JP2001224582A - X-ray ct instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To emit X-rays with equal beam size and uniform energy distribution regardless of energy by selecting X-rays having a necessary single number or a plurality of energies from X-rays having energies of wide range and transmitting them on the same optical axis to the position of a subject. SOLUTION: This X-ray CT instrument comprises a 2-crystal spectroscope consisting of a first crystal 11 and a second crystal 12, an uniforming filter 14 for uniforming the energy distribution of X-ray, and a detector 15. A necessary energy is selected by use of Bragg reflection in the first crystal 11, and the beam is extended by use of asymmetric reflection in the second crystal 12. The thickness of the uniforming filter 14 is set to the value t determined by the equation, T=(-1/μ)×log I/f(x,y)} or an approximate value thereof when the horizontal direction of the plane orthogonal to the X-ray advancing direction is (x), the vertical direction of the plane orthogonal to the X-ray advancing direction is (y), the function showing the incident X-ray intensity distribution is (f), and the emitting X-ray intensity (constant) necessary in the subject position is I, and the absorption coefficient of the filter is μ.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an X-ray CT apparatus, and more particularly, to a CT utilizing synchrotron radiation.

[0002]

2. Description of the Related Art Conventional X-ray CT uses X-rays of an X-ray tube, and thus includes X-rays having a wide range of energy.
Since the transmittance of X-rays increases as the energy increases, the energy component after transmission changes when the thickness of the subject changes. This is called beam hardening and causes an error in an X-ray CT image. On the other hand, if monochromatic X-rays of only one energy are used, the beam hardening phenomenon does not occur, so that the accuracy of CT can be improved. Energy selection can be performed by dispersing white light using crystals such as silicon and germanium.

[0003] Regarding the beam size, since the emitted light itself has a divergence angle, if the transmission distance is increased, the size of the beam irradiates the subject, but the divergence angle is not so large. Therefore, in order to obtain the required beam size, a considerably long transmission distance is required, and the beam line device becomes considerably long. As an example, if the wiggler condition is 2.3 GeV and 7 Tesla 9 poles, the vertical divergence angle is 0.24 mrad, and a beam transmission distance of 200 m or more is required to expand the beam to 50 mm. Since such a long transmission distance is inconvenient, it is desired to irradiate a subject with a beam expanded using asymmetrical reflection of a crystal to shorten the transmission distance. A conventional method for satisfying this specification will be described below.

First, as a technique for extracting X-rays of required energy from white light, Bragg reflection of a crystal is used. The relationship of Bragg reflection is expressed by the following equation (2).

Λn = 2d sin θ Equation (2) λ: wavelength, d: crystal constant, θ: Bragg angle, n: order As can be seen from the equation (2), the energy of the reflected light is the crystal and the incident angle. Depends on

As a method of expanding the beam, asymmetrical reflection of a crystal is used. In this case, the magnification M and the asymmetrical reflection angle α are expressed by the following equations (3) and (4).

(Equation 3) As can be seen from the relations expressed by the formulas (3) and (4), since the Bragg angle is different when the energy is different,
It is impossible to make X-rays of different energies the same magnification by asymmetric reflection of one crystal.

Next, conditions for making incident light and outgoing light to the spectroscope parallel will be described. FIG. 6 shows a two-crystal monochromator model diagram. In FIG. 6, reference numeral 51 denotes a first crystal, 52 denotes a second crystal, 61 denotes light incident on the first crystal 51, 62 denotes light emitted from the first crystal 51, and 63 denotes light emitted from the second crystal 52. The emission light is shown. Other symbols used here are as follows. θB1: Bragg angle of the first crystal 51 θB2: Bragg angle of the second crystal 52 α: Asymmetrical reflection angle of the second crystal 52 βIN: Beam incident angle to the second crystal 52 βOUT: Output angle from the second crystal 52 , The beam incident angle βIN to the second crystal 52 and the second crystal 5
The emission angle βOUT from the light emitting device 2 is expressed by the following expressions (5) and (6).

ΒIN = θB2−α Equation (5) βOUT = θB2 + α Equation (6) In order for the output beam to be always horizontal to the incident beam, the following equation is used based on the relationship shown in FIG. (7) That is, equation (7 ') should be satisfied.

(Equation 5) Here, the following Expression (8) is obtained by substituting Expressions (5) and (6) into Expression (7 ').

ΘB1 = θB2 Equation (8) Therefore, even if the energy of the beam is different, the same crystal (having the same Bragg angle) is used, and if the angle and position of the two crystals are adjusted for each wavelength, the beam becomes Always exits coaxially.

From the above, even if the energy is different,
If the angle and the position are adjusted using the same type of two crystals irrespective of the symmetry or the asymmetry, it is understood that the optical axis is always constant and the light entering and exiting the two-crystal spectroscope is parallel. However,
Furthermore, it is impossible to equalize the beam size at the irradiation position. That is, in the two-crystal spectroscope using asymmetrical reflection, since the magnification changes when the wavelength changes according to the relations of Expressions (3) and (4), it is impossible to equalize the beam size at the irradiation position.

In order to guide the beam to the irradiation position by expanding the beam to the same optical axis and a predetermined size irrespective of the energy, as shown in FIG. It is necessary to prepare 72 and switch to a set of two crystals suitable for the selected energy. Note that reference numeral 73 in FIG. 7 denotes a detector that detects the intensity of the beam transmitted through the subject 100.

However, it is necessary to switch the energy at a high speed in order to solve the problems of shortening the examination time and moving the subject during imaging. On the other hand, in the method in which the whole of the spectral crystal is completely replaced, a large acceleration is applied to the switching device, and there is a problem that the device cannot be realized in terms of mechanical strength. More specifically, if the energy is switched at 25 Hz and the mirror size is 300 mm (size in the amplitude direction) and the half amplitude is 150 mm, an excessive acceleration of 378 G is applied, and it is practically impossible to configure an X-ray wavelength switching device. It becomes possible. For this reason, by providing a filter for cutting off either the primary light or the n-order light in accordance with the timing, two types of energy can be obtained.
A CT image is obtained by irradiating next-order light and n-order light.

[0010]

However, in general, the radiation light energy distribution is not uniform in the vertical direction. According to the optical path diagram shown in FIG.
FIG. 9 shows the results of ray tracing simulation performed at the position of the subject. In FIG. 8, reference numeral 81 denotes an accelerator;
Reference numeral 2 denotes wiggler.

[Simulation conditions] Light source: Wiggler: 2.3 GeV, 7T-9P (λ = 420 mm) σx = 2.8 mm, σy = 0.14 mm σx ′ = 0.12 mrad σy ′ = 0.24 mrad Monochromator: ΔΘ = 2.6 × 10 -4 rad ΔE / E = 0.27% Optical path diagram ... FIG. 8 As shown in FIG. 9, the energy distribution in the vertical direction at the position of the subject is not uniform, and the The sensitivity is
In order to match the point with the lowest X-ray intensity, the subject is irradiated with extra X-rays in a portion where the intensity is high, which is not desirable. Also, when creating an image, accurate information on the energy distribution is required in advance, and the image creation process is complicated.

Accordingly, an object of the present invention is to select X-rays having the required energy or energies from X-rays having a wide range of energies, transmit the X-rays to the position of the subject on the same optical axis, and make the same regardless of the energy. To provide an excellent X-ray CT apparatus capable of irradiating a subject with X-rays having a uniform beam size and energy distribution, thereby not irradiating the subject with extra X-rays and simplifying data processing of a detector. It is.

[0013]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides an X-ray having a wide range of energy.
X-ray C that selects one or more energies of X-rays from the X-rays using a spectral crystal and irradiates the subject with an X-ray to capture an image
The T device has the following features.

According to the first aspect of the present invention, there is provided an intensity distribution equalizing filter for passing X-rays before irradiating the subject to make the intensity distribution of the X-rays irradiating the subject uniform. It is characterized in that the thickness of this filter is limited. The thickness of this filter is defined as x in the horizontal direction of the plane perpendicular to the X-ray traveling direction, y as the vertical direction in the plane perpendicular to the X-ray traveling direction, f is the function showing the incident X-ray intensity distribution, If the output X-ray intensity (constant) is I and the absorption coefficient of the filter is μ, it is either the value of t obtained by the following equation (1) or an approximate value of t.

(Equation 7) In the first aspect of the present invention having this configuration, the expression (1)
By passing through an intensity distribution equalizing filter having a thickness at least a value approximating t obtained by the above, the energy distribution of the X-rays can be made uniform. Therefore, the required energy X-ray
A line is selected, transmitted to the position of the subject along the same optical axis, and the subject can be irradiated with X-rays having the same beam size and a uniform energy distribution regardless of the energy.

According to a second aspect of the present invention, in the first aspect of the present invention, when both X-rays of two energies, ie, primary reflected light and n-order reflected light of the dispersive crystal are used, It has such features. First, it has a primary light extraction filter and an n-order light extraction filter that transmit only one of the primary reflected light and the n-order reflected light and block the other.
The filter for uniformizing the intensity distribution is composed of the primary reflected light and n
A first-order light uniformizing filter and an n-th-order light equalizing filter for equalizing the intensity distribution of the secondary reflected light. The first-order light extraction filter, the n-th-order light extraction filter, the first-order light equalization filter, and the n-th-order light equalization filter are configured such that the X-rays transmitted through any one of the energy extraction filters are the same. After passing through the energy equalizing filter,
It is configured to irradiate the subject. In the invention of claim 2 having this configuration, when two necessary energies are selected from X-rays having a wide range of energy,
Either one can be selected by the extraction filter, and a uniform intensity distribution can be obtained by the equalization filter. Therefore,
By synchronizing and alternately switching the extraction filter and the equalization filter inserted on the optical axis, X-rays of two energies are transmitted on the same optical axis to the subject's position, and the energy distribution is the same regardless of energy. It is also possible to alternately irradiate the subject with uniform two-energy X-rays.

According to a third aspect of the present invention, when the X-ray intensity distribution in the x direction is uniform in the second aspect, the following features are provided. First, the first-order light equalizing filter and the n-th-order light equalizing filter are configured to turn at a common speed on a common circular orbit in the horizontal direction. The first-order light extraction filter, the n-th-order light extraction filter, the first-order light equalization filter, and the n-th-order light equalization filter are arranged such that the X-rays transmitted through one of the energy extraction filters are turned next. It is configured to irradiate the subject after passing through a uniforming filter for the same energy therein. In the invention of claim 3 having this configuration,
When the X-ray intensity in the x direction is uniform, the X-ray intensity of the two energies can be made uniform only by turning the equalizing filter. Therefore, mechanical conditions for switching the equalizing filter are relaxed, and high-speed energy switching is enabled.

The invention according to claim 4 is characterized in that the spectral crystal includes a spectral crystal composed of a plurality of crystals having different reflectivities. In the fourth aspect of the present invention having this configuration, the energy distribution of light emitted from the spectral crystal can be made uniform by appropriately selecting the reflectivity of each crystal constituting the spectral crystal. Therefore, the required energy X-ray
A line is selected, transmitted to the position of the subject along the same optical axis, and the subject can be irradiated with X-rays having the same beam size and a uniform energy distribution regardless of the energy.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment)
As a first embodiment of the present invention, an X-ray CT apparatus according to one embodiment to which the invention described in claim 1 is applied,
This will be described below with reference to FIG.

(Construction) The X-ray CT apparatus according to the present embodiment uses a first crystal 11 and a second crystal 12 for dispersing necessary energy from white light (X-ray having a wide range of energy) 1. And a detector 15 for uniformizing the energy distribution of X-rays emitted from the two-crystal spectroscope 13. Among them, the first crystal 11 of the two-crystal spectroscope 13 selects necessary energy using Bragg reflection, and the second crystal 12 expands the beam using asymmetric reflection.

The thickness of the homogenizing filter 14 is a function indicating the incident X-ray intensity distribution, where x is the horizontal direction of a plane perpendicular to the X-ray traveling direction and y is the vertical direction of the plane perpendicular to the X-ray traveling direction. Is f, the output X-ray intensity (constant) required at the position of the subject is I, and the absorption coefficient of the filter is μ, and is a value t obtained by the following equation (1) or an approximate value thereof.

(Equation 8) In the figure, reference numeral 2 denotes light emitted from the first crystal 11 of the two-crystal spectroscope 13, and reference numeral 3 denotes light emitted from the second crystal 12. 4 indicates X-rays irradiated to the subject 100.

(Operation and Effect) The operation and effect of the present embodiment having the above configuration are as follows. First, necessary energy is selected from the white light 1 emitted from an accelerator (not shown) by the Bragg reflection of the first crystal 11 of the two-crystal spectroscope 13. X reflected by first crystal 11
The line 2 is enlarged to the required size by the asymmetric reflection of the second crystal 12. The X-rays 3 reflected by the second crystal 12 pass through the equalizing filter 14.

In this case, the thickness of the uniformizing filter 14 is
As described above, since it is either the value t obtained by the equation (1) or an approximate value thereof, this uniformization filter 14
Has a constant energy distribution. The reason is that the thickness t obtained by the equation (1) is based on the relationship between the incident intensity and the output intensity of the X-ray transmitted through the filter.
This is because the required strength is defined at the position of the subject. Hereinafter, this point will be described.

First, the X-ray traveling direction is the Z axis, the horizontal direction perpendicular to the Z axis is the X axis, the vertical direction perpendicular to the Z axis is the Y axis, and the intensity distribution of the X-ray selected by the first crystal is f. Let it be represented by (x, y). In this case, the ratio between the incident intensity α and the outgoing intensity (intensity required at the position of the subject) β when transmitted through a filter having a thickness t is determined by the absorption coefficient of the filter (determined by the substance, but taking a different value depending on the energy). When μ is given, it is expressed by the following equation (9).

Β = αexp (−μt) Equation (9) Accordingly, if the intensity required at the position of the subject is I (constant, where I <minf (x, y)), the thickness of the filter is
The value t is obtained by the following equation (1), and t is a function of x and y.

(Equation 10)

The uniformizing filter 14 having a thickness corresponding to the value t obtained by the equation (1) derived as described above.
The energy distribution of the X-rays 4 transmitted through the X-ray becomes uniform, and is applied to the subject 100. Further, even if the thickness of the uniformizing filter 14 does not match the value t obtained by the equation (1),
By approximating at least the value t of equation (1), the energy distribution can be made fairly uniform. Then, the subject 100 is irradiated with the X-rays 4 having transmitted the uniformizing filter 14 and having a uniform energy distribution, and the detector 15 measures the X-ray intensity.

Therefore, according to the X-ray CT apparatus of the present embodiment, X-rays having the required energy are selected from the white light 1 and transmitted to the subject's position along the same optical axis, and have the same beam size regardless of the energy. X with uniform energy distribution
The radiation can be applied to the subject 100.

(Second Embodiment) An X-ray CT apparatus according to a second embodiment of the present invention will now be described with reference to FIGS. 2
This will be described below based on The same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

(Construction) In the X-ray CT apparatus according to the present invention, first, between the two-crystal spectroscope 13 and the detector 15,
An extraction filter 23 including a primary light extraction filter 21 and an n-order light extraction filter 22 for transmitting only one of the primary light and the n-th light separated by the crystal spectroscope 13 and blocking the other. A rotator 24 for switching the extraction filter 23 between the primary light side and the n-order light side is provided. Further, a uniformizing filter 27 including a first-order light equalizing filter 25 and an nth-order light equalizing filter 26 for making the energy distribution of the X-rays emitted from the extraction filter 23 uniform, and the rotating device 24 are synchronized. An insertion device 28 for switching the homogenizing filter 27 between the primary light side and the nth light side is disposed.

Of these, the extraction filters 21 and 22 on the primary light side and the n-order light side of the extraction filter 23 are formed in a semicircular shape from different translucent materials. That is, the primary light extraction filter 21 is made of a semicircular semi-transmissive material made of a substance that transmits only primary light and blocks n-order light. It consists of a semi-circular semi-transmissive material made of a substance that transmits only light and blocks primary light. Then, the extraction filters 21 on the primary light side and the n-th light side,
By rotating a circular extraction filter 23 formed by combining the extraction filters 22 by a rotation device 24, the extraction filters 21 and 22 inserted on the optical axis are switched.

The primary light side of the equalizing filter 27 and n
The uniforming filters 25 and 26 on the next light side have a thickness and a shape suitable for each target wavelength according to the above-described equation (1). That is, the primary light uniformizing filter 25 has a thickness and a shape that make the X-ray intensity distribution of the primary light uniform according to the equation (1), and the n-order light uniforming filter 26 uses the equation ( According to 1), the thickness and the shape are such that the X-ray intensity distribution of the n-order light becomes uniform. Then, the uniformizing filters 2 on the primary light side and the n-order light side are used.
By reciprocating an equalizing filter 27 in which the filters 5 and 26 are arranged in the moving direction by the insertion device 28, the uniformizing filters 25 and 26 inserted on the optical axis are switched.

(Operation / Effect) The operation / effect of this embodiment having the above configuration is as follows. First, necessary energy is selected from white light 1 emitted from an accelerator (not shown) by Bragg reflection of the first crystal 11 of the two-crystal spectroscope 13. The X-ray 2 reflected by the first crystal 11 is enlarged to a required size by asymmetric reflection of the second crystal 12.

In this case, the reflections of the first crystal 11 and the second crystal 12 are Bragg reflections according to the following equation (2).
The primary light and the n-th light are reflected.

Λ n = 2 d sin θ Equation (2) λ: wavelength, d: crystal constant, θ: Bragg angle, n: order Since the Bragg angle and the asymmetric reflection angle of both primary light and n-order light are equal, the following equation is obtained. In the asymmetric reflection of the second crystal 12 according to the equations (3) and (4), the second crystal 12 is enlarged to the same size.

(Equation 12) Therefore, in the X-ray 3 reflected by the second crystal 12,
The optical axes of the primary light and the n-th light overlap.

The X-rays 3 reflected by the second crystal 12 pass through the extraction filter 23. In this case, the rotating device 24
By rotating the extraction filter 23 and switching the extraction filters 21 and 22 inserted on the optical axis,
From the extraction filter 23, of the two types of energy, primary light and n-order light, only X-rays of one of the energies are alternately emitted. That is, in the extraction filter 23, the primary light and the n-th light are alternately selected.

Further, the X-rays 4 from the extraction filter 23
Is transmitted through the homogenizing filter 27. In this case, the homogenizing filter 27 is reciprocated by the insertion device 28 in synchronization with the rotation of the extracting filter 23, and the extracting filters 21 and The equalizing filters 25 and 26 are switched so that a filter on the same energy side as 22 is inserted on the optical axis. That is, at the timing when the primary light is emitted from the extraction filter 23, the primary light is output from the primary light uniforming filter 2 of the uniformizing filter 27.
5 at the timing when the n-th light is emitted from the extraction filter 23, the n-th light is
The uniformizing filters 25 and 26 are switched so as to be incident on the next light uniformizing filter 25.

As a result, for each of the first-order light and the n-th light,
X-rays 4 that have passed through the equalizing filter 27 can have uniform energy distribution because they can be transmitted through the equalizing filters 25 and 26 that conform to that. The X-rays of the primary light and the n-th light having a uniform energy distribution are thus obtained.
The subject 4 is irradiated with the line 4 alternately at regular intervals, and the detector 15 measures the X-ray intensity of each energy.

As described above, in the X-ray CT apparatus of the present embodiment, when two necessary energies are selected from the white light 1, one of them is selected by the extraction filter 23,
A uniform energy distribution can be obtained by the uniformizing filter 27. Therefore, according to the X-ray CT apparatus of the present embodiment, the extraction filter 23 and the equalization filter 27 inserted on the optical axis are alternately switched in synchronization with each other.
X-rays of two energies are transmitted to the position of the subject along the same optical axis, and X-rays of two energies having the same beam size and a uniform energy distribution are transmitted to the subject 100 regardless of the energy.
Can be alternately irradiated. In the present embodiment, the extraction filter 23 and the homogenization filter 27 are arranged between the two-crystal spectroscope 13 and the detector 15. It is also possible to place it before the crystal 11,
In this case, it is apparent that the same operation and effect can be obtained.

Third Embodiment An X-ray CT apparatus according to a third embodiment of the present invention will now be described with reference to FIGS. 3
This will be described below based on In addition, the above-mentioned first and second
The same reference numerals are given to the same portions as those of the embodiment described above, and the description will be omitted.

(Configuration) The X-ray CT apparatus according to the present invention is a modification of the configuration between the extraction filter 23 and the detector 15 in the second embodiment described above, and the other parts are the same as those in the second embodiment. It has the same configuration as the second embodiment.
That is, in the present embodiment, between the extraction filter 23 and the detector 15, the primary light homogenizing filter 31 and the n-th light homogenization filter for uniformizing the intensity distribution of the X-rays emitted from the extraction filter 23. A circular homogenizing filter 33 in which the filters 32 are arranged at different positions on the same horizontal circle, and the homogenizing filter 33 are switched between the primary light side and the n-order light side in synchronization with the rotating device 24. Rotating device 34 is disposed.

In this case, the rotation axes of the equalizing filter 33 and the second rotating device 34 are oriented in the y direction. In addition, since the equalizing filters 31 and 32 on the primary light side and the n-th light side are integrally combined to form the equalizing filter 33, by rotating the equalizing filter 33, the horizontal direction is obtained. It turns on a common circular orbit at a common speed. Further, the rotation device 24 and the second rotation device 3
A shutter 35 that opens and closes on the optical axis of the X-ray 4 from the equalizing filter 33 in synchronization with the shutter 4 is disposed.

Of these, the equalizing filters 31 and 32 on the primary light side and the n-order light side of the equalizing filter 33 are the same as the equalizing filters 2 on the primary light side and the n-order light side in the second embodiment.
As in the case of 5 and 26, the thickness and the shape are suitable for the respective target wavelengths according to the above-described equation (1). When a wiggler or the like is used as the light source of the emitted light, the beam intensity in the x direction is constant.
(No shape change in x-direction).

On the other hand, the primary light side of the equalizing filter 33 and n
The length L (m) of the uniforming filters 31 and 32 on the next light side in the x direction.
m), the time T (msec) required for photographing, the rotation speed n (rpm) of the second rotating device, and the radius r (mm) have the relationship shown in the following equation (10).

(Equation 13) Therefore, the first-order light side and the n-th order light side equalizing filters 31,
The width of 32 (the length in the x direction) is a value of L obtained by the equation (10), and the surface on the incident light side is centered on the rotation axes of the uniformizing filter 33 and the second rotation device 34. Is bent along the circumference of the radius r. Further, even if the uniformizing filters 31 and 32 on the primary light side and the n-order light side allow the X-rays to pass while rotating the homogenizing filter 33, the X-rays passing through one of the filters become the other filters. Are arranged so as not to pass through.

(Operation and Effect) The operation and effect of the present embodiment having the above configuration are as follows. First, the operation until the light passes through the extraction filter 23 is the same as that of the second embodiment described above, and the primary light and the n-th light are emitted from the extraction filter 23 alternately. In this case, the equalizing filters 31 on the primary light side and the n-order light side of the equalizing filter 33,
As described above, the shape of the second rotating device 32 has a width L determined by Expression (10) and has an arcuate shape along the circumference of the radius r. The X-rays incident on the equalizing filters 31 and 32 on the side and the n-th light side are always incident at a right angle, and if the y coordinate is constant, the X-ray transmission distance through the filter is constant. Therefore, since the intensity of the incident X-ray in the x direction is constant, the uniformizing filter 3 on the primary light side and the n-order light side is used.
Even if the first and second rotating devices 34 rotate by the second rotating device 34, the energy distribution of the X-rays 4 emitted from the equalizing filters 31 and 32 on the primary light side and the n-th light side becomes constant.

In this case, the second rotating device 34
The uniformizing filter 33 is rotated in synchronization with the rotation of the extraction filter 23, and as shown in FIG.
Timing 36 at which the primary light is emitted from the extraction filter 23
Then, at the timing 37 when the first-order light enters the first-order light equalization filter 31 of the equalization filter 33 and the nth-order light is emitted from the extraction filter 23, the nth-order light is converted to the nth-order light of the equalization filter 33. The uniformizing filters 31 and 32 are switched so as to enter the light uniformizing filter 32.

As a result, each of the first-order light and the n-th light is
The energy distribution of the X-rays 4 can be made uniform since the light can be transmitted through the uniformizing filters 31 and 32 adapted to the above. Then, by opening and closing the shutter 35 in accordance with the timing at which the X-rays having a uniform intensity distribution is emitted from the equalizing filter 33 and the timing at which the X-rays irradiate the subject 100, the primary light and the n-th light having the uniform energy distribution are obtained. The subject 100 is alternately irradiated with X-rays of the next light, and the detector 15 measures the X-ray intensity of each energy.

As described above, in the X-ray CT apparatus of the present embodiment, when the X-ray intensity in the x-direction is uniform, the X-ray intensity of the primary light and the n-th light can be obtained only by rotating the equalizing filter 33. Can be made uniform. Therefore, compared to the case where the uniformizing filter is reciprocated by the insertion device 28 as in the above-described second embodiment, the mechanical conditions for switching the uniformizing filter are reduced, and energy can be switched at high speed. Becomes

(Fourth Embodiment) An X-ray CT apparatus according to a fourth embodiment of the present invention will now be described with reference to FIGS. This will be described below with reference to FIG. The same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

(Configuration) The X-ray CT apparatus according to the present invention uses the first crystal 11 of the two-crystal spectroscope 13 having different reflectances instead of using the uniformizing filter 14 in the first embodiment. This is changed to a first crystal 41 composed of a plurality of crystals, and the other portions have the same configuration. That is, in the present embodiment, the first crystal 41
As shown in FIG. 5, is composed of n × m (n and m are natural numbers) crystals 42 having the same material and crystal orientation and different reflectivities. Each crystal 42 constituting the first crystal 41
Are selected such that the intensity distribution of the emitted light becomes uniform. For example, at a position where the X-ray intensity is twice the lowest intensity, a crystal having a crystal reflectance of 1/2 of the crystal reflectance at the position where the X-ray intensity is lowest is selected.

(Operation / Effect) The operation / effect of the present embodiment having the above configuration is as follows. First, necessary energy is selected from white light 1 emitted from an accelerator (not shown) by the Bragg reflection of the first crystal 41 of the two-crystal spectroscope 13. The X-ray 2 reflected by the first crystal 41 is enlarged to a required size by asymmetric reflection of the second crystal 12.

In this case, n × m constituting the first crystal 41
Since the individual crystals 42 have the same material and crystal orientation, the selected energy is the same. However, the reflectivity of the n × m crystals 42 is different, and the reflectivity of each crystal 42 is selected so that the intensity distribution of the emitted light becomes uniform. 2
Has a uniform energy distribution. That is, white light 1
The required energy is selected by the Bragg reflection of the first crystal 41, and the energy distribution is constant and reflected. Then, the second crystal 12 is enlarged to a required size by asymmetric reflection. The subject 100 is irradiated with the X-rays 4 having the required size and having a uniform energy distribution obtained in this way, and the X-ray intensity is measured by the detector 5.

As described above, in the X-ray CT apparatus according to the present embodiment, the reflectance of each crystal constituting the first crystal 41 of the two-crystal spectroscope 13 is appropriately selected, so that the The energy distribution of the emitted X-rays 2 can be made uniform. Therefore, it is possible to select X-rays having the required energy from the white light 1 and transmit the X-rays to the subject position along the same optical axis, and irradiate the subject 100 with X-rays having the same beam size and uniform energy distribution regardless of the energy. it can.

(Other Embodiments) The present invention is not limited to the above-described embodiments, and various other modifications can be made within the scope of the present invention.

[0051]

As described above, according to the present invention,
Selects X-rays of the required energy or energies from X-rays having a wide range of energy, transmits the same optical axis to the position of the subject, and generates X-rays with the same beam size and uniform energy distribution regardless of the energy. By making it possible to irradiate the subject, it is possible to provide an excellent X-ray CT apparatus that does not irradiate the subject with extra X-rays and that can easily perform data processing of the detector.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an X-ray CT apparatus according to a first embodiment to which the present invention is applied.

FIG. 2 is a configuration diagram showing an X-ray CT apparatus according to a second embodiment to which the present invention is applied.

FIGS. 3A and 3B are diagrams showing an X-ray CT apparatus according to a third embodiment to which the present invention is applied, wherein FIG. 3A is a configuration diagram, and FIGS. FIG. 3 is a plan view and a cross-sectional view in the optical axis direction.

FIG. 4 is a configuration diagram showing an X-ray CT apparatus according to a fourth embodiment to which the present invention is applied.

FIG. 5 is a perspective view showing a first crystal of FIG. 4;

FIG. 6 is a model diagram of a two-crystal monochromator.

FIG. 7 is a configuration diagram illustrating an example of a conventional X-ray CT apparatus.

FIG. 8 is an optical path diagram showing an example of an optical path to a subject position in a conventional X-ray CT apparatus.

9A and 9B are diagrams showing the results of ray tracing simulation performed using the optical path diagram of FIG. 8, where FIG. 9A is a distribution diagram showing the photon density in the Y-axis direction, and FIG. 9B is a diagram showing the photon density in the X-axis direction. FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... White light 2 ... Outgoing light from a 1st crystal 3 ... Outgoing light from a 2nd crystal 4 ... X-ray irradiated to a test subject 11, 41 ... 1st crystal 12 ... 2nd crystal 13 ... 2 crystal spectroscope 14 , 27, 33 uniform filter 15 detector 21 primary light extraction filter 22 nth light extraction filter 23 extraction filter 24 rotating device 25, 31 primary light uniform filter 26, 32 nth order Light uniformizing filter 28 Inserting device 34 Second rotating device 35 Shutter 42 Crystal

Claims (4)

[Claims] 1. An X-ray CT apparatus that selects one or more energies from among X-rays having a wide range of energy using a spectral crystal and irradiates the subject with an X-ray to capture an image. The filter has an intensity distribution equalizing filter for allowing the X-rays to pass therethrough and irradiating the subject with the X-rays uniformly, and the thickness of the filter is a horizontal plane perpendicular to the X-ray traveling direction. The direction is x, the vertical direction of a plane orthogonal to the X-ray traveling direction is y, the function indicating the incident X-ray intensity distribution is f, the outgoing X-ray intensity (constant) required at the subject position is I, and the absorption coefficient of the filter is where μ is An X-ray CT apparatus, which is one of a value of t and an approximate value of t obtained by: 2. When using both X-rays of two energies, ie, primary reflected light and n-order reflected light of the spectral crystal, only one of the primary reflected light and the n-order reflected light is used. A primary light extraction filter and an nth-order light extraction filter that transmit and block the other, and the intensity distribution equalizing filter is a primary light that equalizes the intensity distributions of the primary reflected light and the nth reflected light, respectively. A primary light extraction filter, the n-order light extraction filter, the primary light uniformization filter, and the n-th light uniformization filter, wherein one of the energy is 2. The X-ray CT apparatus according to claim 1, wherein the X-rays transmitted through the extraction filter for X-rays are then transmitted through the equalizing filter for the same energy, and then irradiated to the subject. 3. When the X-ray intensity distribution in the x direction is uniform, the first-order light equalizing filter and the n-th order light equalizing filter move on a common circular orbit in the horizontal direction at a common speed. The primary light extraction filter, the nth light extraction filter, the primary light equalization filter, and the nth light equalization filter pass through one of the energy extraction filters. 3. The X-ray CT apparatus according to claim 2, wherein the X-rays are configured to irradiate a subject after passing through a uniformizing filter for the same energy during the turning. 4. An X-ray CT apparatus which selects one or more energies of X-rays from X-rays having a wide range of energy by using a spectral crystal and irradiates the subject with an X-ray to capture an image, wherein the spectral crystal is An X-ray CT apparatus including a spectral crystal comprising a plurality of crystals having different reflectances.