WO2014172933A1

WO2014172933A1 - X-ray filter, x-ray filtering system, and movable ct scanner

Info

Publication number: WO2014172933A1
Application number: PCT/CN2013/076025
Authority: WO
Inventors: 徐如祥; 代秋声; 高枫; 张涛
Original assignee: 中国人民解放军北京军区总医院
Priority date: 2013-04-27
Filing date: 2013-05-22
Publication date: 2014-10-30
Also published as: CN103349555A

Abstract

An X-ray filter, an X-ray filtering system, and a movable CT scanner. The X-ray filter comprises a square body (1).A groove (2) is formed in an upper end surface of the square body (1) in an length extending direction, so as to form a centrosymmetric wedge-shaped portion on the square body (1). The X-ray filtering system comprises an X-ray source. The X-ray filter is disposed on an X-ray emergent light path of the X-ray source. The movable scanner comprises the X-ray filtering system. The X-ray filter has excellent performance, and can well make use of functions of the X-ray filter and prevent an examined human body from being hurt by X-rays.

Description

X-ray filter, X-ray filtration system and mobile CT scanner

The present invention claims priority to Chinese Patent Application No. 201310151760.8 entitled "X-Ray Filter, X-Ray Filter System and Mobile CT Scanner" submitted to China National Intellectual Property on April 27, 2013.

Technical field

The present invention relates to the field of medical devices, and in particular to an X-ray filter, an X-ray filter system and a mobile CT scanner.

Background technique

The primary function of the filter is to reduce the radiation dose of low-energy X-rays that are not useful for CT imaging. Placing a filter between the X-ray tube and the human body is a basic safety measure that must be taken to design a CT system.

There is currently no X-ray filter with excellent performance.

Summary of the invention

A brief summary of the invention is set forth below to provide a basic understanding of certain aspects of the invention. It should be understood that this summary is not an exhaustive overview of the invention. It is not intended to identify key or critical aspects of the invention, and is not intended to limit the scope of the invention. Its purpose is to present some concepts in a simplified form as a pre-

It is an object of embodiments of the present invention to provide an X-ray filter having superior performance in view of the above-described deficiencies of the prior art.

In order to achieve the above object, the technical solution adopted by the present invention is:

An X-ray filter comprising a square body, the upper end surface of the square body being provided with a groove along a length extension direction thereof to form a centrally symmetrical wedge portion on the square body.

The present invention also provides an X-ray filtering system, comprising: an X-ray source, wherein the X-ray exiting light path of the X-ray source is provided with the X-ray filter. Another solution provided by the present invention: A mobile CT scanner comprising the above-described X-ray filtering system.

Compared with the prior art, the beneficial effects of the present invention are:

The X-ray filter of the present invention has superior performance, can well function as an X-ray filter, and can prevent X-ray damage to the human body to be inspected, and can be used for an X-ray filter system and a mobile CT scanner.

These and other advantages of the present invention will become more apparent from the detailed description of the preferred embodiments of the invention.

DRAWINGS

The invention may be better understood by referring to the following description in conjunction with the drawings, wherein the same or similar reference numerals are used throughout the drawings. The drawings, which are included in the specification, and in the claims In the drawing:

1 is a schematic structural diagram of an X-ray filter according to an embodiment of the present invention;

2 is a schematic cross-sectional view of an X-ray filter according to an embodiment of the present invention; FIG. 3 is a diagram showing energy shares of X-rays and 20 cm thick after reflection, deposition, and transmission;

4 is a diagram showing a signal-to-noise ratio calculation result (energy integration mode) of a copper filter device according to an embodiment of the present invention;

5 is a diagram showing a signal-to-noise ratio calculation result (energy integration mode) of a filter material made of aluminum according to an embodiment of the present invention;

Figure 6 is a graph showing the energy share of 120 keV X-rays transmitted through different thickness copper plates according to an embodiment of the present invention.

Reference mark:

1-square body;

2-groove, 20 center plane area, 21 edge arc area.

The elements in the figures are only shown for simplicity and clarity and are not necessarily drawn to scale. For example, the dimensions of some of the elements in the drawings may be It can be enlarged with respect to other elements in order to help improve the understanding of the embodiments of the present invention.

detailed description

Exemplary embodiments of the present invention will be described in detail below with reference to the drawings. For the sake of clarity and conciseness, not all features of an actual implementation are described in the specification. However, it should be understood that many implementation-specific decisions must be made in the development of any such practical embodiment in order to achieve the developer's specific objectives, for example, compliance with system and business related constraints, and these Restrictions may vary from implementation to implementation. In addition, it should also be understood that while development work can be very complex and time consuming, such development work is only a routine task for those skilled in the art having the benefit of the disclosure.

It should also be noted that, in order to avoid obscuring the present invention by unnecessary detail, only the device structure and/or processing steps closely related to the solution according to the present invention are described in the drawings and the description. The representations and descriptions of components and processes known to those of ordinary skill in the art that are not relevant to the present invention are omitted.

Referring to Figures 1 and 2, an X-ray filter comprising a square body 1, the upper end surface of the square body 1 is provided with a groove 2 along its length extending direction to form a centrally symmetrical wedge portion on the square body 1.

By providing the X-ray filter of the present invention, it is possible to prevent the X-ray from being damaged to the human body to be inspected.

Specifically, based on the above embodiment, the groove 2 includes: a center plane area 20 and an edge arc area 21 on both sides of the center plane area 20.

The side wall of the groove is curved, and the design is reasonable. Only the groove is provided on the upper end surface, and the lower end surface is a flat surface, which is convenient for processing and has excellent performance.

The arrangement of the above-described shapes of the grooves enhances the performance of the X-ray filter of the present invention.

Specifically, based on the above embodiment, the material of the square body 1 is copper or aluminum, which improves the performance of the filter.

Specifically, based on the above embodiment, referring to Figs. 1 and 2, the center plane region 20 has a thickness H of 0.4 to 0.6 mm.

By setting the center plane area of the groove to a thickness H of 0.4-0.6 mm, the performance of the filter is improved. Specifically, based on the above embodiment, the maximum thickness of the edge arc region 21 is

8-12mm.

By setting the thickness of the edge arc area, the performance of the filter is improved.

Specifically, preferably, the central planar region 20 has a thickness of 0.5 mm, and/or the edge circular arc region 21 has a maximum thickness of 10 mm. The filter mainly has two functions, one is to absorb low-energy X-rays to reduce the dose absorbed by the human body, and the other is to adjust the uniformity of the X-ray beam received by the detector, and at the same time effectively reduce the effective dose of the skin surface in the marginal region of the human body. In order to realize the two functions of the filter, the three parameters of the filter need to be calculated: the material, the thickness H of the central plane region, the thickness H _{1 of the} edge arc region _(> among them, the material and the center plane) The thickness H of the zone is the key to the optimized design of the filter for the head CT scanner. The performance of copper is superior to that of aluminum.

Specifically, based on the above embodiment, the lower end surface of the square body 1 is also provided with a groove, and the groove of the lower end surface is symmetrical with the groove of the upper end surface. There are openings on both sides of the groove. The X-ray filter of the present invention can adopt a butterfly shape, and can also prevent X-rays from harming the human body.

The filtration process of the filter is more complicated. Although low-energy X-rays pass through the filter, most of it can be absorbed directly, but some high-energy X-rays scatter when they pass through the filter. These scattered X-rays, even if their energy is in the energy range required for imaging, can only be treated as noise. Because CT imaging uses the line of focus and detector elements to provide spatial path information for X-rays, image reconstruction is achieved. The scattered X-ray photo has lost the position information of the focus and cannot be used for image reconstruction. Therefore, directly simulating the X-rays generated by the electron beam target through the filter of different parameters, by comparing the energy transmission of the filtered X-rays to compare the advantages and disadvantages of the filter, can not truly reflect the true help of CT imaging The number of X-photons. In addition, it is inaccurate to select the filter directly by the dosimeter to test the X-ray beam of different filters before and after passing through the phantom, even the error is greater, because the effect of scattered photons is also not Eliminated, and its error is amplified by the test process.

In order to solve the above problems, from the viewpoint of signal-to-noise ratio, the present invention provides a calculation formula and an analog calculation method for the optimization design of the filter. Material and center plane area thickness values can be designed using this formula. The calculation formula is as follows:

The material and center plane area thickness of the filter square body is determined by the following formula design: Where E is the energy of the X-photon, M is the material of the filter, H is the thickness of the central plane of the filter; ^Ρ ( ^{£ Μ} ) means that the X-ray photo of the energy is Μ, the thickness is Η The proportion of scattering that does not occur after the filter;

s( ^{£ M i} ) represents the proportion of X-rays of energy E that scatter after passing through a filter of material M and thickness H;

The energy density distribution of the number of X-photons generated by the electron target, and the integral value of the entire energy region is 1;

E0 is the minimum energy in the energy spectrum, E2 is the energy maximum in the energy, and E1 is the energy cut-off point, that is, the X-rays of the energy in the interval [E0, E 1] are the filtering objects of the filter;

Β _Ε = Β χ Έ , the relative ratio of the sum of the fundamental radiation and the detector noise to the number of incident photons, and E is the average energy of the X-ray photons equivalent to the background radiation and detector noise. The helium can be measured experimentally.

The following is a simulation of the physical process of X-rays passing through a 20 cm thick layer of water. The energy ratios of reflection, deposition and transmission are counted. The calculation results are shown in Fig. 3. As can be seen from the figure, as the energy is reduced, the energy deposited in the water mold is getting higher and higher. When the energy is reduced to 30 keV, the energy ratio of X-rays transmitted from it is close to zero. Therefore, X-rays of energy below 30 keV have little contribution to the tomographic imaging of the human body, but only increase the absorbed dose of the human body, which needs to be filtered out by a filter. In Figure 3, □ ——reflection share; Δ—deposition share; 〇—transmission share.

See the signal-to-noise ratio calculation results of the filter

FIG. 5 is a diagram showing a signal-to-noise ratio calculation result (energy integration mode) of a filter material made of aluminum according to an embodiment of the present invention; and FIG. It can be seen from the figure that the thickness of the central plane of the filter is the optimum thickness value, and the signal-to-noise ratio of copper is better than that of aluminum. However, the optimum thickness value is sensitive to background radiation and detector noise. As the BE value increases, not only does the signal-to-noise ratio decrease f艮, but the optimum thickness value also decreases. This means that when the BE value is increased, a relatively high signal-to-noise ratio can be obtained only by increasing the absolute value of the number of useful photons that pass through the filter. Similarly, it can be inferred that if the beam intensity of the CT is weakened, the optimum thickness value of the central plane region of the filter will also become smaller. Because the radiation background and detector noise are approximately constant, if the beam intensity is weakened, the noise is relatively enhanced, and the absolute value of the number of useful photons passing through the filter must be increased to obtain a relatively high signal-to-noise. ratio.

In Figures 4 and 5: Δ - electron energy 140keV, filtering threshold 40keV, noise is 0;

V——electron energy 140keV, filtering threshold 50keV, noise is 0;

〇——Electronic energy 140keV, filtering threshold 40keV, noise 0.01 x 60keV;

*—— Electronic energy lOOkeV, filtering threshold 40keV, noise 0.01 x 60keV.

It can also be seen from the figure that as the incident electron energy decreases, the signal-to-noise ratio decreases rapidly, and the optimum thickness value of the central plane region of the filterless filter does not change much. As the energy threshold increases, the optimum thickness value also increases, and the signal-to-noise ratio decreases greatly. This means that the greater the energy of the filtered X-rays, the thicker the filter is needed, but the useful photon share through the filter will be significantly reduced.

According to the above calculation results, it is known that copper is more suitable than aluminum when the first function of the filter is satisfied, so copper is used to calculate the thickness of the edge of the filter. Since the X-ray photo transmission ratio is closely related to the energy, the higher the energy, the higher the ratio of transmission, so we calculated

120keV X-rays pass through the energy ratio of copper plates of different thicknesses, and the results are wrong! The reference source was not found. .

Calculate the junction ^^, when the Cu thickness is 10mm, the energy share of 120keV X photon transmission is less than 10%. Since the number of X-photons with energy above lOOkeV is small, there are X-rays outside the filter outside the filter in the front of the filter. In order to reduce the space occupied here, 10mm can be used as the edge thickness of the filter. Design reference value. This again shows that the use of copper as a filter material will be superior to aluminum because it allows the filter to be designed to be smaller.

Based on the above calculation results, the filter design is as follows: The material is copper, the edge thickness is 10mm, which is the thickness of the edge arc area, and the thickness of the center plane area is 0.5mm, which is used for CT imaging of the head. The specific shape of the filter will be determined based on the distance of the focus of the X-ray tube from the window and the distance from the center of rotation and the convenience of mounting. A wedge or butterfly shape is preferred.

The present invention also provides an X-ray filtering system comprising: an X-ray source, wherein the X-ray source is provided with the X-ray filter on the X-ray exiting light path. The X-ray filter is placed between the X-ray source and the body to be inspected to prevent damage to the body to be inspected by the X-ray source.

Another solution provided by the present invention: A mobile CT scanner comprising the above-described X-ray filtering system. The X-ray filter of the present invention is used on a mobile CT scanner to prevent X-rays from harming the human body to be examined.

Although the invention and its advantages have been described in detail, it should be understood that Various changes, substitutions and alterations are possible in the case of the spirit and scope of the invention as defined by the appended claims.

Finally, it should also be noted that in this context, relational terms such as first and second are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply these entities. There is any such actual relationship or order between operations. Furthermore, the terms "comprising," "comprising," or "includes" or "includes" are intended to include a non-exclusive inclusion, such that a process, method, article, or device that includes a plurality of elements includes not only those elements but also Other elements, or elements that are inherent to such a process, method, item, or device. In the absence of further limitations, the elements defined by the phrase "comprising a ..." do not exclude the presence of additional elements in the process, method, item, or device that comprises the element.

The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. Various modifications and changes may be made to the above-described embodiments without departing from the spirit and scope of the invention. Therefore, the scope of the invention is to be limited only by the appended claims and their equivalents.

Claims

Claim

An X-ray filter comprising a square body, the upper end surface of the square body being provided with a groove along a length extension thereof to form a centrally symmetrical wedge portion on the square body.

2. The X-ray filter according to claim 1, wherein the groove comprises: a central planar area and an edge circular arc area that abuts both sides of the central planar area.

The X-ray filter according to claim 1 or 2, wherein the material of the square body is copper or aluminum.

The X-ray filter according to claim 3, wherein the central planar region has a thickness of 0.4 to 0.6 mm.

The X-ray filter according to claim 3, wherein the edge arc area has a maximum thickness of 8-12 mm.

The X-ray filter according to claim 3, wherein the center plane area has a thickness of 0.5 mm, and/or the edge arc area has a maximum thickness of 10 mm.

The X-ray filter according to claim 3, characterized in that the lower end surface of the square body is also provided with a groove symmetrical with the groove of the upper end surface.

The X-ray filter according to claim 3, wherein the material of the square body and the thickness of the central plane region are determined by:

Where E is the energy of the X-photon, M is the material of the square body, Η is the thickness of the central plane region of the filter; ^p ( ^{£ M i} ) is the X-photon passing through the material M and having a thickness of Η The proportion of the square filter body after the absence of scattering;

^S ( ^{£ M} , ") represents the proportion of X-rays of energy E that scatter after passing through a filter of material M and thickness Η;

The energy density distribution indicating the number of X photons generated by the electron target, and the integral value of the entire energy interval is 1;

E0 is the minimum energy in the energy spectrum, E2 is the maximum energy of the energy, and E 1 is the energy cut-off point, that is, the X-photons of the energy in the interval [E0, E l] are the filtering objects of the filter; ^B _E = ^B ^ ^E , B is the relative ratio of the sum of the base radiation and the detector noise to the number of incident photons, which is the average energy of the X-photons equivalent to the background radiation and the detector noise.

An X-ray filtering system, comprising: an X-ray source, wherein the X-ray exiting optical path of the X-ray source is provided with the X-ray filter according to any one of claims 1-8.

A mobile CT scanner comprising the X-ray filtering system of claim 9.