JP2018155754A - X-ray detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly versatile X-ray foreign matter inspection device capable of making a foreign matter contained therein stand out regardless of an object to be inspected. SOLUTION: A multi-energy sensor unit capable of spectralizing the energy of X-rays emitted from an X-ray source for each pixel, and the energy of X-rays transmitted through the inspected object based on the X-ray data obtained by the multi-energy sensor. Is obtained as a spectrum, and two types of energy bands most suitable for energy subtraction processing are selected from the spectrum data obtained from the multi-energy sensor. [Selection diagram] FIG. 5

Description

  The present invention relates to an X-ray inspection apparatus that detects foreign matter contained in an inspection object by irradiating the inspection object with X-rays.

  There is a growing need for difficult-to-detect foreign materials, such as detecting bones in chicken and detecting foreign materials in cereals.

  As a conventional foreign matter detection device, an in-line inspection device using an X-ray transmission image is known, but there is little difference between the inspection object and the foreign matter, and stable detection is difficult even with advanced image processing. It has become.

  In view of this, efforts have been made to enable detection of difficult-to-detect foreign substances using a dual energy sensor (see, for example, Patent Document 1). This sensor uses two types of sensors having different energy characteristics to simultaneously image an inspection object, and can obtain two images having different contrasts. A technique for eliminating the influence of the object to be inspected by performing differential processing on the two images and extracting only foreign matters is called energy subtraction.

Patent No. 5616182

  Even if the above energy subtraction technique is used, for example, bones in chicken (particularly soft bones such as triangular bones) are difficult to detect. The reason is that since the energy absorption characteristics of bone are similar to those of the object to be inspected, both of them are erased at the same time when subtraction is performed.

  In order to make it possible to extract bone by using the subtraction technique, it is necessary to perform subtraction using an image having an energy band sensitive to chicken and an image having an energy band sensitive to bone.

  Usually, a sensor with high sensitivity to low-energy X-rays (S sensor) and a sensor with high sensitivity to high-energy X-rays (H sensor) are used to obtain a gray-scale image of X-ray transmission. However, it does not have an energy band suitable for chicken or bone to such an extent that bone can be extracted by subtraction, so that extraction of bone is difficult even if subtraction is performed.

  Also, because the S sensor and H sensor have fixed energy bands as hardware, even if extraction of chicken bones is successful, it may not be an effective energy band for other specimens. There is also a problem of lack of sex.

  As described above, an object of the present invention is to provide a highly versatile X-ray inspection apparatus that can make a foreign matter included in any object to be inspected stand out.

In order to solve the above problems, an X-ray inspection apparatus according to the present invention provides:
An X-ray source for irradiating the inspection object with X-rays;
A multi-energy sensor that detects X-rays in a plurality of energy bands included in transmitted X-rays of the inspection object and outputs an energy spectrum for each pixel;
An image processing unit that selects two types of energy bands suitable for foreign object detection from the plurality of energy bands, and detects foreign substances by energy subtraction from images corresponding to the selected two types of energy bands. is there.

  In the conventional energy subtraction, a sensor with two types of fixed energy characteristics was used, so an appropriate energy band could not be selected according to the object to be inspected. Therefore, after imaging, an image in an appropriate energy band can be selected and processed. In other words, since the X-ray absorption rate differs between the inspected object and the foreign matter having different compositions, a characteristic energy band is obtained in advance, and after imaging, energy subtraction is performed using an image of the obtained energy band. Thus, foreign matter is detected.

  For example, when examining bone in chicken, efficient subtraction can be performed by using two types of energy bands of 40 keV and 60 keV. It is possible to select which energy band can most effectively detect a foreign object by using an object to be inspected and a sample of the foreign object in advance.

For example, as a preliminary setup, attach a sample of chicken and the bone to be detected inside or on its surface, acquire a multi-energy image of chicken, and generate an image that extracts only two types of energy bands from it . These energy bands are E ₁ = {ε | ε _i1 <ε <ε _j1 }, E ₂ = {ε | ε _i2 <ε <ε _j2 }, the image of E ₁ is P ₁ , and the image of E ₂ is P ₂ And In addition, the gray values of P ₁ and P ₂ at a certain pixel (x, y) are defined as p ₁ (x, y) and p ₂ (x, y), respectively.

If the contrast of the image on which energy subtraction is performed is c (x, y), c (x, y) = | p ₁ (x, y) -αp ₂ (x, y) |, 0 ≦ α ≦ 1 This is referred to as a contrast image. α is a parameter determined later.

Since we are in the pre-setup stage now, the chicken-only pixel and the bone-attached pixel are known, and each pixel is (x _A , y _A ), (x _B , y _B ) As a result of subtraction so that the difference in contrast between chicken and bone is the largest, that is, giving the maximum value of | c (x _A , y _A ) -c (x _B , y _B ) | The parameters (ε _i1 , ε _j1 , ε _i2 , ε _j2 , α) may be set.

For the setting, for example, a parameter (ε _i1 , ε _j1 , ε _i2 , ε _j2 , α) that sweeps the parameters and gives the maximum value may be selected. When detecting a foreign object, c (x, y) of the image is calculated and imaged using the parameters (ε _i1 , ε _j1 , ε _i2 , ε _j2 , α) determined in the previous setup. Then, an image from which only bones are extracted can be obtained.

For simplicity of explanation, (x _A , y _A ), (x _B , y _B ) are shown here, but these are expanded to a range with an area and averaged gray value May be used.

  According to the present invention, images of a plurality of energy bands can be obtained by using a multi-energy sensor, and energy subtraction is performed using images of two types of energy bands suitable for foreign object detection. Even if it is an inspection object, the foreign material contained in each can be made to stand out. Therefore, a highly versatile X-ray inspection apparatus can be provided to the market.

The external view of the X-ray detection apparatus which concerns on 1st and 2nd embodiment of this invention. The schematic diagram inside the housing | casing of the X-ray inspection apparatus which concerns on 1st Embodiment of this invention. Imaging of inspection object by line sensor unit. The image of the inspection object imaged by the line sensor unit. The block diagram of the configuration of the X-ray inspection apparatus. The block diagram of a line sensor unit. Data for each pixel of the line sensor unit. Data after calibration of the line sensor unit. An image of the sum of all energy data for each pixel of chicken and bone. 64 energy slice images. An example of an image where chicken and bones are not sufficiently separated. Flow chart of pre-setup to determine optimal parameters. An example of an image with chicken and bones separated. An example of an image binarized after separating chicken and bone. The schematic diagram inside the housing | casing of the X-ray inspection apparatus which concerns on 2nd Embodiment of this invention.

[First Embodiment]
The X-ray inspection apparatus 100 according to the first embodiment of the present invention will be described below with reference to the drawings.

  An X-ray inspection apparatus 100 according to this embodiment is an X-ray inspection apparatus that inspects an inspection object 600 such as food (for example, chicken or a plurality of sausages in a bag) as shown in FIGS. 1 and 2. In particular, the conveyance unit 500 that conveys the inspection object 600, the X-ray source 200 that irradiates the inspection object 600 with X-rays, and the sensor unit 300 that detects the X-rays irradiated from the X-ray source 200, And an image processing unit 400 of FIG. FIG. 5 shows a configuration diagram of the X-ray inspection apparatus.

  The X-ray inspection apparatus 100 is mainly used for detecting foreign matters mixed in food. It is a mechanism that is installed in a food production site, etc., and observes the inside of food using X-ray fluoroscopic images, and detects X-ray images by visual inspection or analysis to detect mixed foreign matter.

  In the X-ray inspection apparatus 100, X-rays are irradiated inside the housing M while the inspection object 600 is being transported by the transport unit 500, and X-rays that have passed through the inspection object 600 are sequentially received by the line sensor unit 300. To do. The received data is converted into digital data by an electronic board (not shown) inside the line sensor unit 300 and transferred to the image processing unit 400. The image processing unit 400 generates a two-dimensional transmission X-ray image and analyzes and determines whether there is a foreign object on the inspection object 600. The result is displayed on the display MT in FIG. 1, and the operator can know the presence or absence of a foreign object. At the same time, the location of foreign matter is shown on the X-ray image of the inspection object.

(Transport section)
The transport unit 500 is provided to transport the inspection object 600 into the inspection room. The transport unit 500 can use various transport mechanisms such as a belt conveyor, a top chain conveyor, and a rotary table. The most common type is a belt conveyor type, and a resin conveyor belt 510 is attached between pulleys before and after the conveyor unit 500. In order to prevent X-rays from leaking, a strip-shaped curtain 550 made of resin mixed with heavy metal is attached to the entrance / exit of the examination room in FIG.

(X-ray source)
The X-ray source 200 irradiates the inspection object 600 transported to the inspection position by the transport unit 500 with X-rays. The X-rays emitted from the X-ray source 200 include X-rays in various energy bands from low energy (long wavelength) to high energy (short wavelength). Although described as “low energy” and “high energy”, “high” and “low” are relatively “high” and “low” among a plurality of energy bands irradiated from the X-ray source 200. It does not indicate a specific range. The same applies hereinafter.

(Multi energy sensor unit)
The X-rays emitted from the X-ray source 200 in FIG. 2 include a wide range from high energy X-rays to low energy X-rays. The multi-energy sensor unit 300 is a sensor with high energy resolution. The sensor unit 300 is a line sensor type in which pixels are arranged in a line, and as shown in FIG. 4, the inspection object 600 conveyed by the conveyance unit 500 is imaged for each line. Are combined into a two-dimensional image. Further, as shown in FIG. 6, the sensor unit 300 includes a light receiving unit 350 and a control unit 360, an external input interface 370 that can be controlled from the outside, and an external output interface 380 that is used for data output and the like. It has. The control unit 360 analyzes the X-rays of a plurality of energy bands detected by the light receiving unit 350, so that an energy spectrum for each pixel is output.

(Control device)
The control device controls the entire X-ray inspection apparatus 100 including the X-ray source 200, the transport unit 500, the sensor unit 300, and other devices, and also performs image processing on data obtained from the sensor unit 300. It has. The image processing unit 400 is configured by a computer and executes data stored in the sensor unit 300 by executing a built-in program to generate a multi-energy image having an energy spectrum for each pixel. Further, by calculating the multi-energy image, foreign matter contained in the inspection object is detected and displayed on the display 910 or a warning is issued by the buzzer 920 to detect the foreign matter to the operator. Tell.

(Generation of images using a multi-energy sensor)
Next, processing by the image processing unit 400 will be specifically described.

(Imaging settings)
When the X-ray is irradiated and the inspection object 600 is transferred by the transfer unit 500 and imaged by the line sensor unit 300 (FIG. 6), the shutter is turned off for each time required to move one pixel of the inspection object 600. 3, the object 600 is imaged in a strip shape. Then, the image on the line is transferred as data to the control device. For example, if the length in the conveyance direction is 1 mm and the conveyance speed is 30 m / min, the shutter time is expressed by the following formula 1.

(Advance preparation)
Next, as pre-preparation for imaging with the multi-energy sensor 300, calibration is performed so that uniform data can be obtained correctly when there is no object 600 to be inspected. For example, since there is some X-ray absorber even if there is no object to be inspected, such as the conveyor belt 510 of the belt conveyor, the cover 370 of the line sensor unit 300, etc., these effects are examined. In addition, since the line sensor itself also varies in sensitivity depending on the pixels, it is also meaningful to measure these simultaneously.

(Setting the dynamic range of the multi-energy sensor)
In the above-described background correction in a normal line sensor, only the brightness is adjusted for each pixel. However, since the multi-energy sensor 300 collects the spectrum for each pixel, the spectrum needs to be corrected. This method will be specifically described below.

For example, consider the case where X-rays with tube voltage V (kV) are irradiated. Let I _D (V, z, ε) be data from the line sensor unit in the energy band ε to ε + Δε of the pixel z when there is no inspection object and no X-rays are irradiated. On the other hand, data from the line sensor unit 300 in the energy band ε to ε + Δε of the pixel z in a state where there is no inspection object and X-rays are irradiated is defined as I _B (V, z, ε). As a major premise, measurement cannot be performed if the light receiving capacity of the sensor overflows, so the tube current value is adjusted so that I _B (V, z, ε) does not exceed the specified value of the line sensor unit 300. There is a need to. For example, the tube current value is reduced so that the maximum value of I _B (V, z, ε) is 90% of the measurement capacity of the line sensor unit.

In the multi-energy sensor 300, the energy from the X-ray source 200 is also spectrumd, but the total energy reaching each pixel from the X-ray source 200 is considered to be constant, and the sum of I _B (V, z, ε) with respect to ε. Is assumed to be constant, so I _B (V, z) = Σ _ε I _B (V, z, ε) is made uniform. Then, an output is obtained as shown in FIG. 7 due to the positional relationship of the line sensor unit 300 and the variation of each pixel.

In such a state where there is variation for each pixel, the subsequent processing becomes complicated, so that calibration is performed so as to be uniform. In other words, I _B (V, z) and I _D (V, z) are constant as shown in FIG. A transformation I ′ (V, z) = aI (V, z) in which Equation 2 which is a straight line representing ξ on the horizontal axis in FIG. 7 is identical to Equation 3 of the straight line representing FIG. ) + b is obtained, and Equations 4 and 5 are obtained.

  Once the calibration parameters a and b are obtained in this way, the raw data from the line sensor unit 300 is converted and used as I ′ (V, z) = aI (V, z) + b. To do. This setting of the dynamic range is effective for a certain tube voltage V (kV). When the tube voltage is changed to V ′ (kV), it is necessary to set the calibration again.

This conversion by calibration may be set electronically by a gain circuit / offset circuit, or digitized data may be digitally calculated by a control device. For example, if the dynamic range of the line sensor unit is 12 bits, it is determined as I _D0 = 500 and I _B0 = 3500 with a margin.

(Imaging the inspection object)
The data transferred from the line sensor unit 300 is sequentially stored by the memory inside the control device, and after the inspection object 600 passes, that is, this imaging continues until reaching a preset imaging length L. . The length L is set longer than the inspected object 600 with a margin according to variations in the inspected object 600, the size of the buffer in the imaging process, and the like. In this manner, the data stored in the memory is connected to generate an image of the inspection object 600.

(Inspection image display)
Since the data of the multi-energy sensor 300 has a spectrum for each pixel, the above imaging result displays, for example, the sum of all the spectra for each pixel, and recognizes the image of the inspection object to the operator. This is displayed on the display 910. This is for easy display for the operator. In actuality, each pixel holds an energy spectrum, and the spectrum data is stored in a memory.

  FIG. 9 shows a connected image obtained by summing up the total energy for each pixel. Note that the dynamic range is adjusted for each energy for each pixel so that the background is uniform using data measured in advance.

For example, if the performance of the multi-energy sensor 300 can collect data by dividing the energy band into 64 steps every 2 keV from 20 keV to 148 keV, 64 energy slice images can be obtained. FIG. 10 shows 64 energy slice images, and each image corresponds to a respective energy band ε _k (k = 0, 1, 2,..., 63). In the figure, they are arranged in the order of k = 0, 1, 2,. The calibration described above is performed in advance.

(How to select appropriate two images)
Next, a method of selecting two images suitable for energy subtraction will be described using a specific example.

  As a prior setup, with the tube voltage of 100 kV in FIG. The obtained image will be described as an example.

In slice image for each energy band shown in FIG. 10, obtains the image P ₂ of the image P ₁ and E ₂ of E _1. The image P ₁ is obtained by selecting slice images in the range of E ₁ from the 64 slice images in FIG. 10 and generating an averaged image for each pixel. The same applies to the image P _2. For example, for ε _i1 = 26 keV, ε _j1 = 32 keV, ε _i2 = 48 keV, ε _j2 = 86 keV, α = 0.71, c (x, y) = | p ₁ (x, y) -αp ₂ (x , y) | is shown in FIG. Then, it turns out that the chicken and bone are not sufficiently separated, the pixel (or region) of chicken only is (x _A , y _A ), the pixel (or region) where the bone is reflected is (x _B , y _B ) It can be seen that | c (x _A , y _A ) −c (x _B , y _B ) | is not the maximum.

As illustrated in the flowchart of FIG. 12, the parameters ε _i1 , ε _j1 , ε _i2 , ε _j2 , α are swept so that | c (x _A , y _A ) -c (x _B , y _B ) | Is obtained. Here, ε _i1 , ε _j1 , ε _i2 , and ε _j2 sweep every 2 keV that is the energy splitting performance of the sensor. However, if α is swept every 0.01, for example, sufficient results can be obtained. FIG. 13 shows the result of imaging using the parameters ε _i1 = 22 keV, ε _j1 = 52 keV, ε _i2 = 28 keV, ε _j2 = 58 keV, and α = 0.40 thus obtained. In this image, it can be seen that chicken and bones are separated.

  In order to make it clearer, the binarization processing of this image is shown in FIG. 14, and it can be seen that chicken is removed and only the bone is clearly extracted. Binarization is a process in which a certain threshold value is set, and pixels brighter than that are painted white, and pixels with lower brightness are painted black. By performing this process, only foreign matter becomes clearer. In addition, it is easy to automatically detect the position of a foreign object by a computer arithmetic unit.

  When the inspection is actually performed in-line, each time the inspection object 600 is imaged, a threshold value is set so that a contrast image is generated using the determined parameters, binarization processing is performed, and only the bone is detected. Set appropriately.

  In these images, random noise is placed on the area other than the inspection object 600, but this can be eliminated by a masking process that detects the presence or absence of the inspection object 600 immediately after imaging. Specifically, a threshold value for masking is set, and an area having a certain brightness or more is determined not to have the inspection object 600 and is not allowed to participate in the calculation. Since this masking can also eliminate arithmetic processing, there is also an advantage that foreign matter detection can be performed at higher speed.

(Optimal tube voltage setting)
Foreign matter detection by the above method can further enhance the effect of foreign matter detection by setting the tube voltage of the X-ray source optimally. Conversely, if the tube voltage setting is not appropriate, a sufficient effect may not be obtained.

  By sweeping the above method with respect to the tube voltage that can be irradiated by the X-ray source, it is possible to obtain the tube voltage at which only foreign matter is most easily detected.

[Second Embodiment]
Hereinafter, an X-ray inspection apparatus 101 according to a second embodiment of the present invention will be described with reference to the drawings.

  In general, X-rays attenuate when they pass through a substance. Therefore, X-rays that have passed through the inspection object and X-rays that have not passed through the inspection object have different energy spectrum distributions. For this reason, apart from attempting to equalize the sensitivity of each pixel when there is no object to be inspected, there are detection values in the state where X-rays are not irradiated, and an object to be inspected (sample 600 described later). It is desirable to make the sensitivity of each pixel uniform in a state where there is an object to be inspected (sample 600) using the detection value in a state where the line is irradiated. Thereby, in addition to the calibration for the energy spectrum distribution of the X-rays not transmitted through the inspection object, the calibration for the energy spectrum distribution of the X-rays transmitted through the inspection object can be performed.

  Here, the X-ray inspection apparatus 101 of the second embodiment emits X-rays to the sample 610 that performs X-ray transmission (absorption) substantially equivalent to the object to be inspected in advance preparation. It is configured so that calibration can be performed in a state where there is an inspection object. In addition, about the structure same as the said 1st Embodiment, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

(sample)
As shown in FIG. 15, the X-ray inspection apparatus 101 includes a sample 610 (sample 610 a and sample 610 b) in the housing M and above the conveyance surface 510. Sample 610 (sample 610a and sample 610b) is not driven by an unillustrated drive mechanism (actuator) so that at least all of the X-rays irradiated from the X-ray source 200 and reaching the light receiving unit 350 do not pass through (X reaching the light receiving unit 350). And a retracted position that does not interfere with all of the lines) and an advanced position that is a position through which all of the X-rays irradiated from the X-ray source 200 and reaching the light receiving unit 350 pass. ing. Specifically, in the sample 610a shown in FIG. 15, the retracted position is a position indicated by a dotted line, and the advance position is a position indicated by a solid line. A similar movement is possible for the sample 610b. Note that the sample 610 (sample 610a and sample 610b) is disposed at a position that does not interfere with the inspection object 600 conveyed at least in the retracted position. Further, the sample 610 (sample 610a and sample 610b) has a thickness (length in a direction perpendicular to the conveyance surface, at least in a portion where X-rays pass through in order to make conditions of X-rays incident on each pixel uniform. Alternatively, the length and the composition in the direction connecting each portion and the center of the X-ray source are uniform.

  The movement of the sample 610 is configured to automatically advance to the advance position by the control unit 361 when, for example, a calibration setting is started in advance preparation (described later). In addition, the sample 610 may be advanced to the advance position based on an operation input (after confirming whether there is a placement object on the transfer surface 510) by the operator. At this time, an appropriate one of the sample 610a and the sample 610b corresponding to the inspection object 600 is selected (advanced) and used for calibration.

(Preparation)
In the second embodiment, I _D (V, z, ε) which is data from the line sensor unit in the energy band ε to ε + Δε of the pixel z in a state where X-rays are not irradiated, In the state where the sample 610 is in the advanced position and irradiated with X-rays (that is, all X-rays incident on the light receiving unit 350 pass through the sample 610), the energy band ε˜ of the pixel z Calibration is performed based on I _B (V, z, ε) which is data from the line sensor unit 300 of ε + Δε. Subsequent processing procedures for calibration (and dynamic range setting, etc.) are the same as those in the first embodiment. As in the first embodiment, the calibration in the absence of the sample 600 (and the object to be inspected) is also performed separately, and there is a passage of the X-ray sample 600 (the sample 600 is in the passage position) and It is also possible to store the calibration setting values when there is no passage (the sample 600 is at the retracted position) and use them as necessary.

  The remaining effects of the second embodiment are similar to those of the aforementioned first embodiment.

[Modification]
In the first embodiment, for the sake of simplification of description, an example in which the point (pixel) of (x _A , y _A ) and (x _B , y _B ) is targeted is shown. It may be expanded to (region occupied by a plurality of pixels), and an averaged gray value, a maximum or minimum value of gray values in the region, a median value, or the like may be used.

  In the second embodiment, the example in which the sample 610 is disposed above the transport unit 500 of the X-ray inspection apparatus has been described. However, the sample 610 may be disposed below the transport unit 500. The sample 610 may be arranged in any way as long as all the X-rays incident on the light receiving unit 350 pass through.

DESCRIPTION OF SYMBOLS 100 X-ray inspection apparatus 200 X-ray source 300 Line sensor unit 350 Light receiving part of line sensor unit 400 Image processing part of control apparatus of X-ray inspection apparatus 500 Conveying part of X-ray inspection apparatus 600 Inspected object

Claims (5)

An X-ray source for irradiating the inspection object with X-rays;
A multi-energy sensor that detects X-rays in a plurality of energy bands included in transmitted X-rays of the inspection object and outputs an energy spectrum for each pixel;
An X-ray comprising: an image processing unit that selects two types of energy bands suitable for foreign substance detection from the plurality of energy bands, and detects foreign substances by energy subtraction from images corresponding to the selected two types of energy bands. Inspection device.   The X-ray inspection apparatus according to claim 1, wherein the image processing unit executes processing for selecting images of two types of energy bands suitable for foreign object detection from a plurality of energy bands in advance setup.   The X-ray inspection apparatus according to claim 2, wherein the image processing unit further selects two types of energy bands that maximize a difference in contrast between images.   The X-ray inspection apparatus according to claim 1, wherein the image processing unit performs preprocessing so that uniform values can be obtained for all energy bands by calibration.   5. The X-ray inspection apparatus according to claim 1, further comprising a transport unit that carries the inspection object into and out of the X-ray irradiation area.