JPH0378760B2 - - Google Patents

Description

Detailed Description of the Invention [Objective of the Invention] (Industrial Field of Application) The present invention relates to an X-ray tomography apparatus, which irradiates the subject with X-rays from multiple directions around the subject, and Measure the intensity of the X-rays that passed through the specimen,
This invention relates to improvements in a computerized tomography scanner (hereinafter referred to as CT scanner) that processes these measured values using a computer to obtain the X-ray absorption coefficient distribution of the tomographic plane of the subject.

(Prior Art) A conventional X-ray tomography apparatus uses a fan-shaped
A detector consisting of an X-ray tube that emits rays, a large number of detection elements that are placed opposite to the X-ray tube with a subject in between and that are necessary to detect the X-rays emitted from the X-ray tube; a data processing device that converts the intensity of X-rays obtained by the instrument into an electrical signal and processes the electrical signal so as to obtain an X-ray absorption coefficient distribution of a tomographic plane of the subject; and the X-ray tube and the detector. The X-ray tube is rotated at each step angle, and the X-ray tube is rotated at each step angle.
mechanical rotation of the X-ray tube and detector around the subject so as to emit radiation and detect the X-rays with the detector over an angular range of one or more revolutions; It consisted of a mechanical department. Alternatively, a detector consisting of a large number of detection elements arranged in a ring around the subject is fixed,
An X-ray method in which only an X-ray tube that emits fan-shaped X-rays is mechanically rotated around the subject one or more times to obtain the data necessary to determine the X-ray absorption coefficient distribution of the tomographic plane of the subject. A tomography device was also installed.

By the way, in conventional X-ray tomography apparatuses, whether the X-ray tube and detector are rotated or the X-ray tube alone is rotated, the mechanical rotation speed has a certain speed, for example, from the viewpoint of speed control. The limit was about 30 rotations per minute. In other words, it takes about 2 rotations for one rotation.
In other words, the scanning time of the X-rays required to photograph the tomographic plane of the subject was approximately 2 seconds. Therefore, during this time, in the case of a subject such as a human body, the subject moves due to breathing, heartbeat, etc.
There was a drawback that the obtained tomographic image of the subject was unclear.

Furthermore, when photographing a series of various tomographic planes of a subject, conventional X-ray tomography equipment
Since the subject was mechanically moved so that the desired tomographic plane of the subject was at the X-ray irradiation position, there was a drawback that positioning etc. took time. In addition, re-alignment also had the drawback of inaccurate measurements due to difficulty in position reproducibility.

(Problems to be Solved by the Invention) The present invention eliminates the above-mentioned drawbacks of conventional X-ray tomography devices, scans X-rays electromagnetically, and automatically controls the generation position, energy, intensity, etc. of X-rays. It is an object of the present invention to provide an X-ray tomography apparatus that can obtain accurate tomographic images of a subject at high speed.

Hereinafter, the present invention will be explained in detail based on one embodiment. In the drawings of the embodiments, common parts are given the same numbers.

FIG. 1 is a schematic diagram of an X-ray tomography apparatus according to the present invention. An electron beam emitted from an electron gun, which will be described later, passes through a plurality of metal plates 1a connected in a ring shape.
By colliding with the target 1 consisting of ~h, X-rays are emitted from the collision point, that is, the X-ray generation point 2. X-ray beam 3 emitted from this X-ray generation point 2
has a spread angle that is sufficient to cover the imaging area 4 of the subject, for example, about 30 degrees.
It is shaped by a collimator placed in a ring shape, which will be described later. The X-ray beam that has passed through the imaging area 4 is detected by a detector 5 comprising a large number of detection elements arranged in a ring shape. The intensity of the X-ray beam detected by this detector 5 is converted into an electrical signal, and this electrical signal is sent to a data processing device such as a data acquisition unit 6 and a data processing device 7 to obtain a tomographic image of the subject. used. Data processing device 7
is passed through the X-ray generation control device 9 so that the X-ray generation point 2 draws a circular orbit 8 on the target 1,
The orbital motion of the X-ray generation point 2 is electromagnetically controlled.
This X-ray generation point 2 is controlled to be located on the circular orbit 8 at every predetermined step angle, for example every 1 degree. Further, the X-rays irradiated onto the subject at each step angle position are detected by the detector 5, and an electrical signal indicating the intensity thereof is sent to a data processing device. The data processing device uses an image reconstruction method such as the well-known convolution method based on the measured values of the intensity of X-rays irradiated from all directions around the subject to create an X-ray image of the tomographic plane of the subject. The linear absorption coefficient is calculated and the result is displayed on the display device 10.

As described above, in order to electromagnetically control the orbital motion of the X-ray generation point 2, the scanning time for rotating the fan-shaped X-ray beam 3 around the subject is extremely short, a few milliseconds, and the obtained tomographic image of the subject is Deterioration in image quality due to specimen movement is reduced, resulting in a tomographic image with good image quality.
Furthermore, since the position of the X-ray generation point 2 is controlled accurately and quickly, the tomographic plane of the subject can be aligned accurately and quickly.

Furthermore, since the target that generates X-rays becomes high temperature upon collision with the electron beam, it is required to have a high density and good heat resistance. In order to process a metal such as tungsten, which is normally used as a target, into something with high density and good heat resistance, it is necessary to apply pressure at high temperature. Although it is very difficult to perform such a process, in the present invention, the target 1 is constructed by connecting a plurality of block-shaped metal plates 1a to 1h in a ring shape.
You can easily create large targets.

FIG. 2 and the following are concrete configuration diagrams of embodiments of the present invention. FIG. 2 is a sectional view of the X-ray tomography apparatus of the present invention, and FIG. 3 is a cross-sectional view of the X-ray tomography apparatus of the present invention, and FIG.
FIG. 2 is a cross-sectional view of the device of the invention;

In FIG. 2, the electron gun 21 has an opening 22 at one end.
The electron gun 21 is connected to one end of a vacuum vessel 23 at one end thereof. This vacuum container 23
is an exhaust hole 24 provided in the wall of this vacuum container.
The degree of vacuum is maintained at about 10 ^-7 Torr by a vacuum pump 26 through an L-shaped exhaust pipe 25 connected to. A focusing device, ie, a focusing coil 27, and a deflection device, ie, a beam deflection yoke 28, are provided at a narrow constricted portion of the vacuum vessel 23 from the side closer to the electron gun 21. Opening 22 of electron gun 21
The electron beam 29 extracted from the electron beam 29 is focused by the focusing coil 27, then deflected by a predetermined angle by the beam deflection yoke 28, and rotated into a cone shape while maintaining the same solid angle.
This electron beam 29 is directed to an auxiliary deflection device provided in a ring shape inside the vacuum container 23, that is, an electrostatic deflection electrode 3.
0 and collides with a predetermined point, that is, an X-ray generation point 2, on the target 1 arranged in a ring shape near the other end of the vacuum chamber 23, and an X-ray beam 3 is emitted.

A metal pipe 31 is welded to this target 1, and a cooling mechanism (not shown) is provided to flow oil or water into the metal pipe 31 in order to absorb the heat released from the target 1 due to the collision of the electron beam. It is provided.

The vacuum container 23 has a cylindrical cavity 32 with an open hole at one end, into which a subject is inserted. A detector 5 is installed in a ring shape near the open end of the cavity 32, and detects the X emitted from the target 1.
Detect line beam 3. As shown in FIGS. 2 and 3, the ring-shaped detector 5 includes a large number of detection elements 33. As shown in FIGS. Collimators 34 and 35 are installed in a ring shape at positions sandwiching the detector 5 from the inside and outside and at positions concentric with the detector 5. The X-ray beam 3 emitted from the X-ray generation point 2 is scanned along a circular trajectory 8 over the target 1 by electromagnetically controlling the focusing coil 27, beam deflection yoke 28, and electrostatic deflection electrode 30. . This X-ray beam 3 is shaped by a collimator 35 into a fan-shaped beam with a thin beam width and a divergence angle of, for example, about 30 degrees, and irradiates the imaging region 4 of the subject. This X-ray beam 3
is attenuated in accordance with the distribution of the X-ray absorption coefficient depending on the tissue of the subject, and is reshaped by the other collimator 34 installed in a ring shape, and the plurality of specific detection elements 33 arranged in a ring shape ' is incident on a part of the detector 5 consisting of '. The intensity of this incident X-ray beam is converted into an electrical signal indicating the intensity by the detector 5, and processed by the data processing device to obtain a tomographic image of the subject.

Note that the detector may also be arranged in an arc shape arranged in an angular range of 180°, for example, instead of in a ring shape.

In this way, since scanning of the X-ray beam 3 can be performed electromagnetically by the focusing device, deflection device, etc., high-speed and accurate scanning is possible. Furthermore, the electron beam can be narrowed down by the focusing coil 27, etc., and the size of the X-ray generation point 2 can be reduced, so that a clear image can be obtained.

FIG. 4 shows a cross-sectional view of the electron gun 21.

When a filament heating power source (not shown) is connected to the coiled filament 41 and energized, a cathode 42 covering the filament 41 is formed.
The electron emitting surface 43 of is heated, and electrons are emitted from this electron emitting surface. Near the front surface of the electron emitting surface 43, a mesh grid 44 is supported by a cylindrical grid support 45 and is electrically insulated from the cathode 42 by an insulator 46.
Furthermore, a funnel-shaped Wehnelt electrode 47 is provided on the front surface of the grid 44. This Wehnelt electrode 47 is supported by a Wehnelt support base 49 which is provided in a concentric cylindrical shape with an insulator 48 interposed between the grid support base 45 and the Wehnelt support base 45 .

This Wehnelt support stand 49 is fixed to a fixing member 51 via an insulator 50. Fixed member 5
1 is connected to the outer wall of an electron gun 21 (not shown), and supports an anode 53 via an insulator 52. Although not shown, electrons are applied to the filament, the Wehnelt electrode 47, the anode 53, and the like from respective power sources. The electrons emitted from the electron emitting surface 43 are focused by the Wehnelt electrode 47, and the electrons emitted from the electron emission surface 43 are focused by the Wehnelt electrode 47. Electron beam 2 from the aperture 54
It becomes 9 and is drawn out. The beam intensity of this electron beam 29 is controlled by the grid 44, and the energy of the beam is varied by varying the value of the voltage applied between the cathode 42 and the anode 53.

Therefore, the beam intensity and energy of the X-ray beam generated when the electron beam 29 collides with the target 1 can also be controlled. In the X-ray tomography apparatus of the present invention, since the X-ray beam can be rotated around the object many times in a short period of time, parameters such as X-ray energy and beam intensity can be further adjusted by using the electron gun. Many types of data can be obtained in a short period of time by changing the X-ray absorption coefficient of the object. For example, the disadvantage that the X-ray absorption coefficient becomes a value containing an error because an actual X-ray beam does not have a constant energy but is distributed over a certain energy range can be solved by the present invention. The image becomes clearer.

FIG. 5 is an enlarged view of the detector portion in the sectional view of the apparatus of the present invention shown in FIG.

The electron beam 29 impinges on the target 1, which is provided with a metal pipe 31 for cooling the target 1.
From the collision point, that is, the X-ray generation point 2, the X-ray beam 3
is released. This X-ray beam 3 is detected by a detector 5 consisting of two sets of detectors 5a and 5b. The detectors 5a and 5b control the position of the X-ray generation point 2 so that the X-ray beams 3a and 3b incident on the detectors 5a and 5b have symmetrical beam shapes, or The position is determined by moving the X-ray beam in a direction across the X-ray beam 3. A wedge-shaped X-ray shielding member 55 is provided between the detectors 5a and 5b. Therefore, unnecessary X-ray exposure to the subject is effectively eliminated. Furthermore, since the X-ray beams 3a and 3b are detected simultaneously by the two sets of detectors 5a and 5b, two images of different tomographic planes of the subject can be obtained at the same time.

Note that the X-ray beam 3 incident on the detectors 5a and 5b
To determine whether or not a and 3b are symmetrical to each other, that is, the position of the X-ray generation point 2, a detector 57 located close to the X-ray generation point 2 is used in addition to the detector 56 located far from the X-ray generation point 2. You can also do that.

FIG. 6 is a diagram showing a modification of FIG. 5.

Detectors 61a, 61b, 61c, 61d, 61
e and 61f are arranged at equal intervals. The collision points 2a, 2 of the electron beam 29 on the target 1 are arranged so that the X-ray beams 3 incident on these detectors 61 are symmetrical or have the same beam shape.
The positions of b, 2c, 2d, and 2e are electromagnetically controlled.

Therefore, since a large number of detectors 5 are arranged and the X-ray beam 3 incident on each detector is electromagnetically controlled, a large number of images of different tomographic planes of the subject can be obtained in a short time.

As described above, according to the present invention, since the scanning of the X-ray generation point is electromagnetically controlled, the scanning time of the X-ray beam is extremely short, the deterioration of image quality due to the movement of the subject is reduced, and a clear tomographic image of the subject is obtained. is obtained. and,
By narrowing down the electron beam that generates the X-rays, the size of the X-ray generation point can be reduced, so a clear tomographic image of the object can be obtained. Furthermore, since the position of the X-ray generation point can be determined accurately and quickly, the positioning of the tomographic plane of the subject can also be accurately and quickly performed.

Furthermore, by changing parameters such as X-ray energy and X
The linear absorption coefficient is obtained. Furthermore, since a plurality of detectors each having a large number of detection elements are arranged and the X-ray beam is electromagnetically scanned, a large number of images of different tomographic planes of the subject can be obtained in a short time.

Furthermore, the target etc. are provided in a single vacuum vessel, and the electron gun that generates X-rays from this target only needs to be connected to one end of the vacuum vessel, which simplifies the structure of the device and makes it easier for the machine to operate. Since a conventional X-ray beam rotation drive device is not required, the device can be made compact.

Furthermore, since the target is composed of a plurality of metal plates, manufacturing is very easy.

It should be noted that the present invention is not limited to the embodiments described in this specification, and of course includes modifications included in the scope of the claims. For example, in an electron gun, the cathode may be of the indirectly heated type. A direct heating type may be used, or an electron gun using a plurality of cathodes may be used.

Further, as a focusing device, an electrostatic electrode may be used for focusing, and the detector may be shaped other than a ring, for example.
They may be arranged in an arc arranged over an angular range of 180°. Furthermore, in order to facilitate the setting of the object, the electron gun may be mounted eccentrically from the central axis of rotation of the X-ray beam, and the container may be tilted to obtain images of different tomographic planes of the object. It may be a structure.

[Effects of the Invention] As described above, according to the present invention, since the scanning of the X-ray generation point is electromagnetically controlled, the scanning time of the X-ray beam is extremely short, the deterioration of image quality due to the movement of the subject is reduced, and a clear subject can be obtained. A tomographic image of the specimen can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the apparatus of the present invention, and FIG.
FIG. 3 is an overall view of an apparatus showing a specific configuration of the present invention. FIG. 4 is a sectional view of an electron gun used in the apparatus of the present invention, FIG. 5 is an enlarged view of a detector portion, and FIG. 6 is a view of a modified example of the detector shown in FIG. 5. 1...Target, 2...X-ray generation point, 5...
Detector, 6... Data collection unit, 7... Data processing device, 9... X-ray generation control device, 10... Display device, 21... Electron gun, 23... Vacuum container, 25...
... L-type exhaust pipe, 26 ... Vacuum pump, 27 ... Focusing coil, 28 ... Beam deflection yoke, 30 ...
Electrostatic deflection electrode, 31...Metal pipe, 33,3
3'...Detection element, 34, 35...Collimator,
41... filament, 42... cathode, 44
...grid, 45...crit support stand, 46,
48, 50, 52... Insulator, 47... Wehnelt electrode, 49... Wehnelt support base, 51... Fixing member, 53... Anode, 55... X-ray shielding member, 61... Detector.

Claims (1)

[Claims] 1. An electron gun that generates an electron beam, an electron beam control device that changes the direction of the electron beam from the electron gun, and an electron beam changed by the control device that collides with each other. It is possible to continuously irradiate X-rays from the colliding part of the electron beam toward the center of the arc from various angles. An X-ray tomography apparatus characterized by having a target arranged in an arc shape. 2. The X-ray tomography apparatus according to claim 1, wherein the target is plate-shaped, and a cooling mechanism for cooling the target is provided in contact with a surface opposite to a surface on which the X-rays collide.