Radioactive source quantitative imaging method based on coded aperture technology and laser radar

Abstract

The invention discloses a radioactive source quantitative imaging method based on a coding aperture technology and a laser radar, and the method comprises the steps: 1), obtaining a coding projection and an energy spectrum of a radioactive source in a target region through a coding aperture gamma camera, and carrying out the decoding calculation of the coding projection, and obtaining a coding reconstruction image O; 2) obtaining radiation hotspots in the image O, and generating a radiation hotspot image; 3) identifying the full-energy peak E of the radioactive source according to the energy spectrum, and calculating the dose rate of the position where the camera is located; 4) acquiring three-dimensional point cloud information of the target area through a laser radar, and acquiring optical video information of the target area through an optical camera; matching and fusing pixels in the radiation hot spot image, the optical video information and the three-dimensional point cloud information according to the azimuth angle; 5) searching three-dimensional point cloud pixels corresponding to the radiation hot spots in the fusion image; obtaining the distance between the radiation source and the camera according to the three-dimensional point cloud pixels corresponding to the radiation hot spots; and 6) carrying out inversion calculation to obtain the activity value of the radioactive source.

Description

Technical Field

[0001] The present invention is applied to radiation imaging fields involving gamma (γ) ray sources, such as radiation protection monitoring, nuclear emergency, and radiation source search in nuclear facilities. The distribution information of imaging radiation hotspots can be obtained and the activity value of imaging radiation hotspots can be given without contacting the radiation source at a long distance, thereby optimizing and improving the radiation source imaging technology, and in particular, it relates to a radiation source quantitative imaging method based on coded aperture technology and laser radar. Background Art

[0002] In the monitoring and investigation of radiation source items, nuclear radiation imaging technology has become an advanced radiation measurement technology that can quickly measure the overall picture of the radiation environment and locate the key radiation hotspots of radiation sources. The existing nuclear radiation imaging method can obtain a two-dimensional pseudo-color image of the distribution of radiation sources. By fusing it with optical video photos, the azimuth of the radiation source can be given in the form of hotspot presentation. However, the existing imaging technology can only give the relative intensity of the radiation hotspots of the radiation source. For example, in the source item survey in nuclear facilities, when multiple radiation hotspots appear in the field of view, the real strength of the hotspots cannot be compared due to different distances. In order to obtain the intensity value (activity or surface dose rate) of the radiation source in the process of imaging the radiation source, it is necessary to obtain the distance value of the hotspot corresponding to the radiation source, and then invert and calculate its intensity. Multi-messenger fusion technology is currently also being applied in the field of radiation imaging. When the imaging system images the radiation source, in addition to obtaining radiation information, an optical video camera can also be added to the system to obtain optical information, so as to visualize the radiation source more intuitively. With the advancement of lidar technology, application cases of installing lidar modules in imaging systems have begun to appear in recent years. For example, a laser radar rangefinder and a Compton (or coded aperture) imaging camera are integrated on a robot platform, and radar scanning modeling of a three-dimensional scene is achieved by roaming in a radiation environment, and then the three-dimensional point cloud data is integrated with the radiation source information to achieve three-dimensional positioning of the radiation source. However, none of these existing radiation imaging technologies can calculate the intensity value of the radiation source, and only attach the hotspot image to the three-dimensional scene in the form of a map, without further calculating the activity of the hotspot.

[0003] In view of the fact that the current radiation imaging technology cannot give the intensity value of the source term, the present invention proposes a quantitative imaging method of radiation sources based on coded aperture technology and lidar, which can perform long-distance imaging positioning and activity calculation of radiation sources, thereby realizing accurate measurement of radiation sources. Summary of the invention

[0004] As a supplement and methodological innovation of the existing radiation imaging method of radioactive sources, the purpose of the present invention is to propose a quantitative imaging method based on coded aperture technology and laser radar that can perform long-distance activity calculation of radioactive sources, aiming at the problem that the existing radiation imaging of radioactive sources can only give the position of the radioactive source but not the intensity (activity or surface dose rate) of the radioactive source, and to provide a new method and means for the imaging and intensity measurement of radioactive sources. The radioactive source quantitative imaging method provided by the present invention can give its activity value while imaging and locating the radiation hotspot of the radioactive source. Compared with the original radiation imaging method, it provides more absolute intensity information of the radioactive source, and can realize the position indication and activity calculation of the radioactive source at a long distance.

[0005] The present invention proposes a radioactive source quantitative imaging method based on coded aperture technology. The flowchart of the method is as follows: Figure 1 As shown, the specific implementation steps include:

[0006] 1. Image the target area through a coded aperture gamma camera, and decode and calculate the coded position projection of the radiation source obtained by the position-sensitive imaging detector in the camera to obtain a coded reconstructed image.

[0007] 2. Perform filtering calculation on the encoded reconstructed image to shield the image noise, obtain the radiation hotspots in the image and generate a radiation hotspot image.

[0008] 3. Identify the total energy peak of the observed radiation source based on the energy information (i.e., energy spectrum) obtained by the imaging detector in the gamma camera, and calculate the dose rate information at the position of the gamma camera based on the energy spectrum.

[0009] 4. The three-dimensional point cloud information of the imaging area is obtained through the lidar, and the optical video information of the imaging area is obtained through the optical camera. The pixels in the three types of image information, namely the radiation hotspot image, the optical video, and the three-dimensional point cloud, are matched in azimuth. The radiation hotspot pixels are first fitted and superimposed on the optical pixels, and the fused pixels of the two are continued to be fitted on the pixels of the three-dimensional point cloud to achieve matching fusion of the three pixels. The final image is a three-dimensional scene with radiation hotspots.

[0010] 5. The distance information between the radiation source corresponding to the radiation hotspot and the gamma camera is obtained through the radar three-dimensional point cloud pixels corresponding to the radiation hotspot pixels. Combined with the radiation source energy information and dose rate information obtained by the gamma camera, the activity value of the radiation source is inverted and calculated.

[0011] The technical solution of the present invention is:

[0012] A method for quantitative imaging of radioactive sources based on coded aperture technology and laser radar, the steps of which include:

[0013] 1) imaging the target area through a coded aperture gamma camera, obtaining the coded projection and energy spectrum of the radiation source in the target area, and decoding and calculating the coded projection to obtain a coded reconstructed image O;

[0014] 2) Obtaining radiation hot spots in the coded reconstructed image O to generate a radiation hot spot image O_rad;

[0015] 3) identifying the total energy peak E of the radiation source according to the energy spectrum, and calculating the dose rate Dose_rate at the location of the coded aperture gamma camera according to the energy spectrum;

[0016] 4) Obtaining the three-dimensional point cloud information of the target area through a laser radar, and obtaining the optical video information of the target area through an optical camera; then matching and fusing the pixels in the radiation hotspot image O_rad, the optical video information, and the three-dimensional point cloud information according to the azimuth angle to obtain a three-dimensional scene graph O_final with the radiation hotspot;

[0017] 5) searching for the three-dimensional point cloud pixels corresponding to the radiation hotspot in the three-dimensional scene graph O_final; obtaining the distance D between the radiation source and the coded aperture gamma camera according to the three-dimensional point cloud pixels corresponding to the radiation hotspot;

[0018] 6) According to The activity value Activity of the radioactive source corresponding to the radiation hotspot is calculated; wherein mfp is the mean free path, and B(E, mfp) represents the accumulation factor.

[0019] Furthermore, the encoded reconstructed image O is filtered to obtain radiation hot spots in the encoded reconstructed image O.

[0020] Furthermore, the method for obtaining the radiation hotspot in the encoded and reconstructed image O is as follows: perform histogram statistics on the pixel values ​​of the encoded and reconstructed image O to obtain the frequency distribution of the pixel values; obtain the maximum pixel value PEAK(O) and the minimum pixel value MIN(O) of the encoded and reconstructed image O; calculate the sum of the pixel values ​​SUM(O) of the encoded and reconstructed image O; then calculate the average value of the image noise NOISE_MEAN(O), the cutoff threshold of the radiation hotspot is CUT(O), and each pixel value in the encoded and reconstructed image O is judged in turn whether it is greater than CUT(O), and the pixels greater than CUT(O) are regarded as the radiation hotspot.

[0021] Furthermore, CUT(O)=|MIN(O)|+NOISE_MEAN(O); N is the total number of pixels of the encoded reconstructed image O.

[0022] Furthermore, a method for obtaining a three-dimensional scene graph O_final with the radiation hotspot is as follows: matching and aligning the fields of view of the radiation hotspot image O_rad, the optical video image and the three-dimensional point cloud image, and then making the radiation hotspot pixels of the radiation hotspot image O_rad transparent and fitting and superimposing them on the corresponding pixels in the optical video image to obtain an image O_rad_opt after the radiation hotspot image O_rad and the optical video image are fused; selecting a field of view scanning angle range of the laser radar to cover the imaging field of view range of the radiation hotspot image O_rad, and the angular resolution of the three-dimensional point cloud pixels is greater than the angular resolution of the radiation hotspot image O_rad; and then superimposing the pixels of the image O_rad_opt on the corresponding pixels of the three-dimensional point cloud image to obtain a three-dimensional scene graph O_final.

[0023] Furthermore, the mean free path T(E) represents the linear energy conversion coefficient, and its value is determined by the energy E.

[0024] A radioactive source quantitative imaging system based on coded aperture technology and laser radar, characterized in that it includes a coded aperture gamma camera, a laser radar, an optical camera and a data processing unit;

[0025] The coded aperture gamma camera is used to image the target area, obtain the coded projection and energy spectrum of the radiation source in the target area, and send them to the data processing unit;

[0026] The laser radar obtains the three-dimensional point cloud information of the target area and sends it to the data processing unit;

[0027] The optical camera acquires optical video information of the target area and sends the information to the data processing unit;

[0028] The data processing unit is used to decode and calculate the coded projection to obtain the coded reconstructed image O, then obtain the radiation hotspot in the coded reconstructed image O, and generate a radiation hotspot image O_rad; and identify the full energy peak E of the radiation source according to the energy spectrum, and calculate the dose rate Dose_rate at the location of the coded aperture gamma camera according to the energy spectrum; and match and fuse the pixels in the radiation hotspot image O_rad, optical video information, and three-dimensional point cloud information according to the azimuth angle to obtain a three-dimensional stereoscopic scene graph O_final with the radiation hotspot; search for the three-dimensional point cloud pixels corresponding to the radiation hotspot in the three-dimensional stereoscopic scene graph O_final, and then obtain the distance D between the radiation source and the coded aperture gamma camera according to the three-dimensional point cloud pixels corresponding to the radiation hotspot; and then calculate the distance D between the radiation source and the coded aperture gamma camera according to the three-dimensional point cloud pixels corresponding to the radiation hotspot. The activity value Activity of the radioactive source corresponding to the radiation hotspot is calculated; wherein mfp is the mean free path, and B(E, mfp) represents the accumulation factor.

[0029] Furthermore, the method by which the data processing unit obtains the radiation hotspot in the encoded and reconstructed image O is: performing histogram statistics on the pixel values ​​of the encoded and reconstructed image O to obtain the frequency distribution of the pixel values; obtaining the maximum pixel value PEAK(O) and the minimum pixel value MIN(O) of the encoded and reconstructed image O; calculating the sum of the pixel values ​​SUM(O) of the encoded and reconstructed image O; and then calculating the average value of the image noise NOISE_MEAN(O), the cutoff threshold of the radiation hotspot is CUT(O), and judging in turn whether each pixel value in the encoded and reconstructed image O is greater than CUT(O), and taking the pixels greater than CUT(O) as the radiation hotspot.

[0030] Furthermore, the data processing unit obtains the three-dimensional scene graph O_final with the radiation hotspot by: matching and aligning the fields of view of the radiation hotspot image O_rad, the optical video image and the three-dimensional point cloud image, and then making the radiation hotspot pixels of the radiation hotspot image O_rad transparent and fitting them on the corresponding pixels in the optical video image to obtain the image O_rad_opt after the radiation hotspot image O_rad and the optical video image are fused; the field of view scanning angle range of the laser radar is selected to cover the imaging field of view range of the radiation hotspot image O_rad, and the angular resolution of the three-dimensional point cloud pixels is greater than the angular resolution of the radiation hotspot image O_rad; and then the pixels of the image O_rad_opt are superimposed on the corresponding pixels of the three-dimensional point cloud image to obtain the three-dimensional scene graph O_final.

[0031] Compared with the prior art, the present invention has the following positive effects:

[0032] 1) Existing radiation imaging technology can generally only provide the hot spot orientation and relative intensity value of the radiation source. The radiation source quantitative imaging method based on coded aperture technology and lidar proposed in the present invention realizes accurate imaging measurement of radiation sources at long distances. The distance information of the radiation source is obtained by lidar to further calculate the activity value of the radiation source, thereby realizing quantitative imaging of the radiation source.

[0033] 2) The radioactive source quantitative imaging method based on coded aperture technology proposed in the present invention is similar to the existing imaging method in terms of workflow. It does not require multi-position or multi-angle measurements of the radioactive source to calculate its activity value. Only a single imaging operation at a fixed point is required to achieve imaging positioning and activity calculation of the radioactive source without adding extra workload.

[0034] As a supplement to the radiation imaging method of radioactive sources, the present invention proposes a quantitative imaging method based on coded aperture technology and laser radar for long-distance activity calculation of radioactive sources. Compared with the original radiation imaging method, it provides more absolute intensity information of the radioactive source, and can realize the azimuth indication and activity calculation of the radioactive source at a long distance. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The present invention is a flow chart of the method.

[0036] Figure 2 This is the energy spectrum obtained by sampling the imaging detector.

[0037] Figure 3 is the projection image of the imaging detector.

[0038] Figure 4 To reconstruct the image.

[0039] Figure 5 is the frequency distribution of pixel values.

[0040] Figure 6 It is the radiation hot spot image after interpolation and smoothing.

[0041] Figure 7 This is a fusion flow chart.

[0042] Figure 8 To fuse the images. DETAILED DESCRIPTION

[0043] The present invention is further described in detail below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention but not to limit the scope of the present invention.

[0044] like Figure 1 As shown, the steps of the present invention include:

[0045] 1. Obtain the coded projection of the radiation source through a coded aperture gamma camera, and decode and calculate the coded projection to obtain a coded reconstructed image.

[0046] 1.1 Select a typical coded aperture gamma camera, whose key components include a coding plate and an imaging detector. The coding pattern of the coding plate can be designed as MURA RANK-19, and the imaging detector is designed as a pixel-type position-sensitive detector with a detector pixel array size of 19×19. The imaging field of view is 40 degrees. The rays emitted by the radiation source at a long distance are modulated by the opening of the coding plate, and a projection of the response count fluctuation is formed on the detector. The mathematical form of the projection is a 19×19 two-dimensional array D.

[0047] 1.2 Perform convolution calculation on the projection array D and the decoding matrix G to obtain the coded reconstructed image O. The mathematical form of the decoding matrix and the reconstructed image is also a 19×19 two-dimensional array. The convolution calculation formula is as follows:

[0048]

[0049] The “%” symbol indicates remainder calculation.

[0050] 2. Perform filtering calculation on the encoded reconstructed image O to shield the image noise and obtain the radiation hotspots in the image.

[0051] 2.1 For the sake of explanation, assume the imaging scenario: a Cs-137 radiation source with an activity of 1 mCi is placed 3 meters away from the gamma camera, the imaging detector is a CsI scintillator 19×19 pixel array, and the energy spectrum obtained by the imaging detector sampling for 1 minute is as follows Figure 2 As shown, the imaging detector projection D is Figure 3 As shown, the encoded reconstructed image O is Figure 4 shown.

[0052] 2.2 The 361 pixel values ​​of the coded reconstructed image O are counted in histogram to obtain the frequency distribution of the pixel values, as shown in Figure 5 As shown, the maximum pixel value PEAK(O) and the minimum pixel value MIN(O) of the coded reconstructed image O are obtained, the sum of the pixel values ​​SUM(O) of the coded reconstructed image O is calculated, and then the average value of the image noise NOISE_MEAN(O) is calculated. The cutoff threshold of the radiation hotspot is CUT(O), and the 361 pixel values ​​in the coded reconstructed image O are judged in turn, and the pixels larger than CUT(O) are regarded as radiation hotspots. Figure 6 The radiation hot spot image O_rad is obtained after deducting image noise and image interpolation and smoothing are performed.

[0053] The calculation formulas for NOISE_MEAN(O) and CUT(O) are:

[0054]

[0055] CUT(O)=|MIN(O)|+NOISE_MEAN(O)

[0056] 3. Find the full energy peak of the radiation source based on the energy spectrum obtained by the gamma camera, and calculate the dose rate information at the location of the gamma camera based on the energy spectrum.

[0057] 3.1 Based on Figure 2 From the energy spectrum shown, we can obtain that the total energy peak position E is 662keV.

[0058] 3.2 According to Figure 2From the energy spectrum shown, the average dose rate obtained by the imaging detector within 1 minute can be calculated as Dose_rate (0.31μSv / h). The dose rate calculation method can be implemented by referring to the common energy-dose rate conversion algorithm.

[0059] 4. Obtain the 3D point cloud information of the imaging area through the laser radar, obtain the optical video information of the imaging area through the optical camera, and fuse the three image information of the radiation hotspot image O_rad, optical video, and 3D point cloud by pixel matching to obtain the final fused image of the three messengers. The fusion principle of radiation imaging, optical video, and 3D point cloud is as follows: Figure 7 shown.

[0060] 4.1 Match the fields of view of the radiation hotspot image O_rad, the optical video image and the radar point cloud image, that is, the fields of view correspond to each other, and then make the radiation hotspot pixels of the 19×19 radiation hotspot image O_rad transparent, and then fit and overlay them on the corresponding pixels in the optical video image to obtain the image O_rad_opt after the radiation hotspot image and the optical video image are fused.

[0061] 4.2 The field of view scanning angle range of the selected laser radar needs to cover the imaging field of view of the radiation image, and the angle resolution of the point cloud pixels is better than that of the radiation image. The O_rad_opt image pixels are superimposed on the radar point cloud image pixels to obtain the final radiation, optical and radar three-messenger fusion image O_final, as shown in Figure 8 shown.

[0062] 5. Obtain the distance information corresponding to the radiation hotspot, combine it with the radiation source energy information and dose rate information obtained by the gamma camera, and inversely calculate the activity value of the radiation source.

[0063] 5.1 Find the point cloud pixel corresponding to the radiation hot spot pixel Pixel in the fused image O_final. According to the distance information D (3m) corresponding to the point cloud pixel and the peak value E (662keV) of the energy information, the dose rate information calculated by the imaging detector in step 3.2 is Dose_rate (0.31μSv / h).

[0064] 5.2 Calculate the activity value Activity (unit: mCi) of the radiation source corresponding to the radiation hotspot. The calculation formula is as follows:

[0065]

[0066] Wherein, mfp represents mean free path, T(E) represents linear energy conversion coefficient, and its value is determined by energy E. B(E,mfp) represents accumulation factor, and its value is determined by energy E and mean free path mfp. C(E) represents energy kerma conversion coefficient, and its value is determined by energy E. Constant 0.76 is fixed unit conversion coefficient. The above coefficients are calculated by table interpolation. Table 1 is the calculation coefficient table of radiation hot spot activity.

[0067] Table 1 is the calculation coefficient table of radiation hot spot activity

[0068]

[0069] First, the mean free path mfp is calculated by interpolation. The ray energy E is 662keV, and the corresponding T(E) is:

[0070]

[0071]

[0072] Then the energy kerma conversion coefficient C(E) is calculated by interpolation method:

[0073]

[0074] Then calculate the cumulative factor B(E,mfp) by interpolation method:

[0075]

[0076] Therefore, the activity value of the radioactive source (unit: mCi) is calculated as:

[0077]

[0078] The above results show that the radiation hotspot quantitative imaging technology proposed in the present invention can obtain the activity value of the radiation source while imaging it at a long distance.

[0079] In summary, the above is only a preferred implementation method of the present invention, and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for quantitative imaging of radioactive sources based on coded aperture technology and laser radar, the steps comprising: 1) imaging the target area through a coded aperture gamma camera, obtaining the coded projection and energy spectrum of the radiation source in the target area, and decoding and calculating the coded projection to obtain a coded reconstructed image O; 2) Obtaining radiation hot spots in the coded reconstructed image O to generate a radiation hot spot image O_rad; 3) identifying the total energy peak E of the radiation source according to the energy spectrum, and calculating the dose rate Dose_rate at the location of the coded aperture gamma camera according to the energy spectrum; 4) Obtaining the three-dimensional point cloud information of the target area through a laser radar, and obtaining the optical video information of the target area through an optical camera; then matching and fusing the pixels in the radiation hotspot image O_rad, the optical video information, and the three-dimensional point cloud information according to the azimuth angle to obtain a three-dimensional scene graph O_final with the radiation hotspot; 5) searching for the three-dimensional point cloud pixels corresponding to the radiation hotspot in the three-dimensional scene graph O_final; obtaining the distance D between the radiation source and the coded aperture gamma camera according to the three-dimensional point cloud pixels corresponding to the radiation hotspot; 6) According to The activity value Activity of the radioactive source corresponding to the radiation hotspot is calculated; wherein mfp is the mean free path, and B(E, mfp) represents the accumulation factor.

2. The method according to claim 1, characterized in that The encoded reconstructed image O is filtered to obtain radiation hot spots in the encoded reconstructed image O.

3. The method according to claim 2, characterized in that The method for obtaining the radiation hotspot in the coded reconstructed image O is as follows: performing histogram statistics on the pixel values ​​of the coded reconstructed image O to obtain the frequency distribution of the pixel values; obtaining the maximum pixel value PEAK(O) and the minimum pixel value MIN(O) of the coded reconstructed image O; calculating the sum of the pixel values ​​SUM(O) of the coded reconstructed image O; then calculating the average value NOISE_MEAN(O) of the image noise, the cutoff threshold of the radiation hotspot is CUT(O), and judging in turn whether each pixel value in the coded reconstructed image O is greater than CUT(O), and taking the pixels greater than CUT(O) as the radiation hotspot.

4. The method according to claim 2, characterized in that: CUT(O)=|MIN(O)|+NOISE_MEAN(O); N is the total number of pixels of the encoded reconstructed image O.

5. The method according to claim 1, 2 or 3, characterized in that: The method for obtaining the three-dimensional scene graph O_final with the radiation hotspot is as follows: match and align the fields of view of the radiation hotspot image O_rad, the optical video image and the three-dimensional point cloud image, and then make the radiation hotspot pixels of the radiation hotspot image O_rad transparent and fit and superimpose them on the corresponding pixels in the optical video image to obtain the image O_rad_opt after the radiation hotspot image O_rad and the optical video image are fused; the field of view scanning angle range of the laser radar is selected to cover the imaging field of view range of the radiation hotspot image O_rad, and the angular resolution of the three-dimensional point cloud pixels is greater than the angular resolution of the radiation hotspot image O_rad; and then the pixels of the image O_rad_opt are superimposed on the corresponding pixels of the three-dimensional point cloud image to obtain the three-dimensional scene graph O_final.

6. The method according to claim 1, 2 or 3, characterized in that: The mean free path T(E) represents the linear energy conversion coefficient, and its value is determined by the energy E.

7. A radioactive source quantitative imaging system based on coded aperture technology and laser radar, characterized in that: Includes coded aperture gamma camera, lidar, optical camera and data processing unit; The coded aperture gamma camera is used to image the target area, obtain the coded projection and energy spectrum of the radiation source in the target area, and send them to the data processing unit; The laser radar obtains the three-dimensional point cloud information of the target area and sends it to the data processing unit; The optical camera acquires optical video information of the target area and sends the information to the data processing unit; The data processing unit is used to decode and calculate the coded projection to obtain the coded reconstructed image O, then obtain the radiation hotspot in the coded reconstructed image O, and generate a radiation hotspot image O_rad; and identify the full energy peak E of the radiation source according to the energy spectrum, and calculate the dose rate Dose_rate at the location of the coded aperture gamma camera according to the energy spectrum; and match and fuse the pixels in the radiation hotspot image O_rad, optical video information, and three-dimensional point cloud information according to the azimuth angle to obtain a three-dimensional stereoscopic scene graph O_final with the radiation hotspot; search for the three-dimensional point cloud pixels corresponding to the radiation hotspot in the three-dimensional stereoscopic scene graph O_final, and then obtain the distance D between the radiation source and the coded aperture gamma camera according to the three-dimensional point cloud pixels corresponding to the radiation hotspot; and then calculate the distance D between the radiation source and the coded aperture gamma camera according to the three-dimensional point cloud pixels corresponding to the radiation hotspot. The activity value Activity of the radioactive source corresponding to the radiation hotspot is calculated; wherein mfp is the mean free path, and B(E, mfp) represents the accumulation factor.

8. The system according to claim 7, characterized in that The method for the data processing unit to obtain the radiation hotspot in the coded reconstructed image O is as follows: perform histogram statistics on the pixel values ​​of the coded reconstructed image O to obtain the frequency distribution of the pixel values; obtain the maximum pixel value PEAK(O) and the minimum pixel value MIN(O) of the coded reconstructed image O; calculate the sum of the pixel values ​​SUM(O) of the coded reconstructed image O; then calculate the average value NOISE_MEAN(O) of the image noise, the cutoff threshold of the radiation hotspot is CUT(O), and determine in turn whether each pixel value in the coded reconstructed image O is greater than CUT(O), and use the pixels greater than CUT(O) as the radiation hotspot.

9. The system according to claim 7, characterized in that The method for the data processing unit to obtain the three-dimensional scene graph O_final with the radiation hotspot is: matching and aligning the fields of view of the radiation hotspot image O_rad, the optical video image and the three-dimensional point cloud image, and then making the radiation hotspot pixels of the radiation hotspot image O_rad transparent and fitting and superimposing them on the corresponding pixels in the optical video image to obtain the image O_rad_opt after the radiation hotspot image O_rad and the optical video image are fused; the field of view scanning angle range of the laser radar is selected to cover the imaging field of view range of the radiation hotspot image O_rad, and the angular resolution of the three-dimensional point cloud pixels is greater than the angular resolution of the radiation hotspot image O_rad; and then superimposing the pixels of the image O_rad_opt on the corresponding pixels of the three-dimensional point cloud image to obtain the three-dimensional scene graph O_final.

Images