JPS6040940A - Tomography apparatus - Google Patents

Abstract

PURPOSE:To make it possible to measure the state of the composition of the inside of a body to be checked accurately, by providing a radiation source, which emits a radiation beam along a predetermined plane, and providing a detector, which is arranged so as to face the body to be checked and detects the intensity of said radiation beam. CONSTITUTION:An X-ray source 2 and a detector 3 for detecting X rays are provided at one end of a mounting base 1 and in the vicinity of a hole 1a so as to face each other through the hole 1a. A stop made of a heavy metal is attached to the side of the X-ray radiating side of the X-ray source 2. By this stop, the X-ray fan beam FB having a flat fan shape can be emitted to the detector 3. The body to be checked is relatively scanned by the radiation source and the detector, with the position of the body to be checked as a center. In this way the tomogram data of the body to be checked is collected. Thus the state of the composition of the inside composition of the body to be checked can be measured accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a tomography apparatus for use in product inspection using a computer tomography scanner.

[Technical background of the invention]

It is important to be able to inspect internal defects such as cavities and cracks in objects such as engine blocks, ceramic plates, or wood, as well as internal composition and structure, in order to maintain quality and check for defective products.

Among these, conventional methods for detecting internal defects include displaying and observing an X-ray fluoroscopic image on a TV monitor using an X-ray television system, or detecting flaws using ultrasonic waves. Although it is possible to see the general appearance of internal defects, it is not possible to determine the composition or structure.Also, when logs have internal defects, it is important to accurately understand their distribution when sawing lumber, but It has been difficult to accurately grasp the state of internal defect distribution in objects of this size.

Therefore, it is conceivable to use a computer tomography scanner (hereinafter referred to as a CT device) as a device that can accurately measure internal defects, composition, structure, etc.

That is, a CT apparatus includes, for example, a radiation source that emits fan-beam X-rays that spread in a flat fan shape, and is placed facing this radiation source through a subject, and is arranged so as to face the radiation source in the direction in which the fan-beam X-rays spread. A detector equipped with a plurality of radiation detection elements is used to detect the tomographic plane of the subject while sequentially rotating the radiation source and the detector in the same direction centering on the subject over a range of 180° to 360° in 1 degree increments. After collecting radiation (X-ray) absorption data from multiple directions, a computer etc. perform image reconstruction processing to reconstruct a tomographic image. Since the image can be reconstructed with multiple gradations, it is possible to understand the state of the tomographic plane in detail.

By the way, when an X-ray tube is used as a radiation source in a CT device, the radiation absorption and collection is performed in 1-degree increments as described above.
Since fan beam X-rays are sequentially irradiated over a range of 80° to 360°, it is necessary to irradiate X-rays for a certain amount of time until the collection is complete when collecting data for a tomographic plane. Therefore, even if the X-ray is a Noggles X-ray, it must be considered in the same way as a continuous X-ray, and therefore consideration must be given to the fact that it is a continuous X-ray.

When detecting the X-ray intensity after passing through the object and calculating the radiation absorption coefficient μ of the X-ray cross section, changes in the X-ray spectrum due to the thickness of the object passing through the object are reflected in the reconstructed image (CT image). This is because it has a negative impact.

In other words, low-energy photons in X-rays are divided into different groups, and as the transmission thickness of the object increases, the quality of the X-rays hardens (the high-energy components of the spectrum become relatively large), and the Ideally, the detected dose ratio R changes linearly as shown in a, but as shown in b, the detected dose ratio R shows non-linear characteristics with respect to the transmission thickness, and as shown in FIG. CT
Even if an image (reconstructed image) is obtained, the radiation absorption coefficient μ will be low in the central part where the transmission thickness is large, and the radiation absorption coefficient μ will originally be as shown in Figure 2 (
Figure 2 (,
), and a false image like this distribution will be formed. Therefore, suppress the fluctuation of the X-ray output or monitor the fluctuation, and compare this fluctuation with the amount received when it actually passes through the object. This is because accurate testing will not be possible unless appropriate data correction is performed in consideration of regional characteristics.

Therefore, a method is usually adopted in which the fluctuations are monitored and a predetermined correction is made in accordance with the fluctuations in the X-ray output and the region-by-area characteristics during passage through the object, which are averaged.

In other words, Figure 3 is a diagram showing the relationship between the actual detected amount of X-rays due to radiation hardening and the normal detected amount.This relationship is expressed algebraically and the correction formula obtained from this is The normal detection amount IN is known from the actual detection amount Id.

However, this correction formula depends on the analyte material, but in the past, there was no way to determine the correction formula for each target material, so it was necessary to rely on an empirical correction formula. It was not possible to make proper corrections, and accurate inspection was not possible.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and it is possible to obtain an accurate radiation absorption coefficient regardless of the size of the radiation transmission thickness, and therefore, it is possible to accurately measure the internal composition of the subject. The object of the present invention is to provide a tomography apparatus using a CT master device.

[Summary of the invention]

That is, in order to achieve the above object, the present invention includes a radiation source that emits a radiation beam along a predetermined plane, and a radiation source that is placed opposite to each other through a subject and detects the intensity of the radiation beam with a predetermined spatial resolution. for collecting radiation absorption data at each position and in each direction of the tomographic plane of the subject by scanning the radiation source and the detector relative to the subject and centering on the subject placement position; a scanning means for scanning, and radiation absorption data rows for each direction corresponding to the tomographic position of the subject obtained by this scanning,
A preprocessing means for correcting the detection output level of the radiation after passing through the subject due to radiation hardening based on a formula showing the error characteristics with respect to a normal value, and also correcting for fluctuations in the radiation output, etc.; a projection data memory for storing output data; a reconstruction means for performing condelusion and backzolojection on the data output from the preprocessing means or the data read from the projection data memory; and the reconstruction means. an image memory for obtaining a reconstructed image by accumulating and storing the data obtained after the fusion calculation at a pixel position corresponding to the back projection position; and a display means for displaying the image in the image memory. , operates in the correction mode to binarize the reconstructed image in the image memory to obtain a binarized image with zero data in the background part, and from this, add data on the radiation transmission path in the cross section of the object. means for determining the relationship between the detected amount of radiation and the length of the radiation transmission path in the cross section of the object, and from this relationship, the relationship between the detected amount of the detector due to radiation hardening and the normal detected amount, a correction coefficient determining means comprising means for second-order differential processing of this and substituting it into the equation of the pre-processing device and a threshold value of an area where no correction for radiation hardening is to be performed and providing it to the pre-processing means; and a correction mode. At times, the preprocessing means is controlled to perform other corrections than the correction for radiation hardening, and the data obtained thereby is stored in a projection data memory, and this data is used to obtain a reconstructed image. After that, the correction coefficient determining means is operated to control the preprocessing means to perform correction for radiation hardening on the data in the projection data memory using the requested coefficients and the threshold value, and the data after this correction is and a control means for controlling image reconstruction using The image obtained by reconstructing the image using the projection data is binarized using the threshold value obtained from the projection data, and from this the detected amount of X-ray path length of the cross section of the object is determined, and from this, the normal X-ray Determine the relationship between the detected amount and the actual amount of X-rays detected due to radiation hardening, determine each coefficient of the equation that reflects the characteristics and the threshold value of the area not affected by radiation hardening, and use these in the preprocessing device. By applying radiation hardening correction using the above-mentioned coefficients to the projection data in the area exceeding the threshold value, and then reconstructing the image, even if the subject changes, the correction mode can be used. It is possible to perform radiation hardening correction corresponding to the subject based on actual measurement values, thereby suppressing the generation of false images due to radiation hardening and obtaining an accurate tomographic image.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 4 is a diagram showing the basic configuration of this device.

In the figure, reference numeral 1 denotes a pedestal that is rotatably supported and has a hole 1a in the center for arranging the subject S. One end of this pedestal 1 and the vicinity of the hole 1a are connected through the hole 1a. X-ray source 2
and a detector 3 for X-ray detection are provided facing each other.

The X-ray source 2 is equipped with a heavy metal diaphragm on the X-ray emission port side, and this diaphragm allows it to emit a fan beam XiF B that is flat and has a fan-like spread toward the detector 3. It has become. The spread angle α of this fan beam X-ray FB is preset to such an extent that it can cover the opening diameter of the hole 1a in the pedestal 1.

Further, the detector 3 is made up of a plurality of radiation detection elements 3a that output electrical signals according to the intensity of radiation and are arranged in parallel at predetermined intervals in the direction of spread of the fan beam X-ray FB, so that each radiation The detection element 3a detects the intensity of X-rays arriving from the X-ray source 2 through an X-ray path (referred to as an X-ray path) connecting each radiation detection element 3a and the X-ray source 2.

Each output of the radiation detection element 3a is given to a calculation control unit 4 that controls the entire CT apparatus, and this calculation control unit 4 receives a 5OCT image of the subject obtained by recombining the output of the detector 3. Display device 5 using a cathode ray tube or the like to display etc.
is connected. Note that 6 is a drive device that rotationally drives the pedestal 1.

FIG. 5 is a block diagram showing the configuration of the calculation control unit 4, and 20 in the figure is an imaging system comprising the gantry 1, the X-ray source 2, the detector 3, and the drive device 6. Yota 5 is a display device.

2 is a console for the operator to interact with the system (that is, give various instructions to the system, etc.), 22 is a control device that controls the entire system according to the contents of commands from the console 21, and 23 is a control device for exchanging data, etc. 24 is a path for scanning (rotation scanning) the gantry 1 of the imaging system 20 according to a command from the control device 22, and also performs X-ray exposure control and a detection signal output by the detector 3. is collected and integrated on each radiation detection element side, and digital data is obtained by analog-to-digital conversion (A/] conversion) from the analog data obtained in each X-ray/gas unit for each projection direction, and the data is sent out. data collection equipment,
25 is a preprocessing device that sequentially processes the data sent from the data collection device 24 (X-ray absorption data, that is, X-ray intensity data), performs radiation quality hardening correction, and X-ray intensity correction (the generation of X-rays is constant). Therefore, a part of the X-rays output from the X-ray source is detected by a reference detector (not shown) that monitors the X-rays emitted from the X-ray source. (correction so that the X-ray intensity is the same as the value in the pigeon house), detection system characteristic correction (detector
(correction of temporal fluctuations in detection systems such as integrators and converters). Further, the preprocessing device 25 is provided with a command register for registering corrections to be performed, and the command register is used to select whether or not to apply the various corrections described above.

Note that the radiation hardening correction is based on the normal detection amount I as shown in Figure 3.
The relationship between N and the actual detection amount Id due to radiation hardening is expressed by a quadratic equation, and IN is calculated from Id.

When Id<It, IN = Id When Id≧T, IN = aI/+b I d+c
.=(1) However, a@b@c is a coefficient, and 17 is a threshold value, which are determined by a correction coefficient determining device to be described later, and 1 is written into a register in the preprocessing device 25. And from Id to I
The conversion to N is performed by the hardware of the preprocessing device 25 for performing the conversion.

Further, the preprocessing device 25 determines the corrected data for each X-ray A? when the Nocra cell beam (each X-ray) path in the projection direction in which the data was obtained, that is, in the X-ray emission direction, is in a parallel state. It has a function to obtain a projection data string by performing replacement processing so as to match the data that should be obtained on the screen.

27 is a projection data memory, and this projection data memory 27 stores projection data for each projection direction output from the preprocessing device 25. If this memory is stored data G(X, θ), then G(X, θ) (X = 0~2Np, , θ=θaX
It is now possible to search in units of K (K = O ~ Nn) θR - 3600). Here, 2Np is the number of channels of the detector, NR is the number of rays, that is, the number of X-ray projections performed by changing the projection direction (the number of exposures), and θR is the switching angle for each projection direction. Therefore, it can be regarded as a matrix or a box as shown in FIG.

26 is a reconstruction device, and this reconstruction device 26 calculates the sum of products (convolution) of each projection data given from the preprocessing device 25 or the projection data memory 27 and a filter function, and projects each value. The image is back-projected (pack projection) in the direction and given to the memory address of the corresponding pixel position on the image memory 28 for each X-ray pass.

The image memory 28 has a memory capacity that is at least the capacity of one screen (for example, 512 x 512 pixels),
It has a function of accumulating and storing data given from the reconstruction device 26.

Further, the stored content Im(x*y) (where x and y are 0<xty≦511 in the above example) can be searched. XI
7 can be considered as the coordinates of the display device 5, as shown in FIG. The image memory 28 is also used as a working memory for the correction coefficient determination device 290.

The correction coefficient determination device 29 operates under the control of the control device 22 and determines the correction coefficients a, a,
b, c, and IT are combined to provide the preprocessing device 25 with the correction coefficient.

Here, the function of the correction coefficient determining device 29 will be explained in more detail.

That is, when the correction coefficient determination device 29 receives an operation command from the control device 22, it first reads the storage contents (reconstructed image data) IM (XIF) in the image memory 28 and determines the intermediate value M. This intermediate value is the average value of the maximum value and the minimum value.

Once this is complete, proceed to the second stage. Here, the reconstructed image data on the image memory 28 is binarized using the intermediate value M as a threshold value to obtain a silhouette of the tomographic image.

This binarized image is stored on the image memory 28 in place of the reconstructed image that has been on the image memory 28 up to now. Since this device specifies objects with a nearly uniform composition, such as iron or ceramic materials, it is possible to obtain shadow pictures with high accuracy even with such a simple threshold value.

Once this is complete, we move on to the third stage. Here, the binarized image and the projection data G(X,
θ), a table of transmission thickness and detected amount ratio (hereinafter referred to as A table) as shown in FIG. 1 is created in a universal memory provided in the correction coefficient determination device 29.

The method for creating Table A is as shown in Figure 8(a). Considering the binarized image obtained from the reconstructed image of the subject S, the subject S portion of this binarized image is II l #, background and Since the hollow part is mainly made of air, the X-ray absorption coefficient is small. Each position of radiation detection element
If we project a straight line (X-ray gas) D connecting the focus point of the X-ray source 2 and X
, θ) will be obtained.

If this is executed for all θ and X and averaged, Table A as shown in FIG. 8(b) will be obtained.

However, since the straight line is drawn on a digital image with a matrix configuration where one screen configuration consists of 512 x 512 pixels,
As shown in FIG. 9, the straight line corresponds to the pixel position closest to the position of the straight line on the image, and it fits like L, and when viewed from the whole, it has a step-like shape. Note that P is each pixel position.

The processing at this third stage may seem complicated at first glance, but it is not so complicated because once it is determined by the hardware, it is a simple process of repetition.

Once this is complete, we move on to the fourth stage. Here, based on Table A, we will introduce a relationship table between the normal detection amount ratio IN and the actual detection amount ratio Id due to radiation hardening as shown in VC Figure 3 (hereinafter referred to as B
table) in universal memory. Since the number of data points is the same as Table A, it can be easily created on the same memory. This created Table B is shown in FIG.

Once this is complete, we move on to the fifth stage. Here, the coefficients a, b, c and threshold value IT of the first equation used in the preprocessing device 25 are determined based on Table B. Since this is a digital value, this determination is made by calculating the difference, and the explanation will be as follows using FIG. 11.

Incidentally, since the apparatus naturally processes only numerical values, there is no image as shown in FIG. 11.

Also, c is a Hb I I7 using Fig. 11(a).
It can be calculated more easily. Here, the problem with the method shown in Figure 11 is the first
Figure 1 (,) can be expressed by a quadratic equation,
In reality, it is an n-dimensional equation, so it cannot be clearly expressed as shown in FIG. Therefore, in this device, I which is approximately '''0#
Select T (the choice of IT does not have much influence) and select the 11th
2a is determined using the IT point in Figure (e). This means that the third-order or higher-order terms of the n-order equation are ignored.

To explain the work in the fifth stage, first, the data in Table B showing the relationship between the normal X-ray detection amount IN detected by the detector 3 and the actual detection amount Id due to radiation hardening (which This is shown in Figure 11(a), and this can be expressed approximately as a formula, as in the first formula, in the range Ia<It, IN=■d, I≧
In the IT range IN = aId”+bI, 1 + c
) is first-order differentiated (actually, it is taken as a difference).

As a result, in the range Ia<It, IH'=2aI, 1 + b, in the range 1d≧IT
...(2) is obtained, and this is shown in a graph as shown in FIG. 11(b).

Differentiate this further. This results in second-order differentiation, which gives us the results that in the range Ia<IT, IN'=O, and in the range Id≧IT, IN"=2a - (3), which is shown in the graph as follows. Figure 11(c)
It will be like this. From this, select IT which is approximately 0# and determine 2a using the point I. As a result, a and IT can be obtained, although the terms after the third order are ignored. If a and IT are determined, b can be determined by considering the slope 2a in FIG. 11(b) and a straight line passing through (ITt 1 ), and C can be determined in the same way.

A, b, c, and IT thus obtained are written into a register in the preprocessing device 25.

Next, the operation of this apparatus having the above-described configuration will be explained.

A subject S is placed in the hole 1a of the mount 1, and a scan command is issued from the console 2. However, here, select between normal scan and correction scan. Here, the correction scan is a scan that resets the correction coefficients, and the normal scan is a scan with the correction coefficients as they are.

When a scan command is issued, the control device 22 selects a scan schedule depending on whether it is a correction scan or a normal scan, and in accordance with this schedule, the control device 22 provides a scan control output to the data acquisition device 24.

Now, to explain the case of the normal scan mode, in this mode, under the control of the control device 22, the data collection bag N, 24 moves the gantry 1 by 180 degrees (
~360°)
At the same time, X-ray exposure control is performed to generate fan beam X-rays FB from the X-ray source 2 at each angular position.

This fan beam X-ray FB passes through the hole 1a of the mount 1
The radiation enters the detector 3 arranged opposite to the radiation source 2, and the detector 3
0 is detected by each radiation detection element 3a as an electrical signal corresponding to each incident X-ray intensity.

The detected electrical signals for each radiation detection element are individually integrated by an integrator of the data acquisition device 24, and converted into digital data. Then, these digital data for each radiation detection element are sent to the preprocessing device 25.

- After data collection in the projection direction and transmission to the preprocessing device 25 is completed, the data collection device 24 then rotates the pedestal 1 by 1°, performs X-ray exposure control, and collects the next data. . In this way, data is collected over the range from 0° to 180° (or 360°).

On the other hand, upon receiving data for each ray detection element sequentially sent from the data acquisition device membrane 24 for each projection direction, the preprocessing device 25 performs corrections such as X-ray intensity correction and detection system characteristic correction for each zone. Then, data in the same projection direction (data obtained by parallel beams) is sent to the projection data memory 27 and the reconstruction device 26 in a sequence. When the reconstruction device 26 receives this data, it performs deconpolation on this data, and further performs back projection and stores the result at the address of the corresponding pixel position in the image memory 28.

Condelusion and backpronometry are performed on the data obtained by successively changing the projection angle in this way, and the data are accumulated and stored in corresponding pixel positions on the image memory 28.

When the above operations for all projection angles are completed, a completion signal is output from the reconstruction device 26 to the control device 22. As a result, the control device 22 sequentially reads the data on the image memory 28, converts it into a video signal by D/A converting it, and then supplies it to the display device 5 to display it as a reconstructed image on the display device 5. Then, the control device 22 issues a message to the console 21 indicating that the scan is complete.

The above has been a description of the normal scan mode, but the correction scan mode will now be described.

When this mode is specified, the control device 22 selects a correction scan schedule when a scan command is issued, and the control device 22 provides a scan control output to the data acquisition device 24 in accordance with this schedule. Then, the data acquisition device 24 controls the drive device 6 under the control of the control device 22 to sequentially rotate the gantry 1 over 180° (~360°) in 1° increments, and also rotates the X-ray source at each angular position. 2, X-ray exposure control is performed to generate fan beam X-rays FB.

This fan beam X-ray FB is transmitted through the hole Ja of the mount 1.
Electricity is incident on the detector 3 arranged opposite to the radiation source 2IC, and is detected by each radiation detection element 3a of the detector 30, corresponding to the intensity of each incident X-ray.

Detected as a signal.

The detected electrical signals for each radiation detection element are individually integrated by an integrator of the data acquisition device 24, and converted into digital data. Then, these digital data for each radiation detection element are sent to the preprocessing device 25.

- After data collection in the projection direction and transmission to the preprocessing device 25 is completed, the data collection device 24 then rotates the pedestal 1 by 1°, performs X-ray exposure control, and collects the next data. . In this way, data is collected over the range from 0° to 180° (or 360°).

On the other hand, upon receiving the data for each radiation detection element sequentially sent from the data acquisition device 24 for each projection direction, the preprocessing device 25 performs all the above-mentioned corrections except for the radiation hardening correction for each data, and The data in the same projection direction (data obtained by the Nocra cell beam) is sent to the projection data memory 27 and the reconstruction device 26 in a row.

When the reconstruction device 26 receives this data, it performs convolution on this data, and further performs pack pronoection and stores the result at the address of the corresponding pixel position in the image memory 28.

In this way, convolution and packzolojection are performed on the data obtained by successively changing the projection angle, and the results are cumulatively stored in corresponding pixel positions on the image memory 28.

When the above operations for all projection angles are completed, a completion signal is output from the reconstruction device 26 to the control device 22.

Then, the control device 22 then operates the correction coefficient determination device 29 to start executing the correction coefficient setting procedure as described above.

That is, the correction coefficient determining device 29 first reads the data in the image memory 28 and calculates the intermediate value M from these data. Next, the data in the image memory 28 (reconstructed image data) is sequentially binarized using the thus obtained intermediate value M as a threshold value.

Next, the correction coefficient determination device 29 uses the binarized image obtained by this binarization to create the above-mentioned table A of path length and detection amount ratio x. Then, correction coefficient determining device 2
9 is the normal detected amount of X-rays from this table A. Table B is created showing the relationship between Id and the actual detected amount Id due to radiation hardening.

Next, the data in Table B is subjected to differential processing to determine the normal detected amount IN of X-rays and the actual detected amount I due to radiation hardening.
The coefficients a, b, and c in the equation (first equation) of the characteristic (FIG. 11(a)) showing the relationship with d and the threshold value T of the change point are determined.

The correction coefficient determining device 29 then calculates a and bIc.

The ITs are sent to the preprocessing device 25 and stored in a register in the preprocessing device 25 that stores these a*b ter ITs. Then, the correction coefficient determination device 29 notifies the control device 22 that the correction coefficient determination work has been completed.

Then, in response to this, the control device 22 next sends the projection data in the projection data memo town 27 to the preprocessing device 25. Since this projection data is data that has not been subjected to m-quality hardening correction, the first
Perform correction using the formula.

The control device 22 returns the data corrected by the preprocessing device 25 to the projection data memory 27, and also returns the data corrected by the preprocessing device 25 to the reconstruction device 2.
Send to 6. Then, the reconstruction device 26 sequentially performs convolution and backzolojection, and stores the results at the address of the corresponding pixel position in the image memory 28.

Convolution and back projection are respectively performed on the data obtained by successively changing the projection angle in this way, and the data are accumulated and stored in corresponding pixel positions on the image memory 28.

When the above operations for all projection angles are completed, a completion signal is output from the reconstruction device 26 to the control device 22. As a result, the control device 22 sequentially reads the data on the image memory 28, converts it into a video signal by D/A converting it, and supplies it to the display device 5, on which the reconstructed image is displayed. The control device 22 is a conso/I/21
A message indicating the completion of scanning will be displayed.

In this way, in the correction scan mode, the projection data of the object is saved with various corrections except for radiation hardening, and the image obtained by reconstructing this projection data is used as an intermediate image of the projection data. The value is binarized as a threshold, and from this the detected amount for each X-heave path length of the cross section of the object is determined, and from this, the relationship between the normal detected amount of X-rays and the actual detected amount of X-rays due to radiation hardening is determined. The coefficients of the formula that reflect the characteristics and the threshold value of the area not affected by radiation hardening are given to the preprocessing device, and the radiation quality using the above coefficients is applied to the projection data of the area exceeding the threshold value. Since hardening correction is added and post-reconstruction is performed, even if the object changes, by using the correction scan mode, radiation hardening correction can be performed based on the actual measurement values and is therefore accurate. It becomes possible to obtain accurate tomographic images.

Therefore, it becomes possible to measure internal composition changes with high precision for specimens with relatively uniform internal compositions, such as metals, ceramics, wood, and the like.

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. Rotate around the subject to collect data (R
-R type equipment is shown, but it is also possible to use a system in which the subject is rotated and the X-ray source and detector are placed in fixed positions, or the X-ray source and detector are parallel to each other with the subject at the center. It can also be applied to CT rack equipment called the 11th and 2nd generation TR system, which moves and rotates (the subject side can also move parallelly and rotationally), and furthermore, the detector is arranged in a circle. Then, the subject is placed in the center and the X-ray source is rotated around the subject to collect data.
Alternatively, the detectors are arranged in a circle, multiple X-ray sources are arranged inside the detector at appropriate intervals, and the subject is placed in the center.
The present invention can also be applied to a so-called fourth generation CT rack system that collects data by sequentially selecting radiation sources and performing X-ray exposure.

Further, in the above embodiment, the radiation hardening correction is approximated by a quadratic equation, but it can also be approximated by a cubic equation or higher using a similar method.

In addition, when obtaining a binarized image, the threshold value M was set to the average value of the projection data, but it is also possible to use other methods that can distinguish the object from other parts depending on the composition of the object, purchase, etc. It is also possible to use the statistical sign of as a threshold value.

Furthermore, this device is not limited to X-rays, but can also use other radiations as long as stable output can be obtained.

〔Effect of the invention〕

As described in detail above, the present invention includes a radiation source that emits a radiation beam along a predetermined plane, and a detector that is disposed facing each other with a subject in between and detects the intensity of the radiation beam with a predetermined spatial resolution. and scanning the radiation source and the detector relative to the subject and around the subject placement position to collect radiation absorption data at each position and in each direction of the subject's tomographic plane. The normal value of the detection output level of radiation after passing through the subject, which is caused by radiation hardening, with respect to the radiation absorption data sequence for each direction corresponding to the scanning means and the tomographic position of the subject obtained by this scanning. a pre-processing means for correcting based on a formula showing error characteristics for and correction for radiation output fluctuations, etc.; a projection data memory for storing output data of the pre-processing means; and a projection data memory for storing output data of the pre-processing means; a reconstruction means that performs convolution and pack projection on the data read out from the projection data memory; and a reconstruction means that accumulates the data obtained by the reconstruction means after the condelusion operation at a pixel position corresponding to the back projection position. an image memory for obtaining a reconstructed image by storing the image; a display means for displaying the image in the image memory; and a display means for displaying the image in the image memory; A means for obtaining a binarized image with zero data and adding data on the radiation transmission path in the cross section of the object to determine the relationship between the detected radiation amount ratio and the length of the radiation transmission path in the cross section of the object; The relationship between the detected amount of the detector due to radiation hardening and the normal detected amount is determined from the relationship, and this is subjected to second-order differential processing to calculate the coefficient to be substituted into the above equation of the preprocessing device and the correction for radiation hardening. a correction coefficient determining means comprising a means for calculating a threshold value of a region in which no processing is to be performed and applying it to the preprocessing means; and controlling the preprocessing means to perform corrections other than the correction for the radiation hardening when in a correction mode; After storing the obtained data in a projection data memory and using this data to obtain a reconstructed image, the correction coefficient determining means is activated to calculate the data in the projection data memory using the requested coefficients and threshold values. The control means controls the preprocessing means to perform correction for radiation hardening, and the control means controls the preprocessing means to perform image reconstruction using the corrected data, and in the correction mode, the projection data of the subject is The image is saved in a state in which various corrections other than the correction for radiation hardening have been applied, and the image obtained by reconstructing the image using this projection data is binarized using a threshold value obtained from the projection data, From this, determine the detected amount on the X-ray path length side of the cross section of the object, and from this calculate the relationship between the normal detected amount of X-rays and the actual detected amount of X-rays due to radiation hardening, and reflect the characteristics. Calculate each coefficient of the equation and the darkness value of the area that is not affected by radiation hardening, give these to the preprocessing device, apply radiation hardening correction using each of the above coefficients to the projection data of the area exceeding the threshold value, and then Since reconstruction is performed, even if the subject changes, by using the correction scan mode, it is possible to perform radiation hardening correction corresponding to the subject based on the actual measurement values, and therefore obtain accurate tomographic images. will be obtained.

Therefore, it is possible to provide a tomography apparatus having features such as being able to accurately measure changes in the internal composition of objects with relatively uniform internal composition, such as metals, ceramics, wood, and the like.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between the detected dose and the X-ray penetration thickness through the specimen, Figure 2 is a diagram to explain the false image caused by changes in the thickness of the specimen, and Figure 3 is the Figure 4 is a diagram showing the relationship between the amount of radiation detected and the amount of X-ray detected in a normal case. Figure 4 is a diagram showing the basic configuration of this device. Figure 5 is a block diagram showing the configuration of the main parts of this device. The figure conceptually shows the data string for each projection angle, Fig. 7 shows the coordinate position of each pixel on the screen of the display device, and Fig. 8M explains the method of determining the relationship between the path length and the detected amount. Figure 9 is a diagram to explain an example of the pixel position of a line drawn for a certain direction IC on a digital image, and Figure 10 is a diagram showing the difference between the detected amount due to radiation hardening and the normal detected amount. FIG. 11, which is a diagram showing an example of the relationship, is a diagram for explaining an example of a procedure for calculating coefficients and dark values. 1... Frame, 2... X-ray source, 3... Detector, 3&
... Radiation detection element, 4 ... Computation control unit, ), 5
...Display device, 20...Photographing system, 21...Console, 22...Control device, 23...Pass, 24...
- Data collection device, 25... Preprocessing device, 26...
Reconstruction device, 27... Projection data memory, 28...
Image □□□ Memory, 29... Correction coefficient determining device. Applicant's agent Patent attorney Takehiko Suzue Figure 6 X U Co II (b) Figure 9

Claims (1)

[Claims] a radiation source that emits a radiation beam along a predetermined plane; a detector that is arranged to face each other across a subject and that detects the intensity of the radiation beam with a predetermined spatial resolution; and the radiation source and the detector. a scanning means for collecting radiation absorption data at each position and in each direction of the tomographic plane of the subject by scanning the subject relative to the subject, and The radiation absorption data rows for each direction corresponding to the tomographic position of the subject are corrected based on a formula that indicates the error characteristics with respect to the normal value of the detection output level of the radiation after passing through the subject, which is caused by radiation hardening. and a preprocessing means for correcting radiation output fluctuations, etc., a projection data memory for storing output data of the preprocessing means, and data output from the preprocessing means or data read from the projection data memory. A reconstruction means that performs convolution and pack projection on the data, and data obtained after the convolution operation by the reconstruction means are accumulated and stored at pixel positions corresponding to the positions of the pack projections. an image memory for understanding the reconstructed image; a display means for displaying the image in the image memory; A means of obtaining a valued image and adding data on the radiation transmission path in the cross section of the object to determine the relationship between the detected radiation amount ratio and the length of the radiation transmission path in the cross section of the object, and from this relationship, the radiation quality. Determine the relationship between the detected amount of the detector due to hardening and the normal detected amount, process this by second-order differential processing, and determine the coefficient to be substituted into the above equation of the preprocessing device and the threshold value of the area where no correction for radiation quality hardening is performed. a correction coefficient determining means comprising a means for first applying the correction coefficient to the preprocessing means; and in a correction mode, controlling the preprocessing means to perform corrections other than the correction for the radiation hardening, and data obtained thereby. is stored in the projection data memory and a reconstructed image is obtained using this data, and then the correction coefficient determining means is activated to determine the radiation quality for the data in the projection data memory using the determined coefficients and threshold values. 1. A tomography apparatus comprising: a control means for controlling a preprocessing means to perform correction for hardening, and for controlling an image reconstruction using the corrected data.