JP2007317383A - Electromagnetic wave generator and x-ray imaging system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-cost, high-luminance and large-intensity X-ray source having a compact X-ray source size of several micrometers, and large in a heat radiation effect of an X-ray target. <P>SOLUTION: In a round accelerator having a charged particle generation means, a charged particle acceleration means, a deflection magnetic field generation means, and the X-ray target arranged on a stable orbit of charged particles, a metal rod having a needle-like tip form having a diameter around 10 μm is used for the X-ray target, and the direction of the needle-like projection part is set vertical to the direction in which the charged particles are orbiting. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electromagnetic wave generation device that uses an accelerator that accelerates charged particles to high energy, collides the accelerated charged particles with a target to generate electromagnetic waves such as X-rays, and an X-ray imaging system using the electromagnetic wave generation device. Is.

As a conventional electromagnetic wave generator using a circular accelerator, a device using an electron storage ring is known. An electromagnetic wave generator using an electron storage ring is composed of an injector and an electron storage ring, and an electron beam accelerated to a predetermined energy is incident on the electron storage ring from the injector and is constant in the electron storage ring. Go around the orbit. A target is disposed on the orbit, and electromagnetic waves such as X-rays are generated by collision with the circulating electron beam. (See Patent Document 1)
Japanese Patent No. 2796071 (particularly paragraph number 0048)

  In an electromagnetic wave generator (Patent Document 1) using such an electron storage ring, a tungsten wire or a carbon thin film is used as an X-ray target in order to repeatedly collide the electron beam with the target. Moreover, in order to reduce the size of the light source of X-rays generated by collision with the circulating electron beam, it is necessary to set the wire diameter to about 10 μm and the thickness of the thin film to about 10 μm. In that case, if the wire diameter or thin film thickness is small, the heat removal effect by heat conduction is small, and for example, even if the wire support is cooled, there is almost no cooling effect. Therefore, the temperature rise when the electron beam collides with the target portion is very large, and there is a problem that the wire and the thin film are melted.

  The present invention has been made to solve the above-described problems, and provides an X-ray target that does not melt even when an electron beam having a higher intensity than conventional ones collides. An object of the present invention is to realize an electromagnetic wave generator capable of generating intense X-rays and an X-ray imaging system using the electromagnetic wave generator.

  The electromagnetic wave generator of the present invention includes a charged particle generating means for generating charged particles, an accelerating means for accelerating the charged particles generated by the charged particle generating means, and deflecting the charged particles accelerated by the accelerating means. Consists of a deflection magnetic field generating means that circulates on the orbit and a metal rod with a tip sharpened like a needle, and generates X-rays by colliding charged particles circulating around the deflection magnetic field generating means with the tip of the metal rod And a target to be made.

  The X-ray imaging system according to the present invention includes charged particle generation means for generating charged particles, acceleration means for accelerating the charged particles generated by the charged particle generation means, and deflecting charged particles accelerated by the acceleration means. A deflecting magnetic field generating means that circulates on a circular orbit, and a metal rod having a needle-like tip pointed, and a charged particle circulated by the deflecting magnetic field generating means collides with the tip of the metal rod to emit X-rays. An electromagnetic wave generator having a target to be generated, an imaging detector for irradiating an irradiated body with X-rays generated by the electromagnetic wave generator to detect the captured image, and processing an image detected by the imaging detector A data processing device for obtaining a fluoroscopic image of the irradiated object is provided.

According to the present invention, since the target is composed of a needle-shaped metal rod, the electron beam can collide with the needle-like portion at the tip of the target to reduce the size of the X-ray light source, while the electron beam collides. Since the temperature rise is removed at a location where the diameter of the base portion of the target is large, it becomes possible to cause high-intensity charged particles to collide with the X-ray target, and X-rays having a high-intensity micro light source size can be generated. An electromagnetic wave generator is obtained.
Further, by using the electromagnetic wave generator of the present invention in an X-ray imaging system, it becomes possible to perform refraction contrast imaging using the difference in refraction of X-rays, and a compact and low-cost X-ray imaging system can be realized. Small cancers can be identified with a low dose. In addition, the difference between the refractive effects of two substances having similar atomic numbers is several hundred times larger than the difference between the conventional absorption effects, and the fluoroscopic identification is possible.

Embodiment 1 FIG.
Embodiment 1 of the present invention will be described with reference to FIGS. Embodiment 1 describes an electromagnetic wave generator that generates X-rays by accelerating an electron beam as charged particles and colliding with a target.
FIG. 1 is a cross-sectional view of an electromagnetic wave generator according to Embodiment 1 of the present invention, which is cross-sectionalized on an electron beam trajectory plane around which an electron beam circulates. 2 is a cross-sectional view taken along the line II-II in FIG. 1, and is a configuration diagram of the X-ray target according to the first embodiment of the present invention. FIG. 3 is an explanatory diagram showing that a charged particle beam approaches the X-ray target according to Embodiment 1 of the present invention. FIG. 4 is an explanatory view showing the state of vibration of the charged particles in the vertical direction when the charged particle beam approaches the X-ray target according to Embodiment 1 of the present invention.

  In FIG. 1, a charged particle generating means 11 has an electron gun and generates charged particles (electron beam). The charged particle accelerating means 12 generates a magnetic field and accelerates charged particles (electron beams) generated by the electroparticle generating means 11 by an electric field based on the magnetic field. The deflecting magnetic field generating means 13 deflects the charged particles accelerated by the charged particle accelerating means 12 by a magnetic field and circulates on the accelerating orbit 15 and is provided in a plurality (four in the figure). As will be described in detail with reference to FIG. 2, the X-ray target 14 is composed of a metal bar having a tip that is pointed like a needle, and charged particles circulating around by the deflection magnetic field generating means 13 collide with the tip of the metal bar. A line is generated. The number of X-ray targets 14 is one in the drawing, but a plurality of X-ray targets 14 may be provided on the orbit of charged particles. The vacuum duct 16 holds accelerated charged particles in a high vacuum, and is configured in an annular shape so that charged particles (electron beams) circulate.

  The charged particle generation means 11 is installed outside the acceleration orbit 15 of charged particles, and the charged particles are circulated counterclockwise. Further, the X-ray target 14 is arranged on the inner side of the orbit of the charged particles, and the direction of the needle-like tip portion of the target is arranged outward when the charged particles orbit the outside of the target. The charged particle acceleration means 12 is disposed at the center of the apparatus. The charged particle generating means 11, charged particle accelerating means 12, deflection magnetic field generating means 13, X-ray target 14 and vacuum duct 16 constitute a circular accelerator.

In the above configuration, an electron beam having a pulse width of several microseconds generated by the charged particle generating means 11 is induced by the magnetic field of the charged particle accelerating means 12 while circling in the vacuum duct 16 by being deflected by the deflecting magnetic field generating means 13. The electric field is accelerated in the circumferential direction of the figure. Thus, the electron beam circulates on the charged particle acceleration orbit 15 by the interaction between the charged particle acceleration means 12 and the deflection magnetic field generation means 13.
The electron beam in this apparatus travels along a substantially circular orbit at the part of the deflecting magnetic field generating means 13, and the part without the deflecting magnetic field generating means 13 travels along a trajectory that is close to a straight line. To do. The angle formed between the magnetic pole end of the deflection magnetic field generating means 13 and the traveling direction of the electron beam is not 90 degrees, and the electron beam is converged by the leakage magnetic field every time it passes through the magnetic pole end and accelerated with a predetermined beam size. Since the electron beam is attenuated in the atmosphere, the electron beam circulates inside the vacuum duct 16 held in a high vacuum. The charged particle accelerating means 12 and the deflecting magnetic field generating means 13 are applied with an alternating magnetic field of about 50 Hz to several tens of kHz by an electromagnet power source (not shown). It is possible to stably circulate and accelerate in a certain area without changing the trajectory.

  The accelerated electron beam moves inward when the relationship between the magnetic field strengths of the charged particle acceleration means 12 and the deflection magnetic field generation means 13 is slightly changed, and collides with the target 14 installed in the stable orbital region to generate X-rays. Since the light source size of the generated X-ray is almost the same as the size of the target 14, the light source size can be reduced if the size of the target 14 is small. The target size can be about several μm, and an X-ray source with a light source size of about several μm can be realized. Since the size of the circulating electron beam is several mm to several hundred mm, few electrons collide with the target 14 in one round. However, since the electrons that have not collided with the target 14 circulate in the stable circulation region, they continue to circulate in the apparatus as they are. And sometime, it always collides with the target 14 and generates X-rays. The X-rays thus generated are taken out from an X-ray take-out port (not shown) and used for a medical diagnostic apparatus such as an X-ray imaging system.

  The circulating electron beam is accelerated to a predetermined energy in a region where it does not collide with the target 14 and then reaches a region where it collides with the target 14 to generate X-rays. Therefore, since the accelerating electron beam circulates in a region where it does not collide with the target 14, the electron beam is not lost unnecessarily by colliding with the target 14 during acceleration. Further, the target 14 is thin with respect to the electron beam circulation direction, that is, the X-ray generation direction so that generated X-rays are not reduced by self-absorption in the target 14. Furthermore, the energy that the electron beam colliding with the target 14 loses with a thin target is very small. For example, when a 1 MeV electron beam collides with a tungsten target having a thickness of 7 μm, only about 1.6% of the energy is lost. The deflecting magnetic field generating means 13 can be designed so as to stably circulate an electron beam having an energy difference of about 20% to 40%, and the electron beam once colliding with the target 14 can continue to circulate stably. Since electrons that have once collided with the target continue to circulate tens of thousands of laps until the next collision with the target, if there is an increase in energy of several eV in one lap, several tens of keV to several hundreds of keV until the next collision occurs. There is an increase in energy. Therefore, it becomes possible to make the electron beam collide with the target 14 many times, and high-intensity X-rays can be generated.

  By the way, as described above, removal of heat generated by the collision is a major technical problem in order to make charged particles of a large current collide with the X-ray target 14. In order to make a fine point light source X-ray, it is necessary to use a fine X-ray target and support the target with a thin wire, etc. However, with a thin wire, the heat conduction is small and the temperature rises so that the fine target and the thin wire dissolve. Because it will end up. Therefore, in the present invention, as shown in FIG. 2, the target 14 is a metal rod having a needle-like tip. In other words, the X-ray target 14 was composed of a base portion 14a having a large diameter (about 0.5 mm in diameter), a tapered needle-like projection portion 14b, and a metal rod support structure 14c. The diameter Φ of the tip of the needle-like protrusion 14b is about 20 μm to 5 μm, preferably about 5 μm, but is shown visually thick in the drawing. Further, the length s of the needle-like protrusion 14b is several hundred μm to several mm. Various materials can be used as the material of the X-ray target 14 depending on the purpose, but materials having a high melting point, a low expansion coefficient, and a high thermal conductivity such as tungsten, tantalum, molybdenum, Metals such as carbon are used. In FIG. 2, an electron beam cross section 21 that is a charged particle that circulates in the accelerator is schematically shown.

  When the relationship between the magnetic field strengths of the charged particle accelerating means 12 and the deflection magnetic field generating means 13 is set to a predetermined value, the electron beam cross section 21 that is a charged particle gradually approaches the needle-like protrusion 14 b of the target 14. The approach is shown in FIG. FIG. 3 shows the electron beam cross section 21b after the elapse of time Δt. At time Δt, the relationship between the magnetic field strengths of the charged particle acceleration means 12 and the deflection magnetic field generation means 13 is controlled so that the electron beam cross section approaches the needle-like protrusion 14b by ΔD. At this time, the time for the charged particles to approach by the diameter Φ of the tip of the needle-like protrusion 14b is set to 10 times or more of the time for the charged particles (electron beam) to circulate in the circular accelerator (circulation time).

  FIG. 4 schematically shows one charged particle in the electron beam cross section 21 which is a charged particle. The charged particles do not circulate around the accelerator in one orbit, but circulate around the one orbit while vibrating (betatron oscillation). That is, a charged particle 41 is obtained by plotting a cross section of each charged particle in the electron beam cross section 21. That is, the charged particles 41 can oscillate so as to vibrate in the vertical direction as shown by the arrows in the figure and almost completely cover the electron beam section 21. Therefore, if the charged particles are gradually brought closer to the needle-like protrusion 14b as shown in FIG. 3, all the electron beams in the vertical direction can collide with the needle-like protrusion 14b, and the diameter is about 7 μm. X-rays from the light source can be generated. The charged particles colliding with the needle-like protrusions 14b lose some energy but continue to circulate thereafter.

  With the above configuration, the electron beam collides with the needle-like protrusion 14b at the tip of the target to reduce the size of the X-ray light source, while the temperature rise due to the collision of the electron beam increases the diameter of the base portion 14a of the target. Since heat is removed at the location, charged particles with high intensity can collide with the X-ray target. In this way, high-intensity X-rays with a small light source size can be generated.

Embodiment 2
FIG. 5 is a cross-sectional view of an electromagnetic wave generator according to Embodiment 2 of the present invention, which is cross-sectionalized on an electron beam trajectory plane around which an electron beam circulates. FIG. 6 is an enlarged view of the vicinity of the X-ray target shown in FIG.
5, the same reference numerals as those in FIG. 1 are the same as those in FIG. The shield 51 is for preventing unnecessary charged particles from colliding with the target 14, is made of a metal plate, and is made of tungsten or tantalum, which is the same as the material of the target 14.

  Among the charged particles that continue to circulate, a certain electron beam collides with the base 14a having a large diameter of the target 14 after a certain number of laps, resulting in noise with respect to the X-ray point light source. Therefore, as shown in FIG. 6, the electron beam is dumped to the upstream side of the circular orbit different from the X-ray target 14 in the circular accelerator, that is, the shielding that prevents the electron beam from colliding with the base portion 14a of the target. A body 51 was placed. By doing so, if there is no shield 51, it becomes possible to remove in advance the charged particle beam that collides with the root portion 14a having a large diameter, and an X-ray point light source with a good SN ratio can be realized. Although the shield 51 is provided on the upstream side of the X-ray target 14 in FIG. 5, the same effect can be obtained even if provided on the downstream side. However, the shield 51 does not have to be placed at an arbitrary position of the circular accelerator, but needs to be arranged at a position where the charged particles come inside due to the horizontal vibration of the circulating electron beam.

Embodiment 3
FIG. 7 is a cross-sectional view of an electromagnetic wave generator according to Embodiment 3 of the present invention, which is cross-sectionalized on an electron beam trajectory plane around which an electron beam circulates. In FIG. 7, the same reference numerals as those in FIG. 1 are the same as those in FIG.
In the first embodiment, the target 14 is disposed on the inner side of the acceleration orbit 15 of the charged particles. However, in the third embodiment, the target 14 is disposed on the outer side of the acceleration orbit 15 of the charged particles. When the target 14 is arranged outside the charged particle acceleration orbit 15, the charged particle generating means 11 is preferably installed inside the charged particle acceleration orbit 15. This third embodiment also has the same effect as the first embodiment.

  The charged particle accelerating means 12 and the deflecting magnetic field generating means 13 are applied with an alternating magnetic field of about 50 Hz to several tens of kHz by an electromagnet power source. If the relationship between the two magnetic field strengths is set to a predetermined value, the electron beam does not greatly change its trajectory. Stable acceleration in a certain area. The accelerated electron beam moves outward when the relationship between the magnetic field strengths of the charged particle acceleration means 12 and the deflection magnetic field generation means 13 is slightly changed, and collides with the target 14 installed in the stable orbital region to generate X-rays. Further, the X-ray target 14 is arranged on the orbit of the charged particle so that the direction of the needle-like tip of the target is directed inward when the charged particle is circulating inside the target 14.

  Also in the third embodiment, similarly to the second embodiment, by providing a shield 51 for preventing unnecessary charged particles from colliding with the target 14, noise to the X-ray point light source is reduced. I can do it. In this case, the shield 51 does not have to be placed at an arbitrary position of the circular accelerator, but needs to be arranged at a position where the charged particles come to the outside by the horizontal vibration of the circulating electron beam.

Embodiment 4
FIG. 8 is a schematic configuration diagram of an X-ray imaging system showing the fourth embodiment of the present invention using the electromagnetic wave generating device shown in the first to third embodiments of the present invention. The electromagnetic wave generating device 71, the imaging detector 73, and the data The processing unit 74 is configured. Any of the electromagnetic wave generators described in the first to third embodiments is used as the electromagnetic wave generator 71.
High-intensity X-rays 75 generated by the electromagnetic wave generator 71 are irradiated to a human body 72 that is an irradiated body, and detected by an imaging detector 73. The image detected by the imaging detector 73 is processed by the data processing device 74 to become a fluoroscopic image.

  Since the electromagnetic wave generator 71 can generate high-intensity X-rays having a light source size of several μm to several tens of μm, it is possible to perform refraction contrast imaging, which is an imaging method using minute X-ray refraction. Conventionally, since it could only be realized with a synchrotron radiation device such as Spring 8 having a diameter of about several hundreds of meters, medical utilization did not proceed. However, in the present invention, an electromagnetic wave generator of the same level as that of a conventional X-ray tube or a more compact Since refraction contrast imaging can be realized using 71, it is considered that medical use is greatly promoted. When the refraction contrast imaging method is used, it is possible to perform imaging with emphasis on the boundary between minute substances having different densities, and further, an enlarged image can be taken, so that a minute cancer of about several mm can be identified. In addition, since a captured image based on refraction contrast can realize a high contrast that is 10 times or more that of a conventional absorption contrast captured image, it is possible to realize imaging with a low exposure dose of about 1/10 compared to the conventional imaging method.

It is sectional drawing of the electromagnetic wave generator by Embodiment 1 of this invention. It is a block diagram of the X-ray target by Embodiment 1 of this invention. It is explanatory drawing which shows that a charged particle beam approaches the X-ray target by Embodiment 1 of this invention. It is explanatory drawing which shows the mode of the vibration of the charged particle vertical direction when a charged particle beam approaches the X-ray target by Embodiment 1 of this invention. It is sectional drawing of the electromagnetic wave generator by Embodiment 2 of this invention. It is an enlarged view of the X-ray target vicinity by Embodiment 2 of this invention. It is sectional drawing of the electromagnetic wave generator by Embodiment 3 of this invention. It is a schematic block diagram of the X-ray imaging system by Embodiment 4 of this invention.

Explanation of symbols

11: Charged particle generation means, 12: Charged particle acceleration means,
13: deflection magnetic field generating means, 14, target,
14a: a metal rod, 14b: a needle-like protrusion, 14c: a metal rod support structure,
15: Accelerated orbit of charged particles 16: Vacuum duct
21: sectional view of charged particle beam, 41: charged particle,
51: Shielding body 71: Electromagnetic wave generator,
72: irradiated object, 73: imaging detector,
74: Data processing device, 75: X-ray

Claims (5)

  Charged particle generating means for generating charged particles, accelerating means for accelerating charged particles generated by the charged particle generating means, and generation of a deflecting magnetic field for deflecting charged particles accelerated by the accelerating means to circulate on a circular orbit Electromagnetic wave generation comprising: a means for forming an X-ray by colliding the charged particle rotating around by the deflection magnetic field generating means with the tip of the metal rod, and a target composed of a metal rod whose tip is pointed like a needle apparatus.   The direction of the needle-like tip of the target is directed outward when the charged particles circulate outside the target, and directed toward the inside when the charged particles circulate inside the target. The electromagnetic wave generator according to claim 1, wherein the electromagnetic wave generator is disposed.   The electromagnetic wave generator according to claim 1 or 2, wherein a diameter of a needle-like tip portion of the target is 20 µm to 5 µm.   3. The shield according to claim 2, wherein a shield that shields the charged particles is disposed inside or outside the orbit of the charged particles in order to avoid collision of the charged particles other than the needle-like tip of the target. Electromagnetic wave generator.   Charged particle generating means for generating charged particles, accelerating means for accelerating charged particles generated by the charged particle generating means, and generation of a deflecting magnetic field for deflecting charged particles accelerated by the accelerating means to circulate on a circular orbit And an electromagnetic wave generator comprising a target that is made up of a metal rod whose tip is pointed like a needle, and generates X-rays by colliding charged particles circulating around the deflection magnetic field generating unit with the tip of the metal rod An imaging detector for irradiating the irradiated body with X-rays generated by the electromagnetic wave generator and detecting the captured image; and processing the image detected by the imaging detector to obtain a fluoroscopic image of the irradiated body An X-ray imaging system provided with a data processing device.

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