JP7437337B2 - Internal state imaging device and internal state imaging method - Google Patents

Description

The present invention relates to an internal state imaging device and an internal state imaging method for visualizing the internal state of a structure using radiation.

As an example of a device that does not require high radiation energy and can reliably determine the presence or absence of an object near the surface of an object to be inspected, such as a casting, by using backscattered radiation, Patent Document 1 describes A rotary table that holds and rotates the object to be inspected is provided in front of the object in the radiation irradiation direction, and a radiation detector that detects backscattered radiation from the object to be inspected on the rotary table via a collimator, and the radiation. Equipped with a reconstruction calculation device that constructs a CT image using the output of the detector, the object to be inspected is placed on a rotary table so that the center of the inspection area approximately coincides with the condensing point of the collimator, and the inspection area is moved through the rotation table. The object to be inspected is placed on the rotary table so that the axis of rotation passes through it, and the rotary table is rotated within an angular range of 180° to collect backscattered radiation data and use it to construct a tomographic image. It is described that the presence or absence of defects in the vicinity of the surface is inspected using radiation having enough energy to reach the inspection area in the vicinity of the surface without passing through the surface.

Further, as an example of an object imaging system using backscattered radiation, Patent Document 2 describes the following technology. The imaging system includes a radiation source that illuminates the object, and the radiation source is rotationally movable about the object. The imaging system also includes a detector that detects backscattered radiation from the object. The detector is positioned on substantially the same side of the object such that the light source and detector are rotationally movable about the object. The detector may be separated into multiple detector segments such that each segment has a single line of sight of projection through the object and detects radiation only along that line of sight. The restricted line of sight allows each detection segment to separate the desired components of the backscattered radiation. The radiation source and detector collect multiple images of the object at different rotation angles and can be moved independently of each other about the object. Multiple images can be used to generate a three-dimensional reconstruction of the object.

Japanese Patent Application Publication No. 2008-232765 Japanese Patent Application Publication No. 2013-174587

Social infrastructure equipment, such as bridges, tunnels, power cables, and railways, is aging rapidly. In order to maintain and manage these infrastructure devices, there is a need for automation and higher efficiency through the advancement of inspection technology.

Defects caused by aging include those that appear on the surface and those that occur internally, but early detection of internal defects is particularly important in order to prevent accidents.

To inspect the interior, it is common to use a method of acquiring density information of the object using electromagnetic waves such as radar, X-rays, and gamma rays that pass through the object. Examples include radiographic examination and X-ray CT (Computed Tomography).

However, these methods require scanning the object while being sandwiched between a radiation source and a sensor, and are difficult to apply to large structures or objects to which only one side can be accessed.

In addition, even in tests that do not use complicated scanning, such as radiographic tests, since the transmitted signal is a signal integrated along the radiation irradiation direction (hereinafter referred to as the depth direction), defects that occur in the object It is difficult to determine the position three-dimensionally.

As a method for dealing with such problems, for example, Patent Document 1 describes a radiation generation source, a rotary table, a radiation detector, and a method provided between the radiation detector and the object to be inspected on the rotary table. A method is described in which a tomographic image is constructed by comprising a collimator and a reconstruction calculation device, and by rotating the rotary table within an angular range of 180° so that the center of the inspection area coincides with the focal point of the collimator. be.

In addition, in Patent Document 2, a radiation source and a sensor are placed on the same side of an object, backscattered radiation from the object that is generated when the object is irradiated with radiation is detected, and the backscattered radiation is restored from the estimated value. There is a description of a method for restoring the density distribution of an object by performing repeated calculations to minimize the difference between the detected backscattered radiation and the detected backscattered radiation.

In the method described in Patent Document 1, the radiation source and the sensor are placed on the same side of the object, allowing access from one side, but the radiation path is limited by a collimator and imaged by rotation. However, since the counting rate of the number of backscattered photons is generally small, if the path of the radiation is limited and each point is measured, it will take a long time for the entire measurement.

Furthermore, in the inspection method described in Patent Document 2, the radiation source and the sensor are placed on the same side of the object, making it possible to estimate the three-dimensional density distribution of the object. However, calculating the inverse problem of formulating a nonlinear integral equation regarding the scattered radiation intensity, estimating the density distribution of the object, and minimizing the difference is extremely complicated. In an environment where the scattered radiation is a small signal and there is a lot of noise, the influence of errors is large, and it is generally difficult to solve the inverse problem.

In other words, if it were possible to irradiate a wide range of radiation and image the internal state of the inspection area all at once without limiting the radiation path using a collimator or solving an inverse problem, it would be faster and more efficient. It is expected that internal inspections will become possible. However, if a wide range of radiation is irradiated, the position where the radiation is scattered inside the object cannot be specified, and therefore the corresponding pixel cannot be determined in a forward-problematic manner, making it impossible to image the object.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an internal state imaging device and an internal state imaging method that can image the internal state of an inspection area more quickly than before in radiation scattering measurement. With the goal.

The present invention includes a plurality of means for solving the above problems, and one example is an internal state imaging device that images the internal state of an object by radiation scattering measurement. a radiation source that emits monochromatic radiation over a range towards the radiation source; a detector that detects scattered photons caused by the monochromatic radiation emitted from the radiation source at different positions; and photons of the scattered photons detected by the detector; an energy measurement device that measures energy and intensity; and one or more pixels corresponding to the scattering position from the photon energy and intensity measured by the energy measurement device, and a pixel value calculated, and the calculated pixel value. and an image reconstruction device that counts up by the positions of a plurality of detectors .

According to the present invention, the internal state of the inspection area can be imaged more quickly than in the past. Problems, configurations, and effects other than those described above will be made clear by the description of the following examples.

1 is a block diagram showing the overall configuration of an internal state imaging device according to a first embodiment of the present invention. FIG. 2 is a conceptual diagram in the case of a single detector for explaining the internal imaging method according to the first embodiment. FIG. 3 is a conceptual diagram in the case of two detectors for explaining the internal imaging method according to the first embodiment. It is an example of the energy spectrum obtained by the i-th detector in the internal imaging method according to the first example. FIG. 3 is a conceptual diagram showing a method of calculating pixels and pixel values in the internal imaging method according to the first example. 3 is a flowchart showing a first internal state imaging method according to the first example. 7 is a flowchart showing a second internal state imaging method according to the first embodiment. FIG. 2 is a conceptual diagram of an internal state imaging device and method according to a second embodiment of the present invention. 7 is a flowchart showing an internal state imaging method according to a second embodiment. FIG. 7 is a conceptual diagram of an internal state imaging device and method according to a third embodiment of the present invention. 7 is a flowchart showing an internal state imaging method according to a third embodiment. FIG. 7 is a conceptual diagram of an internal state imaging device and method according to a fourth embodiment of the present invention. FIG. 7 is a conceptual diagram of an internal state imaging device and method according to a fourth example. It is a flowchart which shows the internal state imaging method based on 4th Example.

Embodiments of the internal state imaging device and internal state imaging method of the present invention will be described below with reference to the drawings. In the drawings used in this specification, the same or corresponding components are given the same or similar symbols, and repeated description of these components may be omitted.

<First example>
A first embodiment of an internal state imaging device and an internal state imaging method of the present invention will be described with reference to FIGS. 1 to 7.

First, the overall configuration of the internal state imaging device will be described using FIG. 1. FIG. 1 shows the overall configuration of an internal state imaging device.

The internal state imaging device 1 of this embodiment shown in FIG. 1 is a device for imaging the internal state of a subject 102 by radiation scattering measurement, and includes a radiation source 101 that emits monochromatic radiation and detects scattered photons. It includes a plurality of detectors 106 that measure photon energy and intensity, an energy measurement device 107 that measures photon energy and intensity, an image reconstruction device 108, a display device 109, and a recording device 110.

The radiation source 101 is a radiation source that emits monochromatic radiation in a range toward the subject 102, and is, for example, a monochromatic gamma ray source. Note that the color is not limited to monochrome, and may be semi-monochrome. Furthermore, an element that emits radiation of a specific energy can also be used as the radiation source 101.

Note that quasi-monochromatic radiation here means radiation that has a single peak in the energy spectrum but whose spread (half-width) cannot be ignored, and monochromatic radiation has a single peak and its shall mean radiation whose extent is substantially negligible. Alternatively, monochromatic radiation refers to quasi-monochromatic radiation whose half width is particularly small.

Specific types include, for example, radioactive isotopes Cs-137, Zn-65, Be-7, Cr-51, Co-58, Mn-54, Hg-203, Sr-85, F-18, There are Ga-68, Al-28, and K-42. Furthermore, gamma rays generated by laser inverse Compton scattering can also be considered monochromatic.

Gamma rays 104 emitted from the radiation source 101 irradiate a wide range of the subject 102 . For example, if the radiation source 101 is a point ray source, it is conceivable to put the radiation source 101 as a point ray source into a cover that is open to a desired range of the subject 102 to be irradiated with gamma rays 104 emitted in 360 degrees. At this time, by providing a mechanism such as a collimator in the opening, a so-called fan beam or cone beam can be formed to provide a certain directivity and limit the area of interest to the beam irradiation range.

Gamma rays 104 emitted from the radiation source 101 generate scattered radiation 105 by Compton scattering inside the subject 102, which is detected by one of the plurality of detectors 106. The object 102 is an infrastructure structure made of concrete or metal, and defects 103 such as foreign matter, cracks, and peeling may occur inside the object.

The detector 106 is a plurality of gamma ray detectors having energy resolution, and a plurality of detectors 106 are provided to detect scattered photons generated by monochromatic radiation emitted from the radiation source 101 at different positions. The relative coordinates (xi, yi, zi) of each detector 106 with the radiation source 101 as the origin are known or can be measured by a configuration that measures relative coordinates. Each of the plurality of detectors 106 is preferably arranged in the same direction as the radiation source 101 with respect to the surface of the subject 102.

Examples of gamma ray detectors include Ge semiconductors, CdTe semiconductors, CdZnTe semiconductors, Si semiconductors, Perovskite structure semiconductors, LaBr ₃ scintillators, CsBr ₃ scintillators, LYSO scintillators, LSO scintillators, GAGG scintillators, CsI scintillators, NaI scintillators, BGO scintillators, Any one or more of a GSO scintillator, a GPS scintillator, a La-GPS scintillator, a LuAG scintillator, a SrI scintillator, etc. can be used.

The energy measurement device 107 is a device for measuring the photon energy and intensity of scattered photons detected by the plurality of detectors 106, and the energy measurement device 107 is a device for measuring the photon energy and intensity of scattered photons detected by the plurality of detectors 106. The peak value of the gamma ray photon (scattered photon) detected by the device 106i is processed to calculate the photon energy Ei. As shown in FIG. 1, the energy measuring device 107 can be composed of the same number of processing device groups as the detector 106, but it can also be a single processing device.

The image reconstruction device 108 is a device that calculates one or more pixels corresponding to the scattering position from the photon energy and intensity measured by the energy measurement device 107 for each of the plurality of detectors 106 to calculate a pixel value. The operating principle of the image reconstruction device 108 will be described below with reference to FIGS. 2 to 5.

The image reconstruction device 108 reconstructs the subject according to formula (1) based on the photon energy Ei obtained by processing the signal of the i-th detector with the energy measurement device 107 and the emission energy Ein of the radiation source 101. The scattering angle θi of Compton scattering that occurs inside 102 is calculated.

Here, E0 is approximately 511 keV. Assuming that the radiation source is the origin (0, 0, 0), the scattering point candidate (x, y, z ) exist in countless numbers and cannot be narrowed down to just one.

However, a set of such scattering point candidates (x, y, z) has a shape as shown in FIG. In FIG. 2, the irradiation range of gamma rays 104 emitted from the radiation source 101 is represented by a fan-shaped fan beam, and the above positional relationship is shown using coordinates such that the plane containing this fan beam matches the plane of the paper. It is. However, this is for explaining the present invention in an easy-to-understand manner, and the configuration of the present invention is not limited thereby. Naturally, the same method can be applied to a wider range of irradiation methods such as cone beam irradiation.

In FIG. 2, first, a circle passing through the coordinates (0, 0, 0) of the radiation source 101, the coordinates (xi, yi, zi) of the detector 106i, and the coordinates (xs, ys, zs) of the true scattering point 202 is drawn. think.

Next, when this circle is rotated around the straight line connecting the coordinates (0, 0, 0) of the radiation source 101 and the coordinates (xi, yi, zi) of the detector 106i, the coordinates of the true scattering point 202 are determined. The point where the rotation surface on the side containing (xs, ys, zs) (a set of such points forms an iso-energy surface 203) and the irradiation range 201 of the gamma ray 104 intersects is a scattering point candidate (x, y, z ) is a set 204. Even if the coordinates (xs, ys, zs) of the true scattering point 202 are unknown, the set 204 of scattering point candidates (x, y, z) whose scattering angle is θi is determined from the circumferential angle theorem. You can ask for it.

The image reconstruction device 108 holds a three-dimensional (or two-dimensional) image having pixels (voxels or pixels) obtained by dividing a region corresponding to real space into appropriate sizes. Every time a photon is detected by the i-th detector, scattering point candidates (x, y, z) are determined as described above, and the pixel values of all pixels including those points are counted up.

As described above, the image reconstruction device 108 counts up the pixel values of all pixels including the plurality of scattering point candidate points (x, y, z). In this case, the image will not reflect the internal state.

FIG. 3 shows the case where two detectors (106, 106') are used.

As shown in FIG. 3, by using a plurality of detectors 106, equal energy surfaces 203, 203', that is, sets 204, 204', are obtained by the number of detectors 106, but the coordinates of the true scattering point 202 (xs , ys, zs), the pixel values are accumulated by the number of detectors 106, that is, the number of sets 204, 204'. On the other hand, among the sets 204 and 204', at candidate points other than the true scattering point 202, pixel values are integrated only for one detector 106 or detector 106'.

Therefore, as the number of detectors 106 increases, the pixel including the coordinates (xs, ys, zs) of the true scattering point 202 will be emphasized, whereas the pixel value including the candidate point will be emphasized by one detector 106. Since there is only addition, it can ultimately be treated as small noise (generally called an artifact).

FIG. 4 is an example of an energy spectrum 401 obtained by the i-th detector 106i. In FIG. 4, when energy E is specified, the number of photons Ci(E) detected by the detector 106 with that energy is obtained. If N detectors 106 are used, N sets of such energy spectra can be obtained.

FIG. 5 is a conceptual diagram showing a method of calculating a pixel 502 and a pixel value I (x, y, z) in an imaging region 501 from an energy spectrum 401. The pixel value can be calculated according to Equation (2) below.

Here, (x, y, z) are the coordinates of the pixel 502, and the photon energy Ei (x, y, z) detected by the i-th detector 106i corresponding to the pixel 502 is expressed by the following formula (3). It can be calculated according to

As mentioned above, E0 is approximately 511 keV. Furthermore, cosθi can be calculated according to the following equation (4).

Here, the energy spectrum Ci(E) may include not only Compton scattering reflecting the internal state of the subject 102 but also incident photons from the surroundings as a background signal. In order to remove such background, the pixel value calculated using the energy spectrum obtained by measuring without placing the subject 102 may be subtracted from the energy spectrum obtained with the subject 102 placed. can.

In the manner described above, pixel values can be calculated.

Returning to FIG. 1, the display device 109 is a display device such as a display that displays the pixel values calculated by the image reconstruction device 108. As for the display method, it may be possible to display the information in three dimensions on a display, or it may be recorded as data in a computer's recording device 110 such as a memory or a hard disk.

Next, refer to FIGS. 6 and 7 for a method of imaging the internal state of the subject 102 by radiation scattering measurement according to the present embodiment, which is suitably executed by the internal state imaging apparatus 1 according to the present embodiment described above. and explain. FIG. 6 is a flowchart showing the first internal state imaging method, and FIG. 7 is a flowchart showing the second internal state imaging method.

First, a radiation source 101 and a plurality of detectors 106 are placed at measurement points on the subject 102 (step S11). This step S11 corresponds to the step of arranging the radiation source 101 and the detector 106 at the measurement point. At this time, each of the plurality of detectors 106 is preferably arranged in the same direction as the radiation source 101 with respect to the surface of the subject 102.

Next, the positions of the radiation source 101 and each of the plurality of detectors 106 are recorded (step S12). This step S12 corresponds to a step of recording the arrangement positions of the radiation source 101 and the detector 106.

Thereafter, a wide range of the subject 102 is irradiated with gamma rays 104 from the radiation source 101 . Then, scattered photons generated inside the subject 102 by the irradiation with the gamma rays 104 are detected by each of the plurality of detectors 106, and an energy spectrum is recorded from the detected values by the energy measuring device 107 (step S13). This step S13 includes a step of emitting radiation from the radiation source 101 and detecting scattered photons generated inside the subject 102 with the detector 106, and a step of recording the energy spectrum of the radiation detected by the detector 106. Equivalent to.

Next, the image reconstruction device 108 selects one pixel corresponding to the irradiation area in real space from the previously recorded energy spectrum (step S14). This step S14 corresponds to the step of selecting pixels corresponding to the radiation irradiation area.

Thereafter, the pixel value of the pixel selected in step S14 is calculated according to formulas (2) to (4) (step S15). This step S15 is a step of calculating the corresponding energy from the positional relationship between the radiation source 101, the detector 106, and the pixel, and a step of calculating the pixel value to be added to the pixel from the calculated energy and the recorded energy spectrum. Equivalent to.

Next, it is determined whether the calculation of the pixel values of all pixels has been completed (step S16). If it is determined that there are still pixels remaining, the process returns to step S14, another pixel is selected, and the calculation is performed again.

On the other hand, when it is determined that the calculation of the pixel values of all pixels has been completed, the process advances to step S17, and the calculation results are displayed on the display device 109 (step S17), and the calculation results are displayed on the recording device 110. Record and complete the process. This step S17 corresponds to the step of displaying pixel values.

The above describes the procedure for performing image reconstruction after measuring the energy spectrum.

Apart from the procedure shown in FIG. 6, by calculating the corresponding pixel each time a photon is detected and calculating the pixel value, it is possible to display the calculation results in real time. The procedure will be explained below using FIG. 7.

First, the radiation source 101 and the detector 106 are placed at a measurement point, and the pixel value is initialized to 0 (step S21). A part of this step S21 corresponds to the step of arranging the radiation source 101 and the detector 106 at the measurement point.

Next, the positions of the radiation source 101 and the plurality of detectors 106 placed in step S21 are recorded (step S22). This step S22 corresponds to a step of recording the arrangement positions of the radiation source 101 and the detector 106.

After that, gamma rays 104 are irradiated from the radiation source 101 to a wide area of the subject 102, and the detector 106 detects one photon. At the timing of the detection, the energy measuring device 107 records the energy of the photon (step S23). This step S23 corresponds to a step of emitting radiation from the radiation source 101 and detecting scattered photons generated inside the subject 102 with the detector 106, and a step of recording the energy of the radiation detected by the detector 106. do.

Next, from the positions and energy of the radiation source 101 and the detector 106, the scattering angle θi is calculated according to formula (1), and the scattering point candidate point (x, y , z), that is, the intersection of the iso-energy surface 203 and the irradiation range of the gamma rays 104. Then, a plurality of pixels including such candidate points (x, y, z) are selected (step S24). This step S24 corresponds to the step of calculating the scattering angle from the positions and energy of the radiation source 101 and the detector 106, and the step of selecting pixels having the same scattering angle.

Next, the pixel values of the plurality of pixels selected in step S24 are counted up (+1) (step S25). This step S25 corresponds to the step of adding the number of detections to the pixels.

Next, it is determined whether the current count value has become a sufficient statistic for the target internal state imaging accuracy (step S26). If it is determined that the statistical amount is still insufficient, the process returns to step S23, scattered photons are detected again, and pixel selection and pixel value calculation are performed again.

On the other hand, when it is determined in step S26 that sufficient statistics have been obtained, the measurement is ended and the process proceeds to step S27, where the calculation results are displayed on the display device 109 (step S27) and recorded. Recording is performed on the device 110 to complete the process. This step S27 corresponds to the step of displaying the pixels to which the number of detections has been added.

Next, the effects of this embodiment will be explained.

The internal state imaging device 1 according to the first embodiment of the present invention described above includes a radiation source 101 that emits monochromatic radiation in a range toward a subject 102, and scattered photons generated by the monochromatic radiation emitted from the radiation source 101. a detector 106 that detects the scattered photons at different positions; an energy measuring device 107 that measures the photon energy and intensity of the scattered photons detected by the detector 106; An image reconstruction device 108 that calculates a pixel value by calculating one or more corresponding pixels is provided.

This makes it possible to irradiate a wide range of radiation to the internal region within the subject 102 and image the internal state of the examination region all at once. Therefore, it is possible to avoid an increase in the time required for the entire measurement without performing complicated processing.

Further, the method of imaging the internal state of the subject 102 by radiation scattering measurement includes a step of arranging the radiation source 101 and the detector 106 at a measurement point, and a step of recording the arrangement positions of the radiation source 101 and the detector 106. , a step of irradiating radiation from a radiation source 101 and detecting scattered photons generated inside the subject 102 with a detector 106, a step of recording an energy spectrum of the radiation detected by the detector 106, and a step of recording the energy spectrum of the radiation detected by the detector 106; a step of selecting a pixel corresponding to the pixel, a step of calculating the corresponding energy from the positional relationship of the radiation source 101, the detector 106, and the pixel, and a pixel value to be added to the pixel from the calculated energy and the recorded energy spectrum. By having the step of calculating , the same effect as that obtained by the internal state imaging device 1 described above can be obtained.

Furthermore, the method includes the steps of arranging the radiation source 101 and the detector 106 at measurement points, and recording the arrangement positions of the radiation source 101 and the detector 106. a step of emitting radiation from the radiation source 101 and detecting scattered photons generated inside the subject 102 with the detector 106; a step of recording the energy of the radiation detected by the detector 106; 101 and the position of the detector 106, as well as calculating the scattering angle from the energy; selecting pixels with the same scattering angle; adding the number of detections to the pixels; By including the step of displaying, the same effect as that obtained by the internal state imaging device 1 described above can be obtained. Furthermore, this method has the advantage that pixel values can be obtained in real time.

In addition, since the plurality of detectors 106 are arranged in the same direction as the radiation source 101 with respect to the surface of the subject 102, it is possible to easily arrange a plurality of detectors 106, and it is also possible to time can be made shorter.

Furthermore, by further providing a display device 109 that displays the pixel values calculated by the image reconstruction device 108, the obtained results can be easily understood.

<Second example>
An internal state imaging device and internal state imaging method according to a second embodiment of the present invention will be described using FIGS. 8 and 9. FIG. FIG. 8 is a conceptual diagram of an internal state imaging apparatus and method according to the second embodiment, and FIG. 9 is a flowchart showing the internal state imaging method.

The internal state imaging device of the second embodiment uses a detector generally called a Compton camera 801 as a detector. As shown in FIG. 8, when a scattered photon is detected, the Compton camera 801 measures the photon energy, and can limit the candidate incident direction of the photon to the side surface of a cone 802 with the Compton camera 801 as the apex.

The apex angle of this cone 802 can be calculated by the Compton camera 801, and the formed cone 802 is generally called a Compton cone. Using this principle, a set of scattering point candidates (x, y, z) calculated from the scattered photon energy and the position of the Compton camera 801 is calculated by processing similar to the calculation processing described in the first embodiment. By calculating the intersection points 803 and 804 between the energy plane 203, the irradiation range 201 of the gamma rays 104, and the Compton cone 802, the pixels of candidate points can be further narrowed down.

Note that, as in the first embodiment, there are multiple scattering point candidates (x, y, z) found by one Compton camera 801, and it is not possible to narrow it down to one point, so a plurality of Compton cameras 801 are provided.

Note that all the detectors used do not need to be the Compton camera 801, and one or more of the plurality of detectors may be mixed with the Compton camera 801 and use a gamma ray detector or the like as in the first embodiment.

Next, the internal state imaging method of this embodiment will be explained using FIG. 9.

In the process of this embodiment shown in FIG. 9, among the internal state imaging steps described in FIG. 7, step S31 and step S32 are executed in place of step S24.

As shown in FIG. 9, after step S23, a Compton cone 802 is calculated (step S31). Subsequently, candidate pixels corresponding to the intersections of the equal energy surface 203, the irradiation range, and the Compton cone 802 are selected (step S32).

Furthermore, in step S25, as in the first embodiment, the pixel values of the plurality of pixels selected in step S24 are counted up (+1).

The other configurations and operations are substantially the same as those of the internal state imaging device and internal state imaging method of the first embodiment described above, and the details will be omitted.

The internal state imaging device and internal state imaging method according to the second embodiment of the present invention also provide substantially the same effects as the internal state imaging device and internal state imaging method according to the first embodiment described above.

Furthermore, by using the Compton camera 801 as the detector 106 and calculating the Compton cone 802 in the step of selecting pixels, and selecting the intersection of pixels that have the same scattering angle as the Compton cone 802 as a candidate pixel, Since candidates for photon incident directions can be limited, calculation load can be reduced. Therefore, pixel values can be obtained more quickly, and the device configuration can be simplified.

<Third Example>
An internal state imaging device and internal state imaging method according to a third embodiment of the present invention will be described with reference to FIGS. 10 and 11. FIG. 10 is a conceptual diagram of an internal state imaging apparatus and method according to the third embodiment, and FIG. 11 is a flowchart showing the internal state imaging method.

In the internal state imaging device of the third embodiment, unlike the internal state imaging device 1 of the first embodiment, the number of detectors 106 is one, and the relative positions of the radiation source 101 and the detector 106 are variable. , the relative positional relationship 1002 thereof is configured to change from moment to moment. Therefore, a position measuring unit 1001 is further provided that measures the relative coordinates of the detector 106 with respect to the radiation source 101 at the timing when the detector 106 detects a photon.

In this example, since the position of the detector 106 is changed, a plurality of detection data of scattered photons are obtained at different measurement positions, so it is difficult to reconstruct an image of the internal state using only a single detector 106. I can do it. Naturally, it is also possible to configure a plurality of detectors 106, in which case pixel values can be obtained more quickly.

Next, the internal state imaging method of this example will be explained using FIG. 11.

In the process of this embodiment shown in FIG. 11, among the steps of internal state imaging described in FIG. 7, step S41 is executed in place of step S22.

As shown in FIG. 11, after step S21, the relative position of the detector 106 with respect to the radiation source 101 at the timing when the photon is detected by the variable-position detector 106 is measured and recorded (step S41).

Subsequent steps S23 to S27 are similar to those in the first embodiment, but in step S24, candidate pixels are selected using the measured relative positions of the radiation source 101 and the detector 106. If it is determined in step S26 that sufficient statistics have not been obtained, the process returns to step S41 to detect scattered photons again, measure the relative position of the detector 106 to the radiation source 101, select pixels, and Performs pixel value calculations. If it is determined in step S26 that sufficient statistics have been obtained, the measurement ends, and in step S28, the calculation results are displayed on the display device 109 and recorded in the recording device 110.

The other configurations and operations are substantially the same as those of the internal state imaging device and internal state imaging method of the first embodiment described above, and the details will be omitted.

The internal state imaging device and internal state imaging method according to the third embodiment of the present invention also provide substantially the same effects as the internal state imaging device and internal state imaging method according to the first embodiment described above.

Furthermore, in the step of making the relative position between the radiation source 101 and the detector 106 variable and recording the positions of the radiation source 101 and the detector 106, the relative position of the detector 106 with respect to the radiation source 101 is measured and a pixel is selected. In step, candidate pixels are selected using the measured relative positions of the radiation source 101 and the detector 106, thereby eliminating the need to provide a plurality of detectors 106.

Note that, as the detector 106 in this embodiment, the Compton camera 801 can be used as in the second embodiment.

<Fourth example>
An internal state imaging device and an internal state imaging method according to a fourth embodiment of the present invention will be described with reference to FIGS. 12 to 14. FIG. 12 and 13 are conceptual diagrams of an internal state imaging apparatus and method according to the fourth embodiment, and FIG. 14 is a flowchart showing the internal state imaging method.

In the internal state imaging device of the fourth embodiment, as shown in FIG. 11 in the internal state imaging device 1 of the first embodiment, the energy measuring device 107C measures the radiation detection time and uses a predetermined time width. It has a simultaneous detection determination unit 1201 that determines whether or not the radiation detected in the two is simultaneous.

In addition, as shown in FIG. 11, the image reconstruction device 108C also determines the position of the detector 106 that detected the radiation that was determined to have reached the detector 106 at the same time (that is, the position of the radiation that reached the detector 106). ) and photon energy to calculate pixels and pixel values.

FIG. 12 shows a method for calculating pixel values when scattered photons are detected non-simultaneously by the i-th detector 106i and the j-th detector 106j. As shown in FIG. 12, when scattered photons are detected non-simultaneously, candidate pixels are calculated using the method shown in the first embodiment.

FIG. 13 shows a method of calculating pixel values when scattered photons are simultaneously detected by the i-th detector 106i and the j-th detector 106j in the same positional relationship of the detectors 106 as in FIG. 12. . In this way, when scattered photons are detected at the same time, Compton scattering occurs inside one of the detectors 106i or 106j, and the scattered photons are detected by the other detector 106j or detector 106i. You can think about it.

Assuming that Compton scattering occurs at the i-th detector 106i and the scattered photons are detected at the j-th detector 106j, the Compton cone 802 can be drawn as follows, similar to the second embodiment. . The Compton cone 802 has a central axis that is a straight line connecting the coordinates of the i-th detector 106i and the j-th detector 106j, and the half-apex angle θc is calculated according to the following equation (5).

Here, Ei is the energy imparted to the i-th detector 106i by the photon scattered inside the object 102, and Ej is the energy imparted to the i-th detector 106i by the scattered photon Compton-scattered by the i-th detector 106i. It is the energy given to E0, and E0 is 511 keV.

The equal energy surface 203 can be drawn using the relative coordinates of the i-th detector 106i with respect to the position of the radiation source 101 and the scattering angle calculated from Ei replaced by Ei+Ej in Equation (1).

Since the non-simultaneous event shown in FIG. 12 and the simultaneous event shown in FIG. 13 are contradictory to each other, it is possible to image the internal state using each event. When displaying the final image, it is possible to display them independently, or to reduce artifacts by weighted addition of pixel values, while effectively utilizing detected events to create an image in a short time. becomes possible.

Next, the internal state imaging method of this example will be explained using FIG. 14.

As shown in FIG. 14, after photon energy is recorded in step S23 in the internal state imaging process described in FIG. 7, it is determined whether simultaneous detection is performed (step S51). This step S51 corresponds to a step of measuring the detection time of radiation and determining whether or not the radiations detected within a predetermined time width are simultaneous.

If it is determined in step S51 that they are not simultaneous, the process proceeds to step S24, and the intersection of the equal energy surface 203 and the radiation irradiation range is selected as a candidate pixel, as in the first embodiment (step S24). Thereafter, weights of pixel values for non-simultaneous events are set (step S52), and the pixel values of the pixels selected with these weights are counted up (+weight) (step S54). Thereafter, it is determined whether the current count value has become a sufficient statistic for the target internal state imaging accuracy (step S26).

On the other hand, if it is determined in step S51 that they are simultaneous, the Compton cone 802 is calculated (step S31). Subsequently, the intersection of the equal energy surface 203, the irradiation range, and the Compton cone 802 is selected as a candidate pixel (step S32).

After that, weights of pixel values for simultaneous events are set (step S53), and the pixel values of the pixels selected with these weights are counted up (+weight) (step S54). Thereafter, it is determined whether the current count value has become a sufficient statistic for the target internal state imaging accuracy (step S26).

The weight selected in step S52 or step S53 described above can be given in advance using some kind of input unit.

Note that instead of counting up pixel values in real time, it is possible to image the non-simultaneous events and the simultaneous events independently, and then change the weights and add the respective images with weights for display. In this case, the values can be added and displayed with weights.

The other configurations and operations are substantially the same as those of the internal state imaging device and internal state imaging method of the first embodiment described above, and the details will be omitted.

The internal state imaging device and internal state imaging method according to the fourth embodiment of the present invention also provide substantially the same effects as the internal state imaging device and internal state imaging method according to the first embodiment described above.

The method further includes a step of measuring radiation detection time and determining whether or not the radiations detected within a predetermined time width are simultaneous; A scattering angle is calculated from the position of the radiation source 101, the position of the detector 106, and the energy, and pixels with the same scattering angle are selected. If it is determined that they are simultaneous, a Compton cone 802 is calculated and the Compton cone 802 is By selecting the intersection of pixels that have the same scattering angle as candidate pixels, it is possible to visualize the internal state using each event, and obtain highly accurate pixel values that more accurately depict the inside of the object 102. I can do it.

Furthermore, by setting weights for cases in which it is not determined to be simultaneous and cases in which it is determined to be simultaneous, the pixel values of the selected pixels are added with weights, thereby reducing artifacts and making effective use of detected events. Imaging can be done in a short time.

In addition, by holding internal state images for cases in which it is not determined to be simultaneous and cases in which it is determined to be simultaneous, and by calculating and composing the internal state images, more accurate pixel values can be obtained.

<Others>
Note that the present invention is not limited to the above-described embodiments, and includes various modifications. The above-mentioned embodiments have been described in detail to explain the present invention in an easy-to-understand manner, and the present invention is not necessarily limited to having all the configurations described.

Further, it is also possible to replace a 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. Furthermore, it is also possible to add, delete, or replace some of the configurations of each embodiment with other configurations.

1... Internal state imaging device 101... Radiation source 102... Subject (object)
103... Defect 104... Gamma ray 105... Scattered radiation 106, 106', 106a, 106b, 106c, 106d, 106e, 106f, 106i, 106j... Detector 107, 107C... Energy measurement device 108, 108C... Image reconstruction device 109... Display device 110... Recording device 201... Irradiation range 202... True scattering points 203, 203'... Equal energy plane 204, 204'... Set of candidate points for pixels to be selected 401... Energy spectrum 501... Imaging area 502... Pixel 801 ... Compton camera 802 ... Cone, Compton cone 803, 804 ... Intersection of Compton cone and equal energy surface 1001 ... Position measurement unit (position sensor)
1002... Relative positional relationship 1201... Simultaneous detection determination section (coincidence counting section)
1202...Calculation section

Claims (14)

An internal state imaging device that images the internal state of a target by radiation scattering measurement,
a radiation source that emits a range of monochromatic radiation toward the object;
a detector for detecting scattered photons produced by the monochromatic radiation emitted from the radiation source at different positions;
an energy measurement device that measures photon energy and intensity of the scattered photons detected by the detector;
One or more pixels corresponding to the scattering position are calculated from the photon energy and intensity measured by the energy measuring device, a pixel value is calculated, and the calculated pixel value is counted up by the positions of the plurality of detectors. An internal state imaging device comprising: an image reconstruction device. The internal state imaging device according to claim 1,
An internal state imaging device, wherein the detector is arranged in the same direction as the radiation source with respect to the surface of the object. The internal state imaging device according to claim 1,
An internal state imaging device characterized in that a Compton camera is used as the detector. The internal state imaging device according to claim 1,
The detector has a variable position relative to the radiation source,
An internal state imaging device further comprising a position sensor that measures the relative position of the detector with respect to the radiation source. The internal state imaging device according to claim 1,
The energy measurement device has a coincidence unit that measures radiation detection time and determines whether or not the radiation detected within a predetermined time width is simultaneous;
The internal state imaging device, wherein the image reconstruction device includes a calculation unit that calculates pixels and pixel values from the position and energy of radiation that simultaneously reaches the detector. The internal state imaging device according to claim 1,
An internal state imaging device further comprising a display device that displays the pixel values calculated by the image reconstruction device. A method of imaging the internal state of an object by radiation scattering measurement, the method comprising:
placing a radiation source and a detector at the measurement point;
recording the placement positions of the radiation source and the detector;
irradiating radiation from the radiation source and detecting scattered photons generated inside the object with the detector;
recording an energy spectrum of radiation detected by the detector;
a step of selecting pixels corresponding to the radiation irradiation area;
calculating the corresponding energy from the positional relationship of the radiation source, the detector, and the pixel;
calculating a pixel value to be added to the pixel from the calculated energy and the recorded energy spectrum ,
Execute each step above multiple times at different positions or timings,
An internal state imaging method characterized by further comprising the step of adding the obtained pixel values obtained at each arrangement position when the arrangement position is changed . A method of imaging the internal state of an object by radiation scattering measurement, the method comprising:
placing a radiation source and a detector at the measurement point;
recording the placement positions of the radiation source and the detector;
irradiating radiation from the radiation source and detecting scattered photons generated inside the object with the detector;
recording the energy of radiation detected by the detector;
calculating a scattering angle from the positions of the radiation source and the detector and the energy;
selecting pixels with the same scattering angle;
adding a detection number to the pixel;
displaying the pixels to which the number of detections has been added ;
An internal state imaging method characterized by performing each of the above steps multiple times at different positions or timings . The internal state imaging method according to claim 8,
A Compton camera is used as the detector,
An internal state imaging method characterized in that, in the step of selecting the pixels, a Compton cone is calculated, and an intersection point of pixels having the same scattering angle as the Compton cone is selected as a candidate pixel. The internal state imaging method according to claim 7 or 8,
The relative position of the radiation source and the detector is variable;
In the step of recording the positions of the radiation source and the detector, measuring the relative position of the detector with respect to the radiation source;
An internal state imaging method, wherein in the step of selecting the pixel, a candidate pixel is selected using the measured relative position between the radiation source and the detector. The internal state imaging method according to claim 8,
further comprising the step of measuring the detection time of the radiation and determining whether or not the radiation detected within a predetermined time width is simultaneous;
In the step of selecting the pixels,
If it is determined that they are not simultaneous, calculate the scattering angle from the position of the radiation source, the position of the detector, and the energy, and select pixels with the same scattering angle,
If it is determined that they are simultaneous, a Compton cone is calculated, and an intersection of pixels having the same scattering angle as the Compton cone is selected as a candidate pixel. The internal state imaging method according to claim 11,
An internal state imaging method characterized by setting weights for cases in which it is not determined to be simultaneous and cases in which it is determined to be simultaneous, and adding pixel values of the selected pixels with weights. The internal state imaging method according to claim 11,
An internal state imaging method characterized by having internal state images for cases in which it is not determined to be simultaneous and cases in which it is determined to be simultaneous, and calculating and synthesizing the internal state images. The internal state imaging method according to claim 7,
An internal state imaging method, further comprising the step of displaying the pixel values.

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