JP4569763B2 - X-ray CT system - Google Patents

Description

  The present invention relates to an industrial X-ray CT apparatus, and more particularly to an X-ray CT apparatus capable of CT imaging by offset scanning.

  As a method for observing the internal structure or the like of various industrial products without destruction, a method for obtaining a tomographic image to be observed using an X-ray CT apparatus is conventionally known. In an industrial X-ray CT apparatus used for such an application, generally, a subject is mounted between an X-ray source and an X-ray detector arranged opposite to each other and placed on the X-ray optical axis (x-axis). A configuration is adopted in which a rotary table that provides rotation around a perpendicular rotation axis (z-axis) is arranged. In this configuration, a subject is mounted on a rotary table and rotated while irradiating X-rays, and each pixel output of the X-ray detector, that is, X-ray transmission data is captured at each minute rotation angle, and the data is reconstructed. By doing so, a tomographic image of the subject along the plane (xy plane) orthogonal to the rotation axis is obtained.

In such an industrial X-ray CT apparatus, a normal scan and an offset scan are conventionally known as a method of collecting X-ray transmission data of a subject, in other words, as a method of CT imaging. In the normal scan, as shown in a schematic plan view in FIG. 7 , the rotation axis (rotation axis of the rotary table) R of the subject provided between the X-ray source 81 and the X-ray detector 82 is converted into the X-ray optical axis L. In this method, X-ray transmission data is collected in a state provided above or in the vicinity thereof. In this case, the CT imaging possible region (scan region or tomographic image field) is a region represented by An in the drawing.

On the other hand, in the offset scan, as shown in the schematic plan view of FIG. 8 , the rotation axis R of the subject provided between the X-ray source 81 and the X-ray detector 82 is set with respect to the X-ray optical axis L. A method of collecting X-ray transmission data in a state shifted in a direction (y direction) orthogonal to both the direction of the X-ray optical axis L (x direction) and the direction of the rotation axis R (z direction), In this case, the CT imaging possible area is an area represented by Ao in the figure.

The switching between the normal scan and the offset scan is conventionally performed by moving the rotation axis R as shown in FIGS. 7 and 8 , in other words, by moving the rotation table in the y-axis direction (for example, patents). Reference 1).
Japanese Patent No. 3616928

  By the way, in the X-ray CT apparatus, generally, it is important to accurately grasp the projection position of the rotation axis for rotating the subject onto the X-ray detector, and the rotation during actual CT imaging is performed. If the axis position deviates from the assumed position, it may cause image quality degradation such as blurring or noise. In addition, other geometrical deviations such as tilt and inclination are corrected at the time of reconstruction, but there are various image quality even when the geometrical deviation is different from what it was supposed to be. Causes deterioration.

  On the other hand, with the advancement of technology, the industrial X-ray CT apparatus has been able to obtain tomographic images with higher magnification and higher resolution. Is enlarged and projected on the X-ray detector, and the influence becomes large.

In the offset scanning method, as shown in a schematic plan view in FIG. 9 , the line or plane connecting the X-ray source 81 and the rotation axis R and the light receiving surface of the X-ray detector 82 are orthogonal to each other. Therefore, it is necessary to project the data output from the actual X-ray detector 82 as if there is a virtual X-ray detector at the position indicated by 820 in the figure, This correction calculation for projection requires time, and causes image blurring and tomographic image noise by image processing of discrete digital data.

Furthermore, the offset scan is originally capable of obtaining a wider CT imaging area with the same magnification if the size of the light receiving surface of the X-ray detector is the same as that in the normal scan. , the area is limited to the area indicated by Ao shown in FIG.

The main problem of the present invention is that the projection position of the rotation axis onto the X-ray detector can be made more accurate than the conventional offset scanning method, and a line or plane connecting the X-ray source and the rotation axis can be obtained. an X-ray detector and is always perpendicular to, and at the same time eliminating the need for the correction operation for the projection shown in FIG. 9, is to provide an X-ray CT apparatus capable of reducing the cause of noise or the like. Another object of the present invention is to provide an X-ray CT apparatus capable of obtaining a wider CT imaging region even if the same X-ray detector is used as compared with the conventional offset scanning method. .

  In order to solve the above-mentioned main problem, an X-ray CT apparatus according to a first aspect of the present invention includes a subject mounted between an X-ray source and an X-ray detector arranged to face each other and an X-ray from the X-ray source. A rotary table is provided that rotates around a rotation axis (z axis) orthogonal to the linear optical axis (x axis), and the subject is rotated by the rotation table and captured at a predetermined rotation angle. In an X-ray CT apparatus provided with reconstruction calculation means for reconstructing a tomographic image of a subject along a plane orthogonal to the rotation axis using X-ray transmission data of the subject, the X-ray detector is connected to the X-ray detector. Detector moving means for moving in a direction (y-axis direction) orthogonal to both the optical axis and the rotation axis is provided, and the detector moving means is at least near the center of the effective width in the y-axis direction of the X-ray detector. A state located on the X-ray optical axis; The X-ray detector is configured to move between the vicinity of one end portion of the effective direction width on the X-ray optical axis, and the reconstruction calculation means includes It is characterized by being configured to selectively execute each reconstruction calculation program for offset scanning.

Further, The invention according to claim 3, by using the configuration of the invention according to claim 1 that performs offset scan by shifting the X-ray detector-side without shifting the rotation axis relative to the X-ray optical axis, In order to solve the other problems described above, an X-ray beam from an X-ray source is mounted by mounting a subject between an X-ray source and an X-ray detector arranged opposite to each other, as in the previous inventions. A rotation table is provided for rotating about a rotation axis (z axis) orthogonal to the axis (x axis), and the rotation table is used to rotate the subject while the subject is captured at every predetermined rotation angle. In an X-ray CT apparatus provided with reconstruction calculation means for reconstructing a tomographic image of a subject along a plane orthogonal to the rotation axis using X-ray transmission data, the X-ray detector is connected to the X-ray optical axis. And a direction orthogonal to both the rotation axis ( Detector moving means for moving in the axial direction). The detector moving means includes at least a first end portion of the effective width in the y-axis direction of the X-ray detector located on the X-ray optical axis. The X-ray detector moves further away from the X-ray optical axis in the y-axis direction from the first state, and all the effective widths in the y-axis direction of the X-ray detector are The X-ray detector is configured to move between a second state not located above, and the reconstruction calculation means rotates the subject around the rotation axis in the first and second states. This is characterized by reconstructing a tomographic image of a subject using a reconstruction calculation program for offset scanning using the X-ray transmission data acquired in this way.

In the inventions according to claims 1 and 2 above, the rotary table is fixed so that the rotary shaft is positioned on the optical axis and does not move in the y-axis direction (claim 3 ). ) Can be adopted.

  The present invention seeks to solve the main problem by shifting the X-ray detector rather than shifting the rotation axis (and hence the rotation table) for rotating the subject relative to the X-ray optical axis.

  That is, in the invention according to claim 1, detector moving means for moving the X-ray detector in a direction (y-axis direction) orthogonal to the two directions of the X-ray optical axis (x-axis) and the rotation axis (z-axis). And at least the vicinity of the center of the effective width in the y-axis direction of the X-ray detector is located on the X-ray optical axis, and the vicinity of one end of the effective width in the y-axis direction is the X-ray optical axis. The X-ray detector can be moved between the upper positions.

  According to this configuration, the normal scan and the offset scan can be switched while the rotation axis is positioned on the X-ray optical axis. With this configuration, the influence of the positioning mechanism error when switching from the normal scan to the offset scan can be reduced as compared with the conventional case. That is, when switching between normal scan and offset scan by moving the rotation axis as in the prior art, the positioning error of the rotation axis (deviation between the assumed position and the actual rotation axis) is enlarged on the X-ray detector. On the other hand, in the invention according to claim 1, the positioning error of the X-ray detector is not enlarged, and greatly contributes to the improvement of the image quality particularly when CT imaging is performed at a high magnification.

  Also, when performing an offset scan by shifting the X-ray detector side in the y-axis direction, the rotation axis of the subject may be positioned on the X-ray optical axis, so that the line connecting the X-ray source and the rotation axis or The plane is always orthogonal to the light-receiving surface of the X-ray detector, eliminating the need for the conventional correction calculation for projection shown in FIG. 10 and reducing the amount of calculation, as well as due to digital errors during the calculation. Noise can be eliminated.

On the other hand, the invention according to claim 2 uses a configuration in which the X-ray detector is shifted in the y-axis direction with respect to the X-ray optical axis to perform the offset scan, so that the CT imaging possible region is significantly larger than the conventional one. It is possible to make it wide.

That is, in the invention according to claim 2 , the X-ray detector is in the offset scan state in each of the above-described inventions, that is, the first end portion of the effective width in the y-axis direction of the X-ray detector is positioned on the X-ray optical axis. The X-ray detector is moved further away from the X-ray optical axis in the y-axis direction from the first state and the first state, and all the effective widths in the y-axis direction of the X-ray detector are The X-ray detector can be moved between the second state not located above. Then, a tomographic image of the subject is reconstructed using both of the X-ray transmission data groups obtained by CT imaging in the first and second states.

  For example, in this configuration, if the second state moves the X-ray detector from the first state in the y-axis direction by an amount corresponding to the effective width in the y-axis direction of the detector, the actual y-ray detector y X-ray equivalent data equivalent to an offset scan using an X-ray detector having an effective width in the same direction that is twice the effective width in the axial direction can be obtained, and the CT imaging region can be substantially enlarged. Can do.

In each of the above inventions, since the offset scan is performed at a position where the X-ray detector side is shifted in the y-axis direction with respect to the X-ray optical axis, the rotation axis of the rotary table is on the X-ray optical axis. Therefore, it is possible to adopt a configuration in which the rotary table is fixed without being moved in the y-axis direction, as in the invention according to claim 3 . According to this configuration, by positioning the rotation axis on the X-ray optical axis at the time of shipment of the apparatus or the like, the rotation axis does not deviate from the X-ray optical axis, resulting in a decrease in image quality. It does not occur.

  According to the first aspect of the present invention, the normal scan and the offset scan are switched by shifting the X-ray detector side, so that mechanical positioning is performed as compared with the case where the conventional rotary table (rotating shaft) is switched. The error is not enlarged and does not affect the X-ray transmission data, and if the same positioning accuracy mechanism is used, the image quality of the tomographic image can be improved. Mechanism can be used.

Further, since the offset scan can be performed with the rotation axis positioned on the X- ray optical axis, the line or plane connecting the X-ray source and the rotation axis is orthogonal to the X-ray detector, It is no longer necessary to perform a correction operation for projecting transmission data from an actual X-ray detector onto a virtual detector plane orthogonal to a line or plane connecting the X-ray source and the rotation axis, as in an offset scan by a conventional apparatus, The calculation time can be shortened, and at the same time, there is no deterioration in image quality due to a digital error that occurs during the correction calculation.

According to the second aspect of the present invention, the radius of the CT imaging possible region can be substantially doubled as compared with the conventional offset scan. Further, since the light receiving surface of the X-ray detector necessary for obtaining the same CT imaging possible region can be reduced, the cost can be reduced in that case.

According to the invention of claim 3 , since the rotating shaft does not move in the direction orthogonal to both the X-ray optical axis direction and the rotating shaft direction when the apparatus is used, the X-ray optical axis is preliminarily set when the apparatus is shipped. By adjusting so that the rotation axis is positioned above, there is no possibility of various problems due to the X-ray optical axis and the rotation axis not matching.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram of an embodiment of the present invention. FIG. 1A is a diagram showing a schematic plan view showing a mechanical configuration and a block diagram showing a system configuration. FIG. It is a schematic front of a structure.

  An X-ray detector 2 is disposed opposite to the X-ray generator 1, and a rotary table 3 is disposed therebetween. The turntable 3 rotates around a rotation axis R along the z-axis direction orthogonal to the X-ray optical axis L (x-axis direction) from the X-ray generator 1 and rotates around the subject W mounted thereon. Provides rotation about axis R.

  The X-ray generator 1 generates X-rays corresponding to a tube voltage and a tube current supplied from an X-ray controller (not shown) in a cone beam shape from the X-ray focal point 1a. The X-ray detector 2 is a detector having a two-dimensional light receiving surface, and in this example is an FPD (flat panel detector). The X-ray detector 2 can be moved in the y-axis direction orthogonal to the two directions of the X-ray optical axis L and the rotation axis R by the detector moving mechanism 4. As shown in FIG. 1A, the movement range is such that the center of the effective width in the y-axis direction of the X-ray detector 2 is positioned on the X-ray optical axis L, and FIG. As shown, the vicinity of one end portion of the effective width in the y-axis direction of the X-ray detector 2 is located on the X-ray optical axis L.

  In this example, the turntable 3 can be moved only in the x-axis direction (X-ray optical axis L direction) and the z-axis direction (rotation axis R direction) by the xz moving mechanism 5, and in the y-axis direction. The rotation axis R is fixed at a fixed position on the X-ray optical axis L.

  The rotary table 3 is rotated by a drive signal from the rotary table drive circuit 11, the detector moving mechanism 4 moves the X-ray detector 2 in the y-axis direction by a drive signal from the detector moving mechanism drive circuit 12, and The xz moving mechanism 5 moves the rotary table 3 in the x-axis direction and / or the z-axis direction by a drive signal from the xz moving mechanism drive circuit 13. The rotary table drive circuit 11, the detector moving mechanism drive circuit 12 and the xz moving mechanism drive circuit 13 are placed under the control of the personal computer 14. The personal computer 14 is connected with a tomogram reconstruction calculation device 15, and is also connected with an operation unit 16 such as a mouse, a keyboard, or a joystick, and a display 17 for displaying a tomogram or the like. .

  During CT imaging, the subject W placed on the rotary table 3 is irradiated with X-rays, and the subject W is rotated around the rotation axis R by a minute angle, and X-ray detection is performed at each rotation angle. X-ray transmission data from the scanner 2 is taken into the tomogram reconstruction calculation device 15. In this tomographic image reconstruction calculation device 15, a normal scan reconstruction program and an offset scan reconstruction program are installed. Of these, a program selected by operating the operation unit 16 is used. By reconstructing the X-ray transmission data of the subject W, a tomographic image along the slice plane (xy plane at an arbitrary position in the z-axis direction) set through the operation unit 16 is constructed and displayed on the display unit 17. To do.

  When normal scanning is selected, the X-ray detector 2 is positioned at the position shown in FIG. 1A, that is, the center of the effective width in the y-axis direction of the X-ray detector 2 is on the X-ray optical axis L. In this state, CT imaging is performed while the subject W is mounted and rotated about the rotation axis R. In this case, the CT imaging possible region (scan region or tomographic image field) is a region indicated by An in FIG.

  On the other hand, when the offset scan is selected, the X-ray detector 2 is positioned on the X-ray optical axis L in the position shown in FIG. 2, that is, near one end of the effective width in the y-axis direction of the X-ray detector 2. In this manner, the X-ray detector 2 is automatically moved when the drive signal is supplied from the personal computer 14 to the detector moving mechanism 4, and CT imaging is performed while rotating the subject W around the rotation axis R in this state. Do. The CT imaging possible area in this case is an area indicated by Ao in FIG.

  The points to be particularly noted in the above embodiment are that the X-ray detector 2 side moves when the offset scan is selected, and the rotary table 3 does not move in the y-axis direction but the rotation axis R is on the X-ray optical axis L. It is the point that remains located. As a result, in the case of a conventional apparatus that moves the rotary table 3 in the y-axis direction during offset scanning, the positioning error is enlarged and projected onto the X-ray detector, whereas in the above-described embodiment, The positioning error of the X-ray detector 2 is directly reflected in the projection data without being enlarged. Therefore, according to the embodiment of the present invention, it is possible to suppress deterioration in image quality due to positioning errors, particularly when CT imaging is performed at a high magnification.

  Moreover, since CT imaging is performed by offset scanning while the rotation axis R of the rotary table 3 is positioned on the X-ray optical axis L, the line or plane connecting the X-ray source (focus) 1a and the rotation axis R is X The correction operation for projecting each pixel output of the X-ray detector onto a virtual plane orthogonal to the X-ray optical axis L as in the conventional apparatus is maintained in a state orthogonal to the light receiving surface of the line detector 2. The calculation time can be shortened because it is unnecessary, and at the same time, the image quality is not deteriorated due to the digital error during the calculation.

Next, an embodiment of the invention according to claim 2 will be described. Figure 4 (A) represent a schematic plan view of the main part, in FIG. (B) shows a schematic plan view after movement of the X-ray detector 2. In FIG. 4 , the description of the xz moving mechanism of the rotary table 3 is omitted to avoid complicating the description. Although not shown, the system configuration of the personal computer 14 and the tomographic image reconstruction calculation device 15 is also the same as that of the example of FIG.

This example is the same as the previous examples in that the rotation axis R of the turntable 3 is positioned on the X-ray optical axis L and the position in the y-axis direction is unchanged. The difference from the example is the movement range of the X-ray detector 2 in the y-axis direction. That is, the movement range of the X-ray detector 2 by the detector moving mechanism 4 in this example, at least, as shown in FIG. 4 (A), is near one end of the y-axis direction effective width of the X-ray detector 2 X When the X-ray detector 2 is moved further away from the X-ray optical axis L than the state where the X-ray detector 2 is positioned on the line optical axis L, all the pixels of the X-ray detector 2 It is between the state which is not located on the optical axis L. Figure 4 (A) and the moving distance in the y-axis direction of the X-ray detector 2 (B) is a slightly shorter distance than the y-axis direction the effective width of the X-ray detector 2.

  In this embodiment, after performing CT imaging in both the state of FIG. 5A and the state of FIG. 5B, using both X-ray transmission data obtained by each of these CT imaging, The tomographic image is reconstructed. Specifically, two transmission images obtained at the same rotation angle in the states (A) and (B) are combined and treated as a transmission image obtained by one wide detector, The rotation angle is obtained, and this is regarded as data by a normal offset scan, and the reconstruction calculation is performed.

This method can be intuitively explained as follows. That is, when the CT imaging in the state shown in FIG. 4 (A), the CT imaging region is a circular region shown by Ao1 in FIG 5 (A). Further, when the CT imaging in the state shown in FIG. 4 (B), CT imaging region is an annular region indicated by Ao2 in FIG (B). Therefore, by combining the X-ray transmission data obtained by each of these CT scans, as shown in FIG. 6 , X-ray transmission data of a circular area represented by Ao1 + Ao2 can be obtained.

  The tomographic image reconstruction calculation device 15 constructs a tomographic image of a subject by using a reconstruction program for offset scanning using all the data obtained by these two CT scans. This makes it possible to obtain a tomographic image field having the same width as when CT imaging is performed by offset scanning using an X-ray detector having an effective width in the y-axis direction twice as large. Therefore, according to this embodiment, a wide CT imaging area can be obtained using an X-ray detector having a small effective width, and when the apparatus configuration for obtaining the same CT imaging area is compared with the conventional apparatus, Cost can be greatly reduced.

  Here, in each of the above embodiments, the rotary table 3 is configured not to move in the y-axis direction. However, the present invention is not particularly limited to this configuration, and the rotary table 3 can be rotated according to the application. The table 3 may be moved in the y-axis direction.

  In the above embodiments, the X-ray detector 2 is moved in the x-axis direction as necessary. However, the X-ray detector 2 is moved in the x-axis direction as necessary. Of course, can be adopted.

Furthermore, although the example which used FDP was shown for the X-ray detector 2, what combined the image intensifier and the CCD camera can also be used. However, when an X-ray detector comprising an image intensifier and a CCD camera is used in the embodiment of FIG. 4 , distortion correction of the X-ray detector is performed at each position before and after the movement of the X-ray detector in the y-axis direction. It is necessary to calibrate and create a table in relation to the y-axis position, and to synthesize X-ray transmission data after correcting each so that Ao1 and Ao2 shown in FIG. 6 are connected.

In the block diagram of embodiment of this invention, the figure (A) which shows together the schematic top view showing a mechanical structure, and the block diagram showing a system structure, and a schematic front view (B) It is. FIG. 5 is a schematic plan view showing a state in which an offset scan is performed by moving the X-ray detector 2 in the y-axis direction in the embodiment of the present invention. It is explanatory drawing of each CT imaging | photography possible area | region in the case of performing a normal scan (A) and the case of performing an offset scan (B) by embodiment of this invention. FIG. 2 is an explanatory diagram of a configuration of an embodiment of the invention according to claim 2 , and (A) and (B) are schematic plan views of main parts before and after moving the X-ray detector 2, respectively. It is explanatory drawing of CT imaging | photography possible area | region (B) in the state of the same figure (B) and CT imaging possible area | region (A) in the state of FIG. 5 (A). It is explanatory drawing of the substantial CT imaging | photography possible area | region by embodiment of FIG. It is explanatory drawing of the arrangement | positioning at the time of normal scanning by the conventional X-ray CT apparatus, and CT imaging possible area | region. It is explanatory drawing of the arrangement | positioning at the time of the offset scan by the conventional X-ray CT apparatus, and CT imaging possible area | region. It is explanatory drawing of the correction | amendment calculation of the data of the X-ray detector required at the time of the offset scan in the conventional X-ray CT apparatus.

1 X-ray generator 1a X-ray focus (X-ray source)
2 X-ray detector 3 Rotating table 4 Detector moving mechanism 5 xz moving mechanism 11 Rotating table driving circuit 12 Detector moving mechanism driving circuit 13 xz moving mechanism driving circuit 14 Personal computer 15 Tomographic image reconstruction calculation device 16 Operation unit 17 Display Instrument L X-ray optical axis R Rotating axis W Subject

Claims (3)

A subject is mounted between the X-ray source and the X-ray detector arranged opposite to each other, and rotation is given about a rotation axis (z-axis) orthogonal to the X-ray optical axis (x-axis) from the X-ray source. A rotation table is provided, and the rotation table is used to rotate the subject while using the X-ray transmission data of the subject captured at every predetermined rotation angle. In an X-ray CT apparatus provided with reconstruction calculation means for reconstructing a tomogram,
Detector moving means for moving the X-ray detector in a direction (y-axis direction) perpendicular to both the X-ray optical axis and the rotation axis is provided, and the detector moving means includes at least the X-ray detector. The X-ray detector between a state where the vicinity of the center of the effective width in the y-axis direction is located on the X-ray optical axis and a state where the vicinity of one end of the effective width in the same direction is positioned on the X-ray optical axis X-ray CT characterized in that the reconstruction calculation means is configured to selectively execute respective reconstruction calculation programs for normal scan and offset scan apparatus. A subject is mounted between the X-ray source and the X-ray detector arranged opposite to each other, and rotation is given about a rotation axis (z-axis) orthogonal to the X-ray optical axis (x-axis) from the X-ray source. A rotation table is provided, and the rotation table is used to rotate the subject while using the X-ray transmission data of the subject captured at every predetermined rotation angle. In an X-ray CT apparatus provided with reconstruction calculation means for reconstructing a tomogram,
Detector moving means for moving the X-ray detector in a direction (y-axis direction) perpendicular to both the X-ray optical axis and the rotation axis is provided, and the detector moving means includes at least the X-ray detector. A first state in which the vicinity of one end of the effective width in the y-axis direction is located on the X-ray optical axis, and a direction in which the X-ray detector is further away from the X-ray optical axis in the y-axis direction from the first state The X-ray detector is configured to move and move the X-ray detector between a second state in which all of the effective width in the y-axis direction of the X-ray detector is not located on the X-ray optical axis, and the reconfiguration The calculation means reconstructs the tomographic image of the subject by the reconstruction calculation program for offset scan using the X-ray transmission data acquired by rotating the subject around the rotation axis in the first and second states. X-ray CT apparatus characterized by performing. 3. The X-ray CT apparatus according to claim 1, wherein the rotary table is fixed so that a rotation axis is positioned on the X-ray optical axis and does not move in the y-axis direction. 4. .

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