CT scanning system error correction method and device, equipment and storage medium

Abstract

The embodiment of the invention provides a CT scanning system error correction method and device, equipment and a medium. The CT scanning system error correction method comprises the steps that first attenuation data of a target motif based on multi-energy X rays at different rotation angles are determined; determining a measurement attenuation path of the X-ray passing through the target die body at different rotation angles; determining second attenuation data of the single-energy X-ray passing through the target motif at different rotation angles according to a measurement attenuation path and a conversion factor between the attenuation data and the attenuation path under the single-energy X-ray; determining first target attenuation data and second target attenuation data under the target measurement attenuation path according to the first attenuation data and the second attenuation data; and determining a mapping function between the single-energy X-ray attenuation data and the multi-energy X-ray attenuation data in different target measurement attenuation paths according to the first target attenuation data and the second target attenuation data in the target measurement attenuation paths. Beam hardening correction is realized, and detector response consistency correction is also realized.

Description

Technical Field

[0001] The present invention relates to the technical field of CT scanning and related technologies, and in particular to a method, device, equipment and storage medium for error correction of a CT scanning system. Background Art

[0002] CT scanning systems are widely used in industry and medical fields. In CT scanning systems, CT image reconstruction is based on the Lambert-Beer Law. Based on, the formula is the propagation path length, is the initial light intensity, For the spread The light intensity after the length, is the attenuation coefficient. For monoenergetic X-ray is a constant. For multi-energy X-rays, since the proportion of low-energy photons will gradually decrease during propagation (i.e., ray hardening), It is no longer a constant. Therefore, the CT scanning system needs to perform ray hardening correction in the multi-energy X-ray scene. In addition, the detector module of the CT scanning system usually contains multiple channels. Different channels respond differently to X-rays of the same light intensity, which will cause artifacts in image reconstruction. Simple air correction can ensure the consistency of the response of different channels to X-rays that have not been attenuated by the phantom. However, when the multi-energy X-ray passes through the phantom, its energy changes. Air correction cannot guarantee the consistency of the response of different detection channels at this time. At this time, nonlinear correction is required to ensure the consistency of the detector's response to X-rays after different attenuations.

[0003] In the prior art, by scanning a water phantom placed away from the center of rotation, all detection channels can detect X-rays that have penetrated water of different thicknesses, and then use the data for hardening correction, nonlinear correction and other analyses. In this process, in order to improve the statistics, it is often necessary to increase the current, perform multiple scans and other operations. Due to limitations such as the thermal capacity of the lamp tube, such operations often greatly increase the time for data collection and analysis. In addition, in order to obtain water attenuation data that is equivalent to the size of an adult body, it is often necessary to scan an oversized water phantom, which increases the cost of the phantom and the difficulty of operation. Summary of the invention

[0004] The embodiments described herein provide a method, apparatus, device and storage medium for CT scanning system error correction to solve the problems existing in the prior art.

[0005] In a first aspect, according to the present disclosure, a method for correcting errors in a CT scanning system is provided, comprising: Determine first attenuation data of a target phantom based on multi-energy X-rays at different rotation angles, wherein the target phantom includes a first phantom and a second phantom, and centers of the first phantom and the second phantom do not overlap with a rotation center; Calculating a first attenuation path of the X-ray passing through the first phantom and a second attenuation path of the X-ray passing through the second phantom at different rotation angles, and determining a measured attenuation path of the X-ray passing through the target phantom at different rotation angles according to the first attenuation path and the second attenuation path; Determine second attenuation data of the monoenergetic X-ray passing through the target phantom at different rotation angles according to the measured attenuation path and a conversion factor between the attenuation data and the attenuation path under the monoenergetic X-ray; Determine first target attenuation data and second target attenuation data under a target measurement attenuation path according to the first attenuation data and the second attenuation data; A mapping function between the mono-energy X-ray attenuation data and the poly-energy X-ray attenuation data under different target measurement attenuation paths is determined according to the first target attenuation data and the second target attenuation data under the target measurement attenuation path.

[0006] In some embodiments of the present disclosure, determining first attenuation data of the target phantom based on multi-energy X-rays at different rotation angles includes: Acquire initial attenuation data of the target phantom based on multi-energy X-rays at different rotation angles, wherein the initial attenuation data includes a detector channel and a scanning angle; Obtain air attenuation data; The initial attenuation data is corrected based on the air attenuation data to obtain first attenuation data.

[0007] In some embodiments of the present disclosure, determining the measured attenuation path of the X-ray passing through the target phantom at different rotation angles according to the first attenuation path and the second attenuation path includes: Summing a first attenuation path of the X-ray passing through the first phantom and a second attenuation path of the X-ray passing through the second phantom at the same rotation angle to obtain an initial measured attenuation path of the X-ray passing through the target phantom at different rotation angles; According to the relationship between the first attenuation data and the preset attenuation data, the initial measured attenuation path is processed to obtain a measured attenuation path.

[0008] In some embodiments of the present disclosure, the processing of the initial measured attenuation path to obtain the measured attenuation path according to the relationship between the first attenuation data and the preset attenuation data includes: When the pulse width of the first attenuation data is different from the pulse width of the preset attenuation data, determining an adjustment distance from the center of the first mold body and the center of the second mold body to the rotation center; When the timing of the pulse peak of the first attenuation data is different from the timing of the pulse peak of the preset attenuation data, determining the adjustment deflection angle of the first phantom circle center and the second phantom circle center; According to the adjustment distance and the adjustment deflection angle, the initial measurement attenuation path is adjusted to obtain a measurement attenuation path.

[0009] In some embodiments of the present disclosure, determining first target attenuation data and second target attenuation data under a target measurement attenuation path according to the first attenuation data and the second attenuation data includes: Acquire a first correlation between the first attenuation data and the rotation angle, a second correlation between the second attenuation data and the rotation angle, and a third correlation between the measured attenuation path and the rotation angle; According to the first correlation between the first attenuation data and the rotation angle, the second correlation between the second attenuation data and the rotation angle, and the third correlation between the measured attenuation path and the rotation angle, the first attenuation data and the second attenuation data determine the first target attenuation data and the second target attenuation data under the target measured attenuation path.

[0010] In some embodiments of the present disclosure, before determining the mapping function between the monoenergetic X-ray attenuation data and the polyenergetic X-ray attenuation data under different target measurement attenuation paths according to the first target attenuation data and the second target attenuation data under the target measurement attenuation path, the method further includes: Determine a first initial attenuation path according to a relationship between the first attenuation path and a first preset attenuation path, and determine a second initial attenuation path according to a relationship between the second attenuation path and a second preset attenuation path; Determining a first initial rotation angle corresponding to the first initial attenuation path, and determining a second initial rotation angle corresponding to the second target attenuation; Determining an initial rotation angle according to the first initial rotation angle and the second initial rotation angle; According to the first initial attenuation path and the second initial attenuation path at different initial rotation angles, a measurement attenuation path of the X-ray passing through the target phantom at different initial rotation angles is determined.

[0011] In some embodiments of the present disclosure, it also includes: In response to receiving the multi-energy X-ray attenuation data of the test phantom at the test angle, determining the single-energy X-ray attenuation data of the test phantom at the test angle according to a mapping function between the single-energy X-ray attenuation data and the multi-energy X-ray attenuation data in the target measurement attenuation path; According to the monoenergetic X-ray attenuation data of the test phantom at different test angles, back-projection reconstruction is performed to obtain the scanned image.

[0012] In a second aspect, according to the present disclosure, a CT scanning system error correction device is provided, comprising: A first attenuation data determination module is used to determine first attenuation data of a target phantom based on multi-energy X-rays at different rotation angles, wherein the target phantom includes a first phantom and a second phantom, and the centers of the first phantom and the second phantom do not overlap with the rotation center; a measurement attenuation path determination module, configured to calculate a first attenuation path of the X-ray passing through the first phantom and a second attenuation path of the X-ray passing through the second phantom at different rotation angles, and determine a measurement attenuation path of the X-ray passing through the target phantom at different rotation angles according to the first attenuation path and the second attenuation path; A second attenuation data determination module is used to determine second attenuation data of the monoenergetic X-ray passing through the target phantom at different rotation angles according to the measured attenuation path and a conversion factor between the attenuation data and the attenuation path under the monoenergetic X-ray; a target attenuation data associating module, configured to determine first target attenuation data and second target attenuation data under a target measurement attenuation path according to the first attenuation data and the second attenuation data; The mapping function determination module is used to determine the mapping function between the monoenergetic X-ray attenuation data and the polyenergetic X-ray attenuation data under different target measurement attenuation paths according to the first target attenuation data and the second target attenuation data under the target measurement attenuation path.

[0013] In a third aspect, according to the present disclosure, there is provided a computer device, including: one or more processors; a storage device for storing one or more programs, When the one or more programs are executed by the one or more processors, the one or more processors implement any method as described in the first aspect.

[0014] In a fourth aspect, according to the content of the present disclosure, a computer-readable storage medium is provided, on which a computer program is stored, and when the program is executed by a processor, it implements any method as described in the first aspect.

[0015] The CT scanning system error correction method, device, equipment and medium provided by the embodiments of the present disclosure first determine the first attenuation data of the target model based on multi-energy X-rays at different rotation angles; and calculate the first attenuation path of the X-ray passing through the first model and the second attenuation path of the X-ray passing through the second model at different rotation angles, and determine the measured attenuation path of the X-ray passing through the target model at different rotation angles based on the first attenuation path and the second attenuation path; then determine the second attenuation data of the monoenergetic X-ray passing through the target model at different rotation angles based on the measured attenuation path and the conversion factor between the attenuation data and the attenuation path under the monoenergetic X-ray; further determine the first target attenuation data and the second target attenuation data under the target measurement attenuation path based on the first attenuation data and the second attenuation data; finally, determine the mapping function between the monoenergetic X-ray attenuation data and the multi-energy X-ray attenuation data under different target measurement attenuation paths based on the first target attenuation data and the second target attenuation data under the target measurement attenuation path. The attenuation of multi-energy X-rays is corrected to the attenuation of mono-energy X-rays under the same path, and beam hardening correction is achieved. Since the same mono-energy attenuation coefficient is selected when establishing the mapping process of multi-energy X-rays to mono-energy X-rays for all detector channels, the mapping also achieves detector response consistency correction. In addition, the information of lamp energy spectrum and filtering system is not applicable in the process of realizing beam hardening correction and detector response consistency correction. Therefore, when the lamp energy spectrum or filtering system changes significantly, such as the filter is deflected during installation, the correction algorithm is still effective.

[0016] The above description is only an overview of the technical solution of the embodiment of the present application. In order to more clearly understand the technical means of the embodiment of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the embodiment of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings of the embodiments will be briefly described below. It should be noted that the drawings described below only relate to some embodiments of the present disclosure, but are not intended to limit the present disclosure, wherein: Figure 1 is a flow chart of a CT scanning system error correction method provided by an embodiment of the present disclosure; Figure 2 It is a structural schematic diagram of a CT scanning system error correction device provided by an embodiment of the present disclosure; Figure 3 It is a structural diagram of a computer device provided in an embodiment of the present disclosure.

[0018] In the drawings, reference numerals with the same last two digits correspond to the same elements. It should be noted that the elements in the drawings are schematic and not drawn to scale. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solution and advantages of the embodiments of the present disclosure clearer, the technical solution of the embodiments of the present disclosure will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present disclosure, rather than all of the embodiments. Based on the described embodiments of the present disclosure, all other embodiments obtained by those skilled in the art without creative work also fall within the scope of protection of the present disclosure.

[0020] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by a person skilled in the art to which the subject matter of the present disclosure belongs. It will be further understood that terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the specification and the relevant art, and will not be interpreted in an idealized or overly formal form unless otherwise explicitly defined herein. As used herein, a statement that two or more parts are "connected" or "coupled" together shall mean that the parts are joined together directly or through one or more intermediate components.

[0021] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase "embodiments" in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0022] The term "and / or" in this article is only a description of the association relationship of the associated objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists, A and B exist at the same time, and B exists. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0023] Furthermore, in all embodiments of the present disclosure, terms such as “first” and “second” are used only to distinguish one component (or a part of a component) from another component (or another part of a component).

[0024] In the description of the present application, unless otherwise specified, “plurality” means more than two (including two), and similarly, “plurality groups” means more than two (including two).

[0025] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings.

[0026] Based on the problems existing in the prior art, the present disclosure provides a method for correcting errors in a CT scanning system. Figure 1 is a flow chart of a CT scanning system error correction method provided by an embodiment of the present disclosure, such as Figure 1 As shown, the specific process of the CT scanning system error correction method includes: S110 , determining first attenuation data of the target phantom based on multi-energy X-rays at different rotation angles.

[0027] The target phantom includes a first phantom and a second phantom, and the centers of the first phantom and the second phantom do not overlap with the rotation center.

[0028] In a specific implementation, if it is desired to obtain large path attenuation data, it is necessary to make the vertical projections of the first phantom and the second phantom on the scanning bed overlap as much as possible, and at this time, the line connecting the center of the first phantom and the center of rotation and the line connecting the center of the second phantom and the center of rotation should be 0° or 180°; if it is desired to obtain small path attenuation data, it is necessary to avoid overlapping the vertical projections of the first phantom and the second phantom on the scanning bed as much as possible, and at this time, the line connecting the center of the first phantom and the center of rotation and the line connecting the center of the second phantom and the center of rotation should be 90° or 270°, and the distance from the center of the first phantom to the center of rotation and the distance from the center of the second phantom to the center of rotation are as large as possible. Adjusting the placement of the first phantom and the second phantom can adjust the overlap of their projections.

[0029] The embodiments of the present disclosure do not specifically limit the positions of the first phantom and the second phantom. If it is necessary to obtain a mapping function between large-path single-energy X-ray attenuation data and multi-energy X-ray attenuation data, the line connecting the center of the first phantom and the rotation center and the line connecting the center of the second phantom and the rotation center are set to 0° or 180°. If it is necessary to obtain a mapping function between small-path single-energy X-ray attenuation data and multi-energy X-ray attenuation data, the line connecting the center of the first phantom and the rotation center and the line connecting the center of the second phantom and the rotation center are set to 90° or 270°. The embodiments of the present disclosure do not specifically limit this.

[0030] In addition, the sizes of the first phantom and the second phantom need to be selected according to the object to be scanned in actual application and the geometric information of CT, which is not specifically limited in the embodiments of the present disclosure.

[0031] As a specific implementable method, determining the first attenuation data of the target model based on multi-energy X-rays at different rotation angles includes: obtaining initial attenuation data of the target model based on multi-energy X-rays at different rotation angles, wherein the initial attenuation data includes the detector channel and the scanning angle; obtaining air attenuation data; and correcting the initial attenuation data based on the air attenuation data to obtain the first attenuation data.

[0032] Specifically, the scanning device is rotated by controlling a suitable current. For example, the target phantom is scanned by sampling 1100 scanning angles per circle with a current of 300 mA. After scanning, the initial attenuation data of the target phantom based on multi-energy X-rays at different rotation angles are obtained. , where i represents different scanning angles and j represents different detector channels. Then scan the air under the same conditions to obtain air attenuation data Finally, the initial attenuation data is corrected based on the air attenuation data to obtain the first attenuation data, and the obtained first attenuation data satisfies: .

[0033] In addition, as a preferred implementation, the error of the determined attenuation data can be reduced by controlling the rotating device to rotate multiple times and averaging the attenuation data at different numbers of revolutions and the same scanning angle.

[0034] By selecting the first phantom and the second phantom of appropriate sizes and combining the placement of the first phantom and the second phantom, large path attenuation data or small path attenuation data can be obtained, thereby reducing the dependence on large-size phantoms during the calibration process.

[0035] In addition, compared with the prior art that scans a single phantom, the present application scans the first phantom and the second phantom, reducing the channel to only detect air attenuation data at certain scanning angles. This situation not only causes a waste of resources, but also causes the detector to directly withstand high-energy X-ray radiation, increasing detector damage.

[0036] S120, calculating a first attenuation path of the X-ray passing through the first phantom and a second attenuation path of the X-ray passing through the second phantom at different rotation angles, and determining a measured attenuation path of the X-ray passing through the target phantom at different rotation angles based on the first attenuation path and the second attenuation path.

[0037] As a preferred implementation mode, based on the first attenuation path and the second attenuation path, a measured attenuation path of the X-ray passing through the target model at different rotation angles is determined, including: summing the first attenuation path of the X-ray passing through the first model and the second attenuation path of the X-ray passing through the second model at the same rotation angle to obtain an initial measured attenuation path of the X-ray passing through the target model at different rotation angles; based on the relationship between the first attenuation data and the preset attenuation data, processing the initial measured attenuation path to obtain a measured attenuation path.

[0038] Specifically, according to the relationship between the first attenuation data and the preset attenuation data, the initial measurement attenuation path is processed to obtain the measurement attenuation path, including: when the pulse width of the first attenuation data is different from the pulse width of the preset attenuation data, determining the adjustment distance from the center of the first model body and the center of the second model body to the rotation center; when the timing of the pulse peak of the first attenuation data is different from the timing of the pulse peak of the preset attenuation data, determining the adjustment deflection angle of the center of the first model body and the adjustment deflection angle of the center of the second model body; according to the adjustment distance and the adjustment deflection angle, the initial measurement attenuation path is adjusted to obtain the measurement attenuation path.

[0039] After the first phantom and the second phantom are placed in the scanning device, a first attenuation path of the X-ray passing through the first phantom and a second attenuation path of the X-ray passing through the second phantom at different rotation angles can be measured according to the placement positions of the first phantom and the second phantom, and then the first attenuation path of the X-ray passing through the first phantom and the second attenuation path of the X-ray passing through the second phantom at the same rotation angle are summed to obtain the attenuation path of the X-ray of the target phantom at the rotation angle. In this way, the attenuation path of the X-ray of the target phantom at different rotation angles is calculated in turn, and then the initial measured attenuation path of the X-ray passing through the target phantom is determined according to the attenuation path of the X-ray passing through the target phantom at different rotation angles.

[0040] As an example, if the X-axis coordinate and Y-axis coordinate of the center of the cross-section of the first mold body satisfy:

[0041]

[0042] The X-axis coordinate and Y-axis coordinate of the center of the cross section of the second model satisfy:

[0043]

[0044] At this time, the first attenuation path of the X-ray passing through the first phantom satisfies:

[0045]

[0046] The second attenuation path of X-rays passing through the second phantom satisfies:

[0047]

[0048] in, represents the X-axis coordinate of the center of the cross section of the first model, represents the Y-axis coordinate of the center of the cross section of the first model, Represents the distance from the center of the first model to the rotation center, is the cross-sectional radius of the first model, is the deflection angle of the center of the first mold (the eccentric angle of the mold directly below the rotation center is 0° as the benchmark), represents the X-axis coordinate of the center of the cross section of the second model, represents the Y-axis coordinate of the center of the cross section of the second model, Represents the distance from the center of the second model to the rotation center, is the cross-sectional radius of the second die, is the deflection angle of the center of the second phantom (the eccentricity angle of the phantom directly below the rotation center is 0° as the benchmark), is the ray source rotation angle, is the angle between the line connecting the ray source to the detector channel and the line connecting the ray source to the rotation center, is the distance from the ray source to the rotation center.

[0049] Get in After the first attenuation path of the first mode and the second attenuation path of the second mode under the rotation angle, The first attenuation path of the first mode and the second attenuation path of the second mode under the rotation angle are summed to obtain Measured attenuation paths of the target phantom under rotation angles.

[0050] In actual operation, the placement position of the target phantom often deviates from the preset position to a certain extent. Therefore, there is a certain difference between the initial measured attenuation path of the X-ray passing through the target phantom at different rotation angles calculated according to the above formula and the actual path. At this time, by fitting the first attenuation data and the preset attenuation data, according to the relationship between the pulse width of the first attenuation data and the pulse width of the preset attenuation data after fitting, and the relationship between the timing of the pulse peak of the first attenuation data and the timing of the pulse peak of the preset attenuation data, the positions of the first phantom and the second phantom are adjusted to change the deflection angle of the center of the first phantom and the distance from the center of the first phantom to the rotation center, as well as to change the deflection angle of the center of the second phantom and the distance from the center of the second phantom to the rotation center.

[0051] Specifically, when the pulse width of the first attenuation data is smaller than the pulse width of the preset attenuation data, the positions of the first model body and the second model body are adjusted respectively to increase the distance from the center of the first model body to the rotation center, and the distance from the center of the second model body to the rotation center; when the pulse width of the first attenuation data is larger than the pulse width of the preset attenuation data, the positions of the first model body and the second model body are adjusted respectively to reduce the distance from the center of the first model body to the rotation center, and the distance from the center of the second model body to the rotation center; when the timing of the pulse peak of the first attenuation data is earlier than the timing of the pulse peak of the preset attenuation data, the positions of the first model body and the second model body are adjusted respectively to increase the deflection angle of the center of the first model body, and the deflection angle of the center of the second model body; when the timing of the pulse peak of the first attenuation data is later than the timing of the pulse peak of the preset attenuation data, the positions of the first model body and the second model body are adjusted respectively to reduce the deflection angle of the center of the first model body, and the deflection angle of the center of the second model body.

[0052] In a specific implementation, the adjustment distances from the center of the first model circle and the center of the second model circle to the rotation center can be determined according to the pulse width of the first attenuation data and the pulse width of the preset attenuation data, the adjustment deflection angles of the center of the first model circle and the second model circle can be determined according to the timing of the pulse peak of the first attenuation data and the timing of the pulse peak of the preset attenuation data, and then the adjustment distance and the distance from the center of the first model circle to the rotation center are summed to obtain the target distance from the center of the first model circle to the rotation center, the adjustment distance and the distance from the center of the second model circle to the rotation center are summed to obtain the target distance from the center of the second model circle to the rotation center, the adjustment deflection angle and the deflection angle of the center of the first model circle are summed to obtain the target deflection angle of the center of the first model circle, the adjustment deflection angle and the deflection angle of the center of the second model circle are summed to obtain the target deflection angle of the center of the second model circle, and finally the target distance from the center of the first model circle to the rotation center, the target distance from the center of the second model circle to the rotation center, the target deflection angle of the center of the first model circle and the target deflection angle of the center of the second model circle are substituted into the above formula to obtain the measured attenuation path.

[0053] It should be noted that the preset attenuation data is attenuation data generated based on monoenergetic X-rays at different rotation angles at a preset position of the target phantom.

[0054] S130, determining second attenuation data of the monoenergetic X-ray passing through the target phantom at different rotation angles according to the measured attenuation path and the conversion factor between the attenuation data and the attenuation path under the monoenergetic X-ray.

[0055] Regardless of whether the target phantom is under mono-energy X-ray or poly-energy X-ray, when the rotation angle is the same, the attenuation path is fixed, and the conversion factor between the attenuation data and the attenuation path under mono-energy X-ray is a fixed value, and the attenuation data and the attenuation path of the mono-energy X-ray passing through the target phantom satisfy the following relationship: Therefore, when the measured attenuation paths of the target phantom at different rotation angles are known and the conversion factor between the attenuation data and the attenuation paths under the monoenergetic X-ray is known, the second attenuation data of the monoenergetic X-ray passing through the target phantom at different rotation angles can be obtained.

[0056] S140: Determine first target attenuation data and second target attenuation data in a target measurement attenuation path according to the first attenuation data and the second attenuation data.

[0057] In a specific embodiment, the first target attenuation data and the second target attenuation data under the target measurement attenuation path are determined according to the first attenuation data and the second attenuation data, including: obtaining a first correlation relationship between the first attenuation data and the rotation angle, a second correlation relationship between the second attenuation data and the rotation angle, and a third correlation relationship between the measurement attenuation path and the rotation angle; according to the first correlation relationship between the first attenuation data and the rotation angle, the second correlation relationship between the second attenuation data and the rotation angle, and the third correlation relationship between the measurement attenuation path and the rotation angle, the first attenuation data and the second attenuation data are determined.

[0058] Specifically, according to step S110, the first attenuation data at different rotation angles can be obtained, and therefore, according to the first attenuation data at different rotation angles, the first correlation between the first attenuation data and the rotation angle can be obtained. According to step S120, the measured attenuation path of the target model at different rotation angles can be obtained, and therefore, according to the measured attenuation path of the target model at different rotation angles, the third correlation between the measured attenuation path and the rotation angle can be obtained. According to step S130, the second attenuation data at different rotation angles can be obtained, and therefore, according to the second attenuation data at different rotation angles, the second correlation between the second attenuation data and the rotation angle can be obtained.

[0059] After obtaining the first correlation between the first attenuation data and the rotation angle, the second correlation between the second attenuation data and the rotation angle, and the third correlation between the measured attenuation path and the rotation angle, if a rotation angle of the scanning device is selected, the measured attenuation path at the rotation angle can be determined according to the third correlation between the measured attenuation path and the rotation angle, and then the first attenuation data at the rotation angle can be determined according to the first correlation between the first attenuation data and the rotation angle, and the second attenuation data at the rotation angle can be determined according to the second correlation between the second attenuation data and the rotation angle, and finally the first attenuation data and the second attenuation data under the measured attenuation path are obtained, that is, the first target attenuation data and the second target attenuation data under the target measured attenuation path.

[0060] S150, determining a mapping function between the monoenergetic X-ray attenuation data and the polyenergetic X-ray attenuation data under different target measurement attenuation paths according to the first target attenuation data and the second target attenuation data under the target measurement attenuation path.

[0061] After step S140 determines the first target attenuation data and the second target attenuation data under the target measurement attenuation path, a mapping function between the monoenergetic X-ray attenuation data and the polyenergetic X-ray attenuation data under different target measurement attenuation paths is constructed according to the first target attenuation data and the second target attenuation data.

[0062] After constructing the mapping function between the mono-energy X-ray attenuation data and the multi-energy X-ray attenuation data under different target measurement attenuation paths, in the actual scanning process, when the scanning device is rotated to a test angle, the measurement attenuation path of the measurement model at the test angle can be obtained, and then the mapping function between the mono-energy X-ray attenuation data and the multi-energy X-ray attenuation data corresponding to the measurement attenuation path is found, and then according to the mapping function between the mono-energy X-ray attenuation data and the multi-energy X-ray attenuation data corresponding to the measurement attenuation path, the collected multi-energy X-ray attenuation data is converted into mono-energy X-ray attenuation data, and then the image can be reconstructed according to the Lambert-Beer law.

[0063] The CT scanning system error correction method provided by the embodiment of the present disclosure first determines the first attenuation data of the target model based on the multi-energy X-ray at different rotation angles; and calculates the first attenuation path of the X-ray passing through the first model and the second attenuation path of the X-ray passing through the second model at different rotation angles, and determines the measured attenuation path of the X-ray passing through the target model at different rotation angles according to the first attenuation path and the second attenuation path; then determines the second attenuation data of the mono-energy X-ray passing through the target model at different rotation angles according to the measured attenuation path and the conversion factor between the attenuation data and the attenuation path under the mono-energy X-ray; and then determines the first target attenuation data and the second target attenuation data under the target measurement attenuation path according to the first attenuation data and the second attenuation data; finally, determines the mapping function between the mono-energy X-ray attenuation data and the multi-energy X-ray attenuation data under different target measurement attenuation paths according to the first target attenuation data and the second target attenuation data under the target measurement attenuation path. The attenuation of multi-energy X-rays is corrected to the attenuation of mono-energy X-rays under the same path, and beam hardening correction is achieved. Since the same mono-energy attenuation coefficient is selected when establishing the mapping process of multi-energy X-rays to mono-energy X-rays for all detector channels, the mapping also achieves detector response consistency correction. In addition, the information of lamp energy spectrum and filtering system is not applicable in the process of realizing beam hardening correction and detector response consistency correction. Therefore, when the lamp energy spectrum or filtering system changes significantly, such as the filter is deflected during installation, the correction algorithm is still effective.

[0064] Based on the above embodiment, before executing step S150, the method further includes: According to the relationship between the first attenuation path and the first preset attenuation path, the first initial attenuation path is determined, and according to the relationship between the second attenuation path and the second preset attenuation path, the second initial attenuation path is determined; the first initial rotation angle corresponding to the first initial attenuation path is determined, and the second initial rotation angle corresponding to the second target attenuation is determined; the initial rotation angle is determined according to the first initial rotation angle and the second initial rotation angle; according to the first initial attenuation path and the second initial attenuation path at different initial rotation angles, the measured attenuation path of the X-ray passing through the target model at different initial rotation angles is determined.

[0065] Specifically, in the interval where the path length of the X-ray passing through the phantom varies greatly between two adjacent rotation angles, some minor errors in the prepared phantom, such as the processing error of the phantom size and the fitting error of the phantom eccentric position, will cause a large change in the mapping relationship. In addition, since the phantoms all have a shell made of non-aqueous material, the proportion of the shell made of non-aqueous material in these intervals is relatively large, which will also cause a large change in the mapping relationship. In order to reduce the impact of such errors and improve the accuracy and stability of the algorithm, we can eliminate the data in these intervals. This solution adopts the following elimination method: in step S120, the first attenuation path of the X-ray passing through the first phantom and the second attenuation path of the X-ray passing through the second phantom at different rotation angles are calculated respectively, firstly, the first attenuation path of the first phantom is selected, the first attenuation path of the first phantom is compared with the first preset attenuation path, and the first attenuation path whose first attenuation path is greater than the first preset attenuation path is selected to form a first initial attenuation path, and the second attenuation path of the second phantom is selected, the second attenuation path of the second phantom is compared with the second preset attenuation path, and the second attenuation path whose second attenuation path is greater than the second preset attenuation path is selected to form a second initial attenuation path, and then the first initial rotation angle corresponding to the first initial attenuation path and the second initial rotation angle corresponding to the second initial attenuation path are obtained, and then the intersection of the first initial rotation angle and the second initial rotation angle is obtained to obtain the initial rotation angle, and finally the first target attenuation path corresponding to the initial rotation angle is screened out from the first initial attenuation path, and the second target attenuation path corresponding to the initial rotation angle is screened out from the second initial attenuation path, and then the first target attenuation path and the second target attenuation path at the same initial rotation angle are summed to obtain the measured attenuation path of the X-ray passing through the target phantom at different initial rotation angles.

[0066] It should be noted that the first preset attenuation path is determined based on the diameter of the first model body and the wide window factor, and the second preset attenuation path is determined based on the diameter of the second model body and the wide window factor.

[0067] By screening the measured attenuation path, the screened data can improve the accuracy of hardening correction and nonlinear correction and improve image quality.

[0068] Based on the above embodiments, Figure 2 FIG. 1 is a schematic diagram of a structure of an error correction device for a CT scanning system provided by an embodiment of the present disclosure. Figure 2 As shown, the CT scanning system error correction device includes: A first attenuation data determination module 210 is used to determine first attenuation data of a target phantom based on multi-energy X-rays at different rotation angles, wherein the target phantom includes a first phantom and a second phantom, and the centers of the first phantom and the second phantom do not overlap with the rotation center; A measurement attenuation path determination module 220 is used to calculate a first attenuation path of the X-ray passing through the first phantom and a second attenuation path of the X-ray passing through the second phantom at different rotation angles, and determine a measurement attenuation path of the X-ray passing through the target phantom at different rotation angles according to the first attenuation path and the second attenuation path; A second attenuation data determination module 230 is used to determine second attenuation data of the monoenergetic X-ray passing through the target phantom at different rotation angles according to the measured attenuation path and a conversion factor between the attenuation data and the attenuation path under the monoenergetic X-ray; The target attenuation data association module 240 is used to determine the first target attenuation data and the second target attenuation data under the target measurement attenuation path according to the first attenuation data and the second attenuation data; The mapping function determination module 250 is used to determine the mapping function between the monoenergetic X-ray attenuation data and the polyenergetic X-ray attenuation data under different target measurement attenuation paths according to the first target attenuation data and the second target attenuation data under the target measurement attenuation path.

[0069] The CT scanning system error correction device provided by the embodiment of the present disclosure first determines the first attenuation data of the target model based on the multi-energy X-ray at different rotation angles; and calculates the first attenuation path of the X-ray passing through the first model and the second attenuation path of the X-ray passing through the second model at different rotation angles, and determines the measured attenuation path of the X-ray passing through the target model at different rotation angles according to the first attenuation path and the second attenuation path; then determines the second attenuation data of the mono-energy X-ray passing through the target model at different rotation angles according to the measured attenuation path and the conversion factor between the attenuation data and the attenuation path under the mono-energy X-ray; further determines the first target attenuation data and the second target attenuation data under the target measurement attenuation path according to the first attenuation data and the second attenuation data; finally, determines the mapping function between the mono-energy X-ray attenuation data and the multi-energy X-ray attenuation data under different target measurement attenuation paths according to the first target attenuation data and the second target attenuation data under the target measurement attenuation path. The attenuation of multi-energy X-rays is corrected to the attenuation of mono-energy X-rays under the same path, and beam hardening correction is achieved. Since the same mono-energy attenuation coefficient is selected when establishing the mapping process of multi-energy X-rays to mono-energy X-rays for all detector channels, the mapping also achieves detector response consistency correction. In addition, the information of lamp energy spectrum and filtering system is not applicable in the process of realizing beam hardening correction and detector response consistency correction. Therefore, when the lamp energy spectrum or filtering system changes significantly, such as the filter is deflected during installation, the correction algorithm is still effective.

[0070] In a specific embodiment, determining first attenuation data of the target phantom based on multi-energy X-rays at different rotation angles includes: Acquire initial attenuation data of the target phantom based on multi-energy X-rays at different rotation angles, wherein the initial attenuation data includes a detector channel and a scanning angle; Obtain air attenuation data; The initial attenuation data is corrected based on the air attenuation data to obtain first attenuation data.

[0071] In a specific implementation, determining the measured attenuation path of the X-ray passing through the target phantom at different rotation angles according to the first attenuation path and the second attenuation path includes: Summing a first attenuation path of the X-ray passing through the first phantom and a second attenuation path of the X-ray passing through the second phantom at the same rotation angle to obtain an initial measured attenuation path of the X-ray passing through the target phantom at different rotation angles; According to the relationship between the first attenuation data and the preset attenuation data, the initial measured attenuation path is processed to obtain a measured attenuation path.

[0072] In a specific implementation, the processing of the initial measured attenuation path to obtain the measured attenuation path according to the relationship between the first attenuation data and the preset attenuation data includes: When the pulse width of the first attenuation data is different from the pulse width of the preset attenuation data, determining an adjustment distance from the center of the first mold body and the center of the second mold body to the rotation center; When the timing of the pulse peak of the first attenuation data is different from the timing of the pulse peak of the preset attenuation data, determining the adjustment deflection angle of the first phantom circle center and the second phantom circle center; According to the adjustment distance and the adjustment deflection angle, the initial measurement attenuation path is adjusted to obtain a measurement attenuation path.

[0073] In a specific implementation, determining first target attenuation data and second target attenuation data under a target measurement attenuation path according to the first attenuation data and the second attenuation data includes: Acquire a first correlation between the first attenuation data and the rotation angle, a second correlation between the second attenuation data and the rotation angle, and a third correlation between the measured attenuation path and the rotation angle; According to the first correlation between the first attenuation data and the rotation angle, the second correlation between the second attenuation data and the rotation angle, and the third correlation between the measured attenuation path and the rotation angle, the first attenuation data and the second attenuation data determine the first target attenuation data and the second target attenuation data under the target measured attenuation path.

[0074] In a specific implementation, before determining the mapping function between the monoenergetic X-ray attenuation data and the polyenergetic X-ray attenuation data under different target measurement attenuation paths according to the first target attenuation data and the second target attenuation data under the target measurement attenuation path, the method further includes: Determine a first initial attenuation path according to a relationship between the first attenuation path and a first preset attenuation path, and determine a second initial attenuation path according to a relationship between the second attenuation path and a second preset attenuation path; Determining a first initial rotation angle corresponding to the first initial attenuation path, and determining a second initial rotation angle corresponding to the second target attenuation; Determining an initial rotation angle according to the first initial rotation angle and the second initial rotation angle; According to the first initial attenuation path and the second initial attenuation path at different initial rotation angles, a measurement attenuation path of the X-ray passing through the target phantom at different initial rotation angles is determined.

[0075] In a specific embodiment, it also includes: In response to receiving the multi-energy X-ray attenuation data of the test phantom at the test angle, determining the single-energy X-ray attenuation data of the test phantom at the test angle according to a mapping function between the single-energy X-ray attenuation data and the multi-energy X-ray attenuation data in the target measurement attenuation path; According to the monoenergetic X-ray attenuation data of the test phantom at different test angles, back-projection reconstruction is performed to obtain the scanned image.

[0076] The present application also provides a computer device. Figure 3 , Figure 3 This is a basic structural block diagram of the computer device in this embodiment.

[0077] The computer device includes a memory 510 and a processor 520 that are connected to each other through a system bus. It should be noted that the figure only shows a computer device with components 510-520, but it should be understood that it is not required to implement all the components shown, and more or fewer components can be implemented instead. Among them, those skilled in the art can understand that the computer device here is a device that can automatically perform numerical calculations and / or information processing according to pre-set or stored instructions, and its hardware includes but is not limited to microprocessors, application specific integrated circuits (Application Specific Integrated Circuit, ASIC), field-programmable gate arrays (Field-Programmable Gate Array, FPGA), digital signal processors (Digital Signal Processor, DSP), embedded devices, etc.

[0078] Computer devices can be computing devices such as desktop computers, notebooks, PDAs, and cloud servers. Computer devices can interact with users through keyboards, mice, remote controls, touch pads, or voice control devices.

[0079] The memory 510 includes at least one type of readable storage medium, and the readable storage medium includes a non-volatile memory or a volatile memory, such as a flash memory, a hard disk, a multimedia card, a card-type memory (such as an SD or DX memory, etc.), a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM), an electrically erasable programmable read-only memory (EEPROM), a programmable read-only memory (PROM), a magnetic memory, a magnetic disk, an optical disk, etc., and the RAM may include a static RAM or a dynamic RAM. In some embodiments, the memory 510 may be an internal storage unit of a computer device, such as a hard disk or a memory of the computer device. In other embodiments, the memory 510 may also be an external storage device of a computer device, such as a plug-in hard disk, a smart memory card (SMC), a secure digital (SD) card, or a flash card (Flash Card), etc., equipped on the computer device. Of course, the memory 510 may also include both an internal storage unit of the computer device and an external storage device thereof. In this embodiment, the memory 510 is generally used to store an operating system and various application software installed on the computer device, such as the program code of the above method, etc. In addition, the memory 510 may also be used to temporarily store various data that have been output or are to be output.

[0080] The processor 520 is generally used to perform the overall operation of the computer device. In this embodiment, the memory 510 is used to store program codes or instructions, the program code includes computer operation instructions, and the processor 520 is used to execute the program codes or instructions stored in the memory 510 or process data, such as running the program code of the above method.

[0081] In this article, the bus can be an Industry Standard Architecture (ISA) bus, a Peripheral Component Interconnect (PCI) bus, or an Extended Industry Standard Architecture (EISA) bus, etc. The bus system can be divided into an address bus, a data bus, a control bus, etc. For ease of representation, only one thick line is used in the figure, but it does not mean that there is only one bus or one type of bus.

[0082] Another embodiment of the present application also provides a computer-readable medium, which may be a computer-readable signal medium or a computer-readable medium. A processor in a computer reads a computer-readable program code stored in the computer-readable medium, so that the processor can execute the functional actions specified in each step or a combination of steps in the above method; and generate a device for implementing the functional actions specified in each block or a combination of blocks in the block diagram.

[0083] Computer-readable media include but are not limited to electronic, magnetic, optical, electromagnetic, infrared memory or semiconductor systems, devices or apparatuses, or any appropriate combination of the foregoing, the memory is used to store program codes or instructions, the program codes include computer operating instructions, and the processor is used to execute the program codes or instructions of the above methods stored in the memory.

[0084] For the definitions of memory and processor, please refer to the description of the aforementioned computer device embodiment and will not be repeated here.

[0085] In the several embodiments provided in the present application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic, for example, the division of modules or units is only a logical function division, and there may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0086] Each functional unit or module in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0087] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions to enable a computer device (which can be a personal computer, server, or network device, etc.) or a processor (processor) to execute all or part of the steps of the various embodiments of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM), random access memory (RAM), disk or optical disk, etc., and other media that can store program codes.

[0088] Unless the context clearly indicates otherwise, the singular form of the words used herein and in the appended claims includes the plural and vice versa. Thus, when referring to the singular, the plural form of the corresponding term is generally included. Similarly, the words "comprise" and "include" are to be interpreted as inclusive rather than exclusive. Likewise, the terms "include" and "or" should be interpreted as inclusive unless such interpretation is expressly prohibited herein. Where the term "example" is used herein, particularly when it is located after a group of terms, the "example" is merely exemplary and illustrative and should not be considered exclusive or comprehensive.

[0089] Further aspects and scopes of adaptability become apparent from the description provided herein. It should be understood that various aspects of the present application can be implemented individually or in combination with one or more other aspects. It should also be understood that the description and specific embodiments herein are intended for purposes of illustration only and are not intended to limit the scope of the present application.

[0090] Several embodiments of the present disclosure are described in detail above, but it is obvious that those skilled in the art can make various modifications and variations to the embodiments of the present disclosure without departing from the spirit and scope of the present disclosure. The protection scope of the present disclosure is defined by the attached claims.

Claims

1. A CT scanning system error correction method, characterized in that: include: Determine first attenuation data of a target phantom based on multi-energy X-rays at different rotation angles, wherein the target phantom includes a first phantom and a second phantom, and centers of the first phantom and the second phantom do not overlap with a rotation center; Calculating a first attenuation path of the X-ray passing through the first phantom and a second attenuation path of the X-ray passing through the second phantom at different rotation angles, and determining a measured attenuation path of the X-ray passing through the target phantom at different rotation angles according to the first attenuation path and the second attenuation path; Determine second attenuation data of the monoenergetic X-ray passing through the target phantom at different rotation angles according to the measured attenuation path and a conversion factor between the attenuation data and the attenuation path under the monoenergetic X-ray; Determine first target attenuation data and second target attenuation data under a target measurement attenuation path according to the first attenuation data and the second attenuation data; A mapping function between the mono-energy X-ray attenuation data and the poly-energy X-ray attenuation data under different target measurement attenuation paths is determined according to the first target attenuation data and the second target attenuation data under the target measurement attenuation path.

2. The method according to claim 1, characterized in that The determining of first attenuation data of the target phantom based on multi-energy X-rays at different rotation angles includes: Acquire initial attenuation data of the target phantom based on multi-energy X-rays at different rotation angles, wherein the initial attenuation data includes a detector channel and a scanning angle; Obtain air attenuation data; The initial attenuation data is corrected based on the air attenuation data to obtain first attenuation data.

3. The method according to claim 1, characterized in that The step of determining, according to the first attenuation path and the second attenuation path, a measurement attenuation path of X-rays passing through the target phantom at different rotation angles includes: Summing a first attenuation path of the X-ray passing through the first phantom and a second attenuation path of the X-ray passing through the second phantom at the same rotation angle to obtain an initial measured attenuation path of the X-ray passing through the target phantom at different rotation angles; According to the relationship between the first attenuation data and the preset attenuation data, the initial measured attenuation path is processed to obtain a measured attenuation path.

4. The method according to claim 3, characterized in that The processing of the initial measured attenuation path to obtain the measured attenuation path according to the relationship between the first attenuation data and the preset attenuation data includes: When the pulse width of the first attenuation data is different from the pulse width of the preset attenuation data, determining an adjustment distance from the center of the first mold body and the center of the second mold body to the rotation center; When the timing of the pulse peak of the first attenuation data is different from the timing of the pulse peak of the preset attenuation data, determining the adjustment deflection angle of the first phantom circle center and the second phantom circle center; According to the adjustment distance and the adjustment deflection angle, the initial measurement attenuation path is adjusted to obtain a measurement attenuation path.

5. The method according to claim 1, characterized in that The determining, according to the first attenuation data and the second attenuation data, first target attenuation data and second target attenuation data under the target measurement attenuation path comprises: Acquire a first correlation between the first attenuation data and the rotation angle, a second correlation between the second attenuation data and the rotation angle, and a third correlation between the measured attenuation path and the rotation angle; According to the first correlation between the first attenuation data and the rotation angle, the second correlation between the second attenuation data and the rotation angle, and the third correlation between the measured attenuation path and the rotation angle, the first attenuation data and the second attenuation data determine the first target attenuation data and the second target attenuation data under the target measured attenuation path.

6. The method according to claim 1, characterized in that Before determining the mapping function between the monoenergetic X-ray attenuation data and the polyenergetic X-ray attenuation data under different target measurement attenuation paths according to the first target attenuation data and the second target attenuation data under the target measurement attenuation path, the method further includes: Determine a first initial attenuation path according to a relationship between the first attenuation path and a first preset attenuation path, and determine a second initial attenuation path according to a relationship between the second attenuation path and a second preset attenuation path; Determining a first initial rotation angle corresponding to the first initial attenuation path, and determining a second initial rotation angle corresponding to the second target attenuation; Determining an initial rotation angle according to the first initial rotation angle and the second initial rotation angle; According to the first initial attenuation path and the second initial attenuation path at different initial rotation angles, a measurement attenuation path of the X-ray passing through the target phantom at different initial rotation angles is determined.

7. The method according to claim 1, characterized in that Also includes: In response to receiving the multi-energy X-ray attenuation data of the test phantom at the test angle, determining the single-energy X-ray attenuation data of the test phantom at the test angle according to a mapping function between the single-energy X-ray attenuation data and the multi-energy X-ray attenuation data in the target measurement attenuation path; According to the monoenergetic X-ray attenuation data of the test phantom at different test angles, back-projection reconstruction is performed to obtain the scanned image.

8. A CT scanning system error correction device, characterized in that: include: A first attenuation data determination module is used to determine first attenuation data of a target phantom based on multi-energy X-rays at different rotation angles, wherein the target phantom includes a first phantom and a second phantom, and the centers of the first phantom and the second phantom do not overlap with the rotation center; a measurement attenuation path determination module, configured to calculate a first attenuation path of the X-ray passing through the first phantom and a second attenuation path of the X-ray passing through the second phantom at different rotation angles, and determine a measurement attenuation path of the X-ray passing through the target phantom at different rotation angles according to the first attenuation path and the second attenuation path; A second attenuation data determination module is used to determine second attenuation data of the monoenergetic X-ray passing through the target phantom at different rotation angles according to the measured attenuation path and a conversion factor between the attenuation data and the attenuation path under the monoenergetic X-ray; a target attenuation data associating module, configured to determine first target attenuation data and second target attenuation data under a target measurement attenuation path according to the first attenuation data and the second attenuation data; The mapping function determination module is used to determine the mapping function between the monoenergetic X-ray attenuation data and the polyenergetic X-ray attenuation data under different target measurement attenuation paths according to the first target attenuation data and the second target attenuation data under the target measurement attenuation path.

9. A computer device, characterized in that: include: one or more processors; a storage device for storing one or more programs, When the one or more programs are executed by the one or more processors, the one or more processors implement the method according to any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the method according to any one of claims 1 to 7 is implemented.

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