An x-ray based super-resolution CT imaging method

Abstract

This invention relates to an X-ray-based super-resolution CT imaging method, comprising: an industrial CT system performing a first CT scan on the object under optimal detection conditions, and sequentially acquiring a projection image of the object at intervals; moving the X-ray source along a direction parallel to the detector by a distance *d*, and performing a second CT scan on the object using the same detection process as described above; translating the X-ray source upwards along the focal axis of the first and second CT scans, and performing a third CT scan on the object using the same detection process as described above; adding the projection images of the object acquired during the three CT scans to obtain a final super-resolution projection image; mapping the final super-resolution projection image to a 16-bit image, and then performing CT reconstruction on the 16-bit image to obtain a CT image. This method improves the detection spatial resolution under hardware limitations.

Description

Technical Field

[0001] This invention relates to the field of industrial CT system technology, and in particular to an X-ray-based super-resolution CT imaging method. Background Technology

[0002] X-ray nondestructive testing (NDT) is one of the most widely used NDT techniques. It utilizes the strong penetrating power of X-rays and their interaction with matter to perform nondestructive testing of the internal structure, defects, and composition of objects. With the development of digital technology, digital radiography (DR) and computed tomography (CT) imaging are becoming increasingly prevalent.

[0003] In X-ray inspection, spatial resolution is a core issue limiting defect detection capabilities. First, the geometric dimensions of the X-ray source focal spot cause a penumbra effect; micro-focal sources are costly and power-limited, making it difficult to penetrate thick workpieces. Second, the pixel size, crosstalk, and noise of the detector lead to loss of detail; high-resolution detectors struggle to maintain a large field of view. Third, there is a conflict between geometric magnification and scattered radiation, as well as positioning errors, resulting in increased image blurring after magnification. Ultimately, this leads to a decrease in actual resolution in CT and DR images, making the detection of minute cracks and inclusions extremely difficult.

[0004] Due to the ultra-short wavelength and strong penetrating power of X-rays, it is difficult to apply the focusing techniques used for visible light. Therefore, methods to improve the clarity of X-ray detection images mainly include the following aspects: 1. Developing high-power, micro-focus X-ray sources to reduce geometric penumbra and lower geometric unsharpness; 2. Using high-resolution detectors to reduce pixel size and improve the conversion efficiency and signal-to-noise ratio from X-rays to visible light; 3. Optimizing the imaging geometry and rationally controlling the magnification to achieve a balance between clarity and penetration; 4. Employing digital image processing algorithms to improve detail through noise reduction, sharpening, edge enhancement, and contrast stretching. However, the above methods suffer from low power and limited penetration of micro-focus X-ray sources, resulting in high costs; narrow field of view and decreased sensitivity of high-resolution detectors; and the tendency to amplify scattering and vibration errors through optimized imaging geometry. Digital image processing methods only optimize the display and cannot compensate for missing original information, and over-processing can easily produce artifacts. Therefore, current super-resolution CT imaging methods are limited by hardware and structure, making it difficult to effectively improve image clarity. Therefore, further improvements to existing technologies are needed. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an X-ray-based super-resolution CT imaging method that improves the detection spatial resolution under hardware constraints, in contrast to the above-mentioned prior art.

[0006] The technical solution adopted by this invention to solve the above-mentioned technical problems is: an X-ray-based super-resolution CT imaging method, characterized by comprising the following steps:

[0007] Step 1: Determine the optimal inspection process for the industrial CT system used to inspect the object under test; The industrial CT system includes X-ray sources, a turntable, and detectors arranged in sequence at intervals, with the object under test placed on the turntable;

[0008] Step 2: The industrial CT system performs the first CT scan on the object under the optimal detection process described in Step 1, and then performs subsequent CT scans at intervals. Acquire a projection image of the object being measured. This represents the total number of projected images acquired.

[0009] Step 3: Move the X-ray source along a direction parallel to the detector by a distance d. Perform a second CT scan on the object under test using the same detection process as in Step 2. The starting position of the object under test in the second CT scan is the same as the starting position in the first CT scan in Step 2, and the scans are performed sequentially at intervals. Acquire a projection image of the object being measured;

[0010] Step 4: Move the X-ray source from Step 3 upwards along the central axis of the focal points of the first and second CT scans, by a distance of [distance missing]. The same detection process as in step 3 is used to perform a third CT scan on the object under test. The starting position of the object under test in the third CT scan is the same as the starting position in the second CT scan in step 3, and the scans are performed sequentially at intervals. Acquire a projection image of the object being measured;

[0011] Step 5: Add the projected images of the object acquired during the three CT scans together to obtain the final super-resolution projected image;

[0012] Step 6: Map the final super-resolution projection image to a 16-bit image, and then perform CT reconstruction on the 16-bit image to obtain a CT image.

[0013] Preferably, the optimal detection process in step 1 includes at least tube voltage, tube current, integration time, and sampling amplitude. The optimal focal size and optimal magnification of the X-ray source.

[0014] Preferably, the specific process for determining the optimal focal size of the X-ray source is as follows:

[0015] The focal size of the X-ray source used in the first CT scan was [missing information]. ;

[0016] Set the desired focus size Then the X-ray source is moved in a direction parallel to the detector, and the distance moved is... The second CT scan was performed using the same detection process as the first CT scan.

[0017] The X-ray source for the second CT scan is shifted upwards along the central axis between the focal points of the first and second CT scans, with a shift distance of [distance missing]. Using the same detection process as the second CT scan, a third CT scan was performed, and the area of ​​the focal overlap region was calculated for the three CT scans. And based on the area of ​​the focal overlap region during three CT scans Obtain the focal size after focusing; this focal size is the optimal focal size of the X-ray source.

[0018] Preferably, the focal point of each CT scan is fitted into a circle, and the formula for calculating the area S of the overlapping region of the focal points in three CT scans is:

[0019]

[0020] And according to Then obtain the focal size to be used. The proposed focal size This is the optimal focal size for the X-ray source.

[0021] Preferably, the specific process for determining the optimal magnification is as follows:

[0022]

[0023] in, For the effective beam width of industrial systems, Let be the physical dimensions of each element in the detector. This is the magnification factor. , This represents the distance from the X-ray source to the detector. The distance from the X-ray source to the center of the turntable;

[0024] Given the optimal focal size of the X-ray source, substitute it into the above... The optimal magnification can be calculated using the formula. .

[0025] Compared with the prior art, the advantages of the present invention are: by moving the focus twice and superimposing the projected image after the focus movement, a super-resolution image is obtained. This method breaks through the limitations of detector element size, magnification ratio and sampling number of industrial CT systems, improves the detection spatial resolution under hardware limitations, and is applicable to DR imaging systems and CT imaging systems with adjustable magnification ratio. Attached Figure Description

[0026] Figure 1 This is a schematic diagram showing the superposition of focal points during the first and second CT scans in an embodiment of the present invention;

[0027] Figure 2 This is a schematic diagram of the focal overlap during three CT scans in an embodiment of the present invention;

[0028] Figure 3 This is a test card projection image acquired during the first CT scan in an embodiment of the present invention;

[0029] Figure 4 This is a focal image of the test card during the first CT scan in an embodiment of the present invention;

[0030] Figure 5 This is a test card projection image acquired during the first CT scan in an embodiment of the present invention;

[0031] Figure 6 This is the image obtained by adding the projected images acquired after the first CT scan test card and the second CT scan test card in this embodiment of the invention;

[0032] Figure 7 This is a focal image superimposed from the first CT scan test card and the second CT scan test card in an embodiment of the present invention;

[0033] Figure 8 This is a focal image superimposed on three CT scan test cards in an embodiment of the present invention. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0035] The X-ray-based super-resolution CT imaging method in this embodiment includes the following steps:

[0036] Step 1: Determine the optimal inspection process for the industrial CT system used to inspect the object under test; The industrial CT system includes X-ray sources, a turntable, and detectors arranged in sequence at intervals, with the object under test placed on the turntable;

[0037] The optimal detection process should include at least tube voltage, tube current, integration time, and sampling amplitude. The optimal focal size and optimal magnification of the X-ray source;

[0038] Based on the thickest region that X-rays need to penetrate at the placement angle of the object under test, the tube voltage and tube current required for X-ray detection are calculated, and these calculated tube voltage and tube current are used as the optimal detection parameters for the industrial CT system to adapt to the current object under test. In specific implementation, the set values ​​of tube voltage and tube current required by the industrial CT system for X-rays to penetrate different thicknesses can be obtained by looking up tables. Additionally, the integration time and the number of sampling amplitudes are also considered. The information is obtained based on the requirements of the material, structure, and detection accuracy of the object being measured.

[0039] The specific process for determining the optimal focal size of the X-ray source in this embodiment is as follows:

[0040] The focal size of the X-ray source used in the first CT scan was [missing information]. ;

[0041] Set the desired focus size Then the X-ray source is moved in a direction parallel to the detector, and the distance moved is... The second CT scan was performed using the same detection process as the first CT scan.

[0042] The X-ray source for the second CT scan is shifted upwards along the central axis between the focal points of the first and second CT scans, with a shift distance of [distance missing]. Using the same detection process as the second CT scan, a third CT scan was performed, and the area of ​​the focal overlap region was calculated for the three CT scans. And based on the area of ​​the focal overlap region during three CT scans Obtain the focal size after focusing; this focal size is the optimal focal size of the X-ray source.

[0043] If the focal point of each CT scan is fitted into a circle, then the formula for calculating the area S of the overlapping region of the focal points in three CT scans is:

[0044]

[0045] And according to Then obtain the focal size to be used. The proposed focal size This is the optimal focal size of the X-ray source;

[0046] like Figure 1 The image shows a diagram illustrating the superposition of focal points during the first and second CT scans; as shown... Figure 2The image shown is a schematic diagram of the focal overlap during three CT scans. Figure 2 The distance between the centers of the three circles is d.

[0047] In this embodiment, the specific process for determining the optimal magnification is as follows:

[0048]

[0049] in, For the effective beam width of industrial systems, Let be the physical dimensions of each element in the detector. This is the magnification factor. , This represents the distance from the X-ray source to the detector. The distance from the X-ray source to the center of the turntable;

[0050] Given the optimal focal size of the X-ray source, substitute it into the above... The optimal magnification can be calculated using the formula. ;

[0051] The aforementioned maximum spatial resolution of a CT system can be theoretically calculated using the cutoff frequency (COF) of an industrial CT system. Effective beam width of industrial CT systems The relation is:

[0052]

[0053] in, The unit is line pairs per millimeter;

[0054] Step 2: The industrial CT system performs the first CT scan on the object under the optimal detection process described in Step 1, and then performs subsequent CT scans at intervals. Acquire a projection image of the object being measured. This represents the total number of projected images acquired.

[0055] Before the first CT scan, the detector needs to be corrected for dark, bright and bad pixels under the current best detection process. When the first CT scan begins, the X-ray source continuously emits beams (X-rays), the turntable carries the object being measured and rotates at a constant speed, the detector works continuously to collect the intensity of X-rays irradiated on its surface and obtain the projected image of the object being measured at the current projection angle, and the angle of the object being measured at the start of the CT scan is recorded and set as 0 degrees.

[0056] Step 3: Move the X-ray source along a direction parallel to the detector by a distance d. Perform a second CT scan on the object under test using the same detection process as in Step 2. The starting position of the object under test in the second CT scan is the same as the starting position in the first scan in Step 2, and the scans are performed sequentially at intervals. Acquire a projection image of the object being measured;

[0057] Step 4: Move the X-ray source from Step 3 upwards along the central axis of the focal points of the first and second CT scans, by a distance of [distance missing]. The same detection process as in step 3 is used to perform a third CT scan on the object under test. The starting position of the object under test in the third CT scan is the same as the starting position in the second CT scan in step 3, and the scans are performed sequentially at intervals. Acquire a projection image of the object being measured;

[0058] Step 5: Add the projected images of the object acquired during the three CT scans together to obtain the final super-resolution projected image;

[0059] The formula for calculating the final super-resolution projected image in this embodiment is:

[0060]

[0061] in, For the first In the super-resolution projection image The grayscale value of the location, ∈{1,2,… }; The first CT scan was used to collect the data. In the projected image of the object under test The grayscale value of the location, The first image acquired during the second CT scan In the projected image of the object under test The grayscale value of the location, The image was acquired during the third CT scan. In the projected image of the object under test The grayscale value of the location.

[0062] Step 6: Map the final super-resolution projection image to a 16-bit image, that is, adjust the grayscale value to between 0 and 65535; then perform CT reconstruction on the 16-bit image to obtain the CT image.

[0063] To verify the method of the present invention, this embodiment is tested on a three-dimensional cone-beam array CT system, and the spatial resolution test card of industrial CT is verified; the spatial resolution test card is made of steel and contains line pairs with a diameter of 10-2.

[0064] First CT scan: Based on the test card's settings, the tube voltage was 400kV, tube current 1.8mA, 1.5mm Cu filter was used, and a small focal spot (approximately 0.4mm) was employed. SOD=1000mm, SDD=1200mm; integration time 300ms; 1440 projection images were obtained. A series of 360-degree circumferential projection images of the test card were obtained. Figure 3 For one of the images, the image resolution is 1408×1340; at this time, the focus is as follows: Figure 4 As shown;

[0065] Second CT scan: The desired focal spot size was set to 0.3mm, while the original focal spot size was 0.4mm. The X-ray source was moved by 0.1mm. The same process as the first scan was used (tube voltage, tube current, integration time, number of sampling frames). The tube voltage was 400kV, the tube current was 1.8mA, and a 1.5mm Cu filter was used. A small focal spot size of approximately 0.4mm was used; SOD=1000mm, SDD=1200mm. The integration time was 300ms, and the number of projection frames was 1440. A series of 360-degree circumferential projection images of the test card were obtained. Figure 5 One of the images has a resolution of 1408×1340; the projection image obtained by adding the projection image acquired during the first CT scan to the projection image acquired during the second CT scan is shown below. Figure 6 As shown; the superimposed focal point is as follows Figure 7 As shown;

[0066] Third CT scan: After the second CT scan, the X-ray source is moved upwards along the central axis of the focal points of the first and second CT scans, by a distance of [distance missing]. A third CT scan was performed.

[0067] The focal point is obtained by adding the projected images of the object acquired during three CT scans, as shown below. Figure 8 As shown in the comparison. Figure 4 , Figure 7 and Figure 8 As can be seen, the focal point becomes smaller after two superpositions, and the focal point becomes even smaller after three superpositions.

[0068] According to the present invention As can be seen from the calculation formula, the smaller the size of the X-ray source's focal spot and detector, the smaller the effective beam width, and the higher the limit spatial resolution of the CT system. Among these factors, the X-ray source focal spot is the most significant influencing factor. Medium-to-high power X-ray sources (450kV) are limited by the high-temperature tolerance of the target material, and currently, the focal spot size can only be controlled at the micrometer level. This results in a limit to the spatial resolution of medium-to-high power industrial CT systems. When the focal spot size is large, neither reducing the detector size nor increasing the magnification can effectively improve the spatial resolution of the CT system. Therefore, reducing the focal spot size is the most direct way to improve the limit spatial resolution. This invention combines X-ray projection imaging with a CT scanning design to break through the system's limit spatial resolution on a general CT system. Under the same CT system and process, spatial resolution can be improved by more than 20% through three-stage superposition.

[0069] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A super-resolution CT imaging method based on X-rays, characterized in that... Includes the following steps: Step 1: Determine the optimal inspection process for the industrial CT system used to inspect the object under test; The industrial CT system includes X-ray sources, a turntable, and detectors arranged in sequence at intervals, with the object under test placed on the turntable; Step 2: The industrial CT system performs the first CT scan on the object under the optimal detection process described in Step 1, and then performs subsequent CT scans at intervals. Acquire a projection image of the object being measured. This represents the total number of projected images acquired. Step 3: Move the X-ray source along a direction parallel to the detector by a distance d. Perform a second CT scan on the object under test using the same detection process as in Step 2. The starting position of the object under test in the second CT scan is the same as the starting position in the first CT scan in Step 2, and the scans are performed sequentially at intervals. Acquire a projection image of the object being measured; Step 4: Move the X-ray source from Step 3 upwards along the central axis of the focal points of the first and second CT scans, by a distance of [distance missing]. The same detection process as in step 3 is used to perform a third CT scan on the object under test. The starting position of the object under test in the third CT scan is the same as the starting position in the second CT scan in step 3, and the scans are performed sequentially at intervals. Acquire a projection image of the object being measured; Step 5: Add the projected images of the object acquired during the three CT scans together to obtain the final super-resolution projected image; Step 6: Map the final super-resolution projection image to a 16-bit image, and then perform CT reconstruction on the 16-bit image to obtain a CT image.

2. The super-resolution CT imaging method according to claim 1, characterized in that: The optimal detection process in step 1 includes at least tube voltage, tube current, integration time, and sampling amplitude. The optimal focal size and optimal magnification of the X-ray source.

3. The super-resolution CT imaging method according to claim 2, characterized in that: The specific process for determining the optimal focal size of an X-ray source is as follows: The focal size of the X-ray source used in the first CT scan was [missing information]. ; Set the desired focus size Then the X-ray source is moved in a direction parallel to the detector, and the distance moved is... The second CT scan was performed using the same detection process as the first CT scan. The X-ray source for the second CT scan is shifted upwards along the central axis between the focal points of the first and second CT scans, with a shift distance of [distance missing]. Using the same detection process as the second CT scan, a third CT scan was performed, and the area of ​​the focal overlap region was calculated for the three CT scans. And based on the area of ​​the focal overlap region during three CT scans Obtain the focal size after focusing; this focal size is the optimal focal size of the X-ray source.

4. The super-resolution CT imaging method according to claim 3, characterized in that: If the focal point of each CT scan is fitted into a circle, then the formula for calculating the area S of the overlapping region of the focal points in three CT scans is: And according to Then obtain the focal size to be used. The proposed focal size This is the optimal focal size for the X-ray source.

5. The super-resolution CT imaging method according to claim 4, characterized in that: The specific process for determining the optimal magnification is as follows: in, For the effective beam width of industrial systems, Let be the physical dimensions of each element in the detector. This is the magnification factor. , This represents the distance from the X-ray source to the detector. The distance from the X-ray source to the center of the turntable; Given the optimal focal size of the X-ray source, substitute it into the above... The optimal magnification can be calculated using the formula. .

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