Method for imaging a closed internal cavity of an aeroengine using a positron emission tomograph based on an embedded rotating flat panel detector device

Abstract

The application discloses a method for imaging airtight inner cavity of an aero-engine by using a low-cost positron emission tomography device with good imaging quality, and the gamma photon detection mechanism of the positron emission tomography device comprises an embedded rotary flat plate detection device and a ring-shaped detection device; the ring-shaped detection device comprises a cylindrical mounting frame, and the inner wall of the cylindrical mounting frame is covered with second gamma photon detection crystals; the embedded rotary flat plate detection device comprises a mounting flat plate and a driving device for driving the mounting flat plate to rotate around the central axis of the ring-shaped detection device, and the mounting flat plate is provided with a plurality of first gamma photon detection crystals; the central angle of the cylindrical mounting frame corresponding to the first gamma photon detection crystals of the first detection crystal array is 60-90 degrees; and the diameter of the second detection crystal array is 1.6-2.6 times the distance between the first detection crystal array and the central axis of the ring-shaped detection device.

Description

Technical Field

[0001] This invention relates to the fields of positron emission tomography (PET) imaging devices and image reconstruction, and more particularly to a method for imaging the sealed cavity of an aero-engine using a positron emission tomography scanner based on an embedded rotating flat plate detector. Background Technology

[0002] Positron emission tomography (PET) is a technique that uses high-energy gamma photons generated during positron annihilation to image and characterize the internal state of an object. The gamma photons produced by positron annihilation have stable directional and energy characteristics, are unaffected by changes in external environments such as electric fields, magnetic fields, and temperature, and can penetrate dense metals and other materials. This gives PET technology a unique advantage in industrial non-destructive testing. Utilizing the annihilation phenomenon, positron annihilation technology has become a non-destructive detection and analysis method for studying the material structure (surface and internal defects) and electronic state (electron momentum distribution) of materials such as metals, semiconductors, high-temperature superconductors, and polymers.

[0003] Existing PET equipment is cylindrical and equipped with a large number of gamma photon detector crystals. However, the price of gamma photon detector crystals increases significantly with the improvement of their resolution. In order to reasonably control costs, it is difficult to equip PET equipment with a large number of high-resolution gamma photon detector crystals. As a result, when existing PET equipment is used for non-destructive testing in the aerospace industry, the resolution is low when imaging closed cavities due to the inherent low resolution of the detector crystals and the complex internal environment of aero-engines. Summary of the Invention

[0004] In response to the problems mentioned in the background art, the present invention aims to provide a low-cost, high-quality positron emission tomography (PET) scanner based on an embedded rotating flat plate detector for imaging the sealed internal cavity of an aero-engine.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a method for imaging the sealed internal cavity of an aero-engine using a positron emission tomography scanner based on an embedded rotating flat plate detection device, comprising the following steps:

[0006] Step 1: Prepare a radioactive nuclide by thoroughly mixing the radioactive nuclide with aviation kerosene;

[0007] Step 2: Inject the mixture of radioactive nuclide and aviation kerosene into the sealed cavity of the aircraft engine;

[0008] Step 3: The aircraft engine, after being filled with a mixture of radioactive nuclides and aviation kerosene, is placed on a fixed detection platform at the center of a positron emission tomography (PET) scanner;

[0009] The gamma-ray detection mechanism of this positron emission tomography (PET) scanner includes an embedded rotating flat plate detection device and a ring detection device. The ring detection device includes a cylindrical mounting frame disposed around the periphery of the fixed detection stage in the scanner frame, with the inner wall of the cylindrical mounting frame covered with second gamma-ray detection crystals. The embedded rotating flat plate detection device includes a mounting base, on which a mounting plate is movably mounted. The mounting plate is located between the inner side of the cylindrical mounting frame and the outer periphery of the fixed detection stage. The mounting plate is radially adjustable along the cylindrical mounting frame. The mounting base is equipped with a drive device that drives the mounting plate to rotate around the central axis of the ring detection device. A plurality of first gamma-ray detection crystals are arranged flat on the mounting plate. The total length of the first gamma-ray detection crystals on the mounting plate is equal to the total length of the second gamma-ray detection crystals disposed on the inner wall of the cylindrical mounting frame. Moreover, the resolution of the first gamma-ray detection crystals is higher than that of the second gamma-ray detection crystals.

[0010] The first gamma-photon plate detector crystal, fixed on the mounting plate, forms the first detector crystal array, and the second gamma-photon detector crystal of the ring detector forms the second detector crystal array; the central angle of the cylindrical mounting frame corresponding to the first gamma-photon detector crystal part of the first detector crystal array is 60°-90°; and the diameter of the second detector crystal array is 1.6-2.6 times the distance between the first detector crystal array and the central axis of the ring detector.

[0011] Step 4: Start the servo drive motor and positron emission tomography scanner. The first and second plate detector crystal arrays, which rotate with the ring guide rail, perform real-time data acquisition of gamma photon pairs generated by the annihilation of the radionuclide-labeled aviation kerosene mixture in the sealed cavity of the aero-engine at any angle.

[0012] Step 5: Perform three-dimensional image reconstruction on the γ-photon cone beam data detected by the first and second detector crystal arrays to obtain high-resolution imaging of the sealed internal cavity of the aero-engine; the γ-photon cone beam data is used to reconstruct the image based on an iterative algorithm, specifically including:

[0013] The likelihood function obtained by making the detected data follow a Poisson distribution is:

[0014]

[0015] Among them, A ij To detect the probability of the j-th voxel detected by the combination of the first and second γ-photon detector crystals of the i-th pair of γ-photon pairs generated by annihilation, p j y represents the pixel value of the j-th pixel. i Indicates the projected value;

[0016] A set of cone-beam detection data is D ij The likelihood function corresponding to this data is:

[0017]

[0018] Given that the current image is p k After taking the logarithm of both sides of the above equation, find the expectation of ln(L(p)).

[0019]

[0020] By finding the maximum value of the above equation and taking the first-order partial derivative, we obtain the iterative reconstruction formula:

[0021]

[0022] As a preferred embodiment, the resolution of the first γ-photon detector crystal is more than 20% higher than that of the second γ-photon detector crystal.

[0023] As a preferred embodiment, the embedded rotating flat plate detection device includes a pair of annular guide rails, with at least a pair of pulleys movably disposed within the annular guide rails. All pulleys are fixedly connected to a mounting base, and the mounting base is provided with the mounting plate.

[0024] As a preferred embodiment, the pair of annular guide rails are respectively disposed on the outer sides of both ends of the cylindrical mounting frame.

[0025] As a preferred embodiment, the driving device includes an annular drive rack mounted on one of the annular guide rails and a servo drive motor mounted on a mounting base. The output shaft of the servo drive motor is provided with a drive gear that cooperates with the drive rack.

[0026] As a preferred embodiment, the mounting base is provided with a lead screw mechanism arranged radially along the cylindrical mounting frame, as well as a servo adjustment motor and transmission device for driving the lead screw mechanism. The mounting plate is movably mounted on the mounting base and connected to the movable block of the lead screw mechanism.

[0027] The beneficial effects of this invention are as follows: The gamma photon detection mechanism includes an embedded rotating flat plate detection device and a ring detection device. The ring detection device includes a cylindrical mounting frame disposed around the periphery of the fixed detection stage in the scanner frame, with the inner wall of the cylindrical mounting frame covered with second gamma photon detection crystals. The embedded rotating flat plate detection device includes a mounting base, on which a mounting plate is movably mounted. The mounting plate is located between the inner side of the cylindrical mounting frame and the outer periphery of the fixed detection stage. The mounting plate's radial position is adjustable along the cylindrical mounting frame. The mounting base is equipped with a driving device that drives the mounting plate to rotate around the central axis of the ring detection device. A plurality of first gamma photon detection crystals are arranged flat on the mounting plate. The total length of the first gamma photon detection crystals on the mounting plate is equal to the total length of the second gamma photon detection crystals disposed on the inner wall of the cylindrical mounting frame. Furthermore, the resolution of the first gamma photon detection crystals is higher than that of the second gamma photon detection crystals. Only a small number of high-resolution first gamma photon detection crystals are needed to significantly improve the detection rate of gamma photons and reduce data loss caused by photon noncollinearity, thereby resulting in a higher data sampling rate for gamma photons and improved imaging quality. The rotating first and second detector arrays perform real-time data acquisition at arbitrary angles of the gamma photon pairs generated by the annihilation of the radionuclide-labeled aviation kerosene mixture in the sealed cavity of the aero-engine; and perform three-dimensional image reconstruction on the gamma photon cone beam data detected by the first and second detector arrays to obtain high-resolution imaging of the sealed cavity of the aero-engine. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the gamma photon detection mechanism of the present invention.

[0029] Figure 2 This is a schematic diagram of the positron emission tomography scanner of the present invention.

[0030] Figure 3 This is a schematic diagram showing the positional relationship between the gamma photon detection mechanism of the present invention, the fixed detection platform, and the aircraft engine to be tested.

[0031] Figure 4 This is a side view schematic diagram of the embedded rotating flat plate detection device of the present invention.

[0032] In the figure: 1 First detection crystal array, 2 Second detection crystal array, 3 Aircraft engine to be tested, 4 Scanner frame, 5 Fixed detection table, 6 Cylindrical mounting frame, 7 First γ-photon detection crystal, 8 Mounting plate, 9 Circular guide rail, 10 Pulley, 11 Mounting base, 12 Circular drive rack, 13 Servo drive motor, 14 Drive gear, 15 Lead screw mechanism, 16 Servo adjustment motor, 17 Transmission device. Detailed Implementation

[0033] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0034] like Figure 1-4 As shown, a method for imaging a sealed cavity of an aero-engine using a positron emission tomography scanner based on an embedded rotating flat plate detector includes the following steps:

[0035] Step 1: Prepare a radioactive nuclide by thoroughly mixing the radioactive nuclide with aviation kerosene;

[0036] Step 2: Inject the mixture of radioactive nuclide and aviation kerosene into the sealed cavity of the aircraft engine;

[0037] Step 3: The aircraft engine, after being filled with a mixture of radioactive nuclides and aviation kerosene, is placed on the fixed detection stage 5 at the center of the positron emission tomography scanner;

[0038] The gamma-ray detection mechanism of this positron emission tomography (PET) scanner includes an embedded rotating plate detection device and a ring detection device. The ring detection device includes a cylindrical mounting frame 6 disposed around the periphery of the fixed detection stage 5 in the scanner frame 4. The inner wall of the cylindrical mounting frame 6 is covered with second gamma-ray detection crystals. The embedded rotating plate detection device includes a mounting base 11, on which a mounting plate 8 is movably mounted. The mounting plate 8 is located between the inner side of the cylindrical mounting frame 6 and the outer periphery of the fixed detection stage 5. The mounting base 11 is equipped with a drive device for rotating the mounting plate 8 around the central axis of the ring detection device, and the radial position of the mounting plate 8 along the cylindrical mounting frame 6 is adjustable. A plurality of first gamma-ray detection crystals 7 are arranged flat on the mounting plate 8. The total length of the first gamma-ray detection crystals 7 on the mounting plate 8 is equal to the total length of the second gamma-ray detection crystals disposed on the inner wall of the cylindrical mounting frame 6. The resolution of the first gamma-ray detection crystals is 30% higher than that of the second gamma-ray detection crystals.

[0039] The embedded rotating flat plate detection device includes a pair of annular guide rails 9, which are respectively arranged on the outer sides of both ends of the cylindrical mounting frame 6, avoiding the influence of the annular guide rails 9 on imaging and improving imaging quality. At least one pair of pulleys 10 are movably arranged inside the annular guide rails 9, and all pulleys 10 are fixedly connected to the mounting base 11, on which the mounting plate 8 is mounted. The driving device includes an annular drive rack 12 mounted on one of the annular guide rails 9, and a servo drive motor 13 mounted on the mounting base 11. The output shaft of the servo drive motor 13 is provided with a drive gear 14 that cooperates with the drive rack. The mounting base 11 is provided with a lead screw mechanism 15 arranged radially along the cylindrical mounting frame 6, a servo adjustment motor 16 driving the lead screw mechanism 15, and a transmission device 17. The mounting plate 8 is movably mounted on the mounting base 11 and connected to the movable block of the lead screw mechanism 15.

[0040] The first γ-photon flat plate detector crystal fixed on the mounting plate 8 forms the first detector crystal array 1, and the second γ-photon detector crystal 7 of the ring detector forms the second detector crystal array 2; the central angle of the cylindrical mounting bracket 6 corresponding to the first γ-photon detector crystal 7 of the first detector crystal array 1 is 60°; and the diameter of the second detector crystal array 2 is 1.6-2.6 times the distance between the first detector crystal array 1 and the central axis of the ring detector.

[0041] Step 4: Start the servo drive motor 9 and the positron emission tomography scanner. The first plate detector crystal array 1 and the second detector crystal array 2, which rotate with the ring guide rail 9, perform real-time data acquisition of γ photon pairs generated by the annihilation of the radionuclide-labeled aviation kerosene mixture in the sealed inner cavity of the aero-engine.

[0042] Step 5: Perform three-dimensional image reconstruction on the γ-photon cone beam data detected by the first detector crystal array 1 and the second detector crystal array 2 to obtain a high-resolution image of the sealed internal cavity of the aero-engine:

[0043] Images are reconstructed from γ-photon cone beam data acquired at arbitrary angles using an iterative algorithm.

[0044] The detected data follows a Poisson distribution, and the corresponding likelihood function is:

[0045]

[0046] Among them, A ij To detect the probability of the j-th voxel detected by the combination of the first and second γ-photon detector crystals of the i-th pair of γ-photon pairs generated by annihilation, p j y represents the pixel value of the j-th pixel. i This represents the projected value.

[0047] A set of cone-beam detection data is D ij The likelihood function corresponding to this data is:

[0048]

[0049] Given that the current image is p k After taking the logarithm of both sides of the above equation, find the expectation of ln(L(p)).

[0050]

[0051] By finding the maximum value of the above equation and taking the first-order partial derivative, we obtain the iterative reconstruction formula:

[0052]

[0053] The method of this invention patent is based on the inherent resolution of the existing detector, by adding an embedded rotating flat plate detector crystal to improve the imaging resolution, thereby further improving the resolution on the basis of the inherent resolution.

[0054] In this imaging system, the response lines between the first γ-photon detector crystal in the first detector array 1 and all the second γ-photon detector crystals in the second detector array 2 form a fan-shaped beam. The width of the first γ-photon detector crystal in the first detector array 1 is denoted as w1, the width of the second γ-photon detector crystal in the second detector array is denoted as w2, and the distances from the object to the first detector array 1 and the second detector array 2 are denoted as d1 and d2, respectively. The magnification factor of the fan-shaped beam is...

[0055] The image resolution Rp of this imaging system is a function of the detector array width and the distance from the object to the detector array:

[0056]

[0057] In the formula, Rs is the effective source size, including the positron range effect.

[0058] The above embodiments are merely illustrative of the principles and effects of the present invention, as well as some examples of its application, and are not intended to limit the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these modifications and improvements are all within the scope of protection of the present invention.

Claims

1. A method for imaging a sealed cavity of an aero-engine using a positron emission tomography scanner based on an embedded rotating flat plate detector, comprising the following steps: Step 1: Prepare a radioactive nuclide by thoroughly mixing the radioactive nuclide with aviation kerosene; Step 2: Inject the mixture of radioactive nuclide and aviation kerosene into the sealed cavity of the aircraft engine; Step 3: The aircraft engine, after being filled with a mixture of radioactive nuclides and aviation kerosene, is placed on a fixed detection platform at the center of a positron emission tomography (PET) scanner; The gamma-ray detection mechanism of this positron emission tomography (PET) scanner includes an embedded rotating flat plate detection device and a ring detection device. The ring detection device includes a cylindrical mounting frame disposed around the periphery of the fixed detection stage in the scanner frame, with the inner wall of the cylindrical mounting frame covered with second gamma-ray detection crystals. The embedded rotating flat plate detection device includes a mounting base, on which a mounting plate is movably mounted. The mounting plate is located between the inner side of the cylindrical mounting frame and the outer periphery of the fixed detection stage. The mounting plate is radially adjustable along the cylindrical mounting frame. The mounting base is equipped with a drive device that drives the mounting plate to rotate around the central axis of the ring detection device. A plurality of first gamma-ray detection crystals are arranged flat on the mounting plate. The total length of the first gamma-ray detection crystals on the mounting plate is equal to the total length of the second gamma-ray detection crystals disposed on the inner wall of the cylindrical mounting frame. Moreover, the resolution of the first gamma-ray detection crystals is higher than that of the second gamma-ray detection crystals. The first gamma-photon plate detector crystal, fixed on the mounting plate, forms the first detector crystal array, and the second gamma-photon detector crystal of the ring detector forms the second detector crystal array; the central angle of the cylindrical mounting frame corresponding to the first gamma-photon detector crystal part of the first detector crystal array is 60°-90°; and the diameter of the second detector crystal array is 1.6-2.6 times the distance between the first detector crystal array and the central axis of the ring detector. Step 4: Start the servo drive motor and positron emission tomography scanner. The first and second plate detector crystal arrays, which rotate with the ring guide rail, perform real-time data acquisition of gamma photon pairs generated by the annihilation of the radionuclide-labeled aviation kerosene mixture in the sealed cavity of the aero-engine at any angle. Step 5: Perform three-dimensional image reconstruction on the γ-photon cone beam data detected by the first and second detector crystal arrays to obtain high-resolution imaging of the sealed internal cavity of the aero-engine; the γ-photon cone beam data is used to reconstruct the image based on an iterative algorithm, specifically including: The likelihood function obtained by making the detected data follow a Poisson distribution is: Among them, A ij To detect the probability of the j-th voxel detected by the combination of the first and second γ-photon detector crystals of the i-th pair of γ-photon pairs generated by annihilation, p j Let y represent the pixel value of the j-th pixel. i Indicates the projected value; A set of cone-beam detection data is D ij The likelihood function corresponding to this data is: Given that the current image is p k After taking the logarithm of both sides of the above equation, find the expectation of ln(L(p)). By finding the maximum value of the above equation and taking the first-order partial derivative, we obtain the iterative reconstruction formula:

2. The method for imaging a sealed cavity of an aero-engine using a positron emission tomography scanner based on an embedded rotating flat plate detector according to claim 1, characterized in that, The resolution of the first γ-photon detector crystal is more than 20% higher than that of the second γ-photon detector crystal.

3. The method for imaging a sealed cavity of an aero-engine using a positron emission tomography scanner based on an embedded rotating flat plate detector according to claim 1 or 2, characterized in that, The embedded rotating flat plate detection device includes a pair of annular guide rails, and at least a pair of pulleys are movably arranged inside the annular guide rails. All pulleys are fixedly connected to the mounting base, and the mounting plate is provided on the mounting base.

4. The method for imaging a sealed cavity of an aero-engine using a positron emission tomography scanner based on an embedded rotating flat plate detector according to claim 3, characterized in that, The pair of annular guide rails are respectively located on the outer sides of both ends of the cylindrical mounting frame.

5. The method for imaging a sealed cavity of an aero-engine using a positron emission tomography scanner based on an embedded rotating flat plate detector according to claim 3, characterized in that, The driving device includes an annular drive rack mounted on an annular guide rail and a servo drive motor mounted on a mounting base. The output shaft of the servo drive motor is provided with a drive gear that cooperates with the drive rack.

6. The method for imaging a sealed cavity of an aero-engine using a positron emission tomography scanner based on an embedded rotating flat plate detector according to claim 2, characterized in that, The mounting base is equipped with a lead screw mechanism arranged radially along the cylindrical mounting frame, as well as a servo adjustment motor and transmission device for driving the lead screw mechanism. The mounting plate is movably mounted on the mounting base and connected to the movable block of the lead screw mechanism.

Images