A SPECT Intrinsic Spatial Nonlinearity Correction Model

Abstract

The present invention discloses a SPECT inherent spatial nonlinearity correction model, comprising a sequentially stacked protective plate, a first shielding plate, a hollow plate, and a second shielding plate. The protective plate and the first shielding plate are each provided with a first array of holes and a second array of holes, the first array of holes and the second array of holes being arranged in a one-to-one correspondence. The hollow plate is provided with a hollow region filled with a liquid radioactive source. The present invention has the advantage of high correction accuracy.

Description

Technical Field

[0001] The present invention relates to the field of single photon emission computed tomography (SPECT) equipment control and performance detection, and in particular to a SPECT inherent spatial nonlinearity correction model. Background Art

[0002] Single-Photon Emission Computed Tomography (SPECT) is a tomographic imaging technique for radiopharmaceuticals (such as 99mTc) that emit only a single gamma photon per decay. SPECT is typically designed based on the principles of an Anger gamma camera. The core detector consists of a collimator, a large-area scintillation crystal, a photomultiplier tube (PMT), and localization logic circuitry. Gamma photons generated by the radiopharmaceutical pass through the collimator and project onto the large-area scintillation crystal, which converts the gamma photons into visible light. A PMT array on the back of the crystal converts the scintillation light from the large-area scintillation crystal into an electrical signal and amplifies it. Depending on the location within the crystal where the gamma photon generates the scintillation light, the weighting of the scintillation light among the PMTs varies, resulting in different pulse amplitudes for each PMT. The localization logic circuit calculates the X and Y signals of the gamma photon's incident position and the energy of the gamma photon based on the pulse signals received from the PMTs.

[0003] Ideally, assuming scintillation photons propagate uniformly in all directions, the light flux entering a particular photomultiplier tube is proportional to the solid angle subtended by the photocathode relative to the scintillation point, while the photomultiplier tube's output amplitude is proportional to the light flux incident on the photocathode. When a gamma photon scintillates in a crystal, multiple adjacent photomultiplier tubes receive the scintillation photon and output a voltage signal, the amplitude of which depends on the distance to the scintillation point. The Anger camera uses these signals to determine the location of the scintillation point using the centroid method. When the position response curve of a single photomultiplier tube to scintillation photons is an isosceles triangle with half the length of the base equal to the distance from the photomultiplier tube center, the position signal and output amplitude are linearly related.

[0004] However, in reality, the curve of the photomultiplier tube's output amplitude versus the scintillation point's position is not a perfect isosceles triangle. Instead, it exhibits some fluctuation from the center of the photomultiplier tube to either side. Therefore, the relationship between the position signal and the output amplitude of the gamma camera is not linear. This translates to a curved image for a straight object.

[0005] When the X and Y signals generated by the gamma camera probe do not change linearly with the position of the radiation source, image nonlinearity will occur. Therefore, when the gamma camera uses the center of gravity method for positioning, it will inevitably lead to nonlinear spatial response, causing image distortion, which is an inherent error of the gamma camera.

[0006] In addition to the aforementioned causes, spatial nonlinearity also arises from the nonuniformity of large-area scintillators and light guides, variations in the sensitivity of photomultiplier tubes, and malfunctions in the photomultiplier tubes and electronic circuits. This combination of factors leads to spatial distortion in gamma cameras. Furthermore, due to inherent errors, this distortion cannot be eliminated simply by improving the gamma camera's hardware structure; instead, inherent spatial nonlinearity correction is required to improve the distorted image.

[0007] In spatial distortion, the most intuitive description is that a point on an actual object deviates from its actual position after being imaged by a gamma camera, resulting in image distortion. Therefore, the purpose of performing inherent spatial nonlinear correction is to restore the point on the gamma camera image to its correct position.

[0008] Typically, inherent spatial nonlinearity correction requires the use of one or more lead grid models in the X and Y directions. Using this model, a radioactive source is placed at a certain distance perpendicular to the center of the model, creating a flood source that illuminates the model. This creates an image of the lead grid slits on the crystal. Based on the collected original image and the theoretical image of the model, the correspondence between the original image and the theoretical image is determined, generating a correction table for that direction. After completing correction in one direction, the model is switched to the other direction and the correction is repeated.

[0009] There are several problems with this model:

[0010] 1. Although a radioactive source can be approximately formed at a certain distance to irradiate the model, the placement of the radioactive source is often subject to human placement deviation or tooling error, resulting in the gamma rays passing through each lead seam not being completely consistent. There will be certain deviations in the gamma rays passing through different lead seams.

[0011] Second, there will be a certain irradiation angle between the radiation source and the lead gap. Some rays will pass through the lead gap obliquely and hit the crystal, instead of passing through the lead gap perpendicular to the model. As a result, the width of the gamma rays passing through each lead gap cannot reach the ideal value.

[0012] Third, since calibration needs to be done separately in the X and Y directions, a complete calibration requires multiple model changes. Due to the above defects, the accuracy of the calibration is affected and the calibration process takes a long time.

[0013] Fourth, since a radioactive source needs to be placed at a long distance to irradiate the model, the radiation area is increased, and radiation protection within a certain area becomes very difficult, and the staff are at risk of external radiation. Summary of the Invention

[0014] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a SPECT inherent spatial nonlinear correction model with high correction accuracy.

[0015] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0016] A SPECT inherent spatial nonlinearity correction model includes a sequentially stacked protective plate, a first shielding plate, a hollow plate, and a second shielding plate. The protective plate and the first shielding plate are respectively provided with a first hole array and a second hole array, the first hole array and the second hole array being arranged in a one-to-one correspondence. A hollow area is provided in the hollow plate, and the hollow area is filled with a liquid radioactive source.

[0017] As a further improvement of the above technical solution:

[0018] A liquid inlet and a liquid outlet are provided on the side of the hollow plate, and a liquid inlet valve and a liquid outlet valve are installed on the liquid inlet and the liquid outlet respectively.

[0019] The liquid radioactive source fills the entire hollow area without any bubbles.

[0020] The hollow plate is a transparent plate.

[0021] The stacking connection is achieved by using adhesive.

[0022] The adhesive coating thickness does not exceed 1 mm.

[0023] The protective plate is one of an aluminum plate, a plastic plate, and a carbon fiber plate.

[0024] The material of the first shielding plate is lead alloy, tungsten alloy or a material having a gamma ray shielding function.

[0025] The second shielding plate is made of a material selected from the group consisting of lead alloy, tungsten alloy, and materials capable of shielding gamma rays.

[0026] On a plane parallel to the upper surface of the model, the outline projection line of the first hole array is located within the outline projection line of the hollow area.

[0027] Compared with the prior art, the advantages of the present invention are:

[0028] Compared with the lead grid model, the liquid radioactive source of the SPECT inherent spatial nonlinearity correction model of the present invention is arranged adjacent to the first hole array and the second hole array. The rays passing through the first hole array and the second hole array are more uniform and the rays at each point are consistent, so the correction accuracy is higher. The arrangement of the first hole array and the second hole array makes it possible to complete the inherent spatial nonlinearity correction in the X and Y directions by only using one model for one correction, which can reduce the use of correction models, reduce the workload and correction time, save time and effort, and improve work efficiency. The liquid radioactive source in the second shielding plate and the hollow plate of the present invention makes it unnecessary to place a radioactive source at a long distance during correction, thereby reducing the risk of workers being exposed to additional radioactive exposure and reducing the radiation range. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a structural diagram of the SPECT inherent spatial nonlinear correction model of the present invention.

[0030] Figure 2 It is a structural schematic diagram of the SPECT inherent spatial nonlinear correction model of the present invention from another perspective.

[0031] Figure 3 It is a structural decomposition diagram of the SPECT inherent spatial nonlinear correction model of the present invention.

[0032] Figure 4 It is a cross-sectional view of the SPECT inherent spatial nonlinear correction model of the present invention.

[0033] The reference numerals in the figure indicate: 1, protective plate; 11, first hole array; 2, first shielding plate; 21, second hole array; 3, hollow plate; 31, hollow area; 4, second shielding plate; 5, liquid inlet valve; 6, liquid outlet valve; DETAILED DESCRIPTION

[0034] The present invention will be further described in detail below with reference to the accompanying drawings and specific examples. Unless otherwise specified, the instruments and materials used in the present invention are commercially available.

[0035] Example 1:

[0036] like Figures 1 to 4As shown, the SPECT inherent spatial nonlinearity correction model of this embodiment includes a sequentially stacked protective plate 1, a first shielding plate 2, a hollow plate 3, and a second shielding plate 4. The protective plate 1 and the first shielding plate 2 are respectively provided with a first hole array 11 and a second hole array 21, with the first hole array 11 and the second hole array 21 arranged in a one-to-one correspondence. The hollow plate 3 is provided with a hollow region 31 filled with a liquid radioactive source. Compared to the lead grid model, the SPECT inherent spatial nonlinearity correction model of the present invention transmits more uniform radiation through the first hole array 11 and the second hole array 21, with consistent radiation at every point, resulting in higher correction accuracy. The arrangement of the first hole array 11 and the second hole array 21 allows for correction of inherent spatial nonlinearity in both the X and Y directions using only one model, reducing the number of correction models, the workload, and the time required for correction, saving time and effort, and improving work efficiency. The liquid radioactive source within the second shielding plate 4 and the hollow plate 3 of the present invention eliminates the need for a remotely located radioactive source during calibration, reducing the risk of additional radiation exposure to workers and narrowing the radiation range.

[0037] The second shielding plate 4 can shield the gamma rays emitted by the liquid radioactive source in the hollow area 31 to prevent personnel from being exposed to radiation hazards.

[0038] Protective plate 1 and first shielding plate 2 are each provided with a first hole array 11 and a second hole array 21. These holes are arranged in a one-to-one relationship, with identical hole positions and diameters. This allows gamma rays to pass through hollow plate 3 and irradiate the crystal. The first and second hole arrays 11, 21 are composed of multiple circular holes evenly arranged in the horizontal and vertical directions.

[0039] The areas of the protection plate 1, the first shielding plate 2, the hollow plate 3, and the radiation shielding plate 4 are all identical. They are arranged closely in the order of the protection plate 1, the first shielding plate 2, the hollow plate 3, and the radiation shielding plate 4.

[0040] The hollow plate 3 has a liquid inlet and outlet on its side, communicating with the hollow region 31 within the hollow plate 3. These inlet and outlet ports are respectively fitted with an inlet valve 5 and an outlet valve 6. These valves are on-off valves that, when closed, prevent the liquid radioactive source from escaping. They are tightly connected to the hollow plate 3 via threads.

[0041] The liquid radioactive source fills the entire hollow area 31 and is free of bubbles. Bubbles within the hollow area 31 could affect the calibration effect. The radiation emitted by the liquid radioactive source in the hollow area 31 of the present invention passes through the first and second aperture arrays 11, 21, uniformly irradiating the object. If bubbles are present, some areas where the first and second aperture arrays 11, 21 are located may not receive radiation from the liquid radioactive source, affecting the calibration.

[0042] The hollow plate 3 is transparent, and the hollow region 31 inside can be seen from the side of the hollow plate 3. The hollow plate 3 is a flat plate with a sealed rectangular hollow region 31 inside. The thickness of the hollow region 31 is uniform throughout. The hollow region 31 is evenly filled with a liquid radioactive source, such as a radiopharmaceutical such as 99mTc or 131I.

[0043] The stacking connection is achieved by adhesive stacking connection, that is, the protection plate 1 , the first shielding plate 2 , the hollow plate 3 , and the second shielding plate 4 are tightly bonded together by gluing.

[0044] The adhesive coating thickness does not exceed 1mm.

[0045] The protection plate 1 is an aluminum plate, a plastic plate, a carbon fiber plate or other materials with a certain strength, and is used to protect the orifice plate from deformation due to external forces (such as bumps, collisions, etc.).

[0046] The material of the first shielding plate 2 is lead alloy, tungsten alloy or other materials having the function of shielding gamma rays.

[0047] The second shielding plate 4 is made of lead alloy, tungsten alloy or other materials having the function of shielding gamma rays.

[0048] In this embodiment, on a plane parallel to the upper surface of the model, the outline projection of the first hole array 11 lies within the outline projection of the hollow region 31. The area of the hollow region 31 needs to cover the entire area of the first hole array 11. The liquid radiation source does not form an irradiation angle with the first hole array 11; the radiation passes perpendicularly through the first hole array 11 and irradiates the crystal.

[0049] The water inlet valve 5 and the water outlet valve 6 are tightly connected to the hollow plate 3 through threads and communicate with the hollow area 31 in the hollow plate 3.

[0050] The liquid radioactive source in the hollow area 31 is injected through the water inlet valve 5 and discharged through the water outlet valve 6 .

[0051] The cross-sections of the protective plate 1, the first shielding plate 2, the hollow area 31, the hollow plate 3, and the radiation shielding plate 4 are rectangular or circular, and are selected based on the shape of the SPECT probe to be corrected; the cross-sectional dimensions need to be designed based on the outer dimensions of the corrected SPECT probe; and the thickness dimensions need to be designed accordingly based on the performance parameters of the SPECT probe design.

[0052] The aperture sizes and array arrangements of the first hole array 11 and the second hole array 21 in the protection plate 1 and the first shielding plate 2 are designed accordingly based on the dimensions of the SPECT probe to be calibrated and the performance parameters of the SPECT probe design.

[0053] The material of the protection plate 1 is one of materials with a certain strength, such as aluminum plate, plastic plate, carbon fiber plate, etc., and is used to protect the orifice plate from deformation due to external forces (such as bumps, collisions, etc.).

[0054] The present invention requires injecting a liquid radioactive source into hollow region 31 when in use. When not in use, the liquid radioactive source inside hollow region 31 is drained. A high-concentration liquid radioactive source is first dissolved in water to obtain a larger amount of liquid radioactive source, which is then injected into the mold. The liquid radioactive source is a mixture of radioactive source and solvent. In this embodiment, the solvent is water or a non-corrosive and non-toxic aqueous solution.

[0055] Although the present invention has been disclosed above with reference to preferred embodiments, this is not intended to limit the present invention. Any person skilled in the art can, without departing from the scope of the technical solution of the present invention, utilize the technical content disclosed above to make many possible changes and modifications to the technical solution of the present invention, or modify it into an equivalent embodiment with equivalent changes. Therefore, any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the scope of protection of the technical solution of the present invention.

Claims

1. A SPECT intrinsic spatial nonlinearity correction model, characterized by: The invention comprises a protective plate (1), a first shielding plate (2), a hollow plate (3), and a second shielding plate (4) which are sequentially stacked and connected. The protective plate (1) and the first shielding plate (2) are respectively provided with a first hole array (11) and a second hole array (21). The first hole array (11) and the second hole array (21) are arranged in a one-to-one correspondence. A hollow area (31) is provided in the hollow plate (3), and the hollow area (31) is filled with a liquid radioactive source.

2. The SPECT inherent spatial nonlinearity correction model according to claim 1, characterized in that: A liquid inlet and a liquid outlet are provided on the side of the hollow plate (3), and a liquid inlet valve (5) and a liquid outlet valve (6) are installed on the liquid inlet and the liquid outlet, respectively.

3. The SPECT inherent spatial nonlinearity correction model according to claim 1, characterized in that: The liquid radioactive source fills the entire hollow area (31) and has no bubbles.

4. The SPECT inherent spatial nonlinearity correction model according to claim 3, characterized in that: The hollow plate (3) is a transparent plate.

5. The SPECT inherent spatial nonlinearity correction model according to claim 1, characterized in that: The stacking connection is achieved by using adhesive.

6. The SPECT inherent spatial nonlinearity correction model according to claim 5, characterized in that: The adhesive coating thickness does not exceed 1 mm.

7. The SPECT inherent spatial nonlinearity correction model according to claim 1, characterized in that: The protective plate (1) is one of an aluminum plate, a plastic plate, and a carbon fiber plate.

8. The SPECT inherent spatial nonlinearity correction model according to claim 1, characterized in that: The material of the first shielding plate (2) is a material having the function of shielding gamma rays.

9. The SPECT inherent spatial nonlinearity correction model according to claim 1, characterized in that: The material of the second shielding plate (4) is a material having the function of shielding gamma rays.

10. The SPECT inherent spatial nonlinearity correction model according to claim 1, characterized in that: On a plane parallel to the upper surface of the model, the contour projection line of the first hole array (11) is located within the contour projection line of the hollow area (31).

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