JP2007082663A - Multi-color x-ray measuring apparatus and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multi-color X-ray measuring apparatus and method which are capable of simultaneously detecting a plurality of monochromatic X-rays of different wavelengths included in multi-color X-rays and obtaining the intensity or the ratio of the plurality of detected monochromatic X-rays included in the multi-color X-rays in a state where a plurality of photons are made incident simultaneously in time. <P>SOLUTION: The multi-color X-ray measuring apparatus is provided with a first X-ray detector 12 on the upstream side, a second X-ray detector 14 on the downstream side and an arithmetic device 20. The two X-ray detectors 12 and 14 are laminated with each other so that multi-color X-rays (two kinds of monochromatic X-rays 1a and 2a) successively and simultaneously pass therethrough. By the arithmetic device 20, from the detection efficiencies G<SB>11</SB>, G<SB>21</SB>, G<SB>12</SB>and G<SB>22</SB>of the respective X-ray detectors for the monochromatic X-rays of the respective wavelengths λ<SB>1</SB>and λ<SB>2</SB>, transmission efficiencies A<SB>12</SB>and A<SB>22</SB>until the monochromatic X-rays of the respective wavelengths λ<SB>1</SB>and λ<SB>2</SB>are made incident on the second X-ray detector 14 and the detection strengths V<SB>1</SB>and V<SB>2</SB>of the respective X-ray detectors, the respective intensities I<SB>1</SB>and I<SB>2</SB>or the ratio of the two kinds of monochromatic X-rays 1a and 2a made incident on the first X-ray detector 12 is computed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an apparatus and method for simultaneously receiving and measuring polychromatic X-rays including a plurality of monochromatic X-rays having different wavelengths.

X-ray is an electromagnetic wave having a wavelength of about of about ^{0.01~100Å (10- 12 ~10- 8 m)} , these X-rays shorter in wavelength (λ = 0.01~1Å) hard X-rays, the wavelength Long X-rays (λ = 1 to 100Å) are called soft X-rays. In the present application, “monochromatic X-ray” means X-ray having a substantially constant wavelength.

X-ray tubes and synchrotron radiation are widely known as X-ray generation sources.
An X-ray tube is an apparatus that generates X-rays by accelerating thermoelectrons obtained by heating a filament in a vacuum at a high voltage to collide with a metal anode (target).
X-rays generated from the X-ray tube are composed of continuous X-rays due to bremsstrahlung of electrons and characteristic X-rays that are emission line spectra. Characteristic X-rays are monochromatic X-rays and are used for applications that require X-rays of a specific wavelength.

Synchrotron radiation (SR light) is X-rays generated when the orbit of an electron beam accelerated to a speed close to the speed of light is changed by a powerful magnet in a ring accelerator (synchrotron) and the orbit is changed.
SR light is an extremely powerful X-ray source (by 10 ³ times or more) as compared with an X-ray tube, and is used in a field that requires high X-ray intensity.
A small X-ray generator using a small linear accelerator has already been proposed (for example, Non-Patent Document 1).

On the other hand, X-ray CT apparatuses are widely known as apparatuses using monochromatic X-rays. The X-ray CT apparatus is an apparatus that obtains a two-dimensional cross-sectional image of an object by irradiating the object to be measured with X-rays from different directions, measuring the absorption thereof, and reconstructing the image by a computer.
In an X-ray CT apparatus, a monochromator composed of two crystal plates is usually used as means for obtaining monochromatic X-rays from radiated light.

  Further, in order to increase the measurement accuracy of electron density, a mixed two-color X-ray CT apparatus using two types of monochromatic X-rays having different mixing ratios of the main wave and the harmonic has been proposed (for example, Non-Patent Document 2).

On the other hand, X-ray detectors for detecting X-ray intensity and images are proportional counters using gas ionization, scintillation counters using solid fluorescence, and semiconductor detectors using solid semiconductor ionization. , Etc. are conventionally known.
In addition, Non-Patent Documents 3 and 4 and Patent Documents 1 and 2 have already been disclosed as X-ray detectors.

As shown in FIG. 7, the “small X-ray generator” of Non-Patent Document 1 generates an X-ray 54 by colliding an electron beam 52 accelerated by a small accelerator 51 (X-band accelerator tube) with a laser 53. It is something to be made. The multi-bunch electron beam 52 generated by the RF electron gun 55 (thermal RF gun) is accelerated by the X-band accelerator tube 51, collides with the pulse laser beam 53, and generates hard X-rays 54 having a time width of 10 ns by Compton scattering. Is done.
This apparatus is miniaturized by using, as RF, an X band (11.424 GHz) that is four times the frequency of the S band (2.856 GHz) generally used in linear accelerators. For example, the X-ray intensity (number of photons) ): About 1 × 10 ⁹ photons / s, pulse width: generation of intense hard X-rays of about 10 ps is predicted.

As shown in FIG. 8, the “mixed two-color X-ray CT apparatus” of Non-Patent Document 2 includes a rotary filter 61, a monochromator 62, a collimator 63, a transmission ion chamber 64, a scatterer 65, a slide / rotary table 66, A NaI detector 67 and a plastic scintillation counter 68 are provided. A 40 keV main wave X-ray and an 80 keV double harmonic X-ray are extracted from the synchrotron radiation 69 a by the monochromator 62, and the 40 keV X ray and 80 keVX are extracted by the rotary filter 61. The mixing ratio of the rays is adjusted, the scattered X-ray spectrum from the scatterer 65 is observed with the NaI detector 67, the mixing ratio is measured, the size of the mixed two-color X-ray 69b is shaped with the collimator 63, and the transmission ion A plastic scintillation counter 68 that passes through the chamber 64 and the subject 60. Strength is to measure the.
With this device, the measurement accuracy of the electron density is improved, and an image image of the electron density and effective atomic number has been successfully created.

  The flat panel detector of Non-Patent Document 3 has a structure similar to that of a flat panel such as a notebook PC, and changes X-rays into light intensity with a thin CsI film, and changes it into an electric signal intensity with a photodiode. Is. This flat panel detector has a feature that the effective area of the detector can be large, for example, about 43 cm × 43 cm, and the whole is very thin and easily transmits X-rays.

  The X-ray imaging device of Non-Patent Document 4 can make use of the difference in absorption wavelength to clearly draw material-emphasized color imaging of different metal materials and minute steps of thick objects. It is applied to an X-ray detector and enables construction of a clear CT reconstruction image.

  The radiation detector of Patent Document 1 is a radiation detector including a scintillator and a light detector for detecting light emission of the scintillator. The scintillator is mainly composed of Ce, an emission center ion, and Gd, Al, Ga, O. It is an oxide phosphor having a garnet structure as an element.

  The X-ray detector exchange system of Patent Document 2 aims at switching a plurality of X-ray detectors by remote control, and a plurality of X-ray detectors having different sensitivities are detachably arranged. A motor driver that rotates the switch, a motor controller that replaces the X-ray detector by rotating the motor of the switch according to the measured X-ray intensity, and programming that allows the X-ray detector to be replaced unattended It consists of a control computer.

Katsuhiro Dobashi, et al., “Development of small hard X-ray source using X-band linac”, 2002 Makoto Sasaki, et al., “Development of mixed two-color X-ray CT system”, Medical Physics Vol. 23 Supplement No. 2 April 2003 PHILIPS flat panel detector, Internet <URL: http: // www. medical. philips. com / jp / products / xray / products / radiography / flat_panel >> Toru Aoki, et al., “E-40, room temperature CdTe X-ray imaging device with wavelength discrimination function”, 11th Image Sensing Symposium, Internet <URL: http: // www. ssii. jp / SSII05_recommend. pdf>

JP 2005-095514 A, “Radiation detector and X-ray CT apparatus using the same” JP-A-2005-140611, “X-ray detector replacement system”

In the conventional angiography and two-color X-ray CT using the difference method, for example, two types of monochromatic X-rays having different wavelengths are used and switched in a short time.
In this case, for example, in dynamic angiography, it is necessary to obtain an image by switching monochromatic X-rays in such a short time that it can be considered that the blood vessel is not moving. Even in the case of two-color X-ray CT, it is necessary to switch between the two types of single-color X-rays in the shortest possible time in order to prevent the quality of the reconstructed image from being deteriorated due to the change in the state of the subject.

However, it is very difficult to switch a plurality of monochromatic X-rays at a high speed, and it is practically impossible to avoid image misalignment.
Therefore, it has been studied to simultaneously use polychromatic X-rays including a plurality of monochromatic X-rays having different wavelengths. In this case, since the image of the subject can be acquired simultaneously with a plurality of single color X-rays, there is an advantage that a clear image can be obtained without any image misalignment.

In this case, in order to create an image image of the transmission coefficient, electron density, and effective atomic number of the subject portion from the intensity of the X-ray transmitted through each portion of the subject, a plurality of monochromatic X-rays included in the transmitted multicolor X-rays Each strength or ratio is required.
However, in general, the X-ray detector measures the total energy dropped by the X-rays on the detector as a charge amount, and can measure the energy only when the incident photon is single. When a plurality of photons are incident at the same time, the total energy of the incident X-ray photons can be detected, but the energy for each wavelength cannot be detected in principle.

  The present invention has been developed to solve the above-described problems. That is, an object of the present invention is to simultaneously detect a plurality of monochromatic X-rays having different wavelengths included in a polychromatic X-ray and to include the detected polychromatic X-ray in a situation where a plurality of photons are incident simultaneously. Another object of the present invention is to provide a multicolor X-ray measuring apparatus and method that can determine each intensity or ratio of a plurality of monochromatic X-rays.

According to the present invention, a multicolor X-ray measurement apparatus that measures multicolor X-rays including a plurality of monochromatic X-rays having different wavelengths λ _i (i = 1, 2,... N; n is an integer of 2 or more). There,
The multicolor X-rays are stacked so as to pass through sequentially, and a plurality of Xs for detecting each intensity V _j (j = 1, 2,... M; m is an integer of 2 or more) of the passing multicolor X-rays. A line detector;
A multicolor, comprising: an arithmetic unit that calculates each intensity or a ratio of a plurality of monochromatic X-rays incident on the most upstream X-ray detector from the detection intensity V _j of each X-ray detector. An X-ray measurement apparatus is provided.

According to a preferred embodiment of the present invention, the arithmetic device comprises:
Detection efficiencies G _{ij of the} plurality of X-ray detectors for each wavelength λ _i ;
Transmission efficiency A _ij until the monochromatic X-rays of the respective wavelengths λ _i are incident on the plurality of X-ray detectors,
Each intensity I _i (i = 1, 2,... N) of a plurality of monochromatic X-rays incident on the most upstream X-ray detector or a ratio thereof is calculated from the detection intensity V _j of each X-ray detector. .

According to a preferred embodiment of the present invention, the polychromatic X-ray includes two types of monochromatic X-rays having different wavelengths λ ₁ and λ ₂ ,
The plurality of X-ray detectors includes an upstream first X-ray detector and a downstream second X-ray detector stacked on each other,
The arithmetic unit is
Detection efficiencies G ₁₁ and G ₂₁ of the first X-ray detector and detection efficiencies G ₁₂ and G ₂₂ of the second X-ray detector for the wavelengths λ ₁ and λ ₂ ,
Transmission efficiencies A ₁₂ and A ₂₂ until the monochromatic X-rays of the wavelengths λ ₁ and λ ₂ enter the _second X-ray detector;
From the detected intensities V ₁ and V ₂ of the first X-ray detector and the second X-ray detector, the respective intensities of the two types of monochromatic X-rays incident on the first X-ray detector according to the following formulas (1) and (2) I ₁ and I ₂ are calculated.
V ₁ = I ₁ × G ₁₁ + I ₂ × G ₂₁ (1)
V ₂ = I ₁ × A ₁₂ × G ₁₂ + I ₂ × A ₂₂ × G ₂₂ (2)

According to another preferred embodiment of the present invention, the polychromatic X-ray includes three types of monochromatic X-rays having different wavelengths λ ₁ , λ ₂ , and λ ₃ ,
The plurality of X-ray detectors includes an upstream first X-ray detector, an intermediate second X-ray detector, and a downstream third X-ray detector stacked on each other,
The arithmetic unit is
For each of the wavelengths λ ₁ , λ ₂ , λ ₃ , the detection efficiency G ₁₁ , G ₂₁ , G ₃₁ of the first X-ray detector, the detection efficiency G ₁₂ , G ₂₂ , G _{32 of} the second X-ray detector, Detection efficiency G ₁₃ , G ₂₃ , G _{33 of the} 3X-ray detector,
Transmission efficiency A ₁₂ , A ₂₂ , A ₃₂ until the monochromatic X-rays of the respective wavelengths λ ₁ , λ ₂ , λ ₃ are incident on the second X-ray detector, and transmission until they are incident on the third X-ray detector Efficiency A ₁₃ , A ₂₃ , A ₃₃ ,
From the detection intensities V ₁ , V ₂ , and V _{3 of} the first X-ray detector, the second X-ray detector, and the third X-ray detector, the first X-ray detector is expressed by the following equations (3), (4), and (5). Intensities I ₁ , I ₂ , and I ₃ of the three types of monochromatic X-rays incident on the light are calculated.
V ₁ = I ₁ × G ₁₁ + I ₂ × G ₂₁ + I ₃ × G ₃₁ (3)
_{V 2 = I 1 × A 12} × G 12 + I 2 × A 22 × G 22 + I 3 × A 32 × G 32 ··· (4)
V ₃ = I ₁ × A ₁₃ × G ₁₃ + I ₂ × A ₂₃ × G ₂₃ + I ₃ × A ₃₃ × G ₃₃ (5)

  Further, an absorber having different transmission efficiency for the monochromatic X-rays having the respective wavelengths λi is provided between the plurality of stacked X-ray detectors. The absorber preferably contains a specific element to be subjected to differential imaging.

Further, according to the present invention, a multicolor X-ray measurement method for measuring multicolor X-rays including a plurality of monochromatic X-rays having different wavelengths λ _i (i = 1, 2,... N; n is an integer of 2 or more). Because
A plurality of X-ray detectors are stacked and arranged so that the polychromatic X-rays pass through sequentially at the same time,
Detecting each intensity V _j (j = 1, 2,... M; m is an integer of 2 or more) of the polychromatic X-rays passing through each X-ray detector;
A multicolor X-ray measurement method is provided, wherein each intensity or ratio of a plurality of monochromatic X-rays incident on the most upstream X-ray detector is calculated from each detected intensity Vj.

According to the apparatus and method of the present invention, a plurality of X-ray detectors stacked so that multicolor X-rays pass through at the same time, and the X-ray on the most upstream side from the detection intensity V _j of each X-ray detector. A multi-color that passes through each X-ray detector in a situation where a plurality of photons are incident simultaneously in time. Each intensity V _j (j = 1, 2,... N) of X-rays is detected, and from this, each intensity of a plurality of monochromatic X-rays or a ratio thereof can be calculated.

That is, in a situation where a plurality of photons are incident simultaneously in time, the detection efficiency G _ij of the plurality of X-ray detector for a monochromatic X-ray of each wavelength lambda _i, a plurality of X-ray is monochromatic X-rays of each wavelength lambda _i The transmission efficiencies A _ij until they are incident on the detector are different from each other, and these can be obtained in advance by a test or the like. Therefore, using these values, the detection intensity V _j of each X-ray detector is calculated by the above-described equation. (1) It can be represented by (2), or formulas (3) to (5).
Therefore, each intensity | strength of several monochrome X-rays or its ratio can be calculated from these formula | equation using an arithmetic unit.

Therefore, the apparatus and method of the present invention is combined with a mixed (multi-wavelength) monochromatic X-ray source such as an undulator of a synchrotron radiation facility or a Compton scattered X-ray source, two-color (multi-color) X-ray CT, dynamic difference imaging, etc. In addition to speeding up image acquisition with two-color X-ray CT, it is possible to realize complete dynamic difference imaging.
Further, in other polychromatic X-ray applications, it is not necessary to consider X-ray wavelength switching, detector wavelength switching, and the like, and convenience is improved.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In each figure, common portions are denoted by the same reference numerals, and redundant description is omitted.

First, the principle of the present invention will be described.
As described above, an X-ray is an electromagnetic wave having a wavelength of about of about ^{0.01~100Å (10- 12 ~10- 8 m)} , if the wavelength is substantially constant monochromatic X-rays, the wavelength lambda [Å] and photons There is a relationship of the formula (6) between the energy E [keV].
E = 12.4 / λ (6)
Therefore, in the monochromatic X-ray, the wavelength λ [Å] and the photon energy E [keV] have a one-to-one correspondence. For example, in the examples described later, the wavelength λ of monochromatic X-rays having photon energies of 15 keV and 30 keV. Are 0.83 and 0.41, respectively.

Further, the X-ray intensity I when X-rays pass through a substance with a distance of x is expressed by Expression (7).
I = I ₀ exp (−μx) (7)
Here, I ₀ is the X-ray intensity before entering the material, and μ is the linear absorption coefficient.
It is known that the linear absorption coefficient generally varies depending on the substance and wavelength. For example, in the case of the same substance, the longer the wavelength is, the more the line absorption coefficient is increased, so that the transmission becomes difficult. On the contrary, the shorter the wavelength is, the more the line absorption coefficient is decreased and the light is easily transmitted.

If the density is ρ, equation (7) can be rewritten as equation (8).
I = I ₀ exp (−μ / ρ) (ρx) (8)
This μ / ρ is called a mass absorption coefficient and is known to have a value specific to a substance. This mass absorption coefficient is small when the X-ray wavelength is short and is large when the X-ray wavelength is long, but it generally has a discontinuous absorption edge in the middle rather than a continuous change.

However, equation (9) is approximately established between the respective absorption edges.
μ / ρ = k × λ ³ × Z ³ (9)
Here, k is a constant and Z is an effective atomic number. From this equation, it can be seen that if the absorption edge is ignored for a certain wavelength, the absorption coefficient generally increases as the element becomes heavier, and X-rays are difficult to pass.

FIG. 1 is a principle diagram of an apparatus (for example, an X-ray CT apparatus) to which the multicolor X-ray measuring apparatus of the present invention is applied. In this figure, it is assumed that two types of monochromatic X-rays having different wavelengths λ ₁ and λ ₂ are transmitted through a subject and the X-ray intensities I ₁ and I ₂ after passing are measured.
In this case, if the incident X-ray intensities I ₁₀ and I ₂₀ are known, μ ₁ and μ ₂ are determined from the equation (7), and the following equations (9a) and (9b) satisfying the above (9) are obtained.
μ ₁ / ρ = k × λ ₁ ³ × Z ³ (9a)
μ ₂ / ρ = k × λ ₂ ³ × Z ³ (9b)
The unknowns in the equations (9a) and (9b) are only ρ and Z of the substance, and ρ and Z of the substance can be obtained by solving these two equations.
Note that the above-described equation (9) is an approximate equation, and an equation with higher accuracy is actually used.

In the example of FIG. 1 described above, it is assumed that the X-ray intensities I ₁ and I ₂ after the passage of each monochromatic X-ray material can be measured separately. However, in a situation where multiple photons are incident simultaneously, if a single X-ray with different wavelengths is detected simultaneously with an ordinary X-ray detector, the total intensity (ie, total energy) of the multiple monochrome X-rays is measured. Therefore, it is impossible in principle to distinguish and measure this.
The present invention solves this problem and makes it possible to detect a plurality of monochromatic X-rays at the same time and determine the intensity of each of the monochromatic X-rays or the ratio thereof.

FIG. 2 is an overall configuration diagram showing the first embodiment of the multicolor X-ray measuring apparatus of the present invention. In this figure, the polychromatic X-ray measuring apparatus 10 of the present invention is an apparatus for measuring polychromatic X-rays including two types of monochromatic X-rays 1a and 2a having different wavelengths λ ₁ and λ ₂ .

The multicolor X-ray measurement apparatus 10 includes an upstream first X-ray detector 12, a downstream second X-ray detector 14, and a computing device 20. The first X-ray detector 12 on the upstream side and the second X-ray detector 14 on the downstream side are stacked on each other so that multicolor X-rays (two types of monochromatic X-rays 1a and 2a) pass through in sequence. In addition, the arithmetic unit 20 uses the respective intensities of the two types of monochromatic X-rays 1a and 2a incident on the first X-ray detector 12 from the detection intensities V ₁ and V ₂ of the _first X-ray detector 12 and the second X-ray detector 14. It has a function of calculating I ₁ , I ₂ or a ratio thereof.

In FIG. 2, when the detection efficiencies of the first X-ray detector 12 for monochromatic X-rays with wavelengths λ ₁ and λ ₂ are G ₁₁ and G ₂₁ , the detection intensity V ₁ of the _first X-ray detector 12 is expressed by the equation (1). It is represented by
V ₁ = I ₁ × G ₁₁ + I ₂ × G ₂₁ (1)
Also, assuming that the transmission efficiencies until the monochromatic X-rays of wavelengths λ ₁ and λ ₂ are incident on the second X-ray detector 14 are A ₁₂ and A ₂₂ , two types of monochromatic X-rays incident on the second X-ray detector 14. The intensities I _1b and I _2b of _1b and _2b are expressed by equations (10a) and (10b).
I _1b = I ₁ × A ₁₂ (10a)
I _2b = I ₂ × A ₂₂ (10b)
Therefore, if the detection efficiency of the second X-ray detector 14 for monochromatic X-rays with wavelengths λ ₁ and λ ₂ is G ₁₂ and G ₂₂ , the detection intensity V ₂ of the _second X-ray detector 14 is expressed by Equation (2). Is done.
V ₂ = I ₁ × A ₁₂ × G ₁₂ + I ₂ × A ₂₂ × G ₂₂ (2)

The arithmetic unit 20 is, for example, a PC (personal computer), and the detection efficiencies G ₁₁ and G ₂₁ of the first X-ray detector 12 and the second X-ray detector 14 for monochromatic X-rays of the wavelengths λ ₁ and λ ₂ . Detection efficiency G ₁₂ , G ₂₂ , transmission efficiency A ₁₂ , A ₂₂ until the monochromatic X-rays of the wavelengths λ ₁ , λ ₂ enter the _second X-ray detector 14, the first X-ray detector 12, and the second X From the detected intensities V ₁ and V _{2 of the} line detector 14, the intensities I ₁ and I ₂ of the two types of monochromatic X-rays incident on the first X-ray detector 12 are obtained by the above-described equations (1) and (2). It comes to calculate.

That is, until the first X-ray detector 12 and the second X-ray detector 14 are incident on the second X-ray detector 12 and the detection efficiencies G ₁₁ and G ₂₁ for the monochromatic X-rays having the wavelengths λ ₁ and λ ₂ described above. The transmission efficiencies A ₁₂ and A ₂₂ are different from each other, and since these can be obtained in advance by a test or the like, the intensities I ₁ and I 2 of the two types of monochromatic X-rays are obtained from the above-described equation using these values. I ₂ or its ratio can be calculated.

FIG. 3 is an overall configuration diagram showing a second embodiment of the multicolor X-ray measurement apparatus of the present invention. In this figure, the polychromatic X-ray measuring apparatus 10 of the present invention includes an absorber having different transmission efficiencies for monochromatic X-rays of wavelengths λ ₁ and λ ₂ between a first X-ray detector 12 and a second X-ray detector 14. 18 is provided. The absorber 18 preferably contains a specific element to be subjected to differential imaging, for example. Other configurations are the same as those in FIG.

In FIG. 3, if the transmission efficiency of the absorber 18 with respect to the monochromatic X-rays of the wavelengths λ ₁ and λ ₂ is B ₁ and B ₂ , the monochromatic X-rays of the wavelengths λ ₁ and λ ₂ are detected on the downstream side of the second X-ray. The transmission efficiencies A ₁₂ and A ₂₂ until entering the device 14 change to the transmission efficiencies B ₁ and B ₂ .
However, since the transmission efficiencies B ₁ and B ₂ can also be obtained in advance by testing or the like, the transmission efficiencies A ₁₂ and A ₂₂ including the influence of the absorber can be obtained in advance using these values.
Accordingly, even in this case, two types of incident light to the first X-ray detector are obtained from the detection intensities V ₁ and V _{2 of the first} X-ray detector 12 and the second X-ray detector 14 according to the above-described equations (1) and (2). The intensities I ₁ and I ₂ of the monochromatic X-rays can be calculated.

That is, even when the absorber is used, the first X-ray detector is always obtained by the equations (1) and (2) by using the “transmission efficiency until it enters the X-ray detector including the transmission efficiency of the absorber”. The intensities I ₁ and I ₂ of the two types of monochromatic X-rays incident on 12 can be calculated.
The same applies to other examples described later.

FIG. 4 is an overall configuration diagram showing a third embodiment of the multicolor X-ray measurement apparatus of the present invention. In this figure, the polychromatic X-ray measuring apparatus 10 of the present invention is an apparatus for measuring polychromatic X-rays including three types of monochromatic X-rays 1a, 2a and 3a having different wavelengths λ ₁ , λ ₂ and λ _3. It is.

The multicolor X-ray measurement apparatus 10 includes an upstream first X-ray detector 12, an intermediate second X-ray detector 14, a downstream third X-ray detector 16, and a computing device 20. The three X-ray detectors 12, 14, and 16 are stacked on each other so that multicolor X-rays (three types of monochromatic X-rays 1a, 2a, and 3a) pass through sequentially. The arithmetic unit 20 includes three types of light incident on the first X-ray detector 12 from the detection intensities V ₁ , V ₂ , and V ₃ of the first X-ray detector 12, the second X-ray detector 14, and the third X-ray detector 16. Each of the intensities I ₁ , I ₂ , I ₃ of the monochromatic X-rays 1a, 2a, 3a or a ratio thereof.

In FIG. 4, the detection efficiencies G ₁₁ , G ₂₁ , G ₃₁ of the first X-ray detector ₁₂ and the detection efficiencies G ₁₂ , G ₂₂ , of the second X-ray detector 14 for the respective wavelengths λ ₁ , λ ₂ , λ ₃ . G ₃₂ , detection efficiencies G ₁₃ , G ₂₃ , and G ₃₃ of the _third X-ray detector 16 and monochromatic X-rays having wavelengths λ ₁ , λ ₂ , and λ ₃ until they enter the second X-ray detector 14. It is assumed that the transmission efficiencies A ₁₂ , A ₂₂ , A ₃₂ and the transmission efficiencies A ₁₃ , A ₂₃ , A ₃₃ until they enter the third X-ray detector 16 are obtained in advance by an examination or the like.
In this case, the detection intensities V ₁ , V ₂ , and V ₃ of the X-ray detectors 12, 14, and 16 are expressed by the following formulas (3), (4), and (5). The intensities I ₁ , I ₂ , and I ₃ of the three types of incident monochromatic X-rays can be calculated.
V ₁ = I ₁ × G ₁₁ + I ₂ × G ₂₁ + I ₃ × G ₃₁ (3)
_{V 2 = I 1 × A 12} × G 12 + I 2 × A 22 × G 22 + I 3 × A 32 × G 32 ··· (4)
V ₃ = I ₁ × A ₁₃ × G ₁₃ + I ₂ × A ₂₃ × G ₂₃ + I ₃ × A ₃₃ × G ₃₃ (5)

Also in this example, absorbers (not shown) having different transmission efficiencies for monochromatic X-rays of the wavelengths λ ₁ , λ ₂ , and λ ₃ are provided between the three X-ray detectors 12, 14, and 16. It is preferable. Moreover, this absorber preferably contains a specific element to be subjected to differential imaging, for example.

Next, in FIG. 1, the subject is irradiated with monochromatic X-rays of two wavelengths λ ₁ and λ ₂ whose wavelengths (energy) are known, and the transmitted X-rays are detected by the multicolor X-ray measuring apparatus 10 of the present invention. The case will be described.
In this case, the polychromatic X-ray measuring apparatus 10 to be used is, for example, as shown in FIG. 2, and the first X-ray detector 12 installed downstream of the subject and the second X-ray detector installed further downstream thereof. 14.
Further, third and fourth X-ray detectors may be installed. Moreover, although it is preferable to install the X-ray absorber 18 between adjacent X-ray detectors like FIG. 3, it is not essential and free space may be sufficient.

The detection efficiency of X-rays in each X-ray detector generally differs depending on the X-ray energy. Here, the detection efficiency for the first wavelength λ ₁ in the first X-ray detector 12 is G ₁₁ , and the detection efficiency for the second wavelength λ ₂ (here, shorter than the first wavelength λ ₁ ) is G ₂₁ . . Further, the detection efficiencies G ₁₂ and G ₂₂ of the second X-ray detector 14 for the wavelengths λ ₁ and λ ₂ are used.
The respective intensities of the wavelengths incident on the first X-ray detector 12 are I ₁ and I _2, and the transmission efficiency until the monochromatic X-rays of the wavelengths λ ₁ and λ ₂ enter the _second X-ray detector A is A. ₁₂ , A ₂₂ (the X-rays incident on the second X-ray detector 14 are A ₁₂ times or A ₂₂ times the X-rays incident on the first X-ray detector 12). At this time, the detection intensities V ₁ and V ₂ at the respective X-ray detectors 12 and 14 can be expressed as the above-described equations (1) and (2).

Thereby, each intensity | strength of the X-ray which injects into the 1st X-ray detector 12 can be represented with Formula (11a) (11b).
I ₂ = (V ₂ × A ₂₂ × G ₁₂ -V ₁ × G ₁₁ )
_{/ (A 12 × G 12 ×} G 21 -A 22 × G 11 × G 22) ··· (11a)
I ₁ = (V ₁ × A ₂₂ × G ₂₂ −V ₂ × G ₂₁ )
_{/ (A 22 × G 11 ×} G 22 -A 12 × G 12 × G 21) ··· (11b)

In general, A ₁₂ and A ₂₂ are different (depending on the wavelength and the substance of the X-ray absorber), and by measuring V ₁ and V ₂ , the equations (11a) and (11b) are used to calculate the first X-ray detector 12. Each intensity of incident X-rays, that is, the mixing ratio of X-rays can be known.

When X-rays have three wavelengths, let A ₁₃ , A ₂₃ , and A ₃₃ be the X-ray transmittance for each wavelength at all detectors and X-ray absorbers existing in front of the third X-ray detector 16. The signal intensity of each X-ray detector is expressed as the above-described equations (3), (4), and (5).
Accordingly, when this equation is solved for the incident X-ray intensities I ₁ , I ₂ , and I ₃ of the most upstream X-ray detector, the mixing ratio of each wavelength can be determined.
Further, when the number of detectors is larger than the number of wavelengths, the error of the estimated value of the wavelength mixing ratio can be estimated by applying the least square method to the above equation.

Further, as an example, in the case of application to differential imaging using a K edge of a specific element, the ratio of X-ray attenuation at each wavelength is obtained by using the specific element to be subjected to differential imaging as the X-ray absorber 18. (That is, the ratio of A ₁₂ and A ₂₂ is increased), and imaging with high accuracy can be realized.

The same applies to the case where X-rays have three or more wavelengths, and the mixing ratio of each wavelength can be obtained by installing X-ray detectors by the number of wavelengths.
In this case, for a plurality of monochromatic X-rays having different wavelengths λ _i (i = 1, 2,..., N; n is an integer of 2 or more), a plurality (m; m is 2 or more) equal to or more than the number of wavelengths. An integer) X-ray detector.
A plurality of X-ray detectors are stacked such that the multicolor X-rays pass through sequentially at the same time, and the intensity V _j of the multicolor X-rays passing through (j = 1, 2,... M; m is an integer of 2 or more) Are detected respectively.
Calculation unit 20, and the detection efficiency G _ij of the plurality of X-ray detectors for each wavelength lambda _i, and transmission efficiency A _ij to monochromatic X-rays of each wavelength lambda _i is incident on the plurality of X-ray detector , Each intensity I _i (i = 1, 2,... N) of a plurality of monochromatic X-rays incident on the most upstream X-ray detector or a ratio thereof is calculated from the detected intensity V _j of each X-ray detector. To do.

In addition, according to the method of the present invention, using the plurality of X-ray detectors and the arithmetic device described above,
A plurality of X-ray detectors are stacked and arranged so that multicolor X-rays pass through sequentially at the same time,
Detecting the intensity V _j (j = 1, 2,... M; m is an integer of 2 or more) of the polychromatic X-rays passing through each X-ray detector,
The intensity of each of a plurality of monochromatic X-rays incident on the most upstream X-ray detector or the ratio thereof is calculated from each detected intensity Vj.

In the above-described embodiments, the interval between the X-ray detectors is not essential, and may be formed in close contact with each other, for example.
Further, it is preferable that each X-ray detector constituting the present invention has a large number of detectors arranged two-dimensionally so that a two-dimensional image can be taken simultaneously. With this configuration, it is possible to calculate the intensity of each of a plurality of monochromatic X-rays or the ratio thereof, and simultaneously capture an X-ray image transmitted through the subject.

Examples of the present invention will be described below.
In the simplest embodiment, two X-ray detectors 12 and 14 are arranged as shown in FIG. The X-ray detector is preferably as uniform as possible in transmission efficiency and detection efficiency. For example, the flat X-ray detector shown in Non-Patent Document 3, a semiconductor detector using an ionization action of a solid semiconductor, or a thin detector It is preferable to use a combination of a CsI film and a CCD.
In particular, since CsI (cerium iodide) has a high X-ray absorption rate, highly efficient detection is possible.
Further, in order to avoid bleeding of the image at the downstream second X-ray detector 14 due to X-ray scattering or the like in the upstream second X-ray detector 12, each X-ray detector is extremely close or appropriate. It is desirable to keep the distance apart.

  Here, let us consider a case where the multicolor X-ray measurement apparatus of FIG. 2 detects two color X-rays of 15 keV and 30 keV. In this case, the wavelengths λ of monochromatic X-rays with photon energies of 15 kev and 30 keV are 0.83Å and 0.41Å, respectively.

FIG. 5 shows the X-ray transmittance in the first X-ray detector 12 when the CsI layer of the first X-ray detector 12 is 100 μm, and the layers other than CsI are ignored. The calculation is based on the calculation program of Lawrence Berkeley National Laboratory, USA (
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At 15 keV, 7.6% of X-rays are transmitted, and near 30 keV, 68% of X-rays are transmitted. X-rays that are not transmitted are absorbed and detected as signals. X-rays transmitted through the first X-ray detector 12 are detected by the second X-ray detector 14. At this time, the CsI layer of the second X-ray detector 14 should be as thick as possible unless there is a special problem. However, if it is too thick, the acquired image may be blurred due to X-ray scattering in the CsI layer, or fluorescence scattering and attenuation.

  FIG. 6 shows the X-ray transmittance of the second X-ray detector 14 when the CsI layer of the second X-ray detector 14 is 300 μm. At 15 keV, 0.45% is transmitted, and at 30 keV, 32% is transmitted. Assuming that X-rays are not attenuated at portions other than CsI of the detector, and all the absorption at the CsI portion is detected, the X-ray detection efficiency of the entire apparatus is 99.9% at 15 keV, around 30 keV Then, it becomes 97.8%.

As described above, each intensity of incident X-rays is calculated by the equations (11a) and (11b) from the X-ray transmittance and detection efficiency. In this embodiment, A ₁₂ = 0.076, A _{22 = 0.68, G 11 = 1-0.076 =} 0.924, G 21 = 1-0.68 = 0.32, G 12 = 1-0.0045 = 0.9955, G 22 = 1-0 .32 = 0.68.

  In addition, this invention is not limited to embodiment mentioned above, Of course, it can change variously in the range which does not deviate from the summary of this invention.

It is a principle figure of the apparatus which applies the polychromatic X-ray measuring apparatus of this invention. 1 is an overall configuration diagram showing a first embodiment of a polychromatic X-ray measurement apparatus of the present invention. It is a whole block diagram which shows 2nd Embodiment of the polychromatic X-ray measuring apparatus of this invention. It is a whole block diagram which shows 3rd Embodiment of the polychromatic X-ray measuring apparatus of this invention. This is the X-ray transmittance when the CsI layer of the first X-ray detector is 100 μm. This is the X-ray transmittance when the CsI layer of the second X-ray detector is 300 μm. 1 is a schematic diagram of a “small X-ray generator” in Non-Patent Document 1. FIG. 2 is a schematic diagram of “mixed two-color X-ray CT apparatus” of Non-Patent Document 2. FIG.

Explanation of symbols

1a, 1b Monochromatic X-ray with wavelength λ ₁
2a, 2b monochromatic X-ray with wavelength λ ₂ ,
3a, 3b monochromatic X-ray with wavelength λ ₃ ,
10 Multicolor X-ray measuring device,
12 Second X-ray detector,
14 second X-ray detector,
16 3rd X-ray detector,
18 absorber, 20 arithmetic unit

Claims (7)

A multicolor X-ray measurement apparatus that measures multicolor X-rays including a plurality of monochromatic X-rays having different wavelengths λ _i (i = 1, 2,... N; n is an integer of 2 or more),
A plurality of X-rays that are stacked so that the multicolor X-rays pass through sequentially and detect the intensity V _j (j = 1, 2,... M; m is an integer of 2 or more) of the passing multicolor X-rays. A detector;
A multicolor, comprising: an arithmetic unit that calculates each intensity or a ratio of a plurality of monochromatic X-rays incident on the most upstream X-ray detector from the detection intensity V _j of each X-ray detector. X-ray measuring device. The arithmetic unit is
Detection efficiencies G _{ij of the} plurality of X-ray detectors for each wavelength λ _i ;
Transmission efficiency A _ij until the monochromatic X-rays of the respective wavelengths λ _i are incident on the plurality of X-ray detectors,
Each intensity I _i (i = 1, 2,... N) of a plurality of monochromatic X-rays incident on the most upstream X-ray detector or a ratio thereof is calculated from the detection intensity V _j of each X-ray detector. The multicolor X-ray measuring apparatus according to claim 1. The polychromatic X-ray includes two types of monochromatic X-rays having different wavelengths λ ₁ and λ ₂ ,
The plurality of X-ray detectors includes an upstream first X-ray detector and a downstream second X-ray detector stacked on each other,
The arithmetic unit is
Detection efficiencies G ₁₁ and G ₂₁ of the first X-ray detector and detection efficiencies G ₁₂ and G ₂₂ of the second X-ray detector for the wavelengths λ ₁ and λ ₂ ,
Transmission efficiencies A ₁₂ and A ₂₂ until the monochromatic X-rays of the wavelengths λ ₁ and λ ₂ enter the _second X-ray detector;
From the detected intensities V ₁ and V ₂ of the first X-ray detector and the second X-ray detector, the respective intensities of the two types of monochromatic X-rays incident on the first X-ray detector according to the following formulas (1) and (2) Calculate I ₁ and I ₂ ,

V ₁ = I ₁ × G ₁₁ + I ₂ × G ₂₁ (1)
V ₂ = I ₁ × A ₁₂ × G ₁₂ + I ₂ × A ₂₂ × G ₂₂ (2)

The multicolor X-ray measuring apparatus according to claim 1. The polychromatic X-ray includes three kinds of monochromatic X-rays having different wavelengths λ ₁ , λ ₂ and λ ₃ ,
The plurality of X-ray detectors includes an upstream first X-ray detector, an intermediate second X-ray detector, and a downstream third X-ray detector stacked on each other,
The arithmetic unit is
For each of the wavelengths λ ₁ , λ ₂ , λ ₃ , the detection efficiency G ₁₁ , G ₂₁ , G ₃₁ of the first X-ray detector, the detection efficiency G ₁₂ , G ₂₂ , G _{32 of} the second X-ray detector, Detection efficiency G ₁₃ , G ₂₃ , G _{33 of the} 3X-ray detector,
Transmission efficiency A ₁₂ , A ₂₂ , A ₃₂ until the monochromatic X-rays of the respective wavelengths λ ₁ , λ ₂ , λ ₃ are incident on the second X-ray detector, and transmission until they are incident on the third X-ray detector Efficiency A ₁₃ , A ₂₃ , A ₃₃ ,
From the detection intensities V ₁ , V ₂ , and V _{3 of} the first X-ray detector, the second X-ray detector, and the third X-ray detector, the first X-ray detector is expressed by the following equations (3), (4), and (5). Calculating the intensities I ₁ , I ₂ , and I ₃ of the three types of monochromatic X-rays incident on

V ₁ = I ₁ × G ₁₁ + I ₂ × G ₂₁ + I ₃ × G ₃₁ (3)
_{V 2 = I 1 × A 12} × G 12 + I 2 × A 22 × G 22 + I 3 × A 32 × G 32 ··· (4)
V ₃ = I ₁ × A ₁₃ × G ₁₃ + I ₂ × A ₂₃ × G ₂₃ + I ₃ × A ₃₃ × G ₃₃ (5)

The multicolor X-ray measuring apparatus according to claim 1.   2. The monochromatic X-ray mixture ratio measurement according to claim 1, further comprising: an absorber having a different transmission efficiency for the monochromatic X-rays having the respective wavelengths λi between the plurality of stacked X-ray detectors. apparatus.   The multicolor X-ray measurement apparatus according to claim 5, wherein the absorber contains a specific element to be subjected to differential imaging. A multicolor X-ray measurement method for measuring multicolor X-rays including a plurality of monochromatic X-rays having different wavelengths λ _i (i = 1, 2,... N; n is an integer of 2 or more),
A plurality of X-ray detectors are stacked and arranged so that the polychromatic X-rays pass through sequentially at the same time,
Detecting the intensity V _j (j = 1, 2,... M; m is an integer of 2 or more) of the polychromatic X-rays passing through each X-ray detector,
A multicolor X-ray measurement method, comprising: calculating each intensity or a ratio of a plurality of monochromatic X-rays incident on the most upstream X-ray detector from each detected intensity Vj.

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