Substance identification device and substance identification method

Abstract

The objective is to provide a substance identification device and a substance identification method that can identify substances even when multiple substances with similar X-ray transmission characteristics are present. [Solution] The substance identification device of the present invention is characterized by comprising: an image acquisition unit that images an object to be measured with X-rays of different energies and acquires at least one cross-sectional image for each energy; a shape determination unit that determines the shape of the object to be measured based on the cross-sectional image; a substance limiting unit that limits a coordinate range formed by connecting coefficients corresponding to a plurality of pre-registered substances in a substance identification map composed of coefficients obtained by converting the pixel values ​​of the cross-sectional image to coefficients of standard substances, based on the bulk density obtained from the shape of the object to be measured; and a substance identification unit that determines whether or not the value of the substance composition ratio calculated from the coefficients obtained by converting the pixel values ​​is included in the coordinate range limited by the substance limiting unit.

Description

[Technical Field]

[0001] The present invention relates to a substance identification device and a substance identification method. [Background technology]

[0002] As a technique for evaluating the amount of a target substance contained in a mixture composed of multiple substances, the technique described in Patent Document 1 can be cited. Patent Document 1 discloses a technique in which "an X-ray CT apparatus of an embodiment displays an image within an object based on projection data obtained by scanning the object, and has a generation unit, a conversion unit, an image forming unit, and a identification unit. The generation unit generates multiple projection data by scanning the object with X-rays of different energies. The conversion unit converts the multiple projection data into multiple new projection data corresponding to multiple reference substances. The image forming unit forms multiple reference substance images corresponding to multiple reference substances by reconstructing the multiple new projection data converted by the conversion unit. The identification unit identifies the target substance based on the correlation of the pixel values ​​of the multiple reference substance images." [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2013 / 047403 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Patent Document 1 states that when there are multiple target substances and multiple substances with similar X-ray transmission characteristics and overlapping coordinate positions exist in a reference substance image (hereinafter referred to as a substance identification map), it becomes difficult to identify the substances.

[0005] The object of the present invention is to provide a substance identification device and a substance identification method that can identify substances even when there are multiple substances with similar X-ray transmission characteristics. [Means for solving the problem]

[0006] The substance identification device of the present invention is characterized by comprising: an image acquisition unit that images an object to be measured with X-rays of different energies and acquires at least one cross-sectional image for each energy; a shape determination unit that determines the shape of the object to be measured based on the cross-sectional image; a substance limiting unit that limits a coordinate range formed by connecting coefficients corresponding to a plurality of pre-registered substances in a substance identification map composed of coefficients obtained by converting the pixel values ​​of the cross-sectional image to coefficients of standard substances, based on the bulk density obtained from the shape of the object to be measured; and a substance identification unit that determines whether or not the value of the substance composition ratio calculated from the coefficients obtained by converting the pixel values ​​is included in the coordinate range limited by the substance limiting unit.

[0007] Furthermore, the substance identification device of the present invention is characterized by comprising: an image acquisition process that images an object to be measured with X-ray CT of different energies and acquires a plurality of acquired cross-sectional images; a shape determination process that determines the shape of the object to be measured based on the plurality of cross-sectional images, at least one of which has been acquired for each energy; a limiting processing unit that limits the coordinate range formed by connecting the coefficients corresponding to a plurality of pre-registered substances in a substance identification map composed of coefficients obtained by converting the pixel values ​​on the plurality of cross-sectional images acquired in the image acquisition process, based on the bulk density obtained from the shape of the object to be measured; and a substance identification processing unit that determines whether or not the value of the substance composition ratio calculated from the coefficients obtained by converting the pixel values ​​is included in the coordinate range limited by the limiting processing unit.

[0008] Furthermore, the present invention provides a method for identifying a substance, characterized by imaging an object to be measured with X-rays of different energies, acquiring at least one cross-sectional image for each energy, determining the shape of the object to be measured based on the cross-sectional image, limiting a coordinate range formed by connecting the coefficients corresponding to a plurality of pre-registered substances in a substance identification map composed of coefficients obtained by converting the pixel values ​​of the cross-sectional image to coefficients of standard substances, based on the bulk density obtained from the shape of the object to be measured, and determining whether the value of the substance composition ratio calculated from the coefficients obtained by converting the pixel values ​​is included within the limited coordinate range.

Advantages of the Invention

[0009] According to the present invention, even when there are a plurality of substances having similar X-ray transmission characteristics, it is possible to provide a substance identification device and a substance identification method capable of identifying substances.

[0010] Problems, configurations, and effects other than those described above will be clarified by the description of the following embodiments.

Brief Description of the Drawings

[0011] [Figure 1] An example of a configuration diagram of a substance identification device according to Example 1 is shown. [Figure 2] Another example of an X-ray source and a radiation detector is shown. [Figure 3] A flowchart of a substance identification process according to Example 1 is shown. [Figure 4] It is a diagram for explaining an example of the operation of a shape determination unit according to Example 1. [Figure 5] It is a diagram for explaining an example of the operation of a substance limitation unit and a substance identification unit according to Example 1. [Figure 6] An example of a configuration diagram of a substance identification device according to Example 2 is shown. [Figure 7] A flowchart of a substance identification process according to Example 2 is shown. [Figure 8] An explanatory diagram for explaining an example of X-ray transmission amount calculation according to Example 2.

Modes for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments are examples for explaining the present invention, and for the sake of clarity of explanation, appropriate omissions and simplifications have been made. The present invention can be implemented in various other forms. Unless otherwise particularly limited, each component may be singular or plural.

[0013] In the drawings, the positions, sizes, shapes, ranges, etc. of the respective components shown may not represent the actual positions, sizes, shapes, ranges, etc. in order to facilitate understanding of the invention. Therefore, the present invention is not necessarily limited to the positions, sizes, shapes, ranges, etc. disclosed in the drawings.

Example

[0014] In this example, an example of specifying the amount of a substance contained in a container containing substances of any shape and composition is shown.

[0015] FIG. 1 is an example of a configuration diagram of a substance identification device according to Example 1. In the substance identification device, a measurement object 100 is installed on a rotary table 120, and an X-ray source A111 and an X-ray source B112 using different X-ray energies, and a radiation detector 130 are installed so as to sandwich the measurement object 100. Further, an optical camera 150 for observing the measurement object 100 and the rotary table 120 is installed.

[0016] It is connected to a control unit 140 that controls the X-ray source A111, the X-ray source B112, the radiation detector 130, and the optical camera 150.

[0017] The control unit 140 includes an image acquisition unit 141 that acquires different X-ray CT images, a shape determination unit 142 that determines the shape of the measurement object from the CT images that are pixel values, and a substance limitation unit 143 that limits candidate substances constituting the measurement object 100 from information on the shape and bulk density (apparent density) of the measurement object 100. Further, it includes a substance identification unit 144 that identifies the substance of the measurement object from the limited candidate substances. The X-ray image may be a single cross-section, but the accuracy can be improved with a plurality of CT images.

[0018] In this example, it is assumed that the X-ray source A111 handles lower X-ray energy than the X-ray source B112. The energies of the X-ray source A111 and the X-ray source B112 are made different so as to exceed the error range due to conditions such as measurement and device arrangement.

[0019] The bulk density of a material can be obtained using at least one of the following: a database, X-ray CT, and an optical camera.

[0020] The image acquisition unit 141 synchronizes the X-ray source A111, X-ray source B112, radiation detector 130, and rotary table 120, and controls the rotation of the rotary table 120 to irradiate the object to be measured 100 with X-rays from a 360-degree direction, so that the amount of X-ray transmission can be measured by the radiation detector.

[0021] Then, the system controls the acquisition of a CT image by reconstructing the image from the measured X-ray transmission amount. At this time, the pixel value (CT value) of the CT image is expressed by equation (1). CT value = ln(I0 / I) / t = μ ···(1) Here, I0 is the X-ray dose irradiated from the X-ray source, I is the X-ray transmission amount detected by the radiation detector, t is the pixel size, and μ is the linear attenuation coefficient of the object being measured (100). The CT value is calculated by dividing the natural logarithm of I0 / I by t.

[0022] The shape determination unit 142, the material limitation unit 143, and the material identification unit 144 will be explained in detail using Figures 3, 4, and 5, respectively.

[0023] Figure 2 shows another example of an X-ray source and radiation detector. This is an example of a different combination of X-ray source and radiation detector configuration for a material identification device. In Figure 1, two X-ray sources A111 and B112 were used, but this example uses only one X-ray source.

[0024] In an example where the X-ray energy is changed using an absorber, the configuration involves placing an absorber 114 between a single X-ray source 113 and a radiation detector 130. In this case, by removing the absorber or replacing it with an absorber of a different material or thickness, the same results as those obtained by imaging with X-ray sources A111 and B112 can be obtained.

[0025] Furthermore, in the example where X-ray energy is discriminated using a radiation detector, the configuration consists of a single X-ray source 113 and an energy-discriminating radiation detector 131 having a signal processing circuit for discriminating energy. In this case, since the X-ray energy emitted from a single X-ray source forms a continuous energy spectrum, the same results as those obtained by imaging with X-ray sources A111 and B112 can be obtained by measuring the amount of X-ray transmission for each energy using the energy-discriminating radiation detector 131.

[0026] In this way, by using X-ray sources that emit different energies, absorbers that change the X-ray energy, or radiation detectors that can discriminate X-ray energy, it is possible to image the object to be measured with X-rays of different energies.

[0027] Figure 3 shows a flowchart of the substance identification process according to Example 1. In step S1, the image acquisition unit 141 acquires CT images of two or more energies.

[0028] In step S2, the shape determination unit 142 identifies the shape of the object to be measured from the CT image.

[0029] In step S3, the material limiting unit 143 limits the coordinate range on the material identification map, which is composed of coefficients obtained by converting pixel values ​​(CT values) on multiple cross-sectional images acquired in the image acquisition process, based on the bulk density determined from the shape identified in step S2, by connecting values ​​(material composition ratios) corresponding to multiple pre-registered materials.

[0030] In this embodiment, a substance identification map is used as an example to clearly explain the determination process. However, the determination can be made by calculation, without being limited to creating a substance identification map.

[0031] In step S4, the substance identification unit 144 calculates the substance composition ratio corresponding to the object to be measured based on the pixel values ​​(CT values) of the CT image acquired in step S1, determines whether the calculated substance composition ratio falls within the coordinate range limited in step S3, and identifies the substances contained in the object to be measured.

[0032] Figure 4 illustrates an example of the operation of the shape determination unit according to Embodiment 1. One method for determining the shape is to create a plot with the CT value and the error in the CT value on two axes. The error in the CT value is a standardized value according to the size of the object being measured. In this case, when the size of the object being measured is larger than the pixel size of the CT image (block 310), the CT value and the error in the CT value are linearly proportional. When the size of the object being measured is smaller than the pixel size of the CT image (powder 320), the error in the CT value becomes larger than linearly proportional.

[0033] Alternatively, in addition to the method shown in Figure 4, if the object to be measured is in a container, methods can be used to distinguish between powder if it conforms to the shape of the container and lumps if it does not. Another method involves changing the threshold value of the CT value and using that threshold to perform binarization and contour extraction for determination. Furthermore, if the inside of the object to be measured is observed with an optical camera, methods can be used to determine the shape by observing it with the optical camera.

[0034] Figure 5 illustrates an example of the operation of the substance limiting unit and the substance identification unit according to Example 1. The substance limiting unit 143 creates a substance identification map composed of coefficients obtained by converting the CT values. There are various ways to define the axes of the substance identification map, but one example is the ratio of CT values. The horizontal and vertical axes of the substance identification map are determined from equations (2) and (3). CT(E L ) = μ1(E L )c1+μ2(E L )c2···(2) CT(E H ) = μ1(E H )c1+μ2(E H )c2···(3) Here, E Lis the low-energy X-ray energy, E H is the high-energy X-ray energy, μ1 is the mass attenuation coefficient of the first standard substance, and μ2 is the mass attenuation coefficient of the second standard substance. Also, CT(E L ) is the CT value obtained from Equation 1 when irradiating the X-ray source A111, and CT(E H ) is the CT value obtained from Equation 1 when irradiating the X-ray source B112.

[0035] The axis of the substance identification map is, for example, CT(E L ) which is the CT value of Equation (2), and the ratio of the CT value obtained by dividing Equation (2) by Equation (3), which is CT(E L ) / CT(E H ), or CT(E H ) which is the CT value of Equation (3), and the ratio of the CT value obtained by dividing Equation (3) by Equation (2), which is CT(E H ) / CT(E L ), or any combination thereof, etc. can be taken.

[0036] At this time, the mixture of substance A, substance B, and air becomes the coordinate range connecting the points of substance A, substance B, and air, and considering the bulk density, the coordinate range is limited to coordinate range 450. Also, the mixture of substance B, substance C, and air becomes the coordinate range connecting the points of substance B, substance C, and air, and considering the bulk density, the coordinate range is limited to coordinate range 460. In the information composed of the coefficients of the first standard substance and the second standard substance, among the coordinate ranges including the measured points, by limiting the coordinate range considering the bulk density, even when there are a plurality of substances with similar X-ray transmission characteristics, the substances can be identified. In this embodiment, although connected by a straight line, it becomes a curve when the particle shapes of substance A and substance B are different.

[0037] In the substance specifying unit, the substance is specified based on the coordinate range limited by the substance limiting unit. For example, assuming that point 410 is obtained from Equations (2) and (3). In this case, since it is located within the coordinates connecting substance A, substance B, and substance C, it can be understood that the measurement object is a mixture of substance A, substance B, and substance C that does not contain air (the bulk density and the true density are the same).

[0038] If point 420 is obtained, it can be determined that the object being measured is either substance A, substance B, and air, or a mixture of substance A, substance C, and air. In this case, the mixture of substance A, substance B, and air can take on coordinate range 450 in Figure 5 if its bulk density is 60-80% of substance A (porosity 40-20%) and 40-70% of substance B (porosity 60-30%). Coordinate range 450 is the range of bulk densities that each substance can take. In other words, coordinate range 450 is the range that the mixture of substance A, substance B, and air can take.

[0039] A mixture of substance A, substance C, and air can have a coordinate range of 460 if its bulk density is 20-50% of substance A (porosity 80-50%) and 30-50% of substance C (porosity 70-50%). In this way, the bulk density allows us to determine the ratio of multiple substances to air and identify the substances.

[0040] Since point 420 is located within the coordinate range 450, it can be determined that it is a mixture of substance A, substance B, and air. Furthermore, by calculating the coefficients when the substance determined in the substance limiting section is used as a standard substance, the composition ratio of the substances can be calculated.

[0041] As described above, this embodiment provides a substance identification device and substance identification method that can identify substances even when there are multiple substances with similar X-ray transmission characteristics. This is achieved by having an image acquisition unit that images an object to be measured with X-rays of different energies and acquires at least one cross-sectional image for each energy; a shape determination unit that determines the shape of the object to be measured based on the cross-sectional image; a substance limitation unit that limits a coordinate range formed by connecting coefficients corresponding to a plurality of pre-registered substances, based on the bulk density determined from the shape of the object to be measured, using information composed of coefficients obtained by converting the pixel values ​​of the cross-sectional image; and a substance identification unit that determines whether the substance composition ratio calculated from the coefficients obtained by converting the pixel values ​​is included within the coordinate range limited by the substance limitation unit. [Examples]

[0042] This example illustrates the detection of powdered explosives contained in carry-on luggage.

[0043] Figure 6 shows an example of the configuration diagram of the substance identification device according to Example 2. There are three differences from Example 1. First, the table 620 on which the object to be measured is placed does not have a rotation function. Second, the image acquired during image acquisition is not a CT image, but an X-ray transmission image, which is an X-ray transmission image that is the pixel value of the measured X-ray transmission amount. Third, an X-ray transmission amount calculation unit 645 is added to determine the X-ray transmission amount for each substance from the X-ray transmission image.

[0044] Figure 7 shows a flowchart of the substance identification process according to Example 2. There are three differences from Example 1. First, the CT image becomes an X-ray transmission image. Second, the CT value becomes the X-ray transmission amount. Third, a step S73 is added in which the difference in X-ray transmission amount is calculated from overlapping regions in the X-ray transmission image.

[0045] Figure 8 shows an explanatory diagram illustrating an example of X-ray transmission amount calculation according to Example 2. Assume that the object to be measured is a container 800 of any shape containing three substances. In this case, the X-ray transmission amount of substance 801 is the value obtained by subtracting the X-ray transmission amount at the location where only container 800 is present from the X-ray transmission amount at the location where both container 800 and substance 801 are present. The X-ray transmission amount of substance 802 is the value obtained by subtracting the X-ray transmission amount at the location where only container 800 is present from the X-ray transmission amount at the location where both container 800 and substance 802 are present. The X-ray transmission amount of substance 803 is the value obtained by subtracting the X-ray transmission amount at the location where both container 800 and substance 802 are present from the X-ray transmission amount at the location where container 800, substance 803, and substance 802 are present.

[0046] Unlike Example 1, in this Example 2, it is not necessary to image the object to be measured from different angles, thus enabling material identification in a shorter measurement time.

[0047] As described above, in this embodiment, an image acquisition process is provided which images an object to be measured with X-ray CT of different energies and acquires multiple cross-sectional images; a shape determination process is provided which determines the shape of the object to be measured based on the multiple cross-sectional images, at least one of which has been acquired for each energy; a limiting processing unit is provided which uses information composed of coefficients obtained by converting the pixel values ​​on the multiple cross-sectional images acquired in the image acquisition process to limit the coordinate range formed by connecting the coefficients corresponding to a plurality of pre-registered substances, based on the bulk density determined from the shape of the object to be measured; and a substance identification processing unit is provided which determines whether the substance composition ratio calculated from the coefficients obtained by converting the pixel values ​​is included in the coordinate range limited by the limiting processing unit. This makes it possible to provide a substance identification device and a substance identification method that can identify substances even when there are multiple substances with similar X-ray transmission characteristics. [Explanation of Symbols]

[0048] 100...Object to be measured, 111...X-ray source A, 112...X-ray source B, 120... Rotating table, 130... Radiation detector, 140... Control unit, 150... Optical camera.

Claims

1. An image acquisition unit that images the object to be measured with X-rays of different energies and acquires at least one cross-sectional image for each energy, A shape determination unit that determines the shape of the object to be measured based on the cross-sectional image, In a substance identification map obtained by converting the pixel values ​​of the cross-sectional image into coefficients of standard substances, a substance limiting section limits the coordinate range formed by connecting the coefficients corresponding to a plurality of pre-registered substances based on the bulk density obtained from the shape of the object to be measured, A substance identification device characterized by having a substance identification unit that determines whether the value of the substance composition ratio calculated from the coefficient obtained by converting the pixel value is included within the coordinate range limited by the substance limiting unit, thereby identifying the substance contained in the object to be measured.

2. In the substance identification device according to claim 1, The material identification device is characterized in that the image acquisition unit images the object to be measured using X-ray CT of different energies and acquires a CT image.

3. In the substance identification device according to claim 1, The material identification device is characterized in that the image acquisition unit comprises an X-ray source that irradiates with different energies, an absorber that changes the X-ray energy, or a radiation detector capable of discriminating X-ray energy, as means for imaging the object to be measured with X-rays of different energies.

4. In the substance identification device according to claim 1, The material identification device is characterized in that the shape determination unit acquires information on the bulk density of the material using at least one of a database, X-ray CT, and optical camera.

5. In the substance identification device according to claim 1, The substance limiting unit is characterized in that, in a substance identification map composed of coefficients of a first standard substance and a second standard substance, the coordinate range including the measured point is limited by taking into consideration bulk density.

6. Image acquisition processing involves imaging the object to be measured using X-ray CT at different energies and obtaining multiple cross-sectional images from the acquired images. A shape determination process that determines the shape of the object to be measured based on a plurality of cross-sectional images, at least one of which is acquired for each energy level, In a substance identification map composed of coefficients obtained by converting pixel values ​​on multiple cross-sectional images acquired in the image acquisition process into coefficients of standard substances, a limiting processing unit limits the coordinate range connecting the coefficients corresponding to multiple pre-registered substances based on the bulk density obtained from the shape of the object to be measured, A substance identification device characterized by having a substance identification processing unit that determines whether the value of the substance composition ratio calculated from the coefficient obtained by converting the pixel value is included in the coordinate range limited by the limiting processing unit, thereby identifying the substance contained in the object to be measured.

7. The object to be measured is imaged with X-rays of different energies, and at least one cross-sectional image is acquired for each energy level. Based on the aforementioned cross-sectional image, the shape of the object to be measured is determined. In a substance identification map composed of coefficients obtained by converting pixel values ​​on the cross-sectional image into coefficients of standard substances, the coordinate range connecting the coefficients corresponding to a plurality of pre-registered substances is limited based on the bulk density obtained from the shape of the object to be measured. A method for identifying a substance, characterized by determining whether the value of the material composition ratio calculated from the coefficient obtained by converting the pixel value is included within the limited coordinate range.

8. In the method for identifying a substance according to claim 7, A method for identifying a substance, characterized in that when acquiring the cross-sectional image, the object to be measured is imaged using X-ray CT of different energies, and a CT image is acquired.

9. In the method for identifying a substance according to claim 7, A method for identifying a substance, characterized in that when acquiring the cross-sectional image, the image is acquired using an X-ray source that irradiates with different energies, an absorber that changes the X-ray energy, or a radiation detector capable of discriminating X-ray energy.

10. In the method for identifying a substance according to claim 7, A method for identifying a substance, characterized in that, when determining the shape of the object to be measured, information on the bulk density of the substance is obtained by at least one of a database, X-ray CT, and optical camera.

11. In the method for identifying a substance according to claim 7, A method for identifying a substance, characterized in that, when limiting the coordinate range, the coordinate range is limited by considering bulk density within the coordinate range that includes the measured point, using information composed of coefficients of a first standard substance and a second standard substance.

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