JPH04212335A - Rotary cathode x-ray tube device - Google Patents

Abstract

PURPOSE:To improve the efficiency of X-ray generation by shortening the distance between a cathode filament and an anode target and to allow the rapid execution of photographing with lessened labor by constituting the above device in such a manner that the device is not restricted by the length of a testee body and a usable degree of vacuum is obtd. in an early period. CONSTITUTION:This device has a hollow annular vacuum vessel 5 which is formed with an insertion hole 2 for the testee body at the center, an annular anode target 8 which is installed and fixed in this vacuum vessel 5, an annular cathode filament 14 which is disposed to face the anode target 8 in the vacuum vessel 5, an annular rotating body 9 which is disposed between the anode target 8 and the cathode filament 14 in the vacuum vessel 5, is supported rotatably around the axial center X of the insertion hole 2 for the testee body and is provided with a small hole for passing selection beam at a prescribed position in its circumferencial direction, and a stator 10 which rotates the rotating body 9 around the axial center X of the insertion hole 2 for the testee body.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention provides
Rotating cathode X for X-ray CT configured to be able to irradiate radiation
It relates to a wire tube device.

0002

2. Description of the Related Art Conventional rotating cathode X-ray tube devices include, for example, as shown in Japanese Patent Application Laid-Open No. 56-22037.
An electron generation source is provided at the top of a conical flask-shaped vacuum container, a cylindrical rotating shield is placed around the electron source, and a small hole is provided in the rotating shield to regulate the direction of electron emission. The rotary shield is rotated to irradiate the entire circumference of the target with electrons emitted from the small hole, and the X-rays generated from the target are directed toward the object located in the recess formed in the center of the vacuum chamber. Some are configured to irradiate the entire circumference, and others are configured to irradiate the entire circumference, and as shown in JP-A-63-103392, a hollow ring-shaped vacuum container has a large number of filaments, a grid for electron beam control for each filament, and a An anode target that receives the electron beam that has passed through the grid is arranged in a ring shape, and the operating filament and the corresponding grid are electrically rotated using a reed switch, etc., and the X
A device configured to irradiate a line is known.

0003

[Problems to be Solved by the Invention] However, with the former conventional device, since the depth of the central recess of the vacuum container cannot be made large, there is a limit to the imaging length of the object, and the object cannot be inserted into the recess. There is a problem of being mentally pressured when doing so. Furthermore, since the distance between the electron source and the target is long, not only the efficiency of X-ray irradiation becomes low, but also there are the following drawbacks.

Since the electrons emitted from the electron source head toward the target while being repelled, the longer the distance, the larger the spread angle of the electron beam becomes. It becomes difficult to set the shape of the hole. It is well known that the general property of X-ray tubes is that the amount of thermionic electrons is determined by the heating current value to the filament, which is the electron source, and the tube current value is limited by the amount of thermionic electrons. In addition, if we try to obtain the same tube current value when the distance between the electron beam source and the target is relatively long and short, the longer the distance, the more the amount of hot electrons, that is, the amount of hot electrons flowing into the filament. The property is that the heating current must be increased. However, the filament has a temperature tolerance, and it is not possible to increase the tube current limit by heating the filament until it exceeds the temperature tolerance (this tube current limit is called the emission cutoff value). Therefore, the longer the distance, the lower the emission cut-off value determined by the filament temperature tolerance, and the narrower the setting range of the X-ray conditions.

Furthermore, in the latter conventional apparatus, since a large number of independent filaments are activated in sequence, X-rays are generated in a pulsed manner, which limits the resolution of tomographic images. Additionally, devices that generate X-rays in a pulsed manner require higher filament temperature and tube current than those that generate X-rays continuously, which has the disadvantage of shortening the filament's lifespan. Ta.

The present invention has been made in view of the above circumstances, and the invention according to claim 1 improves the vacuum container and reduces the distance between the cathode filament and the anode target. In addition to improving the efficiency of line generation,
The object of the present invention is to obtain a usable degree of vacuum at an early stage without being constrained by the length of a subject, and to enable rapid imaging with less effort. The object of the invention is to avoid deterioration in image quality caused by secondary X-rays due to bounced electrons, and furthermore, the invention according to claim 3 is directed to uniformizing the amount of X-rays incident on the detector. The purpose is to improve the accuracy of a full-circumference tomographic image of a photographed object.

[0007]

[Means for Solving the Problem] In order to achieve the above-mentioned object, the invention according to claim 1 provides a hollow ring-shaped vacuum container having a specimen insertion hole formed in the center, and the vacuum container. A ring-shaped anode target installed and fixed inside the
a ring-shaped cathode filament arranged and fixed opposite to the anode target in the vacuum vessel; and a ring-shaped cathode filament disposed between the anode target and the cathode filament in the vacuum vessel, around the axis of the subject insertion hole. a ring-shaped rotating body that is rotatably supported by the ring and has a small hole for passing an electron beam at at least one location in the circumferential direction;
and a driving means for rotating the rotating body around the axis of the subject insertion hole.

[0008] Furthermore, in order to achieve the above-mentioned object, the invention according to claim 2 has a structure in which the rotating body according to claim 1 is located closer to the axis of the specimen insertion hole than the anode target. A shielding member for shielding secondary X-rays due to bounced electrons is provided so as to rotate together, and an opening is provided in the shielding member to allow X-rays to pass from the focal point of the anode target toward the axis of the subject insertion hole. Configure.

Further, in order to achieve the above-mentioned object, the invention according to claim 3 covers the opening of the shielding member according to claim 2, and extends from the center of the opening in the circumferential direction of the rotating body. X with different thickness so that the transmission length becomes larger on both sides
It is configured by providing a radiation dose adjustment member.

0010

[Operation] According to the structure of the rotating cathode X-ray tube device of the invention according to claim 1, the filament arranged in a ring shape is always energized and emits electron beams from its entire circumference. The anode target is irradiated with only the electron beam that has passed through the small hole, and X-rays are generated from a part of the circumference. By rotating the rotating body, the X-ray generation site moves in the circumferential direction, and can irradiate the entire circumference of the subject located at the center of the vacuum container.

According to the configuration of the rotating cathode X-ray tube device of the invention according to claim 2, when the anode target is irradiated, some of the electrons bounce off the anode target and then irradiate the area around the focal point of the anode target. The shielding member can prevent secondary X-rays generated from around the focal point by the bounced electrons from entering the X-ray detector.

According to the configuration of the rotating cathode X-ray tube device of the invention according to claim 3, when the X-rays generated from the focal point of the anode target are incident on the X-ray detector, the axis of the subject insertion hole Because the distance between the focal point and the X-ray detector adjacent to the X-ray detector in the center of the incident range in the circumferential direction is shorter than the distance between the focal point and the X-ray detector connected by a virtual straight line passing through the heart. The closer the X-ray detector is to the center of the incident range, the lower the amount of X-rays that enter it.
By attenuating the radiation through the radiation dose adjustment member, the amount of X-rays incident on each X-ray detector can be made uniform.

[0013]

Embodiments Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 7 is an overall schematic perspective view of a high-speed X-ray CT using the rotating cathode X-ray tube device according to the present invention. In this figure, 1 indicates a gantry, into which a subject is inserted A hole 2 is formed to penetrate from the front and back, and a rotating cathode X-ray tube device A, which will be described later, is installed so as to surround the subject insertion hole 2. Reference numeral 3 denotes a vertically movable bed on which the subject M is placed, and its top plate 4 is adapted to slide horizontally back and forth to extend into the subject insertion hole 2.

Next, a first embodiment of the rotating cathode X-ray tube apparatus A will be described based on the longitudinal sectional side view of FIG. 1, the enlarged sectional view of main parts of FIG. 2, and the sectional view of FIG. 3.

In these figures, reference numeral 5 denotes a hollow ring-shaped vacuum container in which the specimen insertion hole 2 is formed in the center, and the pressure is reduced by a vacuum pump 6. The vacuum container 5 is constructed by airtightly connecting a front container portion 5a and a rear container portion 5b made of a non-magnetic material such as glass via two inner and outer O-rings 7.
Only the rear wall 5c of the rear container portion 5b, the surrounding area of the filament terminal 15, and the surrounding area of the sliding contact terminal 19 are formed of an insulating material.

Reference numeral 8 denotes a ring-shaped anode target fixedly mounted on the inner surface of the rear wall 5c of the rear container portion 5b;
Its surface is slightly inclined toward the axis X side of the subject insertion hole 2.

Reference numeral 9 denotes a ring-shaped rotating body that is rotatably incorporated in the front container portion 5a, and is formed into a ring shape by connecting a large number of ferrite magnet pieces in the circumferential direction. The north and south poles of each magnet piece are alternately arranged at the left end (in the figure).

Reference numeral 10 denotes a ring-shaped stator as a driving means disposed close to the front surface of the front container portion 5a, and the rotating body 9 is driven to rotate at a frequency of 10 to 100 Hz by controlling the supply of electricity to the stator 10. Ru.

Reference numeral 11 denotes magnetic bearing coils that levitate and support the rotating body 9 freely, and are installed at multiple locations in the circumferential direction on the outer circumferential surface of the front container portion 5a and on the front and rear outer surfaces of the stepped portion formed near the outer circumference. ing. Note that the radial and axial positions of the rotating body 9 are detected by bearing sensors 12 and 13 each consisting of a proximity switch, etc., and each magnetic bearing coil is installed so that the rotating body 9 is levitated and supported concentrically with the center of the container. 1
1 is controlled to be energized.

Reference numeral 14 denotes a cathode filament serving as an electron gun arranged and fixed in a ring shape inside the front container portion 5a so as to face the anode target 8, and a pair of filament terminals 15 provided on the front wall. AC power supply 1 through
6.

Reference numeral 17 denotes a ring plate-shaped grid portion integrally connected from the rear of the rotary body 9 so as to isolate the anode target 8 and the cathode filament 14, and the ring plate-like grid portion 17 has a ring plate-like grid portion that is connected at a pitch of 120° in the circumferential direction. A small hole 18 for electron beam passage is formed. Further, the inner peripheral edge of this grid 17 is connected to a sliding contact terminal 19 provided on the inner peripheral wall of the front container portion 5a.
It is electrically connected to the negative side of the grid power supply 20 via the small hole 18, and is configured to focus and control the electron beam (a) passing through the small hole 18 to irradiate the anode target 8.

Reference numeral 21 denotes a DC high voltage power supply, the positive side of which is connected to the anode target 8, and the negative side connected to the cathode filament 14.
Of the electron beams (a) emitted from the entire circumference, only those that have passed through the small hole 18 irradiate the target 8 and generate X-rays (b), which are directed to the subject M in the subject insertion hole 2. X from 3 directions
The line is now illuminated.

Reference numeral 22 denotes a ring-shaped X-ray detector disposed close to the rear side of the vacuum container 2, which detects the amount of X-rays transmitted through the subject M and transmits the detected amount to an analysis device (not shown).

This rotating cathode X-ray tube apparatus A is constructed as described above, and by rotating the rotating body 9 together with the grid section 17 by 120 degrees, a full-circumference tomographic image of the subject M can be taken. can. Incidentally, when the grid portion 17 with three small holes 18 is driven and rotated at 20°, the distance is 17 m.
s will allow you to shoot all around.

FIG. 4 is a vertical sectional side view showing a second embodiment of the rotating cathode X-ray tube device, FIG. 2 is an enlarged sectional view of the main parts, and
FIG. 6 is a sectional view taken along the Z-Z line in FIG. 4. According to this second embodiment, the rotating body 9 incorporated in the front container part 5a is
An outer ring 9a rotatably supported by a fixed outer ring 23 via a ball 24 and an inner ring 9b rotatably supported by a fixed inner ring 25 via a ball 26 are connected by a grid portion 17. The rotating body 9 is also rotationally driven by the stator 10. Furthermore, the grig portion 17 includes a fixed outer ring 23, a ball 24, and an outer ring 9a.
It is connected to the grid power supply 20 via.

FIG. 8 is a cross-sectional view of the main parts of a third embodiment of the rotating cathode X-ray tube apparatus. A shielding member 27 that shields secondary X-rays due to bounced electrons is rotatably connected to the shielding member 27. An opening 29 is formed through which the wire passes. In the figure, 30
indicates a collimator that adjusts the width of X-rays irradiated to the subject M, that is, the slice width for photographing a full-circumference tomogram of the subject M.

Next, FIG. 9 shows the effect of the shielding member 27.
The explanation will be based on a schematic front view of. The width of the opening 29 in the circumferential direction of the rotating body 9 is set so that the X-rays generated at the focal point 28 enter the X-ray detector 22 within a predetermined range. As the anode target 8 is irradiated, some of the electrons bounce off the anode target 8 and are then irradiated around the focal point 28 of the anode target 8, and secondary X-rays are generated from around the focal point 28 by the bounced electrons. When this occurs, the shielding member 27 blocks secondary
It is possible to reduce the amount of secondary X-rays incident on the X-ray detector 22 and avoid deterioration in image quality.

The position where the shielding member 27 is provided is as follows:
As shown by the two-dot chain line 27a in FIG. 9, since the range of incidence on the X-ray detector 22 is set, the width of the aperture 29a inevitably increases as the distance from the focal point 28 increases. Since the region S2 that cannot be shielded by the shielding member 27 becomes large, a position closer to the focal point 28 is preferable.

Furthermore, as shown in the schematic front view of FIG.
The shielding member 27 has an X-ray irradiation member made of aluminum or the like that covers the opening 29 and has a thickness that varies so that the transmission length increases from the center of the opening 29 to both sides of the rotating body 9 in the circumferential direction. A quantity adjusting member 31 is provided and configured to equalize the amount of X-rays incident on the X-ray detector 22.

That is, when the X-rays generated from the focal point 28 of the anode target 8 are incident on the X-ray detector 22,
X-ray detection adjacent to the X-ray detector 22 in the center of the incident range in the circumferential direction Vessel 22
Since the distance between the X-ray detector 22 at both ends of the incident range and the focal point 28 (the virtual straight line connecting the X-ray detector 22 at both ends of the incident range and the focal point 28 is indicated by L2) becomes shorter (L1>L2), the X-ray detector at the center of the incident range 2
However, the X-rays generated from the focal point 28 of the anode target 8 are passed through the X-ray dose adjustment member 31, and the attenuation amount of the X-rays is reduced as the distance from the center of the aperture 29 increases. X at the time it reaches each X-ray detector 22
This ensures that the doses are equal to each other.

In the embodiment described above, the rotating body 9 is rotationally driven by the stator 10 from the outside, but it can also be driven by a brushless motor.

[0033]

As explained above, according to the rotating cathode X-ray tube device of the invention according to claim 1, the following effects can be obtained. (2) Since the distance between the cathode filament and the anode target can be reduced, X-rays can be generated efficiently, and the shape of a small hole for forming a focal point of a predetermined size on the anode target can be easily set. ■Also, because the distance between the cathode filament and the anode target can be reduced, the tube current limit value (emission cutoff value) can be increased compared to conventional equipment, and the setting range of X-ray conditions can be expanded. . ■ Since the cathode filament operates continuously, there is no need to raise the filament temperature and increase the tube current, unlike when operating intermittently.
The life of the cathode filament can be extended. ■
Since the vacuum container is ring-shaped with a subject insertion hole formed in the center, there is no restriction on the length of the subject, and any part of the subject can be imaged efficiently with one insertion. ■
Since the specimen insertion hole is a short through hole in the axial direction,
Even if it is inserted through the head, there is no compression tube, so you can have your images taken with confidence. ■ The ring-shaped vacuum container has a small volume, so even if the degree of vacuum is lowered, it takes less time to reach a usable degree of vacuum, allowing for quick start of imaging at the start of operation or after restarting operation after maintenance. It became so.

According to the rotating cathode X-ray tube device of the invention according to claim 2, the shielding member can prevent secondary X-rays generated from around the focal point due to bounced electrons from entering the X-ray detector. Therefore, it is possible to avoid deterioration in the image quality of the captured full-circumference tomographic image of the subject due to secondary X-rays due to bounced electrons.

According to the rotating cathode X-ray tube device of the invention according to claim 3, since the amount of X-rays incident on each X-ray detector from the focal point of the anode target is made uniform, the amount of X-rays between adjacent X-ray detectors is uniform. It is possible to eliminate the difference in shading and improve the accuracy of the all-round tomographic image of the object being photographed.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional side view showing a first embodiment of a rotating cathode X-ray tube device.

FIG. 2 is an enlarged sectional view of the main part of FIG. 1;

FIG. 3 is a sectional view taken along the Y-Y line in FIG. 1.

FIG. 4 is a longitudinal sectional side view showing a second embodiment of the rotating cathode X-ray tube device.

FIG. 5 is an enlarged sectional view of the main part of FIG. 4;

6 is a sectional view taken along the line Z-Z in FIG. 4. FIG.

FIG. 7 is an external perspective view of an X-ray CT using the rotating cathode X-ray tube device of the present invention.

FIG. 8 is a longitudinal sectional side view showing a third embodiment of a rotating cathode X-ray tube device.

FIG. 9 is a schematic front view illustrating the function of the shielding member.

FIG. 10 is a schematic front view illustrating the function of the X-ray dose adjustment member.

[Explanation of symbols]

2...Subject insertion hole 5...Vacuum container 8...Anode target 9...Rotating body 10...Stator as driving means 14... Cathode filament as an electron gun 18... Small hole 27...shielding member 28...Focus 29...Aperture 31...X-ray irradiation amount adjustment member b...electron beam X…Axis of the specimen insertion hole

Claims (3)

[Claims] 1. A hollow ring-shaped vacuum container having a specimen insertion hole formed in the center, a ring-shaped anode target installed and fixed in the vacuum container, and a ring-shaped anode target that faces the anode target in the vacuum container. a ring-shaped cathode filament arranged and fixed in the vacuum container, and disposed between the anode target and the cathode filament in the vacuum container,
A ring-shaped rotating body is rotatably supported around the axis of the subject insertion hole and has a small hole for passing an electron beam at at least one circumferential location, and the rotating body is connected to the subject insertion hole. A rotating cathode X-ray tube device comprising a drive means for rotating the tube around the axis of the tube. 2. The rotating body of claim 1 is provided with a shielding member positioned closer to the axis of the subject insertion hole than the anode target so as to rotate together with the shielding member for shielding secondary X-rays due to bounced electrons, A rotating cathode X-ray tube device, wherein the shielding member is provided with an opening through which X-rays pass from the focal point of the anode target toward the axis of the subject insertion hole. 3. Covering the opening of the shielding member according to claim 2,
A rotating cathode X-ray tube device provided with an X-ray irradiation amount adjustment member having a different thickness so that the transmission length increases from the center of the opening to both sides in the circumferential direction of the rotating body.