JPS63168600A - X-ray source - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an x&a source for the generation of Xi suitable for medical diagnostic and therapeutic purposes as well as material physics analysis and testing.

PRIOR ART It is known to generate X-rays for medical diagnosis in X-ray tubes by braking electrons in the region of the anode. The resulting bremsstrahlung radiation ranges from 20 keV to 100 keV. The use of conventional X-ray tubes for medical purposes still does not seem ideal,
This is because only a portion of the radiation generated can be used for the desired effect. Objects that are irradiated for a continuous spectrum of radiation, whether for examination, analysis, diagnostic imaging or radiotherapy, have not only the desired energy range but also the desired range. It is also exposed to radiation parts that exist outside of the body. The dose delivered to the object also contains, in the case of an examination, a considerable dose of X-rays, which is essentially undesirable. This disadvantage also arises for therapeutic purposes.

Regarding materials physical testing and analysis, x! ! Also for solid-state analytical investigations, such as the structural analysis of gases on metal surfaces or metals on semiconductors, where a finely adjustable radiation source in the range of
The use of monochromatically tunable radiation sources in the line range is of great importance.

[Problems to be Solved by the Invention] The object of the invention is to provide an X-ray source that emits monochromatic X-rays with high intensity and high degree of polarization.

[Means for solving the problem] This object is based on the invention, in which a crystal for channeling of electrons or positrons of defined energy is provided, the charged particles being periodically accelerated emitting electromagnetic radiation. Emission of photons is performed based on the effect and is achieved by adjusting the energy of the electron or positron bombardment to adjust the emitted photon to a desired magnitude of X-ray energy.

The <xvi source according to the invention exploits the effect that radiation is generated by channeling charged particles in suitable crystals. A suitable generation of X-rays in a narrow energy range suitable for medical diagnostic and therapeutic purposes as well as materials physics analysis is carried out. Physicians or technicians working with the xi device are protected and strong and expensive shielding measures can be omitted. The X-ray source according to the invention is particularly suitable, in conjunction with a suitable detector system, for the treatment and examination of diseases of the heart and circulatory system.

Within the framework of the invention, the implantation energy of the charged particles can be adjusted in such a way that monochromatic X-rays are generated in the desired range for medical diagnostics and therapy or for solid-state analysis purposes. This desired range is approximately 5keV to 250keV.
It is between V. The production of monochromatic X-rays is based on channeled radiation emitted by electrons or positrons as they penetrate the crystal under channeling conditions. By utilizing this physical effect, the following three properties can be utilized.

a) The energy of photons can be easily changed by changing the energy of electrons (positrons) that collide with the crystal. The resulting radiation can be used in many ways for medical diagnostic and therapeutic applications and for elemental and solid state analysis tests.

b) The spectrum of the photons is very narrow (i'I range), avoiding the drawbacks of conventional x&! sources emitting a broadband spectrum.

As a result, in medical diagnostic applications, a patient can be irradiated with only radiation energy that is meaningful to the patient. This therefore results in a saving in the amount of Mi compared to conventional radiation sources.

C) The emitted radiation is focused, i.e. emitted as a radiation that is significantly angularly restricted in the forward direction.

This is important in connection with scanning procedures (411j!
(omission of mechanical aperture and shutter).

Another important aspect is based on the fact that the resulting x6 is polarized. Polarized X-rays have not hitherto been utilized in medical radiography. This allows the radiation properties to be studied. For industrial applications of polarized X-rays, the conventionally used expensive means for polarization are therefore unnecessary.

[Examples] Next, the present invention will be described in detail based on drawings including two embodiments of the X-ray source based on the present invention.

The generation of monochromatic X-rays is based on an effect that has been extensively studied in the past in basic research in solid state physics.

This effect is based on the following idea. That is, the spectral intensity distribution of the radiation emitted from a transversely accelerated charge (technical example of a herring chrotron setup fiR) is primarily related to the radius of curvature. If we succeed in replacing the dimensions, which are necessarily macroscopic in the case of synchrotrons, by the spacing of atoms, we can shift the photon spectrum to relatively high energies and at the same time relatively large intensities, keeping other parameters unchanged. Possibilities open up.

the law of nature? :17 (A, M, Ku+5akhov), Journal of the Physical Society of the Soviet Union, JETP Volume 45 (197
7), page 791, this idea can be realized as follows. In other words, the crystal is
Electrons (positrons) and therefore charged particles that "channel" through the system undergo periodic lateral acceleration and, as a result, emit electromagnetic radiation. The energy of the emitted radiation is uniquely related to the energy of the channeling particles. The trajectory of the channeling particles runs in one plane or along the -axis by appropriate selection of the plane of crystal symmetry or axis of crystal symmetry. In this case, as shown in Fig. 1a or 1b, this is called planar channeling or axial channeling. In both figures, the symbol B indicates the trajectory of the particle, and the symbol G indicates the crystal lattice. In the former case, the channeling particle undergoes a periodic motion constrained transversely to the axis of symmetry of the crystal; in crystal physics, this motion is defined by the zero particle energy (in the MeV range) determined by the transverse intracrystal electric field potential. (electrons or positrons), a quantum mechanical description of the channeling motion is required. The solution to this description is only certain discrete energy eigenvalues, which correspond to the stationary configuration of the lateral component of the trajectory, as is usually found in quantum mechanical problems. Radiative transitions occur between these discrete energy levels, emitting electromagnetic radiation.

The emitted photon undergoes a Doppler shift due to the mass increase due to relativity of an electron or positron moving longitudinally (parallel to the axis of crystal symmetry) at the speed of light.

As a result, the strong forward radiation energy 5ω is
It is related on the one hand to the intracrystal electric field strength and on the other hand to the speed at which electrons (positrons) penetrate the crystal β = v/c. The following formula holds.

5ω=5ωo/(1-βcosθ) however iωo=5c　2Vo/mob here 02 Direction of emitted photon relative to particle direction.

The sum of the 5C blank constant and the speed of light divided by 2π.

vo: potential strength of the average lateral intracrystal field potential when a harmonic potential is applied.

mQc': Rest energy of electron (positron).

At the forward angle (O in θ), the following equation holds for the relationship between the radiant energy and the particle implantation energy ¥-.

25 out of 5 ω 0 γ 3 / γ: (1-β 2 ) l/2 = E/ moC 2 where E indicates the particle implantation energy.

Table 1 shows the characteristics of crystalline silicon, which has often been used in basic research, and crystalline tungsten, which is noteworthy in terms of potential.
A relationship between photon energy and particle energy is described.

Relationship between particle bombardment energy and average radiated energy for Tomo-Yu electron channeling.

Here, 0.5 keV to about 250 keV (
7) X-rays are most suitable for medical diagnostic and therapeutic applications. In particular, a range of 20 keV to 100 keV is advantageous for diagnostic applications. A value of 40 keV is typical for standard applications, such as thoracic applications. In radiotherapy, 1OkeV to 30)c
The R range of eV is particularly important for tumor applications or photon-activated therapy. Treatment of deep-seated tumors requires tenoenergy exceeding 30 keV and up to 250 keV. 065ke for elemental analysis by X-ray inspection
The range from V to about 100 keV is important. The figures listed here should be considered as special cases. New developments in medicine self-evidently allow for expansion of scope.

Said generation of channeled radiation has three characteristics:

a) Easy tunability of photon energy by changing the electron (proton quasiton) implantation energy.

b) Monochromatization of the X-ray spectrum that can be applied while saving doses, adaptation of the X-ray energy to medical problems (object adaptation) and X&! of xvi. The possibility of adaptation to conversion devices is particularly advantageous.

C) The spectral intensity distribution is better than conventional X-ray sources.

FIG. 2a schematically shows an installation capable of generating X-rays using the method of channeled radiation for medical diagnostic and therapeutic applications as well as material physics examinations. The installation comprises an electron (positron) source l for continuous or pulsed operation in combination with an electron (positron) accelerator 2. The most important main requirement for an accelerator is the provision of electrons (positrons) of a defined energy and a defined current value. The radiation guiding system focuses the particle beam S onto the crystal 4 by means of a collimator 3 within a so-called critical channeling angle. The crystal 4 is fixed on a goniometer in order to enable appropriate adjustment of the defined axis of crystal symmetry.

In order to separate the emitted X-ray dose from the particle beam S, a magnet 5 is provided behind the crystal 4, which deflects the charged particle beam S from the emitted X-ray dose in the forward direction and guides it to the radiation trap 8. An auxiliary monochromator system 6 can be used to reduce the background bremsstrahlung radiation contained in the photon radiation before the radiation reaches the target 7 (for example an X-ray film).

The accelerator 2 is required to have good radiation quality and minimize energy ambiguity. The energy range of the accelerator is 10MeV to loOM
It should be in the eV range. The exact data depends on the desired photon energy and the type of crystal used. electric f
The flow of (positrons) can be relatively small, yet a large flow of photons is obtained. The accelerator 2 shown in FIG. 2a, which has to work with currents on average between 20 lA and 1004 A, is a microtron, in which the electrons move in circular orbits of increasing radius with increasing energy. It functions to move along. However, all orbits touch at a common point. A suitable microtron is, for example, a Scanditronic (5ka
150cm to 200c from nditronix)
It is sold in a ring diameter of m. Electron radiation is 2gs
It pulsates with a pulse width of approximately 20m5 to mops and a pulse pause width of about 20m5. The peak current is approximately 100mA. Recent developments based on superconducting technology are also obviously suitable.

However, it is also possible to arrange the accelerator 2 in the form of a compact storage ring, as shown in FIG. 2b.

Here, electrons are injected from the microtron along the middle of the straight line into the storage ring, which is operated on the so-called "race track" principle by means of magnets M1 and M2. Thereby, a constant current of electrons flows along the storage ring for a very long time (of the order of an hour) with a fixed energy, and the high-frequency unit H1 is then affected by attenuation losses (e.g. in the crystal) during the orbit. A position-sensitive detector, not shown here, which compensates for the losses due to the received electrons, serves as a position monitor for the maintenance of the desired radiation quality.

The critical angle of the particle with respect to the axis of crystal symmetry φcri = γ−1
High requirements are placed on the particle beam quality due to the important boundary condition that the particles channel only when colliding at angles within /2.

Furthermore, since each particle beam has a finite radiation power, a suitable focusing element, for example a magnet or an electronic diaphragm, is provided as a collimator 3, which focuses the radiation divergence angle of the particle beam relative to the incidence on the crystal. ensure that it is as small as possible. Here, the radiation divergence angle is as much as 0.5mra
Efforts are made to be less than d.

Based on the mechanism of radiation generation, the temporal configuration of the electron (positron) radiation determines the temporal configuration of the emitted electromagnetic radiation. By appropriate selection of a defined pulse train of the particle beam, the particle beam is then converted into a corresponding photon pulse.

To ensure precise adjustment of the crystal axis relative to the particle beam S, the crystal 4 is placed on a goniometer. Goniometer control should be performed using a computer whenever possible. The accuracy of angle adjustment is 0.0 for both angles.
It should be 01°.

Crystals suitable for the generation of channeled radiation are those with a Debye temperature as high as possible in order to keep thermally excitable lattice vibrations, which lead to spectral line broadening effects, as small as possible. From this point of view, diamond crystals and Si crystals having well-known crystal structures are considered suitable. Si crystals have the great advantage of being available in high quality due to the high purity requirements in microelectronics. Relatively heavy series such as germanium, nickel and gold are also suitable. Particular attention is given here to high atomic numbers, which result in relatively high intracrystalline electric field strengths, thus allowing the use of small particle energies for relatively similar photon energies.

Tungsten crystals are very advantageous due to their very high atomic number. Binary element series such as LiF, MgF2, BN and BeO, which have already proven suitable for basic research in solid state physics, are likewise suitable for use. A summary for the generation of 50 keV photons for a crystal thickness of 20 JLm and an average electron current of 10 ILA is given in Table 2 below.

Table 2 Electron energy required for generation of 50 keV photons in various crystal systems.

In order to separate the particle beam from the photon beam emitted in the forward direction, a deflection magnet 5 must be provided behind the goniometer with the crystal system, as shown in FIGS. 2a and 3a.

A filter system 6 in the form of a double monochromator (see FIGS. iZa and 2b) is used for improving the monochromaticity ratio ΔE/E of the substantially monochromatic photon beam of the channeled radiation. For the crystal described above, ΔE/E is approximately 0.1. Another important feature is the reduction of background bremsstrahlung radiation associated with blocking effects as electrons penetrate the crystal.

The causes of this background are that the focusing of the radiation into the critical channeling angle is not complete enough, and that there are vacancies or impurities (lattice defects) in the crystal, technical limitations on the construction of the monochromator. The concept is ``Nuclea Instruments and Methods''.
l.

In5tr, and Math,) J A f's
No. 246 (1986), pages 297 to 30
9 and pages 365 to 376, ``Proceedings of the International Committee on X-ray and Vacuum Ultraviolet Synchrotron Radiation Instruments,'' Stanhood University, California, where so-called grazing incidence A mirror device is particularly recommended.

The electromagnetic radiation thus generated impinges on the target 7. Targu 2 You can grab any object, living or inanimate, in front of the door. This object 1
can be any object to be tested or analyzed, or can be a patient to be examined by X-ray diagnosis or treated by X-ray therapy. target 7
can be an X-ray film or a location-sensitive receiver for X-rays, but this only enumerates one pair of possibilities.

3a or 3b shows the entire equipment and the functions of the components corresponding to FIG. 52a or 2b. The control unit 9 comprises a plurality of control modules, which are electrically coupled to various components of the installation. For example, module 10 supplies power to the accelerator 2, module 11 supplies power to the magnets and focusing elements, modules 12, 13, 14 have goniometer control, crystal monochromator control and vacuum device 15, as shown in FIG. 3b. If necessary, the module 11 also supplies electrical energy to the high-frequency unit H1.

The equipment according to Figures 3a and 3b is dimensioned so that it can be easily accommodated in a hospital or industrial laboratory. A vacuum system 15 consisting of a pump system and a vacuum-safe power supply or case structure provides sufficient vacuum in the area of the electron radiation source.

The relatively high directional focusing of the channeled radiation
The position of the strongly focused or directed radiation is suitable for directing the radiation into the scanning mode without employing an aperture system as is normally used in the case of wire tubes.
In contrast to the wide radiation cross-section in the case of a line source, it is precisely known.

The emitted X-rays of conventional X-ray tubes have a broad continuous energy spectrum. As shown in FIG. 4a, continuity in frequency is seen with a so-called characteristic line at constant frequency or energy. As shown in FIG. 4b, a similarly wide continuous energy spectrum without characteristic lines gives the spectral intensity distribution of a conventional synchrotron.

In contrast, X-rays generated by channeling exhibit a narrow frequency band; the typical intensity distribution shown in Figure 4c is very narrow for discrete spectral lines, i.e. filtering means may be employed. typically less than 10%, so the patient is exposed to approximately only the desired spectral intensity.

In FIGS. 4a, 4b, and 4c, the number of photons per second is plotted on the vertical axis, and the X-ray energy in keV is plotted on the horizontal axis.

With the easily tunable energy of photons it is possible to implement so-called multispectral methods in radiology. If the crystal selection is appropriate, 40keV to 50keV or 90keV, +:m, 100k
It is possible to simultaneously generate eV substantially monochromatic X-rays. These different energies allow simultaneous display of bone and soft tissue despite different absorption properties. The feasibility of edge-subtractive color mixing appears particularly attractive in angiography, where contrast agents are used at the edge of the absorption range to achieve enhanced contrast of the imaged object with minimal radiation dose. An image is created by the lower and upper sides of the energy.

By selecting BN or BeO crystals, the absorption edge energy of the contrast agent iodine (3 k e V in EK), respectively, is obtained by special adjustment of the electron energy (7) Two almost monochromatic X-spectral lines on the upper and lower sides This can be achieved in particular by generating a .

When the intensities of both spectral lines are chosen to have the same thickness in front of the object, the transmission of the object and the detector (e.g. Na1
After detection in (Th) detector or Si detector),
Subtractive mixing of both spectral lines produces large signal differences in the case of iodine, and virtually similar signal differences in the case of soft tissue and bone.

x&! The point of view of easy adjustability of energy is advantageous. This is because the same radiation source can be used for diagnosis and treatment.

Another important possibility is the generation of polarized radiation. It can be applied to a variety of medical, industrial, and trace component analysis applications where polarized radiation is a problem.

Trace elements can be detected in vivo and in vitro based on characteristic X-rays. In vivo measurements are even more sensitive when polarized X-rays are used. This is because the scattered radiation generated in the thick sample can then be removed.
Qualitative and quantitative detection of various elements in the human body can be carried out with appropriate [T] of X-ray energy. So elements such as arsenic, mercury, cadmium and other heavy metals can be detected with one excitation source.

The X-rays that can be generated are strongly focused, narrow-band, monochromatic, suitable for scanning use and polarized for all standard applications of X-ray diagnostics, such as in mammography, pediatric medicine, etc., in the thoracic region. It can be carried out. In angiography, the applicability of edge subtraction mixed color angiography is particularly important. In cancer research, elements such as iodine, which are deposited in the canal cells of particular species, can be selectively irradiated by suitable adjustment of the photon energy.

Computed tomography devices produce images of three-dimensional electron density distributions in medical or industrial non-destructive testing, as is well known. This device requires that X-rays pass through the object to be inspected from various angles. This is accomplished by rotating the x-ray tube around the object under examination, which requires a relatively long scanning time. According to the invention, it is possible to precisely measure Compton-scattered X-rays in an object to be examined upon excitation by scanning radiation of controlled monochromatic energy. It is thereby possible to reproduce the three-dimensional distribution of the electron density in the examination object without moving the patient or the radiation source. Moreover, the use of different energies allows for the formation of images that are compatible with different human tissues, as known from standard radiography.

An installation for generating substantially monochromatic xii of variable energy can operate, for example, as follows. i.e. 18 p.
20 keV to 13 m using electrons in the energy range of lOMeV to 60 M e V channeling in the (110) direction through a diamond crystal of m thickness.
Nearly monochromatic photons of 0 keV can be generated. I
= average electron current of 20 ILA and 0,5 mr in the crystal
For a radiation divergence angle of ad FWHM, the photon flow rate ranges from 1 to 3×1010 quanta/S (Table 3
reference).

The radiation is focused strongly in the < +iJ direction with a solid angle ΔΩ=π/″f2.

If Si crystals are used, at least 10
0. An average electron current of A is available. Even higher currents can be used when using tungsten crystals.

In the case of the currently available radiation guide system for the electron acceleration base in question here, a radiation divergence angle of 0.2 mrad FWHM is obtained. This would increase the photon flow in Table 4 by a factor of 1 to 2.

u (110) for a 18gm thick diamond crystal
Relationship between directional radiation energy and photon flow (average electron flow is 20 lA).

and-1 Relationship between radiation energy and photon current (in the 10% band) for various crystals for an average electron current of 100 lA.

? The application of spectral subtractive color mixing to angiography in which coronary arteries or blood vessels are viewed solely by surrounding contrast injection is a significant advance. This is because this application simplifies the examination (reduces risk by omitting catheter introduction procedure). Additionally, increased patient processing speed results. As described in U.S. Pat. No. 4,432,370, an absorption-edge subtractive color mixing method is proposed, in which a synchrotron radiation source and a downstream crystal double monochromator device are used to perform subtractive color mixing. Obtaining monochromatic X-rays necessary for color mixing. This synchrotron radiation source can technically be replaced by a much cheaper channeled radiation source in the cylinder, and the radiation source must be tuned by selection of electronic energy to be able to match the radiation energy to the contrast agent, BN Depending on the choice of crystal or BeO crystal, both X-spectral lines above or below 3 keV (when the contrast agent is iodine) can be produced simultaneously. Thereby the time-consuming energy change methods required in the case of synchrotrons are superseded. 31 for displaying small blood vessels with a diameter of approximately 0.5 mm.
About 10 i/c in a monochromatic spectral line at keV
Requires a photon flow of m7s. This value results from a required image dose of approximately 200 μH for a 0.5 mm diameter lumen representation in the case of a signal to noise ratio greater than 100.

Since the subtractive color image should be created within 1 heartbeat, an exposure time of about 15 m5 at most is allowed.

Using a channeled radiation source and a tungsten crystal,
When the electron energy is about γ=30 and the average current is 100 lA, a photon current of 10111 photons/cm's can be generated for an X-spectral line of 30 eV. This photon stream is of the desired magnitude. The distance between crystal and detector is 2
In the case of m, a partial surface of ΔF=130 cm2 is irradiated with radiation. This is still too small to satisfactorily display the gold coronary artery system. However, by scanning in a plane, a desired larger diagnostically relevant area can be examined.

[Brief explanation of the drawing]

Figures 1a and 2b are perspective views showing a state in which charged particles channel a crystal along a lattice symmetry plane or a lattice symmetry axis, respectively, and Figures 2a and 2b are respectively based on the present invention. Schematic top views of different embodiments;
3a and 3b are perspective views including a control unit of the radiation source shown in FIGS. 2a and 2b, respectively, and FIGS. 4a to 4c are respectively an X-ray tube, a synchrotron, and a radiation source according to the present invention. These are examples of spectrum diagrams of X-rays generated in 2.War/Accelerator, 4.Crystal, B.S.Fist/Electron (positron) flow, R.Pot φ electromagnetic radiation (X-ray). c: j, ', -': 2nd FIGlb FIG 2'a m

Claims (1)

[Claims] 1) A crystal (4) for channeling electrons or positrons of defined energy is provided, which emits photons based on the effect that periodically accelerated charged particles emit electromagnetic radiation. An X-ray source characterized in that the emitted photons are adjusted to a desired level of X-ray energy by adjusting the implantation energy of electrons or positrons. 2) A facility is provided with an accelerator (2) for generating a stream of electrons or positrons of the desired energy, in which the electrons or positrons pass through a closed annular path incorporating a crystal to be channeled. The X-ray source according to claim 1, characterized in that the X-ray source rotates. 3) An X-ray source according to claim 1 or 2, characterized in that the implantation energy is adjusted to generate X-rays with an energy in the range of 0.5 keV to 250 keV. 4) An X-ray source according to any one of claims 1 to 3, characterized in that it is used in an imaging X-ray instrument in the form of a sector X-ray scanner.