JPS61153934A - Variable focus x-ray tube - Google Patents

Abstract

PURPOSE:To move the focus ion an anode target by required amount with low deflection voltage by arranging a pair of electrostatic deflection electrodes at the inside of the focus groove of a focusing electrode forming a cathode structure while isolating electrically from the focusing electrode. CONSTITUTION:A rotary anode 21 supported on a rotor 33 and a cathode ray structure 35 for producing an electron beam held an a cathode support 34 are contained in a vacuum container 29 while facing each other to constitute a rotary anode X-ray tube. Here, the cathode structure 35 is formed by arranging a thin board filament cathode 42 for emitting electrons in a recess in the bottom of a focus groove 40 made in a focusing electrode 39 while arranging a pair of electrostatic deflection electrodes 44 made of metal plate in a recess 43 near the cathode 42 while insulating from the deflection electrode 39 through an insulation board 45. since it is deflected in such region where the acceleration filed of electron beam is relatively low, the focus on the anode target 37 can be moved effectively with low deflection voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to an improvement in an X-ray tube with a variable focal position suitable for use in, for example, an X1lii imaging device for medical diagnosis.

[Technical background and problems of the invention]

In X-ray photography using the xi*m shadow device that is in practical use today, the resolution and contrast of reproduced images are often impaired by scattered X-rays generated from within the subject. On the other hand, in recent years, there has been a strong desire to develop a device that can take images at high speed and in a short time.In this case, it is necessary to increase the amount of XII radiation, but in general, the amount of scattered X-rays increases accordingly. , the S/N ratio of the image decreases.

In order to increase the amount of emitted X-rays, it has been considered to use, for example, a cylindrical rotating anode target and to deflect the electron beam generated from the cathode assembly a predetermined distance by an N magnetic deflection device. However, this has the disadvantage of being complicated in structure and large in size, and lacking in practicality. On the other hand, as disclosed in Japanese Unexamined Patent Publication No. 53-7190, an X-ray generator is configured to deflect and scan an electron beam on a substantially linear or planar anode target to move the X-ray focal point. , this X
An Xm imaging device has also been proposed in which an X-ray shielding plate with a pinhole or an X-ray transmission slit is placed between the ray generator and the subject, and an XSII image detector is placed behind it to reproduce the X-ray image. . However, the device disclosed in the same publication still has
With a line generator, it is difficult to obtain the necessary and sufficient XIIm, and there are various problems in practical use.

[Purpose of the invention]

The present invention solves the above-mentioned problems and provides a variable focus X-ray tube that has a relatively simple structure and is highly practical.

[Summary of the invention]

This invention is characterized in that a pair of electrostatic deflectors Nli for beam deflection are arranged inside a focusing groove of a focusing electrode constituting a part of the cathode structure, electrically insulated from the focusing electrode. This is a variable focal position X5il tube.

As a result, the electron beam is electrostatically deflected in a region where the accelerating electric field is relatively low, so that the focal point on the anode target can be moved by the required amount with a small deflection voltage. In particular, it has the advantage of being manufactured in a shape that is almost the same as the normal type of rotating anode X-ray tube that has been in practical use for some time.

[Embodiments of the invention]

The present invention will be explained in detail below. Identical parts are designated by the same reference numerals.

First, an example of an Xm imaging apparatus suitable for using the X-ray tube of the present invention will be explained with reference to FIG. That is, the rotating anode of the present invention (
an XWA generator (22) having a built-in X-ray tube with an ), an X-ray image detector (26) disposed behind the subject (25), and a display device (27) or a display device (not shown) that processes electrical signals obtained by the X-ray image detector (26). It also includes a signal processing device (28) that sends a reproduced image signal to the recording device. X
As will be described later, the ray generator (22) has an umbrella-shaped rotating anode target provided in a vacuum container and is rotatable by a drive motor, and the rays are generated from a cathode structure provided opposite to the umbrella-shaped rotating anode target. The electron beam collides and an X-ray beam is generated. The X11A focus (F) points on the target with an arrow (
3), and the x from this X-ray focus (F)
The LA beam is passed through each slit (23) of a slit plate (24) made of an X-ray shielding material, and a plurality of fan-shaped X-ray beams generated behind the slit plate (24) are irradiated onto the subject (25).

Information on the position of the X-ray focal point (F) determined by the deflected and scanned electron beam is always supplied to the signal processing device (28) as an electrical signal. The slit plate (24) is made of a thin plate of heavy metal such as lead, and has eleven or more elongated slits (23) formed in it, the longitudinal direction of which is xII.
It is arranged in a direction perpendicular to the moving direction (S) of the focal point (F). Note that the slit (23) has aluminum<AI
The structure may be filled with a metal having high X-ray transmittance such as beryllium (Be) or beryllium (Be). Xls image detector (26
) is large enough to cover the area to be photographed of the subject.
It has a ray scintillator, receives an X-ray image by the X-ray beam at each instant of passing through each slit (23) as shown by the symbol (A> in the figure), and obtains an electrical signal corresponding to this Xll image.X The ray image detector (2G) may be, for example, a combination of an X-ray fluorescence intensifier tube (Xll) and an image pickup tube with a light guide layer-type imaging target, or a flat plate-like detector in which a large number of minute X-ray detection elements are arranged. A scintillator, etc. is used.An example of the dimensions of each part is the X-ray focus of the X[1 generator (
F) has an elliptical shape with a minor axis of 0.41 and a major axis of 2.5 mm,
The effective X-ray focal point (F) seen from the slit plate direction is approximately 0.4
The electron beam is applied obliquely onto the anode target so as to form a circular shape of I. And the moving distance of the focal point (F) is 5m
lThe distance from this focal position to the slit plate (24) is 1
m(r*). The slit plate (24) has a thickness of 2++1
An R1 lead plate is used, and 100 slits (23) are formed parallel to each other with a slit width of 0.2 mm and a pitch interval of 21111. The distance from this slit plate to the X-ray detection surface of X-ray image detection device F (26) is the same <
1+l1(F=). The X-ray detection surface is a square with a side length of approximately 50 cm. The object (25) is placed in an area closer to the detection device.

Next, the present invention will be explained in detail with reference to FIGS. 2 to 5. The vacuum container (29) is formed by making both ends of a large-diameter metal container (30) smaller in diameter, and glass containers (31) and (32) hermetically sealed together. In this vacuum vessel, a rotating anode (21) supported by a rotor (33) is protruded from one side, and an electron beam (e) held by a cathode support (34) is protruded from the other side.
) A cathode structure for generation (knot) is provided eccentrically and protruding from the tube axis. The rotating anode (21) is made of graphite block (
An anode target (37) made of heavy metal is provided on top of the target (36). Then, X-rays are emitted from the X-ray emission window (38) in the direction of the arrow (X).

The cathode structure includes a thin plate-shaped electron-emitting filament cathode (42) disposed in a bottom recess (41) of a focusing groove (40) formed in a focusing electrode (39).

Four parts (43) and (43) are formed near the filament cathode position of the focusing groove (40), and a pair of electrostatic deflection electrodes (44) and (44) made of metal plates are formed in these recessed parts.
is arranged electrically insulated from the focusing electrode (39). The deflection electrodes (44), (44) extend long along the longitudinal direction of the filament cathode (42) and are disposed facing the electron beam path, and the lead (46) is drawn out by an insulator (45). has been done.

In the operation of this X-ray tube, it is silent! Approximately the same average potential as that of the focusing electrode is applied to the qi deflection electrode, and a deflection voltage is applied to deflect the electron beam, which has an elongated cross section and a strip shape, generated from the filament cathode in a direction perpendicular to its longitudinal direction. As a result, the electron beam focus is approximately on the focal trajectory (47) as shown by the arrow (S) on the anode target.
is moved a predetermined distance along V.

And especially deflection! Since ffi is placed close to the filament cathode inside the focusing groove, it minimizes i.
A deflection force is applied to the beam in a region where the electric field for accelerating the electron beam from the target is relatively low, and a predetermined distance m is applied to the beam with a relatively low deflection voltage.
It can be moved in the s direction. For example, if the cathode-electrode beam acceleration voltage is 100 kV, the distance from the top surface of the focusing electrode to the anode target is 12 mm, and the filament cathode and focusing electrode are operated at the same potential, then the position 0.51 from the filament cathode Position the lower end of the deflection electrode at , and set the distance between both deflection electrodes to 101! lI, the width of the deflection electrode along the beam path is 3nv, and the depth of the focusing groove is 1101I1, then the deflection voltage applied between the pair of deflection electrodes is 19k.
The beam focus on the target is 2.511 to one side at about V
111 deflection movement. Moreover, by making the average potential of the deflection electrode the same as that of the focusing electrode, there is almost no adverse effect on the focusing action of the electron beam.

In the embodiment shown in FIGS. 6 and 7, the focusing groove (40) is formed in a tapered shape as a cathode structure (body), and a ceramic insulating plate (51 ) A pair of deflection electrodes (44) made of a metal film deposited on the negative side of the deflection electrode (44) are arranged so as to face each other. The insulating plate (51) is adhered to and supported by the focusing electrode (39) by an adhesive layer (52) formed around the periphery. Then, the lead (46) is passed through the insulating plate (51) and drawn out to the outside.

The X-ray tube of this embodiment also has the same functions and effects as those of the previous embodiment, and is particularly easy to assemble because the deflection electrode is made of a metal film adhered to an insulating plate.

Note that the insulating plate (51) has a deflection electrode (
44) and the adhesive layer (52) to increase the withstand voltage therebetween.
3) may be formed integrally.

In the embodiment shown in FIG. 9, the focusing electrode (39) is formed into a cup shape by press working as the cathode structure (body).
A recess (4) formed at the bottom of the tapered focusing groove (40)
3), a pair of deflection electrodes (44), (44) are arranged in an insulated manner. At the bottom of this focusing electrode, there is a beam transmission hole (54) with dimensions narrower than the distance between both deflection electrodes.
It is formed. Furthermore, this bottom has a focusing groove bottom recess (
A focusing electrode auxiliary block (39a) on which a filament cathode (42) is arranged is bonded to 41).

As a result, in the focusing groove region including the bottom opening (41) in the focusing electrode, the filament cathode arrangement region and the deflection electrode arrangement region are substantially separated, so that the beam focusing effect is further improved.

The embodiment shown in FIG. 10 uses a coiled filament cathode (42) as the cathode assembly (crosspiece). Moreover, the focusing groove (40) is enlarged in a stepwise manner.

The embodiment shown in FIG.
is deflected and moved along the X-ray emission direction as shown by the arrow (S). This can be done by arranging the filament cathode, focusing groove, and deflection electrode in a longitudinal direction substantially along the tangential direction of rotation of the target. In this case, since the X-ray focal point viewed from the X-ray emission direction is in the form of an elongated line, it is used by arranging it parallel to the longitudinal direction of the slits of the slit plate shown in FIG. Note that the average potential of the electrostatic deflection electrode is not limited to being the same as the potential of the focusing electrode, but a different average potential may be applied as long as it is close to the focusing electrode potential.

Further, the potential of the focusing electrode with respect to the cathode is not limited to the same potential, and the focusing electrode may be operated with a negative potential or a positive potential with respect to the cathode.

〔Effect of the invention〕

As explained above, in the present invention, a pair of electrostatic deflection electrodes for beam deflection are arranged inside the focusing groove of the focusing electrode constituting a part of the cathode structure so as to be electrically insulated from the focusing electrode. This is a variable focal position XM tube characterized by the following characteristics.

And since the deflection electrode is placed on the filament cathode strip inside the focusing groove; a deflection force is applied to the beam in the region where the electron beam acceleration electric field from the anode target is relatively low, and a relatively low deflection voltage is applied to the target. The beam focus can be deflected and moved a predetermined distance. Furthermore, by setting the average potential of the deflection electrode to be the same as or close to that of the focusing electrode, the focusing effect of the electron beam is hardly affected.

In this way, a highly practical variable focal position X-ray tube has the advantage of being manufactured in a shape that is almost the same as the normal rotating anode X-ray tube that has been in practical use.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing an example of an xwall shadow @ installation using the X-ray tube of the present invention, FIG. 2 is a vertical cross-sectional view of essential parts showing an embodiment of the X-ray tube of the present invention, and FIG. Its cross-sectional view, No. 4
The figure is a vertical cross-sectional view of the main part, FIG. 5 is an enlarged perspective view of the main part,
FIG. 6 is a vertical cross-sectional view of main parts showing another embodiment of the present invention, and FIG.
The figure is a perspective view of the main part, FIG. 8 is a cross-sectional view of the main part showing still another embodiment, FIG. 9 is a longitudinal sectional view of the main part showing still another embodiment of the present invention, and FIG. 10 is a still another embodiment. FIG. 11 is a longitudinal cross-sectional view of a main part showing an embodiment, and FIG. 11 is a plan view of a main part showing still another embodiment. (21)... Rotating anode, (29)... Vacuum vessel, (
35) - Cathode structure, (37) Anode target, (38) Xll1I radiation window, (39) Focusing electrode, (40) Focusing groove, (42)... - Filament cathode, (43)... recess, (44)... electrostatic deflection electrode, (51)... insulating plate, (F)... focus,
(S) Focus movement direction, (e)...electron beam, (X
)...X-ray radiation direction. Agent Patent Attorney Noriyuki Chika (and 1 other person) Figure 1 η Figure 2 Figure 4 Figure 5 Figure 6 Figure 8 S2 Figure 9 Figure 10 Figure 11

Claims (3)

[Claims] (1) A cathode assembly including an electron emitting cathode disposed inside a focusing groove formed in an electron beam focusing electrode, and an anode target disposed opposite to the cathode assembly; In a variable focal position X-ray tube configured so that the electron beam generated from the structure is electrically deflected to move the X-ray focal position on the anode target, an electron beam is placed inside the focusing groove of the focusing electrode. A variable focal position X-ray tube, characterized in that a pair of electrostatic deflection electrodes for beam deflection are arranged electrically insulated from the focusing electrode. (2) The variable focal position X-ray tube according to claim 1, wherein the pair of electrostatic deflection electrodes are disposed within a recess formed in a part of the focusing groove of the focusing electrode. (3) The pair of electrostatic deflection electrodes are made of a conductive film deposited on the surface of a ceramic insulating plate, and the ceramic insulating plate is mechanically bonded to a part of the focusing electrode. Variable focus position X-ray tube as described in .