JPH10241613A - Rotary anode type x-ray tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray tube, wherein thermionic emission efficiency of a filament for forming a small focal point, which is the smallest, is improved, in the cage that thermionic focal points of different sizes, large, medium, and small, are formed on a rotary anode. SOLUTION: This X-ray tube has three filaments 14a, 14c for generating thermions and is also equipped with an electron gun 13 for forming, on a rotary positive electrode 11, three thermionic focal points which are different in size, that is, large medium, and small and are at least one part overlaps another. In this case, when virtual plane P normal to a region, where the focal points are formed on the rotary positive electrode 11 is drawn, the filament 14a which forms the small focal point is positioned on one side of the virtual plane P and the filaments 14b, 14c forming the large focal point, and the medium focal point respectively are positioned on the other side of the virtual plane P.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention improves the thermoelectron emission efficiency of a filament forming the smallest small focal point when a focal point of thermoelectrons having different sizes, large, medium and small, is formed on a rotating anode. To a rotating anode X-ray tube.

[0002]

2. Description of the Related Art A rotating anode type X-ray tube is an electron tube that irradiates the rotating anode with thermoelectrons generated from an electron gun and generates X-rays from the anode. It's being used. In this case, different X-ray doses are used depending on applications such as fluoroscopy and continuous imaging.
For example, fluoroscopy is performed with a small amount of X-rays, and continuous imaging is performed with a larger amount of X-rays than in fluoroscopy. Therefore, a small focus having a small focus is mainly used for fluoroscopy with a small X-ray dose, and a large focus or a middle focus is mainly used for continuous imaging with a large X-ray dose.

As described above, in the conventional rotary anode type X-ray tube,
In order to obtain an X-ray dose according to the application such as a part to be imaged, a purpose, and a required resolution, an electron gun for forming a focal point of thermoelectrons having different sizes, large, medium, and small, is incorporated.

Here, a conventional rotating anode type X-ray tube for forming focal points of thermoelectrons having different sizes will be described with reference to FIG. Reference numeral 31 denotes a rotating anode having a trapezoidal cross section, which is configured to rotate around an axis O. And
At a portion corresponding to the oblique side of the trapezoidal cross section, an irradiation region 32 of thermoelectrons for generating X-rays is provided. Further, an electron gun 33 is arranged to face the irradiation area 32 of the rotating anode 31. The electron gun 33 has a structure in which focal points F of large, medium, and small thermoelectrons having different sizes and at least partially overlapping each other are formed in the irradiation region 32. For example, a filament 34a for small focus is provided at the center. A filament 34b for large focus is provided on the left side,
A filament 34c for a middle focus is provided on the right side. The three filaments 34a, 34b, 34c have their longitudinal directions extending vertically from the front side to the rear side in the drawing, and when viewed from the irradiation area 32 side, as shown in the circle in FIG. The longitudinal directions are parallel and arranged in one direction.

The filaments 34a, 34b, 3
A focusing electrode 35 for forming a small focal point is provided in front of 4c.
a, a focusing electrode 35b for forming a large focus, and a focusing electrode 35c for forming a middle focus. The rotating anode 31 and the electron gun 33 are housed in a vacuum envelope (not shown), so that X-rays generated by the rotating anode 31 can be taken out of the vacuum envelope.

In the above-described configuration, the thermoelectrons generated by the small focus filament 34a are focused by the focusing electrode 35a to form the smallest focus in the irradiation area 32. The thermoelectrons generated by the filament 34b for the large focus and the filament 34c for the middle focus are respectively focused on the focusing electrode 35b.
b and the focusing electrode 35c to form the largest focal point and a focal point of an intermediate size in the irradiation area 32.

By the way, the filament 34a for small focus and the focusing electrode 35a located at the center are connected to the rotating anode 31.
The thermoelectrons generated from the filament 34a are directly opposed to the irradiation region 32 of the irradiation region 3 as indicated by an arrow Ya.
2 and travels substantially straight to the irradiation area 32.
Also, the filaments 34b and 34 for the large focus and the middle focus are used.
The thermoelectrons emitted from c advance in an arc to the irradiation region 32 as shown by arrows Yb and Yc.

[0008]

The small focal point of a rotating anode type X-ray tube has hitherto been often used for continuous fluoroscopy, and the imaging tube current is about 5 mA. However, in recent years, digital technology has advanced and diagnostic technology has advanced, and the peak value of the imaging tube current has increased to about 100 mA. In addition, intermittent fluoroscopy, in which X-rays are intermittently transmitted at certain time intervals, to see through a subject, is common. In the case of such intermittent fluoroscopy, the response of the filament that generates thermoelectrons is delayed. For this reason, a current is supplied to the filament of the electron gun to heat even during the interruption of the fluoroscopy so that a necessary imaging tube current can be obtained during the fluoroscopy. Also, due to an increase in the peak value of the imaging tube current, there has been a demand for increasing the imaging tube current for a small-focus filament.

By the way, when the imaging tube current is increased,
A method of raising the operating temperature of the filament is conceivable.
However, when the operating temperature of the filament is increased, there is a problem that the life of the filament is shortened. For this reason, without raising the operating temperature of the filament, for example, the filament and the focusing electrode are brought closer to the rotating anode, or the filament and the focusing electrode are directly opposed to the irradiation area of the rotating anode as much as possible, so that the A method for increasing the thermionic emission efficiency can be considered.

However, in the conventional rotary anode type X-ray tube, although the filament for the small focus and the focusing electrode face the irradiation area of the rotary anode, the distance from the irradiation area is long, so that the thermionic emission efficiency is low. There are limits to improvement. Further, a method of arranging the filament and the focusing electrode for the small focal point at the position of the filament and the focusing electrode for the large focal point and the middle focal point where the distance to the irradiation area is relatively short is conceivable. However, the positions of the large-focus and middle-focus filaments and the focusing electrode are greatly inclined with respect to the irradiation area due to the presence of the filament and the focusing electrode located at the center. For this reason, there is a limit in improving the thermionic emission efficiency.

An object of the present invention is to solve the above-mentioned drawbacks and to provide a rotary anode type X-ray tube in which the thermoelectron emission efficiency of a filament forming the smallest focus is increased.

[0012]

SUMMARY OF THE INVENTION The present invention has a rotating anode for generating X-rays by irradiating thermoelectrons, and three filaments for generating the thermoelectrons. And an electron gun for forming, on the rotating anode, focal points of three thermoelectrons, which are different and at least partially overlap each other, in a region where the focal point is formed on the rotating anode. When a vertical virtual plane is drawn, one filament forming a small focal point is located on one side of the virtual plane, and two filaments forming a large focal point and a medium focal point are placed on the other side of the virtual plane. It is characterized by being located.

[0013] Further, three filaments are arranged side by side in one direction, and a filament forming a small focal point is located at an end.

[0014] Further, the present invention is characterized in that three filaments are arranged at positions corresponding to each vertex of the triangular shape.

According to the above configuration, when a virtual plane perpendicular to the region on the rotary anode where the focal point is formed is drawn, the filament forming the small focal point is located on one side of the virtual plane, and the large focal point is formed. And two filaments forming the mid-focal point are located on the other side of the virtual plane. In this case, the filament forming the small focal point can be arranged near the virtual plane. Accordingly, the inclination of the filament forming the small focus and the focusing electrode with respect to the thermoelectron irradiation surface of the rotating anode, for example, the inclination of the opening of the front surface of the focusing electrode forming the small focus with respect to the thermoelectron irradiation surface can be reduced, and the thermoelectron emission efficiency can be reduced. Can be higher. In addition, when increasing the imaging tube current, the operating temperature of the filament is not increased,
A long-life rotary anode X-ray tube can be realized.

[0016]

FIG. 1 shows an embodiment of the present invention.
A description will be given with reference to the schematic structural diagram of FIG. Reference numeral 11 denotes a rotating anode that generates X-rays by irradiation of thermoelectrons, has a trapezoidal cross section, and has a structure that rotates around an axis O.
An irradiation region 12 of thermoelectrons for generating X-rays is provided in a portion corresponding to the oblique side of the trapezoidal cross section.

Further, an electron gun 13 is arranged so as to face the thermoelectron irradiation region 12. As shown in FIG. 1A, the electron gun 13 is provided with three filaments 14a, 14b and 14c for generating thermoelectrons in order from left to right in the figure. The three filaments 14a, 14
b, 14c have a longitudinal direction extending from the front side to the back side perpendicular to the drawing, and when viewed from the irradiation area 12, FIG.
Are arranged in one direction with their longitudinal directions being parallel.

Also, three filaments 14a, 14
b, 14c, each filament 14a, 14c
Focusing electrodes 15a, 15b, and 15c that respectively focus thermoelectrons emitted from b and 14c are arranged. For example, the thermoelectrons generated by the filament 14a are
The light is converged at 5a, advances in the direction of the arrow Ya, and forms the smallest focal point F in the irradiation area 12. Also, the filament 14b
The thermoelectrons generated by the filament 14c are focused on the focusing electrode 1
5b and the focusing electrode 15c, focus in the directions of the arrows Yb and Yc, and apply a large focus or a focus F of an intermediate size to the irradiation area 1.
2 is formed. In addition, the large formed in the irradiation area 12
The three medium and small focal points are at least partially overlapped with each other.

When a virtual plane P perpendicular to the surface of the irradiation area 12 and extending from the front surface to the rear surface in the drawing is drawn, the filament 14a forming the small focal point is
And at a position as close as possible to the virtual plane P. Further, the two filaments 14b and 14c forming the large focal point and the medium focal point are in the virtual plane P
Is provided on the other side. In FIG. 1B,
The virtual plane P is indicated by a line segment PP.

The rotating anode and the electron gun are housed in a vacuum envelope (not shown) so that X-rays generated by the rotating anode can be taken out of the vacuum envelope.

According to the above configuration, the filament 14a and the focusing electrode 15a forming a small focal point can be arranged at a position close to the irradiation area 12 on one side of the virtual plane P. Further, the angle θ of the inclination of the opening portion on the front surface of the focusing electrode 15a with respect to the surface of the irradiation region 12, that is, the angle θ with respect to the virtual plane P can be reduced.
Therefore, the emission efficiency of thermoelectrons is improved.

Next, another embodiment of the present invention will be described with reference to FIG. In FIG. 2, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and overlapping description is partially omitted.

FIG. 2A shows each filament 14a,
FIG. 2B is a view as viewed from the direction in which the filaments 14b and 14c extend, and FIG. 2B is a view as viewed from a direction perpendicular to the direction in which the filaments 14a, 14b and 14c extend. , Each filament 14 from the side of the irradiation area 12
It is the figure which looked at a, 14b, and 14c direction. In the case of this embodiment, two filaments 14b and 14c forming a large focus and a middle focus are arranged side by side. And
The filament 14a forming the small focus is the filament 1
4b, 14c, each filament 14b,
14c is displaced in the longitudinal direction. Therefore, the three filaments 14a, 14b, 14c are arranged at positions corresponding to the respective vertices of the substantially triangular shape.
Then, a virtual plane perpendicular to the surface of the irradiation area 12 is denoted by a symbol P in FIGS. 2A and 2B, and is also shown in FIG.
In the figure, the line segment is indicated by PP. Also in this case, one filament 14a forming a small focal point is located on one side of the virtual plane P and is provided as close as possible to the virtual plane P. Further, the two filaments 14b and 14c forming the large focal point and the medium focal point are provided on the other side of the virtual plane P.

The two filaments 14b and 14c forming the large focal point and the medium focal point are located on the same plane,
Further, they are arranged so that their longitudinal directions are parallel to each other. The filament 14a forming the small focal point is located on a plane intersecting with the filaments 14b and 14c forming the large focal point and the medium focal point, so that the inclination angle θ of the irradiation area 12 with respect to the plane is reduced. In this case, the focusing electrode 15 provided on the two filaments 14b and 14c
The opening portions on the front surfaces of the filaments b and 15c and the opening portion on the front surface of the filament 14a forming the small focal point are not on the same plane, but have a structure intersecting at a certain angle.

According to the above configuration, the filament 14a for small focus and the focusing electrode 15a can be arranged at a position close to the irradiation area 12. In addition, filament 1 for small focus
4a and the inclination of the focusing electrode 15a with respect to the surface of the irradiation region 12, for example, the angle of the opening of the front surface of the focusing electrode 15a with respect to the irradiation region 12 and the virtual plane P can be reduced, and the thermionic emission efficiency can be improved.

[0026]

According to the present invention, it is possible to realize a rotary anode X-ray tube in which the filament that forms the smallest focal point has a high thermoelectron emission efficiency.

[Brief description of the drawings]

FIG. 1 is a schematic structural diagram illustrating an embodiment of the present invention.

FIG. 2 is a schematic structural diagram illustrating another embodiment of the present invention.

FIG. 3 is a schematic structural diagram illustrating a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Rotating anode 12 ... Thermionic irradiation area 13 ... Electron gun 14a ... Filament forming a small focus 14b ... Filament forming a large focus 14c ... Filament forming a middle focus 15a-15c ... Focusing electrode P ... Virtual plane F … Thermal electron focus O… Rotating axis of rotating anode

Claims (3)

[Claims] 1. A rotating anode that generates X-rays by irradiating thermoelectrons, and three filaments that generate the thermoelectrons, and are different in size from large, medium, and small, and at least partially overlap. A rotating anode type X-ray tube comprising: an electron gun for forming three hot electron focal points on the rotating anode.
When drawing a virtual plane perpendicular to the area where the focal point is formed on the rotating anode, one filament forming the small focal point is located on one side of the virtual plane and forming the large focal point and the medium focal point A rotating anode type X-ray tube, wherein two filaments are located on the other side of the virtual plane. 2. The rotary anode X-ray tube according to claim 1, wherein three filaments are arranged side by side in one direction, and a filament forming a small focal point is located at an end. 3. The rotating anode type X-ray tube according to claim 1, wherein three filaments are arranged at positions corresponding to respective vertices of the triangular shape.