WO2014175762A1

WO2014175762A1 - Device and method for x-ray generation

Info

Publication number: WO2014175762A1
Application number: PCT/RU2013/000361
Authority: WO
Inventors: Taras Vladimirovich BONDARENKO; Georgy Borisovich SHARKOV; Yuriy Alexeevich BASHMAKOV
Original assignee: Siemens Aktiengesellschaft
Priority date: 2013-04-25
Filing date: 2013-04-25
Publication date: 2014-10-30

Abstract

The invention relates to a device (1) and a method for X-ray generation, the device (1) comprising an electron emitter (2) for generating an electron beam (3). An accelerator (4) accelerates the electrons of the electron beam (3) and generates an accelerated electron beam (5). A crystal (6) is arranged in the trajectory of the accelerated electron beam (5). The crystal (6) is designed to let electrons of the accelerated electron beam (5) pass through the crystal (6) and to generate an X-ray beam (10).

Description

DEVICE AND METHOD FOR X-RAY GENERATION

DESCRIPTION The invention relates to a device for X-ray generation comprising an electron emitter for generating an electron beam and an accelerator for accelerating the electrons of the electron beam and thus generating an accelerated electron beam. The invention further relates to a method for X-ray generation, in particular for medical imaging. X-rays are widely used in medical applications such as angiography and mammography. In these branches of medical imaging it is desirable that X-ray radiation is narrow-band in order to obtain high contrast images of the investigated part of the body and to reduce the dose delivered to the patient. Another demand to an X-ray source for these types of medical imaging is the possibility to tune the X-ray energy in order to use it with different types of contrast agents and different human body thickness, in particular in angiography.

Methods for generating X-rays with the desired monochromaticity for medical applications are, for example, described in US 6141400 A, US 7436926 B2, US 201 1/0038455 Al, and US 5157704 A. In the respective X-ray devices described in these documents, an X-ray tube according to the state of the art is utilized. In the X- ray tube electrons with an energy of several keV are emitted from a cathode to an anode serving as target. Non-monochromatic bremsstrahlung and characteristic X-ray radiation are emitted by the electrons that strike the anode surface. The X-ray then passes through a filter that cuts out low energy bremsstrahlung and leaves the working energy X-ray spectrum including characteristic lines and mid-to-high energy bremsstrahlung. Finally, the filtered X-rays illuminate a fluorescent target, and fluorescent monochromatic X-rays are generated. In these methods the intensity of fluorescent X-rays is relatively low. Also, a variation of the X-ray energy is not feasible. US 6 332 017 Bl describes a system for generating tunable monochromatic X-rays. The X-ray generation is here based on the inversed Compton scattering principle. In the device for X-ray generation a pulsed electron beam is generated by a conventional photocathode, and a linear accelerator is utilized to accelerate the electrons of the electron beam. The electron beam is focused to a beam diameter of 50-200 μπι using a focusing magnet. The electrons are then directed through an electron beam transport line into a small evacuated beam pipe containing a beam interaction zone. Additionally to the electron beam a pulsed infrared beam is generated simultaneously by a conventional tabletop laser. This infrared beam is directed into a vacuum chamber containing a beryllium mirror. The mirror is oriented to target the infrared beam towards the opposing electron beam. Thus the infrared beam and the electron beam collide at the interaction zone. As a consequence, the infrared photons are converted to a beam of X-ray photons. This X-ray beam leaves the interaction zone on a path that is almost collinear with the electron beam path. The X-ray beam is directed to an array of graphite mosaic crystals. The X-rays deflect off of the crystals at relatively shallow angles into a beam transport pipe. The beam transport pipe delivers the X-ray beam towards the imaging target.

Such a system for monochromatic X-ray generation is relatively laborious.

It is therefore the object of the present invention to provide a device and a method for X-ray generation of the initially mentioned type, by means of which monochromatic X-rays can be generated particularly easily. This object is solved by a device having the features of claim 1 and by a method having the features of claim 1 1. Advantageous embodiments with convenient developments of the invention are specified in the dependent claims.

The device according to the invention comprises a crystal which is arranged in the trajectory of the accelerated electron beam. The crystal is designed to let electrons of the accelerated electron beam pass through the crystal and to generate an X-ray beam in this manner. This design is based on the finding that electrons traveling through the crystal interact with nuclei of the crystal and generate X-rays. It is in fact the oscillating movement of the electrons on their way through the crystal and along lattice planes of the crystal that produces narrow-band, monochromatic X-rays. Also, a directed X-ray beam is generated by the traveling of electrons through the crystal.

The device uses the channeling of the electrons passing through the crystal and these channeling electrons irradiate an electromagnetic radiation that lies in keV to tens of keV regions. Thus with the device monochromatic X-rays can be readily generated. One factor that allows influencing the energy of the generated X-ray beam is the energy of the accelerated electron beam.

The high monochromaticity of the generated X-ray beam results in a high contrast of the image obtained with the X-ray beam, while a low background dose rate is achieved. This makes the device particularly well suited for medical imaging.

Particularly high intensities of the X-ray beam can be obtained, if the crystal is a monocrystal. As the channeling is dependent on the crystal lattice, utilizing a monocrystal allows for a very intense interaction between the electrons passing through the monocrystal and generating X-rays by their oscillating movement along the lattice planes of the monocrystal. In the monocrystal it can very easily be ensured that the electrons passing through the monocrystal actually follow the monocrystal's lattice planes.

Thus due to the homogeneity of the crystal lattice in the monocrystal, a narrow-band, i.e. monochromatic X-ray beam can be generated particularly easily.

The crystal can be made of silicon, for example. This material yields good results and is particularly well affordable. However, in a further advantageous embodiment the crystal is made of diamond. Because of its high thermal conductivity, heat which is generated by focusing the accelerated electron beam on the crystal can very well be dissipated from the crystal made of diamond.

It has further proven to be advantageous, if the crystal is arranged in a goniometric device designed to align lattice planes of the crystal with an axis of the accelerated electron beam. By adjusting the orientation of the crystal's lattice planes with the axis of the accelerated electron beam, it can readily be ensured the during all their way through the crystal the channeling of the electrons leads to the generation of the monochromatic X-ray beam Thus, there is a possibility of easily varying the generated X-ray energy from about 1 keV to 40 keV in real-time mode. This tunable energy values cover up most of the entire X-ray energy range which is desirable in medical imaging.

Preferably, the crystal can be oriented in at least three different spatial directions of the crystal by the goniometric device. This enables particularly well to tune the energy of the generated X-ray beam. By orientating the crystal in a desired direction relative to the accelerated electron beam, the existence of different distances between lattice planes in the crystal can be exploited. If the crystal is oriented in a way that the distance between lattice planes along which the electrons of the accelerated electron beam travel is relatively small, particularly high energy X-ray beams can be generated.

Preferably, the crystal is arranged in a way providing the X-ray beam in an orientation which is coaxial with an orientation of the electron beam within the accelerator. Thus the generated X-ray beam can particularly easily be directed to a detector.

It has further proven to be advantageous, if the crystal has a thickness of about 1 μιη to 60 μηι. A crystal of such a thickness facilitates an easy passing of the electrons through the crystal, while still creating an X-ray beam of a desired energy. This is in particular true, if the crystal has a thickness perpendicular to the direction of the accelerated electron beam of about 5 μιη. In a further advantageous embodiment the device comprises a filter unit downstream of the crystal, which is designed to strain the X-ray beam from high energy radiation. Thus, the X-ray beam is particularly well adapted for medical applications. In a further advantageous embodiment the accelerator is designed to accelerate the electrons of the electron beam to an energy of about 3 MeV to 50 MeV. With such an energy the accelerated electrons readily pass through the crystal. Preferably, the accelerator provides high accelerating field gradients to obtain beam acceleration to tens of MeV with only moderate levels of electron beam defocusing.

Preferably, the device comprises a collimating unit designed to focus the accelerated electron beam on the crystal. Such a collimating unit readily transforms the profile of the electron beam to a desired shape that facilitates the passing of the electrons through the crystal.

Still further the device comprises an electron beam deflecting unit arranged downstream of the crystal, which is designed to deflect the electrons having passed the crystal to an electron dump. Thus the electron beam is separated from the generated X-ray beam and does not interfere with a target.

According to a further aspect of the invention, in a device of the initially mentioned type a crystal is arranged in the trajectory of the accelerated electron beam, wherein the crystal is a monocrystal designed to generate an X-ray beam. In the method for X-ray generation according to the invention, an electron beam is generated by an electron emitter, and the electrons of the electron beam are accelerated by an accelerator generating an accelerated electron beam. The accelerated electron beam is directed towards a crystal, wherein electrons of the accelerated electron beam pass through the crystal. An X-ray beam is generated by the electrons passing through the crystal. This method particularly easily allows for generating monochromatic X-rays. The preferred embodiments presented with respect to the devices for X-ray generation and the advantages thereof correspondingly apply to the method for X-ray generation and vice versa. The features and feature combinations mentioned above in the description as well as the features and feature combinations mentioned below in the description of figures and/or shown in the figures alone are usable not only in the respectively specified combination, but also in other combinations or alone without departing from the scope of the invention.

Further advantages, features and details of the invention are apparent from the claims, the following description of preferred embodiments as well as based on the drawings. Therein show: FIG 1 schematically a narrow-band X-ray source utilizing a monocrystal in a trajectory of an electron beam to generate monochromatic X-rays; and

FIG 2 schematically plane channeling of the electrons through the lattice of the monocrystal.

A device 1 designed as narrow-band X-ray source for medical applications is schematically shown in FIG 1. The device 1 comprises an electron emitter or electron gun 2. This electron gun 2 generates an electron beam 3 with preferably about tens of μΑ mean beam current.

The electron beam 3 is accelerated in a linear accelerator 4 preferably to an energy of 3 to 50 MeV. The linear accelerator 4 provides high accelerating field gradients to achieve these electron beam 3 accelerations with only low electron beam 3 defocusing.

A collimating system is integrated in the accelerator 4. This collimating system transforms the electron beam 3 to the desired shape. An accelerated electron beam 5 having the desired shape exits the accelerator 4 and passes through a monocrystal 6 preferably made of diamond.

The monocrystal 6 is clamped in a goniometer 7 which enables setting an angle between the crystal lattice of the monocrystal 6 and a trajectory of the accelerated electron beam 5. In the monocrystal 6 the electrons of the accelerated electron beam 5 pass through the monocrystal 6 following the direction of crystalline planes or lattice planes 8 in the monocrystal 6. FIG 2 schematically shows two lattice planes 8 of the monocrystal 6 and serves for illustrating the plane channeling of the electrons. Pathways 9 indicated in FIG 2 illustrate the oscillating movement of the electrons passing through the monocrystal's 6 lattice. As shown by the pathways 9, the electrons generally follow the direction of the lattice planes 8.

During this oscillating movement of the electrons of the accelerated electron beam 5 the monocrystal 6 irradiates electromagnetic radiation which is preferably in the region of keV to tens of keV. Thus an X-ray beam 10 is generated, the energy of which depends on the energy of the accelerated electron beam 5 and on the crystal lattice sizes. The goniometer 7 allows to align different lattice planes 8 of the monocrystal 6 with the accelerated electron beam 5. Thus the existence of different distances between the lattice planes 8 of the monocrystal 6 according to its orientation can be exploited. Therefore by adjusting the angle between the lattice planes 8 of the monocrystal 6 and the accelerated electron beam 5 by means of the goniometer 7, the energy of the generated X-ray beam 10 can easily be varied. This allows the generation of X-ray beam 10 energy from 1 keV to 40 keV in real-time mode. The X-ray generation device 1 based on the monocrystal 6 channeling process thus provides the X-ray beam 10 with tunable energy values that will cover most of all X-ray energy ranges demanded by medical imaging. Furthermore the generated X-ray beam 10 exhibits a high monochromaticity. This allows particularly high contrasts in the obtained images and a low background dose rate.

After interaction with the monocrystal 6 the utilized electron beam 5 is dumped to a collector 1 1 or electron dump. To achieve this, an electron deflecting unit 12 is arranged downstream of the monocrystal 6. This deflecting unit 12 causes the electron beam 5 which has passed through the monocrystal 6 to deviate from the trajectory of the X-ray beam 10.

The X-ray beam 10 is preferably strained from high energy radiation photons by a filter 13 arranged downstream of the deflecting unit 12. Alternatively, a reflecting crystal may be utilized for filtering. The filtered X-ray beam 10 possesses high monochromatic X-ray properties when it reaches a detector 14.

As the X-ray radiation obtained in this device 1 provides the possibility of changing the radiation energy in a wide range, in particular the X-ray energy ranges desired for medical imaging applications such as angiography and mammography can be obtained with the device 1.

Claims

1. Device (1) for X-ray generation comprising an electron emitter (2) for generating an electron beam (3) and an accelerator (4) for accelerating the electrons of the electron beam (3) and generating an accelerated electron beam (5),

characterized in that

a crystal (6) is arranged in the trajectory of the accelerated electron beam (5), wherein the crystal (6) is designed to let electrons of the accelerated electron beam (5) pass through the crystal (6) and to generate an X-ray beam (10).

2. Device according to claim 1 , characterized in that the crystal (6) is a monocrystal.

3. Device according to claim 1 or 2, characterized in that the crystal (6) is made of diamond.

4. Device according to any one of claims 1 to 3, characterized in that the crystal (6) is arranged in a goniometric device (7) designed to align lattice planes (8) of the crystal (6) with an axis of the accelerated electron beam (5).

5. Device according to any one of claims 1 to 4, characterized in that the crystal (6) is arranged in a way providing the X-ray beam (10) in an orientation which is coaxial with an orientation of the electron beam (3) within the accelerator (4).

6. Device according to any one of claims 1 to 5, characterized in that the crystal (6) has a thickness of about 1 μηι to 60 μηι, in particular of about 5 μηι.

7. Device according to any one of claims 1 to 6, characterized in that the device (1) comprises a filter unit (13) downstream of the crystal (6), which is designed to strain the X-ray beam (10) from high energy radiation.

8. Device according to any one of claims 1 to 7, characterized in that the accelerator (4) is designed to accelerate the electrons of the electron beam (3) to an energy of about 3 MeV to 50 MeV.

9. Device according to any one of claims 1 to 8, characterized in that the device (1) comprises a collimating unit designed to focus the accelerated electron beam (5) on the crystal (6).

10. Device according to any one of claims 1 to 9, characterized in that the device (1) comprises an electron beam deflecting unit (12) arranged downstream of the crystal (6) and designed to deflect the electrons having passed the crystal (6) to an electron dump (1 1).

1 1. Method for X-ray generation, wherein an electron beam (3) is generated by an electron emitter (2) and the electrons of the electron beam (3) are accelerated by an accelerator (4) generating an accelerated electron beam (5), characterized in that the accelerated electron beam (5) is directed towards a crystal (6), wherein electrons of the accelerated electron beam (5) pass through the crystal (6) and an X-ray beam (10) is generated by the electrons passing through the crystal (6).