JP2010075553A - X-ray computed tomography system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve the reduction of exposure while suppressing the deterioration of image quality in a cone beam CT. <P>SOLUTION: This X-ray computed tomography system includes an X-ray tube 3 for producing X-rays, an X-ray detector 8 opposed to the X-ray tube 3 through a subject, a reconstitution secton 13 for reconstituting image data on the basis of the projection data detected by the X-ray detector 8, a first X-ray filter 5 arranged between the X-ray tube 3 and the subject and constituted so as to make the intensity of X-rays in a peripheral part lower than that of X-rays in a central part in relation to the fan angle direction crossing the body axial direction of the subject at a right angle and a second X-ray filter 6 arranged between the X-ray tube 3 and the subject and constituted so as to make the intensity of X-rays in the peripheral part lower than that of X-rays in the central part in relation to the body axial direction. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an X-ray computed tomography apparatus that enables helical scanning.

  In recent years, multi-slice CT (multi-row CT), which can multi-detect detectors in the body axis direction of a subject and scan a wide range of data at a time, has become mainstream. This scanning method greatly contributes to shortening of examination time, improvement of spatial resolution, and expansion of imaging application range (for example, heart, whole body, etc.).

  One of the factors that greatly affects the image quality of multi-slice CT is the effect of cone angle. In general, it is known that image quality deteriorates when reconstruction calculation is performed with the same weight on projection data with a large cone angle and projection data with a small cone angle. In recent years, as an algorithm for reducing this influence, a method has been developed in which projection data with a large cone angle is reduced in weight, and projection data with a small cone angle is increased in weight and reconstructed. In this method, the image quality is improved by reducing the contribution to the reconstruction calculation of projection data with a large cone angle. However, when collecting projection data, the contribution to the reconstruction calculation is large when the projection data is collected. In addition, the subject is irradiated with X-rays having the same intensity even in a large portion.

  An object of the present invention is to provide an X-ray computed tomography apparatus capable of reducing exposure while suppressing deterioration in image quality in cone beam CT.

  An X-ray computed tomography apparatus according to a first aspect of the present invention includes an X-ray tube that generates X-rays, an X-ray detector that faces the X-ray tube through a subject, and the X-ray detection A reconstruction unit that reconstructs image data based on the projection data detected by the instrument, and a central portion with respect to the fan angle direction that is disposed between the X-ray tube and the subject and is orthogonal to the body axis direction of the subject A first X-ray filter configured such that the X-ray intensity in the peripheral portion is lower than that in the portion, and is disposed between the X-ray tube and the subject, and the X portion in the peripheral portion rather than the central portion in the body axis direction. A second X-ray filter configured to reduce the line intensity.

  An X-ray computed tomography apparatus according to a second aspect of the present invention includes an X-ray tube that generates X-rays, an X-ray detector that faces the X-ray tube through a subject, and the X-ray detection A reconstruction unit that reconstructs image data based on projection data detected by the instrument, and a peripheral part that is arranged between the X-ray tube and the subject and that is closer to the central part in the body axis direction of the subject. And an X-ray filter configured to reduce the X-ray intensity.

  An X-ray computed tomography apparatus according to a third aspect of the present invention includes an X-ray tube that generates X-rays, an X-ray detector that faces the X-ray tube through a subject, and the X-ray detection A reconstruction unit that reconstructs image data based on the projection data detected by the instrument, and a central portion with respect to the fan angle direction that is disposed between the X-ray tube and the subject and is orthogonal to the body axis direction of the subject An X-ray filter configured so that the X-ray intensity in the peripheral portion is lower than that in the central portion in the body axis direction so that the X-ray intensity in the peripheral portion is lower than that in the portion.

  According to the present invention, in the cone beam CT, it is possible to reduce exposure while suppressing image quality deterioration.

  Embodiments of the X-ray computed tomography apparatus according to the present invention will be described below. The X-ray computed tomography apparatus includes a rotating / rotating type (ROTATE / ROTATE-TYPE) in which an X-ray tube and an X-ray detector are combined into one body and rotating around the subject, and an array in a ring shape. There are various types such as fixed / rotate (STATIONION / ROTATE-TYPE) in which a large number of detection elements are fixed and only the X-ray tube rotates around the subject. The present invention is applicable to any type. is there. In the present embodiment, the rotation / rotation type will be described.

  FIG. 1 is a diagram showing the configuration of a computed tomography apparatus according to an embodiment of the present invention. A gantry 1 supports an annular or disk-shaped rotating frame 2 in a rotatable manner. The rotating frame 2 includes an X-ray tube 3 and an X-ray detector 8 so as to face each other with a subject placed on the top plate 7 in the imaging region. Here, for the sake of explanation, the rotation axis of the rotary frame 2 is the Z axis, the imaging central axis connecting the focal point of the X-ray tube 3 and the center of the X-ray detector 8 is the Y axis, and the axis orthogonal to the YZ plane is the X axis. It prescribes. During imaging, the subject is typically placed in the imaging area so that the body axis substantially coincides with the Z axis. This XYZ coordinate system constitutes a rotational coordinate system with the Z axis as the center of rotation.

  The control unit 11 executes a helical scan in which the X-ray tube 3 moves in a spiral as viewed from the subject by controlling the rotation of the rotating frame 2 and the slide of the top plate 7 in synchronization. Specifically, the rotating frame 2 continuously rotates at a constant angular velocity, the top plate 7 moves at a constant velocity, and X-rays are generated from the X-ray tube 3 continuously or at every predetermined angle.

  A collimator 4 having a typically square or rectangular opening for limiting the solid angle of the X-ray is attached to the X-ray emission window of the X-ray tube 3. The X-ray from the X-ray tube 3 is formed into a pyramid shape by the collimator 4. This X-ray shaped into a pyramid is called a cone beam X-ray. As shown in FIG. 1, the spread angle of the cone beam X-ray in the X-axis direction is defined as a fan angle (α).

  A first X-ray filter 5 and a second X-ray filter 6 that change the X-ray intensity distribution are installed between the X-ray tube 3 and the subject. The first X-ray filter 5 and the second X-ray filter 6 are made of a material such as aluminum or plastic, for example.

  In the case of the multi-slice type, the X-ray detector 8 is an array of a plurality of detector elements having a plurality of channels in the fan angle direction (X axis, channel direction) in the rotation axis direction (Z axis, slice direction). is there. In the case of a two-dimensional array type, the X-ray detector 8 has a plurality of X-ray detection elements distributed densely in both the channel direction (X axis) and the slice direction (Z axis).

  A data acquisition unit (DAS) 9 is connected to the X-ray detector 8. The data collection unit 9 includes an IV converter that converts a current signal of each channel of the X-ray detector 8 into a voltage, and an integrator that periodically integrates the voltage signal in synchronization with an X-ray generation period. An amplifier that amplifies the output signal of the integrator and an analog / digital converter that converts the output signal of the amplifier into a digital signal are attached to each channel. Data collected by the data collection unit 9 (referred to as pure raw data) is sent to the preprocessing unit 12 via the non-contact type or slip ring type data transmission unit 9 using light or magnetism.

  The preprocessing unit 12 performs preprocessing such as correction of non-uniform sensitivity between channels on the pure raw data, and correction of extreme signal intensity reduction or signal dropout mainly due to the X-ray strong absorber by the metal part. . Based on the data corrected by the preprocessing unit 12 (referred to as raw data and projection data), the reconstruction unit 13 is configured to use a fan beam reconstruction method (fan beam convolution back projection method) or a felt comp Image data (volume data or multi-slice data) is reconstructed by a cone beam reconstruction method typified by a method. The image processing unit 14 generates a two-dimensional image from volume data or multi-slice data by MPR processing (cross section conversion processing) or rendering processing. The generated two-dimensional image is displayed on the image display unit 15.

Hereinafter, the X-ray filter according to the present embodiment will be described with reference to the drawings.
2A is a front view of the first X-ray filter 5 and the second X-ray filter 6, FIG. 2B is a side view of the first X-ray filter 5 and the second X-ray filter 6, and FIG. 3 is a perspective view of the first X-ray filter 5. is there. As shown in FIGS. 2A, 2B, and 3, the first X-ray filter 5 is a so-called wedge filter. The first X-ray filter 5 has a function of reducing low energy components of X-rays that are absorbed by the subject and do not reach the X-ray detector 8. Further, the first X-ray filter 5 is configured so as to correct the shift of the dynamic range between the central portion and the peripheral portion of the X-ray detector 8 which is caused by the fact that the X-ray absorption by the subject is less as the periphery of the subject. Is done. That is, with respect to the fan angle direction (X axis), the X-ray transmitted through the peripheral portion of the first X-ray filter 5 is configured to have lower intensity than the X-ray transmitted through the central portion. Therefore, as shown in FIG. 2A or FIG. 3, when the first X-ray filter 5 is made of a uniform material, the central portion is thin and the peripheral portion is thick along the fan angle direction (X axis). Due to the structure of the first X-ray filter 5 as described above, the X-ray absorption difference when the X-ray spread in the fan angle direction (X axis) passes through the subject does not become too large. Does not fall short of dynamic range. The first X-ray filter 5 is selectively used according to the diameter of the field of view (FOV). Therefore, the first X-ray filter 5 is supported by the rotating frame 2 so as to be replaceable.

  Now, the second X-ray filter 6 will be described. The shape of the second X-ray filter 6 differs depending on the type of reconstruction processing. First, a full reconstruction in which reconstruction is performed using projection data for approximately 360 degrees will be described, and then half reconstruction in which reconstruction is performed using projection data for approximately (180 + fan angle (α)) degrees. The case of will be described. The reconstruction unit 13 approximately uses the fan beam reconstruction method when the cone angle is small, and uses the cone beam reconstruction method when the cone angle is large. Here, the reconstruction unit 13 performs reconstruction using the cone beam reconstruction method. The case where it comprises is demonstrated. First, how the cone angle is handled in the reconstruction process will be described with reference to FIG.

  FIG. 4 is a diagram for explaining the cone angle in the full reconstruction. In the helical scan, the control unit 11 collects projection data while rotating the X-ray tube 3 and the X-ray detector 8 on the rotating frame 2 while moving the top plate 7 at a constant speed. When the movement of the X-ray tube 3 is viewed from the subject, the X-ray tube 3 appears to move spirally as shown in FIG. Consider an example in which the point a of the cross section D is reconstructed. To reconstruct the point a, actually measured projection data for −180 degrees to +180 degrees from this position is required. The positions P and Q of the X-ray tube 3 are within this range. FIG. 5 is a diagram showing X-ray tube positions P and Q on the reconstructed section D. FIG. As shown in FIG. 5, the X-ray tube positions P and Q are at opposite positions on the reconstructed section D. However, as can be seen from FIG. 4, the angle q (cone angle q) formed by the X-ray beam from the position Q to the point a and the reconstructed section D is the X-ray beam from the position P to the point a. The angle is larger than the angle p (cone angle p) formed by the reconstructed section D. Therefore, if the projection data related to the position P and the projection data related to the position Q are processed with the same weight, the image is degraded due to the influence of the difference in cone angle.

  In order to correct this problem, the cone angle formed by the X-ray beam and the reconstructed cross section D is calculated, and the projection data based on the X-ray beam having a small cone angle has a large weight, and the X-ray beam has a large cone angle. The projection data based is reconstructed with a reduced weight. The angle range where the cone angle is small is the range of the cone angle formed by the X-ray beam in the range of (−90−α / 2) to (+ 90 + α / 2) degrees from the reconstruction cross section D. . That is, in FIG. 4, it is in the range of s degrees to t degrees.

Next, the function of the second X-ray filter 6 will be described.
6A shows the position of the X-ray tube and the reconstruction area when viewed from the reconstruction section D, with the horizontal axis as the body axis direction (Z axis) and the vertical axis as the imaging center axis direction (Y axis). FIG. As shown in FIG. 6A, the X-ray tube 3 at a position of (−90−α / 2) degrees from the reconstructed section D is (A), and the X-ray tube 3 at a position of 0 degrees is (B ), The X-ray tube 3 at the position of (+ 90 + α / 2) degrees is defined as (C). Here, the helical pitch (HP) is defined as the distance that the top plate 7 moves while the X-ray tube 3 rotates 360 degrees. Then, the distance between the X-ray tube 3 (A) and the X-ray tube 3 (C) is HP · ((180 + α) / 360). The mesh area shown in FIG. 6A is a reconstruction area that enables field of view (FOV). This mesh area is an area where measured data can be collected from all positions of the X-ray tube 3 (A) to the X-ray tube 3 (C). That is, this mesh area is a reconstruction area corresponding to the movement range of the (−90−α / 2) degree to (+ 90 + α / 2) degree of the X-ray tube 3. Here, regarding the body axis direction (Z axis), the length of the reconstruction area is L1. As shown in FIG. 6A, the length (L1) of the reconstruction region is the distance between the X-ray tube 3 (A) and the X-ray tube 3 (C), that is, HP · ((180 + α) / 360). To be determined. The X-ray (broken line) generated from the X-ray tube 3 (B) is narrowed in the body axis direction (Z-axis) by the second X-ray filter 6, but the width of the narrowed X-ray (solid line) is This is determined based on the length (L1) of the reconstruction area.

  FIG. 6B is a diagram illustrating the positions of the X-ray irradiation field and the reconstruction area, with the vertical axis representing the fan angle direction (X axis) and the horizontal axis representing the body axis direction (Z axis). The mesh region shown in FIG. 6B includes an X-ray irradiation field corresponding to the X-ray tube 3 (A), an X-ray irradiation field corresponding to the X-ray tube 3 (B), and the X-ray tube 3 (C ) Overlaps with the X-ray irradiation field corresponding to. That is, this mesh area is a reconstruction area.

  FIG. 6C is a diagram in which the position of the thin portion of the second X-ray filter 6 and the reconstruction area is represented by the imaging central axis (Y axis) on the vertical axis and the body axis (Z axis) on the horizontal axis. . As shown in FIG. 6 (c), the length (L2) of the thin portion of the X-ray filter 6 is determined based on the length (L1) of the reconstruction area in the body axis direction (Z axis).

  FIG. 7 is a diagram for explaining the relationship between the length (L1) of the reconstruction region and the length (L2) of the thin portion of the second X-ray filter 6 with respect to the body axis. As shown in FIG. 7, the length (L1) of the reconstruction area, the length (L2) of the thin portion of the second X-ray filter 6, and the distance (H1) between the X-ray tube 3 and the second filter 6 The distance (H2) between the X-ray tube 3 and the reconstruction area is similar. Based on this similar system, the length (L2) of the thin portion of the second X-ray filter 6 is determined. Considering the explanation of FIG. 6A, the length (L2) of the thin portion of the second X-ray filter is determined based on HP · ((180 + α) / 360), that is, the helical pitch (HP). I understand.

  The second X-ray filter 6 has a shape as shown in FIGS. 2A, 2B, and 8. FIG. 8 is a perspective view of the second X-ray filter 6. As shown in FIGS. 2A, 2B, 8, and 9, the second X-ray filter 6 is composed of a thin portion near the center with respect to the body axis direction (Z axis), and a thick portion around the periphery. . FIG. 9 is a view of the second X-ray filter viewed from the Y-axis direction. As shown in FIG. 9, the cone beam X-ray has a large cone angle, that is, a range other than (−90−α / 2) degrees to (+ 90 + α / 2) degrees, and in FIG. The portion where the X-ray beam in a range other than t degrees passes through the second X-ray filter 6 is thickened. That is, the X-ray beam that has passed through the thick portion of the second X-ray filter 6 does not enter the mesh region of FIG. 6A or 6B. Further, the cone beam X-ray has a small cone angle, that is, a range corresponding to (−90−α / 2) degrees to (+ 90 + α / 2) degrees, or in a range of s degrees to t degrees in FIG. A portion where the X-ray beam passes through the second X-ray filter 6 is thinned. The X-ray beam that has passed through the thin portion is incident on the mesh region of FIG. 6A or 6B.

  As shown in the description of FIG. 7, the length (L2) of the thin portion along the body axis direction (Z-axis) is determined based on the helical pitch (HP). Since the length (L2) of the thin portion of the second X-ray filter 6 depends on the helical pitch (HP), the second X-ray filter 6 can be exchanged according to the helical pitch (HP). An example of the thickness ratio between the thin portion and the thick portion of the second X-ray filter 6 is about 1: 3.

  FIG. 10 shows the X-ray intensity distribution after the X-rays have passed through the second X-ray filter 6. The vertical axis represents the X-ray intensity, and the horizontal axis represents the position (cone angle) of the X-ray beam. As can be seen from FIG. 10, the X-ray intensity is lower in the other ranges than in the range where the cone angle is in the range of s degrees to t degrees. Note that the range of (−90−α / 2) degrees to (+ 90 + α / 2) degrees is an approximate guideline. For example, it is a range in which an X-ray beam having a cone angle corresponding to −90 degrees to +90 degrees is irradiated. The thickness of the second X-ray filter 6 is reduced to a range in which an X-ray beam having a cone angle corresponding to −90 degrees to (−90−α / 2) degrees and +90 degrees to (+ 90 + α / 2) degrees is irradiated. May be increased. Further, the thickness may change from the position irradiated with the X-ray beam having a cone angle corresponding to around (−90−α / 2) degrees and around (+ 90 + α / 2) degrees.

  Since the second X-ray filter 6 is composed of a single member, the X-ray intensity in the X-ray transmitted through the second X-ray filter 6 has a small cone angle, that is, the X-ray intensity in the range of cone angle s degrees to t degrees. It will decline. Therefore, another X-ray filter 60 different from the second X-ray filter 6 as shown in FIG. As shown in FIG. 11, the second X-ray filter 60 is composed of a member whose X-ray intensity does not decrease, such as an acrylic plate, and a member whose X-ray intensity decreases, such as aluminum. The X-ray filter 60 is configured by bonding aluminum or the like to a portion of the base such as an acrylic plate that reduces the X-ray intensity. The X-ray transmitted through the second X-ray filter 60 configured in this manner does not decrease in intensity in a range where the cone angle is small, and decreases in intensity only in a range where the cone angle is large.

  FIG. 12 is a diagram for explaining a form different from the second X-ray filter 6 and the second X-ray filter 60. As shown in FIG. 12, the second X-ray filter 61 is configured such that the central portion is the thinnest with respect to the body axis direction (Z axis) and the thickness increases from the center toward the periphery. FIG. 13 is a diagram showing the X-ray intensity distribution after the X-rays have passed through the second X-ray filter 61. The vertical axis represents the X-ray intensity and the horizontal axis represents the position (cone angle) of the X-ray beam. As shown in FIG. 13, the X-ray transmitted through the central portion of the second X-ray filter 61 corresponding to a cone angle of 0 degree has the highest intensity, and the intensity of the X-rays decreases with increasing intensity.

  Next, the second X-ray filter 62 in the case of half reconstruction will be described. First, how the cone angle is handled in half reconstruction will be described.

  In half reconstruction, reconstruction processing is performed using actually measured projection data for (−90−α / 2) to (+ 90 + α / 2) degrees from the reconstruction section D. Even in the half reconstruction, the projection data based on the X-rays having a large cone angle is reduced in weight, and the projection data based on the X-rays having a small cone angle is increased in weight to perform reconstruction processing. In the half reconstruction, it is necessary to consider duplication of projection data due to X-rays spreading in a fan shape.

  Therefore, the second X-ray filter 62 is formed as shown in FIG. FIG. 14 is a diagram of the second X-ray filter 62 viewed from the Y-axis direction. As shown in FIG. 14, the thin portion is displaced with a certain slope (g) along the channel direction (X axis). 15 is a sectional view of the position M in the channel direction of the second X-ray filter 62 in FIG. 14, and FIG. 16 is a sectional view of the position N in the channel direction of the second X-ray filter 62 in FIG. As can be seen by comparing FIG. 15 with FIG. 16, the thickness of the second X-ray filter 62 varies depending on the position in the channel direction (X axis). However, the length (L2) of the thin position in the body axis direction (Z axis) does not change depending on the position in the channel direction. The length (L2) of the thin position in the body axis direction (Z axis) is determined based on the helical pitch (HP) as described above. The inclination angle (g) of the thin portion of the second filter 62 with respect to the body axis direction (Z axis) is determined based on the helical pitch (HP). More specifically, the tilt angle (g) increases as the helical pitch (HP) increases.

  Cone beam X-rays that have passed through the second X-ray filters 6, 60, 61, 62 and whose X-ray intensity is attenuated at a large cone angle are transmitted through the subject, detected by the X-ray detector 8, and collected. Projection data is obtained via the unit 9 and the preprocessing unit 12. The projection data is weighted based on the cone angle by the reconstruction unit 13 and reconstructed into image data. Here, since the cone angle is large, the projection data based on the X-ray beam whose intensity is reduced by the second X-ray filters 6, 60, 61 and 62 is processed by the reconstruction unit 13 with a reduced weight. However, the projection data based on the X-ray beam having a large cone angle is projection data that hardly contributes to the image quality without passing through the second X-ray filters 6, 60, 61 and 62. Therefore, the image quality of the image obtained based on the projection data whose intensity is reduced according to the cone angle by passing through the second X-ray filters 6, 60, 61, 62 is the second X-ray filters 6, 60, 61. , 62 is almost equal to the image quality of the image based on the projection data obtained without transmitting.

  In the above description, the first X-ray filter 5 and the second X-ray filter 6 or the second X-ray filter 60 or the second X-ray filter 61 or the second X-ray filter 62 are provided. However, the present invention is not limited to this, and only the second X-ray filters 6, 60, 61, 62, that is, the X-ray filter configured so that the X-ray intensity in the central portion is lower than the peripheral portion in the body axis direction. There may be. In addition, the X-ray filter 63 can simultaneously satisfy the functions of the first filter 5 and the second X-ray filter 6 or the second X-ray filter 60 or the second X-ray filter 61 or the second X-ray filter 62 with one X-ray filter. May be. 17, FIG. 18, FIG. 19, and FIG. 20 are diagrams for explaining the X-ray filter 63. FIG. 17 is a view of the X-ray filter 63 as seen from the front (YX plane) of the gantry 1, FIG. 18 is a cross-sectional view as seen from position E in FIG. 17, and FIG. 19 is a cross-sectional view as seen from position F in FIG. 20 is a cross-sectional view as seen from position G in FIG. As shown in FIGS. 17 to 20, the X-ray filter 63 has a lower X-ray intensity in the peripheral direction than the central portion of the X-ray with respect to the fan angle direction. Also, the X-ray intensity at the periphery is reduced. That is, the X-ray filter 63 is configured to be thinner in the vicinity of the central portion than in the vicinity of the peripheral portion in the fan angle direction, and is thinner in the vicinity of the central portion than in the vicinity of the peripheral portion in the body axis direction. Consists of parts.

  Thus, according to the present invention, in cone beam CT, it is possible to reduce exposure while suppressing image quality deterioration.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

The figure which shows the structure of the X-ray diagnostic apparatus in this embodiment. The figure which looked at the 1st X-ray filter and the 2nd X-ray filter of FIG. 1 from the front of the mount frame. The figure which looked at the 1st X-ray filter and 2nd X-ray filter of FIG. 1 from the side of the mount frame. The perspective view of the 1st X-ray filter of FIG. The figure which shows the relationship between the reconstruction process and cone angle | corner in this embodiment. The figure which shows the positional relationship of X-ray tube position (alpha) and (beta) seen from the reconstruction cross section in FIG. The figure explaining the position of the X-ray tube of FIG. 1, a reconstruction area | region, and a 2nd X-ray filter. The figure which shows the relationship between the length (L1) of a reconstruction area | region, and the length (L2) of the thin part of a 2nd X-ray filter. The perspective view of the 2nd X-ray filter of FIG. 1 in the case of performing a full reconstruction process. The figure which looked at the 2nd X-ray filter of Drawing 8 from the Y-axis direction. The figure which shows intensity distribution of the X-ray after passing the 2nd X-ray filter of FIG. The perspective view of the 2nd X-ray filter different from FIG. 8 in the case of performing a full reconstruction process. The figure which shows the 2nd X-ray filter different from FIG. 8 and FIG. The figure which shows intensity distribution of the X-ray after passing the 2nd X-ray filter of FIG. The figure which looked at the 2nd X-ray filter of Drawing 1 from the Y-axis direction in the case of performing half reconstruction processing. FIG. 15 is a cross-sectional view of the second X-ray filter of FIG. 14 as viewed from a position M with respect to the channel direction. FIG. 15 is a cross-sectional view of the second X-ray filter of FIG. 14 as viewed from a position N with respect to the channel direction. The front view of the X-ray filter provided with both the function of the 1st X-ray filter of FIG. 1, and the function of the 2nd X-ray filter. Sectional drawing regarding the position E of the X-ray filter of FIG. Sectional drawing regarding the position F of the X-ray filter of FIG. Sectional drawing regarding the position G of the X-ray filter of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Mount, 2 ... Rotating frame, 3 ... X-ray tube, 4 ... Collimator, 5 ... 1st X-ray filter, 6 ... 2nd X-ray filter, 7 ... Top plate, 8 ... X-ray detector, 9 ... Data collection part DESCRIPTION OF SYMBOLS 10 ... Data transmission part, 11 ... Control part, 12 ... Pre-processing part, 13 ... Reconstruction part, 14 ... Image processing part, 15 ... Image display part.

Claims (12)

An X-ray tube that generates X-rays;
An X-ray detector facing the X-ray tube via a subject;
A reconstruction unit that reconstructs image data based on projection data detected by the X-ray detector;
A first X-ray filter that is arranged between the X-ray tube and the subject and configured such that the X-ray intensity in the peripheral portion is lower than that in the central portion with respect to the fan angle direction orthogonal to the body axis direction of the subject. When,
A second X-ray filter disposed between the X-ray tube and the subject and configured to have a lower X-ray intensity at a peripheral portion than at a central portion in the body axis direction. X-ray computed tomography apparatus.   2. The X-ray computed tomography apparatus according to claim 1, wherein the second X-ray filter is configured with a thinner portion in the vicinity of the central portion than in the vicinity of the peripheral portion in the body axis direction.   2. The X-ray filter according to claim 1, wherein the second X-ray filter is configured with a member whose X-ray intensity does not decrease at a central portion and a member whose X-ray intensity decreases at a peripheral portion in the body axis direction. Line computed tomography equipment.   The X-ray computed tomography apparatus according to claim 2, wherein the second X-ray filter has a length of the thin portion in the body axis direction determined based on a helical pitch.   The X-ray computed tomography apparatus according to claim 1, wherein the second X-ray filter is replaceable. The reconstruction unit reconstructs image data based on projection data for about 360 degrees,
In the second X-ray filter, the vicinity of the central portion in the body axis direction is configured with a thinner portion than the vicinity of the peripheral portion, and the position of the thin portion and the position of the thick portion in the body axis direction is a fan. 2. The X-ray computed tomography apparatus according to claim 1, wherein the X-ray computed tomography apparatus is configured to be constant regardless of the position in the angular direction. The reconstruction unit reconstructs image data based on projection data for about 360 degrees,
2. The X-ray according to claim 1, wherein the second X-ray filter is configured such that the central portion is thinnest in the body axis direction and becomes thicker as the distance from the center portion increases along the body axis direction. Computer tomography equipment. The reconstruction unit reconstructs image data based on projection data for about 180 degrees + fan angle,
The second X-ray filter is configured with a thinner portion in the vicinity of the central portion in the body axis direction than in the vicinity of the peripheral portion, and the position of the thin portion in the body axis direction depends on the position in the fan angular direction. The X-ray computed tomography apparatus according to claim 1, wherein the apparatus is configured to change.   The second X-ray filter is configured such that the position of the thin portion with respect to the body axis direction changes from one end to the other end in the fan angle direction based on a helical pitch. The X-ray computed tomography apparatus according to claim 8. An X-ray tube that generates X-rays;
An X-ray detector facing the X-ray tube via a subject;
A reconstruction unit that reconstructs image data based on projection data detected by the X-ray detector;
An X-ray filter that is disposed between the X-ray tube and the subject and is configured such that the X-ray intensity in the peripheral portion is lower than the central portion in the body axis direction of the subject. A featured X-ray computed tomography system. An X-ray tube that generates X-rays;
An X-ray detector facing the X-ray tube via a subject;
A reconstruction unit that reconstructs image data based on projection data detected by the X-ray detector;
It is arranged between the X-ray tube and the subject and is centered in the body axis direction so that the X-ray intensity in the peripheral part is lower than the center part in the fan angle direction perpendicular to the body axis direction of the subject. An X-ray computed tomography apparatus comprising: an X-ray filter configured so that an X-ray intensity in a peripheral portion is lower than that in a portion.   In the fan angle direction, the X-ray filter has a thinner portion near the central portion than the peripheral portion, and the central portion in the body axis direction has a thinner portion than the peripheral portion. The X-ray computed tomography apparatus according to claim 11.

Images