JP2007097610A - X-ray imaging system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray imaging system using a small-sized X-ray source. <P>SOLUTION: The X-ray imaging system comprises the X-ray source 2 arranged inside a vacuum envelope 5 and provided with a field emission type electron source 6 for emitting electrons and an anode 7 for emitting X-rays by the incidence of the electrons, and an X-ray image detector 4 arranged at a position at which the X-ray is made incident for detecting the image signals of X-ray images according to intensity of the incident X-ray, and images X-ray phase contrast images. In the X-ray imaging system, the field emission type electron source 6 is provided with a support substrate 61 and a drift layer 63 composed by alternately laminating a semiconductor layer 63a composed of a metal oxide and an insulator layer 63b, the X-ray source 2 is provided with the anode 7 in the electron emitting direction of the field emission type electron source 6, and the X-rays are emitted through the anode 7. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an X-ray imaging system, and more particularly to an X-ray imaging system using an X-ray source including a field emission electron source.

  Conventionally, in X-ray imaging, X-rays are absorbed or scattered when the X-rays pass through a subject, and the intensity changes. An image obtained by converting an image signal based on such an X-ray intensity change and detecting the image signal is referred to as an absorption contrast X-ray image. On the other hand, since X-rays are electromagnetic waves, refraction and diffraction occur as in the case of visible light. The image contrast obtained by this property is called phase contrast, and it is known that a high-quality X-ray image can be obtained by utilizing this phenomenon.

  As an X-ray imaging system for obtaining an X-ray phase contrast image, a system using a thermionic emission X-ray source as shown in Patent Document 1 is known. The thermionic emission type X-ray source emits X-rays that radiate radially from an opening of a predetermined size. A magnified image is taken using the emitted X-rays to obtain a phase contrast image.

  Also, as shown in Patent Document 2, a breast image capturing apparatus that enables X-ray phase contrast imaging is known. A mammography apparatus described in Patent Document 2 has an X-ray source that emits X-rays to a subject, detects a subject table that fixes the subject so as to face the X-ray source, and detects X-rays transmitted through the subject An X-ray image detector is provided.

  Here, the X-ray source used in the conventional X-ray imaging apparatus is provided with a thermionic emission type electron source as a cathode, and the cathode is heated to emit thermoelectrons, between the cathode and the anode. X-rays are generated when the thermionic electrons are guided to the electric field and collide with the anode. Therefore, it is necessary to provide both the cathode heating means and the cathode-anode electric field generating means, which increases the size of the apparatus and makes the X-ray imaging apparatus itself large. It was. Further, since a filament power source is used as a heating means, there is a problem that it is difficult to improve durability.

Accordingly, a planar field emission electron source in which a large number of conductive silicon films and insulating silicon oxide films are alternately stacked on a support substrate made of n-type silicon using a thin film stacking technique. Has been developed (see, for example, Patent Document 3). According to such a field emission type electron source, an electric field is applied to the cathode and electrons are emitted based on the principle of the ballistic electron emission phenomenon. There is an advantage that it does not occur.
JP 2004-248699 A JP 2004-229900 A JP 2002-352698 A

  However, in such an X-ray imaging apparatus, in order to obtain a high-quality X-ray image, imaging is performed in a short period of time so that high-output X-rays are irradiated and the image is not blurred due to movement of the subject. There is a need to. In particular, in X-ray phase contrast imaging, which is enlargement imaging, if the focal spot diameter of the X-ray source is large, geometrical sharpness becomes large and the X-ray image is blurred. Therefore, an X-ray source having a small focal spot diameter is used. High power X-ray irradiation is required. On the other hand, an image blurred due to the movement of the subject cannot be used for diagnosis. For this reason, it is necessary to re-photograph, the exposure amount of the subject increases, and the adverse effect of exposure becomes a problem when the subject such as a medical site is a patient.

  In such a field emission type electron source, in order to improve the electron emission capability, it is necessary to form a silicon film with high crystallinity having a large electron mean free process as the above-described silicon film. When such a highly crystalline silicon film is formed by a normal film formation method, it is generally necessary to raise the temperature of the support substrate to about 1000 ° C., and the support substrate to be formed is required to have very high heat resistance. There was a problem that.

  In addition, when obtaining such a highly crystalline silicon film, the temperature of the support substrate differs greatly between the formation of the silicon film and the formation of the silicon oxide film. When a large number of silicon films and insulating silicon oxide films are alternately laminated, the interface between the silicon film and the silicon oxide film is distorted due to the difference in thermal expansion coefficient between the silicon film and the silicon oxide film, There has been a problem that the electron emission efficiency is greatly reduced due to the destruction of the interface.

  On the other hand, when a silicon film is formed at a lower temperature of the support substrate, the silicon film becomes in an amorphous state, and there is an electron mean free process, which is an important physical property value required in the above-described ballistic electron emission phenomenon. There is a problem that the electron emission capability is remarkably lowered and the heat conduction efficiency is lowered, the temperature of the field emission electron source is increased, and the durability is deteriorated.

  As described above, the X-ray source using any of the above-described electron sources has no electron source excellent in electron emission efficiency and durability, and the apparatus itself has been enlarged.

  The present invention has been made in view of these points, and an object thereof is to provide an X-ray imaging system using a miniaturized X-ray source.

In order to solve the above-mentioned problem, the invention according to claim 1 is an X-ray imaging system.
An X-ray source disposed in a vacuum envelope and provided with a field emission electron source that emits electrons by applying an electric field; and an anode that emits X-rays upon incidence of the electrons;
An X-ray image detector disposed at a position where the X-rays are incident, and detecting an image signal of the X-ray image according to the intensity of the incident X-rays;
In an X-ray imaging system that captures an X-ray phase contrast image,
The field emission electron source includes a support substrate, and a drift layer in which semiconductor layers and insulator layers made of metal oxide are alternately stacked,
The X-ray source includes the anode in the electron emission direction of the field emission electron source, and transmits the X-ray through the anode.

  According to the first aspect of the present invention, the field emission electron source provided in the X-ray source includes a support substrate and a drift layer in which semiconductor layers and insulator layers are alternately stacked. In the drift layer, a semiconductor layer is formed of a crystalline metal oxide. Further, an anode is provided in the electron emission direction of the field emission electron source, and X-rays are emitted through the anode by the incidence of electrons from the field emission electron source.

The invention described in claim 2 is the X-ray imaging system according to claim 1,
The field emission electron source includes a pair of electrodes for applying an electric field in the stacking direction across the drift layer,
The thickness of the anode is in the range of 0.1 to 100 μm.

  According to the second aspect of the present invention, the field emission electron source includes a pair of electrodes for applying an electric field in the stacking direction of the drift layer, and electrons are emitted from the drift layer through the electrodes. The generated electrons enter an anode having a film thickness of 0.1 to 100 μm provided in the electron emission direction of the electrode, and the generated X-rays are transmitted through the anode and emitted.

The invention described in claim 3 is the X-ray imaging system according to claim 2,
The thickness of the anode is in the range of 1 to 10 μm.

  According to the third aspect of the present invention, the field emission electron source includes the surface electrode in the electron emission direction of the drift layer, and electrons are emitted from the drift layer through the surface electrode. The emitted electrons enter an anode having a thickness of 1 to 10 μm, and X-rays are emitted with high generation efficiency and transmission efficiency.

According to a fourth aspect of the present invention, in the X-ray imaging system of the first aspect,
The X-ray source includes a pair of electrodes for applying an electric field in the stacking direction across the drift layer, and the electrode provided in the electron emission direction of the drift layer of the electrodes includes the anode. The film thickness of the anode is in the range of 1 nm to 1 μm.

  According to the fourth aspect of the present invention, the field emission electron source emits electrons from the drift layer by applying an electric field through a pair of electrodes. The emitted electrons are incident on an anode having a thickness of 1 nm to 1 μm provided in the electron emission direction of the drift layer, and X-rays are emitted.

The invention described in claim 5 is the X-ray imaging system according to claim 4,
The thickness of the anode is in the range of 10 to 100 nm.

  According to the fifth aspect of the present invention, the field emission electron source emits electrons from the drift layer. The emitted electrons enter an anode having a thickness of 10 to 100 nm, and X-rays are emitted with high generation efficiency and transmission efficiency.

The invention described in claim 6 is the X-ray imaging system according to any one of claims 1 to 5,
A high voltage power source for applying a high voltage for accelerating electrons between the anode and the field emission electron source is provided.

  According to invention of Claim 6, a high voltage can be applied and an electron can be accelerated between an anode and a field emission type electron source.

The invention described in claim 7 is the X-ray imaging system according to any one of claims 1 to 6,
A subject table for positioning a subject is disposed between the X-ray source and the X-ray image detector, and a distance R1 from the X-ray source to the subject table is 0.25 to 3 m. The distance R2 from the subject table to the X-ray image detector is 0.25 to 3 m, and the focal spot size of the X-ray source is 1 to 300 μm.

  According to the seventh aspect of the present invention, the focal point size of the opening of the X-ray source is 1 to 300 μm, and the X-ray source is such that 0.25 ≦ R1 ≦ 3 and 0.25 ≦ R2 ≦ 3. Since the object table and the X-ray image detector are arranged, the edge effect is large, and the blurring of the image due to the geometrical sharpness due to the focal diameter can be suppressed to be small, and a clear phase contrast can be easily obtained.

The invention according to claim 8 is the X-ray imaging system according to any one of claims 1 to 7,
The thickness of the semiconductor layer is in the range of 1/1000 to 5/4 of the mean free path of electrons in the semiconductor layer, and the relative dielectric constant of the semiconductor layer is 1 of the relative dielectric constant of the insulator layer. It is characterized by being in the range of 5 to 100 times.

  According to the invention described in claim 8, electrons injected from one electrode by applying a voltage to the pair of electrodes in a state where the relative dielectric constant of the semiconductor layer and the insulator layer is set as described above. Is not scattered by the semiconductor layer, and the insulator layer can be accelerated by a sufficient electric field to make the electrons ballistic.

The invention according to claim 9 is the X-ray imaging system according to any one of claims 1 to 8,
The semiconductor layer has a thermal conductivity in the range of 0.05 to 100 W / cm · K.

  According to the ninth aspect of the present invention, when electrons are emitted by applying a voltage to the pair of electrodes in a state where the thermal conductivity of the semiconductor layer is set as described above, sufficient thermal radiation is obtained. It is possible to suppress the temperature of the field emission electron source from rising.

The invention according to claim 10 is the X-ray imaging system according to any one of claims 1 to 9,
The semiconductor layer is made of zinc oxide.

  According to the invention described in claim 10, when zinc oxide is used for the semiconductor layer, it is crystallized at a lower temperature, and the orientation in the c-axis direction is increased on various support substrates. The electron emission capability of the electron source can be improved. In addition, such a field emission electron source having a good electron emission capability can be manufactured more stably.

The invention according to claim 11 is the X-ray imaging system according to any one of claims 1 to 10,
The main component of the insulator layer is at least one selected from insulating oxides, nitrides, and oxynitrides.

  According to the eleventh aspect of the invention, the durability of the insulator layer can be improved by using the above-mentioned compound as the main component of the insulator layer.

The invention described in claim 12 is the X-ray imaging system according to claim 11,
The main component of the insulator layer is at least one selected from silicon oxide, silicon nitride, and silicon oxynitride.

  According to the invention described in claim 12, by using the above-mentioned compound as the main component of the insulator layer, the conventional semiconductor manufacturing process can be utilized when forming the insulator layer, and the field emission type An electron source can be easily manufactured.

According to the first aspect of the present invention, since the field emission type electron source is provided, it is not necessary to provide a power source for the filament as in the case of the thermionic emission type electron source, and the entire apparatus is enlarged. Can be prevented, and the size of the X-ray source can be reduced. Therefore, it is possible to reduce the size of the entire apparatus used in the X-ray imaging system. Further, since electrons emitted from the field emission electron source pass through the anode provided in the electron emission direction, it is not necessary to apply an electric field between the anode and the cathode, and the X-ray source can be further downsized. Is possible.
In addition, the field emission electron source can be manufactured at a lower temperature for crystallization compared to the case of stacking silicon films, and is easy to manufacture.
In addition, it is possible to reduce the temperature difference of the support substrate when alternately laminating the semiconductor layer and the insulator layer, preventing the occurrence of distortion at the interface between the semiconductor layer and the insulator layer and the destruction of the interface. Thus, a decrease in electron emission efficiency can be prevented.
In addition, since the metal oxide used for the semiconductor layer has ionic bonds in the crystal lattice, it is more flexible than covalently bonded silicon, and is advantageous when it is curved.

  According to the second or third aspect of the invention, since the anode having a predetermined film thickness is provided, the generation efficiency of the output X-rays with respect to the incident electrons is high and the transmission efficiency of the output X-rays is also high. It is possible to emit a line. Further, since secondary electrons are emitted even if they are generated at the anode, heat generation in the anode due to collision between the anode and the secondary electrons is avoided, and heat generation at the anode can be suppressed.

  According to the invention described in claim 4 or 5, since the anode having a predetermined film thickness is provided, the generation efficiency of output X-rays with respect to incident electrons is high and the transmission efficiency of output X-rays is also high. It is possible to emit a line. Further, since secondary electrons are emitted even if they are generated at the anode, it is possible to suppress the heat generation of the anode. In addition, an electric field can be applied to the anode to function as an electrode. Furthermore, since one of the pair of electrodes for applying an electric field to the field emission electron source has a function as an anode, it is possible to emit electrons and accelerate electrons toward the anode with a simpler configuration. Can be performed.

  According to the sixth aspect of the present invention, the electron emission efficiency of the field emission electron source can be improved by accelerating the electrons with high energy and causing the electrons to collide with the anode. Line output efficiency can be improved. Also, high energy X-rays can be obtained.

  According to the seventh aspect of the present invention, a clear phase contrast image can be easily obtained.

  According to the eighth aspect of the present invention, the electron emission efficiency of the X-ray source can be improved.

  According to the ninth aspect of the present invention, the durability of the field emission electron source can be improved and the influence of the heat generated by the field emission electron source on other members constituting the X-ray source can be reduced. The durability of the X-ray source itself can be improved.

  According to the invention described in claim 10, the electron emission efficiency of the X-ray source can be improved.

  According to the invention described in claim 11, the durability of the X-ray source can be improved.

  According to invention of Claim 12, a field emission type electron source can be manufactured easily and an X-ray source can be manufactured easily.

  An embodiment of an X-ray imaging system according to the present invention will be described below with reference to the drawings. However, the scope of the invention is not limited to the illustrated examples.

[First embodiment]
As shown in FIG. 1, an X-ray image capturing apparatus 1 according to the first embodiment of the present invention captures an X-ray phase contrast image using refraction of X-rays in so-called general imaging. An X-ray source 2 that emits radiation in a predetermined direction is provided. In the X-ray emission direction, a subject table 3 for positioning the subject H and an X-ray image detector 4 for detecting an X-ray image based on the X-rays transmitted through the subject H are sequentially arranged. Here, the distance between the X-ray source 2 and the subject table 3 is R1, and the distance between the subject table 3 and the X-ray image detector 4 is R2.

  First, the configuration of the X-ray source 2 will be described.

  As shown in FIG. 2, the X-ray source 2 of this embodiment includes a vacuum envelope 5 made of an insulator or an insulator having a metal part in part. The inside of the vacuum envelope 5 is kept in a high degree of vacuum, and the inside of the vacuum envelope 5 includes a field emission electron source 6 that emits electrons by applying an electric field, and X-rays by the incidence of the electrons. And an anode 7 for emission. An X-ray output window 8 serving as an opening through which X-rays pass is provided in the direction in which X-rays are emitted from the vacuum envelope 5.

  Here, the size of the X-ray output window 8, that is, the focus size D is 1 to 300 μm, preferably 10 to 250 μm, and more preferably 50 to 200 μm. In general, the X-ray output window 8 has a square shape, and the length of one side is the focal size D. When the shape of the X-ray output window 8 is a circle, its diameter is indicated. When it is a rectangle, its short side is indicated. As a method for measuring the focus size D, a method using a pinhole camera and a method using a micro test chart are described in JIS Z 4704. Usually, the focus size is a value based on the measurement of the X-ray manufacturer, and is indicated in the product specification. The nominal focal spot size has an allowable range of about ± 50%. Therefore, the effective focus size D measured by the method described in JIS Z 4704 is defined.

  As shown in FIG. 3, the field emission electron source 6 is provided with a flat support substrate 61. On the upper surface of the support substrate 61, a lower electrode 62 connected to the negative electrode of a power source that applies a voltage Ve to the field emission electron source 6 is provided. The voltage Ve is usually 10 to 100V. On the upper surface of the lower electrode 62, there is formed a drift layer 63 in which the semiconductor layers 63a and the insulator layers 63b are alternately stacked so as to have a predetermined number of layers. The predetermined number of layers of the drift layer 63 is usually 10 to 100 layers. A flat surface electrode 64 connected to the positive electrode of the power source is provided on the upper surface of the drift layer 63.

  As the support substrate 61, for example, a soda lime glass, non-alkali glass, quartz, silicon wafer or the like made of a hard material conventionally used in electronic devices can be used, and a flexible plastic can be used. It is also possible to use a configured one. Examples of the plastic material include polyethylene terephthalate (PET), triacetyl cellulose (TAC), cellulose acetate propionate (CAP), polycarbonate (PC), polyethersulfone (PES), and polyethylene naphthalate (PEN). ), Polyimide (PI) or the like can be used, and in order to improve the characteristics of the substrate made of these plastic materials, it is preferable to use a substrate whose surface is subjected to a known surface coating or surface treatment.

As a material of the lower surface electrode 62, for example, a low resistance metal such as Al, Cr, Ta, Au, Ag, Cu, Pt is preferably used. When a silicon wafer is used for the support substrate 61, silicon is used. It is also possible to use a material having a low resistance by performing a high concentration doping treatment. Further, when an optically transparent material is used for the support substrate 61 and the support substrate 61 side has optical characteristics, tin-doped indium oxide (ITO), SnO ₂ or the like is used as the material of the lower surface electrode 62. Or a conductive polymer material such as polystyrene sulfonate polyethylene dioxythiophene (PEDOT: PSS). The thickness of the lower surface electrode 62 is not particularly limited, and when transparency is not required, it can be appropriately set in consideration of electrode resistance, film strength, and workability, and transparency is required. In this case, in addition to the above, the light transmittance can be set as appropriate.

  In forming the lower surface electrode 62 on the support substrate 61, a coating method such as a spin coating method or a roll coating method may be used in addition to a physical vapor deposition method such as a vacuum deposition method or a sputtering method. it can.

As the material of the surface electrode 64, for example, metals such as Au, Pt, W, Ru, and Ir are effective, but Al, Ti, Cr, Mn, Ni, Cu, Ag, Mo, Zr, Ta, Zn, In, Sn, etc. can also be used, and these alloys may be used. Furthermore, as long as it shows conductivity, oxides of the above-described metal materials, for example, highly transparent conductive materials such as SnO ₂ , In ₂ O ₃ , ZnO, composite oxides thereof, polystyrene sulfone A conductive polymer material such as acid polyethylenedioxythiophene (PEDOT: PSS) can also be used. When an optically transparent material is used for the lower surface electrode 62 and the front surface electrode 64, a field emission electron source having a high light transmittance can be obtained.

  In order to efficiently emit electrons from the surface electrode 64, it is preferable to use a material having a small work function as the material of the surface electrode 64, and the smaller the thickness, the better. From the viewpoint of stability, Au, Pt, Ag, Cu or an alloy of these metals can be used. Further, the thinner the surface electrode 64 is, the higher the electron generation efficiency is, and it is preferable that the thickness be in the range of 1 to 50 nm.

  In forming the surface electrode 64 on the upper surface of the drift layer 63, a conventionally used thin film forming method can be used. However, it is preferable to form the surface electrode 64 so as not to damage the drift layer 63. A facing target sputtering method, which is a sputtering method with little damage, a spray coating method, or a plasma CVD method can be used.

As a material of the semiconductor layer 63a, zinc oxide ZnO as an oxide semiconductor, titanium oxide TiO _2, indium oxide _{an In} 2 _{O 3,} tin oxide SnO _2, cadmium oxide CdO, tungsten oxide _W 2 _{O 5,} niobium oxide _Nb 2 O _5. Nickel oxide NiO, strontium titanate SrTiO ₃ etc. can be used, and c-axis oriented crystals can be easily obtained especially near room temperature, and a good quality thin film with few defects is formed by plasma treatment under atmospheric pressure. It is preferable to use zinc oxide ZnO.

  As for the thickness of the semiconductor layer 63a, if the thickness is too thick, electrons injected into the semiconductor layer 63a collide and scatter in the semiconductor layer 63a, and the electron emission efficiency is reduced, but the thickness becomes too thin. Therefore, it becomes difficult to form the semiconductor layer 63a having a uniform thickness without defects, and the thickness of the semiconductor layer 63a is set to 1/1000 to 5 / of the mean free path of electrons in the semiconductor layer 63a. A range of 4 is preferable.

  As the material of the insulator layer 63b, various insulators can be used, and it is particularly preferable to use an inorganic oxide, nitride, or oxynitride having a low relative dielectric constant. Here, as the above-described oxide, for example, silicon oxide, aluminum oxide, tantalum oxide, vanadium oxide, or the like can be used. In particular, it is preferable to use silicon oxide, fluorinated silicon oxide, or carbon-containing silicon oxide SiOC that has a low dielectric constant and can be manufactured by a widely used semiconductor manufacturing technique. For the same reason, silicon nitride is used as a nitride. It is preferable to use silicon oxynitride as the oxynitride.

  The thickness of the insulator layer 63b is set so thin that electrons passing through the semiconductor layer 63a can be tunneled, and generally within a range of 0.5 to 10 nm.

  In forming the drift layer 63, discharge is started under atmospheric pressure or a pressure near atmospheric pressure, the reactive gas introduced into the plasma is excited (dissociated, recombined, or ionized), and then the substrate is formed on the substrate. The film is formed by chemical reaction above. The atmospheric pressure or the pressure in the vicinity thereof is about 20 to 110 kPa, preferably about 93 to 104 kPa.

  On the upper surface side of the field emission electron source 6, an anode 7 that emits X-rays according to incident electrons is provided. Here, the field emission electron source 6 and the anode 7 may be arranged in contact with each other as shown in FIG. 4, or may be arranged with a gap as shown in FIG.

  The anode 7 in this embodiment is a target layer 71 that generates X-rays by the incidence of electrons. The target layer 71 is formed as a main component by appropriately selecting, for example, from metal elements such as molybdenum, rhodium, tungsten, silver, copper, and other metal elements contained in these metal elements as necessary. Has been. Among these, molybdenum, rhodium, and tungsten are preferable, and tungsten is more preferable from the viewpoint of general photography. The target layer 71 is formed as a layer in which these metal elements are mixed, but may be formed as a layer in which layers made of the respective metal elements are laminated. In addition, the thickness of the target layer 71 is preferably 0.1 to 100 μm, and more preferably 1 to 10 μm, from the viewpoints of X-ray output efficiency and transmission efficiency.

  Next, X-ray radiation from the X-ray source 2 will be described.

  First, the inside of the vacuum envelope 5 is brought into a high vacuum state, and the voltage Ve is applied by a power source. Then, electrons are injected from the lower surface electrode 62 into the drift layer 63, and the electrons are drifted by the voltage Ve acting between the lower surface electrode 62 and the surface electrode 64. When the electrons reach the surface electrode 64, they are incident on the anode 7 provided on the upper surface of the surface electrode 64.

  Here, the generated electrons are applied with a voltage Ve in the drift layer 63 and accelerated toward the surface electrode 64. In the present embodiment, since the anode 7 is provided immediately above the surface electrode 64, electrons generated by the field emission electron source 6 are accelerated by the voltage Ve, and the momentum is applied to the target layer 71 of the anode 7. collide. When electrons collide with the metal of the target layer 71, X-rays are generated, and the generated X-rays are transmitted through the anode 7 and emitted upward. The emitted X-ray passes through the X-ray output window 8 of the vacuum envelope 5 and is emitted outward.

  Thus, since the target layer 71 is formed with a predetermined film thickness thinner than that of a normal anode and is provided on the upper surface side of the field emission electron source 6, the X-rays generated in the target layer 71 are generated on the anode 7. And is emitted upward. Therefore, as shown in FIG. 4, when the field emission electron source 6 and the anode 7 are arranged in contact with each other, electrons generated from the field emission electron source 6 efficiently enter the target layer 71 which is the anode 7. Therefore, the X-ray output efficiency can be improved.

Here, in the present embodiment, an electric field is not applied between the field emission electron source 6 and the anode 7, and electrons generated in the field emission electron source 6 are accelerated by the drift layer 63, and the momentum is increased. Although it is assumed to collide with the anode 7, an electric field may be applied between the field emission electron source 6 and the anode 7 as shown in FIG. By connecting a power source for applying a voltage Vc to the field emission electron source 6 and the anode 7 and applying an electric field between the field emission electron source 6 and the anode 7, electrons generated in the field emission electron source 6 are Energy is applied, and high energy X-rays are easily emitted by colliding with the anode 7.
As described above, by applying an electric field between the field emission electron source 6 and the anode 7, the X-ray source 2 easily emits high-energy X-rays. X-ray radiation is possible. In conventional X-ray sources, in order to radiate high-energy X-rays, it was necessary to cause a large amount of electrons to collide with the anode at a high speed. According to the X-ray source 2 of the present embodiment, high energy X-rays can be emitted without causing such harmful effects.

  In the present embodiment, the anode 7 is provided on the upper surface side of the surface electrode 64. However, as shown in FIG. 6, the anode 7 is provided on the upper surface of the drift layer 63 without the surface electrode 64. Also good. In that case, the positive electrode of the power source that applies the voltage Ve is connected to the anode 7, and the negative electrode of the power source is connected to the lower surface electrode 62. When a voltage Ve is applied to the drift layer 63 sandwiched between the anode 7 and the lower electrode 62, electrons are accelerated and emitted from the drift layer 63 toward the anode 7. Therefore, by applying the voltage Ve as shown in FIG. 6, generation of electrons in the drift layer 63 and acceleration of electrons from the drift layer 63 toward the anode 7 can be performed. Thus, in order to function as an electrode of the voltage Ve, the film thickness of the anode 7 is preferably 1 nm to 1 μm, and more preferably 10 to 100 nm from the viewpoints of X-ray output efficiency and transmission efficiency.

  Next, the X-ray image detector 4 will be described.

  The X-ray image detector 4 outputs an X-ray image signal in accordance with the intensity of the incident X-ray. The X-ray image detector 4 includes a so-called digital X-ray detector (FPD) such as a screen film (SF) system that is a so-called analog X-ray imaging system, a computed radiography (CR), and a flat panel X-ray detector (FPD). An X-ray imaging system can be used.

  CR and FPD are used for the digital X-ray imaging system. This feature is that image processing can be easily performed to convert image information into digitized electrical signals. In the analog X-ray imaging system, since X-ray image detection and X-ray image display are performed by the same silver halide film, there is a limitation from the X-ray image display function when designing the image detection function. , 100% of that ability cannot be demonstrated. However, in the digital X-ray imaging system, since the X-ray image detector 4 and the image display are functionally separated, the capability as the X-ray image detector 4 can be fully exploited. For example, in both CR and FPD, the dynamic range of image detection is wider than that of the SF system and is about 4 digits.

Here, image processing in the digital X-ray imaging system will be described.
When the digital X-ray imaging system is used for phase contrast imaging, it is important in the present invention to process the obtained image signal to form an easy-to-view image.

  Since it is a preferable condition that the phase contrast image shooting is performed with an enlargement of 1.2 to 3 times and is preferable, it can be diagnosed without a sense of incongruity with the past image by returning to the conventional contact image size. Further, when reducing the image, it is preferable to match the minimum pixel size or standard pixel size of an output device such as an imager. Alternatively, it is preferable to reduce the pixel size to an integer multiple of the minimum pixel size. When the pixel size is reduced to an integer multiple of the output pixel size, it is preferable to perform phase contrast imaging with an enlargement factor equal to or close to the conventional contact image size.

  When forming an output image using the obtained image signal, it is fundamental to form an output image with a linear image density with respect to the image signal. An image output image can be drawn by converting into an S-shaped curve in accordance with a conventional SF system. It is also possible to select a portion having a large signal value or a portion having a small signal value and form an image output image with a moderate contrast. In addition, it is preferable to output the image signal area above a certain level at the maximum image density of the image output device or image output film. In a conventional SF system image, a maximum image density contrast is depicted near density 1. The digital image contrast is preferably 1 to 3, but in the case of a breast image, it is preferable to draw in the range of 2.5 to 5. Further, it is preferable to output the image signal in the image area range so that it falls within the range of 70 to 100% in the minimum density and maximum density areas of the output image.

  In the phase contrast image, the edge of the subject H is emphasized. Furthermore, it is preferable to further enhance the edge portion by so-called blur mask processing. When this edge image enhancement is performed, it is possible to suppress an increase in image noise by increasing the enhancement as the image signal intensity change is larger and reducing the enhancement as the image signal intensity change is smaller. In addition, in order to decompose the obtained image signal into spatial frequencies and obtain an image suitable for each diagnostic region, it is preferable to perform enhancement processing with the spatial frequency.

  The obtained phase contrast image is superimposed on past captured images to emphasize pathological changes, so-called time-difference processing, or lesion information is input to a computer in advance, and the possibility of lesions compared with the obtained image information It is preferable to use so-called CAD (Computed Assisted Diagnosis) that displays the image on the image.

  Regarding the output of the phase contrast X-ray image, unlike the analog X-ray image capturing system in the digital X-ray image capturing system, the X-ray image detector and the X-ray image display device are separated from each other. Can be displayed. That is, a hard copy of a transparent image displayed as an image similar to a conventional SF system, a reflective hard copy mainly used for reference, or a so-called soft copy such as a cathode ray tube (CRT) or a liquid crystal Is output. The density of display of these images is preferably 8 bits or more, more preferably 10 bits or more. The maximum image density is preferably 2.5-5. In particular, when displaying a breast image, the image density is preferably 3 or more, and more preferably 3.8 or more.

  Next, an X-ray imaging system will be described.

  As shown in FIG. 1, the X-ray imaging apparatus 1 arranges a subject table 3 that positions a subject H between an X-ray source 2 and an X-ray image detector 4. Further, a distance marking rail 12 on which the distance between the X-ray source 2 and the X-ray image detector 4 is marked is installed between the X-ray source 2 and the X-ray image detector 4. As an installation base for the X-ray source 2, at least one of the infrared light position detector 9 for measuring the distance R <b> 1 with the subject base 3 and the X-ray source 2 or the X edge image detector 4 on the distance marking rail 12 is used. And a drive motor 10 serving as a drive source to be moved. An operating device 11 is connected to the X-ray source 2 and the X-ray image detector 4. The operation device 11 includes an image display monitor 11a, a keyboard 11b, a control device 11c, and an X-ray source control device 11d. The detected X-ray image is output to the imager 13.

  In this embodiment, the patient is imaged in a standing position. However, in the case of imaging in a lying state, that is, in a lying position, the X-ray source 2, the subject table 3 and the X-ray image detector 4 are installed in the vertical direction. The X-ray source 2 is arranged above or below. Further, the X-ray source 2, the subject table 3 and the X-ray image detector 4 can be incorporated and fixed in one apparatus. On the other hand, when arranged separately, the X-ray image detector 4 having a side length of 50 cm or more can be used. In such a large size, the X-ray image detector 4 is used to prevent vibrations or the like. It is preferable that the number of supporting columns is plural. In the phase contrast imaging, the distance R2 between the subject H fixed on the subject table 3 and the X-ray image detector 4 is set to 0.25 m or more, so the X-ray grid used in the conventional close-up imaging is unnecessary. Yes, the device can be simplified.

  In X-ray phase contrast imaging, since a distance R2 is placed between the subject H and the X-ray image detector 4, it is preferable to provide a jig so that unnecessary objects do not enter the X-ray irradiation path. It is preferable to automatically measure the distances of the X-ray source 2, the subject table 3, and the X-ray image detector 4. It is preferable to calculate an enlargement ratio based on the distance data and to use it for determining X-ray imaging conditions. A terminal for measuring the X-ray intensity can be installed on the X-ray image detector 4 or the subject table 3, and the imaging conditions can be determined based on the value. Also, in order to distinguish between X-ray phase contrast image capturing and conventional close-contact imaging, a device that does not emit X-rays when the imaging condition is set to close-contact imaging when the distance relationship is to perform X-ray phase contrast image capturing. It is preferable to equip the X-ray source 2.

  When photographing with an analog X-ray image photographing system, a cassette equipped with a silver salt film and an X-ray screen is used as the X-ray image detector 4. After taking an X-ray image, the silver salt film is taken out from the cassette and developed by an automatic processor or the like. An image is drawn on the processed film obtained, and the image is observed on a light box (Shawkasten) equipped with a fluorescent lamp or the like. After observing the image, it may be stored in a predetermined place as it is for a certain period, and may be taken out and observed as necessary. It is also possible to digitize the image information with a film digitizer, process the image, and display the image separately. In this case, the image information is stored as digital information.

  When photographing with a digital X-ray imaging system, in the case of CR, a cassette containing a stimulable phosphor plate is used as the X-ray image detector 4, and a CR plate with a stimulable plate reader is integrated. The apparatus may be used as the X-ray image detector 4. When using a cassette, an X-ray image is read by setting the cassette in the image reading apparatus after imaging. When the FPD is used, the X-ray source 2, the subject table 3, and the FPD as the X-ray image detector 4 may be integrated or may be arranged independently. At this time, the FPD can be used as an automatic X-ray exposure apparatus.

  As shown in FIG. 7, the X-ray image information obtained by the digital X-ray image detector of the X-ray imaging apparatus 1 is subjected to image processing and, if necessary, CAD processing, and image print output and image display Then, it is output to a soft copy or hard copy for image signal storage, etc. and used for image diagnosis. Image information can be sent to a local network in a hospital facility, another medical facility or research facility through a network line, or an Internet line, and image diagnosis can be performed at the sent remote location. When sending such image information as digital image information, it is preferable to comply with a protocol such as the DICOM standard.

  When digital image information is displayed in soft copy or hard copy, medical conditions such as patient data and medical history necessary for diagnosis, distance R1, R2, magnification, and X-ray image detector 4 type and name to be used It is preferable to output it together with information necessary for medical work such as medication, address and name. Moreover, it is preferable to output not only the X-ray phase contrast image but also a medical image such as a past X-ray image, a close-contact photographed image, an X-ray CT image, an MRI image, an endoscopic image, and a fundus photographic image. . In particular, when displayed in soft copy, it is preferable to display all image information and the like necessary for diagnosis using a plurality of screens. After the diagnosis is completed, it can be output and stored as a hard copy, or the hard copy can be provided to a necessary department. In addition, an image signal can be stored in a magneto-optical recording material or the like as an electric signal, and an image desired to be read can be reproduced when necessary.

  Next, an X-ray image capturing method by the X-ray image capturing system of the present embodiment will be described.

  First, when the subject H is fixed on the subject table 3, the distance R1 between the X-ray source 2 and the subject table 3 is detected and displayed by the infrared light position detector 9. Further, the distance R2 between the subject table 3 and the X-ray image detector 4 is confirmed from the detection result of the distance R1 and the distance marking rail 12. The user adjusts the positions of the X-ray source 2, the subject table 3, and the X-ray image detector 4 so as to be within a predetermined range while checking the distances R1 and R2. When each is arranged, X-rays are irradiated from the X-ray source 2 in a predetermined direction. The irradiated X-rays pass through the subject H and reach the X-ray image detector 4. Then, an image signal obtained in accordance with the intensity of the X-ray that has reached the X-ray image detector 4 is output to the operation device 11, and image processing is performed based on an instruction via the operation device 11 to generate an X-ray image. Obtained and output to the imager 13.

  Next, X-ray image imaging conditions will be described.

  The present invention uses phase contrast to improve X-ray images. Specifically, using the X-ray source 2 having a focal spot size D of 1 to 300 μm, the distance R1 from the X-ray source 2 to the object table 3 is 0.25 to 3 m, and the object table 3 to the X-ray image detector 4 is used. X-ray imaging conditions in which the distance R2 is 0.25 to 3 m, and an X-ray imaging system that realizes the conditions.

Conditions for photographing a phase contrast image according to the present invention or conditions for easily obtaining edge contrast are described below.
The focus size D of the X-ray source 2 is 1 to 300 μm. The smaller the focus size D is, the larger the edge effect is. There is an advantage that phase contrast is easily obtained. On the other hand, if the focal spot size D is too small, the obtained edge width is narrowed, and particularly difficult to detect with a digital detector. Therefore, 10 to 250 μm, more preferably 50 to 200 μm is preferable. The voltage Ve is set in consideration of the appearance of phase contrast in accordance with the thickness of the subject H and the imaging region. When the target layer 71 containing molybdenum as a main component is used, the phase contrast is more easily obtained as the characteristic X-ray is stronger and the bremsstrahlung component is smaller. Further, the larger the distances R1 and R2, the easier it is to obtain the phase contrast, and the enlargement ratio is represented by (R1 + R2) / R1. Here, both the distances R1 and R2 are preferably 0.25 to 1.5 m, and the distance (R1 + R2) is preferably 0.5 to 3 m. The imaging conditions are set according to the enlargement ratio and the thickness and part of the subject H. It should be noted that all of the conditions disclosed here that can easily provide the phase contrast can be explained by the theory of X-ray refraction by geometric optics.

  As described above, according to the X-ray imaging system of the present embodiment, the X-ray source 2 includes the field emission electron source 6 having a high electron emission capability and high durability as described above. Thus, an X-ray source having excellent durability can be obtained. Thereby, in a medical field etc., imaging | photography for a short time is attained, generation | occurrence | production of the blurring of the image which arises by a to-be-irradiated object moving can be prevented, and diagnostic performance can be improved. In addition, since re-imaging due to image blur can be eliminated, unnecessary exposure to the patient can be reliably prevented.

  Further, since the X-ray source 2 includes the field emission electron source 6, it is not necessary to provide a filament power source unlike the thermoelectron emission electron source, and the thermoelectron emission electron source is used as the X-ray source. Compared to the case where the X-ray source 2 is used as a source, it is possible to prevent the X-ray source 2 from being enlarged. Furthermore, since the target layer 71 having a predetermined thickness is arranged on one surface side of the field emission electron source 6, X-rays generated in the target layer 71 are transmitted through the anode 7 and emitted, and therefore, between the cathode and the anode. There is no need to apply a voltage, and the size of the X-ray source 2 can be reduced. Furthermore, by forming the target layer 71 thinner than before, the generated X-rays can be transmitted, and secondary electrons generated by collisions between electrons and metals are transferred to the outside of the target layer 71. By releasing, heat generation in the anode due to collision between the anode 7 and the secondary electrons can be suppressed. Therefore, it is not necessary to cool the anode 7, and the X-ray source 2 of the apparatus can be simplified. In addition, it is possible to reduce the size of the X-ray imaging apparatus used in the X-ray imaging system. Further, the position of the anode 7 is fixed, and it is not necessary to provide a rotating mechanism of the anode unlike an X-ray source having a conventional rotating anode, and the X-ray source 2 can be reduced in size and simplified.

  Note that the present invention can also be applied to an X-ray imaging system or a tomosynthesis system using a so-called C-arm whose X-ray source 2 or X-ray image detector 4 changes its position.

  As shown in FIG. 8, an X-ray imaging apparatus 15 using a C arm is attached to a subject table 3, a C arm 16 that is rotatable while the subject table 3 is at the center position, and one end of the C arm 16. The X-ray source 2 and the X-ray image detector 4 attached to the other end of the C-arm 16 are provided. Since the C-arm 16 is rotatable with the subject table 3 as the center position, the distance R1 between the X-ray source 2 and the subject table 3 and the distance R2 between the subject table 3 and the X-ray image detector 4 remain constant. The irradiation angle of the X-ray on the subject H can be freely adjusted.

  As shown in FIG. 9, the X-ray imaging apparatus 17 used in the tomosynthesis system includes an X-ray source 2, a subject table 3 and an X-ray image detector 4 arranged in the X-ray irradiation direction. It has been. The X-ray source 2 is movable in a predetermined direction (in the direction of the arrow in the figure), and the X-ray source 2 is moved to irradiate the subject H from various directions. Thus, a plurality of pieces of X-ray image information are detected. Then, a three-dimensional image inside the subject is taken from a plurality of pieces of X-ray image information obtained.

  In such an X-ray imaging system or tomosynthesis system using the C-arm, in order to obtain a good tomographic image or a three-dimensional X-ray phase contrast image, the focus size D of the X-ray source 2 is 1 to 300 μm, The distance R1 from the X-ray source 2 to the subject table 3 is preferably 0.25 to 3 m, and the distance R2 from the subject table 3 to the X-ray image detector 4 is preferably 0.25 to 3 m.

  Furthermore, a longer distance R1 is preferable because the phase contrast effect becomes larger and the image becomes clearer. However, if the distance R1 is too long, the apparatus itself is increased in size. Therefore, it is preferable that 0.5m ≦ R1 ≦ 1m. A longer distance R2 is preferable because it can increase the phase contrast effect of the refracted X-rays by transmitting through the subject. However, if the distance R2 is too long like the distance R1, the apparatus becomes larger, so that 0.5 m ≦ R2 ≦ 1 m is preferable. The larger the focal spot size D, the larger the X-ray output (the irradiation X-ray dose per unit time increases). However, if the focal spot size D is too large, the image will be blurred due to geometrical sharpness, so 50 μm ≦ D ≦ 200 μm. 70 μm ≦ D ≦ 120 μm is preferable.

[Second Embodiment]
The X-ray imaging system of this embodiment performs breast imaging. In the mammography apparatus 18 of the present embodiment, an X-ray source 2, a subject table 3, and an X-ray image detector 4 are arranged along the vertical direction, and are directed upward toward the subject H as an imaging region of the patient. The second embodiment is different from the first embodiment in that an X-ray image is taken by irradiating with X-rays.

  As shown in FIG. 10, the mammography apparatus 18 includes an X-ray source 2 that emits X-rays downward, an X-ray image detector 4 that detects an X-ray image based on the incident X-rays, and Are arranged along the vertical direction. Here, the X-ray source 2 and the X-ray image detector 4 of the present embodiment are the same as those of the first embodiment. A subject table 3 for positioning the subject H is provided between the X-ray source 2 and the X-ray image detector 4. Above the subject table 3, a compression plate 19 for pressing and fixing the subject H from above is disposed so as to be movable up and down.

  In the X-ray source 2 in the present embodiment, molybdenum, rhodium, and tungsten are preferable as the main component of the target layer 71 of the anode 7, and molybdenum or rhodium is more preferable from the viewpoint of mammography.

  Here, the distance between the X-ray source 2 and the subject table 3 is R1, the distance between the subject table 3 and the X-ray image detector 4 is R2, and the distance between the X-ray source 2 and the X-ray image detector 4 is R3. To do. The distance between the X-ray source 2 and the X-ray image detector 4 is used to obtain an X-ray phase contrast image having a high contrast at the boundary portion of the subject H due to the X-ray phase shift that occurs when the subject H is transmitted. R3 is preferably 0.75 m or more, and the distance R2 between the subject table 3 and the X-ray image detector 4 is preferably 0.25 m or more.

  Note that the edge effect due to the phase contrast becomes larger when the distance R2 is larger. However, when the distance R2 is too large with respect to the distance R1, the sharpness is deteriorated due to the influence of the blur of the penumbra. Therefore, it is desired from the aspect of image quality improvement that both the distance R2 and the distance R1 are large. On the other hand, if these distances are too large, the whole breast image photographing apparatus 18 becomes large, which causes a problem for the convenience of handling the size of the photographing room and the breast image photographing apparatus 18.

  From the above viewpoint, it is preferable that the distance R3 between the X-ray source 2 and the X-ray image detector 4 is 0.85 m or more in obtaining an X-ray phase contrast image in mammography. On the other hand, for the convenience of handling the apparatus, it is preferable that the distance R3 between the X-ray source 2 and the X-ray image detector 4 is 2 m or less. At this time, the object table 3 is preferably provided so that the distance R1 to the X-ray source 2 is 0.5 to 1 m and the distance R2 to the X-ray image detector 4 is 0.25 to 1 m. It is preferable for obtaining image quality. The distance R3 between the X-ray source 2 and the X-ray image detector 4 is set to 0.9 to 1.65 m, and the distance R1 between the X-ray source 2 and the object table 3 is set to 0.6 to 0.75 m. More preferably, the distance R2 between the subject table 3 and the X-ray image detector 4 is 0.3 to 0.9 m.

  In addition, in order to achieve phase contrast over penumbra blur and obtain a sharp image, the upper limit of the focus size D of the X-ray source 2 is determined from the distance R1, distance R2, or radiation physical characteristics. On the other hand, in order to obtain a radiation dose of a certain level or more, a certain focus size D is required, so that the lower limit value is determined. For this reason, in order to perform X-ray phase contrast imaging in a normal medical facility, the focal spot size D needs to be 1 to 300 μm, preferably 10 to 250 μm, and more preferably 50 to 200 μm.

Next, a mammography method in this embodiment will be described.
First, when the subject H is placed on the subject table 3, the compression plate 19 is lowered to press the subject H. Thereafter, X-rays are irradiated and an X-ray image is taken in the same manner as in the first embodiment. In the present embodiment, the X-ray source 2, the subject table 3, and the X-ray image detector 4 are arranged along the vertical direction, so that the X-rays irradiated downward from the X-ray source 2 The light passes through H and reaches the X-ray image detector 4, and an image corresponding to the intensity is detected.

  As described above, according to the mammography apparatus 18 of the present embodiment, the X-ray source 2 having high output and excellent durability can be obtained as in the first embodiment. Further, by using the field emission electron source as the cathode for the X-ray source 2, the X-ray source 2 can be reduced in size and durability, and the mammography apparatus 18 used in the X-ray imaging system can be used. Miniaturization can be achieved.

  In the mammography apparatus 18 in the present embodiment, the positions of the X-ray source 2 and the X-ray image detector 4 are fixed. However, a system that uses a C-arm in mammography as in the first embodiment. And tomosynthesis system can be used and can be changed as appropriate.

It is a side view of the X-ray imaging device in a first embodiment. It is sectional drawing of the X-ray source 2 which concerns on this invention. It is sectional drawing of the field emission type electron source which concerns on this invention. It is a schematic block diagram which shows another example of a field emission type electron source. It is a schematic block diagram which shows another example of a field emission type electron source. It is a schematic block diagram which shows another example of a field emission type electron source. It is a block diagram which shows the output of the digital X-ray image information based on this invention. It is a top view of the X-ray imaging device which uses C arm. It is a front view of the X-ray imaging device used in a tomosynthesis system. It is a side view of the breast imaging device in a second embodiment.

Explanation of symbols

1, 15, 17 X-ray imaging apparatus 2 X-ray source 3 Subject table 4 X-ray image detector 5 Vacuum envelope 6 Field emission electron source 7 Anode 8 X-ray output window 18 Mammography apparatus 61 Support substrate 62 Lower surface Electrode 63 Drift layer 63a Semiconductor layer 63b Insulator layer 64 Surface electrode 71 Target layer H Subject

Claims (12)

An X-ray source disposed in a vacuum envelope and provided with a field emission electron source that emits electrons by applying an electric field; and an anode that emits X-rays upon incidence of the electrons;
An X-ray image detector which is disposed at a position where the X-ray is incident and detects an image signal of the X-ray image according to the intensity of the incident X-ray;
In an X-ray imaging system that captures an X-ray phase contrast image,
The field emission electron source includes a support substrate, and a drift layer in which semiconductor layers and insulator layers made of metal oxide are alternately stacked,
The X-ray imaging system, wherein the X-ray source includes the anode in an electron emission direction of the field emission electron source, and transmits the X-ray through the anode. The field emission electron source includes a pair of electrodes for applying an electric field in the stacking direction across the drift layer,
The X-ray imaging system according to claim 1, wherein a film thickness of the anode is in a range of 0.1 to 100 μm.   The X-ray imaging system according to claim 2, wherein the thickness of the anode is in the range of 1 to 10 μm.   The X-ray source includes a pair of electrodes for applying an electric field in the stacking direction across the drift layer, and the electrode provided in the electron emission direction of the drift layer of the electrodes includes the anode. The film thickness of the anode is in the range of 1 nm to 1 μm, and the X-ray imaging system according to claim 1.   The X-ray imaging system according to claim 4, wherein the thickness of the anode is in the range of 10 to 100 nm.   The X-ray imaging system according to any one of claims 1 to 5, further comprising a high-voltage power supply that applies a high voltage for accelerating electrons between the anode and the field emission electron source.   A subject table for positioning a subject is disposed between the X-ray source and the X-ray image detector, and a distance R1 from the X-ray source to the subject table is 0.25 to 3 m. The distance R2 from the subject table to the X-ray image detector is 0.25 to 3 m, and the focal point size of the X-ray source is 1 to 300 μm. The X-ray imaging system according to one item.   The thickness of the semiconductor layer is in the range of 1/1000 to 5/4 of the mean free path of electrons in the semiconductor layer, and the relative dielectric constant of the semiconductor layer is 1 of the relative dielectric constant of the insulator layer. The X-ray imaging system according to claim 1, wherein the X-ray imaging system is in a range of 5 to 100 times.   The X-ray imaging system according to claim 1, wherein the semiconductor layer has a thermal conductivity in a range of 0.05 to 100 W / cm · K.   The X-ray imaging system according to claim 1, wherein the semiconductor layer is made of zinc oxide.   The X-ray according to claim 1, wherein a main component of the insulator layer is at least one selected from insulating oxides, nitrides, and oxynitrides. Image shooting system.   The X-ray imaging system according to claim 11, wherein a main component of the insulator layer is at least one selected from silicon oxide, silicon nitride, and silicon oxynitride.

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