JPH0327046B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a radiation tomography inspection apparatus that uses radiation to obtain a cross-sectional image of an object to be inspected and then inspects the object.

[Technical background of the invention]

There is a radiation tomography inspection device called a computer tomography scanner (hereinafter referred to as CT scanner) as a device that can non-destructively and accurately measure internal defects, composition, structure, etc. of objects.

This device includes, for example, a radiation source that emits fan beam X-rays that spread out in a flat fan shape;
placed facing this radiation source through the subject,
Using a detector with a plurality of radiation detection elements arranged in the direction of spread of the Fan beam X-ray, the radiation source and the detector are moved in the same direction centering on the subject at an angle of, for example, 180° to 360° in one degree increments. This system collects X-ray absorption data from multiple directions on the tomographic plane of the subject while rotating sequentially, and then performs image reconstruction processing using a computer, etc., to reconstruct the tomographic image. Since images can be reconstructed in as many as 2,000 tones depending on the composition, it is possible to understand the state of the tomographic plane in detail.

This kind of CT scanner is so-called 3rd generation, and in addition, an X-ray source that emits pencil beam X-rays and a detector are installed opposite to this X-ray source, and the X-ray source and detector are connected to each other. The so-called first generation pencil beam X-ray is a narrow fan beam X-ray, in which the X-ray is traverse-scanned along the fault line of the object to be inspected, rotated by a predetermined angle after each traverse-scan, and the traverse-scan is performed again.
The so-called second generation, which can be said to be an improved version of the first generation, uses a detector with several detection elements and performs the above-mentioned traverse scan and rotational scan. There are various types of CT scanners, such as the so-called fourth generation, in which only the X-ray source is rotated and scanned, using a detector equipped with detection elements and an X-ray source that emits wide fan beam X-rays.

Incidentally, in such a CT scanner, an X-ray tube is generally used as an X-ray source when collecting X-ray absorption data. Since the X-rays emitted from the X-ray tube have an energy distribution, each X-ray path connecting the X-ray source and each X-ray detection element (this
The detection data of each X-ray detection element is affected by radiation hardening depending on the thickness of the object during the radiation path (referred to as the radiation path).

In other words, the X-rays emitted from the X-ray tube are so-called white X-rays, which include a range of energy spectra from high to low.On the other hand, among the X-rays in each energy spectrum, those with low energy are emitted within the subject. There is a characteristic that the attenuation rate is large when the energy is high, and the attenuation rate is low when the energy is high. Therefore, if the thickness of the object being examined during the X-ray path is thick, the X-rays in the low-energy spectrum will be greatly attenuated, leaving the X-rays in the high-energy spectrum. This is generally referred to as radiation hardening, but due to this radiation hardening, X-rays that are attenuated according to the thickness and composition of the subject should be detected, but instead of being detected due to the absorption of The data will be different from the original value.

Therefore, for example, when a CT scanner is used to examine the tomographic plane of a cylindrical body made of a material with a homogeneous single composition, a circular image with homogeneous density should be obtained as a CT reconstructed image. This results in an uneven reconstructed image, such as an image in which the density gradually changes from region to region.

This can lead to misidentification when inspecting the object, so beam hardening correction (beam hardening correction; BH correction) is applied to reconstruct the image.

Conventionally, this radiation hardening correction is performed by first calculating the detection output of the radiation detection element (I/I ₀ ; however, I ₀ is
Detection output when no object exists in the line path,
I is the detection output when the object is present in the X-ray path), then the amount of X-ray attenuation on each X-ray path τ _e =
(ln I ₀ /I) is calculated, and a correction is added to this to calculate the corrected attenuation amount τ. This is called BH correction.
A characteristic curve showing the amount of correction at this time is shown in FIG.

That is, in the figure, A is a correction curve by X-rays of a single energy spectrum, and in the case of a single energy, there is no effect of radiation hardening, so the correction curve becomes a straight line. B is a correction curve for X-rays with energy distribution, and the larger the attenuation amount τ _e , that is, the larger the object transmission length, the greater the influence of radiation hardening, so the curve is curved to remove this influence. It becomes a characteristic.

This correction curve differs depending on the substance constituting the subject, and is usually determined by the average substance composition of the subject.

However, in the case of such conventional methods, the correction curve is corrected using a curve that is close to the average material composition of the specimen, so it inherently contains errors, and the thicker the transmission thickness of the specimen, the greater the effect of this. The radiation hardening correction was incomplete because it appeared largely.

Therefore, when testing a homogeneous, circular object,
Note that the reconstructed image becomes non-uniform, and this tendency becomes more pronounced especially in the case of a subject having a long and narrow cross section in which the X-ray transmission thickness differs greatly depending on the direction.

This is because the curves representing the above-mentioned correction differ depending on the substance (element), so if the composition (mixing ratio) of the substance differs in some parts, it is difficult to use the same correction curve for different transmission paths. This is due to the fact that it is impossible to begin with.

Another factor is that the correction characteristic curve is inappropriately selected. Especially when inspecting various objects one after another, such as with an industrial CT scanner, it is virtually impossible to perform basic measurements to determine the optimal correction curve for each object each time. In reality, the most suitable correction curve was selected from among several prepared correction curves for correction.

[Purpose of the invention]

The present invention was made in view of the above circumstances, and
It is an object of the present invention to provide a radiation tomography examination apparatus that can perform optimal radiation hardening correction and reconstruct images with high fidelity.

[Summary of the invention]

That is, in order to achieve the above object, the present invention projects a set tomographic plane of a subject from each direction using radiation having a range of energy distribution, and detects the projected radiation with spatial resolution. In the apparatus for obtaining radiation absorption data for each of the projection directions and performing image reconstruction processing using these radiation absorption data to obtain a reconstructed image corresponding to the radiation absorption rate at each position on the tomographic plane, A function that compares the integral value of the radiation attenuation distribution obtained from the radiation absorption data with the integral value of the reference projection direction for each projection direction, and calculates a coefficient that depends on each projection direction according to the difference. , in order to equalize the integrated values in each projection direction, a function of radiation attenuation-corrected attenuation characteristic set in advance is corrected by the coefficient to obtain a function of radiation attenuation-corrected attenuation characteristic for each projection direction. and a function to correct the radiation absorption data in the corresponding projection direction using the obtained function, and image reconstruction is performed using the radiation absorption data after the radiation hardening correction. A preset radiation attenuation-corrected attenuation characteristic function is used to make the integrated values of the radiation attenuation distribution obtained from the radiation absorption data for each projection direction approximately equal in each of the projection directions. A coefficient is calculated for each projection direction according to the difference between the integral value for each projection direction and the integral value for the reference projection direction, and the function is corrected with this coefficient for each projection direction. By correcting the radiation absorption data in the corresponding projection direction using the radiation attenuation-corrected attenuation characteristic function, we can calculate the effect of each projection direction on the change in radiation hardening due to the thickness of the subject, which changes in each projection direction. The effects of radiation hardening can be corrected by taking into account the effects of radiation hardening, thereby making it possible to perform optimal radiation hardening correction, and performing image reconstruction using radiation absorption data after this radiation hardening correction. To be able to get good quality images without.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in Figures 1 to 6.
This will be explained with reference to the figures. FIG. 1 is a block diagram showing the configuration of an apparatus according to the present invention, and here a second generation CT scanner is shown as an example. In the figure, 1 is an X-ray tube that emits fan beam X-rays FX with a relatively narrow divergence angle, and 2
is placed facing this X-ray tube 1, and the fan beam X
This is an X-ray detector formed by arranging a plurality of X-ray detection elements in parallel over the spread width of the ray FX, and can detect the X-ray intensity from the X-ray tube 1 with spatial resolution. Reference numeral 3 denotes a translation frame for fixing and holding the X-ray tube 1 and the X-ray detector 2 and for traverse scanning them. This translation frame 3 is provided with an oval hole 3a extending in the traverse scan direction at the center, and the X-ray tube 1 and the X-ray detector 2 face each other via this hole 3a. Reference numeral 4 denotes a rotating frame having a hole 4a in the center and having a ring shape.
A guide 4b is provided on the rotary frame 4, and the translation frame 3 is slidably held by the guide 4b, so that the translation frame 3 can traverse scan the rotation frame 4. Reference numeral 5 denotes a fixed frame that holds the rotating frame 4, and the rotating frame 4 is rotatably held on the fixed frame 5, and the rotating frame 4 is rotationally driven by a rotation driving section 6 provided on the fixed frame 5. There is a structure. Further, the rotating frame 4 is provided with a translational drive mechanism 7 using, for example, a rack and pinion, and the translational drive mechanism 7 allows the translational frame 3 to be traverse scanned.

8 is a table for placing a subject placed in the center hole 4a of the rotary frame 4, and 9 is a subject on this table 8. Reference numeral 10 denotes a data acquisition device, which integrates the output of each detection element of the radiation detector 2 for a predetermined period of time for each X-ray exposure, and obtains data corresponding to the amount of X-ray transmission (X-ray absorption amount) from the integrated value. It's something you get. 11 is the central processing unit (CPU)
and controls the entire system.

12 is a reconfiguration circuit, and the data acquisition device 10
Based on the data collected by
Image reconstruction processing is performed under the control of This reconfiguration circuit 12 is constructed as shown in FIG.

That is, 12-1 is a preprocessing device that receives X-ray absorption data for each projection (projection direction) collected by the data collecting device 10, and performs logarithmic transformation, gain correction, and offset correction on the data. Pretreatment is performed. Reference numeral 12-2 is a BH correction device, which performs correction on this preprocessed data in accordance with the above-described correction curve to obtain BH-corrected data. Reference numeral 12-3 denotes a BH auxiliary correction device, which further corrects the data corrected by the BH correction device 12-2 so as to correspond to a target correction curve.

Here, I will explain BH auxiliary correction.

Generally, when radiation has a single energy, when a subject is projected from each projection direction using parallel beams (parallel X-rays), the integral value of each attenuation distribution is constant regardless of the projection direction.

This situation is shown in FIG. In the figure, XR is a parallel beam X-ray, 30 is an object with a trapezoidal cross section, and D _y is attenuation at each projection position t of the object 30 obtained by projecting with a parallel beam X-ray parallel to the y-axis. It's the amount. In addition, D _x is each projection position t of the subject 30 obtained by projecting with parallel beam X-rays parallel to the x-axis.
is the attenuation amount when projected in the y-axis direction and
When projected in the x-axis direction, the shape of the subject 30,
Although the thickness differs in each projection direction, the integral value of D _y , that is, the integral value of area S ₁ and D _x , that is, the area
S ₂ will be equal. This is because the same cross-section is projected, and radiation hardening does not occur with single-energy X-rays. Therefore, even if the projection direction is different on the same cross-section of the object 30, within that cross-section The integrated values of X-ray attenuation are all the same.

However, in reality, since the X-rays used have an energy distribution, radiation hardening occurs, and S ₁ and S ₂ have different areas. Therefore, a radiation hardening correction is performed to correct the radiation hardening, but since the correction function used is not appropriate, an area difference still occurs between S ₁ and S ₂ .
The BH auxiliary correction device 12-3 is for performing this correction, and is based on the following principle.

Figure 4 shows the optimal auxiliary correction coefficient g(τ) for the X-ray absorption value by the X-ray beam with the attenuation amount τ after the radiation quality hardening correction.
It shows _the characteristic curve _of can do. In other words, the coefficient (1-kθg(τ)) consisting of the auxiliary correction coefficient g(τ) and the coefficient kθ that depends on the projection direction θ of the X-ray on the cross section of the asymmetric object is calculated as the X-ray after radiation hardening correction. By multiplying the absorption data, the above D _x , D _y ,...
...areas S ₁ , S ₂ , ...S _o which are the integral values of each of D _o
can be made equal to each other.
In other words, with T ₀ as a constant, ∫(1+k〓g(τ))τ dt=T ₀ ...(1) Find k〓 so that (1) is satisfied, and τ′=(1+k〓g(τ))τ ... According to (2), the attenuation amount τ' after supplementary correction for a certain attenuation amount τ is determined and used as X-ray absorption data for subsequent reconstruction.

In other words, regarding the attenuation amount τ that is corrected by adding radiation hardening correction to the attenuation amount obtained from the measured value, the supplementary corrected attenuation amount τ′ obtained by further adding radiation hardening correction to the attenuation amount obtained from the measured value is used for subsequent re-examination. Used as X-ray absorption data for construction.

The above g(τ) is a predetermined characteristic curve, and can be obtained from the curve (function) used for radiation hardening correction. For example, as shown in Figure 7, the correction curve obtained from the measurement of the transmission length and X-ray transmittance of a specific material, the attenuation amount _{τ e} obtained from the X-ray measurement value is plotted on the vertical axis. , and a value obtained by multiplying the transmission length by a constant (corrected attenuation amount τ) is taken on the horizontal axis, and a correction curve indicated by B is created from the measured values, and this is used for radiation hardening correction.

If the object to be examined is made of the same material as the above-mentioned specific material, by performing radiation hardening correction, the corrected attenuation amount τ becomes a value proportional to the transmission length, which means that the correction has been made correctly.

Here, since there is no radiation hardening in single energy spectrum X-rays (ideal X-rays), which are ideal X-rays, the correction curve becomes straight line A. X-ray (white X
line) shows a correction characteristic B. Also,
The shape of the correction curve differs depending on the substance, and on the other hand, general specimens have a combination of substance types, and the way the combination differs depending on the X-ray transmission path, so the curve B obtained for the above specific substance was used. Errors will be included if only the radiation hardening correction is performed.

Therefore, supplementary correction is performed to remove this error. Since the degree to which the correction curve deviates from the ideal X-ray (difference between curve B and straight line A) differs depending on the material, the auxiliary correction coefficient g (τ _e ) for correcting the difference is, for example, a correction for a specific material. A function of the difference between curve B and straight line A is used. That is, let {τ( _τe ) _B −τ( _τe ) _A } be g( _τe ). However, this is just an example, and there is no need to stick to this. Also, T ₀ is a certain arbitrary projection direction θ ₀
The integral value of the attenuation τ without supplementary correction T ₀ =∫τ (θ=θ ₀ ) dt ...(3) can be used, and k〓 is k〓=T ₀ −∫τ dt/∫ g(τ)r dt ...(4). Therefore, τ' can be determined by the second equation using this k〓. In addition, the second equation can be expressed as a general equation as τ'=f(k〓,τ)...(5), and as a result, the auxiliary correction coefficient attenuation τ' can be expressed as a certain correction curve g(τ). It is converted into a function that changes the curvature according to a coefficient that depends on the projection direction for each projection direction, that is, a coefficient that depends on the transmission thickness of the object that changes for each projection direction, and based on the relationship between this and the attenuation amount τ It is what is required. Further, as long as the relationship is expressed by the fifth expression, the relationship is not limited to the second expression, and in practice, the optimum relationship f(k〓, τ) may be selected.

Based on this principle, the BH auxiliary correction device 12-3 corrects the BH obtained by the BH correction device 12-2.
Using the corrected X-ray absorption data, calculate each k〓,
This BH-corrected X-ray absorption data is subjected to BH supplementary correction using this k〓 to obtain true X-ray absorption data.

Generally, the BH auxiliary correction does not necessarily need to be applied to the data τ after log transformation, but may be applied to the data I ₀ /I before log transformation.

In this case, the correction can generally be expressed by the formula τ'=f(k〓, I ₀ /I) (5').

FIG. 8 shows a conversion curve (correction curve) based on this equation (5'). As you can see from this figure 8,
The conversion of I ₀ /I→τ′ shown in equation (5′) is performed using a different conversion curve for each projection direction.
This can be said to be a BH correction that includes conversion. The above conversion curve is when k = 0,
Matches the log curve.

Although the example described so far has been an auxiliary BHC correction using one parameter k, more generally a plurality of parameters k ₁ , k ₂ , etc. can be used.

In the case of two parameters, the correction formula can be expressed as τ′=f(k ₁ 〓, k ₂ 〓, τ) ……(5″).

The function f can be selected so that the displacement of the correction curve differs depending on the combination of k ₁ 〓 and k ₂ 〓.
This situation is shown in FIGS. 9a, b, and c.

In this case, select and set the ratio of k ₁ 〓 and k ₂ 〓 according to the subject.

12-4 is a convolver, which uses the X-ray absorption data after BH auxiliary correction and convolves it with a convolution function to obtain projection data for each angular projection direction for reconstruction. It is something.

Further, 12-5 is a back projector that back projects this projection data to generate a reconstructed image. The reconfigurable circuit 12 is formed by the steps 12-1 to 12-5 described above.

The explanation will be given by returning to FIG. 1 again. Reference numeral 13 denotes a control console, which serves as a man-machine interface and provides various drive control outputs to the system under the control of the CPU 11. Reference numeral 14 denotes a CRT display, which displays the reconstructed image and other necessary information. Reference numeral 15 denotes an X-ray control section, which generates a high pulse voltage when receiving an X-ray exposure command from the control console 13 to control the X-ray tube 1.
It generates pulsed X-rays. 16
is a mechanism control unit which receives control output from the control console 13 and generates drive outputs for the translation drive unit 7 and rotation drive unit 6, and controls the X-ray tube 1 and the X-ray detector 2.
This is for performing a traverse scan and rotationally driving the subject 9 by a predetermined rotation angle unit each time a traverse scan is completed.

Next, the operation of this device having the above configuration will be explained. First, in response to a command from the CPU 11, the control console 13 gives an X-ray exposure command to the X-ray control section 15. Then, the X-ray control unit 15 generates a high pulse voltage and applies it to the X-ray tube 1, so that the X-ray tube 1 emits a pulsed and narrow fan beam X-ray FX.
occurs.

This fan beam X-ray FX enters each X-ray detection element of the opposing X-ray detector 2 via the subject 9, and each X-ray detection element outputs a detection signal corresponding to the intensity of the incident X-ray. , data collection device 10
is input. Then, this data collection device 10
integrates the detection signal until the next fan beam X-ray is irradiated, and converts it into a digital value corresponding to the integrated value. This digital value is stored in the memory within the CPU 11 in association with the detection element position and the traverse position.
It is assumed that the rotation frame 4 and the translation frame 3 are at the origin position at the initial stage.

In this way, one pulse of Fan beam X-ray
When the collection of X-ray absorption data by FX is completed, the control console 13 gives a translation drive command to the mechanism control unit 16 to perform a traverse scan of a predetermined pitch of the translation frame 3, and thereby the mechanism control unit 16 performs the translation. A drive output is applied to the drive unit 7 to perform the above-mentioned traverse scan. Then, the control console 13 gives an X-ray exposure command to the X-ray control section 15. As a result, the fan beam X-ray FX is irradiated again, and data collection is performed as described above. Note that data collection can be similarly achieved by irradiating X-rays in pulses and performing traverse scans continuously. When this operation is repeated and the traverse scan is performed to the terminal side, the control console 13 then gives a rotation operation command to the mechanism control section 16. As a result, the mechanism control section 16 applies a drive output to the rotary drive section 6 to rotate the rotary frame 4 by a predetermined rotation angle. Therefore, since the rotating frame 4 is rotated by the predetermined rotation angle with respect to the subject 9, the fan beam X-ray FX is rotated by this angle.
The projection angle changes. Then control console 1
3 gives an X-ray exposure command to the X-ray control unit 15, the fan beam X-ray FX is exposed, and the above-mentioned data collection is performed. Then, each time X-rays are irradiated, a traverse scan is performed in the opposite direction, and when the end is reached, rotational drive is performed again by a predetermined rotation angle, and the traverse scan is repeated. In this way, X-ray absorption data is collected from a direction of 180° at intervals of 0.6°, for example.

When data collection is completed, the CPU 11 converts the collected X-ray absorption data into X-ray absorption data at each detection position when parallel beams are used for each projection direction, and Absorption data is processed by preprocessing device 12
-1, preprocessing such as logarithmic transformation, gain correction, and offset correction is performed. This preprocessed X-ray absorption data is then sent to the BH correction device 12-2, where radiation hardening correction is performed. Next, this corrected X-ray absorption data is sent to the BH auxiliary correction device 12-3, where the above-mentioned k〓 is determined based on the radiation quality hardening corrected X-ray absorption data for each projection, Using this calculated k〓 for each projection direction,
The above-mentioned radiation hardening auxiliary correction is performed on the radiation hardening corrected X-ray absorption data in the corresponding projection direction to obtain true X-ray absorption data.

This X-ray absorption data is sent to a convolver 12-4 where it is convolved, and then sent to a back projector 12-5 where it is back projected and a reconstructed image is generated. The data of this reconstructed image is
The image is sent to the CRT display 14 via the CPU 11 and displayed there as an image.

In this way, after the radiation hardening correction, the error in the correction is known from the corrected data, and the radiation hardening auxiliary correction is added to correct this error. The radiation hardening correction can be almost completely corrected, and density unevenness due to radiation hardening is therefore eliminated, making it possible to obtain a high-quality reconstructed image.

In industrial CT scanners, various objects are often examined one after another, and it is virtually impossible to select and use the most suitable radiation hardening correction curve for each object each time. This is because the number of radiation hardening correction curves to be prepared increases, and it is difficult to select which correction curve is optimal.

In the present invention, several types of radiation hardening correction curves are prepared in advance according to the target specimen composition, a characteristic curve considered to be appropriate is selected, and radiation hardening correction is performed based on this. After that, auxiliary correction is added to remove the error, thereby making it possible to compensate for the above-mentioned drawbacks of the conventional method.

Next, other embodiments of the present invention will be described. The image reconstruction processing section essentially consists of a CPU 11 and a reconstruction circuit 12. Moreover, since image reconstruction is mainly based on calculations, preprocessing, radiation hardening correction,
The radiation hardening auxiliary correction, convolution, and back projection can also be performed by software processing by the CPU 11.

Of course, some of these can also be processed by software. In addition, the radiation hardening correction device 12
-2 can be removed and the radiation hardening correction can be performed only by the radiation hardening auxiliary correction device 12-3.

The block diagram of the reconfigurable circuit 12 in this case is shown in Figure 5.
As shown in the figure.

In this case, the radiation hardening auxiliary correction device 12-3 uses T ₀ =∫τ(θ=θ ₀ )·(1+g(τ))dt (3′) instead of the third equation.

According to this method, the radiation hardening correction curve is a straight line,
Since the curve itself is corrected so as to have optimum characteristics for each projection direction, substantially the same effect as in the previous embodiment can be achieved with a simpler reconstruction circuit.

Further, as shown in FIG. 6, it is also possible to adopt a configuration in which only the BH auxiliary correction portion of the configuration shown in FIG. 2 is replaced by software processing by the CPU 11. In this case, since it is a conventional system configuration except for the BH auxiliary correction part, the CPU 11 has a processing program for the BH auxiliary correction, and the CPU 11 performs the BH auxiliary correction on the X-ray absorption data after the BH correction. By applying this to the convolver 12-4, the present invention can be easily applied to conventional devices.

It should be noted that the present invention is not limited to the embodiments described above and shown in the drawings, but can be implemented with appropriate modifications within the scope of the gist thereof.For example, in the above embodiments, a second generation CT scanner may be used. As explained as an example, first generation, third generation or detection elements are arranged in a circle and the subject is placed in the center.
The 4th generation, in which only the ray tube rotates, detecting elements are arranged in a circle, the subject is placed in the center, and multiple X-ray tubes are placed at predetermined intervals, and the X-ray tubes used for X-ray exposure are sequentially switched. The present invention can be applied to various other CT scanners such as the fifth generation CT scanner. (However, among the above methods, when data is collected using a fan beam, BH assistance is performed after the data is sorted into a set of parallel beams.) Also, radiation hardening occurs if the radiation has an energy distribution. Therefore, it is applicable not only to X-rays but also to all CT scanners that use radiation sources with energy distribution.

〔Effect of the invention〕

As described in detail above, according to the present invention, it is possible to provide a radiation tomography examination apparatus that can perform optimal radiation hardening correction and obtain high-quality reconstructed images.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention;
Figure 2 is a block diagram showing the configuration of the reconstruction circuit, Figure 3 is a diagram for explaining radiation hardening, and Figures 4, 8, and 9 are correction curves for radiation hardening auxiliary correction. FIGS. 5 and 6 are main part configuration diagrams showing a modification of the present invention, and FIG. 7 is a diagram showing a conventional radiation hardening correction curve and a correction curve using single energy X-rays. 1...X-ray tube, 2...X-ray detector, 10...data acquisition device, 11...CPU, 12...reconfiguration circuit, 12-1...preprocessing device, 12-2...
BH correction device, 12-3...BH auxiliary correction device,
12-4... Convolver, 12-5... Back projector, 13... Control console, 14...
CRT display, 15...X-ray control unit, 16
...mechanism control section.

Claims (1)

[Claims] 1. By projecting radiation having a width in energy distribution from each direction on a set tomographic plane of the subject, and detecting the projected radiation with spatial resolution, in an apparatus that obtains radiation absorption data and performs image reconstruction processing using these radiation absorption data to obtain a reconstructed image corresponding to the radiation absorption rate of each position on the tomographic plane,
The radiation attenuation distribution or its integral value obtained from the radiation absorption data for each of the projection directions is compared with the radiation attenuation distribution or integral value of the projection direction that is the reference for each of the projection directions, and each projection is adjusted according to the difference. A function to obtain a coefficient that depends on each direction, and a function of the radiation attenuation-corrected attenuation characteristic set in advance to equalize the radiation attenuation distribution or integral value in each projection direction is corrected by the coefficient, and the function is calculated in each projection direction. A radiation hardening correction means is provided, which has a function of obtaining a function of radiation attenuation-corrected attenuation characteristic for each time, and a function of correcting radiation absorption data in the corresponding projection direction using the obtained function. A radiation tomography examination apparatus characterized in that image reconstruction is performed using radiation absorption data after radiation hardening correction. 2. The radiation according to claim 1, wherein the radiation hardening correction uses radiation absorption data corrected by an approximate radiation attenuation-corrected attenuation characteristic function selected in advance according to the composition of the subject. Fault inspection device. 3. The radiation tomography examination apparatus according to claim 1, wherein the radiation hardening correction uses the collected radiation absorption data of the non-radial hardening correction.