of the X-ray tube 1 can be acquired accurately and appropriately. Further, since the moving mechanism 15 is provided in the C-shaped arm 5, it is possible to easily realize moving the wedge filter 13 relative to the X-ray tube 1.

  Next, Embodiment 2 of the present invention will be described with reference to the drawings. In addition, about the same structure as Example 1, detailed description is abbreviate | omitted by attaching | subjecting the same code | symbol. FIG. 4 is a block diagram illustrating a schematic configuration of the tomography apparatus according to the second embodiment, and FIG. 5 is a cross-sectional view of main parts of the tomography apparatus cut along a tomographic plane.

  In the tomography apparatus according to the second embodiment, the X-ray tube 1 that irradiates the subject M with X-rays and the FPD 3 are fixed. Therefore, the irradiation axis A does not move.

  Further, in place of the top plate described in the first embodiment, the second embodiment includes a rotary table 41 that rotates the subject M and a base 43 that holds the rotary table 41. The rotary table 41 is positioned so that the rotation axis B intersects the irradiation axis A. Then, the subject M in the standing posture is placed at the predetermined position 41a so that the body axis C of the subject M is eccentric from the rotation axis B. The base 43 is fixed to the floor, and a rotation drive mechanism (not shown) for rotating the rotary table 41 is provided therein. Here, a plane formed on the subject M by the irradiation axis A by the rotational movement of the subject M is referred to as a tomographic plane H. The rotation sensor 45 indirectly measures the rotational movement amount of the subject M by detecting the rotation amount of the rotary table 41. The rotary table 41 and the rotary drive mechanism correspond to the rotating means in this invention. The rotation sensor 45 corresponds to the measuring means in this invention.

  A moving mechanism 46 is connected to the single wedge filter 13. The moving mechanism 46 moves the wedge filter 13 in parallel along the ellipse G in the tomographic plane H between the X-ray tube 1 and the subject M. As shown in the figure, the center point g of the ellipse G is desirably on the irradiation axis A. In addition, it is desirable that the major axis of the ellipse G is the one axis u direction orthogonal to the irradiation axis A in the tomographic plane H, and the minor axis is the irradiation axis A direction. However, the ellipse G is not limited to this, and can be appropriately changed as long as the wedge filter 13 can always move between the X-ray tube 1 and the subject M. The moving mechanism 46 corresponds to the moving means in this invention.

  The filter control unit 47 controls the moving mechanism 46 to move the wedge filter 13. The position information acquisition unit 49 calculates relative position information of the irradiation axis A, the rotation axis B, and the body axis C based on the detection result from the rotation sensor 45 described above, and outputs the relative position information to the filter control unit 19. The filter control unit 47 calculates a moving amount for moving the wedge filter 13 based on the relative position information, and controls the moving mechanism based on the calculated moving amount. The filter control unit 47 and the position information acquisition unit 49 are a central processing unit (CPU) that reads and executes a predetermined program, a RAM (Random-Access Memory) that stores various information, a storage medium such as a fixed disk, and the like. Realized. The filter control unit 47 and the position information acquisition unit 49 correspond to the control unit and the position information acquisition unit in the present invention, respectively.

The position information acquisition unit 49 and the filter control unit 47 will be described in more detail. In the storage unit included in the position information acquisition unit 49, position information of the irradiation axis A, the rotation axis B, and the tomographic plane H is set in advance as known position information. The position information acquisition unit 49 refers to the rotation plane and the body axis based on the rotational movement amount of the subject M detected from the rotation sensor 45 and referring to the known position information when the subject M rotates. The position information of the body axis point c, which is the intersection with C, is obtained. Furthermore, the rotation angle θ ₁ formed by the irradiation axis A and the straight line connecting the intersection point a of the irradiation axis A and the rotation axis B and the body axis point c is calculated. This rotation angle θ ₁ corresponds to the relative position information described above.

  Also in the storage unit of the filter control unit 47, the following known position information is set in advance. That is, the first distance D1 between the emission source point e and the rotation axis B (intersection point a), the third distance D3 between the emission source point e and the center g, the body axis point c, and the rotation axis B ( Eccentric distance r between intersection point a).

  When the subject M rotates, the filter control unit 47 calculates the displacement component Iu in the major axis direction and the displacement component IA in the minor axis direction with respect to the center point g, and the combination thereof is used as the movement amount of the wedge filter 13. . Specifically, it is given by Equation (2) and Equation (3).

Here, k is a positive constant of 1 or less. Note that the value of k may be 1, and in this case, the ellipse G is a circle with a center g. The first, the third distance D1, D3 and eccentricity r is both constant and amount of movement F changes depending only on the rotation angle theta _1. The amount of movement F is such that the portion where the attenuation amount (attenuation degree) of the wedge filter 13 is the smallest (low) is positioned on a straight line connecting the irradiation source point e and the body axis point c, and This is a value for increasing / decreasing the distance SSD between the irradiation source point e and the wedge filter 13 in accordance with the increase / decrease in the distance SOD with respect to the body axis point c.

  Next, the operation of the tomography apparatus according to the second embodiment will be described.

The rotary table 41 rotates around the rotation axis B with the subject M placed thereon. At this time, the rotation sensor 45 detects the amount of movement of the rotary table 41 and outputs it to the position information acquisition unit 49. The position information acquisition unit 49 determines the rotation angle θ ₁ based on the rotational movement amount of the subject M according to the detection result of the rotation sensor 45. Filter control section 47 calculates the amount of movement F of moving the wedge filter 13 based on the rotation angle theta _1, controls the wedge filter 13 based on the calculated amount of movement.

  When the subject M rotates, the X-ray tube 1 irradiates the subject M with X-rays from various angles. The irradiated X-ray is attenuated by passing through the wedge filter 13 and the subject M. The FPD 3 detects attenuated X-rays.

  Thus, according to the tomography apparatus according to the second embodiment, the filter control unit 47 controls the wedge filter 13 on the ellipse G, so that the position of the subject M varies with respect to the X-ray irradiation field. The wedge filter 13 is moved in the same direction as the direction, and the distance between the wedge filter 13 and the irradiation source point e is changed according to the variation in the size of the subject M with respect to the X-ray irradiation field. Thereby, it can suppress more effectively that the intensity | strength of X-ray exceeds the upper limit of the dynamic range of FPD3.

  Next, Embodiment 3 according to the present invention will be described with reference to the drawings. In addition, about the same structure as Example 1, detailed description is abbreviate | omitted by attaching | subjecting the same code | symbol.

  FIG. 6 is a block diagram showing the overall configuration of a multi-slice type X-ray CT apparatus which is an embodiment of the tomography apparatus of the present invention.

  The X-ray CT apparatus according to the third embodiment includes an X-ray tube 2 that irradiates a subject M with an X-ray fan beam (hereinafter simply referred to as an X-ray), and a number of X-ray detection elements 4a in the X-ray spreading direction. A multi-channel X-ray detector 4 arranged in a line (sideways spread), and a gantry 61 that rotatably accommodates the X-ray tube 2 and the X-ray detector 4 while facing each other. I have. The rotation mechanism 63 rotates the X-ray tube 2 and the X-ray detector 4 around the rotation axis B intersecting with the X-ray irradiation axis A. The rotation control unit 65 operates the rotation mechanism 63 to control the rotational movement of the X-ray tube 2 and the X-ray detector 64. The X-ray tube 2, the X-ray detector 4, the rotation mechanism 63, and the rotation control unit 65 correspond to the irradiation means, detection means, rotation means, and rotation control means in this invention, respectively.

  A moving mechanism 67 is connected to the single wedge filter 13. The moving mechanism 67 rotates the wedge filter 13 along an arc in the tomographic plane H. In the third embodiment, the center of the arc is matched with the irradiation source point e. The moving mechanism 67 corresponds to the moving means in this invention.

  The filter control unit 69 controls the moving mechanism 65 to move the wedge filter 13. The position information acquisition unit 71 receives the operation amount input from the rotation control unit 65 described above, calculates relative position information of the irradiation axis A, the rotation axis B, and the body axis C, and outputs the relative position information to the filter control unit 19. . The filter control unit 69 described above calculates a movement amount for rotating the wedge filter 13 based on the position information, and controls the movement mechanism 67 based on the calculated movement amount. The filter control unit 69 and the position information acquisition unit 71 are a central processing unit (CPU) that reads out and executes a predetermined program, a RAM (Random-Access Memory) that stores various types of information, a storage medium such as a fixed disk, and the like. Realized. The filter control unit 69 and the position information acquisition unit 71 correspond to the control unit and the position information acquisition unit in this invention, respectively.

The position information acquisition unit 71 and the filter control unit 69 will be described in more detail. Position information (known) of the body axis point c (the intersection of the rotation axis B and the body axis C) is set in advance in the storage unit included in the position information acquisition unit 71. Then, the position information acquisition unit 71 obtains position information of the irradiation axis A and the emission source point e based on the operation amount obtained from the rotation control unit 65. Then, a second angle θ ₂ formed by the straight line connecting the body axis point c and the emission source point e and the irradiation axis A is calculated with reference to the known position information. This second angle θ ₂ corresponds to the relative position information described above.

  The filter control unit 69 moves the wedge filter 13 so that the portion where the attenuation amount (attenuation degree) of the wedge filter 13 is the smallest (low) is located on a straight line connecting the emission source point e and the body axis point c. Is calculated.

The filter control unit 69 obtains the rotation angle of the wedge filter 13 with respect to the irradiation axis A as the movement amount of the wedge filter 13. In this case, the amount of movement is given by the second angle theta ₂ equal angles.

  According to such a tomography apparatus according to the third embodiment, the shape of the subject M viewed from the X-ray tube 2 and the shape of the wedge filter 13 itself can always maintain a complementary relationship. As a result, it is possible to effectively realize the suppression of the X-ray intensity below the upper limit value of the dynamic range of the X-ray detector 4.

  Since the position information acquisition unit 71 calculates the rotational movement amount of the X-ray tube 2 based on the operation amount of the rotation control unit 65, a rotation sensor or the like that measures the rotational movement amount of the X-ray tube 2 can be omitted. .

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

(1) In the above-described first and second embodiments, the relative position information is the rotation angle θ ₁ , but is not limited to this as long as the amount of movement of the filter 13 can be obtained appropriately. For example, a straight line connecting the body axis point c as described in Example 3 and the emission source point e, the second angle theta ₂ formed by the illumination axis A may be a relative position information.

  In each of the above-described embodiments, the amount of movement of the wedge filter 13 has been described. However, if the wedge filter 13 can be moved or rotated on a straight line connecting the emission source point e and the body axis point c, the design is appropriately made. Can change.

  For example, the movement amount of the wedge filter 13 may be obtained by obtaining the positional relationship between the emission source point e and the body axis point c as relative position information. For example, when the X-ray tube 1 (2) rotates, the subject M is fixed, so the position information of the body axis point c is known. Therefore, the position information acquisition unit 21 (71) calculates the position of the emission source point e with respect to the body axis point c. The filter control unit 19 (69) controls the moving mechanism 15 (67) so that the wedge filter 13 is positioned between the emission source point e and the body axis point c. When the subject M rotates, the position information of the emission source point e is known and the position information acquisition unit 49 obtains the body axis point c with respect to the emission source point e. The processing may be substantially the same.

  (2) In each of the above-described embodiments, the portion where the attenuation amount (attenuation degree) of the wedge filter 13 is the smallest (low) is positioned on the straight line connecting the emission source point e and the body axis point c. . However, if the X-ray intensity can be made uniform to the extent that the upper limit value of the dynamic range of the FPD 3 can be prevented, it is strictly not positioned on the straight line connecting the emission source point e and the body axis point c. In addition, the attenuation of the wedge filter 13 is not limited to the smallest part but may be the vicinity thereof. Alternatively, the vicinity of the thinnest part of the wedge filter 13 may be changed to be positioned on a straight line connecting the emission source point e and the body axis point c.

  (3) In the first and second embodiments described above, the rotation axis B of the X-ray tube 1 and the FPD 3 has been described so as to intersect the irradiation axis A. However, as long as a desired tomographic image is obtained, the rotation axis B and the irradiation axis. A may be strictly orthogonal or not orthogonal.

  (4) In the first and second embodiments described above, one axis u is described as an axis orthogonal to the irradiation axis A in the tomographic plane H. However, the present invention is not limited to this, and irradiation is performed at an arbitrary angle within the tomographic plane H. An axis that intersects with the axis A may be a single axis u. Even in this case, the moving mechanism 15 can move the wedge filter 13 in the changing direction of the subject M within the X-ray irradiation field. However, in the case of Example 1, when the single axis u is orthogonal to the irradiation axis A, the movement amount of the wedge filter 13 is minimized, and the efficiency is high.

(5) In the third embodiment described above, the center of the arc that rotates the wedge filter 13 is set to the same position as the emission origin e, but is not limited thereto. If the arc is between the X-ray tube 2 and the X-ray detector 4, an arbitrary point may be the center. In this case, the filter control unit 69 calculates the movement amount of the wedge filter 13 as it is without using the second angle θ ₂ as it is.

  (6) In the first and second embodiments described above, the rotation sensor 11 for measuring the movement amount of the C-shaped arm 5 or the rotation sensor 45 for measuring the rotation amount of the rotary table 41 is provided. If the amount of rotational movement of the tube 1 or the subject M can be measured, the sensor can be appropriately changed to a sensor that measures other physical quantities. For example, the rotational movement amount may be obtained by a method of measuring the position of the X-ray tube 2 or the subject M using an optical sensor, or a method of measuring the in-plane pressure of the rotary table 41, or the projection of the subject M. The rotational movement amount may be obtained from the detection result of the FPD 3 on which the image is projected.

  (7) In each of the above-described embodiments, either the irradiation axis A or the body axis C, or the first, second, third distances D1, D2, D3 and the eccentric distance r have been described as known. You may comprise so that it may obtain by measuring.

  (8) In each of the embodiments described above, the X-ray tubes 1 and 2 irradiate X-rays, and the FPD 2 and the X-ray detector 4 detect X-rays, but are not limited to X-rays. The present invention can also be applied when irradiating and detecting radiation, electromagnetic waves, and light other than X-rays.

  (9) In each of the above-described embodiments, the medical X-ray imaging apparatus is used. However, the present invention is not limited to this. For example, the present invention can also be applied to a radiation imaging apparatus used in industrial fields such as non-destructive inspection, RI (Radio Isotope) inspection, and optical inspection, and in the nuclear power field. In each embodiment, the subject M is described, but the subject M is not limited to the human body.

1 is a block diagram illustrating a schematic configuration of a tomography apparatus according to Embodiment 1. FIG. It is principal part sectional drawing of the tomography apparatus cut | disconnected by the tomographic plane. 3A is a virtual X-ray intensity profile obtained after passing through only the subject M, and FIG. 3B is a virtual X-ray intensity profile obtained after passing only through the wedge filter. FIG. 3C is a profile of the actual X-ray intensity transmitted through the wedge filter and the subject M. 6 is a block diagram illustrating a schematic configuration of a tomography apparatus according to Embodiment 2. FIG. It is principal part sectional drawing of the tomography apparatus cut | disconnected by the tomographic plane. FIG. 6 is a block diagram illustrating a schematic configuration of an X-ray CT apparatus according to Embodiment 3. It is principal part sectional drawing of the tomography apparatus which concerns on a prior art. FIG. 8A shows a virtual X-ray intensity profile obtained after transmitting only the subject M, and FIG. 8B shows a virtual X-ray intensity profile obtained after transmitting only the wedge filter. FIG. 8C shows a profile of the actual X-ray intensity transmitted through the wedge filter and the subject M2.

Explanation of symbols

1, 2 ... X-ray tube 3 ... Flat panel X-ray detector (FPD)
DESCRIPTION OF SYMBOLS 4 ... X-ray detector 5 ... C-shaped arm 7, 63 ... Rotation mechanism 11, 45 ... Rotation sensor 13 ... Wedge filter 15, 46, 67 ... Movement mechanism 19, 47, 69 ... Filter control part 21, 49, 71 ... Position information acquisition unit 41 ... Rotary table 43 ... Base 65 ... Rotation control unit M ... Subject A ... Irradiation axis B ... Rotation axis a ... Intersection C ... Body axis c ... Body axis point D1 ... First distance D2 ... First 2 distance D3 ... 3rd distance r ... Eccentric distance F ... Movement amount G ... Ellipse H ... Fault plane Iu ... Displacement component in long axis direction IA ... Displacement component in short axis direction u ... 1 axis θ ₁ ... Rotation angle θ ₂ ... Second angle

Claims (4)

In a tomography apparatus that irradiates a subject with electromagnetic waves emitted from an irradiating means through an attenuator having a high attenuation at an end and obtains a tomographic image based on data detected by the detecting means, the irradiating means emits the tomographic image. The irradiation means and the detection means, or a rotation means for rotating the subject around the rotation axis intersecting the irradiation axis of the electromagnetic wave, and the irradiation means within the tomographic plane formed by the rotation movement by the rotation means Moving means for moving the attenuation body relative to the body, and the body axis of the subject, the irradiation axis, and the Control means for controlling the moving means based on positional information relative to the rotating shaft to move the attenuation body ,
The intersection of the tomographic plane and the body axis is a body axis point, and the position where the electromagnetic wave is emitted on the irradiation axis is an emission source point. , And control to be located on a straight line connecting the emission source point and the body axis point,
The tomography apparatus characterized in that the moving means translates the attenuator along a circle or ellipse in the tomographic plane . 2. The tomography apparatus according to claim 1 , wherein the position information includes a rotation angle formed by a straight line connecting the intersection of the irradiation axis and the rotation axis and the body axis point, and the irradiation axis. Tomography equipment. The tomography apparatus according to claim 2 , wherein the irradiation unit by the rotational movement or a measurement unit that measures a rotational movement amount of the subject and a position at which the rotation angle is calculated based on a measurement result of the measurement unit. And a tomography apparatus comprising: an information acquisition unit. The tomography apparatus according to claim 2 , wherein a rotation control unit that controls the rotational movement by operating the rotation unit, and a position information acquisition unit that calculates the rotation angle based on an operation amount of the rotation control unit. A tomography apparatus comprising:

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