JP3210357B2 - X-ray tomography equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[Object of the invention]

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray tomography apparatus, and more particularly to an X-ray tomography apparatus capable of high-speed scanning of X-rays and capable of forming clear tomographic images with less occurrence of artifacts. Related to the device.

[0003]

2. Description of the Related Art A subject is irradiated with X-rays from various directions around the subject such as a human body, the intensity of the X-rays transmitted through the subject is measured by a detector, and the measured value is processed by a computer. 2. Description of the Related Art An X-ray tomography apparatus (X-ray CT apparatus) for obtaining an X-ray absorption coefficient distribution on a tomographic plane of a subject is widely used as a diagnostic facility in a hospital or the like.

[0004] The X-ray CT apparatus which is widely used today is as follows.
Due to the difference in the arrangement of the X-ray source and the X-ray detector,
There are various systems from generation to fifth generation.

[0005] FIG. 3 is a diagram of a third type which is currently widely used.
FIG. 1 is a schematic front view showing a configuration of a next generation X-ray CT apparatus. This third-generation CT apparatus irradiates a fan-shaped X-ray beam 3 from the X-ray tube 1 so as to enclose the entire subject 2,
This is an apparatus for receiving the intensity of an X-ray beam 3 transmitted through a plurality of X-ray detectors 4 arranged in an array at several opposing positions and collecting projection data from each angle. The X-ray tube 1 and the X-ray detector 4 are integrally formed so as to hold the subject 2 therebetween, and are configured to mechanically rotate integrally with the subject 2 in the direction indicated by the arrow.

FIG. 4 is a schematic diagram showing a configuration of a fourth-generation X-ray CT apparatus. In this fourth-generation CT apparatus, an X-ray detector 4a is fixedly arranged around the entire space around the subject 2 and the subject 2 is irradiated with an X-ray beam 3 while rotating only the X-ray tube 1a. This is a device that collects projection data of the specimen 2 from each direction. In this method, since the imaging is performed only by rotating the X-ray tube 1a, the reliability is mechanically high and the imaging time is reduced to about 1 to 10 seconds.

FIG. 5 is a sectional view showing a configuration example of a fifth generation type X-ray CT apparatus. This fifth-generation system does not mechanically rotate the X-ray source around the subject, but focuses the electron beam 6 emitted from the electron gun 5 on a focusing device 7, a deflection yoke 8, and an electrostatic deflection electrode 9. X is accelerated and deflected to collide with a predetermined position of the target 10 arranged in a ring shape.
A line beam 3 is generated. The X-ray detector 4b is arranged in an arc shape on the inner periphery of the target 10 formed in a ring shape. In order not to block the X-ray beam 3 emitted from the target 10, a path for the X-ray beam 3 is formed at the center of the X-ray detector 4b, or the X-ray detector 4b and the target 10 are connected. The structure which arranges by offset is adopted.

According to this method, X-rays are electronically obtained by deflecting the electron beam without relying on mechanical means.
Since the position of the radiation source is moved on the target 10, the X-ray source can be rotated at a high speed, and an imaging time of about 50 mS and a scanning speed of about 17 scan / sec can be obtained.
Ultra-high-speed imaging becomes possible, which is extremely effective for imaging moving organs such as the heart.

[0009]

However, in the conventional third-generation and fourth-generation X-ray CT apparatuses, the rotation period of the gantry rotating unit on which the X-ray tube is mounted is limited due to the structural strength of the X-ray tube. It was extremely difficult to reduce the time to less than one second.

That is, as a conventional X-ray source, a rotating anode type X-ray tube generally having a high load rating is used, and this X-ray tube is a disk as an anode rotatably held in a vacuum vessel. And a filament disposed as a cathode and facing the target.
Electrons emitted from the cathode by energizing and heating the filament collide with the anode and generate X-rays. By the way, in this type of X-ray tube, a high-weight target formed of a metal material having a high heat capacity such as tungsten (W) is employed in order to increase the generation efficiency of X-rays.
However, most of the energy of electrons not converted to X-rays is converted to heat, and the target portion is heated to a high temperature. Under such a high temperature environment, there is a limit to the durability of a shaft or a bearing that holds a high-weight target in a freely rotatable manner at a high speed, and when the entire X-ray tube incorporating this high-speed rotating body is rotated together with a gantry rotating unit. In addition, the strength of the shaft and the bearing is restricted, and it is difficult to perform high-speed rotation with a rotation cycle of 1 second or less.

On the other hand, in the fifth generation type X-ray CT apparatus, as shown in FIG. 5, an X-ray detector 4b is arranged in an arc shape on the inner peripheral side of a target 10 formed in a ring shape. Have. Therefore, in order to irradiate the subject 2 with the X-ray beam 3 from the X-ray source, the X-ray detector 4 close to the X-ray source is required.
b denotes each X-ray detector 4b so as not to block the X-ray beam 3.
It is indispensable to provide a beam path at the center in the axial direction, or to offsetly arrange the X-ray detector 4b and the target 10.

Therefore, when the position of the X-ray source is changed, the slice planes are not the same, and there is a problem that an artifact is easily generated and a clear and high-precision tomographic image is hardly obtained.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is possible to perform X-ray scanning at a high speed, generate less artifacts, and form a clear tomographic image. It is an object to provide a line tomography apparatus. [Configuration of the invention]

[0014]

In order to achieve the above object, an X-ray tomography apparatus according to the present invention is arranged in an arc in an angle range of approximately 360 degrees, and an X-ray generated by colliding an electron beam. A target for irradiating a beam in the direction of a subject disposed at the center of the arc; and an X-ray detector disposed in an arc shape centered on an electron beam irradiation point on the target and detecting an X-ray dose transmitted through the subject. Detector, a rotation mechanism for mechanically rotating the X-ray detector around an arc center of a target arranged in an arc, a rotation angle of the X-ray detector, and a generation position of the X-ray beam And control means for controlling the irradiation state of the electron beam in association with

[0015]

According to the X-ray tomography apparatus having the above-mentioned structure, a method of electromagnetically controlling the orbital motion of an X-ray generation point on a target by causing an electron beam to collide with a target arranged in an arc shape. Since the X-ray detector is employed, there is no need to rotate the X-ray tube in the scanning direction as in the related art. Thereby, the transmitted X-ray dose from different directions of the subject can be measured. That is, since the X-ray tube is not included in the object to be mechanically rotated, it is possible to rotate the X-ray detector at a high speed without being restricted by the strength of the bearing shaft of the conventional X-ray tube. The time can be significantly reduced.

Further, since the X-ray detector has a structure that rotates without blocking the X-ray source, there is no need to offset the X-ray detector and the target as in the conventional fifth-generation system. The slice plane is the same regardless of the position set in the circumferential direction of the source target. Therefore, a clear and high-precision tomographic image can be reconstructed with few artifacts.

[0017]

An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an overall view of the apparatus showing a specific configuration of an embodiment of the apparatus of the present invention, and FIG. 2 is a sectional view showing the configuration of an embodiment of the apparatus of the present invention. The same elements as those in the conventional example shown in FIG.

That is, the X-ray tomography apparatus according to the present embodiment is arranged in an arc in an angle range of 360 °, and the X-ray beam 3 generated by colliding the electron beam 6 is arranged at the center of the arc. A target 10 for irradiating in the direction of the subject 2, an X-ray detector 4 c arranged on an arc centered on the electron beam irradiation point F on the target 10 and detecting an X-ray amount transmitted through the subject 2, A rotation mechanism 11 for rotating the X-ray detector 4c around the arc center C of the target arranged in an arc,
A control mechanism 12 for detecting a rotational position of the X-ray detector 4c and controlling a collision position of the electron beam 3 such that a focal point of the electron beam 3 is formed at a fixed position of the target 10 facing the rotational position; Data collection device 13 for converting an X-ray beam intensity signal from X-ray detector 4c into a digital electric signal
And a data processing device 14 for reconstructing a tomographic image based on the digital electric signal.

The control mechanism 12 includes an X-ray detector 4c.
The mechanism control unit 15 for detecting the rotation angle θ of the electron beam 6 and outputting the irradiation position F ′ of the electron beam 6 corresponding to the rotation angle θ as a signal, and the focus of the electron beam 6 based on the output signal from the mechanism control unit 15. And an X-ray control unit 16 that electromagnetically deflects the electron beam 6 to control an X-ray generation point so that the X-ray is formed at a fixed position of a target facing the X-ray detector 4c.

Further, the surface on which the ring-shaped target 10 is arranged and the surface on which the X-ray detector 4c is arranged are configured to be flush with each other.

As shown in FIG. 2, an electron gun 5 for emitting an electron beam 6 is provided at the left end of the apparatus main body, and this electron gun 5 is connected to one end of a vacuum vessel 17. The vacuum vessel 17 is maintained at a degree of vacuum of about 10 ^-7 Torr by a vacuum pump 18 through an L-shaped exhaust pipe connected to an exhaust hole provided in a wall of the vacuum vessel. A focusing coil 19 as a focusing device 7 and a deflecting device, that is, a beam deflecting yoke 8 are provided at a position of a narrow portion of the vacuum vessel 17 from the side close to the electron gun 5. The electron beam 6 extracted from the opening of the electron gun 5 is applied to the focusing coil 1.
After being narrowed down by 9, it is deflected by a predetermined angle by the beam deflection yoke 8, and is rotated in a cone shape while maintaining the same solid angle. The electron beam 6 is deflected again by an auxiliary deflecting device provided in a vacuum vessel 17 in a ring shape, that is, an electrostatic deflecting electrode 9, and a predetermined electron beam of a target 10 arranged in a ring shape near the other end of the vacuum vessel 17. An X-ray beam 3 is emitted by colliding with a beam irradiation point F, that is, an X-ray generation point. The target 10 is provided with a metal pipe 20.
By circulating a cooling medium such as water, heat emitted from the target 10 due to collision of the electron beam 6 is discharged to the outside of the system.

The electron beam 6 emitted from the electron gun 5 is
By colliding with the target 10 made of a ring-shaped metal plate, the X-ray beam 3 is emitted from the collision point, that is, the electron beam irradiation point F. X released
The X-ray beam 3 is emitted by an X-ray detector 4c arranged in an angle range that can sufficiently cover the imaging region 21 including the subject 2. The X-ray detector 4c rotates under the control of the mechanism control unit 15 around the arc center C of the ring-shaped target 10 at a high rotation speed of 1 second or less, and calculates the transmitted X-ray dose at each rotation position. To detect. The mechanism control unit 15 detects the rotation angle θ of the X-ray detector 4c, and detects the X-ray detector 4 at the rotation angle θ.
A signal is output to the X-ray control unit 16 so that the electron beam 6 is focused on a fixed position of the target 10 facing c. The X-ray control unit 16 electromagnetically controls the focusing device 7, the deflection yoke 8, and the electrostatic deflection electrode 9 so that the focal point of the electron beam 6 is formed at a fixed position on the target 10. Also in this case, control is performed so that the plane on which the focal position F on the target 10 moves and the plane on which the light receiving surface of the X-ray detector 4c rotates are coplanar.

The X-ray beam intensity (X-ray transmission amount) detected by the X-ray detector 4c is converted into an electric signal, converted into a digital signal by the data collection device 13, and transmitted to the data processing device 14. . The data processing device 14 uses the image reconstruction method as a basis for the X-rays on the tomographic plane (slice plane) of the subject 2 based on the measured values of the transmission intensities of the X-rays emitted from all directions around the subject 2. The absorption coefficient is calculated, and the result is displayed on a display device (not shown) as a tomographic image.

As described above, according to the X-ray tomography apparatus according to the present embodiment, the electron beam 6 collides with the target 10 arranged in an arc shape, so that the orbital motion of the X-ray generation point F is electromagnetically controlled. And a method of generating X-rays at an arbitrary position is adopted. Therefore, there is no need to rotate the X-ray tube in the scanning direction as in the conventional case, and the X-ray tube is opposed to the collision position of the electron beam with the target. X-ray detector 4
By mechanically rotating c by the rotation mechanism 11, the transmitted X-ray dose from different directions of the subject 2 can be measured. That is, since only the X-ray detector 4c is mechanically rotated, the X-ray detector 4c can be rotated at a high speed without being restricted by the strength of the bearing shaft of the conventional X-ray tube. The photographing time can be significantly reduced.

Further, since the X-ray detector 4c has a structure that rotates without interrupting the X-ray source, there is no need to offset the X-ray detector and the target as in the conventional fifth-generation system. The slice plane is the same regardless of the position set in the circumferential direction of the target of the radiation source.
Therefore, a clear and high-precision tomographic image can be reconstructed with few artifacts.

According to the apparatus of the present embodiment, only the X-ray detector 4c is mounted on the rotating mechanism 11 of the gantry (gantry), and there is no need to mount an X-ray tube. This eliminates the need to mount high-weight equipment such as a high-pressure slip ring for connecting the X-ray and a high-frequency generator (HFG) for X-ray generation, greatly simplifying the system configuration of the apparatus.

[0027]

As described above, according to the X-ray tomography apparatus of the present invention, the orbital motion of the X-ray generation point on the target is made electromagnetic by colliding the electron beam with the target arranged in an arc. It is not necessary to rotate the X-ray tube in the scanning direction as in the past, and the X-ray detector is rotated by the rotating mechanism so as to face the collision position of the electron beam against the target. By mechanically rotating, the amount of transmitted X-rays from different directions of the subject can be measured. That is, since the X-ray tube is not included in the object to be mechanically rotated, it is possible to rotate the X-ray detector at a high speed without being restricted by the strength of the bearing shaft of the conventional X-ray tube. The time can be significantly reduced.

Further, since the X-ray detector has a structure that rotates without interrupting the X-ray source, there is no need to offset the X-ray detector and the target as in the conventional fifth-generation system. The slice plane is the same regardless of the position set in the circumferential direction of the source target. Therefore, a clear and high-precision tomographic image can be reconstructed with few artifacts.

[Brief description of the drawings]

FIG. 1 is an overall view of a specific configuration of an embodiment of an X-ray tomography apparatus according to the present invention.

FIG. 2 is a schematic sectional view showing one embodiment of the device of the present invention.

FIG. 3 is a schematic diagram showing a configuration example of a third-generation X-ray tomography apparatus.

FIG. 4 is a schematic diagram showing a configuration example of a fourth-generation X-ray tomography apparatus.

FIG. 5 is a schematic diagram showing a configuration example of a fifth generation X-ray tomography apparatus.

[Explanation of symbols]

 1, 1a X-ray tube (X-ray source) 2 Subject 3 X-ray beam 4, 4a, 4b, 4c X-ray detector 5 Electron gun 6 Electron beam 7 Focusing device 8 Deflection yoke 9 Electrostatic deflection electrode 10 Target Reference Signs List 11 rotation mechanism 12 control mechanism 13 data collection device 14 data processing device 15 mechanism control unit 16 X-ray control unit 17 vacuum vessel 18 vacuum pump 19 focusing coil 20 metal pipe 21 imaging area F, F 'electron beam irradiation point (X-ray generation Point) C Target arc center (X-ray detector rotation center)

────────────────────────────────────────────────── (5) References JP-A-53-46295 (JP, A) JP-A-56-41659 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) A61B 6/00-6/14

Claims (5)

(57) [Claims] 1. A target which is arranged in an arc in an angle range of about 360 degrees and is irradiated with an X-ray beam generated by colliding an electron beam in a direction of a subject arranged at a center of the arc, and a target on the target. An X-ray detector arranged in an arc shape with the electron beam irradiation point as a center and detecting the amount of X-ray transmitted through the subject, and the X-ray detector having the arc center of a target arranged in an arc as a rotation center. A rotation mechanism for mechanically rotating the X-ray detector; and control means for controlling the irradiation state of the electron beam by associating a rotation angle of the X-ray detector with a position where the X-ray beam is generated. An X-ray tomography apparatus characterized by the above-mentioned. 2. The X-ray tomography apparatus according to claim 1, wherein a surface on which the target is arranged and a surface on which the X-ray detector is arranged are on the same plane. 3. The X-ray tomography apparatus according to claim 1, wherein the control unit changes a collision position of the electron beam on the target according to a rotational position of the X-ray detector. 4. The control means detects a rotational position of the X-ray detector, and a focus of the electron beam is formed at a fixed position of a target facing the X-ray detector at the rotational position. 2. The X-ray tomography apparatus according to claim 1, wherein a collision position of the electron beam is controlled. 5. The method according to claim 1, wherein the control unit controls a collision position of the electron beam such that a focal point of the electron beam is formed at a position of the target at the center of the arc of the X-ray detector. The X-ray tomography apparatus according to claim 4.