JP2007271468A - Low exposure x-ray inspection method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low exposure X-ray inspection device employing a super-sensitivity semiconductor radiation imager by photon counting operation and a low output high energy X-ray source. <P>SOLUTION: A semiconductor radiation detector of super-sensitivity using CdTe is arranged in a plane shape and constituted so as to acquire a two-dimensional image. An X-rays detection signal from each semiconductor radiation detector is processed by a signal processing circuit, but a circuit for performing the discriminating operation with the signal intensity is provided in this case. Further, this discriminating operation is processed at high speed so that it is finished within the incident time of one photon. Thus, energy level of incident X-ray becomes clear, and the incident amount every energy level can be counted. An RGB image signal is created from an intensity image signal determined in each energy band, and is displayed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an X-ray inspection method and apparatus replacing a metal detector.

For security reasons, some public facilities have been equipped with metal detectors to check for dangerous items such as knives of visitors. However, since checking by a metal detector is limited to metal, there is a question about its effectiveness, and in recent years, inspection apparatuses using X-rays are being introduced. However, with X-ray inspection devices, exposure to the human body is a problem, and there are very few introductions among public facilities.
Up to now, there has been a low-exposure X-ray apparatus, but it uses a stimulable phosphor sheet (see Patent Document 1), and lacks immediacy. In addition, there are images that use different X-ray energies, but a filter is used in the X-ray generation source (see Patent Document 2).
Japanese Patent Laid-Open No. 10-268450 JP 2003-279503 A

In order to minimize the influence on the human body, it is required to reduce the amount of X-ray exposure.
For this purpose, we have developed an ultra-sensitive semiconductor radiation detector and proposed a low-exposure X-ray inspection method and apparatus that can be used as an X-ray imaging device (imager) and minimizes exposure to the human body. To do.

The present invention provides a low-exposure X-ray inspection apparatus using an ultra-sensitive semiconductor radiation imager by a photon counting operation and a low-output high-energy X-ray source. In particular, it is a low-exposure inspection apparatus that can be applied to the human body, and can be applied to a place where a conventional metal detector is used.
As the ultra-sensitive semiconductor radiation detector, one using CdTe is typically adopted. This semiconductor radiation detector is arranged in a plane and configured to obtain a two-dimensional image.
An X-ray detection signal from each semiconductor radiation detector is processed by a signal processing circuit. At this time, a circuit for performing a discrimination operation according to the signal intensity is provided. Furthermore, this discrimination operation is processed at high speed so as to be completed within the time when one photon is incident. As a result, the energy level of the incident X-ray is determined, and the incident amount for each energy level can be counted.

1. This is an inspection device that can be miniaturized using an ultra-sensitive semiconductor radiation detector by photon counting operation as an imager.
2. High linearity is mainly used because high energy radiation with low absorbed dose is mainly used. Low energy radiation is cut by a filter.
3. A semiconductor radiation detector, for example CdTe suitable for high energy radiation, is used.
4). Contrast, which is a problem in low-dose imaging, is obtained by using a photon counting operation imager with high quantitativeness to obtain a much higher contrast at the same dose than before, and an image with a high degree of freedom from accurate imaging data. Arithmetic processing is possible, and high functionality can be achieved as required.
5). The imager employed in the present invention has a radiation discrimination function, and removes the influence caused by the generation of scattered radiation, which is unavoidable in principle when using radiographic imaging, particularly high-energy radiation, and obtains high contrast and image quality. When the substance to be measured is determined, extractive imaging can be performed by calculation between images of a plurality of energy band images, and further, low-exposure and high-contrast imaging can be performed.

The basic idea is as follows.
1. A simple method and apparatus for placing a subject between an ultra-sensitive radiation imager for photon counting operation and a low-power high-energy X-ray source.
2. If the imager is a two-dimensional type, a moving image can be captured. If the line scanner type is used, a still image can be captured by moving an object, and any format may be selected depending on the application.
3. However, from the concept of low exposure, taking into account the radiation dose to the place other than the measurement location, if the measurement range can be measured at once with a two-dimensional imager, the inspection time can be shortened accordingly, resulting in lower exposure.
4). By using only the high energy band that easily penetrates the human body at a low dose (the low energy band is removed with a filter), a transmission image can be obtained with an absorbed dose equivalent to or lower than the backscatter system applied to the human body. Can do.
5). High-degree-of-freedom computations such as contrast adjustment that lead to lower exposure are possible with image data with high quantitativeness and energy discrimination function generated by photon counting operation.

  The photon counting type imager detects charges generated when one X-ray or γ-ray photon is incident on a radiation detection element typified by cadmium telluride (CdTe). The number of generated charges is proportional to the energy of incident photons. Therefore, the energy of the incident photon can be determined by discriminating the peak value of the signal obtained as the output. The discrimination operation must be completed before the next photon is incident. For an environment where photons are continuously incident, the time window is narrowed and energy is discriminated at the time interval when one photon is incident. . Further, the number of incident photons per unit time is reduced by attenuation by a thin plate such as iron or lead so that the number of photons can be counted. After that, counting is performed for each discriminated energy category.

FIG. 1 shows a transmission type X-ray inspection apparatus for an inspection object.
1 is an X-ray source, 2 is an inspection object, and 3 is a photon counting imager. X-rays from the X-ray source (1) pass through the inspection object and project an image of the object on the photon counting imager.
The two-dimensional image obtained by the photon counting imager (3) is discriminated by energy and is colored by energy band and displayed on the display means (5) by the signal processing circuit (4). If the display means is not capable of multicolor display, display such as gradation display and contour display is performed. Alternatively, the screen may be divided and image display for each energy band may be performed.
If there is an abnormality in the X-ray transmittance of the inspection object, it is displayed on the screen as a color change or irregular contour lines. If the object itself contains a radioactive substance, X-rays from the object are captured by a photon counting imager and imaged. In this case, since the energy is different from that of the X-ray from the original X-ray source (1), it can be displayed on the image in a distinguishable manner by energy discrimination.

FIG. 2 shows an example of signal processing of a captured image.
The signal processing circuit (4) receives the image signal from the photon counting imager (3) and inputs it to the image processing circuit (6, 6 ′, 6 ″) for each energy band. In the image processing circuit, contrast adjustment, Processing such as luminance adjustment and γ correction is performed, and a signal is supplied to the color drive circuit (7, 7 ′, 7 ″). In the color driving circuit, the signal from the image processing circuit is converted into a color signal such as an RGB (red, green, blue) coordinate system signal or an XYZ coordinate system signal.
Further, if necessary, the image processing circuit performs inter-image calculations such as difference calculation and product calculation between the energy band signals. Depending on the situation, the signal intensity of each energy band may be converted into power and added, and pseudo color display (display method for changing the color according to the signal level) may be performed based on the total value. It is useful to make these processes switchable as desired.
FIG. 3 shows a conceptual diagram of the photon counting imager. 11 is CdTe, 12 is an amplifier, 13 is a comparator for performing energy discrimination, and 14 is a counter. Different voltages V1, V2, V3... Are applied to the other input of the comparator (13), respectively, so that energy discrimination is possible. A collimator (15) is provided as necessary. This is a single unit, and a plurality of units are arranged on the surface to constitute an imager (imaging device).
Alternatively, a line scanner is configured by arranging a plurality of units in a straight line. At this time, by moving the line scanner or the object, scanning is performed to obtain a surface image.

FIG. 4 shows an example in which after the energy discrimination is performed by the comparator (13), the exclusive OR circuit (16) performs counting for each energy band. The discrimination voltages V1, V2, V3 ... are set as V1>V2> V3 ...., and when the input signal exceeds the discrimination voltage, a counting pulse is output. . By providing an exclusive OR circuit (16), pulses corresponding to energy levels exceeding V1, pulses corresponding to energy levels exceeding V2 and not exceeding V1, pulses corresponding to energy levels exceeding V3 and not exceeding V2 Are individually input to the counter (14).
In FIG. 5, the energy discrimination is performed by the comparator (13), the output pulses are counted by the counter (14), and then the high energy side count value is subtracted from the low energy side count value by the subtractor (17). This is an example of obtaining a count value for each energy band. In this case as well, the discrimination voltages V1, V2, V3 ... are set as V1>V2> V3 ..., and when the input signal exceeds the discrimination voltage, the counting pulse Is output. The count value on the low energy side includes a count value corresponding to the high energy component, and a subtracter (17) is provided to remove this count value. The subtraction process itself may be performed in the signal processing circuit (4) at the subsequent stage.

  Because it is a low-exposure type, it is possible to inspect the possession of transmission-type dangerous goods even for the human body, and it can be replaced with conventional metal detectors.

Diagram showing overall configuration The figure which shows the signal processing example of a captured image Diagram showing the concept of photon counting imager The figure which shows the example which provides exclusive OR circuit (16) and counts according to energy zone The figure which shows the example which provides a subtraction circuit (17) and outputs a count value according to energy band

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 X-ray source 2 Inspection object 3 Photon counting imager 4 Signal processing circuit 5 Display means 6 Image processing circuit 7 Color drive circuit 11 CdTe
12 amplifier 13 comparator 14 counter 15 collimator 16 exclusive OR circuit 17 subtraction circuit

Claims (4)

An inspection object is inserted between the low-output high-energy X-ray source and the plurality of X-ray detectors, X-ray image information of the inspection object is acquired from the X-ray detector, and the acquired image information is converted into X-rays. A low-exposure X-ray inspection method that discriminates by energy band, obtains intensity for each discriminated X-ray energy band, and displays the obtained intensity image signal on a display. The low-exposure X-ray inspection method according to claim 1, further comprising performing inter-image computation between image signals obtained for each X-ray energy band. X-ray image of X-ray image of the object acquired from the low-output high-energy X-ray source, a plurality of X-ray detectors provided apart from the low-output high-energy X-ray source, and the X-ray detector A low-exposure X-ray inspection apparatus comprising means for discriminating by energy band, means for obtaining intensity for each discriminated energy band, and a display for displaying the obtained intensity image signal. 4. The low-exposure X-ray inspection apparatus according to claim 3, further comprising means for performing an inter-image calculation between image signals obtained for each X-ray energy band.

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