JP2013098168A - Transmission type x-ray tube and reflection type x-ray tube - Google Patents

Abstract

A transmission X-ray tube and a reflection X-ray tube using a filter material that removes unnecessary radiation are provided.
A transmission X-ray tube includes a target material and a filter material. The target has at least one element, and X-rays are generated when the element is excited. X-rays have the energy of elemental characteristic Kα radiation and Kβ radiation, which are used to form an image of an object by X-ray collisions. The filter material through which the X-rays pass has K absorption edge energy, which is higher than the energy of the emitted Kα radiation and lower than the energy of the Kβ radiation. The thickness of the filter material is at least 10 microns less than 3 millimeters.
[Selection] Figure 5

Description

  The present invention generally relates to transmissive X-ray tubes and reflective X-ray tubes. In particular, the present invention relates to a transmissive X-ray tube and a reflective X-ray tube that use a filter material that removes unwanted radiation.

  In medical imaging technology, low-energy radiation dose can be reduced by using low-Z filters such as aluminum, molybdenum, yttrium, and copper, and by referring to the filter thickness equivalent to aluminum. It is well known that low energy radiation doses can be reduced. Generally, such filter thicknesses are in the same range of 0.5 to 1.2 millimeters as aluminum equivalent filters, which remove low energy, long wavelength x-rays, especially for medical imaging. Reduce potentially harmful and unwanted radiation. Unfortunately, such filters also remove most of the useful x-rays.

  In non-destructive inspection, filters are usually not used. However, there are cases where high-quality images are obtained for objects imaged by non-destructive inspection by imaging by radiation of intrinsic Kα rays from the target of the X-ray tube. In this case, it is also one of the objects of the present invention to remove unnecessary high-energy photoelectrons that cause damage to energy characteristics.

  In medical imaging, chemical imaging agents, such as iodine, gadolinium, and barium compounds, provide high contrast to the surrounding soft tissue depending on their density and atomic number. Their atomic numbers (iodine: Z = 53, barium: Z = 56, gadolinium: Z = 64) are important because the K absorption edge is in an energy band that is particularly advantageous for the typical X-ray energy spectrum. Because there is. The K absorption edge is iodine: 33.17 keV, barium: 37.44 keV, gadolinium: 50.24 keV. The contrast is maximized when the photoelectron energy of the X-ray is slightly above the K absorption edge energy of the chemical imaging agent.

  In selecting the optimal spectrum for a particular clinical diagnosis, not only the contrast requirements, but also the amount of transmission that passes through the body cross section must be generated to limit the radiation dose to the patient.

  In the case of non-destructive inspection imaging of various industrial products, each industrial product has one optimum energy for obtaining the highest image quality. Such industrial products include, but are not limited to, all kinds of electronic circuit boards, integrated circuits, LEDs and lithium batteries. However, in order to generate a high flux having such optimum energy, inevitably, high-energy photoelectrons exceeding the optimum energy are simultaneously generated. Such high energy photoelectrons are not necessary. This is because these photoelectrons reduce the contrast of the image. Further, when too many X-rays that are not essential for forming an image collide with the sensor, sensor overload becomes a problem.

  For a reflective x-ray tube, the spectrum of the x-ray beam is determined by the anode material, filter material and thickness combination, and the voltage of the electron tube selected for its diagnosis. The thickness of the target is not a critical issue.

  What is needed in X-ray imaging applications is an X-ray spectrum having a large number of photoelectrons in a narrow and well-defined X-ray photoelectron energy band, which provides a high image contrast. There is also a need for a method of removing photoelectrons having an energy higher and / or lower than that energy band. On the other hand, minimizing the decrease in flux in the energy band is necessary to maximize image quality. The ratio of useful energy band flux to higher energy band should be maximized within the limits of temperature management of the X-ray tube. In medical imaging applications, significant added value is provided by methods that simultaneously reduce unwanted low energy photoelectrons and significantly reduce the radiation dose to the patient. For inanimate object imaging, photoelectron energy can be as low as 15-20 keV, while in general medical imaging, photoelectron energy starts around 30 keV, and for high energy imaging it can be as low as 600 keV. Can be high.

  Such a filtering scheme is applicable to both reflective and transmissive X-ray tubes. When using a transmission X-ray tube, what is needed is a way to optimize the ratio of useful X-rays to high energy photoelectrons above the useful X-ray energy band. In medical applications, what is needed is a method for optimizing the ratio of useful x-rays to the radiation dose received by a patient while simultaneously reducing the number of high energy photoelectrons above their useful energy band. It is. In a reflective X-ray tube, it is not allowed to optimize the flux using the thickness of the target, and is therefore limited to adjusting the thickness and composition of the filter material. The same desired result is obtained by the adjustment.

  The present invention relates to a transmissive X-ray tube, and this transmissive X-ray tube uses a filter material that removes unnecessary radiation.

  The present invention relates to a reflective X-ray tube, which uses a filter material that removes unwanted radiation.

  According to the present invention, a transmission X-ray tube having a target material and a filter material is provided. The target material has at least one element, and generates X-rays when the element is excited. The generated X-rays include the characteristic Kα radiation of the element and the energy of the characteristic Kβ radiation for forming an image of the object by the collision of the X-rays. The filter material through which X-rays pass has K absorption edge energy, and the K absorption edge energy is higher than the energy of Kα radiation emitted from the element and lower than the energy of Kβ radiation. Also, the thickness of the filter material is at least 10 microns and less than 3 millimeters.

  In one embodiment of the present invention, the target material includes an element, a compound, an alloy, an intermetallic compound, or a composite material, and these element, compound, alloy, intermetallic compound, or composite material includes scandium, titanium, vanadium, Chromium, manganese, iron, cobalt, nickel, copper, zinc, germanium, yttrium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, tin, barium, lanthanum, cerium, neodymium, gadolinium, terbium, dysprosium, holmium, Erbium, thulium, ytterbium, lutetium, hafnium, tantalum, tungsten, rhenium, iridium, platinum, gold, thorium, uranium, or combinations thereof are included.

  In one embodiment of the present invention, the filter material includes an element, a compound, an alloy, an intermetallic compound, or a composite material, and these elements, compounds, alloys, intermetallic compounds, or composite materials include titanium, yttrium, gadolinium, Ruthenium, vanadium, samarium, neodymium, thorium, holmium, palladium, cobalt, cesium, niobium, tantalum, molybdenum, copper, chromium, iridium, erbium, rhodium, europium, indium, hafnium, rubidium, thulium, zinc, antimony, terbium, Includes zirconium, manganese, nickel, rhenium, strontium, tungsten, nickel, cadmium, gallium, technetium, lutetium, dysprosium, iron, ytterbium, or combinations thereof

  In one embodiment of the invention, the thickness of the target material is 5 to 500 microns.

  In one embodiment of the present invention, a transmission X-ray tube is used as an X-ray source in an X-ray microscope.

  In one embodiment of the present invention, a transmission x-ray tube is used to obtain an image in medical imaging.

  The present invention provides a reflective X-ray tube having a target material and a filter material. The target material has at least one element, and generates X-rays when the element is excited. The generated X-ray includes energy of the characteristic Kα radiation and characteristic Kβ radiation of the element for forming an image of the object by the collision of the X-ray. The filter material through which X-rays pass has K absorption edge energy, and the K absorption edge energy is higher than the energy of Kα radiation emitted from the element and lower than the energy of Kβ radiation. Also, the thickness of the filter material is at least 10 microns and less than 3 millimeters.

  In one embodiment of the present invention, the target material includes an element, a compound, an alloy, an intermetallic compound, or a composite material, and these element, compound, alloy, intermetallic compound, or composite material includes scandium, titanium, vanadium, Chromium, manganese, iron, cobalt, nickel, copper, zinc, germanium, yttrium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, tin, barium, lanthanum, cerium, neodymium, gadolinium, terbium, dysprosium, holmium, Erbium, thulium, ytterbium, lutetium, hafnium, tantalum, tungsten, rhenium, iridium, platinum, gold, thorium, uranium, or combinations thereof are included.

  In one embodiment of the present invention, the filter material includes an element, a compound, an alloy, an intermetallic compound, or a composite material, and these elements, compounds, alloys, intermetallic compounds, or composite materials include titanium, yttrium, gadolinium, Ruthenium, vanadium, samarium, neodymium, thorium, holmium, palladium, cobalt, cesium, niobium, tantalum, molybdenum, copper, chromium, iridium, erbium, rhodium, europium, indium, hafnium, rubidium, thulium, zinc, antimony, terbium, Includes zirconium, manganese, nickel, rhenium, strontium, tungsten, nickel, cadmium, gallium, technetium, lutetium, dysprosium, iron, ytterbium, or combinations thereof

  In one embodiment of the present invention, a reflective X-ray tube is used as an X-ray source in an X-ray microscope.

  In one embodiment of the invention, a reflective x-ray tube is used to obtain an image in medical imaging.

  If the x-ray photoelectron beam contains photoelectrons having an energy slightly higher than the K absorption edge of the filter material, the filter material will strongly absorb a given photoelectron beam, which is well known to those skilled in the art. If a filter material having an absorption edge between the energy of Kα rays and Kβ rays in the incident X-ray photoelectron beam can be found, the use of this filter material significantly reduces the intensity of Kβ rays compared to Kα rays. And this filter material is defined as a Kβ filter.

  The present invention discloses a transmission X-ray tube designed with a target thickness between 5 and 500 microns, and this transmission X-ray tube can be combined with a Kβ filter. The Kβ filter is selected from the following two viewpoints. That is, the viewpoint of removing unnecessary high-energy X-rays for improving image quality, and the viewpoint of removing unnecessary low-energy X-rays for reducing the radiation dose of the patient in application in the medical field.

  The present invention also discloses a reflective X-ray tube used in medical imaging and non-destructive imaging, and a filter designed to reduce radiation dose. This filter reduces the radiation dose to a much lower level than low-Z filters such as aluminum and copper. This filter also does not reduce X-rays useful for imaging, while simultaneously reducing high energy photoelectrons that exceed the K-ray energy of the target material of the reflective X-ray tube.

  Thick target materials of transmission X-ray tube and reflection X-ray tube are scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, germanium, yttrium, niobium, molybdenum, ruthenium, rhodium, palladium , Silver, tin, barium, lanthanum, cerium, neodymium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, hafnium, tantalum, tungsten, rhenium, iridium, platinum, gold, thorium, uranium (But not limited to) selected from materials that are likely to be used.

  The thickness of the selected Kβ filter varies between about 10 microns and 3 millimeters.

  Using the Kβ filter of the present invention, both medical images and non-destructive imaging are formed. Medical images include images of the patient's chest, lungs, joints and limbs, head, abdomen, and gastrointestinal x-ray examinations, as well as to direct radiation to the exact location of the patient's body to be treated with high-energy radiation therapy. The image used is included in, but not limited to. Also, in non-destructive inspection images, objects to be imaged include circuit boards, ball grid array circuits, separated electrical components, microelectromechanical system (MEMS) devices, small animals, organic samples, geological samples, semiconductor chip packages, Many other inanimate objects used in various other industries are included, but are not limited to these. The X-ray tube and Kβ filter included here have applications such as an X-ray source of an X-ray microscope in many nondestructive inspections.

  The present invention relates to imaging using X-rays. The present invention solves important problems, particularly in the field of medical imaging, but is applicable to all other types of X-ray imaging, including non-destructive imaging of inanimate objects. The present invention can be applied to X-ray imaging using both a reflection type X-ray tube and a transmission type X-ray tube, and the X-ray tube may be a fixed target tube or a rotary anode tube. The present invention can also be applied to the total energy of X-rays used in medical imaging and non-destructive imaging. The present invention introduces a method for reducing x-rays below or above the useful x-ray energy band, which is selected from the output spectrum of any x-ray tube. For X-ray applications requiring highly concentrated monochromatic X-rays, the present invention discloses a method using a combination of a thick transmissive or reflective X-ray tube target and a Kβ filter of a predetermined material and thickness. This Kβ filter significantly reduces the Kβ emission of the X-ray target. The application of an X-ray tube using the filter of the present invention provides a quasi-monochromatic X-ray source for an X-ray microscope.

1 is a schematic view of a transmission X-ray tube that generates X-rays and passes the X-rays through a filter according to the present invention. 1 is a schematic diagram of a reflective X-ray tube and its components that generate X-rays and pass the X-rays through a filter according to the invention. It is a graph display of an output spectrum of a transmission X-ray tube having a gadolinium target and an output spectrum when passing through an aluminum and copper filter. The output spectrum of a transmission X-ray tube having a gadolinium target having a thickness of 20 microns is displayed in a graph and is not passed through a filter. The graph shows the output spectrum of a transmission X-ray tube having a gadolinium target and the output spectrum of a transmission X-ray tube having a samarium filter. The graph shows a spectrum of a transmission X-ray tube having a thick tantalum target and a spectrum when passing through a filter made of a conventional low-Z material. The spectrum of a tantalum target having a thickness of 50 microns and a tantalum target having a thickness of 100 microns is graphically displayed and does not pass through a filter. The graph shows the output spectrum of a transmission X-ray tube having a tantalum target having a thickness of 100 microns and the output spectrum of a transmission X-ray tube having a ytterbium filter having a thickness of 80 microns. The output spectrum of the reflection type X-ray tube is displayed in a graph, and the comparison is made between a case where a standard low-Z filter material is transmitted and a case where an ytterbium filter having a thickness of 80 microns is added. The output from a transmission X-ray tube having a molybdenum target and the output when passing through a niobium filter are displayed in a graph. The output flux from the transmission X-ray tube of the present invention is displayed in a graph, and thulium filters having three different thicknesses are used for the transmission X-ray tube. The transmission X-ray tube of the present invention has a tantalum target.

  The transmission X-ray tube of FIG. 1 comprises a vacuum housing element 7 and an end window anode 1, which is disposed at the end of the housing exposed to the atmosphere. An X-ray target foil element 2 is provided on the end window anode element 1. In some x-ray tubes with end windows, the x-ray target and end window are made of the same material, but this eliminates the need for separate end window materials through which the x-rays pass. If the target material is thick and strong enough to keep the X-ray tube in a vacuum, there is no need to separate the end window material. The cathode element 3 simulating electrical or photoelectrons emits electrons that are accelerated along the electron path element 4 and impinge on the anode target element 8 that generates X-rays. The power supply element 6 is connected between the cathode and the anode and applies an acceleration force to the electron beam. X-rays generated in element 8 are emitted from the X-ray tube through the end window. Any focusing mechanism element 5 that is normally electrically biased focuses the electron beam above, below, or toward the spot on the target. The size at which the spot on the target surface is maximized is referred to as the focal spot size or spot size. X-rays contain both Kα and Kβ characteristic radiation, which are specific to at least one element of the target material. In a preferred embodiment of the present invention, a transmission x-ray tube has a target that can be as thin as 5 microns, while it can be as thick as 200 microns, and these are provided on the end window. It is done. If the target foil and end window are made of the same material, the thickness can be increased to 500 microns. In a preferred embodiment of the present invention, the output of the transmission x-ray tube is filtered through a Kβ filter having a filter thickness between 10 microns and 3 mm.

  FIG. 2 schematically shows a reflection type X-ray tube having a vacuum housing, in which a cathode element 12 and an anode element 14 are located. The anode element 14 includes an X-ray target provided on a substrate, which removes heat generated when the X-ray strikes the anode. The electrons are emitted from the cathode in any way known to those skilled in the art. A power supply element 6 is connected between the cathode and the anode and provides an electric field. The electric field accelerates the electrons emitted from the cathode along the electron path 10 and collides with the anode element 14 at a certain spot. As a result, an X-ray beam element 13 is generated and then emitted through the side window element 11 and out of the X-ray tube. The reflective X-ray tube takes in X-rays generated from the same side as the target with which the electron beam collides. X-rays contain both Kα and Kβ characteristic radiation, which are specific to at least one element of the target material, and are useful in forming images of objects that the generated X-rays impinge on. In a preferred embodiment of the present invention, the output of the transmission x-ray tube is filtered through a Kβ filter having a filter thickness between 10 microns and 3 mm.

  Open-type transmissive X-ray tubes are commonly used for imaging other applications that require high resolution in addition to electronic circuits. When a high multiplication factor is required for imaging an object, this open type transmission X-ray tube may be used instead as an X-ray source. A closed type X-ray tube is sealed in a vacuum state, while an open type or “pump down” X-ray tube has an attached vacuum pump that continuously evacuates the X-ray tube. In normal use, X-ray tube components that are prone to failure during operation can be replaced periodically. For the purposes of this invention, transmissive X-ray tubes include both open and closed transmissive X-ray tubes unless otherwise stated.

  Unless otherwise specified, X-ray tube spectral data were measured on an Amptek XR-100 model with a 1 mm thick CdTe sensor and a 10 mil (0.254 mm) Be filter. The sensor was installed at a distance of 1 meter from the X-ray tube, and a tungsten collimator with a 100 μm diameter collimator hole was installed in front of the sensor. Various tube currents and irradiation times were used.

  The Kβ filter, whether it is a transmission X-ray tube or a reflection X-ray tube, is formed by an element whose K absorption edge is located between the Kα ray and the Kβ ray of the X-ray target. Table 1 below shows the materials that form a suitable Kβ filter in the present invention for each possible target material.

  FIG. 3 represents the output of a transmission X-ray tube having a 20 micron thick gadolinium target. The applied voltage of this X-ray tube is 80 kVp. Element 17 represents the output spectrum of the x-ray tube, which is for thick gadolinium targets without filtering other than self-filtering. Although a target with a thickness of 20 microns is used, the thickness of the target can range from less than 5 microns to several hundred microns. Element 18 represents the output spectrum of the same X-ray tube, which is through a low Z aluminum filter with a thickness of 1.5 mm. Element 19 also represents the output spectrum, which passes through a filter corresponding to 9 mm thick aluminum. Gadolinium filtering with a conventional low Z filtering scheme does not reduce the radiation dose and at the same time does not provide sufficient flux to use an image contrast agent such as iodine or barium.

FIG. 4 represents an X-ray output spectrum from a transmission X-ray tube having a 20 micron thick gadolinium target. Here, the elements 20 and 21 are output spectra when the voltages are applied as 80 kVp and 90 kVp, respectively, which are not filtered except for the self-filtering of the thick transmission target. Barium can be imaged using gadolinium. This is because the mass absorption coefficient of barium is 22.4 cm ² / gm at 42.7 keV (Kα of gadolinium). In addition, iodine, which is an imaging agent, can be imaged using gadolinium. This iodine has a mass absorption coefficient of 18.46 cm ² / gm at 42.7 keV. Gadolinium is extremely suitable as a source of Kα radiation, which provides effective contrast from any barium and iodine imaging agent in the captured image. Increasing the gadolinium target thickness allows additional self-filtering on the output spectrum with a slight decrease in useful flux of 42.7 keV.

  FIG. 5 shows a preferred embodiment of the present invention. From Table 1, it can be seen that samarium is one of the two Kβ filter materials of gadolinium. A 50 micron thick samarium is used to filter the output of a transmission x-ray tube having a 20 micron thick gadolinium target as described above. The samarium filter is computationally applied to the output of gadolinium at 90 kVp. This is shown in FIG. Element 22 shows the spectrum of the gadolinium target at 90 kVp without passing through the filter. Element 23 indicates how many counts are reduced in each energy band by a 50 micron samarium Kβ filter. In the gadolinium Kα energy band, the energy decreases only by about 10%, while in the energy band of 45-50 keV (gadolinium Kβ: 48.69 keV), the energy decreases by about 40%. The count of photoelectrons with a photoelectron energy of 35 keV or less is reduced by 58%, and the radiation dose to the patient is significantly reduced. In addition, the output energy of 45 to 90 keV is reduced by 30%, and the deterioration of contrast is reduced. This deterioration in contrast results from high energy photoelectrons that are not useful for image formation. Here, a gadolinium target having a thickness of 20 microns is used as an example, but the target thickness may be as thin as 5 microns or as thick as 200 microns. If the gadolinium target is more than 100 microns thick and the acceleration voltage of the X-ray tube is as high as 150 kVp, the filter thickness can be reduced to 10 microns to reduce the resulting filtering effect. The output of Kα can be further increased, or the thickness of the filter can be increased to 3 millimeters.

  FIG. 6 is a graphical representation of the output spectrum of a transmission X-ray tube having a tantalum target material with a thickness of 75 microns. The transmission X-ray tube is operated at a tube current of 50 microamperes. And a filter corresponding to aluminum having a thickness of 9 mm, which is generally used in medical imaging. Element 24 represents the output when not passing through the filter. Element 25 represents the output when passing through a low Z filter, corresponding to an aluminum filter with a thickness of 9 mm. In the low photoelectron energy band of 0-40 keV, the X-ray count is reduced by 60.5%, which significantly reduces unwanted low-energy X-rays that cause radiation harmful to the patient. However, at the same time, useful X-rays in the 40-70 keV range are reduced by 60%. X-rays exceeding 70 KeV are considered to represent X-rays that reduce the contrast of the image, but this X-rays is reduced by 26.7%. However, the high energy x-ray dose is relatively increased compared to a 60% reduction in useful x-rays. The output increases from 12.2% when not passing through the filter to 19.3% when passing through the filter. Therefore, the low Z filter effectively reduces the radiation dose to the patient while also reducing the useful x-rays at a high rate. The effect of high energy photoelectrons of about 70 keV is reduced by using a filter.

  In a transmission X-ray tube with a 75-micron transmission target, X-ray self-filtering has already reduced low-energy X-rays, that is, X-rays must pass through a thick target before exiting the end window. Note that this is not possible.

  The X-ray photoelectron energy was compared for energy less than 40 keV, but there are applications where X-rays in the range of 30-40 keV are very important for obtaining high-quality images. Similarly, x-rays with useful x-ray energies of 40-70 keV are arbitrarily chosen to demonstrate the concept of the present invention. Whether for medical or nondestructive testing, each imaging application will have a definition of useful or unwanted x-rays. The filtering technique of the present invention is used to optimize useful x-rays within the limits of allowable tube current while reducing unwanted x-ray photoelectrons that do not contribute to the quality of the x-ray image. Let's go.

  FIG. 7 shows the self-filtering characteristics of a transmission X-ray tube with a thick target foil. Element 26 represents the spectrum of a transmission x-ray tube having a 50 micron thick target. Element 27 represents the spectrum of a transmission x-ray tube having a 100 micron thick target. Both X-ray tubes operate with a tube voltage of 100 kVp and a tube current of 50 μA. Table 2 below summarizes the photoelectron counts for each X-ray tube in each energy band below 40 keV, 40 keV to 70 keV, and 70 kev to 100 keV.

  Useful X-rays in the energy band from 40 keV to 70 keV are reduced by about 34.5%, while X-rays with energy lower than 40 keV, which is thought to increase the radiation dose to the patient, are reduced by 72%. In addition, X-rays in the energy band from 70 keV to 100 keV are reduced by 48.8%, much larger than the useful X-ray reduction.

  In a preferred embodiment of the invention, an additional filter is added to the existing self-filtering that a 100 micron thick target has. The filter material selected from Table 1 can be one of lutetium, thulium, and ytterbilm. FIG. 8 shows the photoelectron counts in each energy band for the spectrum of a transmission X-ray tube having a tantalum target with a thickness of 100 microns. This transmission X-ray tube has a tube voltage of 100 kVp, 50 μA. Operating with tube current. Element 28 shows the data obtained when no additional filter is used. The element 29 is a graph showing the output after passing through the filter obtained when the filter has an ytterbium filter having a thickness of 80 microns. Table 3 below summarizes the differences between the two spectra.

  The amount of unwanted X-rays below 40 keV is further reduced by 68.7%, resulting in a reduction in radiation dose that is harmful to the patient. This reduction is accompanied by a 29.4% reduction in useful X-ray counts in the range of 40-70 keV, but the useful X-ray reduction rate is considerably higher than that of radiation below 40 keV. Low. At energies above 70 keV, as a result of using ytterbium filters, there is a net loss in overall count when compared to useful x-ray loss. When the ytterbium atom emits fluorescence, the absorption energy exceeding 61.322 keV (the K absorption edge of ytterbium) changes to the Kα X-ray of ytterbium having a Kα energy of 52.4 keV, which is not shown in FIG. Kα X-rays are added to useful X-rays that contribute effectively. An 80 micron thick ytterbium filter is used with a 100 micron thick tantalum target at a tube voltage of 100 kVp, which simply means different filter materials, different x-ray tube voltages, different filter thicknesses, and different transmissions. It is used as one means to explain the filter thickness that can use target thickness and different transmission target materials. This filter principle has led to the development of a filtering scheme that is much better than using low-Z materials such as copper and aluminum as filters for X-ray imaging.

  When imaging an inanimate object with the X-rays of the present invention, it is even more important to reduce X-rays that have more energy than the X-rays necessary to form a high quality image. So far, higher energy only reduces the contrast of the image.

  In another preferred embodiment of the present invention, the output is from a reflective X-ray tube that has a tungsten target material and a conventional low-Z material filter such as copper or aluminum. Have. By using a high-Z filter that is smaller than the atomic number of the target material described above, but close to that atomic number, the filter functions more efficiently, resulting in negligible reduction in useful radiation, Reduce radiation dose.

  FIG. 9 shows the output distribution of the X-ray flux from the conventional reflection type X-ray tube. Element 31 represents the spectrum from a reflective x-ray tube having a tungsten target, which operates at a tube voltage of 120 kV and a tube current of 3 mA. Its output passes through a conventional “low-Z” filter corresponding to 9 mm thick aluminum. Element 30 indicates the result of calculation assuming that the output further passes through the filter of the present invention. From Table 1, filter materials for tungsten include hafnium, lutetium, ytterbium and thulium. Ytterbium was selected as a filter with a thickness of 80 microns. Those skilled in the art will appreciate that selecting a target material having a higher Z than ytterbium from Table 1 will change its output to a higher energy output.

  The following Table 4 demonstrates that photoelectrons with energy below 40 kVp are further reduced by 74.8%, and the patient's X-ray radiation dose is significantly reduced, while useful X-rays are only reduced by 38%. Yes. In this data, both the low Z filter combination and the filtering technique of the present invention are used, but the low Z filter can be replaced by a filter of the present invention that greatly improves efficiency. The filter itself emits K-ray fluorescence (not included in FIG. 9) and is necessary to increase the total output of photoelectrons in the useful range of 40-70 keV and to obtain the same image quality. To reduce the amount of tube current.

  In a preferred embodiment, a Kβ filter that is compatible with either transmissive or reflective x-ray tube target material is used as the x-ray source for medical imaging. This medical imaging includes images of the patient's chest, lungs, joints and limbs, head, abdomen, and gastrointestinal X-ray examinations, as well as radiation at the exact location in the patient's body to be treated with high-energy radiation therapy. Images used to derive are included, but are not limited to these.

  In another preferred embodiment of the present invention, a Kβ filter compatible with either a transmission X-ray tube or a reflection X-ray tube target material is used as a quasi-monochromatic X-ray source as a non-monochromatic X-ray source. Used in destructive imaging. Materials to be imaged include circuit boards, ball grid array circuits, isolated electrical components, microelectromechanical system (MEMS) devices, LEDs, lithium batteries, small animals, organic samples, geological samples, semiconductor chip packages, and various other types This includes, but is not limited to, many inanimate objects used in industry. Its use is wide and includes use as an X-ray source of an X-ray microscope.

  FIG. 10 represents one embodiment of the present invention. The tube voltage was measured at 60 kVp using a transmission X-ray tube with a 50 micron thick molybdenum target. Element 32 is the spectrum of a molybdenum X-ray tube without an additional filter and contains 13,409 counts of Kα photoelectrons. The count number of Kβ photoelectrons is 4,076 counts. When an additional 50 micron thick niobium filter is selected and added from Table 1 as the Kβ filter, the calculated Kα radiation reduction is 5,862 counts, while the Kβ radiation reduction is 98 counts. By using a thick molybdenum transmission X-ray tube and a 50 micron thick niobium Kβ filter, the Kα ray of element 31 is reduced to 1 / 2.2, while the Kβ ray is reduced to 1 / 41.6.

  For the entire energy band from 20 keV to 25 keV, the photoelectron count of element 32 is only 37 counts. This represents a very high level of monochromatic Kα radiation from molybdenum X-ray tubes. Although illustrated using molybdenum and niobium, any other target material or Kβ filter material in Table 1 can be used in the same manner.

  FIG. 11 is a graphical representation of the output flux from the transmission X-ray tube of the present invention having a 50 micron thick tantalum target, with three different Kβ filters of the present invention formed of thulium each applied to the output. Has been. The voltage applied to the X-ray tube is 90 kVp, and the tube current is 50 microamperes. After applying the filter, the spectrum is measured. The three filters are 25 microns (element 33), 50 microns (element 34), and 75 microns (element 35), respectively. Table 5 below lists the useful Kα dose as it passes through the filter compared to the amount of unwanted Kβ flux reduction. In addition, a comparison with a low-energy photoelectron quantity such as 15 to 40 keV, which is not used for imaging and is mostly radiation dose, is also described.

  By increasing the thickness of thulium filters from 25 microns to 75 microns, the unwanted Kβ is reduced by approximately 40%, while the unwanted 15-40 keV low energy is reduced by approximately 43%, while the useful Kα emission is It is clear that only about 22% decrease. For low energy photoelectrons and high energy Kβ photoelectrons, the desired reduction is obtained by the single filter of the present invention, resulting in a significant improvement in the radiation dose received by the patient. The thickness used here is for verification purposes only. It is clear that any thickness filter can be used with varying effectiveness. Useful X-ray reduction can be offset by increasing the tube current. Although the amount of increase in tube current is limited, its value is allowed to depend on the total energy impinging on the focal spot on the target of the transmission X-ray tube.

  It will be apparent to those skilled in the art that various modifications and variations can be made to make the structure of the present invention without departing from the scope or spirit of the invention. In light of the foregoing, it is intended that the present invention include the modifications and variations of this invention provided they come within the scope of the following claims and their equivalents.

Claims (11)

Having at least one element that generates X-rays, the elements generate X-rays when excited; A target material containing the energy of the characteristic Kα radiation and the characteristic Kβ radiation;
A filter material having a K absorption edge energy that passes through the X-ray and is higher than the energy of Kα radiation emitted from the element and lower than the energy of Kβ radiation;
A transmission X-ray tube wherein the thickness of the filter material is at least 10 microns and less than 3 millimeters. The transmission X-ray tube according to claim 1, wherein the target material includes an element, a compound, an alloy, an intermetallic compound, or a composite material,
The element, compound, alloy, intermetallic compound or composite material is
Scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, germanium, yttrium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, tin, barium, lanthanum, cerium, neodymium, gadolinium, terbium, Transmission X-ray tubes including dysprosium, holmium, erbium, thulium, ytterbium, lutetium, hafnium, tantalum, tungsten, rhenium, iridium, platinum, gold, thorium, uranium, or combinations thereof. The transmission X-ray tube according to claim 1, wherein the filter material includes an element, a compound, an alloy, an intermetallic compound, or a composite material,
The element, compound, alloy, intermetallic compound or composite material is
Titanium, yttrium, gadolinium, ruthenium, vanadium, samarium, neodymium, thorium, holmium, palladium, cobalt, cesium, niobium, tantalum, molybdenum, copper, chromium, iridium, erbium, rhodium, europium, indium, hafnium, rubidium, thulium, Transmission X-ray tubes containing zinc, antimony, terbium, zirconium, manganese, nickel, rhenium, strontium, tungsten, nickel, cadmium, gallium, technetium, lutetium, dysprosium, iron, ytterbium, or combinations thereof .   The transmission X-ray tube according to claim 1, wherein the target material has a thickness of 5 to 500 microns.   Use of the transmission X-ray tube according to claim 1 as an X-ray source in an X-ray microscope.   Use of a transmission X-ray tube according to claim 1 to obtain an image in medical imaging. Having at least one element that generates X-rays, the elements generate X-rays when excited; A target material containing the energy of the characteristic Kα radiation and the characteristic Kβ radiation;
A filter material having a K absorption edge energy that passes through the X-ray and is higher than the energy of Kα radiation emitted from the element and lower than the energy of Kβ radiation;
A reflective x-ray tube wherein the thickness of the filter material is at least 10 microns and less than 3 millimeters. The reflective X-ray tube according to claim 7, wherein the target material includes an element, a compound, an alloy, an intermetallic compound, or a composite material,
The element, compound, alloy, intermetallic compound or composite material is
Scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, germanium, yttrium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, tin, barium, lanthanum, cerium, neodymium, gadolinium, terbium, A reflective x-ray tube comprising dysprosium, holmium, erbium, thulium, ytterbium, lutetium, hafnium, tantalum, tungsten, rhenium, iridium, platinum, gold, thorium, uranium, or combinations thereof. The reflective X-ray tube according to claim 7, wherein the filter material includes an element, a compound, an alloy, an intermetallic compound, or a composite material,
The element, compound, alloy, intermetallic compound or composite material is
Titanium, yttrium, gadolinium, ruthenium, vanadium, samarium, neodymium, thorium, holmium, palladium, cobalt, cesium, niobium, tantalum, molybdenum, copper, chromium, iridium, erbium, rhodium, europium, indium, hafnium, rubidium, thulium, Reflective x-ray tubes containing zinc, antimony, terbium, zirconium, manganese, nickel, rhenium, strontium, tungsten, nickel, cadmium, gallium, technetium, lutetium, dysprosium, iron, ytterbium, or combinations thereof .   Use of the reflective X-ray tube according to claim 7 as an X-ray source in an X-ray microscope.   Use of a reflective x-ray tube according to claim 7 to obtain an image in medical imaging.

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