JP2024071997A - X-ray device and material classification method using X-rays - Google Patents

Abstract

To provide an X-ray device capable of confirming an outer shape of an inspection object and classifying a material composing the inspection object, and to provide a material classification method using the X-ray device in the X-ray device performing inspection by using X rays.SOLUTION: A material classification method includes an X-ray detection unit and a control unit that arranges an X-ray output unit outputting X rays at a predetermined output value and a predetermined number of detection elements one-dimensionally, detects the X rays by each pixel with one detection element as one pixel, and obtains pixel information regarding a total energy amount showing magnitude of the entire energy of the X rays and a high energy amount showing magnitude of energy at a predetermined value or larger. The control unit applies the X rays to a storage container traveling on a conveyance conveyor, detects transmission X rays through the storage container and acquires the pixel information regarding the transmission X rays from the X-ray detection unit, obtains a change rate of an attenuation coefficient of an object housed in the storage container on the basis of the pixel information, and classifies the object into a predetermined material.SELECTED DRAWING: Figure 1

Description

The present invention relates to the configuration of an X-ray device and a material classification method using the same, and in particular to technology that is effective when applied to the inspection of luggage such as hand luggage and parcels.

X-ray devices are used to check objects stored in containers at baggage inspection areas at airports and other locations. Typically, X-rays are irradiated onto the container, and the transmitted X-rays are obtained to confirm the outer shape of the object.

In this type of inspection, only the external shape of the object can be determined, and the mass of the object cannot be confirmed, making it difficult to determine whether it is a dangerous object or not.

As background technology in this technical field, for example, there is technology such as that in Patent Document 1. Patent Document 1 discloses "an X-ray inspection device that irradiates an inspection object with X-rays from an X-ray irradiation unit, acquires the transmitted X-rays that have passed through the inspection object with an X-ray detection unit, estimates the mass of the inspection object based on the X-ray amount of the acquired transmitted X-rays, and determines whether the estimated mass of the inspection object belongs to any mass class within a predetermined range that has been set in advance."

JP 2010-145135 A

According to the technology of Patent Document 1, when a single object to be inspected exists, it is possible to estimate the mass of the object to be inspected.

However, if the material of the object being inspected is unknown or if multiple objects are mixed in the same storage container, it is not possible to estimate the mass of each object.

The object of the present invention is to provide an X-ray device that performs inspections using X-rays and is capable of classifying the material that constitutes an object to be inspected while checking the external shape of the object, and a material classification method using the same.

In order to solve the above problems, the present invention includes an X-ray output unit that outputs X-rays at a predetermined output value, an X-ray detection unit that linearly arranges a predetermined number of detection elements, with each detection element being one pixel, detects the X-rays at each pixel, and obtains pixel information related to the total energy amount indicating the magnitude of the overall energy of the X-rays and the high energy amount indicating the magnitude of energy equal to or greater than a predetermined value, and a control unit, and the control unit instructs the X-ray output unit to irradiate the X-rays onto a storage container moving on a transport conveyor, detects the transmitted X-rays that have passed through the storage container, obtains the pixel information for the transmitted X-rays from the X-ray detection unit, and calculates the rate of change in the attenuation coefficient of an object stored in the storage container based on the pixel information, and classifies the object into one of the predetermined materials.

The present invention also provides a material classification method using X-rays, which includes the steps of: (a) irradiating a storage container moving on a transport conveyor with X-rays and detecting the transmitted X-rays that have passed through the storage container to obtain pixel information for the transmitted X-rays; (b) determining the rate of change in the attenuation coefficient of an object stored in the storage container based on the pixel information obtained in step (a); and (c) classifying the object into one of the predetermined materials based on the rate of change in the attenuation coefficient determined in step (b).

The present invention provides an X-ray device that performs inspections using X-rays, and is capable of classifying the material that constitutes an object to be inspected while checking the outer shape of the object, and a material classification method using the same.

This allows not only checking the external shape of the object being inspected, but also classifying the material of the object and estimating the mass of each material, helping to determine whether the object is dangerous and contributing to preventing crimes, etc.

Problems, configurations, and advantages other than those described above will become clear from the description of the embodiments below.

1 is a diagram showing an overall outline of an X-ray device according to a first embodiment of the present invention; FIG. 2 is a perspective view showing X-ray irradiation by the X-ray device of FIG. 1. FIG. 2 is a diagram showing an X-ray irradiation unit of the X-ray device of FIG. 1 . 11 is a diagram showing a method for storing the total energy amount and the high energy amount of transmitted X-rays in a storage unit. FIG. FIG. 13 is a diagram showing a method for arranging the change rate of the attenuation coefficient of each pixel information. FIG. 13 is a diagram showing a method for classifying materials using material classification clusters. FIG. 13 is a diagram showing a method of arranging material classification information for each pixel in memory area T1. FIG. 13 is a diagram showing a method for rearranging the normalized total energy for each material. FIG. 13 is a diagram showing a method for calculating a unit mass coefficient. FIG. 13 is a diagram showing a mass correlation coefficient setting curve for each material. FIG. 13 is a diagram showing an example of a material classification cluster. FIG. 1 is a diagram showing a method for detecting an X-ray energy amount by a photon counting method. FIG. 1 is a diagram showing a method for detecting an X-ray energy amount by a scintillator method. FIG. 11 is a diagram showing a material classification method according to a second embodiment of the present invention.

Below, an embodiment of the present invention will be described with reference to the drawings. Note that the same components in each drawing will be given the same reference numerals, and detailed descriptions of overlapping parts will be omitted.

The X-ray device according to the first embodiment of the present invention and the material classification method using the same will be described with reference to Figures 1 to 13.

First, the basic concept of the present invention will be explained using Figures 12 and 13.

The present invention irradiates a storage container with X-rays to obtain transmitted X-rays, obtains the total energy amount and high-energy amount of transmitted X-rays within a unit time, calculates the attenuation coefficient for the total energy amount and the attenuation coefficient for the high-energy amount, divides the attenuation coefficient for the high-energy amount by the attenuation coefficient for the total energy amount to calculate the rate of change of the attenuation coefficient, and estimates the material of the target object based on the rate of change.

X-rays, a type of electromagnetic wave, have the dual nature of wave and particle behavior, just like normal light. The present invention utilizes the particle behavior. X-rays, as a particle beam, have particles, that is, X-ray photons. Each X-ray photon has energy. In the present invention, the amount of energy is defined as the aggregate of energy formed by the aggregation of multiple X-ray photons.

The following relationship holds between the amount of energy I0 of X-rays irradiated to an object within a unit time and the amount of energy I of transmitted X-rays that penetrate the object and are obtained by irradiating the object with X-rays.

I = I0exp(-μx)
Here, μ is the attenuation coefficient, and x is the thickness of the object.

Therefore, the attenuation coefficient can be calculated using the formula μ =- ln(I/I0)/x.

In addition, even if X-rays are emitted at a constant output value from the X-ray output unit that outputs X-rays, the energy of each X-ray photon is not the same, and they are classified into X-ray photons with large energy (high energy) and X-ray photons with small energy (low energy).

In the present invention, the X-rays transmitted through the object are acquired separately as a total energy amount, which indicates the total amount of energy, and a high energy amount, which indicates the total amount of high-energy X-ray photons, and the attenuation coefficients of each are calculated, and the rate of change is calculated.

In addition, clusters are prepared in advance to classify objects according to the rate of change of the attenuation coefficient, and the material of the object is classified according to which cluster the actually calculated rate of change belongs to.

If the attenuation coefficient for total energy is μ1 and the attenuation coefficient for high energy is μ2, the rate of change can be calculated using the following formula. The rate of change is clustered to determine the material to which it belongs.

Rate of change = ln(I2/I0)/ln(I1/I0)
Here, I1 is the total number of photons contained in the transmitted X-ray, I2 is the number of high-energy photons contained in the transmitted X-ray, and ln is the natural logarithm.

This article explains how to obtain total energy and high energy from transmitted X-rays that have passed through an object.

There are two methods for this: photon counting and scintillator.

First, the photon counting method will be described. FIG. 12 shows a method for detecting the amount of X-ray energy using the photon counting method. FIG. 12 shows an example in which X-ray photons 14 of transmitted X-rays are detected by the X-ray detection unit 6 of the X-ray device 1 of this embodiment, which will be described later with reference to FIG. 1.

In this method, an X-ray detection unit 6 is used that classifies X-ray photons 14 input to the X-ray detection unit 6 within a unit time into high-energy and low-energy ones based on a predetermined threshold, counts all the X-ray photons to calculate the total energy amount, counts X-ray photons with high energy to calculate the high energy amount, and outputs the total energy amount and the high energy amount.

Next, the scintillator method will be described. Figure 13 shows a method for detecting the amount of X-ray energy using the scintillator method. Figure 13 shows an example in which X-ray photons 14 of transmitted X-rays are detected by the X-ray detection unit 6 of the X-ray device 1 of this embodiment, which will be described later with reference to Figure 1.

In this method, the X-ray detection unit 6 is composed of two X-ray detection units, X-ray detection unit 6a and X-ray detection unit 6b, and a copper plate 15 is placed in the middle between them. High-energy X-ray photons pass through the copper plate 15, but low-energy X-ray photons do not pass through the copper plate 15. Therefore, the X-ray detection unit 6a outputs the total amount of energy, and the X-ray detection unit 6b detects X-rays that have passed through the copper plate 15, i.e., X-ray photons with high energy, and outputs a high amount of energy.

Next, the specific configuration of the X-ray device of this embodiment and the material classification method using it will be explained using Figures 1 to 11.

Figure 1 shows the overall configuration of the X-ray device 1 of this embodiment. Figure 1 shows a side view (cross-sectional view) of the X-ray device 1, with the Z direction being perpendicular to the floor surface on which the X-ray device 1 is installed, and the X direction being the transport direction of the inspection object 10.

As shown in FIG. 1, the X-ray device 1 of this embodiment mainly comprises a device body 2, a measuring unit 3 that measures the mass of an object 10 to be inspected, and a control unit 4 that controls the device body 2 and the measuring unit 3.

The device body 2 has inside it an X-ray output unit 5 that outputs X-rays, an X-ray detection unit 6 that detects X-rays, and an object detection unit 7 that detects the presence or absence of an object.

The device main body 2 is arranged so that the transport conveyor 9 passes through the inside, and the X-rays 11 output from the X-ray output unit 5 are irradiated onto the inspection object 10 brought into the device main body 2 by the transport conveyor 9, and the transmitted X-rays that pass through the inspection object 10 are detected by the X-ray detection unit 6.

A shielding curtain 8 is installed at the penetration point of the transport conveyor 9 of the device body 2 to prevent the X-rays 11 output from the X-ray output unit 5 from leaking outside the device body 2.

The present invention comprises an X-ray output unit 5 that outputs X-rays at a predetermined output value, an X-ray detection unit 6 that has a predetermined number of detection elements arranged in a one-dimensional manner, with each detection element being one pixel, irradiating an object 10 with X-rays 11, detecting the transmitted X-rays at each pixel, and outputting the total energy amount and high energy amount of the transmitted X-rays as pixel information, a measurement unit 3 that measures the mass of the object, an object detection unit 7 that detects the presence of the object 10, and a control unit 4 that controls the overall movement.

When a storage container containing an object (inspection object 10) moves on the transport conveyor 9, the mass of the storage container is first measured by the measurement unit 3 and the measurement value is sent to the control unit 4. When the storage container moves further and enters the detection range of the object detection unit 7, the object detection unit 7 detects the movement of the storage container and sends a signal that a storage container is present to the control unit 4. When the control unit 4 receives the signal that a storage container is present, it sends a command signal to the X-ray output unit 5 to output X-rays 11, and further obtains the total energy amount and high energy amount of the transmitted X-rays per unit time from the X-ray detection unit 6, and starts the processing required for material classification of the object (inspection object 10) stored in the storage container.

The process of classifying the material of the object (inspection object 10) in the control unit 4 will be described in detail.

Figure 2 shows how X-rays 11 are irradiated onto a storage container 12 and how transmitted X-rays are detected in a line pattern, and Figure 3 shows how the total energy amount and high energy amount of transmitted X-rays are obtained.

The X-ray output unit 5 continuously irradiates X-rays 11 from the starting point A to the ending point B of the storage container 12 moving on the transport conveyor 9. The X-ray detection unit 6 is disposed opposite the X-ray output unit 5 across the transport conveyor 9, and detects the transmitted X-rays that have passed through the object (inspection object 10).

The X-ray detection unit 6 detects transmitted X-rays on a line in one operation, but by continuously detecting transmitted X-rays while the storage container 12 is moving on the transport conveyor 9, it is possible to scan the entire storage container 12 two-dimensionally. As a result, each detection element that makes up the X-ray detection unit 6 is treated as one pixel, and pixel information (consisting of total energy amount and high energy amount) output by each pixel is output to the control unit 4, and the control unit 4 can compose a pixel information group that two-dimensionally pixelates the entire storage container 12 based on this pixel information.

Figure 4 shows a method for storing the total energy amount and high energy amount of transmitted X-rays in the memory unit. The memory unit is configured to be included in the control unit 4.

The left diagram in Figure 4 visualizes the pixel information group acquired by the X-ray detection unit 6, with each square corresponding to one detection element 13 (i.e., one pixel) of the X-ray detection unit 6. C in the diagram indicates the range in which the X-ray output unit 5 outputs in one go and the transmitted X-rays can be detected by the X-ray detection unit 6.

The right diagram in Figure 4 visualizes how a first memory area T1 and a second memory area T2 are set in the memory unit based on the pixel information group in the left diagram, with each square corresponding to a memory area that corresponds to each detection element of the X-ray detection unit 6. Specifically, the normalized total energy amount and normalized high energy amount of the transmitted X-rays are arranged in the memory areas to generate image information as shown in the right diagram.

As shown in FIG. 4, in order to handle all pixel information in a simplified manner within a certain range, the air energy, which indicates the amount of energy in the parts of the storage container 12 where the object (inspection object 10) does not exist, i.e., the air part energy, is set to a maximum value of 1, and the pixel information of the pixels that make up the transmitted X-rays that have passed through the object (inspection object 10) is scaled to calculate the normalized total energy amount and normalized high energy amount for each pixel information. A first memory area T1 and a second memory area T2 are set in the memory unit, the normalized total energy amount is stored in a two-dimensional array in T1, and the normalized high energy amount is stored in a two-dimensional array in T2.

One (X, Y) coordinate in memory areas T1 and T2 corresponds to one pixel, the square marked as the origin in the left diagram is the start point of the linear X-ray detection unit 6, the last opposing square is the end of the X-ray detection unit 6, and the X coordinate increases from the start point to the end in the X-axis direction. Also, the Y coordinate increases in the direction marked as the Y-axis in the left diagram, that is, in the opposite direction to the direction in which the storage container 12 moves on the transport conveyor 9.

Figure 5 shows how to arrange the rate of change of the attenuation coefficient for each pixel information.

Next, the control unit 4 calculates the rate of change of the attenuation coefficient from each pixel information. As already mentioned, the rate of change of the attenuation coefficient for each pixel information can be calculated by dividing the attenuation coefficient for the normalized high energy amount for each pixel information by the attenuation coefficient for the normalized total energy amount. In other words, the rate of change of the attenuation coefficient for pixel information at coordinates (xk, yk) that are k-th in the X-axis direction and k-th in the Y-axis direction can be calculated by the following formula, where μ2(xk, yk) is the attenuation coefficient for the normalized high energy amount and μ1(xk, yk) is the attenuation coefficient for the normalized total energy amount.

Rate of change of attenuation coefficient = μ2(xk,yk)/μ1(xk,yk)
As shown in Fig. 5, the change rates of these attenuation coefficients are arranged in the corresponding (X, Y) coordinates in a third memory area T3 set in the memory unit. In this state, by referring to the corresponding (X, Y) coordinates in the memory area T3 for each pixel belonging to the memory areas T1 and T2, it becomes possible to distinguish the material.

The attenuation coefficient for each normalized total energy amount in memory area T1 is μ1, and the attenuation coefficient for each normalized high energy amount in memory area T2 is μ2, and the rate of change is calculated and stored in a third memory area T3. The so-called dual energy method is used to calculate the rate of change of each attenuation coefficient, thereby distinguishing between materials.

Next, it is determined whether each of the distinguished materials, that is, each pixel to which memory area T1 belongs, belongs to a first material group indicating a material group of heavy metals, a second material group indicating a material group of light metals, or a third material group indicating a material group of resins.

Figure 6 shows how to classify materials using material classification clusters.

The right diagram in Figure 6 is a two-dimensional XY plane plot of the normalized total energy of the pixel information belonging to T1 on the X axis and the rate of change of the attenuation coefficient corresponding to each pixel information on the Y axis.

The normalized total energy T1(xk,yk) stored in memory area T1 is plotted on the horizontal axis, and the rate of change of the attenuation coefficient T3(xk,yk) stored in memory area T3 is plotted on the vertical axis, and each pixel is clustered.

As shown by the broken lines in the right diagram of Figure 6, in the material classification cluster, boundaries for classifying the first material, second material, and third material are noted in advance. This process makes it possible to determine whether each pixel belonging to memory area T1 belongs to the first material, the second material, or the third material.

Figure 7 shows how material classification information for each pixel in memory area T1 is arranged.

As shown in FIG. 7, material classification information for each pixel in memory area T1 is arranged in a fourth memory area T4 set in the memory unit.

The material classification cluster is set as follows:

This process must be carried out and prepared prior to the actual material classification of the target object (inspection object 10). As will be described later with reference to Figure 11, multiple samples of heavy metal (e.g. iron), light metal (e.g. aluminum), and resin (e.g. nine of each) are prepared. Each shape should preferably be a square prism or cylinder. The areas of the top and bottom of all samples are the same, but the heights are different.

X-rays are irradiated onto these samples from the X-ray output unit 5, and pixel information for each is obtained via the X-ray detection unit 6. For this pixel information, the rate of change in the attenuation coefficients of the normalized total energy amount and normalized high energy amount is calculated. Then, the memory regions T1 and T3 described above are created in the memory unit. Furthermore, as shown in the right diagram of Figure 6, the values of memory region T1 are plotted on the X-axis and the values of memory region T3 are plotted on the Y-axis in a two-dimensional space.

This allows clusters of heavy metals, light metals, and resins to be formed. To clarify each cluster area, a line is drawn to connect the midpoints of the plot points for heavy metals and light metals, and a line is drawn to connect the midpoints of the plot points for light metals and resins. Also, by increasing the number of samples, more accurate clusters can be formed.

Next, the mass of each object (test object 10) classified into the three types of material is estimated. Note that this is a simplified mass estimation, and the mass of the storage container 12 is ignored.

Here, since it is not possible to directly estimate the mass of each object (inspection object 10), a common unit mass coefficient (M) is set for the whole, that is, a mass coefficient per pixel common to each object (inspection object 10).

The unit mass coefficient (M) is calculated by dividing the mass of the object (the sum of the mass of the first material, the mass of the second material, and the mass of the third material) by the total number of pixels in the entire object (the sum of Σ the number of pixels of the first material (Gh(k)), Σ the number of pixels of the second material (Gl(k)), and Σ the number of pixels of the third material (Ga(k))). k indicates the normalized total energy.

A more detailed explanation will be given using Figure 8. Figure 8 shows how to rearrange the normalized total energy for each material.

First, as shown in FIG. 8, based on the material classification information arranged in memory area T4, the (X, Y) coordinates arranged in memory area T1 are classified into a first material, a second material, and a third material, and the normalized total energy amounts arranged at the (X, Y) coordinates belonging to the first material in memory area T1 are arranged in a fifth memory area T5 set in the memory unit, the normalized total energy amounts arranged at the (X, Y) coordinates belonging to the second material in memory area T1 are arranged in a sixth memory area T6 set in the memory unit, and the normalized total energy amounts arranged at the (X, Y) coordinates belonging to the third material in memory area T1 are arranged in a seventh memory area T7 set in the memory unit.

In other words, the material information in memory area T4 is applied to the information in memory area T1, and the objects are classified by material and stored in separate memory areas. By storing the objects in separate memory areas for each classified material, it is possible to manipulate the objects individually for each material.

One pixel of the X-ray detection unit 6 corresponds to one (X, Y) coordinate in the memory area in which pixel information is arranged. Therefore, the number of pixels can be calculated by counting the target (X, Y) coordinates in the memory area. Therefore, the number of pixels classified as the first material can be calculated by counting the number of coordinates belonging to memory area T5, the number of pixels classified as the second material can be calculated by counting the number of coordinates belonging to memory area T6, and the number of pixels classified as the third material can be calculated by counting the number of coordinates belonging to memory area T7.

Figure 9 shows how to calculate the unit mass coefficient.

From this information, the unit mass coefficient (M) can be calculated using the following formula, as shown in Figure 9.

Unit mass coefficient (M) = (mass of object) / (area of first material + area of second material + area of third material)
Here, the area occupied by the first material is the number of (X, Y) coordinates belonging to memory area T5, the area occupied by the second material is the number of (X, Y) coordinates belonging to memory area T6, and the area occupied by the third material is the number of (X, Y) coordinates belonging to memory area T7.

Next, we will explain in detail how to estimate the mass of the first material, the second material, and the third material using the mass correlation coefficient of the first material (mh(k)), the mass correlation coefficient of the second material (ml(k)), and the mass correlation coefficient of the third material (ma(k)), which indicate the correlation coefficients (mass correlation coefficients) related to the mass of each material. Note that k indicates the normalized total energy amount, just like the unit mass coefficient (M).

Figure 10 shows the mass correlation coefficient setting curve for each material.

As shown in Figure 10, the mass correlation coefficient indicates the mass distribution of each material at the same normalized total energy amount, and indicates how much of the total mass the first material, second material, and third material have when the normalized total energy amount is the same.

Using these parameters, it is possible to estimate the mass of each material using the following formula:

[Mass estimation formula (1)]
Estimated mass of first material = M × Σ(Gh(k) × mh(k)) ... (1)
Σ(Gh(k) × mh(k)) corresponds to the following formula and is the sum of the products of the number of pixels Gh(k) corresponding to each normalized total photon number and the mass correlation coefficient mh(k).

Gh(0.1)×mh(0.2)＋Gh(0.2)×mh(0.2)＋・・・＋Gh(k)×mh(k)
[Mass estimation formula (2)]
Estimated mass of the second material = M × Σ(Gl(k) × ml(k)) ... (2)
Σ(Gl(k) × ml(k)) corresponds to the following formula and is the sum of the products of the number of pixels Gl(k) corresponding to each normalized total photon number and the mass correlation coefficient ml(k).

Gl(0.1) × ml(0.2) + Gl(0.2) × ml(0.2) + ... + Gl(k) × ml(k)
[Mass estimation formula (3)]
Estimated mass of the third material = M × Σ(Ga(k) × ma(k)) ... (3)
Σ(Ga(k) × ma(k)) corresponds to the following formula and is the sum of the products of the number of pixels Ga(k) corresponding to each normalized total photon number and the mass correlation coefficient ma(k).

Ga(0.1)×ma(0.2)＋Ga(0.2)×ma(0.2)＋・・・＋Ga(k)×ma(k)
Here, M is the unit mass coefficient, Gh(k), Gl(k), Ga(k) are the number of pixels of the first material, the number of pixels of the second material, and the number of pixels of the third material corresponding to the normalized total energy amount, and mh(k), ml(k), ma(k) are the mass correlation coefficient of the first material, the mass correlation coefficient of the second material, and the mass correlation coefficient of the third material corresponding to the normalized total energy amount.

The process of setting the unit mass coefficient (M) and the mass correlation coefficients of each material corresponding to the normalized total energy (k) (mass correlation coefficient mh(k) of the first material, mass correlation coefficient ml(k) of the second material, mass correlation coefficient ma(k) of the third material) is explained below. The following steps 1 to 10 are carried out in order. These steps must also be carried out in preparation prior to actually classifying the material of the object.

[Step 1]
An example of a material classification cluster is shown in Fig. 11. As shown in Fig. 11, a plurality of samples of a first material, a second material, and a third material (nine samples each in Fig. 11) are prepared. The samples used when preparing the material classification cluster may be used.

A two-dimensional XY plane is prepared with the X-axis representing the normalized total energy amount (k) and the Y-axis representing the mass correlation coefficient m(k) corresponding to the normalized total energy amount (k), and a provisional mass correlation coefficient curve is set on the two-dimensional XY plane for the mass correlation coefficient mh(k) for the first material, the mass correlation coefficient ml(k) for the second material, and the mass correlation coefficient ma(k) for the third material. Note that this provisional mass correlation coefficient curve is set as an initial value and may be linear. It is adjusted in the following steps to be corrected so that it becomes an actual curve.

[Step 2]
From the samples prepared in the processing of step 1, one sample each of the first material, the second material, and the third material having the same height are selected, and the three samples are grouped together. The total mass of each group is measured by the measurement unit 3 and obtained by the control unit 4.

[Step 3]
From the groups formed in step 2, one group is selected in descending order of height.

[Step 4]
A command signal is sent from the control unit 4 to the X-ray output unit 5 for the group selected in the process of step 3, and the entire group is scanned while outputting X-rays from the X-ray output unit 5. (The samples made of the first material, the second material, and the third material belonging to the group are irradiated with X-rays simultaneously.)
[Step 5]
During the scan in the processing of step 4, the transmitted X-rays that pass through each sample in the group are detected by the X-ray detection unit 6, and the pixel information of each pixel output from the X-ray detection unit 6 is obtained by the control unit 4.

[STEP 6]
Based on the number of pixels for each of the first material sample, the second material sample, and the third material sample obtained by the processing in step 5 and the pixel information for each pixel, a normalized total number of photons is calculated, and a provisional value for each mass correlation coefficient is set.

here,
Normalized total energy of the first material: kh
Normalized total energy of the second material: kl
Normalized total energy of the third material: ka
Number of pixels of the first material corresponding to kh Gh(kh)
Number of pixels of the second material corresponding to kl Gl(kl)
The number of pixels of the third material corresponding to ka, Ga(ka)
Mass correlation coefficient mh(kh) of the first material corresponding to kh
Mass correlation coefficient ml(kl) of the second material corresponding to kl
Mass correlation coefficient ma(ka) of the third material corresponding to ka
Let us assume that.

[STEP 7]
Calculate the unit mass coefficient (M) by dividing the mass of the entire target group measured in step 2 by the sum of the number of pixels of the sample of the first material, the number of pixels of the sample of the second material, and the number of pixels of the sample of the third material calculated in step 6 (the number of pixels of the entire target group).

Unit mass coefficient (M) = total mass of the target group ÷ total number of pixels in the target group [Step 8]
The unit mass coefficient (M) obtained in the processing of step 7, the number of pixels Gh(kh) and mass correlation coefficient mh(kh) of the first material in the normalized energy amount (kh) of the first material obtained in the processing of step 6, the number of pixels Gl(kl) and mass correlation coefficient ml(kl) of the second material in the normalized total energy amount (kl) of the second material, and the number of pixels Ga(ka) and mass correlation coefficient ma(ka) of the third material in the normalized total energy amount (ka) of the third material are substituted into the following equation to calculate the provisional mass, which is the calculated mass of the entire target group.

Pseudo mass = M × (Gh(kh) × mh(kh) + Gl(kl) × ml(kl) + Ga(ka) × ma(ka))
The actual mass of the entire target group is measured in step 2, so
Adjust mh, ml, and ma so that the provisional mass = the actual mass of the entire target group, and determine the plot positions on the mass correlation coefficient setting curve for each normalized total photon number kh, kl, and ka.

[STEP 9]
The processes from step 3 to step 7 are performed for the other samples in turn to determine the plot positions on the mass correlation coefficient setting curve for each normalized total photon number, thereby making it possible to set the mass correlation coefficient for the prepared sample.

[STEP 10]
After determining the plot positions on the mass correlation coefficient setting curve for each normalized total photon number for all samples, numerical interpolation is performed between each point to make a smooth curve.

The X-ray device of this embodiment and the material classification method using the same described above make it possible to classify the material that constitutes the object to be inspected while checking the external shape of the object.

With reference to FIG. 14, an X-ray device according to a second embodiment of the present invention and a material classification method using the same will be described. FIG. 14 is a diagram showing the material classification method of this embodiment. In this embodiment, an example of detecting dangerous objects stored in suitcases, etc. at a baggage inspection area at an airport, etc. will be described.

In baggage inspection, which is a common type of security check, X-rays are irradiated onto baggage passing through the inspection device, and security inspectors visually detect dangerous objects based on the images that have been sharpened using image processing.

Security inspectors must look at these X-ray images and perform rapid and accurate inspections one after the other. However, thorough inspections can cause congestion and lead to lower customer satisfaction. This conflicting environment places a heavy physical and mental strain on security inspectors.

In this embodiment, therefore, the X-ray device 1 is provided with a function for selecting a specific inspection object 10 from a plurality of objects stored in a storage container (suitcase 16). This function for selecting a specific inspection object 10 is realized, for example, by a security inspector viewing the X-ray image on the monitor and using an input device such as a computer mouse to surround an object for which safety is a concern with a frame.

For the specific selected test object 10, the control unit 4 of the X-ray device 1 applies the material classification method and weight estimation method described in Example 1 to obtain the rate of change in the attenuation coefficient of the selected test object 10 based on the pixel information of the selected test object 10, and classifies each of the multiple materials that make up the selected test object 10 into one of the predetermined materials (e.g., a first material, a second material, or a third material).

Then, the mass of each material is estimated based on the classification, and it is determined whether the selected inspection object 10 is a hazardous object or not based on the estimated mass of each material.

This will help determine whether the object being inspected is dangerous, and contribute to preventing crimes, etc.

The present invention is not limited to the above-described embodiments, but includes various modified examples. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and are not necessarily limited to those having all of the configurations described. It is also possible to replace part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. It is also possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

1...X-ray device, 2...device body, 3...measuring section, 4...control section, 5...X-ray output section, 6, 6a, 6b...X-ray detection section, 7...object detection section, 8...shielding curtain, 9...transport conveyor, 10...inspection object, 11...X-ray, 12...storage container, 13...X-ray detection element (of X-ray detection section 6), 14...X-ray photon, 15...copper plate, 16...suitcase, A...starting end of storage container, B...ending end of storage container, C...transmitted X-ray detection range, T, T1 to T7...storage area.

In order to solve the above problems, the present invention includes an X-ray output unit that outputs X-rays at a predetermined output value, an X-ray detection unit that arranges a predetermined number of detection elements in a one-dimensional manner, with each detection element being one pixel, detects the X-rays at each of the pixels, and obtains pixel information relating to a total energy amount indicating the magnitude of the overall energy of the X-rays and a high energy amount indicating the magnitude of energy equal to or greater than a predetermined value, and a control unit, and the control unit instructs the X-ray output unit to irradiate the X-rays at a storage container moving on a transport conveyor, and detects the transmitted X-rays that have passed through the storage container and obtains pixel information relating to the transmitted X-rays. The pixel information for X-rays is obtained from the X-ray detection unit, and a rate of change in attenuation coefficient is calculated by dividing the attenuation coefficient of a high amount of energy for the object stored in the storage container by the attenuation coefficient of a total amount of energy based on the pixel information. Prior to operating the system, multiple combinations of the same size for material samples to be classified are prepared, the rate of change in the attenuation coefficient for each is calculated and clustered, and lines are drawn between the clusters to clarify the boundaries between the clusters, and the object is classified into one of the specified materials by referring to the material classification clusters prepared in advance .

The present invention also provides a material classification method using X-rays, comprising the steps of: (a) irradiating a storage container moving on a transport conveyor with X-rays, detecting the transmitted X-rays that have passed through the storage container, and acquiring pixel information for the transmitted X-rays; (b) determining a rate of change in attenuation coefficient by dividing the attenuation coefficient of a high amount of energy for an object stored in the storage container by the attenuation coefficient of a total amount of energy based on the pixel information acquired in step (a); and (c) classifying the object into one of predetermined materials based on the rate of change in attenuation coefficient determined in step (b) and material classification clusters that have been prepared in advance prior to operating the system by preparing a plurality of combinations of the same size for material samples to be classified, determining the rate of change in attenuation coefficient for each combination, clustering the combinations, and further drawing lines between the clusters to clarify the boundaries between the clusters.

Claims (13)

an X-ray output unit that outputs X-rays at a predetermined output value;
an X-ray detection unit which arranges a predetermined number of detection elements in a one-dimensional manner, and detects the X-rays at each of the pixels, with each detection element being one pixel, and obtains pixel information relating to a total energy amount indicating the magnitude of the overall energy of the X-rays and a high energy amount indicating the magnitude of energy equal to or greater than a predetermined value;
A control unit,
The control unit is
instructing the X-ray output unit to irradiate the X-rays onto a storage container moving on a transport conveyor, and detecting the transmitted X-rays that have passed through the storage container, and acquiring the pixel information for the transmitted X-rays from the X-ray detection unit;
determining a rate of change in the attenuation coefficient of the object stored in the storage container based on the pixel information;
An X-ray device which classifies the object into one of a predetermined materials. 2. The X-ray device according to claim 1,
The X-ray device is characterized in that the X-ray output unit irradiates the storage container with the X-rays from a starting end to a terminal end thereof as the storage container moves on the transport conveyor. 3. The X-ray device according to claim 2,
An X-ray device characterized in that the specified materials are three materials: a first material, a second material different from the first material, and a third material different from the first material and the second material. 4. The X-ray device according to claim 3,
the control unit acquires the pixel information of the entire container by scanning the X-ray detection unit from the starting end to the ending end,
a normalized total energy amount and a normalized high energy amount are calculated by scaling an air portion energy amount indicating an energy amount of an air portion where the object is not present, with a maximum value of 1, with respect to the total energy amount and the high energy amount included in each of the pixel information corresponding to the transmitted X-rays transmitted through the object;
A first storage area T1 and a second storage area T2 are set in the storage unit;
Two-dimensionally arranging the normalized total energy amount in the T1 to generate a first image information of the object;
The X-ray apparatus further comprises: a first image information unit for generating a second image of the object by two-dimensionally arranging the normalized high energy dose at T2. 5. The X-ray device according to claim 4,
The control unit is
Calculate a first attenuation coefficient indicating an attenuation coefficient corresponding to the normalized total energy amount arranged at each (X, Y) coordinate of the T1;
Calculate a second attenuation coefficient indicating an attenuation coefficient corresponding to the normalized high energy amount arranged in each (X, Y) coordinate of the T2;
and dividing each of the second attenuation coefficients by the first attenuation coefficient of a corresponding (X, Y) coordinate to calculate the rate of change of the normalized high energy amount relative to each of the normalized total energy amounts, and arranging the rate of change in a third memory area T3 set in the memory unit. 6. The X-ray device according to claim 5,
The control unit is
clustering information in which the numerical values arranged at each (X, Y) coordinate of T1 are set as X coordinates and the numerical values arranged at each (X, Y) coordinate of T3 are set as Y coordinates using a material classification cluster indicating a correlation between the normalized total energy amount and the rate of change of the attenuation coefficient, thereby classifying each (X, Y) coordinate as belonging to the first material, the second material, or the third material;
and arranging material classification information as the first material, the second material, and the third material at the (X, Y) coordinates corresponding to T4 indicating a fourth memory area set in the memory unit. 7. The X-ray device according to claim 6,
The control unit is
Based on the material classification information arranged in the T4, each of the (X, Y) coordinates arranged in the T1 is classified into the first material, the second material, and the third material;
The normalized total energy amounts arranged at the (X, Y) coordinates belonging to the first material are arranged in a fifth memory area T5 set in the memory unit;
The normalized total energy amounts arranged at the (X, Y) coordinates belonging to the second material are arranged in a sixth memory area T6 set in the memory unit;
the normalized total energy amounts arranged at the (X, Y) coordinates belonging to the third material are arranged in T7 indicating a seventh memory area set in the memory unit. 8. The X-ray device according to claim 7,
The control unit is
In the T5, the number of (X, Y) coordinates having the same value of the normalized total energy amount (k) is counted to calculate a first pixel number Gh(k);
In the T6, the number of (X, Y) coordinates having the same value of the normalized total energy amount (k) is counted to calculate a second pixel number Gl(k);
In the T7, the number of (X, Y) coordinates having the same value of the normalized total energy amount (k) is counted to calculate a third pixel number Ga(k);
An X-ray apparatus comprising: a mass of the object divided by the sum of the first pixel count group, the second pixel count group, and the third pixel count group to calculate a unit mass coefficient (M) common to the first material, the second material, and the third material. 9. The X-ray device according to claim 8,
the control unit sets mass correlation coefficients mh(k), ml(k), ma(k) (k: normalized photon number) corresponding to the normalized total energies of the first material, the second material, and the third material, respectively, by using a mass correlation coefficient setting curve. 10. The X-ray device according to claim 9,
The control unit calculates the following equations (1) to (3):
Mass of the first material = M(Gh(0.1)mh(0.1)+Gh(0.2)mh(0.2)+...+Gh(k)mh(k))...(1)
Mass of the second material = M(Gl(0.1)ml(0.1)+Gl(0.2)ml(0.2)+...+Gl(k)ml(k))...(2)
Mass of the third material = M(Ga(0.1)ma(0.1)+Ga(0.2)ma(0.2)+...+Ga(k)ma(k))...(3)
An X-ray apparatus comprising: an X-ray detector configured to estimate a mass of the first material, a mass of the second material, and a mass of the third material of the object. 2. The X-ray device according to claim 1,
The X-ray device includes a measurement unit and
a storage container sensor disposed at a rear position of the transport conveyor from the measurement unit,
The mass of the storage container is measured by the measuring unit;
An X-ray device characterized in that when the storage container is detected by the storage container sensor after the measurement unit measures the mass of the storage container, the control unit sends a command signal to the X-ray output unit to start irradiating the X-rays. 2. The X-ray device according to claim 1,
the X-ray device has a function of selecting a specific object from the plurality of objects stored in the storage container;
The control unit calculates a rate of change in the attenuation coefficient of the selected object based on the pixel information of the selected object,
An X-ray apparatus comprising: a detector for detecting a plurality of materials that constitute the selected object; and a detector for detecting a plurality of materials that constitute the selected object. A material classification method using X-rays, comprising:
(a) irradiating an X-ray onto a storage container moving on a transport conveyor, and detecting the transmitted X-ray that has passed through the storage container to obtain pixel information for the transmitted X-ray;
(b) calculating a rate of change in the attenuation coefficient of the object stored in the storage container based on the pixel information acquired in the (a) step;
(c) classifying the object into one of predetermined materials based on the rate of change of the attenuation coefficient obtained in the step (b);
A material classification method comprising the steps of:

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