Two-phase xenon positron tomography system and method

Abstract

The invention belongs to the technical field of nuclear medicine imaging, and particularly relates to a two-phase xenon positron tomography system and method.The two-phase xenon positron tomography system comprises a two-phase xenon detector module, a heat preservation device, a refrigeration purification system and a data acquisition system; the performance of the system is obviously improved by adopting a new material and a new method and correspondingly optimizing the system structure.

Description

Technical Field

[0001] The present application belongs to the field of nuclear medicine imaging technology, and specifically relates to a two-phase xenon positron tomography system and method. Background Art

[0002] A positron-emitting tracer—a protein containing a positron-emitting radioactive atom—is injected into the human body. The tracer participates in the body's metabolic cycle and typically accumulates at higher concentrations in areas of high cell proliferation, such as tumors, compared to normal tissue. The positrons emitted by the tracer annihilate with the electrons within a very short distance, producing a pair of back-to-back photons with an energy of 0.511 MeV that travel along the same straight line. A PET device (positron emission tomography) detects these two photons and identifies the point of annihilation, or the line along which the tracer molecule lies. Based on a large number of observations, it has been shown that tumors and other lesions are more likely to be traversed by this line than other areas. This information is used to reconstruct the distribution of the tracer in the body, and thus the distribution of lesions, providing a visual understanding of the underlying disease. Currently, there are many different types of tracers, each with different mechanisms of action. Therefore, choosing a different tracer can be used to detect different disease states, expanding the capabilities of PET.

[0003] Low-energy (less than 1 MeV) photons deposit energy in materials in two ways: Compton scattering and the photoelectric effect. The photoelectric effect can absorb all the energy of the photon, while Compton scattering can only deposit part of the energy. For 0.511 MeV photons, the probability of the photoelectric effect of xenon is significantly increased (25%), while the photoelectric effect of argon is extremely small and can be ignored. Therefore, the signal strength of the detector developed using xenon is significantly improved. This is conducive to improving the signal-to-noise ratio. In addition, although the cost of the two-phase xenon detector is higher than that of the two-phase argon detector, it is still much lower than the cost of traditional PET, so the economic value is still very high. Summary of the Invention

[0004] In response to the problems of poor spatial resolution and high price of traditional positron tomography machines, the present invention proposes a diphase xenon positron tomography system with significantly improved performance compared to the low-cost and high-precision diphase argon PET. The system is developed based on the principles of diphase xenon and gas multiplication technology.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A two-phase xenon positron tomography system includes a two-phase xenon detector module, a heat preservation device, a refrigeration and purification system, and a data acquisition system;

[0007] Several binary xenon detector modules are provided. When gamma photons strike the liquid xenon in the binary xenon detector module, the emitted scintillation light is collected by a photoelectric conversion device, giving the start time of the event. The generated ionized electrons are transported to the xenon gas, where they are multiplied and amplified and converted into electrical signals for positioning the XY coordinates.

[0008] A heat preservation device for accommodating the two-phase xenon detector module, wherein the heat preservation device is filled with a certain amount of liquid xenon as a heat preservation agent;

[0009] a refrigeration purification system connected to the heat preservation device, for extracting xenon gas from the heat preservation device, condensing it, and then returning it to the heat preservation device to maintain the temperature inside the heat preservation device;

[0010] A data acquisition system is connected to the signal processing electronics board of the two-phase xenon detector module, and is used to acquire data generated by the two-phase xenon detector module and store the data for subsequent analysis.

[0011] Preferably, a certain number of two-phase xenon detector modules are spliced into a ring-shaped detector system and installed in a heat preservation device. The two-phase xenon detector module includes a liquid xenon tank, a photoelectric converter array, an electron multiplier, and a signal processing electronics board. The liquid xenon tank is used to store liquid xenon. The photoelectric converter array is installed on a PCB carrier board, which is arranged on one side of the liquid xenon tank and placed vertically. The photoelectric converter array is used to collect the scintillation light emitted by the liquid xenon. The electron multiplier is arranged above the liquid xenon tank. The signal processing electronics board receives the multiplied electrons generated by the electron multiplier, forms an electrical signal, and sends it to the data acquisition system after processing.

[0012] Preferably, the liquid xenon tank is a tank body formed by splicing or casting transparent acrylic plates, the horizontal cross-section of the liquid xenon tank is trapezoidal, the photoelectric converter array is an array composed of multiple silicon photo avalanche diodes, and the outer side of the liquid xenon tank is installed with annular electrodes with increasing voltage from the bottom upward.

[0013] Preferably, the heat preservation device is a swimming ring-shaped cavity structure for accommodating the two-phase xenon detector modules arranged into a circular detector system; a flange port is provided on the heat preservation device for connecting the data acquisition board in the heat preservation device and an external computer;

[0014] Preferably, the electron multiplier comprises:

[0015] PCB signal sensing board;

[0016] The GEM membrane or other electron multiplying structure is fixed on the PCB signal sensing board and is parallel to the PCB signal sensing board. A total of two or three layers are provided to achieve electron multiplication.

[0017] Preferably, a planar electrode is provided at the bottom of the liquid xenon tank, and a parallel aluminum mesh is provided at the top, and the parallel aluminum mesh is immersed 3-6 mm below the liquid xenon surface in the liquid xenon tank.

[0018] Preferably, a negative high voltage of 10,000 V is set between the planar electrode and the parallel aluminum mesh, forming a strong electric field inside the liquid xenon, pulling the ionized electrons in the liquid xenon toward the liquid surface and passing through the liquid surface into the gas. The electron multiplier is enveloped by the evaporated xenon gas, and the electrons pulled from the liquid xenon are multiplied when passing through the electron multiplier, and are finally absorbed by the PCB signal sensing board to generate an XY coordinate signal.

[0019] A two-phase xenon positron tomography method comprises the following steps:

[0020] S1. Photons enter liquid xenon and react with the extranuclear electrons in the xenon atoms through photoelectric effect or Compton scattering, knocking the electrons out of the atoms.

[0021] S2. The knocked-out electrons then excite and ionize the surrounding xenon atoms, producing scintillation light and ionized electrons. This scintillation light is collected by a photoelectric converter array outside the liquid xenon, generating a time signature signal, recorded as T0. The ionized electrons are pulled upward toward the liquid surface by the strong electric field within the liquid xenon and enter the gaseous xenon, ultimately multiplying in number as they pass through a gas electron multiplier.

[0022] S3. Calculate the X and Y coordinates of the multiplied electrons:

[0023] The large number of multiplied electrons are collected by the PCB signal sensing board on the electron multiplier and processed by the signal processing electronics board to give the X and Y coordinates of the multiplied electrons. Since the original ionized electrons drift vertically upward, the X and Y coordinates are also the X and Y coordinates of the Compton scattering point of the incident photon.

[0024] S4. Calculate the Z direction of the photon scattering position:

[0025] Δt=T1-T0;

[0026] d=vΔt;

[0027] Among them, the time when the PCB signal sensing board senses the signal is T1, and Δt is the time it takes for the original ionized electron to drift from the generation point to the gas electron multiplier;

[0028] Based on the drift velocity v of electrons in liquid xenon, the distance d between the photon scattering point and the signal sensing plate can be calculated as the Z-direction coordinate, thereby realizing the measurement of the photon scattering position XYZ.

[0029] Preferably, liquid xenon is used as a sensitive material for photon detection and is placed in a liquid xenon tank with a temperature between -111.9°C and -108°C; the area outside the liquid xenon tank is saturated xenon vapor, which is naturally evaporated from the liquid xenon; the gaseous xenon can be doped with methane, with a volume ratio of 0-2%, which can effectively suppress discharge.

[0030] Preferably, the probability ratio of the photoelectric effect and Compton scattering between 0.511 MeV photons and xenon is 1:3. The electrons generated by the photoelectric effect absorb all the energy of the incident photons, resulting in a high signal intensity and effectively improving the signal-to-noise ratio. Compared with the prior art, the present application has the following advantages:

[0031] Compared with the patented two-phase argon technology, the advantages and positive effects of the present invention are:

[0032] 1. The density of liquid xenon is 3.52g / cm3, which is 2.5 times that of liquid argon. Therefore, with the same detection efficiency, the thickness of the two-phase xenon detector module can be reduced by 2.5 times, and the number of electronic channels can be reduced accordingly.

[0033] 2. The probability ratio of photoelectric effect and Compton scattering between 0.511MeV photons and xenon is 1:3, while the probability of photoelectric effect in liquid argon is negligible. The photoelectrons generated by the photoelectric effect (0.511MeV) have higher energy than Compton electrons (maximum 0.344MeV). The detector has high signal intensity and high signal-to-noise ratio, which is also conducive to the use of selected photon full-energy peak events to improve the detection signal-to-noise ratio.

[0034] 3. At one atmosphere of pressure, the boiling point of liquid xenon is -111.8 degrees, which is higher than the -186 degrees of liquid argon, reducing the pressure and cost of the refrigeration system.

[0035] 4. The drift velocity of electrons in liquid xenon is 2.5 times higher than that in liquid argon. The fast electron drift velocity can increase the counting rate by 2.5 times.

[0036] 5. The ionization energy of xenon is 15.6eV, which is lower than argon’s 24eV. The light and electron yields are high, and the detector signal intensity will be increased by 60%.

[0037] 6. Methane can be doped into two-phase xenon, but not into two-phase argon, because methane has a high absorption rate for argon scintillation light (128nm), but almost no absorption for xenon scintillation light (178nm) with lower energy, which does not affect the collection of xenon scintillation light. However, in xenon, the addition of methane can significantly improve the electron multiplication gain and stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 A schematic diagram of the overall structure of a two-phase xenon positron tomography system provided in an embodiment of the present invention;

[0039] Figure 2 A schematic diagram of the working principle of a detector module based on two-phase xenon technology provided by an embodiment of the present invention;

[0040] In the above figures, the meanings of the reference numerals are as follows:

[0041] 1. Two-phase xenon detector module; 2. Refrigeration and purification system; 3. Insulation device; 4. Signal connection line; 5. Data acquisition system; 6. Computer; 7. Flange; 8. Photoelectric conversion device array; 9. Electron multiplier; 10. Liquid xenon; 11. Scintillation light; 12. Multiplication electrons; 13. Signal processing electronics board; 14. Incident photons; 15. Ionization electrons; 16. Liquid xenon tank. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described and illustrated in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Based on the embodiments provided by the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work, including but not limited to replacing different photon sensitive materials, light detectors, electron multiplication methods, etc., as well as changing the shape and relative structural design, etc., all fall within the scope of protection of the present invention.

[0043] The embodiment of the present invention provides a two-phase xenon positron tomography system, Figure 1-2 Schematic diagram of the overall structure and the structure of a two-phase xenon detector module according to an embodiment of the present invention.

[0044] refer to Figure 1 As shown, the system at least includes: a two-phase xenon detector module 1, a heat preservation device 3, a refrigeration and purification system 2, a signal connection line 4, a flange port 7, a data acquisition system 5, and a computer 6;

[0045] refer to Figure 2 As shown, the two-phase xenon detector module 1 further includes a liquid xenon tank 16 for storing liquid xenon 10, two layers of electron multiplier films 9 are arranged above the liquid xenon tank 16 and parallel to the liquid xenon liquid surface, and a signal processing electronics board 13. The photoelectric converter array 8 is mounted on a PCB carrier board, which is placed on one side of the liquid xenon tank 16 and is placed vertically, facing the liquid xenon tank;

[0046] The insulation device 3 has a swimming ring-shaped cavity structure, the internal space of which is used to accommodate the two-phase xenon detector modules arranged in a ring. The bottom of the insulation device 3 is filled with a certain amount of liquid xenon as a heat preservation agent. The refrigeration purification system 2 is connected to the insulation device 1, extracting xenon gas from the insulation device 1, condensing it, and then returning it to the insulation device 1 to maintain the low temperature inside the insulation device 1. The data acquisition system 5 is connected to all the two-phase xenon detector modules via signal line 4 and is also connected to a computer outside the insulation device 1.

[0047] In some embodiments, a planar electrode (not shown) is positioned at the bottom of the liquid xenon tank 16, and a parallel aluminum mesh (not shown) is positioned 4 mm below the liquid xenon surface. Furthermore, a high voltage of -10,000 V is applied between the planar electrode and the parallel aluminum mesh, creating an electric field within the liquid xenon. This pulls ionized electrons within the liquid xenon toward the liquid surface, where they pass through and into the electron multiplier, multiplying the electrons. These electrons are ultimately absorbed by the signal sensing plate, generating an XY coordinate signal.

[0048] Next, the working principle and working process of the positron emission tomography system provided by the present invention are described:

[0049] The two-phase xenon positron tomography system is designed based on the two-phase xenon radiation detection technology. The scanning system uses liquid xenon as the sensitive material for photon detection. It is placed in a liquid xenon tank with a temperature set between -111.9℃ and -108℃. The area outside the liquid xenon tank is saturated xenon vapor, which is naturally evaporated from the liquid xenon. The working principle of the two-phase xenon technology is as follows: Figure 2As shown, photons 14 enter liquid xenon and react with the extranuclear electrons in the xenon atoms through the photoelectric effect or Compton scattering, knocking the electrons out of the atoms. The knocked-out electrons then excite and ionize the surrounding xenon atoms, producing scintillation light 11 and ionized electrons 15. Scintillation light 11 is collected by a photoelectric converter array 11 outside the liquid xenon, generating a time marker signal, recorded as T0. The ionized electrons 15 are pulled upward toward the liquid surface by the strong electric field in the liquid xenon and enter the gaseous xenon, ultimately multiplying in number as they pass through the gas electron multiplier 9. The multiplied electrons induce an electrical signal on the PCB signal sensing board, which is processed by the signal processing electronics board 13 to produce the X and Y coordinates of the multiplied electrons. Since the original ionized electrons drift vertically upward, these X and Y coordinates also correspond to the X and Y coordinates of the point where the incident photon experienced Compton scattering or the photoelectric effect. The difference Δt between the signal times T1 and T0 on the PCB sensing board is the time it takes for the primary ionized electron to drift from its generation point to the gas electron multiplier 9. Based on the electron's drift velocity in liquid xenon, the distance d between the photon scattering point and the signal sensing board can be calculated as the Z coordinate, thereby enabling measurement of the photon scattering position (XYZ coordinate). Because the density of liquid xenon is 2.5 times that of liquid argon, the size of the xenon detector module is 40% of that of the argon detector module, providing the same detector efficiency, effectively reducing detector size.

[0050] In order to more clearly and in detail introduce the two-phase xenon positron tomography system provided by the embodiment of the present invention, it will be described below in conjunction with specific embodiments.

[0051] Example 1:

[0052] This embodiment is a positron tomography system, specifically:

[0053] The system at least includes: a two-phase xenon detector module 1, a heat preservation device 3, a refrigeration and purification system 2, a signal connection line 4, a flange port 7, a data acquisition system 5, and a computer 6. The specific structure of each part is as follows:

[0054] Dixenon detector module 1:

[0055] Multiple two-phase xenon detector modules 1 are assembled into a circular ring. The two-phase xenon detector module 1 further includes a liquid xenon tank 16 for storing liquid xenon 10. Two layers of electron multiplier membranes 9 are positioned above the liquid xenon tank 16, parallel to the liquid xenon level. An XY signal sensing board and signal processing electronics board 13 are mounted on a PCB carrier board, which is positioned vertically to one side of the liquid xenon tank 16. The liquid xenon tank 16 is a 10 cm deep, trapezoidal cross-section structure constructed by splicing or casting transparent acrylic sheets. The top base (facing the radiation incident side) is 10 cm, the bottom base is 11.9 cm, and the spacing between the two bases is 3.6 cm. The gas electron multiplier 9 is positioned above the liquid xenon level. The PCB signal sensing board and signal processing electronics board 13 absorb electrons during the multiplication process and generate XY positioning signals.

[0056] The copper strips on the electron multiplier film 9 include x-direction copper strips and y-direction copper strips. The signals of the xy copper strips are sent to the signal processing electronics board 13. Therefore, the signal processing electronics board 13 gives the corresponding X or Y coordinate when it detects which copper strip has a signal.

[0057] Insulation device 3:

[0058] The heat preservation device 3 comprises a heat preservation device body, a flange 7, and a circular track (not shown). The heat preservation device body is a swimming ring-shaped cavity structure with a cross-sectional diameter of 20 cm; the flange 7 is provided on the heat preservation device. The data acquisition system 5 is connected to all two-phase xenon detector modules 1 via signal lines 4 and to the outside world via optical fiber. This reduces the number of internal and external wiring of the heat preservation device 3 to a few, effectively controlling the conduction of external heat.

[0059] Refrigeration purification system 2:

[0060] The refrigeration purification system 2 is connected to the heat preservation device 3 to extract the xenon gas in the heat preservation device 3 and then send it into the heat preservation device 3 after condensation to maintain the low temperature in the heat preservation device 3.

[0061] Data Acquisition System 5:

[0062] The data acquisition system 5 includes a data acquisition board 5 and a computer 6. The signal processing electronics board 13 of each dixenon detector module 1 processes the detector's analog signals, digitizes them, and buffers them. The data acquisition board 5 collects and packages the data from all signal processing electronics boards 13 and sends it to the computer 6.

[0063] A two-phase xenon positron tomography method comprises the following steps:

[0064] S1. Photon 14 enters the liquid xenon and reacts with the extranuclear electrons in the xenon atoms through photoelectric effect or Compton scattering, knocking the electrons out of the atoms.

[0065] S2. The knocked-out electrons then excite and ionize the surrounding xenon atoms, generating scintillation light 11 and ionized electrons 15. Scintillation light 11 is collected by a photoelectric converter array 11 outside the liquid xenon, generating a time marker signal, recorded as T0. The ionized electrons 15 are pulled upward toward the liquid surface by the strong electric field within the liquid xenon and enter the gaseous xenon, ultimately multiplying in number as they pass through the gas electron multiplier 9.

[0066] S3. Calculate the X and Y coordinates of the multiplied electrons:

[0067] The multiplied electrons are sensed by the PCB signal sensing board on the electron multiplier 9 and processed by the signal processing electronics board 13 to give the X and Y coordinates of the multiplied electrons. Since the original ionized electrons drift vertically upward, the X and Y coordinates are also the X and Y coordinates of the Compton scattering point of the incident photon.

[0068] S4. Calculate the Z direction of the photon scattering position:

[0069] Δt=T1-T0;

[0070] d=vΔt;

[0071] The time it takes for the PCB signal sensing board to sense the signal is T1, and Δt is the time it takes for the primary ionized electron to drift from the generation point to the gas electron multiplier 9;

[0072] Based on the drift velocity v of electrons in liquid xenon, the distance d between the photon scattering point and the signal sensing plate can be calculated as the Z-direction coordinate, thereby realizing the measurement of the photon scattering position XYZ.

[0073] Liquid xenon or the sensitive material used for photon detection is placed in a liquid xenon tank with a temperature between -111.9°C and -108°C; the area outside the liquid xenon tank is saturated xenon vapor, which evaporates naturally from the liquid xenon; the gaseous xenon can be doped with methane, with a volume ratio of 0-2%, to effectively suppress discharge.

[0074] The probability ratio of 0.511MeV photons to photoelectric effect and Compton scattering with xenon is 1:3.

[0075] Example 2:

[0076] This example is based on the multi-dimensional comparison of the two-phase xenon PET and the two-phase argon PET shown in Example 1, specifically:

[0077] (1) The detector’s sensitive media are different:

[0078] The principle of photon detection is that photons interact electromagnetically with the sensitive medium within the detector, knocking high-energy electrons out of the atoms of the sensitive medium (argon or xenon in this case). These charged electrons excite and ionize the atoms in their path, producing scintillation light and ionized electrons. Xenon has superior performance, producing more scintillation light and ionized electrons, which improves the signal-to-noise ratio.

[0079] (2) Different electron multiplication performance:

[0080] After ionized electrons transition from the liquid to the gas phase, they are collected and multiplied by an electron multiplier. Because methane does not absorb xenon scintillation light (178 nm) but absorbs the higher-energy argon scintillation light (128 nm), dixenon PET can be doped with methane, but dixenon PET cannot. Methane is a commonly used quenching gas in gas detectors, effectively suppressing discharge and stabilizing the electron multiplication process. This results in a more stable electron multiplication process and a higher multiplication rate in dixenon PET, facilitating signal processing, improving the signal-to-noise ratio, and enhancing detector stability.

[0081] (3) Difference in signal-to-noise ratio:

[0082] The stronger and more stable signal of dixenon PET offers numerous advantages. Firstly, the significantly enhanced and more stable signal makes it more immune to noise, reduces electronics requirements, and provides higher position and energy resolution. This can be experimentally compared and verified by measuring the same energy of x-rays using two different PET techniques. Table 1 lists some key performance comparisons between the new PET and conventional PET.

[0083] Table 1 Differences in indicators between two-phase argon PET and two-phase xenon PET

[0084]

[0085]

[0086] Obviously, the drawings described below are merely examples or embodiments of the present invention. Those skilled in the art can apply the present invention to other similar scenarios based on these drawings without inventive effort. Furthermore, it is understood that while the effort involved in such a development process may be complex and lengthy, for those skilled in the art related to the disclosure of the present invention, any design, manufacturing, or production changes based on the technical content disclosed in the present invention are merely conventional technical means and should not be construed as an inadequacy of the disclosure of the present invention.

[0087] References to "embodiments" in this disclosure mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the disclosure. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described in this disclosure may be combined with other embodiments, unless there is a conflict.

Claims

1. A two-phase xenon positron tomography system, characterized in that: It includes a two-phase xenon detector module, a heat preservation device, a refrigeration and purification system, and a data acquisition system; There are several binary xenon detector modules. When gamma photons hit the liquid xenon in the binary xenon detector modules, the emitted scintillation light is collected by a photoelectric conversion device, giving the start time of the event. The generated ionized electrons are transported to the xenon gas, multiplied and amplified, and converted into electrical signals for positioning XY coordinates; A heat preservation device for accommodating the two-phase xenon detector module, wherein the heat preservation device is filled with a certain amount of liquid xenon as a heat preservation agent; a refrigeration purification system connected to the heat preservation device, for extracting xenon gas from the heat preservation device, condensing it, and then returning it to the heat preservation device to maintain the temperature inside the heat preservation device; A data acquisition system is connected to the signal processing electronics board of the two-phase xenon detector module, and is used to acquire data generated by the two-phase xenon detector module and store the data for subsequent analysis.

2. The binary xenon positron tomography system according to claim 1, characterized in that: A certain number of two-phase xenon detector modules are assembled into a ring-shaped detector system and installed in a heat preservation device. The two-phase xenon detector modules include a liquid xenon tank, a photoelectric converter array, an electron multiplier, and a signal processing electronics board. The liquid xenon tank is used to store liquid xenon. The photoelectric converter array is mounted on a PCB carrier board, which is positioned vertically on one side of the liquid xenon tank. The photoelectric converter array is used to collect scintillation light emitted by the liquid xenon. The electron multiplier is located above the liquid xenon tank. The signal processing electronics board receives the multiplied electrons generated by the electron multiplier, generates an electrical signal, and transmits it to the data acquisition system after processing.

3. The binary xenon positron tomography system according to claim 2, characterized in that: The liquid xenon tank is a tank body formed by splicing or casting transparent acrylic plates. The horizontal cross-section of the liquid xenon tank is trapezoidal. The photoelectric converter array is an array composed of multiple silicon photo avalanche diodes. The outer side of the liquid xenon tank is installed with annular electrodes with increasing voltage from the bottom to the top.

4. The binary xenon positron tomography system according to claim 1, characterized in that: The heat preservation device is a swimming ring-shaped cavity structure for accommodating the two-phase xenon detector modules arranged into a circular detector system; a flange port is provided on the heat preservation device for connecting the data acquisition board in the heat preservation device and an external computer.

5. The binary xenon positron tomography system according to claim 2, characterized in that: The electron multiplier comprises: PCB signal sensing board; The GEM membrane or other electron multiplying structure is fixed on the PCB signal sensing board and is parallel to the PCB signal sensing board. A total of two or three layers are provided to achieve electron multiplication.

6. The binary xenon positron tomography system according to claim 2, characterized in that: A planar electrode is provided at the bottom of the liquid xenon tank, and a parallel aluminum mesh is provided at the top. The parallel aluminum mesh is immersed 3-6 mm below the liquid xenon surface in the liquid xenon tank.

7. The binary xenon positron tomography system according to claim 6, characterized in that: A negative high voltage of 10,000 V is set between the planar electrode and the parallel aluminum mesh, forming a strong electric field inside the liquid xenon, pulling the ionized electrons in the liquid xenon toward the liquid surface and passing through the liquid surface into the gas. The electron multiplier is enveloped by the evaporated xenon gas. The electrons pulled from the liquid xenon are multiplied when passing through the electron multiplier and are finally absorbed by the PCB signal sensing board to generate XY coordinate signals.

8. A two-phase xenon positron tomography method, applicable to the two-phase xenon positron tomography system according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1. Photons enter liquid xenon and react with the extranuclear electrons in the xenon atoms through photoelectric effect or Compton scattering, knocking the electrons out of the atoms. S2. The ejected electrons then excite and ionize the surrounding xenon atoms, generating scintillation light and ionized electrons. The scintillation light is collected by a photoelectric converter array outside the liquid xenon, generating a time marker signal, recorded as T0. The ionized electrons are pulled upwards towards the liquid surface by the strong electric field in the liquid xenon and enter the gaseous xenon, where they are multiplied when they finally pass through the gas electron multiplier. S3. Calculate the X and Y coordinates of the multiplied electrons: The large number of multiplied electrons are collected by the PCB signal sensing board on the electron multiplier and processed by the signal processing electronics board to give the X and Y coordinates of the multiplied electrons. Since the original ionized electrons drift vertically upward, the X and Y coordinates are also the X and Y coordinates of the Compton scattering point of the incident photon. S4. Calculate the Z direction of the photon scattering position: Δt=T1-T0; d=vΔt; Among them, the time when the PCB signal sensing board senses the signal is T1, and Δt is the time it takes for the original ionized electron to drift from the generation point to the gas electron multiplier; Based on the drift velocity v of electrons in liquid xenon, the distance d between the photon scattering point and the signal sensing plate can be calculated as the Z-direction coordinate, thereby realizing the measurement of the photon scattering position XYZ.

9. The two-phase xenon positron tomography method according to claim 8, characterized in that: Liquid xenon, a sensitive substance for photon detection, is placed in a liquid xenon tank with a temperature between -111.9°C and -108°C. The area outside the liquid xenon tank is saturated xenon vapor, which evaporates naturally from the liquid xenon. The gaseous xenon can be doped with methane, with a volume ratio of 0-2%, which can effectively suppress discharge.

10. The two-phase xenon positron tomography method according to claim 8, characterized in that: The probability ratio of photoelectric effect and Compton scattering between 0.511MeV photons and xenon is 1:

3. The electrons generated by the photoelectric effect absorb all the energy of the incident photons, resulting in high signal intensity and effectively improving the signal-to-noise ratio.

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