JP2002055062A - X-ray ct - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray CT which does not require that a center-position calibration jig and a sample be changed over for mounting. SOLUTION: A sample base 10 with the calibration jig is mounted on a rotating table 3a, and the sample 11 is set in the center. The rotating table 3a which is installed at a sample base 3 is raised and lowered, and tungsten wires 10a, which are embedded in a material of satisfactory X-ray transmissivity in the upper part and the lower part are situated in an X-ray beam height. The rotating table 3a is turned and scanned, and the deviation of a rotation center position is detected by a detector 6 to be stored. The sample 11 is situated in the X-ray beam height, the rotating table 3a is turned and scanned, and data is acquired in a data processor 7 from the detector 6. When a tomogram is reconstituted on the basis of the obtained data, spatial coordinates are deviated by a data value indicating the deviation of the rotation center position, a convolution computing operation and a back-projection computing operation are conducted, the calibration of the rotation center position is performed automatically by software, and the tomogram is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray CT apparatus, and more particularly to a jig for calibrating the center of rotation of a non-destructive X-ray inspection apparatus. X-ray C to calibrate the position of data from detectors placed
It relates to a T device.

[0002]

2. Description of the Related Art An X-ray CT apparatus in which an X-ray tube and a detector integrally rotate around an object to collect projection data to obtain a tomographic image of the object is widely used in the medical field. It is used. In this case, a fan-shaped X-ray beam (usually 30 to 50 degrees) having a width enough to cover the imaging area at a time is used, and the detector is a group of several hundred detector elements densely arranged in an arc. It is composed of Then, the detectors are arranged to face the X-ray tube with the subject interposed therebetween, and X-ray passages radially distributed corresponding to the number of detector elements are obtained. In imaging, the X-ray tube and detector are integrated to
When rotated by 0 degrees, the projection data is obtained for each fixed angle, and D
The data is taken into an AS (data collection unit), operated by a high-speed processing unit, image reconstruction is performed, a tomographic image is displayed on a display device, and the data is stored in a magnetic disk device at the same time. In this case, the X-ray tube and the detector rotate while the subject is stationary, but the X-ray tube and the detector are used as an X-ray CT device used as an industrial nondestructive X-ray inspection device. There is an X-ray CT device that rotates the nondestructive inspection object 360 degrees in a fixed state

FIG. 3 shows an X-ray C as a nondestructive X-ray inspection apparatus.
1 shows a side view of a T device. The non-destructive inspection object (center position calibration jig 2 in FIG. 3) is set on a rotating table 3 a rotated at a constant speed by a motor 4 provided on the sample table 3. An X-ray tube 1 and a detector 6 are arranged opposite to the non-destructive inspection object, and a slit 5 for an X-ray having a variable aperture in the horizontal direction is provided to prevent the incidence of scattered X-rays. 6 on the front. In this case, the X-ray tube 1 and the detector 6 are fixed, and the nondestructive inspection object is rotating at a predetermined speed on the turntable 3a. The rotation axis of the non-destructive inspection object is set on a line connecting the X-ray tube 1 and the center of the detector 6. With such an arrangement of each unit, the principle is the same as that of the medical X-ray CT apparatus described above.

The X from the detector 6 of the rotating nondestructive inspection object is
The line transmission signal is sent to the data processing device 7 through the preamplifier. The data processing device 7 includes an A / D converter, a DAS
(Data collection unit), a high-speed processing unit, a controller, a CPU, a magnetic disk, and the like. An image is reconstructed from the acquired data, and a horizontal tomographic image of the nondestructive inspection object is displayed on the monitor 8. Then, by rotating the non-destructive inspection object by changing the height of the turntable 3a,
A tomographic image of each layer is obtained. X-rays from the X-ray tube 1 penetrate the rotating nondestructive inspection object and are projected on the detector 6,
As a method of reconstructing an image from a line transmission signal, a convolution back projection (CBP) method is used. The CPB method obtains two stages of a convolution (convolution) operation and a back projection (backprojection) operation to perform image reconstruction. On the monitor 8 of FIG. 3, the vertical axis indicates the intensity signal in the horizontal direction of the slit 5 of the detector 6 during scanning when the nondestructive inspection object is rotating. When the scanning is completed, a tomographic image is displayed on the monitor 8.

[0005]

The conventional X-ray CT apparatus is constructed as described above. However, the software for image reconstruction assumes that the apparatus is set at a predetermined position and that the acquired data is processed by data processing. It is stored on the device 7 side. Therefore, it is necessary to check the apparatus so as to satisfy these conditions. Then, after the check, the coordinate deviation is corrected and calculated at the time of image reconstruction on the software, or the X-ray tube 1 and the detector 6 are moved on the hardware, or the sample table 3 is moved. It is necessary to set a sample at the center of rotation and scan to reconstruct an image. Unless checked and calibrated, the reconstructed image may produce artifacts, not a clear image, or a distorted image. Therefore, the conventional device,
On the turntable 3a, a center position calibration jig 2 in which a metal wire, for example, a tungsten wire 2a, is embedded vertically in the center of a block on a column made of a material having good X-ray permeability, for example, acrylite resin, is mounted. It is set and rotationally scanned to check whether the tungsten wire 2a coincides with the rotation center of the apparatus. If not coincident, the sample stage 3 is moved or the X-ray tube 1 and the detector are detected. 6 is moved to make the rotation centers coincide, or after inputting a coordinate shift value on software, a non-destructive inspection object is set on the turntable 3a, and data is collected by scanning. Then, an X-ray image was obtained by image reconstruction. In order to perform the above operation before the inspection, there is a troublesome problem that the center position calibration jig 2 must be set every time, removed after checking, and then the nondestructive inspection object must be set on the turntable 3a.

The present invention has been made in view of such circumstances, and sets the center position calibration jig every time, removes the center of rotation after checking it, and then sets the nondestructive inspection object on the turntable. An object of the present invention is to provide an X-ray CT apparatus that can automatically perform a shift correction calculation on software at the time of image reconstruction or correct the position of the apparatus on hardware at the time of image reconstruction.

[0007]

In order to achieve the above object, an X-ray CT apparatus according to the present invention comprises an X-ray tube and an X-ray detector opposed to the sample centered on a rotating table. Then, in an X-ray CT apparatus that reconstructs a tomographic image from X-ray transmission data of a sample obtained by rotation, a metal wire is vertically embedded in the upper and lower centers of the space in which the sample is set. Table with a center position calibration jig consisting of a good block, a lifting mechanism capable of moving the sample table upward and downward, and the metal wire X
By moving to the line scanning position and rotating the sample stage, 2
A circuit for detecting and storing a displacement of the X-ray image position of the metal wire, and when reconstructing a tomographic image from data obtained by rotationally scanning the sample, spatial coordinates are calculated by the data value of the displacement. The convolution operation and the back projection operation are performed with a shift so that the calibration of the center of rotation can be automatically performed.

Further, the X-ray CT apparatus according to claim 2 is provided with a moving mechanism for automatically moving the table for rotating the sample to the rotation center position based on the displacement data, and performs scanning with the sample as the center of rotation. Is what you can do.

The X-ray CT apparatus according to the present invention is configured as described above. A metal wire, for example, a tungsten wire is vertically inserted into a space in which a sample can be set at the center and two centers, that is, the upper and lower centers of the sample. A block with good X-ray permeability, for example, an acrylite resin block, embedded in the sample, is set on a rotary table, the upper and lower metal wires are used as center position calibration jigs, and the sample is set at the center. so,
You can check. When reconstructing a tomographic image from data obtained by rotationally scanning the sample using the data of the displacement, when the spatial coordinates are shifted by the data value of the displacement, a convolution operation and a back projection operation are performed, and the rotation center is calculated. Calibration can be done automatically. Further, the X-ray CT apparatus of the present invention is provided with a moving mechanism for moving the table for rotating the sample, the table can be automatically moved to the rotation center position from the movement deviation data, And can be scanned. Thus, the center of rotation can be checked at the upper and lower portions of the sample and calibration can be automatically performed without removing the jig, so that a tomographic image of the sample can be obtained without labor and time.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the X-ray CT apparatus according to the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing the configuration of the X-ray CT apparatus of the present invention. FIG. 2 shows a perspective view of the sample table 10 with a calibration jig. The X-ray CT apparatus includes an elevating mechanism, an X-ray tube 1, and a detector 6, which can rotate a rotating table 3 a on which a sample 11 is placed by a motor 4 and move the rotating table 3 a up and down.
A sample stage 3 having a moving mechanism that can move in a direction perpendicular to a line connecting the X-ray tube 1, a X-ray tube 1 around a sample 11 on a turntable 3 a, a detector 6 disposed opposite to the X-ray tube 1, A space for setting the sample 11 on the rotation center axis for calibrating the center position, and a block having good X-ray permeability in which a tungsten wire 10a is buried in two places above and below the space for center alignment. Sample table with calibration jig 10
And a circuit for detecting and storing a shift in the X-ray image position of the two tungsten lines 10a by moving the tungsten line 10a to the X-ray scanning position by the elevating mechanism and rotating the sample stage 3, and the sample 11 When reconstructing a tomographic image from data obtained by rotational scanning, a data processing device 7 that shifts spatial coordinates by the data value of the displacement and performs convolution operation and backprojection operation to automatically calibrate the center of rotation; ,
A monitor 8 displays a horizontal direction detection signal detected by the detector 6 through the slit 5 at the time of rotational scanning and a tomographic image reconstructed by the data processor 7 after the rotational scanning is completed.

Sample table 10 with calibration jig for center alignment
As shown in FIG. 2, a semi-cylindrical material 10d made of a material having good X-ray permeability, for example, acrylite resin having a space in the center of which a sample 11 can be set, and upper and lower spaces In this case, a material having good X-ray transparency, for example, blocks 10b and 10c made of an acrylite resin are vertically formed integrally with a tungsten wire 10a buried perpendicular to the central axis. The sample table 3 has a motor 4 inside, a rotary table 3a provided on the upper portion, rotates at a predetermined speed, and has a lifting function capable of moving the rotary table 3a up and down. Further, the X-ray tube 1
A moving mechanism capable of moving in a direction perpendicular to a line connecting the sensor and the detector 6. This moving mechanism can move in conjunction with a shift value of the rotation center position from the data processing device 7. The slit 5 is placed on the front of the detector 6 to remove scattered radiation generated in the sample 11. The detector 6 is a detector in which detector elements each including a scintillator and a photodiode are arranged in an arc shape or a plane in a horizontal direction, a detector including a semiconductor element having an X-ray conversion layer, and an image intensifier. Any of a combination of a TV camera and A / D conversion to capture a signal may be used. The data processing device 7 includes an A / D converter,
A DAS (Data Acquisition Unit), a high-speed arithmetic processing unit, a controller, a CPU, a magnetic disk, and the like are stored. The shift value of the rotation center position detected by the sample table 10 with the calibration jig is stored in a storage device, and the sample 11 is stored. When reconstructing a tomographic image from data obtained by rotational scanning, the spatial coordinates are shifted by the data value of the rotational center shift, convolution operation and back projection operation are performed, and calibration of the rotational center is automatically performed by software. Can be. The monitor 8 displays the intensity of the detection signal in the horizontal direction on the vertical axis during the rotational scanning of the sample 11, and after the rotational scanning, an image is reconstructed from the acquired data.
A horizontal tomographic image of the sample 11 is displayed on the monitor 8.

Next, the operation of the present X-ray CT apparatus will be described. First, the sample table 10 with the calibration jig is set on the turntable 3a. Then, the sample 11 is set in the center space of the sample table 10 with the calibration jig. Next, the turntable 3a is raised, and the tungsten wire 10a embedded below the sample table 10 with the calibration jig is moved to the height of the scanning position of the X-ray beam. Then, the turntable 3a is rotated at a predetermined speed to detect a rotational center shift of the tungsten wire 10a,
The data is stored in the storage circuit. Next, the turntable 3a
To move the tungsten wire 10a buried above the sample table 10 with the calibration jig to the height of the scanning position of the X-ray beam. Then, the turntable 3a is rotated at a predetermined speed, the rotation center deviation of the tungsten wire 10a is detected, and the data is stored in the storage circuit. Then, the deviation of both rotation centers is averaged, and the rotation center deviation value is stored in the storage circuit. Next, the turntable 3a is raised, and the height of the tomographic plane of the sample 11 to be inspected is moved to the height of the scanning position of the X-ray beam. Then, the turntable 3a is rotated at a predetermined speed, the data of the tomographic plane is taken in from the detector 6 to the data processing device 7, and when reconstructing a tomographic image from the data, the spatial coordinates are calculated by the rotation center deviation value. The convolution operation and the back projection operation are performed while being shifted, the rotation center is calibrated automatically, and the tomographic image is displayed on the monitor 8.

In the above embodiment, the calibration based on the shift of the center of rotation is performed by the data processing device 7 using the software for calculation, but the calibration based on the shift of the center of rotation is performed by directly moving the hardware and rotating the hardware. A method of correcting the center may be used. The method of directly correcting the hardware is as follows. The sample table 3 provided with the rotating table 3a on which the sample table 10 with the calibration jig on which the sample 11 is set is mounted is perpendicular to the line connecting the X-ray tube 1 and the detector 6. And a method of moving the X-ray tube 1 and the detector 6 in parallel. In any case, sample table 1 with calibration jig
Based on the shift value of the rotation center detected by the zero tungsten wire 10a, a signal from the data processing device 7 is used to provide a mechanism for automatically moving the hardware.

[0014]

The X-ray CT apparatus according to the present invention is configured as described above, and is located at the upper and lower centers of the space for setting the sample.
A sample table with a center position calibration jig consisting of a block with good X-ray transparency in which a metal wire is buried vertically is placed on a turntable and moved up and down, and a rotational scan with two metal wires is used to detect the deviation value of the center of rotation. Then, when reconstructing a tomographic image from data obtained by rotationally scanning at the height of the sample position, the spatial coordinates are shifted by the data value of the displacement and convolution operation and back projection operation are performed to calibrate the rotation center. Can be performed automatically. Thereby, the automatic calibration can be performed by software without removing the jig, and the labor of the operation can be saved. Also,
The rotating table on which the sample stage with the center position calibration jig is placed is automatically set at right angles to the line connecting the X-ray tube and the center of the detector by the shift value of the rotating center obtained by rotating scanning with two metal wires. And a mechanism that moves the X-ray tube and detector in parallel by the shift value of the center of rotation instead of moving the turntable by moving the sample to the center of rotation. . Thus, the center of rotation can be directly corrected by hardware without removing the jig, and the labor of the operation can be saved.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of an X-ray CT apparatus of the present invention.

FIG. 2 is a view showing a sample table 10 with a calibration jig of the X-ray CT apparatus of the present invention.

FIG. 3 is a diagram showing a conventional X-ray CT apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... X-ray tube 2 ... Center position calibration jig 2a ... Tungsten wire 3 ... Sample stand 3a ... Rotating stand 4 ... Motor 5 ... Slit 6 ... Detector 7 ... Data processing device 8 ... Monitor 9 ... Horizontal direction detection signal 10 ... Sample table with calibration jig 10a ... Tungsten wire 10b ... Block 10c ... Block 10d ... Semi-cylindrical part 11 ... Sample

Claims (2)

[Claims] An X-ray tube and an X-ray detector are arranged opposite to a sample on a rotating table, and its tomographic image is reconstructed from X-ray transmission data of the sample obtained by rotation. In the X-ray CT apparatus, a sample table with a center position calibration jig composed of a block with good X-ray transparency in which a metal wire is buried vertically is provided at the upper and lower centers of a space in which a sample is set, and the sample table is moved upward and downward. An elevating mechanism which can be moved downward, and the elevating mechanism moves the metal wire to the X-ray scanning position and rotates the sample stage to detect and store the displacement of the X-ray image positions of the two metal wires. And a circuit that performs
When reconstructing a tomographic image from data obtained by rotationally scanning a sample, the spatial coordinates are shifted by the data value of the displacement to perform convolution operation and backprojection operation so that the center of rotation can be automatically calibrated. An X-ray CT apparatus characterized by the above-mentioned. 2. An X-ray tube and an X-ray detector are arranged opposite to a sample on a rotating table, and a tomographic image is reconstructed from X-ray transmission data of the sample obtained by rotation. In the X-ray CT apparatus, a sample table with a center position calibration jig composed of a block with good X-ray transparency in which a metal wire is buried vertically is provided at the upper and lower centers of a space in which a sample is set, and the sample table is moved upward and downward. An elevating mechanism which can be moved downward, and the elevating mechanism moves the metal wire to the X-ray scanning position and rotates the sample stage to detect and store the displacement of the X-ray image positions of the two metal wires. An X-ray CT apparatus provided with a circuit for performing the scanning and a moving mechanism for automatically moving the table for rotating the sample to the center of rotation based on the displacement data. .