JPH04227237A - X-ray tube for ct device - Google Patents

Abstract

PURPOSE:To provide a compact X-ray tube for CT device which is short in the body axis direction of an inspected person. CONSTITUTION:A fixed cathode 13 having a thermoelectron emission surface 32 in a ring shaped vacuum tube 12, ring-shaped fixed anode 15, and a ring- shaped rotary cathode 14 having a thermoelectron emission surface 49 opposed to the thermoelectron emission surface 32 and a thermoelectron emission part 41 opposed to the fixed anode 15 are arranged, and the thermoelectrons are emitted towards the fixed anode 15 from the thermoelectron emission part 41, revolution-driving the rotary cathode 14 at high speed in floating in the noncontact state at high speed. Since thermoelectrons collide with the fixed anode 15, X-rays are generated towards the center side of a vacuum tube 12. The X-ray emission position shifts at high speed along the peripheral surface of the fixed anode 15, accompanied with the revolution shift of the rotary cathode 14.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention relates to a CT scanner (CT) which can scan the X-ray emission position on the circumference around the subject at high speed.
computerized tomography)
This invention relates to an X-ray tube for equipment.

0002

[Prior Art] An X-ray CT device uses a 360°
X-ray transmission data collected from multiple directions (or 180 degrees) is image reconstructed to obtain an X-ray absorption rate distribution image in a cross section across the subject. be. In order to collect X-ray transmission data in multiple directions with this X-ray CT device, conventionally,
The ray tube itself is rotated by a rotation mechanism to irradiate X-rays from various directions around the subject.

By the way, when rotating the X-ray tube itself in this way, it takes about 1 second to rotate the X-ray tube once or half a rotation to obtain one tomographic image, so cannot collect data. Therefore,
The above imaging method could not be applied to organs such as the heart, whose movements can only be captured with high-speed images of about 30 frames per second.

Therefore, in recent years, an X-ray tube for a CT apparatus has been proposed which can scan the X-ray generation position on the circumference at a very high speed. The configuration of a conventional X-ray tube for a CT apparatus will be described below with reference to FIG. This X-ray tube for a CT apparatus includes a bell-shaped vacuum tube 1, and an electron gun 2 is connected to the base end of the vacuum tube 1. Inside the vacuum tube 1, a deflection coil 3, a deflection electrode 4, and a ring-shaped target 5 are arranged. The electron beam 6 irradiated from the electron gun 2 is deflected by the deflection coil 3 and the deflection electrode 4 and collides with the target 5.
X-rays 7 are irradiated toward the center. By controlling the deflection coil 3 and the deflection electrode 4, the X-ray emission position (focal point) 8 is scanned at high speed along the circumferential surface of the target 5. X-rays 7 are irradiated from various directions around the examiner M,
For example, the imaging time for one frame of image can be set to about 50 msec.

[0005]

However, the conventional example having such a configuration has the following problems. That is, the conventional X-ray tube for a CT device causes the electron beam 6 to travel in a direction perpendicular to the plane formed by the circumference of the ring-shaped target 5, that is, the X-ray generation position 8, and generates electrons during the travel. Because the beam is deflected, the X-ray generator has a very large shape of approximately 4 m in the direction perpendicular to the plane formed by the ring-shaped target 5 (i.e., in the body axis direction of the subject M). turn into. Therefore, there is a problem in that a large space is required to install an X-ray CT apparatus using such an X-ray generator.

[0006] The present invention was made in view of the above circumstances, and it is possible to scan the X-ray emission position on the circumference around the subject at high speed, and moreover, it is possible to scan the X-ray emission position on the circumference around the subject. The object of the present invention is to provide a compact X-ray tube for a CT device with a short axial length.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the present invention has the following configuration. That is, the present invention provides an X-ray tube for a CT apparatus that scans an X-ray emission position on a circumference around a subject at high speed, which includes (a) a ring-shaped vacuum tube, and (b) inside the vacuum tube. (c) a ring-shaped fixed anode disposed within the vacuum tube; (d) a first thermionic emission surface facing the first thermionic emission surface; (e) levitation means for floating the ring-shaped rotating cathode in a non-contact state; (f) the ring A drive means for rotationally moving the mold rotating cathode.

Specifically, a first thermionic emission surface is formed by disposing a filament on the fixed cathode. The fixed cathode does not necessarily have to be ring-shaped; it is sufficient that the fixed cathode has a first thermionic emission surface that faces the first thermionic receiving surface formed on the ring-shaped rotating cathode. Thermionic electrons emitted from the first thermionic emission surface of the fixed cathode enter the first thermionic receiving surface formed on the ring-shaped rotating cathode. In order to reduce the potential difference between the fixed cathode and the rotating cathode, the areas of the first thermionic emission surface and the first thermionic receiving surface facing each other are set as large as possible, and the distance between the two surfaces is set as small as possible. is preferred.

Thermionic electrons incident on the rotating cathode are irradiated from the thermionic emission portion of the rotating cathode toward the fixed anode in terms of current. At this time, the thermionic emission portion of the rotating cathode is heated by appropriate means. Specifically, a filament is provided in the thermionic emission section. The following two methods are exemplified as means for feeding power to the filament.

First, a first group of magnets is provided around the rotating cathode so that the magnetic poles are alternately reversed along the inner wall of the vacuum tube. A first coil group is disposed around the rotary cathode, and the induced electromotive force generated in the coil group when the rotating cathode is rotated at high speed is applied to a filament provided in the thermionic emission section.

Second, a second thermionic emission surface connected to one end of the filament provided in the thermionic emission section is provided around the rotating cathode, and a second thermionic emission surface facing the second thermionic emission surface is provided around the rotating cathode. A second thermionic receiving surface is fixedly installed inside the vacuum tube, a DC high voltage source is connected between the second thermionic receiving surface and the fixed cathode, and the other end of the filament is connected to the first rotating cathode. is electrically connected to the thermionic receiving surface of the vacuum tube, and irradiates the second thermionic emitting surface with a laser beam from the outside of the vacuum tube. Thereby, current from the DC high voltage source is supplied to the filament through the second thermionic receiving surface and the second thermionic emitting surface. Note that, in order to minimize the potential difference between the second thermionic electron emitting surface and the second thermionic electron receiving surface, it is preferable to set the area of each surface as large as possible and to set the distance between both surfaces as small as possible.

[0012] The means for heating the thermionic emission part of the rotating cathode is not limited to the above-mentioned filament; for example, heating may be performed by directly irradiating the thermionic emission part with a laser beam. good.

Thermionic electrons emitted from the thermionic emission section are accelerated by the high voltage electric field between the fixed anode and the rotating cathode and collide with the fixed anode, causing X-rays to be directed from the fixed anode to the center of the ring-shaped vacuum tube. irradiated.

[0014] When the ring-shaped rotating cathode is driven to rotate at high speed by the driving means to be described later, the ring-shaped rotating cathode floats in a non-contact state. This levitation means includes, for example, a second group of magnets arranged around the rotating cathode so that the magnetic poles are alternately reversed, and a second group of coils fixedly installed in the vacuum tube so as to face this group of magnets. Consists of.

The ring-shaped rotating cathode is rotated by a driving means. This driving means includes, for example, a third group of magnets provided around the rotating cathode so that the magnetic poles are alternately reversed, and a third group of magnets provided outside the vacuum tube so as to face this group of magnets, so that the magnetic poles are sequentially switched. and at least one electromagnetic magnet.

The position at which the thermoelectrons emitted from the rotating cathode are accelerated and collides with the fixed anode moves at high speed on the circumferential surface of the ring-shaped fixed anode as the rotating cathode rotates at high speed. As a result, the X-ray emission position can be scanned at high speed around the body axis of the subject inserted into the hollow part of the ring-shaped vacuum tube.

[0017] It is preferable to configure the rotary cathode so that the heat and electric charges accumulated in the rotating cathode are dissipated to the outside while the X-rays are not being irradiated. For example, a bearing is installed at an appropriate location on the fixed cathode or vacuum tube facing the rotating cathode, and when X-rays are not being irradiated, the rotating cathode is driven to rotate at a low speed to release magnetic levitation, and the rotating cathode is heated by the bearing. By making physical and electrical contact with the rotating cathode, heat and electric charges stored in the rotating cathode are dissipated to the outside via the bearing.

[0018]

[Operation] As described above, according to the X-ray tube for a CT apparatus according to the present invention, thermionic electrons emitted from the first thermionic emission surface of the fixed cathode are Thermionic electrons are incident on the thermionic receiving surface of the rotating cathode, and the thermionic electrons are emitted from the thermionic emission part of the rotating cathode toward the fixed anode. At this time, the rotating cathode levitates in a non-contact state within the ring-shaped vacuum tube and rotates at high speed, so that the thermionic collision position on the fixed anode, that is, the X-ray emission position, moves at high speed on the circumference around the subject. is scanned.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the drawings. <First Example> As shown in FIG. 1, C according to this example
The X-ray tube 11 for the T device includes a ring-shaped vacuum tube 12,
Inside each ring-shaped fixed cathode 13 and fixed anode 15
and are arranged. A ring-shaped rotating cathode 14 is disposed between the fixed cathode 13 and the fixed anode 15 so as to be movable in the circumferential direction. Inside the X-ray tube 11,
A ring-shaped X-ray detector 17 is arranged, and these X-ray tubes 1
1 and the detection unit 17 are covered with a ring-shaped gantry 16. The subject M is inserted into the central hollow part of the gantry 16 so that the body axis thereof is approximately perpendicular to the plane formed by the ring-shaped gantry 16.

The vacuum tube 12, the fixed cathode 13, the rotating cathode 14, and the fixed anode 15 inside the vacuum tube 12 will be explained in more detail. FIG. 2 is a radial cross-sectional view of the vacuum tube 12. As shown in FIG. 2, the ring-shaped fixed cathode 13 includes a thermionic emission filament 31 over a wide range of its inner peripheral surface.

Permanent magnet groups 43 and 44 provided on the rotating cathode 14, and coil groups 45 and 46 provided on the inner wall of the vacuum tube 12 and the fixed cathode 13 opposite to these, magnetize the rotating cathode 14 during high speed rotation. It constitutes a means for levitation. The permanent magnet groups 43 and 44 are arranged so that the magnetic poles of each magnet are alternately reversed in the circumferential direction of the rotating cathode 14. The coil groups 45 and 46 are composed of a plurality of small diameter coils arranged around the inner wall of the vacuum tube 12 and the fixed cathode 13 so as to face the permanent magnet groups 43 and 44. When the rotating cathode 14 rotates at high speed, a magnetic flux is generated in the coil groups 45 and 46 that repels the magnet groups 43 and 44 due to the action of electromagnetic induction, so that the rotating cathode 14
magnetically levitates. Furthermore, during low speed rotation, the above-mentioned magnetic levitation force is weakened, and the rotating cathode 14 is supported by electrically and thermally contacting the bearing 48 provided on the vacuum tube 12 and the fixed cathode 13 on the fixed side.

A permanent magnet group 42 provided around the rotating cathode 14 and a plurality of electromagnetic magnets 47 provided outside the vacuum tube 12 facing the magnet group 42 are used to drive the rotating cathode 14 in rotation. constitutes a means of The magnet group 42 is arranged in the circumferential direction of the rotating cathode 14 so that the magnetic poles of each magnet are alternately reversed. By sequentially switching the magnetic poles of each electromagnetic magnet 47, the rotating cathode 14 is rotationally driven by the magnetic force acting between each electromagnetic magnet 47 and the magnet group 42.

The rotating cathode 14 has a thermionic receiving surface 49 facing a wide thermionic emitting surface 32 on which the filament 31 is disposed in the fixed cathode 13, and the spacing between them is set to be very narrow. ing.

Furthermore, the rotating cathode 1 facing the fixed anode 15
A thermionic emission protrusion 41 is provided on the end face of 4 and protrudes so as to be close to the fixed anode 15 . The thermionic emission protrusion 41 has a thermionic emission surface 32 and a thermionic receiving surface 49.
This is for emitting the electron flow supplied from the fixed cathode 13 through the fixed anode 15 toward the fixed anode 15. A filament 50 is provided on the thermionic emission protrusion 41 .

A permanent magnet group 51 is provided around the inner wall of the vacuum tube 12 so that the magnetic poles are alternately reversed, and a coil group 52 is provided around the rotating cathode 14 in opposition to the magnet group 51. It constitutes a means for supplying power to. When the rotating cathode 14 is driven to rotate at high speed, an electromotive force is generated in the coil group 52 due to the action of electromagnetic induction, and this causes the filament 5 in the thermionic emission protrusion 41 to generate an electromotive force.
Heat 0. Note that instead of the permanent magnet group 51 described above, a group of electromagnetic magnets whose magnetic poles are alternately reversed may be provided around the magnet. By arranging such a group of electromagnetic magnets, the magnetic field strength can be changed by controlling the current flowing through each electromagnetic magnet, so that the current flowing through the filament 50 can be made independent of the rotation speed of the rotating cathode 14. be able to.

Thermionic electrons emitted from the thermionic emission protrusion 41 are accelerated from the rotating cathode 14, which is maintained at approximately the same potential as the fixed cathode 13, toward the high-voltage fixed anode 15, and the collision occurs. X from the position to subject M
A line occurs. This fixed anode 15 is cooled by circulation of cooling oil.

When the rotating cathode 14 is rotating at high speed,
While energizing the filament 31, a high voltage is applied between the fixed cathode 13 and the fixed anode 15. The equivalent circuit at this time is as shown in FIG. 3, where the thermionic electrons generated from the filament 31 of the fixed cathode 13 are emitted from the thermionic emission surface 32, and the thermionic receiving surface 49 of the rotating cathode 14 opposite thereto.
received by. This electron stream is then emitted from the heated filament 50 towards the fixed anode 15. In this case, since the fixed cathode 13 has a wide thermionic emission surface 32, the thermionic emission ability is large. Furthermore, since the thermionic receiving surface 49 of the rotating cathode 14 with a large area faces the thermionic emission surface 32 at a narrow interval, the movement of thermionic electrons between these surfaces is easy. stabilizes at a slightly negative potential.

The rotating cathode 14 includes a permanent magnet group 43,
44 and coil groups 45 and 46 and rotated at high speed without contact, the X-ray emission position can be moved at high speed along the circumferential surface of the ring-shaped fixed anode 15. can.

When the electric current to the filament 31 is cut off and the voltage applied between the fixed cathode 13 and the fixed anode 15 is cut off to stop X-ray generation, the rotating cathode 14 is driven to rotate at a low speed. As a result, the force for magnetically levitating the rotating cathode 14 is weakened, and the rotating cathode 14 is supported in contact with the bearing 48. The equivalent circuit at this time is shown in FIG. Due to the contact between the rotating cathode 14 and the bearing 48,
Heat and electric charges accumulated in the rotating cathode 14 during line generation are dissipated to the outside.

This X-ray tube 11 has a ring-shaped fixed cathode 13 and a fixed anode 15 arranged inside a ring-shaped vacuum tube 12, and a ring-shaped rotating cathode 14 is rotated at high speed between them. It is compact and flat in the axial direction of the examinee M's body. Gantry 16 along with detection unit 17
The overall size of the gantry 16 when housed in the gantry 16 is also compact. In other words, conventional popular CT devices require a mechanism to rotate the heavy (approximately 20 kg) X-ray tube, so the gantry tends to be large (as indicated by the dotted line 1 in Figure 1).
8), since only the rotating cathode 14 is rotated in this way, it is possible to make it more compact. Furthermore, the height of the imaging center where the subject M is placed can be reduced from about 95 cm in conventional popular CT apparatuses to about 80 cm.

<Second Embodiment> A second embodiment of the present invention will be described with reference to FIG. In addition, in FIG. 5, each element indicated by the same reference numeral as each reference numeral shown in FIG. is omitted.

The feature of this embodiment lies in the means for feeding power to the filament 50 provided on the thermionic emission protrusion 41 of the rotating cathode 14. That is, the thermionic emission surface 6 connected to one end of the filament 50 provided on the thermionic emission protrusion 41
1 is formed on a rotating cathode 14, and a thermionic receiving surface 62 opposite to this thermionic emitting surface 61 is fixedly installed in the vacuum tube 12. The thermoelectron receiving surface 62 is formed of a transparent electrode. A DC high voltage source E is connected between this thermionic receiving surface 62 and the fixed cathode 13.
1, and the other end of the filament 50 is electrically connected to the thermionic receiving surface 49 formed on the rotating cathode 13. In addition, the code|symbol E2 in FIG. 5 is an alternating current power supply for supplying electricity to the filament 31 of the fixed cathode 13.

In the X-ray tube for a CT apparatus constructed as described above, a high voltage is applied between the fixed cathode 13 and the fixed anode 15 while rotating the rotating cathode 14 at high speed in a non-contact state. Filament 31 of fixed cathode 13
is energized, and a laser beam is irradiated from the outside of the vacuum tube 12 to the thermionic emission surface 61 through the vacuum tube 12 and thermionic receiving surface 62. Since the thermionic emission surface 61 is disposed around the rotating cathode 14, the laser beam is always incident on the thermionic emission surface while the rotating cathode 14 is rotating. As a result, thermoelectrons are emitted from the thermionic emitting surface 32 of the fixed cathode 13 to the thermionic receiving surface 49 of the rotating cathode 14, and the rotating cathode 1
Thermionic electrons are emitted from the thermionic emitting surface 61 of No. 4 to the thermionic receiving surface 62. As a result, a circuit is formed from the DC high voltage source E1 to the thermionic receiving surface 62, thermionic emitting surface 61, filament 50, thermionic receiving surface 49, thermionic emitting surface 32, and then to the DC high voltage source E1, and the filament 50 is energized. The equivalent circuit at this time is shown in FIG. In addition, E3 in the figure is a DC high voltage source connected between the fixed cathode 13 and the fixed anode 15, and SW is a DC high voltage source connected between the fixed cathode 13 and the fixed anode 15. 14 and the fixed cathode 13 are electrically connected to each other.

When the filament 50 is energized, thermionic electrons are emitted from the thermionic emission protrusion 41 toward the fixed anode 15. When the thermoelectrons collide with the fixed anode 15, X-rays are generated toward the center of the vacuum tube 12, and as the rotating cathode 14 rotates at high speed, the X-ray emission position is scanned at high speed in the circumferential direction. , is the same as in the first embodiment.

<Third Embodiment> A third embodiment of the present invention will be described with reference to FIG. The feature of this embodiment is that the rotating cathode 1
As a means for directly heating the thermionic emission section 41 of No. 4,
The reason is that it uses a laser beam. That is, rotating cathode 1
The laser beam is scanned in synchronization with the rotational movement of vacuum tube 1.
It is also possible to emit thermionic electrons from the thermionic emission part 41 toward the fixed anode 15 by irradiating the thermionic emission part 41 with a laser beam from outside of the thermoelectron emission part 2 and heating the thermionic emission part 41. . According to this embodiment, unlike the first and second embodiments, the structure of the vacuum tube 12 is simplified in that there is no need to provide the filament 50 or a mechanism for feeding power to the rotating cathode 14; It is necessary to separately provide a mechanism for scanning the laser beam around the vacuum tube 12.

Although a mechanism for scanning the laser beam is not particularly shown, for example, a laser beam emitted from a single laser light source is sequentially reflected by a plurality of swinging mirrors disposed around the vacuum tube 12. By rotating the rotating cathode 14
Alternatively, a plurality of laser light sources may be arranged around the vacuum tube 12, and these laser light sources may be used in order to irradiate the thermionic emitter 41 with a laser beam. You can do it like this. Note that the other configurations are the same as those in the first embodiment, so the explanation here will be omitted.

[0037]

As described above, the X-ray tube for CT equipment according to the present invention rotates the rotating cathode floating in a non-contact state within the ring-shaped vacuum tube at high speed, so that the X-ray emission position can be easily detected. It is possible to scan the circumference around the person at high speed. Moreover, the ring-shaped vacuum tube is compact and has a short length in the axial direction of the subject's body, so CT equipped with this vacuum tube
The device itself can also be downsized.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view showing a schematic configuration of a CT apparatus using an X-ray tube according to a first embodiment of the present invention.

FIG. 2 is a radial cross-sectional view showing the detailed configuration of the X-ray tube shown in FIG. 1;

FIG. 3 is an equivalent circuit diagram when the first embodiment device is generating X-rays.

FIG. 4 is an equivalent circuit diagram when the device of the first embodiment is not generating X-rays.

FIG. 5 is a radial cross-sectional view showing the detailed configuration of an X-ray tube according to a second embodiment of the invention.

FIG. 6 is an equivalent circuit diagram when the second embodiment device is generating X-rays.

FIG. 7 is a radial cross-sectional view showing the detailed configuration of an X-ray tube according to a third embodiment of the present invention.

FIG. 8 is a vertical cross-sectional view showing a schematic configuration of a conventional X-ray tube for a CT apparatus.

[Explanation of symbols]

11...X-ray tube for CT device 12...Vacuum tube 13...Fixed cathode 14...Rotating cathode 15...Fixed anode 32...(First) thermionic emission surface 41...Thermionic emission part 42...Permanent magnet group (driving means) 43 , 44...Permanent magnet group (levitation means) 45, 46
... Coil group (levitation means) 47 ... Electromagnetic magnet (driving means) 49 ... (first) thermionic receiving surface

Claims (1)

[Claims] 1. An X-ray tube for a CT apparatus that scans an X-ray emission position on a circumference around a subject at high speed, comprising: a ring-shaped vacuum tube; and a first tube disposed within the vacuum tube. a fixed cathode having a thermionic emission surface; a ring-shaped fixed anode disposed in the vacuum tube; a first thermionic receiving surface facing the first thermionic emission surface; and a first thermionic receiving surface facing the fixed anode. A CT characterized by comprising a ring-shaped rotating cathode having a thermionic emission part, a floating means for floating the ring-shaped rotating cathode in a non-contact state, and a driving means for rotationally moving the ring-shaped rotating cathode. X-ray tube for equipment.