JP2011209089A - Radiation tomographic method and radiation tomographic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify a work for radiation tomography, even if an object to be inspected cannot be moved in a plant piping inspection.SOLUTION: On the assumption that there is no to-be-inspected object, pseudo air data is generated by estimating a radiation intensity detected by a detection element at an arbitrary coordinate position (u, v) based on a distance H between a focus position of a radiation source and a position to which a focus of the radiation source is projected to a detector, the arbitrary coordinate position (u, v) on the detector, a coordinate position (u', v') of an air layer portion reflected to a transmission image data, and a radiation intensity I(u', v') at the coordinate position (u', v') of the air layer portion. An image reconstituting operation is implemented by using the pseudo air data. As a result, even if the object to be inspected object cannot be moved in the plant piping inspection, the work for the radiation tomography can be simplified.

Description

  The present invention relates to a radiation tomography method and a radiation tomography apparatus.

  To ensure the soundness of piping installed in power plants such as nuclear power and thermal power plants, chemical plants, and petroleum plants, X-ray CT equipment capable of tomography is used, and the inner surfaces of these piping are not destructed locally. The need for inspection is increasing. However, the plant piping is often installed in a narrow space. The conventional X-ray CT apparatus produces a tomographic image or a stereoscopic image based on a plurality of projection data obtained by imaging the periphery of the inspection object from an angle direction of 180 ° + radiation fan beam angle or generally 360 °. Due to the construction, the apparatus becomes larger. Therefore, it is difficult to apply an industrial X-ray CT apparatus to inspection of plant piping.

  On the other hand, Patent Document 1 discloses a method for tomographic imaging of local plant piping. In the method of Patent Document 1, it is possible to construct a tomographic image or a stereoscopic image by using a plurality of projection data captured only at an angle smaller than that required by the X-ray CT apparatus. In the pipe inspection, the radiation source and the detector are translated in the long axis direction of the pipe.

JP 2009-276285 A

  In the technique of Patent Document 1, a shield is provided on the upper surface of the radiation detector, and the channel constant is obtained from the relationship between the output of the channel with the shield and the output of other channels. And when the radiation tomography apparatus of patent document 1 calculates | requires a channel constant, this radiation tomography apparatus requires the "initial setting flow" which measures in the state without a subject.

  However, when photographing the local plant piping, the piping already installed cannot be removed. Therefore, in order to acquire the channel constant, it is necessary to move the radiation tomography apparatus to a location different from the subject imaging location. When the imaging apparatus is moved in this way, the imaging apparatus is assembled in a place where there is no subject, alignment is performed, a transmission image is captured, and a channel constant is calculated. Thereafter, the imaging apparatus is installed on the subject, and the subject is imaged after alignment. As described above, the imaging apparatus disclosed in Patent Document 1 has a problem that the setup and man-hours are large, the operation becomes complicated, and the usability is poor.

  An object of the present invention is to simplify the work of radiation tomography even when a subject cannot be moved as in a plant piping inspection.

In the present invention, the distance H between the focal position of the radiation source and the position at which the focal point of the radiation source is projected onto the detector, the arbitrary coordinate position (u, v) on the detector, and the air layer reflected in the transmission image data. When it is assumed that there is no subject based on the radiation intensity I _ref (u ′, v ′) of the coordinate position (u ′, v ′) of the part and the coordinate position (u ′, v ′) of the air layer part, Pseudo air data is generated by estimating the intensity of radiation detected by a detection element at an arbitrary coordinate position (u, v), and image reconstruction calculation is performed using the pseudo air data.

  According to the present invention, it is possible to simplify the radiation tomography work even when the subject cannot be moved as in a plant piping inspection.

It is a figure showing an example of the piping tomography apparatus. It is the figure which showed the concept of the imaging | photography condition by a piping tomography method. It is the figure which showed an example of the three-dimensional image constructed | assembled using the transmission image image | photographed with the piping tomography apparatus. It is the figure which showed an example of the permeation | transmission image of piping. It is a figure showing an example of air data. FIG. 6 is a diagram illustrating an example of an outline of a projection flow in the first embodiment. It is the figure typically demonstrated regarding the pseudo air data estimation method. It is the figure typically demonstrated regarding the pseudo air data estimation method. It is the figure typically demonstrated regarding the pseudo air data estimation method. It is a figure explaining the method in the case of acquiring the data for reference previously and referring. FIG. 10 is a diagram illustrating an example of an outline of a projection flow in Embodiment 2.

  The following embodiments relate to a radiation tomography apparatus and a radiation tomography method, and in particular, a radiation tomography apparatus suitable for visualizing and inspecting the inside of a structure installed at a specific place such as a pipe and the like. The present invention relates to a radiation tomography method.

  Here, an example of piping installed in a power plant will be described with reference to the drawings.

  FIG. 1 shows an outline of a radiation tomography apparatus 501. The apparatus of FIG. 1 shows the case where it installs in a straight pipe.

  The radiation source 1 and the detector 2 are attached by a slide mechanism 3a so as to sandwich the pipe 10 on which the heat insulating material 11 is attached. The slide mechanism 3a slides the radiation source 1 and the detector 2 in the pipe major axis direction by the scanner 3b supported by the instruction leg 3c. The slide mechanism 3 a is a device for sliding the radiation source 1 and the detector 2 in the radial direction of the pipe 10.

  The radiation tomography apparatus moves the radiation source 1 and the detector 2 at a constant speed, performs transmission image capturing at equal intervals during the movement, and acquires a plurality of transmission images 51. The control / image capturing device 21 performs control when capturing a transmission image by the scanner 3b or the detector 2. The storage device 31 stores the captured transparent image 51. Thereafter, the image reconstruction calculation device 22 calls the transmission image 51 from the storage device 31 and constructs a tomographic image or a stereoscopic image. The storage device 32 stores the constructed tomographic image or stereoscopic image. The image measuring device 23 calls a tomographic image (stereoscopic image) from the storage device 32 and performs defect evaluation. Here, the configuration of the control / image capturing device 21, the storage device 31, the image reconstruction calculation device 22, the storage device 32, and the image measurement device 23 shown in FIG. 1 is an example. For example, the storage devices 31 and 32 are the same. It is also possible to use a device. The storage devices 31 and 32 store transmission images, tomographic images, and the like as data.

  FIG. 2 shows the concept of imaging conditions by the radiation tomography apparatus 501. The radiation source 1 and the radiation detector 2 are translated in the long axis direction of the pipe 10, and the radiation detector 2 continuously takes a transmission image 51 of the pipe 10 at a constant interval. The image reconstruction calculation device 22 constructs a tomographic image or a three-dimensional image of a pipe from a set of photographed transmission images 51 using an installed image reconstruction calculation program. The image reconstruction calculation device 22 includes air layer data selection means, air layer data estimation means, storage means, attenuation rate calculation means, and reconstruction calculation means. FIG. 3 is a schematic diagram of the three-dimensional image 101 constructed by the image reconstruction calculation.

  4 and 5 show an example of a transmission image of piping and an example of air data, respectively. As shown in FIG. 4, the transmission image of the pipe is taken as a so-called X-ray photograph. On the other hand, since the air data is data that has passed through the air layer in the absence of the subject, the air data is displayed as an image with almost no change in shading as shown in FIG. A radiation tomography apparatus such as X-ray CT or laminography for pipe inspection scans a subject from each direction when scanning the subject. The radiation tomography apparatus uses data called attenuation rate obtained by logarithmically converting the air data by the respective transmission image data.

  A method for calculating the attenuation rate will be described below. Here, a two-dimensional planar detector (flat panel detector, FPD) is assumed as the detector. The FPD has a large number of minute radiation detection elements arranged vertically and horizontally. As shown in FIG. 4 or 5, the horizontal axis of the image is u, the vertical axis is v, and the attenuation rate at each coordinate is P (u, v). The radiation intensity detected at each coordinate position in the transmission image of the pipe (FIG. 4) is I (u, v), and the radiation intensity detected at each coordinate position in the air data (FIG. 5) is Io (u, v v). At this time, the relationship between P (u, v), I (u, v), and Io (u, v) is expressed by the following equation (1).

That is, the attenuation rate P (u, v) is a numerical value obtained at the position of each radiation detection element. There are a plurality of transmission images of the subject. Therefore, the radiation intensity corresponding to each transmission image is I _i (u, v) (i = 1,..., N). Accordingly, the same number of attenuation rate data as that of the transmission image of the subject exists, and is expressed by the following equation (2).

  Below, in order to simplify notation, it demonstrates based on the notation of (1) Formula.

  The physical meaning of P (u, v) is the rate at which X-rays and γ-rays attenuate as they pass through the subject. And it is shown by (3) Formula.

  Here, μ (x, y, z) represents a linear attenuation coefficient at the coordinate position (x, y, z) within the spatial calculation range in which the image reconstruction calculation is performed. The line attenuation coefficient represents the amount of attenuation when X-rays or γ-rays pass through the substance for a unit length. Further, s represents an integration path in line integration, and here corresponds to a straight line connecting the radiation source and one detection element focused on the FPD. A tomographic image or a three-dimensional image constructed by image reconstruction calculation represents the spatial distribution of the linear attenuation coefficient μ (x, y, z). For this reason, not only the transmission image of the subject but also air data when there is no subject is required. Although the FPD has been described here as an example, the same applies to other detectors such as an image intensifier.

  FIG. 6 shows an outline of the shooting flow. In this embodiment, pseudo air data is created from the air layer portion data reflected in the transmission image data of the pipe. For this reason, the imaging flow of this embodiment does not require the “initial setting flow” performed in Patent Document 1 and the accompanying alignment and the like. Specifically, in the process 1002, the radiation tomography apparatus 501 is mounted in order to photograph a predetermined piping location, and necessary alignment work is performed. Thereafter, processing 1003 performs pipe photography. Processes 1101 and 1102 extract data of the air layer portion reflected in the captured transmission image. Then, the processing 1101 and 1102 perform the radiation intensity detected by the detection element when there is no pipe with respect to a part (corresponding to a gray part on the transmission image) where X-rays are transmitted through the pipe and attenuated on the transmission image. The estimated pseudo air data 52 is obtained by the image reconstruction calculation device 22. In the process 1004, after performing processing such as logarithmic conversion using the obtained pseudo air data 52, the reconstruction calculation means of the image reconstruction calculation device 22 performs image reconstruction calculation. Since the processes 1101 and 1102 are automatically executed on the arithmetic device, no special work on site is required. For this reason, in this embodiment, the “initial setting flow” shown in Patent Document 1 and the work accompanying it can be reduced, so that the usability is improved.

  Next, an example of a specific method for realizing the processes 1101 and 1102 will be described with reference to FIGS. The processing 1101 and 1102 are performed by the image reconstruction calculation device 22.

  FIG. 7 shows the relationship between the radiation source 1, the position at which the focal point of the radiation source 1 is projected onto the detector 2, and the coordinate position (u, v) of one detection element on the detector 2. It is. Here, the origin O of the detector coordinates is a position where the focal point of the radiation source 1 is projected onto the detector 2. And in the part which X-ray permeate | transmitted piping, when it assumes that there is no piping, the intensity | strength of the radiation which a detection element detects is estimated.

  The positional relationship between the radiation source 1 and the detector 2 is that the distance between the focal position of the radiation source 1 and the position 0 where the focal point is projected onto the detector 2 is H, and the radiation detection intensity at the projection position 0 is Io (0, 0), the distance between the focal position of the radiation source 1 and the coordinate position (u, v) on the detector 2 is L, and the radiation detection intensity at the coordinate position (u, v) is Io (u, v).

  Here, the fact that the intensity of X-rays and γ-rays is inversely proportional to the square of the distance is utilized. And the above-mentioned coordinate and distance are expressed by the relationship of (4) Formula.

FIG. 8 schematically shows a method of estimating the intensity of radiation detected by the detection element at the coordinate position (u, v) when it is assumed that there is no pipe at the coordinate position (u, v) transmitted through the pipe. FIG. This estimation method uses data of the air layer portion (u ′, v ′) reflected in the transmission image of the pipe. As shown in the figure, the air layer data selection means selects the coordinate position (u ′, v ′) on the detector 2 from the air layer data, and the radiation intensity I _ref (u ′, v ′) at this position. ′) Is the reference data. At this time, Io (0, 0) is obtained from the equation (4) as follows.

  As a result, assuming that there is no pipe, the air layer data estimation means calculates an estimated value Io (u, v) of the radiation intensity detected by the detection element at an arbitrary coordinate position (u, v) as Io (0 , 0) and (4). This estimated value Io (u, v) becomes pseudo air data and is stored in the storage means. The attenuation rate calculation means calculates the attenuation rate at each coordinate of the detector based on the pseudo air data.

As described above, in this embodiment, the distance H between the focal position of the radiation source and the position at which the focal point of the radiation source is projected onto the detector, the arbitrary coordinate position (u, v) on the detector, and transmission image data. Based on the reflected radiation intensity I _ref (u ′, v ′) at the coordinate position (u ′, v ′) and the coordinate position (u ′, v ′) of the reflected air layer part, The pseudo air data is generated by estimating the intensity of the radiation detected by the detection element at an arbitrary coordinate position (u, v), and image reconstruction calculation is performed using the pseudo air data. Therefore, it is not necessary to remove the radiation tomography apparatus from the piping in order to obtain air data. Therefore, it is not necessary to perform alignment a plurality of times, setup and man-hours are reduced, and usability is improved. Thus, even when the subject cannot be moved as in the case of plant piping inspection, the radiation tomography work can be simplified.

(Modification of Example 1)
The above is a method applicable to an ideal case where there is no noise or the like. However, actually, the acquired data includes noise due to statistical fluctuation of radiation, noise due to the detector circuit, and the like. FIG. 9 is a method that takes into account noise included in acquired data when estimating the intensity of radiation detected by the detection element at the coordinate position (u, v) on the assumption that there is no piping. As in the above case, the coordinate position (u ′, v ′) on the detector 2 is selected from the air layer data, and the radiation intensity I _ref (u ′, v ′) at this position is used as the reference data. To do. If the distance from the origin of this position is r, and the angle between the origin and the straight u-axis connecting this point is θ, u ′, v ′, r and θ are expressed by the following relational expressions.

The dotted line shown in the figure indicates a circle having r as the radius and centered at the origin. I _ref (u ′, v ′) is data on a place on this circumference and corresponding to the air layer portion, and is taken as an average value thereof. By using the average value, the influence of noise can be reduced. Then, Io (0, 0) is calculated by the equation (5). The estimated value Io (u, v) of the radiation intensity at an arbitrary position (u, v) can be calculated from Io (0,0) and (4).

As another method for estimating the intensity of radiation detected by the detection element when it is assumed that there is no pipe, there is a method described below. A plurality of circles having the radius r described above may be used. Specifically, the reference radiation intensity I _ref (u ′, v ′) is obtained for a plurality of radii, and is interpolated from the data. And it is the method of calculating | requiring the estimated value Io (u, v) of the radiation intensity in arbitrary positions (u, v). At that time, as the number of reference radiation intensity values to be obtained increases, the accuracy of estimation by interpolation / extrapolation improves.

It is desirable to consider the influence of scattered radiation when selecting the reference data I _ref (u ′, v ′). Scattered rays are X-rays (or γ rays) scattered mainly by the interaction (Compton scattering) between electrons inside the subject and transmitted X-rays (or γ rays). The influence of scattered radiation is large near the subject and may be significantly higher than the actual air layer value. For this reason, when selecting reference data, it is desirable not to use data in the vicinity of the subject.

  Further, when imaging a subject that is larger than the radiation angle of the radiation source 1 or the detection surface size of the detector 2, it is necessary to move the radiation source 1 or the detector 2 so that the entire subject is accommodated. . In such a case, it is possible to apply the method described in the present embodiment if imaging is performed so that an air layer is reflected at both ends of the subject.

  With the above method, air data acquisition can be simplified because air data can be constructed from data at the time of subject imaging without separately acquiring air data.

  10 and 11 show another embodiment. In this embodiment, air data is acquired in advance in the absence of a subject at least once. This air data is reference air data. Then, in actual imaging, pseudo air data is created by comparing the air layer data reflected during imaging of the subject and the reference air data.

  First, in process 1001, reference air data is acquired in advance in the absence of a subject. In processes 1002 and 1003, the photographing apparatus is mounted on the pipe and the pipe is photographed. In processing 1101a, the data comparison unit of the image reconstruction calculation device 22 compares the reference air data with the transmission image data. Then, the process 1102 creates pseudo air data. Thereafter, in process 1004, the image reconstruction calculation device 22 performs a reconstruction calculation.

  Here, the processing content of the processing 1101a will be described. As shown in FIG. 10, the data comparison means extracts line profiles of the same portion (line segment AA) of the reference air data and the transmission image data, and compares the data. And a data comparison means produces | generates the line profile of the pseudo air data in line segment AA. It should be noted that the detector output values may not match between the air layer portion B of the reference air data and the transmission image data. However, the qualitative trends of the profiles are consistent. Therefore, by applying the profile shape of the reference data based on the value of the air layer portion of the transmission image data, the pseudo air data can be constructed with high accuracy.

  Since the apparatus is assembled locally, there may be a “deviation” in the position at which the radiation source 1 is projected onto the detector 2 during reference air data acquisition and pipe inspection. Therefore, it is desirable to know alignment information such as the position at which the radiation source 1 is projected onto the detector 2 when acquiring the reference air data. If this alignment information is grasped, “deviation” can be grasped quantitatively. Then, when constructing the pseudo air data, it is possible to perform profile fitting in consideration of the “deviation” amount.

  In addition, depending on the imaging target, the voltage of the X-ray generator and the energy of the γ-ray source may be changed. It is desirable to know in advance the detector output relative to the radiation energy of the detector. It is also possible to fit the profile according to the relationship of the detector output to the radiation energy of the radiation source.

  Moreover, the acquisition of the reference air data can be reduced by carrying out the apparatus before carrying it into the site, for example, in advance at the place of delivery, for example. If the reference air data is created once before the device is brought into the field, it is not necessary to re-create it every time it is inspected on site.

  In this embodiment, reference air data is acquired, pseudo air data is created by comparing line profiles in the same part of the reference air data and the transmission image data, and image reconstruction is performed using the pseudo air data. Perform the operation. By using a combination of transmission image data and reference air data, pseudo air data can be constructed with higher accuracy.

  According to the method of this embodiment, pseudo air data can be constructed with high accuracy, and air data acquisition can be simplified.

  By using the method and apparatus of the present invention, when tomography is performed in a narrow place such as piping of a power plant, efficient inspection can be performed by reducing setup and man-hours associated with imaging, and improving usability. Become. The method of the present invention can also be applied to a system that obtains a tomographic image by rotating a subject on a turntable, such as an industrial X-ray CT apparatus.

DESCRIPTION OF SYMBOLS 1 Radiation source 2 Detector 10 Piping 21 Control and image capture device 22 Image reconstruction calculation device 23 Image measurement device 31, 32 Storage device 51 Transmission image 52 Pseudo air data 101 Three-dimensional image 501 Radiation tomography apparatus 1001, 1002, 1003 , 1004, 1101, 1102

Claims (5)

A radiation tomography method for constructing a tomographic image or a three-dimensional image of the subject from the captured transmission image data of the subject, wherein a radiation source and a radiation detector are arranged oppositely across the subject,
The distance H between the focal position of the radiation source and the position at which the focal point of the radiation source is projected onto the detector, an arbitrary coordinate position (u, v) on the detector, and the air reflected in the transmitted image data Based on the coordinate position (u ′, v ′) of the layer portion and the radiation intensity I _ref (u ′, v ′) at the coordinate position (u ′, v ′) of the air layer portion, it is assumed that the subject is not present. A pseudo air data is generated by estimating the intensity of radiation detected by the detection element at the arbitrary coordinate position (u, v),
A radiation tomography method, wherein image reconstruction calculation is performed using the pseudo air data. The radiation tomography method according to claim 1,
The radiation tomography method characterized in that the radiation intensity I _ref (u ′, v ′) is obtained by sampling the circumference of a circle centered on the position where the focal point of the radiation source is projected onto the detector. . A radiation tomography apparatus for constructing a tomographic image or a three-dimensional image of the subject from the captured transmission image data of the subject by arranging a radiation source and a radiation detector oppositely across the subject,
The image reconstruction calculation device includes a distance H between a focal position of the radiation source and a position at which the focal point of the radiation source is projected onto the detector, an arbitrary coordinate position (u, v) on the detector, and the transmission. Based on the coordinate position (u ′, v ′) of the air layer portion reflected in the image data and the radiation intensity I _ref (u ′, v ′) of the coordinate position (u ′, v ′) of the air layer portion, Air layer data estimation means for estimating the intensity of radiation detected by the detection element at the arbitrary coordinate position (u, v) and generating pseudo air data, assuming that there is no subject;
A radiation tomography apparatus comprising: a reconstruction calculation unit that performs an image reconstruction calculation using the pseudo air data. A radiation tomography method for constructing a tomographic image or a three-dimensional image of the subject from the captured transmission image data of the subject, wherein a radiation source and a radiation detector are arranged oppositely across the subject,
Get reference air data in advance,
Compare the line profile in the same part of the reference air data and the transmission image data to create pseudo air data,
A radiation tomography method, wherein image reconstruction calculation is performed using the pseudo air data. A radiation tomography apparatus for constructing a tomographic image or a three-dimensional image of the subject from the captured transmission image data of the subject by arranging a radiation source and a radiation detector oppositely across the subject,
The image reconstruction calculation device
Data reference means for comparing the line data in the same part of the transmission image data and creating pseudo air data by comparing the reference air data acquired in advance;
A radiation tomography apparatus comprising: a reconstruction calculation unit that performs an image reconstruction calculation using the pseudo air data.

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