Integral detection x-ray color imaging method

Abstract

The application discloses an integral detection X-ray color imaging method, which adopts an X-ray tube to emit a wide-spectrum X-ray beam, which penetrates through a detected object and then irradiates an energy-discriminating integral X-ray detector. The detector first selects a high-thickness photon absorber to completely deposit different wavelengths of X-ray energy; then, high-energy X-ray photons have a deep deposition depth, low-energy X-ray photons have a shallow deposition depth, and the photogenerated carrier recombination rate of different X-ray deposition positions is regulated by changing the bias voltage of the detector, so that the detection signals generated by different energy X-ray photons are converted into a nonlinear programming problem; through the optimization solution of the nonlinear programming, the energy and intensity information of the incident X-ray are identified. The method has obvious advantages in detection speed and price.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of photoelectric detection, and in particular to an integral detection X-ray color imaging method. BACKGROUND

[0002] Since X-ray was discovered by Roentgen in 1895, X-ray detection and imaging has become the most important means for people to obtain internal structure information of an object non-destructively, and it has important applications in medical diagnosis and treatment, industrial flaw detection, security detection, space exploration, and material science. Generally, people use an integral detector to obtain information of high-energy X-rays, i.e. the photocurrent is proportional to the total energy of X-rays deposited in the detector within a certain time. People obtain the intensity of X-rays by measuring the size of the photocurrent. The Lambert-Beer law can be used to describe the energy attenuation of X-rays in the detected object

[0003] I = I0e -μd (1)

[0004] In the formula, I0 and I are the intensities of X-rays before and after the X-rays are incident on the detected object, d is the thickness of the detected object, and μ is the linear attenuation coefficient of the detected object. μ is mainly determined by the X-ray interaction cross section, the density and effective atomic number of the object, and it is directly related to the material composition of the detected object. d is only determined by the geometric size of the detected object and is irrelevant to the material composition. The X-ray integral detector can obtain an X-ray grayscale image, and the grayscale value of the image is proportional to the ratio of I / I0. However, as can be seen from formula (1), the parameters μ and d simultaneously affect the ratio of I / I0. Therefore, we cannot directly obtain the composition of the detected object (i.e. solve μ) from the conventional X-ray grayscale image (I / I0), so the conventional X-ray image can only provide morphological information of the detected object, but cannot provide histological information.

[0005] Since the conventional X-ray image cannot provide histological information, doctors or security personnel need to determine what the object is according to the appearance and grayscale distribution of the object provided by the X-ray image. This determination method needs to consume a large amount of manual work, and is highly dependent on the experience of the determiner, and the probability of determination error is relatively high. Therefore, in the field of imaging, it is urgently needed to provide morphological information and histological information of the detected object at the same time. In view of this requirement, people have proposed PET-CT, which can add metabolic information on the basis of morphological information.

[0006] People have been pursuing the goal of obtaining material composition information directly from X-ray images, and have proposed several solutions. According to the basic rule of X-ray imaging, if we know the images of an object under detection irradiated by X-ray beams of several different energies (or wavelengths) at the same time, we can infer the material composition of the object under detection. Therefore, how to obtain the energy information and intensity information of X-rays is a key problem to be solved.

[0007] In photon counting detection, different X-ray photon energies can be identified by setting different thresholds. However, because each detection pulse corresponds to an incident photon, in order to obtain high-quality detection and imaging, a large number of photons need to be recorded. Due to the limitation of sensor carrier transit time, the counting rate of photon counting detection cannot be very high, so the imaging time of photon counting detection is much higher than that of integral X-ray detection, which greatly restricts the detection of dynamic objects. In addition, a basic requirement for photon counting detection to perform photon energy resolution is to capture only the signal generated by one incident photon when each trigger count is triggered. If the incident X-ray flux is large, the number of incident X-ray photons per unit time is large, and it is difficult to ensure that only one X-ray photon detection signal is captured at the trigger edge. Therefore, when the incident X-ray flux is large, the error of the energy spectrum distribution obtained by the photon counting detection is large. Since the detection signal generated by a single incident photon is very weak, a high-gain sensitive charge amplifier needs to be used. In addition, photon counting detectors also require shaping, comparison, and reading circuits, and the cost of these electronic circuits is very high, so the cost of photon counting detectors is much higher than that of integral X-ray detectors. SUMMARY

[0008] The purpose of the present application is to solve some problems existing in the prior art dual-energy detection and photon counting detection for resolving X-ray energy, and to provide an integral detection method for obtaining X-ray color images, and a method for obtaining the shape characteristics and material properties of an object under detection.

[0009] An integral detection X-ray color imaging method, comprising the following steps:

[0010] Step 1): An X-ray source emits an X-ray beam using the bremsstrahlung phenomenon;

[0011] Step 2): The X-ray beam irradiates an energy-resolving integral X-ray detector after passing through an object under detection;

[0012] Step 3): The energy-resolving integral X-ray detector obtains the photocurrent (or photovoltage) signals of the X-ray beam under different detector bias voltages, and then calculates the intensity and energy information of the X-ray according to the photocurrent (or photovoltage) signals;

[0013] Step 4): The signal processing and image processing module calculates the material parameters of the detected object according to the intensity and energy information of the X-ray beam, and assigns colors to the X-ray image using the material parameters to reconstruct the X-ray color image.

[0014] Preferably, in step 2), the intrinsic layer of the energy-resolved integral X-ray detector is a MAPbBr2.5Cl0.5 intrinsic perovskite single crystal with a thickness of more than 1 cm, which completely absorbs the incident X-ray beam; the energy-resolved integral X-ray detector has a unipolar carrier transport characteristic.

[0015] Preferably, the method for making the energy-resolved integral X-ray detector have a unipolar carrier transport characteristic comprises:

[0016] The energy-resolved integral X-ray detector adopts a p-i-n photodiode structure, and the energy band and potential barrier structure of the p-i-n photodiode form unipolar carrier transport;

[0017] The energy-resolved integral X-ray detector collects the work function of the electrode, and forms unipolar carrier transport through a Schottky barrier;

[0018] The energy-resolved integral X-ray detector controls the carrier mobility of the doped region semiconductor material, so that the drift length of a certain kind of photo-generated carrier is less than the transport length of the carrier to the collection electrode, forming unipolar carrier transport;

[0019] The energy-resolved integral X-ray detector uses a solution epitaxy method to epitaxially grow an n-type layer on the upper end surface of the intrinsic perovskite single crystal while doping Cl elements; epitaxially grows a p-type layer on the lower end surface of the intrinsic perovskite single crystal while doping Br elements, forming unipolar carrier transport.

[0020] Preferably, in step 3), assuming that the unipolar carrier is an electron, the drift length L Vn of the electron under different bias voltages is:

[0021] L Vn = μ e τ·V n / d

[0022] Where V n is the bias voltage, n is the number of bias voltages, μ e is the electron mobility, τ is the electron lifetime, and d is the thickness of the energy-resolved integral X-ray detector.

[0023] Assume that the X-ray beam passing through the detected object has 4 photon energies, E1, E2, E3 and E4, the photocurrent I photo-current-Vn is obtained under different bias voltages

[0024]

[0025] where I E1 ,I E2 ,I E3 and I E4 are the photocurrents under the bias voltages of V1, V2, V3 and V4 respectively, and I photo-current-Vn is the intensity of the X-ray with the photon energy of E1, E2, E3 and E4.

[0026] When the number of bias voltages n≥4, the expression of I E1 is converted into a nonlinear programming problem by using the least square method, the nonlinear programming problem is solved, and finally the optimal solutions of I E2 ,I E3 ,I E4 and I E1 are obtained, i.e. the intensity of the X-ray is obtained.

[0027] Preferably, in step 4), the color of the X-ray image is assigned by using the material parameter again, for the X-ray image with the photon energies of E1 and E2, the material parameter is defined as:

[0028]

[0029] I0 is the intensity of the X-ray beam before it is incident on the detected object, and μ is the composition of the detected object.

[0030] The X-ray color image is obtained by color assignment of the X-ray image by using the hue-saturation-intensity (HIS) model, wherein the hue of the X-ray color image is determined by the material parameter R of the detected object, and the saturation S is defined as:

[0031] S=0.9, I<0.2

[0032] S=0.8, 0.2≤I<0.4

[0033] S=0.7, 0.4≤I<0.6

[0034] S=0.6, 0.6≤I<0.8

[0035] S=0.5, I≥0.8

[0036] where I is the intensity of the X-ray color image, and the average value of the intensities of the X-rays with the 4 photon energies E1, E2, E3 and E4 is taken as the image intensity, i.e. I=[I E2 +I E3 +IE4 ] / 4.

[0037] Preferably, in the X-ray color image, the gray scale represents the thickness of the detected object, and the color represents the density of the detected object.

[0038] The beneficial effects of the present application are:

[0039] (1) The present application proposes an integral detection X-ray color imaging method, which can distinguish more energy channels (≥2) compared with the commonly used dual-energy detection method, and the structure of the detection imaging system is simpler, without the need for spatial alignment.

[0040] (2) The present application proposes an integral detection X-ray color imaging method, which uses a signal integration mode compared with the commonly used photon counting detection method, without the need to record the detection pulse of a single photon, so the detection speed is faster. It does not need expensive sensitive charge amplification circuit and shaping circuit, etc., which reduces the cost of the detector.

[0041] (3) The present application proposes an integral detection X-ray color imaging method. In the color image, the color represents the different material properties of the detected object, and the gray scale represents the thickness of the material. This color image improves the recognition and understanding of X-ray images, and provides a new way for further artificial intelligence machine reading. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 (a) is a schematic diagram of the working of the conventional X-ray dual-energy detector double-ball tube parallel arrangement;

[0043] Figure 1 (b) is a schematic diagram of the working of the conventional X-ray dual-energy detector double-ball tube inclined arrangement;

[0044] Figure 1 (c) is a schematic diagram of the working of the conventional X-ray dual-energy detector double-layer detector;

[0045] Figure 2 (a) is a schematic diagram of the conventional photon counting detection structure;

[0046] Figure 2 (b) is a detection pulse waveform after charge amplification and signal shaping of the conventional photon counting detection;

[0047] Figure 2 (c) is a typical gamma ray energy spectrum;

[0048] Figure 3 is a schematic diagram of an integral detection X-ray color imaging system proposed by the present application;

[0049] Figure 4The working mechanism of the energy-resolved X-ray integral detector proposed in the present application;

[0050] Figure 5 The energy-resolved X-ray integral detector composed of perovskite p-i-n photodiode proposed in the present application;

[0051] Figure 6 The working block diagram of integral detection X-ray color imaging proposed in the present application.

[0052] In the figure: 1. High anode voltage X-ray bulb; 2. Low anode voltage X-ray bulb; 3. High-energy X-ray beam; 4. Low-energy X-ray beam; 5. Object to be detected; 6. X-ray detector; 7. Low-energy X-ray detector; 8. Low-energy X-ray filter plate; 9. High-energy X-ray detector; 10. Incident X-ray; 11. X-ray sensor; 13. Generation of photoelectron / hole pairs; 14. Bias high-voltage power supply; 15. Charge amplifier; 16. Shaping circuit; 17. Comparison circuit; 18. Anti-coincidence circuit; 19. Counting circuit; 20, 21, 22. Detection signal pulse after charge amplification; 23. Background signal threshold; 24, 25, 26. Counting pulse after shaping; 27, 28, 29. Energy channel threshold; 30. X-ray source; 31. Exit X-ray beam; 32. Object to be detected; 33. Material with minimum density; 34. Small density material; 35. Medium density material; 36. Large density material; 37, 38, 39. X-ray; 40. Energy-resolved X-ray integral detector; 41. Amplification circuit; 42. X-ray color image; 43. Color 1; 44. Color 2; 45. Color 3; 46. Color 4; 47. X-ray beam; 48, 49, 50, 51. Energy channels E1, E2, E3 and E4; 52. Common electrode of the detector; 53. P-type layer; 54. Intrinsic layer; 55. N-type layer; 56. Pixel electrode; 57. Photoelectron / hole pairs; 58. Unipolar carrier electron transport; 59. Low-energy X-ray photon (E1 and E2) transmission curve; 60. High-energy X-ray photon (E3 and E4) transmission curve; 61. Common electrode ground; 62. Pixel electrode connected to forward bias voltage; 63. Electric field formed by bias voltage; 64. Perovskite crystal p-i-n photodiode; 65. Band diagram of perovskite crystal p-i-n photodiode; 66. N-type layer; 67. X-ray photon absorption layer; 68. P-type layer; 69. Conduction band minimum (CBM) of perovskite crystal; 70. Valence band maximum (VBM) of perovskite crystal; 71. Hole quasi-Fermi level (E Fp ); 72. Electron quasi-Fermi level (E Fn ); DETAILED DESCRIPTION

[0053] The present invention will now be described in detail. This embodiment is implemented based on the technical solution of the present invention, and provides detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiment.

[0054] The first proposed solution was a dual-energy X-ray imaging system, whose basic working principle is as follows: Figure 1 As shown. Figure 1 The dual-energy X-ray imaging system (X-ray tube 1) comprises two X-ray tubes: a high-anode-voltage X-ray tube 1 with a higher anode voltage, producing higher-energy X-rays, and a low-anode-voltage X-ray tube 2 with a lower anode voltage, producing lower-energy X-rays. The two tubes are arranged parallel in space. The object being detected is first irradiated by the X-rays produced by the high-anode-voltage X-ray tube 1, obtaining a high-energy X-ray image. Then, the object is irradiated by the X-rays produced by the low-anode-voltage X-ray tube 2, obtaining a low-energy X-ray image. However, in this solution, the object needs to move in space, increasing the complexity of the imaging system. Furthermore, high-energy and low-energy X-ray imaging cannot be performed simultaneously, requiring time alignment of the images, which introduces significant errors in imaging moving objects. Figure 1 Option b is a variation of option a, where the two X-ray tubes are placed at an angle. This allows high-energy and low-energy X-rays to simultaneously image the object being detected, while avoiding spatial displacement of the object. However, in Figure 1 In the scheme shown in b, the imaging projection angles of high-energy X-rays and low-energy X-rays are different, requiring spatial alignment of the X-ray images. The difference in projection angles between high-energy and low-energy X-rays introduces certain errors into the reconstructed image. Figure 1 c is another technical solution for dual-energy X-ray imaging. It uses only one X-ray tube, but the system is equipped with two detectors: detector 7 detects low-energy X-ray signals, and detector 8 detects high-energy X-ray signals. When the X-rays generated by tube 1 irradiate the object being detected, the X-rays are first projected onto detector 7. This detector uses a relatively thin photon absorption layer, so it can only absorb low-energy X-ray photons and generate the corresponding detection signal. The higher-energy X-ray photons pass through detector 7 and enter the filter layer 8. The main function of filter layer 8 is to further filter low-energy X-rays. Generally, the atomic number and thickness of the filter are selected according to the required X-ray energy, and aluminum or copper plates are generally used as the filter layer material. After passing through filter layer 8, only high-energy photons remain, so detector 9 is used to obtain the high-energy X-ray signal. Figure 1The technical solution of c only needs one X-ray tube and avoids the spatial and temporal alignment of the detected object. However, the technical solution needs two X-ray flat panel detectors, which increases the complexity and cost of the dual-energy X-ray imaging system. In addition, the metal frame and readout circuit of the upper X-ray detector 8 also absorb X-rays, forming some artifacts and causing crosstalk to the image formed by the detector 9.

[0055] In Figure 1 In the dual-energy X-ray imaging system shown in the drawings, although more X-ray tubes or detectors can theoretically identify more energy X-ray information, the structural problems and image processing problems caused by multiple tubes and multiple detectors restrict their practical application. In actual X-ray imaging systems, most applications still use dual-energy imaging. Since two energy X-ray images are not enough to construct high-quality X-ray color images, people are also committed to exploring other X-ray spectral detection methods, such as photon counting detection. Figure 2 A typical photon counting detector structure is shown in FIG. 1.

[0056] Figure 2 A typical photon counting detection structure is shown in FIG. 1. When the incident high-energy photon 10 irradiates the sensor 11, a photo-generated carrier pair 13 is generated through some physical effects such as photoelectric effect. Under the action of the bias voltage 13 of the high-voltage power supply, a bias electric field is formed in the sensor, and the photo-generated electron / hole pair is separated to form a detection current. The physical process of this part is almost the same as that of the integral detector, but the dark current and noise requirements of the sensor are more stringent. Unlike the integral detector, the readout circuit is not through an integration capacitor to accumulate the photo-generated carriers within a certain time, but a series of readout trigger pulses are set, and the readout circuit reads the current or voltage signal at the edge (usually the rising edge) of the trigger pulse, and then the sensitive charge amplifier amplifies the read signal. Figure 2 The left graph of FIG. 2 is a time sequence detection pulse signal obtained after amplification by a sensitive charge amplification circuit. As can be seen from the graph, there are three detection pulses 20, 21 and 22 in the time interval shown in the graph, and their pulse amplitudes are different. Since the readout trigger time is very short, it can be approximately considered that only one incident photon is accepted in one readout pulse, so the signal amplitudes of the detection pulses 20, 21 and 22 are proportional to the energies of the incident photons. We can also set a threshold 23, and consider the part with a signal amplitude less than the threshold 23 as background signal. After shaping the detection pulse, the right graph of FIG. 2 is obtained Figure 2Figure b shows the shaped pulse waveform. Probe pulses 20, 21, and 22, after shaping, correspond to pulses 24, 25, and 26. We can set three thresholds, 27, 28, and 29, corresponding to the three energy channels (or wavelength channels) of the incident X-rays. Based on the amplitude of the probe pulse, we can determine which energy channel the X-ray photon corresponding to that pulse belongs to, ultimately obtaining the waveform shown in Figure b. Figure 2 The X-ray (or gamma-ray) energy spectrum shown in c.

[0057] The technical solution adopted in this invention is: a method for identifying X-ray energy in integration mode and reconstructing color X-ray images using X-ray images of different energies to distinguish the material properties of the detected object. The X-ray imaging system used in this invention is as follows: Figure 3 As shown.

[0058] exist Figure 3 In the imaging system shown, the intensity of the X-ray 31 emitted by the X-ray source 30 is I0. Since conventional X-ray tubes emit X-rays using bremsstrahlung, the X-ray beam 31 has a very broad energy spectrum. Assume that this X-ray beam has n energy channels with photon energies E1, E2, ..., E... n Assuming the object being detected, 32, contains four different components with densities ranging from low to high in four levels, then... Figure 3 This corresponds to sections 33, 34, 35, and 36. Because materials of different densities have different linear attenuation coefficients for X-rays of the same energy, the intensity of the incident X-ray beam 31 is no longer the same at different locations in space after penetrating the object 32. For example... Figure 3 As shown in Figures 37, 38, and 39, these X-rays of different energies and intensities further irradiate detector 40. Detector 40 is an integrating detector, but it can distinguish different energy information of X-rays, which is one of the core aspects of this invention. The physical processes of photogenerated carrier generation and transport after X-rays are incident on the energy-resolved X-ray integrating detector are as follows: Figure 4 As shown.

[0059] exist Figure 4 The X-ray beam passing through the object being probed 47 is assumed to have 4 energy channels, namely E1 (48), E2 (49), E3 (50) and E4 (51). X-ray beams of different energies have different linear attenuation coefficients in the same semiconductor, and the higher the energy of the X-ray, the greater the penetration depth. Figure 4 Tables 59 and 60 give the penetration depths of X-rays with energies E1, E2 and E3, E4, respectively. Since X-rays of different energies have different penetration depths, they... Figure 4The detector, as shown, absorbs light at different longitudinal positions, generating photogenerated electron / hole pairs. These photogenerated electron / hole pairs separate under the influence of a bias electric field and drift towards the common electrode 61 and the pixel electrode 62. To distinguish signals generated by X-rays of different energies, the energy-resolved X-ray integrating detector proposed in this invention needs to possess two characteristics: firstly, the intrinsic layer photon absorption must be sufficiently thick to completely absorb both low-energy and high-energy X-ray photons; secondly, the detector must have unipolar carrier transport characteristics, meaning that only one type of photogenerated carrier can be effectively transported and form a detection current. Figure 4 We assume that the unipolar charge carriers are electrons. Based on the above assumption, we can obtain formula (2).

[0060]

[0061] In formula (2), it is assumed that we apply n different bias voltages V1, V2, ..., V to the pixel electrode 56. n L V1 ,L V2 ,…,L Vn It is the drift length of electrons under different bias voltages, μ e μ is the electron mobility, τ is the electron lifetime, and d is the detector thickness. e τ and d are determined solely by the semiconductor properties and geometry of the detector, and are independent of the energy of the incident X-ray photons and the properties of the object being detected. The number of photogenerated electrons produced by X-rays at different spatial positions of the detector is proportional to the X-ray energy deposited at that position, and these photogenerated electrons can only be collected by the pixel electrode and form a detection photocurrent when the distance from the photogenerated electrons to the pixel electrode is less than the electron drift length. Therefore, the expression for the photocurrent under different bias voltages (3) can be obtained.

[0062]

[0063] In the formula I photo-current-V1 ,I photo-current-V2 ,…,I photo-current-Vn These are the detectors at bias voltages V1, V2, ..., V... n The photocurrents under these conditions can be obtained through readout circuits and are known physical quantities. e L is the electron mobility of the detector's semiconductor material. It can be obtained by characterizing the electrical properties of the semiconductor material and is a known physical quantity. V1 ,L V2 ,…,L Vn I is the drift length of electrons under different bias voltages, which can be calculated using formula (2) and is a known physical quantity. E1 ,I E2 ,IE3 and I E4 Even if the X-ray intensities corresponding to the photon energies E1, E2, E3 and E4, they are the intensity information of different energy X-rays that the detector needs to distinguish. Although I E1 ,I E2 ,I E3 and I E4 Cannot be obtained directly by measuring the current and voltage of the pixel electrode 56, but they can be obtained by solving formula (3). Formula (3) has 4 unknowns I E1 ,I E2 ,I E3 and I E4 , a total of n equations. When the number of bias voltages n≥4, formula (3) can be converted into a nonlinear programming problem using the least squares method, and then the nonlinear programming problem is solved using conventional mathematical methods, and finally the optimal solution of I E1 ,I E2 ,I E3 and I E4 , that is, the X-ray intensities with energies E1, E2, E3 and E4 are identified.

[0064] Further, after identifying the different energy X-ray intensities I E1 ,I E2 ,I E3 and I E4 , the present application proposes to assign colors to the X-ray image of the detected object using material parameters. As can be seen from formula (1), the X-ray image gray scale I / I0 we obtain is simultaneously affected by the thickness d of the detected object and the linear attenuation coefficient μ of the detected object, so it cannot directly reflect the material characteristics of the detected object. However, if we know the X-ray images with photon energies E1 and E2, we have

[0065]

[0066]

[0067] Further, we get

[0068]

[0069]

[0070] According to formula (5), the linear attenuation coefficients of different energy X-rays in the detected object can be further

[0071]

[0072] In formula (6), we define the material parameters R(E1,E2) of the object being detected. As can be seen from formula (6), the material parameters R(E1,E2) are independent of the thickness of the object being detected, and are determined solely by the linear attenuation coefficient μ. Therefore, it can effectively reflect the material properties of the object. Since the linear attenuation coefficient μ of an object is not necessarily unique, several substances may have the same material parameter R(E1,E2). To improve the accuracy of identifying the material properties of the detected object, this invention proposes combining R(E1,E2), R(E1,E3), R(E1,E4), R(E2,E3), R(E2,E4), and R(E3,E4).

[0073] To reconstruct the X-ray color image of the detected object, this invention proposes to assign color values ​​to the X-ray image based on the material parameter R using a hue-saturation-intensity (HIS) model. The hue of the image is determined by the material parameter R of the detected object, while the color saturation can be given by formula (7).

[0074]

[0075]

[0076] In formula (7), S is the color saturation and I is the image intensity. We take the average intensity of the four energy X-rays as the final image intensity, i.e., I = [I(E1) + I(E2) + I(E3) + I(E4)] / 4.

[0077] The aforementioned energy-resolved X-ray integrating detectors must be X-ray detectors that directly convert energy, meaning that the semiconductor material directly absorbs X-ray photons and generates photogenerated carriers using the photoelectric effect. Indirect integrating X-ray detectors using scintillators cannot distinguish the photon energy of X-rays. These energy-resolved X-ray integrating detectors must also completely absorb both high-energy and low-energy X-ray photons and possess unipolar carrier transport characteristics. A typical energy-resolved X-ray integrating detector is a perovskite crystal pin photodiode, whose structure is as follows: Figure 5 As shown:

[0078] exist Figure 5 In the detector structure shown, an intrinsic lead halide mixed perovskite crystal is used as the X-ray photon absorber 67, such as MAPbBr 2.5 Cl 0.5Because this photon absorber contains high atomic number materials such as lead and halogens, it has a high absorption coefficient for X-rays. Furthermore, large-size perovskite crystals can be prepared using solution methods, and by increasing the thickness of the perovskite crystal (making it greater than 1 cm), high-energy X-ray absorption can be maximized. Doping intrinsic perovskite crystals with Cl yields n-type layer 66, such as MAPbBr. 0.2 Cl 2.8 Similarly, doping intrinsic perovskite crystals with Br element yields p-type layers, such as MAPbBr. 2.9 Cl 0.1 By setting a buffer layer to achieve lattice matching between p / i / n semiconductor layers, recombination of photogenerated carriers caused by interface defects can be reduced. Changing the halogen composition in perovskite crystals can not only control the concentration of majority and minority carriers but also alter the band gap of the semiconductor. Through bandgap engineering, it is possible to obtain... Figure 5 The diagram shows the conduction band bottom (CBM), valence band top (VBM), and hole quasi-Fermi level (E). Fp ) and the electron quasi-Fermi level (E Fn As can be seen from the band structure diagram, photogenerated holes generated in the intrinsic absorber are blocked by the VBM barrier of the p-type layer, making it difficult for them to cross the barrier and reach the common electrode 52. Photogenerated electrons, on the other hand, can pass through the n-type layer to reach the pixel electrode 56 relatively smoothly, forming a photoelectron current, thereby realizing unipolar carrier transport in the detector.

[0079] In addition to using the aforementioned band barrier to achieve unipolar carrier transport in the detector, the work function of the common electrode can be selected to build a higher Schottky barrier between the common electrode and the p-type layer, thereby blocking the injection of photogenerated holes. Alternatively, a semiconductor material with low hole mobility can be selected in the p-type layer to reduce the drift length of photogenerated holes, preventing them from effectively reaching the common electrode, thus achieving unipolar electron transport.

[0080] Figure 6 A block diagram of an integral detection color X-ray imaging method proposed in this invention is given. First, an X-ray tube is used as the X-ray emission source 30. Since the X-ray tube uses high-energy electrons to bombard a metal target to emit X-rays through bremsstrahlung radiation, the X-ray beam emitted by the X-ray source 30 contains multiple photon energies and has broadband emission characteristics.

[0081] The wide spectrum X-ray 31 emitted by the X-ray source 30 irradiates the object 32 to be detected. Considering the general case, the density of the object to be detected is not uniform, and the density is divided into 33, 34, 35 and 36 parts from small to large. After the X-ray beam 31 penetrates the object 32 to be detected, the intensity of the rays is modulated by the density and thickness of the object, and the X-ray photons of different energies have different intensities after transmission. Therefore, the X-ray after penetrating the object forms the intensity distribution of 37, 38 and 39. These X-rays are further projected onto the X-ray detector 40.

[0082] The device structure and working mode of the integral X-ray detector 40 are different from those of the conventional X-ray flat panel detector. It is a direct type detector, and the photon absorber 54 is thick, so that low energy X-rays and high energy X-rays can be completely absorbed. By designing the energy band structure 65 of the detector, or designing the work function of the common electrode, or designing the carrier mobility of the doped layer, the detector 40 has the performance of unipolar carrier transport. Change the bias voltage 62 to obtain the photocurrent under different bias voltages. The number n of bias voltages needs to be much larger than the number of energy channels.

[0083] Because the transmission depth of X-rays of different energies in the detector is different, they generate photo-generated carriers 57 at different spatial positions in the detector. Further, we change the electric field distribution 63 of the detector by changing the bias voltage 62 to regulate the transport and recombination of unipolar carriers 58, and obtain the photocurrent distribution as shown in formulas (2) and (3). We convert the model described in formula (3) into a nonlinear programming problem by the least square method, and solve the optimal solution of the nonlinear programming under the constraint condition by using conventional mathematical methods such as Lagrange algorithm, to obtain the intensity distribution of X-rays of different energies after penetrating the object to be detected.

[0084] Further, the physical model described by formulas (4), (5) and (6) is used to calculate the material parameters of the object to be detected. The signal combination of different energy channels improves the characteristic representation ability of the material parameters. Then, the HIS model is used to reconstruct the X-ray color image 42 by formula (7). The colors 43, 44, 45 and 46 correspond to the densities 33, 34, 35 and 36 of the object to be detected respectively, and the gray scale of the image represents the thickness of the object to be detected.

[0085] In the present application, the energy-resolved integral X-ray detector is the core device. Figure 5 It is an energy-resolved X-ray integral detector composed of a perovskite p-i-n photodiode. First, the MAPbBr 2.5 Cl 0.5The intrinsic perovskite single crystal 54 fully absorbs the incident X-ray energy. Then, the n-type layer 55 and the p-type layer 53 are respectively epitaxially grown on the upper and lower end faces of the intrinsic layer by solution epitaxy, wherein the semiconductor properties of the perovskite are changed by adjusting the halogen component. During the preparation process, not only the concentration of halogen doping needs to be adjusted to change the p, n properties, but also the band gap and the state density of the perovskite need to be adjusted by changing the halogen to obtain the CBM, VBM structures shown in 69 and 70, and the Fermi energy levels shown in 71 and 72, so that the detector has a unipolar carrier transport performance.

[0086] It should be understood that, for those skilled in the art, improvements or changes can be made according to the above description, and all these improvements and changes shall belong to the protection scope of the appended claims of the present application.

Claims

1. A method of integral detection x-ray color imaging, characterized in that, The method comprises the following steps: Step 1): an X-ray source emits an X-ray beam by virtue of bremsstrahlung phenomenon; Step 2): the X-ray beam, after passing through a detected object, irradiates an energy-resolving integrating X-ray detector; Step 3): the energy-resolving integrating X-ray detector acquires a photoelectric current or a photoelectric voltage signal of the X-ray beam under different detector bias voltages, and then calculates intensity and energy information of the X-ray beam according to the photoelectric current or the photoelectric voltage signal; Step 4): a signal processing and image processing module calculates material parameters of the detected object according to the intensity and energy information of the X-ray beam, and then assigns colors to an X-ray image by using the material parameters to reconstruct an X-ray color image; in the step 2), a semiconductor material of an intrinsic layer of the energy-resolving integrating X-ray detector completely absorbs the incident X-ray beam; the energy-resolving integrating X-ray detector has a unipolar carrier transport characteristic; in the step 4), the material parameters are defined as follows for the X-ray image with photon energies of E1 and E2: I0 is intensity of the X-ray beam before the X-ray beam is incident on the detected object, is a component of the detected object; the X-ray color image is obtained by assigning colors to the X-ray image by using a hue-saturation-intensity (HIS) model, wherein a hue of the X-ray color image is determined by the material parameter R of the detected object, a saturation degree is defined as: wherein I is intensity of the X-ray color image, and average values of intensities of the X-rays with four photon energies E1, E2, E3 and E4 are taken as the image intensity, i.e. .

2. The integral detection x-ray color imaging method of claim 1, wherein, The method for making the energy-resolved integral X-ray detector have single-polarity carrier transport characteristics comprises: the energy-resolved integral X-ray detector adopts a p-i-n photodiode structure, and single-polarity carrier transport is formed by using the energy band and barrier structure of the p-i-n photodiode; the energy-resolved integral X-ray detector collects electrode work functions, and single-polarity carrier transport is formed by a Schottky barrier; the energy-resolved integral X-ray detector controls the carrier mobility of the doped region semiconductor material, so that the drift length of a certain kind of photo-generated carrier is less than the transmission length of the kind of photo-generated carrier to the collecting electrode, and single-polarity carrier transport is formed; the energy-resolved integral X-ray detector uses a solution epitaxy method to epitaxially and dopedly grow an n-type layer on the upper end face of an intrinsic perovskite single crystal, and simultaneously incorporates Cl elements; an p-type layer is epitaxially and dopedly grown on the lower end face of the intrinsic perovskite single crystal, and simultaneously incorporates Br elements, and single-polarity carrier transport is formed.

3. The integral detection x-ray color imaging method of claim 2, wherein, In step 3), assuming the unipolar charge carriers are electrons, then the drift length of electrons varies under different bias voltages. for: Among them, V n is the bias voltage, and n is the number of bias voltages. It is the electron mobility. d is the electron lifetime, and d is the thickness of the energy-resolved integrating X-ray detector; assuming the X-ray beam passing through the object being detected has four photon energies, E1, E2, E3, and E4, the photocurrent under different bias voltages is obtained. for: where I E1 , I E2 , I E3 and I E4 are the X-ray intensities of the photon energies E1, E2, E3 and E4 respectively; when the number of bias voltages n≥4, the expression of I is converted into a nonlinear programming problem by using the least square method, the nonlinear programming problem is solved, and finally the optimal solutions of I E1 , I E2 , I E3 and I E4 are obtained, i.e. the intensity of the X-ray is obtained.

4. The integral detection x-ray color imaging method of claim 3, wherein, In the X-ray color image, the gray scale represents the thickness of the detected object, and the color represents the density of the detected object.

Images