JP3204036B2 - X-ray device and K-edge filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray apparatus and a K-edge filter used for a bone density measuring apparatus and other substance inspection apparatuses.

[0002]

2. Description of the Related Art An X-ray apparatus used for a bone density measuring apparatus using X-rays is classified into a single energy type (SXA) and a dual energy type (DXA) depending on the measuring method. S
XA is a method of measuring bone density by absorption of a single wavelength of X-rays. A subject is immersed in water similar to human soft tissue,
The thickness is measured in a state where the thickness is approximately uniform, and the thickness of only the bone portion is measured.

On the other hand, DXA measures the soft tissues of the human body also by X-rays. Since water is not used as approximate soft tissues, the accuracy is high, and the burden on the user is reduced.
A is better than A. DXA also has a time division method and a filter method as a method for generating X-rays.

[0004] The time-division method employs two kinds of energy, high and low.
Lines are generated alternately in a time-sharing manner, and the bone density is measured using data for each time. High and low X
The X-ray tube voltage change and the K-edge filter are combined to generate the line, and the conditions are optimized. A detector that does not allow energy separation may be used as the detector. On the other hand, the filter method is a K-edge filter that uses the K-edge absorption characteristics of the X-rays of the substance while keeping the tube voltage constant. It splits into two types of high-low X-rays. On the other hand, since there is no time lag, more accurate measurement is possible.

Conventional K-edge filters are often composed of only one kind of element, and the X-ray intensity near the energy separation boundary of separated X-rays is not sufficiently reduced. There is a problem that the energy region cannot be sufficiently clearly separated. Further, since a rare earth material such as samarium is conventionally used, it is expensive and has a problem in material stability.

[0006] To solve this problem, Japanese Patent Laid-Open No. 5-27 is disclosed.
No. 043 discloses a filter material for a K-edge filter made of a material composed of two or more elements. Specifically, a Gd plate and an Er plate are stacked,
A combination of b and Po is used. In addition,
Each K absorption edge has Gd of about 50 keV, Er of about 57 keV, Pb of about 88 keV, and Po of about 93 keV.
It is.

[0007]

However, in the combinations of the above-mentioned elements, there is a certain difference in the K absorption edge of each element, so that the X-ray energy passing through the filter is as shown in FIG. ), The X-ray intensity near the energy separation boundary of the separated X-rays is not sufficiently reduced, and the low-energy region and the high-energy region cannot be sufficiently clearly separated. There was a problem.

In general, X-rays are greatly affected by beam hardening particularly at low energies. Therefore, simply separating the high energy region from the low energy region will result in an accurate single energy in the low energy region. It was difficult to measure the X-ray intensity. SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems and provides an X-ray apparatus and a K-edge capable of sufficiently separating a low-energy region and a high-energy region from each other and highly unifying the X-ray energy in the low-energy region. The purpose is to provide a filter.

[0009]

In order to achieve the above object, a first X-ray apparatus according to the present invention comprises an X-ray source and a K-edge for separating X-rays generated from the X-ray source into a plurality of energies. A K-absorption edge having a filter and an X-ray detector, wherein the K-absorption edge of the element constituting the K-edge filter is smaller than the smallest K-absorption edge of the elements constituting the K-edge filter. And the K edge filter is composed of a plurality of elements, and the plurality of elements can exist as a solid when the plurality of elements are compounded, and the plurality of elements are of the elements which may be present as a solid when a compound, wherein K d
Element used in the edge filter and used in the X-ray detector
The elements to be obtained are characterized in that they are elements that are closest to each other in the periodic table.

The second X-ray apparatus of the present invention uses iodine and cesium as elements constituting a K-edge filter, and uses tellurium and cadmium as elements constituting an X-ray detector. . Further, a third X-ray apparatus according to the present invention includes an X-ray source, a K-edge filter for separating X-rays generated from the X-ray source into a plurality of energies, and an X-ray detector. The filter is made of at least iodine, cesium and thallium, and the K-edge filter is provided with a light transmitting means and a photodetector.

A fourth X-ray apparatus according to the present invention includes control means for receiving a signal from a photodetector and controlling an X-ray source. A first K-edge filter of the present invention is a K-edge filter using a plurality of elements,
The plurality of elements can exist as a solid when the plurality of elements are compounded, and among the elements that can be present as a solid when the plurality of elements are compounded, each other in the periodic table of the elements It is characterized by being the closest element.

A second K-edge filter according to the present invention uses iodine and cesium as a plurality of elements.

[0013]

According to the present invention, the first aspect of the present invention is provided.
The X-ray apparatus of the present invention can highly unify the separated low-energy side, and can generate X-rays with reduced influence of beam hardening on the low-energy side. Further, the second X-ray apparatus according to the present invention can obtain an optimal combination of elements constituting the K-edge filter and the X-ray detector.

In the third X-ray apparatus according to the present invention, since the K-edge filter is a scintillator having a fast response,
X-ray output can be monitored. Further, the fourth X-ray apparatus of the present invention monitors the output of X-rays,
Since X-ray output control is performed, more accurate X-ray control is possible. Further, the first K-edge filter of the present invention includes:
The K absorption edge of each element becomes the closest value, and it can be reliably separated near the separation boundary between high energy and low energy.

Further, the second K-edge filter of the present invention can obtain an optimum combination of elements.

[0016]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of an X-ray apparatus according to one embodiment of the present invention. In the figure, reference numeral 1 denotes an X-ray source, which outputs a maximum tube voltage of 80 kV. 2 is a K-edge filter for separating X-ray energy from the X-ray source 1,
CsI (cesium iodide) having a thickness of 1 mm was used. Note that Tl (thallium) is further added to CsI.
Reference numeral 3 denotes an X-ray detector for measuring X-rays transmitted through a substance between the X-ray detector 2 and the K-edge filter 2. In this embodiment, a CdTe (cadmium telluride) semiconductor detector is used. Reference numeral 4 denotes an optical fiber connected to the K-edge filter 2, reference numeral 5 denotes a Si optical sensor that detects light from the K-edge filter 2 as a scintillator, and reference numeral 6 controls the X-ray source 1 in response to the detection result of the Si optical sensor 5. It is a control unit. The control unit 1 also displays the detection result.

Each of the elements Cs and I constituting the K-edge filter 2 is an element that can exist as a solid when formed as a compound, and among the elements that can be formed as a solid when formed as a compound, Since the elements are closest to each other in the periodic table, the K absorption edge of I is approximately 33 keV and the value of Cs is approximately 36 keV. It is known that the K absorption edge of an element increases as the atomic number in the periodic table increases.

As shown in FIG. 3 (c), the intensity distribution of the X-rays transmitted through the K-edge filter 2 has a peak in the low energy region near 33 keV. Is observed.
However, since the effect of beam hardening is large on the low energy side, accurate measurement cannot be performed by using the numerical value of the intensity as it is.

For this reason, if a means for compensating for the beam hardening in the low energy region is used, it is possible to perform a measurement with a certain degree of accuracy. Can be realized. The final purpose of separating the energy region is to obtain two X-rays having a certain value of energy and calculate the thickness of the material by calculating using the X-ray intensity of each energy transmitted through the substance, It is to determine the amount of the substance. Therefore, if X-rays with excellent single energy can be obtained, more accurate measurement can be performed.

The present inventor has completely changed his idea from the conventional idea of correcting the effect of beam hardening in the low energy region, and has used the following configuration. This will be described below with reference to the drawings. FIG. 2A is a diagram showing the absorption coefficient of a CdTe semiconductor detector according to one embodiment of the present invention, and FIG. 2B is a diagram showing the absorption coefficient of the CdTe semiconductor and the Ks of CsI.
The figure which shows the relationship with the X-ray which transmitted the edge filter,
(C) is a conceptual diagram of the X-ray energy detected by the detector, and the X-ray energy separated by using the K-edge filter 2 described above.
The line was measured by the CdTe semiconductor detector 3.

In this embodiment, as shown in FIG.
Since d has a K absorption edge at about 27 keV, Te has a K absorption edge at about 32 keV, I has a K absorption edge at about 33 keV, and Cs has a K absorption edge at about 36 keV, a single low-energy X-ray peak is formed near 33 keV. . That is, since the K-absorption edge of the CdTe semiconductor detector 3 itself is about 27 keV and about 32 keV, X-rays having an energy less than this value are hardly detected in a portion where the X-ray intensity is high because the absorption coefficient is low. On the contrary, the portion having a high absorption coefficient has a low X-ray intensity, so that it is difficult to detect the portion. Also, 27 keV
And between 33 keV, the intensity of the X-ray transmitted through the K-edge filter 2 itself is high, and the absorption coefficient is high.
It is very easy to detect.

As is apparent from FIG.
A single peak is measured near V and near 60 keV. The high energy side is hardly affected by the beam hardening, so that the above method on the low energy side may not be used. Also, C
Since dTe has a resolution of 15 to 30 keV, a single peak is formed on the high energy side even if the maximum tube voltage is 50 to 90 kV, but the maximum tube voltage is reduced to reduce the influence of the K absorption edge of W (tungsten). A voltage of about 70 kV is appropriate.

For comparison with this example, an experiment was conducted using a filter using Sn (tin) having a K absorption edge near 29 keV between cadmium and tellurium. The low and high-energy peaks were broad, and the effect as in the present invention could not be obtained. Next, the relationship between the K edge filter 2 and the X-ray energy transmitted therethrough will be described. By using the K edge filter 2, the X-ray transmitted through the K edge filter 2 draws an energy curve as shown in FIG. As is clear from FIG. 3C, the X-ray dose near the energy separation boundary of the separated X-rays is sufficiently reduced.

The present inventor considers the reason as follows. This will be described below with reference to the drawings. FIG. 3A is a diagram illustrating a relationship between X-ray energy and intensity emitted from the X-ray source 1 according to an embodiment of the present invention, and FIG. 3B is a diagram illustrating an absorption coefficient of the K-edge filter. c) is a diagram showing a relationship between X-ray energy and intensity after passing through the K-edge filter.

First, when viewed from the low energy side, as shown in FIG. 3A, the X-ray emitted from the X-ray source 1 gradually increases from the low energy, and the K-edge shown in FIG. Since the X-ray absorption coefficient of the filter 2 decreases on the contrary,
The intensity of the X-ray transmitted through the K-edge filter 2 is shown in FIG.
Will draw a rising graph like. However, the K absorption edge of I exists around about 33 keV, and X
Since the absorption coefficient of the line suddenly increases, the intensity of the X-ray transmitted through the K-edge filter 2 sharply decreases.

Further, the X-ray absorption coefficient of the K-edge filter 2 which has once risen tends to decrease again. However, the intensity of the X-rays emitted from the X-ray source 1 at an energy in the vicinity thereof is very strong, The X-ray intensity transmitted through the filter 2 tends to increase rapidly. However, about 36
Since the K absorption edge of Cs exists near keV this time, X
The X-ray absorption coefficient increases again before the line intensity increases significantly, and the X-ray intensity transmitted through the K-edge filter 2 further decreases.

As described above, the intensity of the X-ray transmitted through the K-edge filter 2 in two stages is reduced. However, since the interval is performed in a very narrow range, the X-ray intensity between Cs and I is reduced. The increase in the line intensity is suppressed to an extremely small level. In this way, the high energy region and the low energy region can be clearly distinguished. This is clearer than FIG. 4 (c) showing a conventional example. 4A shows a relationship between X-ray energy and intensity emitted from the conventional X-ray source 1, and FIG.
FIG. 4 is a diagram illustrating an absorption coefficient of the K-edge filter, and FIG. 4C is a diagram illustrating a relationship between X-ray energy and intensity after passing through the K-edge filter.

In the periodic table of elements, Xe is between I and Cs.
However, the K edge filter 2 needs to be stably present at room temperature. Therefore, among the elements that can be present as a solid when formed as a compound and the elements that can be present as a solid when formed as a compound, I and Cs, which are the elements closest to each other in the periodic table of the elements, are selected. Thus, a very useful K-edge filter 2 that can clearly separate X-ray energy can be obtained.

The thickness of the CsI K-edge filter 2 is determined by the X-ray tube voltage and the intensity distribution of high and low energies. For an X-ray having a maximum energy of 70 keV, the thickness is 0.5 m.
A K-edge filter having a thickness of about m to 2 mm is used. CsI is a stable material, but shows a slight deliquescence depending on humidity. Therefore, it is desirable to coat with a thin aluminum foil or the like.

Further, CsI to which Tl is added is a scintillator having a fast response. That is, light is emitted with good reaction when X-rays are transmitted. For this reason, as shown in FIG.
Using the K edge filter 2 of I as a scintillator,
Take out the output from the end face with optical fiber 4 etc.
The state of the X-ray source 1 can be monitored by detecting with the Si light sensor 5 or the like. When performing high-precision measurement, the stability of the X-ray source 1 is a very important factor. Therefore, a K-edge filter having an X-ray monitor function as in the present invention is very effective. Becomes

It is important that the K-edge filter 2 that transmits X-rays does not disturb X-rays.
CsI, which is a single crystal, is also useful from the viewpoint of X-ray uniformity of the material. Since CsI can manufacture a large and uniform member, it is possible to manufacture a K-edge filter which is extremely inexpensive and uniform as compared with the related art. In this embodiment, the CsI K-edge filter 2 and the CsI
Although the description has been given using the dTe semiconductor detector 3, if the relationship between the K absorption edge of the K edge filter material and the K absorption edge of the detector material has the same relationship as the present invention,
Similar effects can be obtained.

Although the present embodiment has been described using a semiconductor detector, it goes without saying that similar effects can be obtained in other detection systems such as a scintillator detector and an X-ray film.

[0033]

As is apparent from the above description, the X-ray apparatus according to the present invention can highly unify the separated low energy side and reduce the influence of beam hardening on the low energy side. X-rays can be generated. Further, the output of the X-ray can be monitored, and the output of the X-ray is controlled on the basis thereof, so that the X-ray can be more accurately controlled.

In the K edge filter of the present invention, the K absorption edge of each element becomes the closest value, and the K edge filter can be reliably separated near the separation boundary between high energy and low energy. In this way, an extremely inexpensive and uniform K-edge filter having excellent workability and excellent dual energy separation performance can be manufactured, and by combining with a light transmitting means, high performance and high performance can be achieved. An accurate X-ray device can be realized,
The accuracy of a bone density measuring instrument, a substance analyzer, etc. can be improved, and it can greatly contribute to fields such as medical treatment.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an X-ray apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the absorption coefficient, X-ray energy, and intensity of the CdTe semiconductor detector.

FIG. 3 is a diagram showing a relationship between X-ray energy emitted from the X-ray source, intensity, and absorption coefficient.

FIG. 4 is a diagram showing a relationship between X-ray energy emitted from a conventional X-ray source, intensity, and absorption coefficient.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 X-ray source 2 K edge filter 3 CdTe semiconductor detector 4 Optical fiber 5 Si optical sensor 6 Control part

Claims (4)

(57) [Claims] An X-ray source; a K-edge filter for separating X-rays generated from the X-ray source into a plurality of energies;
A detector having a K-absorption edge smaller than the smallest K-absorption edge of the K-absorption edges of the elements constituting the K-edge filter. When used, the K-edge filter is composed of a plurality of elements, and the plurality of elements can be present as a solid when the plurality of elements are formed into a compound, and when the plurality of elements are formed as a compound. Of the elements that can exist as solids in the K-edge filter
An X-ray apparatus, wherein the element to be used and the element used for the X-ray detector are elements which are closest to each other in the periodic table. 2. An X-ray filter according to claim 1, wherein iodine and cesium are used as elements constituting the K-edge filter, and tellurium and cadmium are used as elements constituting the X-ray detector.
Line equipment. 3. An X-ray source, a K-edge filter for separating X-rays generated from the X-ray source into a plurality of energies,
A line detector, wherein the K-edge filter is made of at least iodine, cesium, and thallium, and the K-edge filter is provided with light transmitting means and a light detector.
Line equipment. 4. The X-ray apparatus according to claim 3, further comprising control means for receiving a signal from the photodetector and controlling the X-ray source.