JPH04355037A - Rotary cathode x-ray tube device - Google Patents

Abstract

PURPOSE:To set up an electromagnet in the inside of a vacuum vessel in a condition that the electromagnet, which supports a rotary cathode magnetically levitated, is X-ray shielded and magnetically shielded. CONSTITUTION:Separating rings 11a, 11b of L-shaped section are mounted right/left symmetrically with a rotary cathode 7, arranged in a vacuum vessel 1, serving as the center to divide the inside of the vacuum vessel 1 into two inner/outer chambers. The separating rings 11a, 11b are formed of ferrite stainless steel having together both magnetic shield and X-ray shield effects. An electromagnet 12 is mounted to the outer chamber A to mount an X-ray generating anode target 7 and filament 8 to the divided inner chamber B.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is used in an X-ray CT apparatus that performs tomography of a subject. The present invention relates to a rotating cathode X-ray tube device that irradiates X-rays from the entire circumference of a specimen.

0002

2. Description of the Related Art A partial cross section of a conventional rotating cathode X-ray tube device is shown in FIG. 5 and will be described below. A ring-shaped anode target 41 and a rotating cathode 42 are arranged to face each other inside a ring-shaped vacuum container 40 . The anode target 41 is installed and fixed on the inner peripheral wall surface of the vacuum container 40,
The rotating cathode 42 is supported in a magnetically levitated state by an electromagnetic magnet 43 attached to the outer peripheral wall of the vacuum container 40 .

Rotating cathode 4 facing anode target 41
A filament 44 that emits thermoelectrons for generating X-rays toward the anode target 41 is attached to the surface of 2.
By rotating the rotating cathode 42 with the stator 45, thermionic electrons are irradiated over the entire circumference of the anode target 41, and X-rays are irradiated from the entire circumference direction onto the subject carried into the cavity of the vacuum container 40. It has become.

0004

However, in the conventional rotating cathode X-ray tube device, since the electromagnetic magnet 43 for magnetically levitating the rotating cathode 42 is attached to the outer wall of the vacuum vessel 40, the following problems occur. There was a problem.

(a) The rotating cathode 42 must be magnetically levitated through a gap between the vacuum vessel 40 and the rotating cathode 42 and the outer wall of the vacuum vessel 40. In order to compensate for the attenuation of the magnetic field strength for levitation during that time, electromagnetic magnet 4
It is necessary to increase the power supplied to 3. Additionally, due to the distance, it was difficult to perform delicate (highly accurate) magnetic control. (b) In consideration of the above, in order to bring the distance between the rotating cathode 42 and the electromagnetic magnet 43 as close as possible, the electromagnetic magnet 43 is attached as shown in FIG. 6, for example.

[0006] That is, the iron core 4 formed in a "U-shape"
Both ends of an iron core 46 of an electromagnetic magnet 43 configured by winding an insulating coated coil wire 47 around a vacuum vessel 4
Install it by embedding it in the outer wall of 0. Although this reduces the distance between the electromagnetic magnet 43 and the rotating cathode 42 a little, it is difficult to process the vacuum container 40 for embedding, and it becomes impossible to obtain sufficient mechanical strength. The interior of the vacuum container 40 is kept at a fairly high degree of vacuum in order to generate X-rays, and a considerable external force is applied to the vacuum container 40 due to the pressure difference with the outside atmospheric pressure. The vacuum container 40 is required to have mechanical strength to withstand this and prevent deformation.

(c) The vacuum vessel 40 is made of non-magnetic stainless steel (austenitic stainless steel, the steel type is SUS3).
16, etc.), but the material may change due to the heat generated during the above-mentioned embedding process, and that part may have the properties of a magnetic material. When the material is changed to a magnetic material, the strength of the magnetic field from the electromagnetic magnet 43 is significantly attenuated in that part, causing the problem shown in (a) above again.

The present invention has been made in view of the above circumstances, and is intended to facilitate magnetic control for levitating a rotating cathode, to simplify the manufacture of a vacuum container, and to improve a vacuum container machine. An object of the present invention is to provide a rotating cathode X-ray tube device that can improve the optical strength.

[0009]

[Means for Solving the Problems] In order to achieve the above object, the present invention has the following configuration. That is, the present invention includes a ring-shaped anode target installed and fixed in a ring-shaped vacuum container, and a ring-shaped rotating cathode equipped with an electron emitting part that emits an electron beam for generating X-rays toward the anode target. In a rotating cathode X-ray tube apparatus, the interior of the vacuum vessel is divided into two internal and external chambers by a pair of left and right annular members attached to sandwich the rotating cathode. The anode target and the electron emitting part are arranged in an inner room, the electromagnetic magnet is arranged in an outer room, and the annular member is configured to be able to shield X-rays and magnetism. It is characterized by

0010

[Operation] According to the present invention, the inside of the vacuum container is separated into two chambers, an inner chamber and an outer chamber, using an annular member that shields X-rays and magnetism.
Since the electromagnetic magnet that magnetically supports the rotating cathode is arranged in the outer room, the distance between the electromagnetic magnet and the rotating cathode is extremely close. In addition, since the annular member shields X-rays and magnetism, even if an electromagnetic magnet is installed inside a vacuum container, the magnetic field will not affect the generation of X-rays, and conversely, the generated It has no effect on the

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a partial cross-sectional view of a rotating cathode X-ray tube device. A vacuum vessel 1 serving as a casing of an X-ray tube has two ring plate-shaped outer plates 2a and 2b, whose outer peripheries are connected by an annular outer ring plate 3, and whose inner peripheries are connected by an annular inner ring plate 4. It is formed by

A ring-shaped anode target 6 is installed and fixed on the inner wall of the outer plate 2a through a plurality of insulating insulators 5 attached along its circumferential direction, and a rotating cathode is placed opposite to the anode target 6. 7 is placed. rotating cathode 7
The outer periphery of the anode target 6 is formed into a flange shape, and a filament 8 for emitting thermionic electrons is attached to the flat surface facing the anode target 6. Note that the rotating cathode 7 has a structure in which a cavity is formed in the flange-shaped portion in order to reduce its weight.

A stator 9 for rotationally driving the rotating cathode 7 is attached to the outer peripheral surface of the outer ring plate 3, and the inner ring plate 4 transmits X-rays generated from the thermionic irradiation point of the anode target 6 to the vacuum vessel. An annular X-ray transparent window 10 leading into the cavity 1 is attached. The X-ray transmitting window 10 is made of aluminum that transmits X-rays, and the other parts of the inner ring plate 4, the outer ring plate 3, and the outer plates 2a and 2b are made of stainless steel (austenitic stainless steel) that blocks X-rays. It is made of steel (such as SUS316).

[0014] Between each of the outer plates 2a, 2b and the outer ring plate 3, there is an "L-shaped" cross-sectional shape that is symmetrical about the rotating cathode 7.
Separation rings 11a and 11b are supported with their upper ends sandwiched between them. The separation rings 11a and 11b are made of stainless steel (ferritic stainless steel, the steel type is SUS43), which shields X-rays and also has a magnetic shielding effect.
0), and both are attached with a slight gap G between them from each of the outer plates 2a and 2b. The interior of the vacuum container 1 is divided into two internal and external chambers by these separation rings 11a and 11b.

The above-mentioned anode target 7 and filament 8 are arranged in the divided inner B room, and an electromagnetic magnet 12 for magnetically supporting the rotating cathode 7 is attached to the outer A room. The electromagnet 12 is the separation ring 1
It is constructed by winding a coil wire 14 coated with insulation around two iron cores 13 attached to the side surfaces of the separation rings 11a and 11b. pcs installed.

As described above, since the electromagnetic magnet 12 that supports the rotating cathode 7 by magnetic levitation is installed inside the vacuum vessel 1, the end of the iron core 13 of the electromagnetic magnet 12 must be placed close to the rotating cathode 7. Can be done. Therefore, a relatively small amount of electric power is required to be supplied to the electromagnetic magnet 12, and the attenuation of the strength of the magnetic field generated from the electromagnetic magnet 12 is also small, so that highly accurate magnetic control can be performed relatively easily. In addition, it is not necessary to perform special processing on the outer plates 2a and 2b of the vacuum vessel 1 in order to bring the electromagnetic magnet 12 closer to the rotating cathode 7 as in the conventional example described above.
The production of the wire tube device is simplified, and the mechanical strength of the vacuum container 1 is not reduced.

Furthermore, since the separating rings 11a and 11b are configured to shield X-rays and magnetism, the following disadvantages that occur when the electromagnetic magnet 12 is installed inside the vacuum container 1 are solved. be able to. (1) The X-rays generated within the vacuum vessel 1 are also exposed to the electromagnetic magnet 12, deteriorating the insulating material covering the coil wire 14. This may cause electrical discharge to occur between the coil wire 14 and the iron core 13, which may destroy the electromagnetic magnet 12. (2) The magnetic field generated from the electromagnetic magnet 12 distorts the trajectory of the thermionic beam from the filament 8 toward the anode target 6, causing a shift in the X-ray focal point (X-ray generation point), leading to a decrease in the image quality of the CT image. .

Furthermore, as in this embodiment, the outer panels 2a, 2
When a gap G is provided between the separation rings 11a and 11b, an external force is applied to the vacuum vessel 1 due to the pressure difference between the vacuum pressure inside the vacuum vessel 1 and the atmospheric pressure outside the vacuum vessel 1, causing distortion and deformation. Even if the deformation force occurs, the deformation force
1b and the position of the electromagnetic magnet 12 is not changed, so magnetic control is stabilized. In other words, the relatively thin outer panels 2a and 2b allow some deformation.
The vacuum vessel 1 can be designed to reduce the weight of the X-ray tube device.

Note that in the above embodiment, the separated rings 11a,
11b is made of stainless steel (steel type: SUS430) that has the property of shielding X-rays and magnetism, but it is also possible to make it of other materials. However, in this case, A
Iron foil as a magnetic shielding material is pasted on the room side, and lead foil for shielding X-rays is pasted on the B room side where the anode target 6 and filament 8 are arranged.

By the way, when the electromagnetic magnet 12 is installed in the vacuum container 1 as in the present invention, in addition to the effects of the above-mentioned X-rays and magnetism, this is formed as the temperature of the electromagnetic magnet 12 increases. There is a concern that the substance will vaporize and the vapor pressure will deteriorate the degree of vacuum within the vacuum container 1. To solve this problem, room A and room B may be evacuated separately, but this poses problems such as operating costs. Therefore, as another embodiment, a rotating cathode X-ray tube device with a simple configuration and which does not prevent deterioration of the degree of vacuum will be described below.

<First Alternative Embodiment> FIG. 2 is a front view of a rotating cathode 7 according to the first alternate embodiment, and FIG. 3 is a cross-sectional view taken along line A--A. In this example, a ring plate 21 on which wings 20 are formed is attached to both flat side surfaces of the rotating cathode 7, particularly at positions facing the separation rings 11a and 11b. The blades 20 are convex portions of an uneven portion formed by alternately forming grooves 22 on the surface of a ring plate 21. As shown in FIG. 2, for example, the shape of the groove 22 is such that when the rotating cathode 7 rotates in the rotation direction R, an airflow is generated toward the outside of the rotating cathode 7 (in the direction of the arrow). That is, the rotational force of the rotating cathode 7 is used to form an airflow from the lower room B to the upper room A, thereby preventing the vapor gas from leaking from room A where the electromagnetic magnet 12 is installed to room B. This prevents the deterioration of the vacuum level in Room B, which generates X-rays.

<Second Alternative Embodiment> FIG. 4 shows a sectional view of a rotating cathode 7 according to a second alternative embodiment. In this example, an annular magnetic body 30 is attached to a portion of the rotating cathode 7, and annular permanent magnets 31 and 32 of opposite polarity are arranged at positions sandwiching the magnetic body 30. The magnetic body 30 is integrated with the rotating cathode 7 by a bolt 33 screwed into the cavity of the rotating cathode 7, and the permanent magnets 31, 32 are attached to the separating rings 11a, 11b at the bottom of the flange shape. Then, permanent magnets 31, 32 and magnetic body 30
A magnetic fluid 34 is interposed to fill the gap between the two.

The magnetic fluid 34 is a colloidal solution in which fine particles of ferromagnetic material are stably dispersed in an organic solvent.
, 32 and the magnetic body 30, it functions as a pressure seal. That is, since room A, where the electromagnet 12 is arranged, and room B, which generates X-rays, are completely sealed by the magnetic fluid 34, steam gas from room A can enter room B and cause There is no possibility that the degree of vacuum will deteriorate. Also, permanent magnet 3
Since the permanent magnets 31 and 32 are installed on the A room side which is magnetically separated from the B room by the separation rings 11a and 11b, the magnetic force of the permanent magnets 31 and 32 does not affect X-ray generation.

[0024]

Effects of the Invention As is clear from the above explanation, the rotating cathode X-ray tube device of the present invention has an electromagnetic magnet that supports the rotating cathode by magnetic levitation installed inside the vacuum vessel. It becomes possible to arrange it as close as possible to the cathode. This brings about the following effects. (1) Compared to conventional devices, the magnetic field strength required to magnetically levitate the rotating cathode can be somewhat lowered, and the power supplied to the electromagnetic magnet can be reduced accordingly. In addition, since the magnetic field strength acts on the rotating cathode with almost no attenuation, there is no need to take into account the magnetic field correction for the attenuation.
High-precision magnetic control can be performed relatively easily. (2) Unlike conventional devices, there is no need to perform special processing on the vacuum container to bring the electromagnet closer to the rotating cathode, which simplifies the production of the X-ray tube device and improves the mechanical strength of the vacuum container. It is also possible to improve the When installing an electromagnetic magnet that exhibits this effect inside a vacuum container, the interior of the vacuum container is separated into two chambers using an annular member that mutually shields X-rays and magnetism, and one chamber is equipped with an electromagnetic magnet. Since the magnet is provided, the magnetic field generated from the electromagnetic magnet does not affect X-ray generation, and the X-ray generated within the vacuum container does not affect the electromagnetic magnet.

[Brief explanation of drawings]

FIG. 1 is a partial sectional view of a rotating cathode X-ray tube device according to an embodiment of the present invention.

FIG. 2 is a front view of a rotating cathode according to a first alternative embodiment of the invention.

FIG. 3 is a sectional view taken along line AA in FIG. 2;

FIG. 4 is a partial cross-sectional view of a rotating cathode according to a second alternative embodiment of the invention.

FIG. 5 is a partial cross-sectional view of a conventional rotating cathode X-ray tube device.

FIG. 6 is a simplified side view showing an example of attaching an electromagnetic magnet in a conventional example.

[Explanation of symbols]

1...Vacuum container 6...Anode target 7...Rotating cathode 11a, 11b...separated ring 12...Electromagnetic magnet

Claims (1)

[Claims] Claim 1: A ring-shaped anode target installed and fixed in a ring-shaped vacuum container, and an
In a rotating cathode X-ray tube apparatus that includes a ring-shaped rotating cathode equipped with an electron emitting section that emits an electron beam for generating radiation, and an electromagnetic magnet that supports the rotating cathode by magnetic levitation, the inside of the vacuum vessel is , separating the rotating cathode into two inner and outer chambers by a pair of left and right annular members attached to sandwich the rotating cathode, and arranging the anode target and the electron emission part in the inner chamber;
A rotating cathode X-ray tube device, characterized in that the electromagnetic magnet is disposed in an outer chamber, and the annular member is configured to shield X-rays and magnetism from each other.