JP2000321219A - X-ray ct apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-pray CT apparatus capable of checking whether the X-ray emitting direction from an X-ray source is vertically incident on the center of the input surface of an image intensifier and capable of being corrected in its position. SOLUTION: A phantom 5 having metal wires 1, 2 vertically embedded therein in parallel to the bottom and upper surfaces thereof is set in the center of the front surface of an image intensifier 7 so that the metal wires 1, 2 become vertical. Thereafter, X-ray fluoroscopy is performed and the adjusting distance 13 adjusting the movement of an X-ray source 6 from a point S to a point C is operated from the distance between the X-ray fluoroscopic images of both metal wires by the operation part of a data processor 9 to be displayed on a monitor 10. The position of the X-ray source 6 is moved to the point C on the basis of the distance 13 for the purpose of correction. Or, the adjusting distance 13 is corrected on software to reconstitute an image.

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 method of measuring the direction of X-ray radiation from an X-ray tube of a nondestructive X-ray inspection apparatus and the center of an input surface of an image intensifier. It relates to an alignment device for checking that the lines are coincident.

[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 spread enough to cover the imaging region at a time is used, and the detector is a group of several hundred detector elements densely arranged in an arc shape. 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. 5 shows an X-ray C as a nondestructive X-ray inspection apparatus.
1 shows a side view of a T device. Non-destructive inspection object 14 is motor 15
Is set on the turntable 19 which rotates at a constant speed. An X-ray tube as an X-ray source 6 and an image intensifier 7 as a detector are arranged opposite to the non-destructive inspection object 14 therebetween, and a horizontal aperture is provided to prevent scattered X-rays from entering. An X-ray slit 16 having a variable degree is provided on the front surface of the image intensifier 7. In this case, X
The radiation source 6 and the image intensifier 7 are fixed, and the nondestructive inspection object 14 is rotating at a predetermined speed on the turntable 19. The rotation axis of the non-destructive inspection object 14 is set on a line connecting the X-ray source 6 and the center of the input surface of the image intensifier 7. With such an arrangement of each device, the principle is the same as that of the medical X-ray CT device. The image intensifier 7 as a detector functions not as an element but as an analog detector.

[0004] The image intensifier 7 converts an X-ray image into a visible image and increases the luminance thereof, and can pick up a weak X-ray signal as a signal of brightness. The video signal from the continuous image intensifier 7 of the rotating nondestructive inspection object 14 is detected by the TV camera 8 and sent to the data processing device 9. The data processing device 9 includes an A / D converter, a DAS (data collection unit), a high-speed arithmetic processing device, a CPU, a magnetic disk, and the like.
A horizontal tomographic image of the non-destructive inspection object 14 is displayed on 0. On the monitor 10 of FIG. 5, the horizontal intensity signal (horizontal video signal 17) of the slit 16 in the image intensifier 7 during scanning when the nondestructive inspection object 14 is rotating is displayed on the vertical axis. It was done. When the scanning is completed, a tomographic image is displayed on the monitor 10. If rotational scanning of the nondestructive inspection object 14 is performed while changing the height of the turntable 19, a tomographic image of each layer can be obtained.

[0005]

The conventional CT apparatus for non-destructive X-ray inspection is constructed as described above,
X-rays transmitted from the rotating nondestructive inspection object 14 are projected onto the input surface of the image intensifier 7, and as a method of reconstructing an image from the X-ray transmission signal, convolution back projection (CBP) Law is used. The CPB method obtains two stages of a convolution (convolution) operation and a back projection (backprojection) operation to perform image reconstruction.

In order to obtain a high-quality reconstructed image by performing the convolution operation and the back projection operation, as shown in the plan view of FIG. It is necessary to match with the vertical normal from the input surface center b of the tensifier 7. For example, if the X-ray source 6 is at the point S, the rotation center of the nondestructive inspection object 14 is the point P, and the input surface center b of the image intensifier 7 is set, the nondestructive inspection object X transmitted through 14 points Q
The line data signal is input to a point F on the input surface of the image intensifier 7, while when the X-ray source 6 is at the point C, the X-ray data signal transmitted through the point Q is applied to the image intensifier 7. Is input to point E on the input surface of. Due to such a state in which the spatial coordinates are shifted, the computer determines that the X-ray data signal at the point F transmitted through the point Q is the X-ray data signal transmitted through the point R from the point C. Reconstruct the image by mistake.

[0007] As described above, in the image reconstruction software, it is assumed that the apparatus is set at a predetermined position, and the captured data is stored in the data processing apparatus 9 side. Therefore, it is necessary to check the apparatus so as to satisfy these conditions.
Then, after the check, the position difference between the point S and the point C is corrected and calculated at the time of image reconstruction by software, or the point S of the X-ray source 6 is changed to the point C on the hardware. It is necessary to move the X-ray source to make the X-ray emission direction from the X-ray source 6 coincide with the vertical normal line from the center b of the input surface of the image intensifier 7 before scanning and reconstructing an image.

[0008] The conventional device is non-destructive without checking whether the direction of X-ray emission from the X-ray source 6 coincides with the vertical normal from the center of the input surface of the image intensifier 7. Since the inspection object 14 was rotated and scanned,
There has been a problem that the image reconstructed image may cause artifacts, may not be a clear image, or may be distorted.

The present invention has been made in view of such circumstances, and the radiation direction of the X-ray from the X-ray source 6 coincides with the vertical normal from the center of the input surface of the image intensifier 7. It is an object of the present invention to provide an X-ray CT apparatus capable of checking whether or not the apparatus is in conformity and correcting the position of the apparatus on hardware or performing a shift correction operation on software at the time of image reconstruction. .

[0010]

In order to achieve the above object, an X-ray CT apparatus according to the present invention sets a non-destructive inspection object on a rotating table, and places the X-ray tube around the non-destructive inspection object. In the X-ray CT apparatus in which an imaging system consisting of an image intensifier is arranged in opposition thereto, a flat plate with a good height of X-ray transmittance by embedding metal lines on the surface and a metal plate having a predetermined height on the surface A buried X-ray transparent block
A flat plate and a block are joined so that the two metal wires coincide with each other in the vertical direction, and a phantom is provided at the center of the image intensifier input surface.

Further, according to the X-ray CT apparatus of the present invention, the X-ray is focused at the center of the input surface of the image intensifier based on the distance between the X-ray fluoroscopic images of the two metal wires of the phantom detected by the image intensifier. It is provided with a calculation unit for calculating the coordinate for adjusting the movement of the X-ray source for vertical incidence.

Further, the X-ray CT apparatus according to the third aspect performs convolution operation and backprojection operation by shifting spatial coordinates by the movement adjustment coordinates of the X-ray source calculated by the operation unit when performing image reconstruction. An arithmetic unit is provided.

The X-ray CT apparatus according to the present invention is constructed as described above, and is provided with two vertical metal lines vertically separated in parallel with the input surface at the center of the front surface of the image intensifier input surface. The phantom was set, and from the distance between the X-ray fluoroscopic images of the two metal lines by X-ray fluoroscopy, the movement adjustment coordinates of the X-ray source for perpendicularly entering the input surface of the image intensifier were calculated. The X-ray source can be obtained by moving the X-ray tube or the image intensifier on the hardware to arrange the normal apparatus, or by using the software to adjust the coordinates of the movement of the X-ray source during image reconstruction. By calculating by shifting the spatial coordinates by the amount
A clear CT tomographic image can be obtained.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the X-ray CT apparatus according to the present invention will be described with reference to FIG. FIG. 1 shows a turntable 19 on which an X-ray source 6 and a nondestructive inspection object 14 are placed and rotated by a motor.
, An image intensifier 7, an imaging TV camera 8, a data processing device 9, a display monitor 10, and a phantom 5. It is assumed that the X-ray source 6 has a focal point S, and is shifted from a point C on a normal line perpendicular to the center of the input surface of the image intensifier 7 by an adjustment distance 13. The turntable 19 is connected to the data processing device 9 and is rotated at a constant speed by the motor 15 in conjunction therewith. The center of rotation is indicated by a point P.

The non-destructive inspection object 14 is set on the turntable 19. The image intensifier 7 converts an X-ray transmission image of the non-destructive inspection object 14 into a visible light image to increase the brightness, and plays a role as a detector of the X-ray CT apparatus. This detector is an analog detector and a two-dimensional X
Line input signals can be captured at once. In the case of scanning, in order to capture one-dimensional information, a slit with a variable aperture for the X-ray, which is opened in the horizontal direction, is set in front of the input surface for protection against scattered X-rays. The TV or camera 8 captures an image whose brightness is multiplied on the output surface of the image intensifier 7, and an image pickup tube or a CCD camera is used.

The data processing device 9 includes an A / D converter, a DA
S (data collection unit), high-speed processing unit, CP
U, a magnetic disk, a D / A converter, and the like, and performs a convolution operation and a back projection operation from the acquired data to perform image reconstruction. Then, the phantom 5 is set in front of the image intensifier 7, and a program is provided for calculating a shift (movement adjustment coordinates) between the point S and the point C of the X-ray source 6 from the X-ray fluoroscopic image of the metal wire 1. In addition, a program is provided for calculating the image by shifting the spatial coordinates by the displacement (movement adjustment coordinates) between the points S and C of the X-ray source 6 at the time of image reconstruction. The monitor 10 displays a normal X-ray fluoroscopic image and C
The tomographic image obtained by the T scan is displayed.

An embodiment of the phantom 5 will be described with reference to FIG. As shown in FIG. 2A, a metal wire 2 having a good X-ray transmittance, for example, a metal wire 2
A line (reference line) embedded in the center with a chain line and a predetermined distance on both sides is buried, while a material with good X-ray permeability is also used.
For example, the metal wires 1 are buried on the upper surface of the block of the acrylic plate 3, and the two acrylic plates 4, 3 are mutually perpendicular to the acrylic plate 4 and parallel to each other as shown in FIG. In the separated state, the center chain-shaped metal wire 2 and metal wire 1
And the acrylic plate 3 is adhered so as to overlap. When the phantom 5 is set on the input surface side of the image intensifier 7 as a finished product, the normal line perpendicular to the input surface from the chain-shaped metal wire 2 at the center of the metal wire 2 always passes through the metal wire 1. Is an essential condition.

FIG. 3 is a plan view showing a state in which the phantom 5 is set at the center in front of the input surface of the image intensifier 7 with the X-ray source 6 shifted from the point C on the normal line to the point S. If the distance from the point S of the X-ray source 6 to the input surface of the image intensifier 7 is L, and the height of the phantom 5 (the distance between the two metal lines) is h, the metal line when X-ray fluoroscopy is performed. The X-ray image 1 becomes a projection a on the input surface, and the X-ray image of the chain line of the metal wire 2 becomes the center b. Let Δd be the distance between the projection a and the center b. The following relationship is established from the arrangement of each part. The distance from the point S to the point C (here, referred to as the adjustment distance 13) has a relation equal to (Δd / h) * (L−h). Here, h and L are known values, and Δd
, The adjustment distance 13 (the distance from point S to point C) is known. Therefore, the phantom 5 is X-rayed, the Δd is detected by the TV camera 8, and the signal is input to the data processing device 9 for calculation, whereby the adjustment distance 13 is determined. In the present apparatus, an operation unit for calculating the above relational expression is programmed in the data processing device. Then, the calculated adjustment distance 13 is displayed on the monitor 10.

Next, the operation of the present apparatus will be described. First, the phantom 5 is set so that the metal wire 1 of the phantom 5 is perpendicular to the center of the front surface of the input surface of the image intensifier 7 without setting the nondestructive inspection object 14 on the turntable 19. Next, X-rays are emitted from the point S (focal point) of the X-ray source 6 under X-ray fluoroscopic conditions, so that an X-ray fluoroscopic image of the phantom 5 can be observed on the monitor 10. The approximate deviation can be determined from the relative distance between the reference line displayed on both sides of the chain line at the center of the metal line 2 and the metal line 1, but the adjustment distance 13 is displayed on the monitor 10 at the same time.

Next, a switch (not shown) on the operation panel of the data processing device 9 is selected, and a method of calculating by shifting the space coordinates by the movement adjustment coordinates of the adjustment distance 13 on software is selected. Alternatively, a method of moving the X-ray source 6 or the image intensifier 7 on the hardware in the direction by the adjustment distance 13 is selected. If you choose the latter X
The fluoroscopy is stopped, the X-ray source 6 or the image intensifier 7 is moved by the adjustment distance 13 in that direction, X-ray fluoroscopy is performed, and the same operation is repeated again until the adjustment distance 13 becomes zero. Then, the X-ray fluoroscopy is stopped. Thus, preparations before X-ray CT scanning are completed. When a method is selected by a switch to shift the spatial coordinates by the amount of the movement adjustment coordinates of the adjustment distance 13 on the software using a switch, the data processing device 9 corrects the shift of the adjustment distance 13 from the captured data and performs image reconstruction. Then, a clear CT tomographic image is displayed on the monitor 10.

When the adjustment distance 13 is adjusted on the hardware, the data processing device 9 performs image reconstruction by performing X-ray CT scanning, and can display a clear CT tomographic image on a monitor. . By performing a check using the phantom 5 described above, the present apparatus can determine how much the point S (focal point) of the X-ray source 6 deviates from the vertical normal to the center of the input surface of the image intensifier 7. Detected, the value of the adjustment distance 13 is stored in the data processing device 9, and the adjustment distance 13 can be corrected on software or adjusted on hardware to perform CT scanning, so that clear reconstruction can be performed. Images can be obtained.

In the above embodiment, an X-ray CT scan using a one-dimensional X-ray fan beam has been described. However, when performing a CT reconstruction of a two-dimensional X-ray cone beam (3D), FIG. Such a 3D reconstruction phantom can be used. Using a flat plate having good X-ray transparency, for example, an acrylic plate 4a, a cross-shaped metal wire 2b on the back surface and metal wires 2b '(reference line) are buried in parallel on both sides of the metal wire 2b at a predetermined distance. Similarly, a material having good X-ray transmittance, for example, a material in which a cross-shaped metal wire 1a is buried on the upper end of an acrylic bar 3b is set so that the two cross-shaped metal wires 1a and 2b are parallel and perpendicular to each other. Acrylic plate 4a so that it is horizontal
And the acrylic rod 3b are vertically bonded. Using the 3DCT reconstruction phantom 5a, adjustment in the vertical and horizontal directions can be similarly performed. The above metal wire 2b '(reference line)
Is a parallel line, which is shown in FIG. 4, but is a concentric metal wire (reference line)
However, the same effect can be obtained.

[0023]

The X-ray CT apparatus according to the present invention is constructed as described above, and has two vertical metal plates vertically separated from the input surface in the center of the input surface of the image intensifier. Set the phantom with the X-rays, and adjust the movement of the X-ray source so that the X-rays are perpendicularly incident on the center of the input surface of the image intensifier based on the distance between the X-ray fluoroscopic images of both metal lines by X-ray fluoroscopy Since the data processing device is provided with a calculation unit for calculating the coordinates, the values are used to correct the displacement of the movement adjustment coordinates on software to reconstruct an image, or the X-ray tube or image By moving the intensifier and arranging a normal device, a clear CT tomographic image can be obtained.

[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 diagram showing a phantom of the X-ray CT apparatus of the present invention.

FIG. 3 is a diagram for explaining an adjustment distance of the X-ray CT apparatus of the present invention.

FIG. 4 is a diagram showing a phantom for 3D reconstruction of the X-ray CT apparatus of the present invention.

FIG. 5 is a diagram showing a conventional X-ray CT apparatus that performs CT scanning by rotating a non-destructive inspection object.

FIG. 6 is a diagram for explaining setting conditions when performing CT scanning by rotating a conventional nondestructive inspection object.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Metal wire 1a ... Metal wire 2 ... Metal wire 2b, 2b '... Metal wire 3 ... Acrylic plate 3b ... Acrylic bar 4 ... Acrylic plate 4a ... Acrylic plate 5 ... Phantom 5a ... 3D reconstruction phantom 6 ... X-ray source 7 Image intensifier 8 TV camera 9 Data processor 10 Monitor 11 Metal wire 1
12 ... Image of metal wire 2 13 ... Adjustment distance 14 ... Non-destructive inspection object 15 ... Motor 16 ... Slit 17 ... Horizontal direction video signal 18 ... Video signal 19 ... Tuning table a ... Projection b ... Center C ... Point E ... Point F… Point R… Point S… Point P… Point Q… Point

Claims (3)

[Claims] An X-ray CT apparatus in which a non-destructive inspection object is set on a rotating table, and an X-ray tube and an imaging system comprising an image intensifier are arranged around the non-destructive inspection object. A flat plate having a metal wire embedded in the surface and having good X-ray transparency, and a block having a predetermined height and having a good X-ray transmittance having the metal wire embedded in the surface, the two metal wires are vertically aligned. An X-ray CT apparatus characterized in that a flat plate and a block are joined as described above, and a detachable phantom is provided at the center of the image intensifier input surface. 2. The X-ray CT apparatus according to claim 1, wherein the X-rays are located at the center of the input surface of the image intensifier based on the distance between the X-ray fluoroscopic images of the two metal lines of the phantom detected by the image intensifier. X for normal incidence on
An X-ray CT apparatus, comprising: a calculation unit for calculating a movement adjustment coordinate of a radiation source. 3. An X-ray CT apparatus according to claim 2, wherein at the time of image reconstruction, the convolution operation and the back projection operation are performed by shifting the spatial coordinates by the movement adjustment coordinates of the X-ray source calculated by the operation unit. An X-ray CT apparatus comprising a calculation unit.