JPH06290721A - Rotating anode x-ray tube - Google Patents

Abstract

PURPOSE:To provide cathode structure where a focus position and focus overlap are nearly changed before and after a filament of an X-ray tube is heated. CONSTITUTION:A grove 9 having a width of about 0.2-0.3mm is formed on the center of a focusing body 1, thus weakening rigidity in the center of the focusing body. Accordingly, thermal expansion influence of the focusing body generated by heating a filament is concentrated on the groove 9 in the center, thereby restraining a change in angle of the focusing body. Consequently, a focus position and coincidence thereof are nearly unchanged before and after the filament is heated, resulting in remarkable reduction of artifact on a CT image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a rotary anode X-ray tube,
In particular, it relates to an improvement in the cathode focusing structure.

[0002]

2. Description of the Related Art FIG. 3 shows an example of conventional technology. FIG. 3 shows a cross section of the focusing portion of the cathode of the X-ray tube (direction perpendicular to the longitudinal direction of the focusing groove) with the portion facing the anode facing downward. In FIG. 3, a focusing groove 7 is bored in the focusing body 1, and the coil portion 3a of the filament 3 is arranged in the focusing groove 7. Filament 3 connected to anchor 4
It is supported and fixed to the focusing body 1 via the insulator 5. A focusing body cover 2 is attached to the outer periphery of the focusing body 1, and both are fixed and held by a cathode (not shown) of the X-ray tube. The focusing body 1 and the focusing body cover 2 are coupled to each other by connecting the end portion 1a of the base portion of the focusing body 1 and the large-diameter inner peripheral portion 2a of the focusing body cover 2 to each other.
Are welded together, but the end portion 1b on the front surface (focusing groove side) of the focusing body 1 and the end portion 2 of the small-diameter inner peripheral portion of the focusing body cover 2
Not particularly fixed with b, but with some clearance for assembly convenience
(About 0.1 mm) is open.

An X-ray tube generally has a plurality of filaments 3, and thermoelectrons emitted from these filaments 3 are accelerated by a high voltage applied between the cathodes and anodes in the X-ray tube to be a target of a rotating anode (not shown). No.) and forms a focal point as an X-ray source. FIG. 3 shows an example in which there are two filaments 3. Each filament 3 is heated separately and the focal point on the target is also formed separately. In the X-ray tube, when two focal points are formed on the target, it is desirable that the center positions of the focal points be the same. This is because when the focal points are switched and X-ray irradiation is performed, if the center positions of both focal points are deviated, the X-ray dose distribution received by the light receiving system for detecting X-rays is also deviated.
Furthermore, if a focus is inserted between the light receiving system (for limiting the X-ray exposure range), the influence of the deviation of the X-ray dose distribution will be magnified, and X-ray reception will not be performed properly. .

Further, the orbit of the thermoelectrons emitted from the filament 3 is influenced by the shape and size of the focusing groove 7, the focusing angle 8 on the front surface of the focusing body 1, and so on, so that the focus position is adjusted appropriately. Is the shape and size of the focusing groove 7 and the focusing body angle 8
Are properly combined.

[0005]

The conventional X-ray tube is replaced with an X-ray C
When used in combination with the T-device, the center position of the focal point of the X-ray tube moves with the passage of use time, the positional relationship between the focal point and the X-ray detector shifts, and the X-ray dose received by the X-ray detector changes over time. It can change, resulting in artifacts in the CT image.

In order to clarify the cause of this, the change in focal overlap with time was examined with an X-ray tube having two focal points.
The result is shown in FIG. In FIG. 4A, the horizontal axis represents the focusing body angle, and the vertical axis represents the focus overlap. The graph shows the case where the focusing body is in a cold state (black circle) and the case where it is in a hot state (white circle). The case where the focusing body is in a cold state means that the focusing body is in the initial state of the load application to the X-ray tube when the focusing body is not at a high temperature yet, and indicates the initial state of the focusing body temperature. Is. The case where the focusing body is in a heated state means the focus overlapping when the focusing body reaches a sufficiently high temperature after continuously applying a load to the X-ray tube. It is shown.

FIG. 4 (b) shows how the thermoelectrons emitted from the two filaments of the cathode are focused by the focusing body and collide with the target of the anode to form a focal point. As an example of the electron beam from the filament, a, b,
3 types of c are shown. The focus overlap in the case of the electron beam a is the focus overlap A shown, and the electron beams emitted from the large and small filaments intersect before colliding with the target, and the overlap of the large and small focal points is excessive. It is shown that. The focus overlap in such a state is shown by a + (plus) dimension. In the case of an electron beam, the electron beams emitted from the large and small filaments collide with each other at the same point on the target, so that they show ideal focus overlap. Therefore, the focus overlapping dimension at this time is shown as 0. The focus overlap in the case of the electron beam c is the focus overlap c shown in the figure, and the electron beams emitted from the large and small filaments do not cross (before crossing after passing through the target surface) before colliding with the target. There is no agreement above, indicating that there is insufficient overlap of large and small focal points. The focus overlap in such a state is shown by the- (minus) dimension.

In FIG. 4 (a), it can be seen that the focus overlap changes according to changes in the cold / heat state of the focusing body.
In the case of the same focusing body angle, the focal point overlap in the heat state of the focusing body is smaller than the value in the cold state, and when this is seen on the graph in the cold state, it coincides with that when the focusing body angle 8 is large. There is. This result suggests that as the focus changes from a cold state to a hot state, the focus angle 8 increases, thereby reducing the focus overlap. This can be said when considering the thermal change in the size of the focusing body. When a load is applied to the X-ray tube, the heat generated by filament ignition heats the focusing body 1, and the focusing body 1 rises in temperature. The heat from the filament enters the filament peripheral portion of the focusing body 1 (the lower side of the focusing body 1 in FIG. 3) and conducts heat to the part of the focusing body 1 away from the filament (the upper side of the focusing body 1 in FIG. 3). Go.
Therefore, when the focusing body 1 is heated, the lower side of the focusing body 1 has a high temperature and the upper side of the focusing body 1 has a low temperature.
A temperature difference occurs between the two. As a result, since the lower side of the focusing body 1 has a larger thermal expansion than the upper side of the focusing body 1,
The lower side of the focusing body 1 expands, and the focusing body angle 8 increases.

From the above, according to the present invention, the focus position is prevented from becoming large even if the focus body is in a heat state, and the focus position does not change even when the load of the X-ray tube is applied for a long time. Intended to provide a tube.

[0010]

In order to achieve the above-mentioned object, the present invention provides a plurality of filaments forming a plurality of focal points, and a focusing body having a plurality of focusing grooves for focusing the thermoelectrons emitted from the filaments. A cathode having a focusing body cover for focusing the thermoelectrons in the longitudinal direction of the filament, and a target radiating X-rays upon receiving the thermoelectrons from the filament and rotatably supported by a bearing. A rotary anode X-ray tube hermetically sealed with an anode by a valve is provided with a notch groove in the middle of the focusing groove of the focusing body substantially parallel to the length direction of the focusing groove from the focusing groove surface side. The gap between the focusing grooves is made and the rigidity between the focusing grooves is weakened.

In addition to the above, in the outer periphery of the focusing body, among the gaps between the focusing body and the focusing body cover,
A plurality of thin plate pieces having good thermal conductivity are inserted into a portion of the surface of the focusing groove which is perpendicular to the focusing groove to improve the heat conduction of the portion.

[0012]

The operation of the present invention will be described with reference to FIGS. In FIG. 1 and FIG. 2, the rigidity of the central portion of the focusing body is weakened by the groove 9 cut in the central portion of the focusing body 1.
The plane A is easy to bend. Further, since the thermal expansion of the lower part of the focusing body is configured to extend to 1c, the focusing body 1
There is almost no change in the converging body angle due to thermal expansion.

Further, as shown in FIG. 2, since the focusing body 1 and the focusing body cover 2 are fixed on both upper and lower sides, the radiant heat from the filament flowing into the lower portion of the focusing body is covered by the shim 6 and the welded portion. The temperature is lower in the lower part of the focusing body than in the conventional case, and the entire focusing body undergoes more uniform thermal expansion, so that the degree of expansion is not biased between the upper part and the lower part of the focusing body.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will now be described with reference to FIG.
This will be described with reference to FIG. FIG. 1 is a view showing a cross section of a cathode head according to an embodiment of the present invention. In the figure, the lower part is the side facing the anode. The focusing body 1 has two focusing grooves 7 at the bottom.
In the focusing groove 7, the coiled filament 3 supported by the anchor 4 is arranged. The anchor 4 is supported by the focusing body 1 via an insulator 6. The focusing groove 7 of the focusing body 1 is inclined by a focusing body angle 8 in order to focus the thermoelectrons emitted from the two filaments 3 at the same point on the target surface (not shown) of the anode. In the middle of the two focusing grooves 7, a narrow groove 9 is provided in parallel with the focusing groove 7. Groove 9
Has a width of 0.2 to 0.3 mm and a depth of 0.5 mm or more from the plane A portion of the focusing body 1, and by providing this groove 9, it is perpendicular to this groove 9 of the focusing body 1. The rigidity in the direction can be weakened. The outside of the focusing body 1 is covered with the focusing body cover 2
In the lower part of the figure, a fitting clearance is provided, and in the upper part of the figure, they are fixed by spot welding or the like (for example, a point where 1a and 2a are in contact with each other). The above fitting clearance is about 0.1 mm (clearance between 1b and 2b). In the cathode head of the X-ray tube configured as described above, when the filament 3 is energized and heated, the lower portion of the focusing body 1 shown in FIG. 1 is heated (further, if the target is heated by applying a load to the X-ray tube). The radiation heat also heats the periphery of the focusing groove 7 of the focusing body 1 due to the heat. In the case of the present invention, since the groove 9 is provided between the two converging grooves 7 to weaken the rigidity of this portion, the amount of expansion due to the thermal expansion is the groove 9.
As it extends to the side, the plane A portion of the focusing body 1 bends in the direction of the arrow, and as a result, the change in the focusing body angle 8 becomes very small.

FIG. 2 shows another embodiment of the present invention. Similar to the above-described embodiment, a narrow groove 9 is provided in the middle of the focusing groove 7 of the focusing body 1, and the gap between the lower portion of the focusing body 1 and the lower portion of the focusing body cover 2 (gap between 1b and 2b). ), The shim 6 is inserted and fixed. Shim 6 is 0.1-0.2
Made of a material with a thickness of mm and good thermal conductivity, brazing, welding,
Secure by press fitting. With the above configuration, the heat flowing into the lower portion of the focusing body 1 is conducted to the focusing body cover 2 through the shim 6, so that the temperature rise of the lower portion of the focusing body 1 is suppressed, and its thermal expansion. Is also alleviated, and the effect of suppressing changes in the focusing body angle 8 is greater than that of the configuration of FIG.

In FIG. 2, an example in which the shim 6 is inserted between the lower part of the focusing body 1 and the lower part of the focusing body cover 2 is described.
A similar effect can be obtained by welding between 1b and 2b in FIG.

[0017]

According to the present invention, the focus position and the focus overlap are almost eliminated in a state where the focusing body is not heated immediately after the X-ray tube is actually operated and a state where the focusing body is heated and thermally expanded after the actual operation. Since it is possible to provide a focusing body that does not change much, it is possible to drastically reduce the artifacts in the X-ray CT image.

[Brief description of drawings]

FIG. 1 shows a sectional view of a cathode head according to an embodiment of the present invention.

FIG. 2 shows a cross-sectional view of a cathode head according to another embodiment of the present invention.

FIG. 3 shows a cross-sectional view of a conventional cathode head.

FIG. 4 is a diagram showing a relationship between a focus angle and a focus overlap.

[Explanation of symbols]

 1 Focusing Body 2 Focusing Body Cover 3 Filament 6 Shim 7 Focusing Groove 8 Focusing Body Angle 9 Groove

Claims (2)

[Claims] 1. A plurality of filaments forming a plurality of focal points, a converging body having a plurality of converging grooves for concentrating thermoelectrons emitted from the filament, and a converging body for concentrating the thermoelectrons in the longitudinal direction of the filament. The cathode provided with a cover and thermions received from the filament emit X-rays,
And, in a rotating anode X-ray tube in which an anode provided with a target rotatably supported by a bearing is hermetically sealed by a valve, in the middle of the focusing groove of the focusing body, substantially parallel to the length direction of the focusing groove. A rotary anode X-ray tube characterized in that a notch groove is provided on the focusing groove surface side to form a gap between the focusing grooves and weaken the rigidity between the focusing grooves. 2. A plurality of heat conducting members are provided on the outer periphery of the converging body at a portion of the gap between the converging body and the converging body cover, which is on the side of the converging groove surface and in the direction perpendicular to the converging groove. Rotating anode X according to claim 1, characterized in that means for improving it are inserted.
Line tube.