JP4876047B2 - X-ray generator and X-ray CT apparatus - Google Patents

Description

  The present invention relates to an X-ray generator and an X-ray CT apparatus, and more particularly to an X-ray generator suitable for application to a rotary anode X-ray generator, and an X-ray CT apparatus using the X-ray generator. About.

  An example of the configuration of a conventional rotary anode type X-ray generator is described in US Pat. No. 6,819,741. This rotating anode type X-ray generator has a rotating anode attached to a rotating body provided in a casing, and a cathode disposed to face the rotating anode. The rotating anode and the cathode are provided in a vacuum vessel disposed in the casing. The cathode has a filament and a cable connected to the filament. The cable is placed in the cathode cone and the filament is attached to the tip of the cathode cone.

  A high voltage of 100 kV or more is applied between the rotating anode and the cathode. The electron beam emitted from the filament is accelerated by the high voltage and collides with the surface of the rotating rotating anode (target surface). X-rays are generated by the collision of the electron beams, and the X-rays are emitted to the outside through windows formed in the vacuum vessel and the casing, respectively. In order to prevent the rotating anode and the cathode from being electrically short-circuited by the high voltage applied as described above, a filament is placed on a cathode cone made of an electrical insulating material (ceramics). As this electrical insulating material, it is also known to use glass in addition to ceramics.

US Pat. No. 6,819,741

Glass and ceramics, which are electrical insulating materials used in a rotating anode type X-ray generator to maintain the insulating performance between the rotating anode and the cathode, have a resistivity of 10 ¹⁴ Ω · cm or more, and have a high voltage. It is a material with excellent withstand voltage characteristics. Even when such a high resistivity insulating material is used, creeping discharge occurs when dust adheres to the insulating material portion. In order to prevent the occurrence of such creeping discharge, conventionally, measures are taken to prevent dust from adhering to the insulating material portion. However, even if the rotary anode type X-ray generator is manufactured in a clean room, it is difficult to eliminate dust adhering to the insulating material portion. For this reason, it is inevitable that dust adheres to the insulating material portion of the rotary anode type X-ray generator.

  The objective of this invention is providing the X-ray generator and X-ray CT apparatus which can suppress creeping discharge even when dust adheres to an insulating material.

A feature of the present invention that achieves the above-described object is that a container whose interior is maintained at a negative pressure, an anode installed in the container and having a target portion, and a cathode installed in the container facing the anode are provided. The container is made of an insulating material having a resistivity in the range of 10 ⁸ Ω · cm to 10 ¹² Ω · cm.

According to the present invention having the above characteristics, the insulation is higher in conductivity than the insulating material having a resistivity of 10 ¹⁴ Ω · cm or more, and the resistivity is in the range of 10 ⁸ Ω · cm to 10 ¹² Ω · cm. Since the container is made of a material, even when dust adheres to the latter insulating material, the degree of electric field concentration generated around the dust is reduced. For this reason, since it is possible to suppress the emission of electrons due to the electric field that is the beginning of the creeping discharge, the occurrence of the creeping discharge can be suppressed.

The object is to provide a container whose interior is maintained at a negative pressure, an anode installed in the container and having a target part, and a cathode placed in the container opposite to the anode, the container having a resistivity. Is composed of an insulating material having a resistivity in the range of 10 ⁸ Ω · cm to 10 ¹² Ω · cm, and a first insulating portion having a resistivity in the range of 10 ¹⁴ Ω · cm or more. This can also be achieved by an X-ray generator having two insulating parts.

  According to the present invention, creeping discharge can be suppressed even when dust adheres to the insulating material, and the stop of the X-ray generator can be avoided.

  First, creeping discharge generated in the electrical insulator will be described. FIG. 2 shows a potential distribution when dust 16 adheres to the surface of the insulator (made of glass or ceramics) 15. When the dust 16 is not attached, the equipotential line 17 is perpendicular to the surface of the insulator 15 and is in a parallel state. When the dust 16 adheres to the surface, a phenomenon that the equipotential line 17 is distorted around the dust 16 is observed. This indicates that electric field concentration occurs in the periphery of the dust 16. In such an electric field concentration portion, electrons are emitted from the dust 16 and the insulator 15. Since these electrons generate secondary electrons on the surface of the insulator 15, electron avalanche occurs, leading to creeping discharge.

The inventors examined various measures that can suppress the occurrence of creeping discharge. As a result, by reducing the resistivity of the insulator, that is, by using an insulator having a resistivity of 10 ⁸ Ω · cm to 10 ¹² Ω · cm, a short circuit is caused between the anode and the cathode of the X-ray generator. It has been discovered that it is possible to avoid the occurrence of creeping and suppress creeping discharge even when dust adheres to the insulator. That is, by using an insulator having a resistivity of 10 ⁸ Ω · cm or more, it is possible to avoid a short circuit between the anode and the cathode of the X-ray generator. In addition, by using an insulator having a resistivity of 10 ¹² Ω · cm or less, it is possible to suppress electric field concentration around the dust, to prevent avalanche due to electron emission, and to avoid discharge in the insulator. Can do.

  Examples of the present invention made based on the above examination results will be described below.

An X-ray generator which is a preferred embodiment of the present invention will be described with reference to FIG. 1, taking a rotary anode X-ray generator as an example. The rotating anode type X-ray generator 1 includes an outer container (first container) 2, a vacuum container (second container) 3 that is an inner container, a rotating anode 5, and a cathode 11. The outer container 2 is a metal container, and a lead plate which is a radiation shielding body for shielding unnecessary X-rays when X-rays are generated is stretched on the inner surface thereof. A vacuum vessel 3 whose inside is set to a negative pressure (for example, vacuum) is disposed in the outer vessel 2 and is installed on the inner surface of the outer vessel 2 by a support member (not shown) made of an insulating material. . The vacuum vessel 3 is made of glass that is an insulating material. As this glass, a glass having a resistivity in the range of 10 ⁸ Ω · cm to 10 ¹² Ω · cm is used. As this glass, glass containing V ₂ O ₅ —BaO—P ₂ O ₅ , V ₂ O ₅ —Na ₂ O—P ₂ O ₅ or the like is desirable. The vacuum vessel 3 may be made of ceramics that is an insulating material. A window 4B made of beryllium or the like is provided in the outer container 2. A window 4A made of beryllium or the like is provided in the vacuum vessel 3. The rotating anode 5 and the cathode 11 are disposed in the vacuum vessel 3 so as to face each other. The cathode 11 is attached to the vacuum vessel 3 by a support member 12. The support member 12 is configured by attaching a rod-like member 13 to a plate-like member 14. The cathode 11 is installed on one surface of the plate-like member 14, and the rod-like member 13 is attached to the vacuum vessel 3. The cathode 2 has a filament (not shown) that emits thermoelectrons.

  The rotating anode 5 is attached to a rotating device 7. A target 6 inclined outward in the radial direction of the rotating anode 5 is provided on the rotating anode 5 so as to face the cathode 11. The target 6 is made of a high melting point, high atomic number metal such as tungsten. The rotating device 7 includes a rotor 9 and a stator 10. The rotor 9 is configured by attaching a coil to the rotary shaft 8 and is disposed in the vacuum vessel 3. The rotating shaft 8 is rotatably attached to one end of the vacuum vessel 3. A seal member (not shown) is provided between the rotary shaft 8 and the vacuum vessel 3 in order to keep the inside of the vacuum vessel 3 at a negative pressure. The rotating anode 5 is attached to the rotating shaft 8. The stator 10 to which the coil is attached is disposed between the vacuum vessel 3 and the outer vessel 2 at a position facing the rotor 9. The stator 10 is installed on the inner surface of the outer container 2 by a support member (not shown) made of an insulating material.

  The cathode 11 is connected to the negative terminal of a voltage booster (not shown), and the rotary anode 5 is connected to the positive terminal of the voltage booster. The voltage booster generates a high voltage of 100 kV or higher and applies the high voltage between the rotating anode 5 and the cathode 11. The filament of the cathode 11 is connected to a heating transformer (not shown).

  A mechanism for generating X-rays in the rotary anode X-ray generator 1 described above will be described below. When a current is supplied from the power source to the coils of the rotor 9 and the stator 10, the rotor 9 rotates and the rotating anode 5 also rotates. A high voltage of 100 kV or more is applied between the rotating anode 5 and the cathode 11 from a voltage booster. At the same time, since a current is supplied to the filament of the cathode 11 from the heating transformer, the filament is heated and thermoelectrons are emitted from the filament toward the target 6. The thermoelectrons are accelerated by the action of a high voltage applied between the rotating anode 5 and the cathode 11. The accelerated thermoelectrons collide with the target 6 of the rotating anode 5 to form a focal point. Due to the collision of the thermal electrons, X-rays are generated from the focal point formed on the target 6, and the X-rays are emitted to the outside of the rotary anode X-ray generator 1 through the windows 4 </ b> A and 4 </ b> B.

In this embodiment, since the vacuum container 3 is constituted by an insulating material having a resistivity in the range of 10 ⁸ Ω · cm to 10 ¹² Ω · cm, the insulating material having a resistivity of 10 ¹⁴ Ω · cm or more. The conductivity is higher than that of the vacuum container constituted by the above. For this reason, even if dust adheres to the vacuum container 3, the potential around the dust is neutralized by the conductivity of the insulating material, and the degree of electric field concentration generated around the dust is reduced. In this embodiment, even when dust adheres to the vacuum container 3 made of an insulating material, electrons are not easily emitted from the dust and the insulating material at the electric field concentration portion. Since generation of secondary electrons on the surface of the insulating material, that is, the vacuum vessel 3 due to the electrons is suppressed, even when dust adheres to the vacuum vessel 3, no avalanche occurs and the vacuum vessel 3 Creeping discharge in can be suppressed. By suppressing the creeping discharge, the stop of the X-ray generator can be avoided.

Further, the rotary anode type X-ray generator 1 of this embodiment has the vacuum container 3 made of an insulating material having a resistivity in the range of 10 ⁸ Ω · cm to 10 ¹² Ω · cm. Further, it is possible to prevent a short circuit from occurring between the rotating anode 5 and the cathode 11 through the insulating material, and it is also possible to prevent a discharge from occurring in the insulating material portion.

The vacuum vessel 3 is an insulating material having a resistivity in the range of 10 ⁸ Ω · cm to 10 ¹² Ω · cm, instead of glass having a resistivity in the range of 10 ⁸ Ω · cm to 10 ¹² Ω · cm. You may comprise with ceramics. As this ceramic, for example, it is produced by mixing 1% or more and 20% or less of TiC into Al ₂ O ₂ which is a main raw material having a resistivity within a range of 10 ⁸ Ω · cm to 10 ¹² Ω · cm. Ceramics can be used.

As an insulating material having a resistivity of 10 ⁸ Ω · cm to 10 ¹² Ω · cm that constitutes the vacuum vessel 3, 1% or more and 20% or less of TiO ₂ is mixed into Al ₂ O ₃ as a main raw material. You may use the ceramics produced | generated.

Furthermore, the resistivity constituting the vacuum container 3 as an insulating material in the range of 10 ⁸ Ω · cm of 10 ¹² Ω · cm, and ZrO ₂ in 1% to 30% or less of Fe ₂ O ₃ is a main raw material 1 It is also possible to use ceramics produced by mixing Y ₂ O ₃ in an amount of not less than 4% and not more than 4%.

As an insulating material having a resistivity of 10 ⁸ Ω · cm to 10 ¹² Ω · cm constituting the vacuum vessel 3, 0.1% or more and 1% or less of B and Al ₂ O ₃ are respectively added to SiC as a main raw material. Alternatively, ceramics produced by mixing Y ₂ O ₃ may be used.

  An X-ray generator according to another embodiment of the present invention will be described with reference to FIG. 3, taking a rotary anode X-ray generator as an example. The rotary anode X-ray generator 1A of the present embodiment has a configuration in which the vacuum vessel 3 is replaced with the vacuum vessel 3A in the rotary anode X-ray generator 1 of Embodiment 1, and other configurations are the rotary anode type. This is the same as the X-ray generator 1.

The vacuum vessel 3A used in the rotary anode X-ray generator 1A is made of an insulating material (for example, glass and ceramics described in Example 1) having a resistivity in the range of 10 ⁸ Ω · cm to 10 ¹² Ω · cm. And a second insulating portion 16A, 16B made of an insulating material (for example, glass or ceramics) having a resistivity of 10 ¹⁴ Ω · cm or more. These materials include borosilicate glass and alumina. The 1st insulating part 15 is cyclic | annular, is arrange | positioned between 16 A of 2nd insulating parts and the 2nd insulating part 16B, and is joined to each 2nd insulating part. The first insulating portion and the second insulating portions 16A and 16B are joined by brazing or the like through a metal (for example, Kovar) after the surfaces are metallized with a molybdenum manganese alloy or the like. The rod-shaped member 13 of the support member 12 is attached to the second insulating portion 16A. The rotating shaft 8 is rotatably attached to one end of the second insulating portion 16B. The window 4A made of beryllium or the like is provided in the first insulating portion 15 at a position facing the window 4B.

  In the vacuum vessel 3A, it is preferable to selectively dispose the second insulating portions 16A and 16B having a high resistivity in a portion where the applied electric field is low, and the first insulating portion 15 having a low resistivity in a portion where the electric field is high. In the rotary anode X-ray generator 1A, the cathode 11 having a negative potential, the rotary anode 5 having a positive potential, and the external container 2 having a ground potential are close to each other, and the electric field of the vacuum vessel 3A is increased. The first insulating portion 15 having a low resistivity is disposed. The first insulating portion 15 is disposed in the vicinity of the rotating anode 5 and the cathode 11.

  The rotary anode X-ray generator 1A generates X-rays in the same manner as the rotary anode X-ray generator 1, and emits the X-rays to the outside through the windows 4A and 4B.

  Similarly to the rotary anode X-ray generator 1, the rotary anode X-ray generator 1 </ b> A of the present embodiment can also suppress creeping discharge in the vacuum vessel 3 </ b> A. That is, even if dust adheres to the first insulating portion 15, the degree of electric field concentration generated around the dust is reduced, so that the occurrence of creeping discharge can be suppressed. Since the first insulating part 15 is arranged in the portion where the electric field of the vacuum vessel 3A is high, it is possible to prevent a short circuit between the rotating anode 5 and the cathode 11, and a discharge occurs in the first insulating material part 15. Can also be prevented. In addition, since the low-cost second insulating portions 16A and 16B are installed in the portion where the electric field of the vacuum vessel is low, the cost of the vacuum vessel 3A can be lower than that of the vacuum vessel 3 that becomes the first insulating portion 15 as a whole. it can. Therefore, a cheaper rotary anode type X-ray generator can be obtained. Since the second insulating portions 16A and 16B are disposed in the portion of the vacuum vessel 3A where the electric field is low, creeping discharge does not occur in the second insulating portions 16A and 16B.

  The rotary anode X-ray generators 1 and 1A can be used as an X-ray source of an X-ray CT apparatus. An X-ray CT apparatus to which the rotary anode X-ray generator 1 is applied will be described with reference to FIGS. 4 and 5. The X-ray CT apparatus 21 of this embodiment includes an imaging device 22 and a bed device 27.

  The bed device 27 includes a couch 28 on which a subject (subject) 30 is placed and a support base 29 that supports the couch 28. The couch 28 is attached to the upper end of the support base 29 so that it can move in the longitudinal direction of the couch 28. The imaging device 22 includes a rotating anode X-ray generator 1, a case 23, a radiation detector 24, and a rotating body 25. The imaging device 22 forms an observation region 26 that is a hole into which a subject (subject) 30 is inserted. The rotating anode X-ray generator 1, the radiation detector 24, and the rotating body 25 are disposed in the case 22, and the rotating body 25 surrounds the observation region 26. The rotating body 25 is rotatably installed and is rotated by a motor (not shown). The rotating anode type X-ray generator 1 and the radiation detector 24 are installed on a rotating body 25. With the couch 28 inserted in the observation region 26, the rotary anode X-ray generator 1 and the radiation detector 24 are arranged such that the couch 28 is sandwiched between them. The rotary anode X-ray generator 1 is installed such that the windows 4A and 4B face the couch 28.

  Imaging by the X-ray CT apparatus 21 will be described. The couch 28 on which the subject 30 is placed is inserted into the observation region 26. When the imaging region of the subject 30 is inserted into the observation region 26, the movement of the couch 28 is stopped. As the rotating body 25 turns, the rotary anode X-ray generator 1 and the radiation detector 24 turn around the couch 28, that is, around the subject 30. By supplying current to the coils of the rotor 9 and the stator 10, the rotary anode 5 rotates. A high voltage of 100 kV or more is applied between the rotating anode 5 and the cathode 11 from the voltage booster, and current is supplied to the filament of the cathode 11 from the heating transformer. The thermoelectrons emitted from the filament are accelerated by the action of a high voltage applied between the rotating anode 5 and the cathode 11 and collide with the target 6 of the rotating anode 5. As a result, X-rays are generated at the target 6, and the X-rays pass through the windows 4 </ b> A and 4 </ b> B and are irradiated onto the subject 28 on the couch 28. Since the rotating anode X-ray generator 1 is swiveled as described above, X-rays are irradiated onto the subject 30 from all directions of 360 °. X-rays that have passed through the subject 30 are detected by a radiation detector 24 that rotates together with the rotary anode X-ray generator 1.

  The radiation detector 24 outputs an X-ray detection signal by detecting X-rays. Based on this X-ray detection signal, a tomographic image creation device (not shown) creates tomographic image information on the subject 30.

  Since the X-ray CT apparatus 21 uses the rotary anode X-ray generator 1 in which the occurrence of creeping discharge is suppressed, the interruption of the X-ray CT inspection due to the occurrence of creeping discharge is prevented. For this reason, the time required for the X-ray CT examination is shortened, and the number of persons who can perform the X-ray CT examination can be increased.

  An X-ray CT apparatus using the rotary anode X-ray generator 1 </ b> A instead of the rotary anode X-ray generator 1 can also obtain the effects produced by the X-ray CT apparatus 21 described above.

It is a longitudinal cross-sectional view of the X-ray generator of Example 1 which is one suitable Example of this invention. It is explanatory drawing which shows an equipotential line when dust adheres to the surface of a vacuum vessel in the state in which the voltage is applied to the anode and cathode in the vacuum vessel comprised with the insulating material. It is a longitudinal cross-sectional view of the X-ray generator of Example 2 which is another Example of this invention. It is a block diagram of the X-ray CT apparatus to which the X-ray generator shown in FIG. 1 is applied. It is a front view of the X-ray CT apparatus shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,1A ... Rotary anode type X-ray generator, 2 ... External container, 3 and 3A ... Vacuum container, 5 ... Rotating anode, 6 ... Target, 7 ... Rotating device, 9 ... Rotor, 10 ... Stator, 11 ... Cathode, DESCRIPTION OF SYMBOLS 15 ... 1st insulation part, 16A, 16B ... 2nd insulation part, 21 ... X-ray CT apparatus, 22 ... Imaging device, 24 ... Radiation detector, 25 ... Rotating body, 27 ... Bed apparatus.

Claims (17)

A container in which the inside is held at a negative pressure, an anode installed in the container and having a target portion, and a cathode placed in the container facing the anode,
The X-ray generator according to claim 1, wherein the container is made of an insulating material having a resistivity in the range of 10 ⁸ Ω · cm to 10 ¹² Ω · cm. _2. The X-ray generator according to claim 1, wherein the insulating material is glass containing any one of V ₂ O ₅ —BaO—P ₂ O ₅ and V ₂ O ₅ —Na ₂ O—P ₂ O ₅ . _2. The X-ray generator according to claim 1, wherein the insulating material is a ceramic containing 1% to 20% of TiC and the remainder being substantially Al ₂ O ₃ . _2. The X-ray generator according to claim 1, wherein the insulating material is a ceramic containing 1% to 20% of TiO ₂ and the remainder being substantially Al ₂ O ₃ . _2. The X-ray generation according to claim 1, wherein the insulating material is a ceramic containing 1% to 30% Fe ₂ O ₃ and 1% to 4% Y ₂ O _3, with the remainder being substantially ZrO _2. apparatus. The insulating material includes any of 0.1% to 1% B, 0.1% to 1% Al ₂ O ₃ and 0.1% to 1% Y ₂ O ₃ , and the rest is substantially The X-ray generator according to claim 1, wherein the ceramic is SiC. A container in which the inside is held at a negative pressure, an anode installed in the container and having a target portion, and a cathode placed in the container facing the anode,
The container has a first insulating portion made of an insulating material having a resistivity in the range of 10 ⁸ Ω · cm to 10 ¹² Ω · cm, and an insulating material having a resistivity in the range of 10 ¹⁴ Ω · cm or more. An X-ray generator having a second insulating part constituted by   The X-ray generator according to claim 7, wherein the first insulating portion is disposed in the container in the vicinity of the anode and the cathode. The X-ray generator according to claim 7, wherein the insulating material constituting the second insulating part is one of glass and ceramics having a resistivity in a range of 10 ¹⁴ Ω · cm or more. The insulating material constituting the first insulating _portion, the _{V 2 O 5 -BaO-P 2} O 5 and _{V 2 O 5 -Na 2 O-} P 2 O claim 7 which is a glass containing either ₅ The X-ray generator described. The X-ray generator according to claim 7, wherein the insulating material constituting the first insulating part is a ceramic containing 1% to 20% TiC, and the remainder being substantially Al ₂ O ₃ . The X-ray generator according to claim 7, wherein the insulating material constituting the first insulating portion is a ceramic containing 1% to 20% TiO ₂ and the remainder being substantially Al ₂ O ₃ . The insulating material constituting the first insulating portion is a ceramic containing 1% to 30% Fe ₂ O ₃ and 1% to 4% Y ₂ O _3, with the remainder being substantially ZrO _2. Item 8. The X-ray generator according to Item 7. The insulating material constituting the first insulating portion is any one of 0.1% to 1% B, 0.1% to 1% Al ₂ O ₃ and 0.1% to 1% Y ₂ O ₃ . The X-ray generator according to claim 7, wherein the remaining ceramic is a ceramic that is substantially SiC.   The X-ray generator according to claim 1, further comprising a rotating device that rotates the anode. A bed apparatus for placing a subject, an X-ray generator, a radiation detector for detecting X-rays emitted from the X-ray generator, and a rotating body for rotating the X-ray generator and the radiation detector Prepared,
The X-ray generator includes a container whose interior is maintained at a negative pressure, an anode that is installed in the container and has a target portion, and a cathode that is installed in the container so as to face the anode. ,
An X-ray CT apparatus, wherein the container is made of an insulating material having a resistivity in a range of 10 ⁸ Ω · cm to 10 ¹² Ω · cm. A bed apparatus for placing a subject, an X-ray generator, a radiation detector for detecting X-rays emitted from the X-ray generator, and a rotating body for rotating the X-ray generator and the radiation detector Prepared,
The X-ray generator includes a container whose interior is maintained at a negative pressure, an anode that is installed in the container and has a target portion, and a cathode that is installed in the container so as to face the anode. ,
The container has a first insulating portion made of an insulating material having a resistivity in the range of 10 ⁸ Ω · cm to 10 ¹² Ω · cm, and an insulating material having a resistivity in the range of 10 ¹⁴ Ω · cm or more. An X-ray CT apparatus comprising: a second insulating portion configured by:

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