JPH0326497B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a high-output, large-capacity X-ray tube.

[Technical background of the invention]

Generally, an X-ray tube has a structure as shown in FIG. That is, 1 is a cathode, and the cathode 1 is equipped with a coil-shaped filament 2 that generates thermoelectrons. Electrons emitted from the filament 2 are focused by a focusing electrode 3 and applied between the cathode 1 and anode 4. The electrons are accelerated by the applied high voltage, and are caused to collide with the slope of a truncated cone-shaped target 5 made of heavy metal provided at the end of the cathode 1 of the anode 4, thereby converting them into X-rays. It is designed to emit X-rays.

The point of collision of accelerated electrons on the target 5 is called an X-ray focal point, and since this focal point becomes red-hot due to the collision of electrons, the anode 4 is generally of a rotating type and the target 5 is rotated. 5
Prevent only one point from becoming red hot.

However, if X-rays are emitted for a long period of time, the entire target 5 will become extremely hot and eventually melt, leading to damage to the X-ray tube. Therefore, each X-ray tube has a heat capacity called a heat unit (HU). The conditions of use are determined by the rated value. In other words, the maximum allowable HU is an index indicating the maximum heat capacity that the X-ray tube can allow, and the HU value that accumulates at one time is determined by the tube voltage x tube current x time, and the HU value is determined by the heat dissipation characteristics of the target. × HU value for downtime is X
It recovers during the period when the tube is not exposed to radiation. Therefore, the safety of the X-ray tube is guaranteed if X-rays are irradiated within a range that does not reach the maximum allowable heat unit value.

By the way, in recent years coronary angiography or X-ray CT
The number of X-ray devices that require high-output X-rays continuously for long periods of time has increased.

For example, in the case of coronary angiography, it is necessary to continuously apply 60 to 120 X-ray pulses per second for 7 seconds under the X-ray exposure conditions of 80 KV, 400 mA, and 4 msec, and repeat this approximately 7 times at 3-second intervals.

Furthermore, as for X-ray photographs, the smaller the focal point of the X-ray tube, the smaller the penumbra of the X-rays, and therefore the sharper the photograph can be taken. Currently, focal lengths of 1.2 mm square are mainly used, but ideally a focal length of 0.6 mm square or less is desirable.

However, as the focal point becomes smaller, the current density per unit area on the X-ray tube target increases, and the heating temperature of the focal portion of the target rapidly increases due to electron bombardment from the cathode, making it impossible to withstand the heat generated.

One of the things that limits the X-ray output is the current density per unit area.

The following methods can be used to solve this problem.

(1) Increasing the diameter of the rotating anode (target); (2) Increasing the rotation speed of the rotating anode (target). This is due to the following relationship between the X-ray output and other factors. That is, P=KL ^3/2 d ^1/2 n ^1/2 where P is the output, K is the proportionality constant, L is the focal spot size, d is the focal orbit diameter, and n is the anode rotation speed.

Here, the center of the focal trajectory is approximately from the outer edge of the target.
10mm inside. Therefore, it can be considered that it is proportional to the target diameter.

Currently, the maximum target diameter is generally 125 mm, and experimentally 150 mm or larger diameters have been created. However, even if the diameter is set to 150mm,
The output is only 10% higher than that of the 25mm tube, and even though it is larger, it is not possible to obtain an X-ray tube with a large heat capacity.

The anode rotation speed is generally 3000r.pm or 9000r.pm. Some prototypes are in the 18000r.pm class.

However, as shown in FIG. 1, the anode target is supported only on one side, and rotating the anode target at high speed in this state causes severe wear on the support, making it difficult to extend the life of the anode.

Another factor that limits the x-ray output is the heat capacity of the target.

This relationship is shown in FIG.

FIG. 2 schematically shows how the accumulated HU of the target changes as a result of repeated fluoroscopy using an X-ray TV device and coronary angiography.

To explain the figure, first, a is the starting point of perspective.

Since the X-ray tube output for fluoroscopy is approximately 80KV1mA continuous, the target temperature rises slowly.

This is the part where coronary angiography is performed, and the input at the time of imaging is as shown above.
80KV40mA4msec, which is a very large instantaneous value.

For this purpose, the temperature of the focal point of the target is 3000
It will be around ℃. When this value reaches the melting point of tungsten, the target constituent material, 3380°C, the tungsten melts and the tube is destroyed. Furthermore, if the melting point is not reached, but close to it, tungsten evaporates from the surface significantly, which impairs the life of the X-ray tube. Therefore, during regular use, it must be used at temperatures below 3000℃. This is the maximum allowable heat capacity value.

From is full voltage off, from is fluoroscopic period,
This is the period during which X-ray exposure for photographing is repeated. If this is repeated several times, the amount of heat accumulated in the entire target increases, and therefore the average temperature of the entire target increases.

If this temperature rises, the base temperature will rise, and the focal point temperature of the target will also rise when photographing.

In other words, from the above, the factors that constrain the output are (1) the allowable average heat storage amount, and (2) the maximum allowable heat capacity value.

Of these, (2) is related to instantaneous input, so it can be improved by changing the anode rotation speed and anode diameter.

However, since (1) is related to the average input, it is necessary to increase the heat capacity of the target and improve the cooling rate of the target.

The easiest way to increase heat capacity is to increase the target volume, which is 200 KH.U (unit of heat capacity HU =
Gradual improvement is expected from KW×sec) to 400KH.U and 700KH.U. This means increasing the thickness for the same target diameter.

However, a mere increase in thickness leads to an increase in weight and imposes a heavy load on the bearings of the rotation mechanism of the target, so there is a natural limitation.

For this purpose, attempts have been made to partially change the material of the target to one with low specific gravity and high specific heat.

One example is a tungsten target, (1) a tungsten-molybdenum bonded target, (2) a tungsten-graphite bonded target, and (3) a tungsten-molybdenum-graphite bonded target.

However, these cannot be made unnecessarily large due to constraints on shape, and it is natural that there are constraints.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an X-ray tube that has a large heat capacity, is not subject to many restrictions on the conditions during X-ray output, and can be miniaturized. shall be.

[Summary of the invention]

That is, in order to achieve the above object, the present invention has both ends rotatably supported by a support member provided in a housing forming an X-ray tube, a rotor is formed near at least one end side, and a rotor is formed in the vicinity of at least one end. a first shaft having a shaft gear formed thereon; and a cylindrical first shaft provided on the outer peripheral side of the first shaft;
A shaft gear that meshes with the shaft gear is formed on the inner surface,
Further, a second shaft having a cylindrical X-ray conversion target constituting an anode in the center of the outer side and a rotor formed near at least one end side, and a second shaft supported by the housing and provided with the The first, second By creating a difference in the rotational speed of the second shaft, the second shaft is moved and rotated in the axial direction by the action of the shaft gear of each shaft, and thereby the electrons emitted from the target cathode are The locus of the collision point is spiral, thereby preventing the same part from being constantly heated, and also making it possible to provide strong support by supporting the first shaft at both ends, making it possible to increase the volume of the target. The aim is to increase the heat capacity and realize an X-ray tube with a small focus and high output.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 is a cross-sectional view showing the structure of the present apparatus, and in the figure, reference numeral 31 denotes a hollow cylindrical glass tube with a bulged center, which is an X-ray tube. This tubular body 31 has a small diameter at both ends, and a part of the central bulge is further bulged out to the outside, and a cathode 32 is provided there. The cathode 32 is provided with a filament 32a for emitting thermionic electrons, a focusing electrode 32b is provided on the outside of the filament 32a, and a lead wire 32c is provided to form an electric path between these and the outside of the tube body 31. is provided.

Bearings 33 and 34 are provided inside the tubular body 31 near both ends thereof, and a shaft 35 is rotatably provided with both ends supported by the pair of bearings 33 and 34. As a result, the first shaft 35, which is held at both ends by bearings 33 and 34, is rotatably supported within the tube body 31 made of glass or other material forming a tube bulb. A rotor 35a is formed near one end of the shaft 35 to be driven to rotate by an external magnetic field. The rotor 35a is energized by a rotating magnetic field generated by an energizing coil 36 provided outside the rotor 35a forming position of the tubular body 31 for generating a rotating magnetic field.

Further, a cylindrical second shaft 39 is concentrically disposed on the outer peripheral side of the shaft 35 via clearance bearings 37 and 38. This allows the shaft 39 to be free in both the axial and rotational directions. A thick cylindrical target 40 is attached to the second shaft 39 at its central outer periphery. Further, the second shaft 39 and the first shaft 35 are formed with lead screws (shaft gears) 35b and 39a that mesh with each other, and the movements of the two shafts are caused to have a certain relationship due to the shaft gears 35b and 39a. It's getting old.

Furthermore, the rotor 35 is attached to the second shaft 39.
A rotor 39b is formed near the end in the direction opposite to a.
A rotating magnetic field is applied by a biasing coil 41 for generating an external rotating magnetic field, which is provided on the outside of the tubular body 31 in correspondence with b, and thereby a rotational force is biased.

Next, the operation of this apparatus having the above configuration will be explained.

In the structure as described above, electrons are emitted from the filament 32a while rotating the target 40, and when the electrons are focused on the target, X-rays are emitted from the target at the collision position of the focused electrons. Here, the rotation of the target 40 supplies electric power to the rotation force energizing coils 36, 41, generates a rotating magnetic field, and activates the corresponding rotors 39b, 35.
This is done by rotating the shafts 35 and 39 by rotating the rotors 35a and 39. However, if the rotors 35a and 39b are made to rotate in the same direction, and the rotation speed is the same, the second shaft 35 The shaft 39 rotates together with the first shaft 35 while maintaining its initial position without moving at all.

However, if the shaft gears 35b and 39a of the shafts 35 and 39 are threaded right-handed due to the rotational difference between the shafts 35 and 39 when the rotation speed of the second shaft 39 is high, the rotation speed of the second shaft 39 is high. 35 moves on the first shaft 35 from the right to the left in the figure. If the rotational speed of the second shaft 39 is low, the second shaft 39 moves to the right rather than to the left. If the pitch of the shaft gear is 2 mm, it will move 2 mm in one rotation.

Cathode 32, shafts 35, 39, target 4
When a predetermined voltage is applied between the anode portions composed of 35,
39 by changing the number of rotations and rotating the second
Since the first shaft 35 is moved to one side, the position where the electrons collide on the target 40 is arranged in a spiral shape with a pitch corresponding to the moving speed of the second shaft 39, depending on the target 40. Become.

The movement of the second shaft 39 is shown in FIG.

For example, if 150Hz AC power is applied to the first energizing coil 36, the first shaft 35 will rotate at 900 rpm.
Suppose we want to rotate .

Further, assume that the setting is such that when 150 Hz AC power is applied to the second energizing coil 41, the second shaft 39 rotates at 9000 rpm.

At this time, the frequency of the applied power to the second energizing coil 41 is 165Hz, 150Hz, 135Hz as shown in FIG.
Hz, the rotation speed of the second shaft 39 shows a change corresponding to the frequency change,
Changes to 9900r.pm, 9000r.pm, 8100r.pm.

At this time, if the first shaft 35 is rotating at 9000 rpm, the difference in rotation speed with the first shaft 35, that is, the difference in the rotation speed of the two rotors, is as shown in Figure 4b. +900rpm at 165Hz and 135
It becomes -900r.pm at Hz.

At this time, the first shaft 35 is connected to the bearing 3
3 and 34, so the second
The shaft 39 moves left and right on the first shaft 35 as shown in FIG. 4c. (Pitch 2
mm, so it moves 30mm/sec. ) When something is moving from left to right, it moves from right to left, so when changing direction there is likely to be some inertia, friction, etc., so it is possible that the movement will be somewhat slower.

According to this system, a cylindrical target 40 is used, and the target is reciprocated from side to side along this axis with the axis perpendicular to the electron emission direction. The locus of the focal point becomes a spiral, and unlike the conventional disk-shaped method, heating is not concentrated in the same area, and heat is dispersed, making it thermally stronger, resulting in higher output and smaller focus. In addition, since the left and right reciprocating movement of the target can be achieved only by converting the frequency of the electrical signal, it has the advantage of being extremely easy to control.

In addition, according to this method, since the shaft 23 is supported at both ends, the support is strong, and therefore even if the weight of the target increases, there is no problem in terms of the support structure to some extent, so the volume of the target can be increased. Therefore, it is possible to increase the heat capacity, thereby creating more thermal margin and making it possible to increase the output.

In addition, since the support is strong, the diameter of the target can be increased, and therefore the angular velocity at the target side peripheral surface can be increased, so the heating temperature per unit area can be lowered, and the current density of electrons can be increased. Therefore, high output X-rays can be obtained. Also the rotation speed is 9000r.pm or 18000r.pm
Or even if it is higher than that, the support is strong, so there is little risk of the shaft breaking. Therefore,
It can be rotated at high speeds, and this also allows for large outputs to be obtained.

In addition, in the conventional method as shown in Fig. 1, the electron impact surface of the target is shaken due to high speed rotation, which adversely affects the output characteristics in cases such as X-ray CT, but in the case of the present invention, there is less risk of this because both ends are supported. .

It should be noted that the present invention is not limited to the embodiments described above and shown in the drawings, but can be implemented with appropriate modifications within the scope of the gist thereof.
As shown in the figure, the other end of the first shaft 35 also has a rotor 35a' and a corresponding biasing coil 36'.
It is conceivable to provide a rotor 35b at the other end so that the first shaft 35 rotates more smoothly together with the rotor 35b at the other end. The same applies to the second shaft 39, and there is no problem in providing rotors for applying rotational force at both ends thereof.

Note that the target material is not directly related to the present invention and is therefore not specifically mentioned, but any material may be used as long as it can perform X-ray conversion, and the type of the cathode is similarly not restricted.

〔Effect of the invention〕

As described in detail above, the present invention has both ends rotatably supported by a support member provided in a housing forming an X-ray tube, a rotor is formed near at least one end, and a shaft is provided in the middle part. a first shaft formed with a gear; and a shaft gear formed in a cylindrical shape, provided on the outer peripheral side of the first shaft, and a shaft gear meshing with the shaft gear formed on the inner surface, and an anode formed in the center of the outside side. a cylindrical X-ray conversion target; a second shaft having a rotor formed near at least one end; a cathode supported by the housing and disposed opposite the target; A biasing coil is provided corresponding to each of the rotors to apply an alternating magnetic field to each rotor to drive it to rotate, the target is cylindrical, and the rotation of the first and second shafts is By making a difference in the number, the second shaft is moved and rotated in the axial direction by the action of the shaft gear of each shaft, and thereby the collision point of the electrons emitted from the target cathode is The locus of the shaft is spiral, which prevents the same part of the target from being heated all the time and helps disperse the heat. Also, by supporting the first shaft at both ends, the target can be firmly supported. This makes it possible to increase the volume of the target and increase its heat capacity, so the target is less likely to be damaged even in a high-output device with a small focal point where the density of electron flow is high. , can provide a high-power X-ray tube.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining the configuration of a conventional device.
Fig. 2 is a diagram showing the relationship between the output and heat capacity of the X-ray tube, Fig. 3 is a schematic configuration diagram showing an embodiment of the present invention, and Fig. 4 is a diagram explaining the principle of movement of the target of the device of the present invention. FIG. 5 is a diagram showing a modification of the present invention. 31... tube body, 32... cathode, 32a... filament, 32b... focusing electrode, 33, 34... bearing, 35... first shaft, 35a, 35a', 3
9b...Rotor, 35b, 39a...Shaft gear, 36,
36', 41...Biasing coil, 37, 38...Idle bearing, 39...Second shaft, 40...Target.

Claims (1)

[Claims] 1. A first member rotatably supported at both ends by support members provided in a casing forming an X-ray tube, having a rotor formed near at least one end side and a shaft gear formed in an intermediate portion. a shaft, and a cylindrical X-ray converter, which is provided on the outer peripheral side of the first shaft, has a shaft gear meshing with the shaft gear formed on its inner surface, and has a cylindrical X-ray converter constituting an anode in the center of the outer side. A second shaft having a rotor formed near at least one end thereof, a cathode supported by the casing and disposed opposite to the target, and a second shaft having a rotor formed near at least one end thereof, a cathode supported by the casing and disposed opposite to the target, An X-ray tube characterized by comprising biasing coils which are provided in correspondence with each other and apply an alternating magnetic field to each rotor to drive it to rotate.