Energy correction method, storage medium and photon counting CT equipment

Abstract

The present invention discloses an energy correction method, storage medium, and photon counting CT equipment. The energy correction method includes: obtaining a correspondence between the photon energy corresponding to each of a plurality of pixels and a threshold code; determining a reference correspondence for the plurality of pixels; and optimizing the correspondence between the photon energy corresponding to each pixel and the threshold code based on the reference correspondence to obtain a target correspondence between the photon energy and the threshold code for each pixel. This method can achieve the original energy correction objective while reducing energy spectrum inconsistencies between pixels.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic computer tomography, and in particular to an energy correction method, a storage medium and a photon counting CT device. Background Art

[0002] In the photon energy-resolving detection system, the threshold code corresponding to each pixel is obtained by converting the energy threshold through the functional relationship obtained by energy correction. However, the current energy correction is performed pixel by pixel. Due to the inherent systematic errors of the energy correction method and the inherent differences between pixels, there is a certain energy spectrum inconsistency between each pixel after energy correction. Summary of the Invention

[0003] The present invention aims to solve at least one of the technical problems in the related art to a certain extent. To this end, the first object of the present invention is to provide an energy correction method that can reduce the energy spectrum inconsistency between pixels while achieving the original energy correction purpose.

[0004] A second object of the present invention is to provide a computer-readable storage medium.

[0005] The third object of the present invention is to provide a photon counting CT device.

[0006] To achieve the above-mentioned purpose, the first aspect of the present invention proposes an energy correction method, which includes: obtaining the correspondence between the photon energy corresponding to each pixel in a plurality of pixels and the threshold code; determining the reference correspondence of the plurality of pixels; optimizing the correspondence between the photon energy corresponding to each pixel and the threshold code according to the reference correspondence, and obtaining the target correspondence between the photon energy of each pixel and the threshold code.

[0007] According to the energy correction method of an embodiment of the present invention, a correspondence between the photon energy corresponding to each of a plurality of pixels and a threshold code is obtained, a reference correspondence between the plurality of pixels is determined, and the correspondence between the photon energy corresponding to each pixel and the threshold code is optimized based on the reference correspondence, thereby obtaining a target correspondence between the photon energy and the threshold code for each pixel. Thus, by optimizing the correspondence between the photon energy corresponding to each pixel and the threshold code based on the reference correspondence, energy spectrum inconsistency between pixels can be reduced. The correspondence between the photon energy corresponding to each pixel and the threshold code can be obtained by correction based on the original energy correction purpose, thereby achieving the original energy correction purpose while reducing energy spectrum inconsistency between pixels.

[0008] To achieve the above-mentioned purpose, a second embodiment of the present invention provides a computer-readable storage medium on which an energy correction program is stored. When the energy correction program is executed by a processor, the above-mentioned energy correction method is implemented.

[0009] According to the computer-readable storage medium of the embodiment of the present invention, based on the aforementioned energy correction method, it is possible to reduce the energy spectrum inconsistency between pixels while achieving the original energy correction purpose.

[0010] To achieve the above-mentioned objectives, an embodiment of the third aspect of the present invention proposes a photon counting CT device, comprising: a photoelectric conversion unit, for converting photons into a first electrical signal; a readout unit, the readout unit comprising a plurality of pixels, each pixel comprising a comparator and a counter, the comparator being used to compare the first electrical signal with a second electrical signal corresponding to a corresponding threshold code, and the counter being used to increase the photon count value by one when the first electrical signal is greater than the second electrical signal; a setting unit, for converting the energy threshold setting value of the corresponding pixel into a threshold code of the corresponding pixel based on the energy correction result of each pixel, and converting the threshold code of the corresponding pixel into a second electrical signal, wherein the energy correction result is obtained by the energy correction method provided in the above-mentioned embodiment.

[0011] According to the photon counting CT device of an embodiment of the present invention, a corresponding relationship between the photon energy corresponding to each pixel of a plurality of pixels and a threshold code is obtained through a given unit, a reference corresponding relationship of the plurality of pixels is determined, and the corresponding relationship between the photon energy corresponding to each pixel and the threshold code is optimized based on the reference corresponding relationship to obtain a target corresponding relationship between the photon energy and the threshold code of each pixel, thereby achieving the original energy correction purpose while reducing the energy spectrum inconsistency between pixels.

[0012] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 A schematic diagram of a portion of the structure of a photon counting CT device according to an embodiment of the present invention;

[0014] Figure 2 is a flow chart of an energy correction method according to one embodiment of the present invention;

[0015] Figure 3 Schematic diagram of the k-dege characteristic of metallic gadolinium;

[0016] Figure 4 Schematic diagram of a process for obtaining a threshold code corresponding to a k-edge value of a calibration object according to one embodiment of the present invention;

[0017] Figure 5 Schematic diagram of a process for obtaining a threshold code corresponding to a k-edge value of a calibration object according to another embodiment of the present invention;

[0018] Figure 6A schematic diagram of a process for obtaining a reference correspondence according to an embodiment of the present invention;

[0019] Figure 7 FIG. 1 is a schematic diagram of a computer-readable storage medium according to an embodiment of the present invention. DETAILED DESCRIPTION

[0020] The following describes embodiments of the present invention in detail, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and are not to be construed as limiting the present invention.

[0021] Figure 1 FIG. 1 is a partial structural diagram of a photon counting CT device according to an embodiment of the present invention. Figure 1 As shown, photon counting CT device 500 may include an emitter, a detector, and processing circuitry.

[0022] The emitter may be a tube for emitting photons, such as X-rays. The detector may include a photoelectric conversion unit 510 for converting photons into a first electrical signal. The processing circuit may include a readout unit 520 and a setting unit 530, wherein the readout unit 520 includes a plurality of pixels (no less than two, such as pixel 1, pixel 2, ..., pixel n), each pixel including a comparator (such as comparator 1, comparator 2, ..., comparator n) and a counter (such as counter 1, counter 2, ..., counter n), the comparator being configured to compare the first electrical signal with a second electrical signal corresponding to a corresponding threshold code, and the counter being configured to increment a photon count value by one when the first electrical signal is greater than the second electrical signal; the setting unit 520 is configured to convert an energy threshold setting value of the corresponding pixel into a threshold code of the corresponding pixel based on a target correspondence between the photon energy and the threshold code of each pixel (i.e., an energy correction result), and convert the threshold code of the corresponding pixel into a second electrical signal. Optionally, a rectification and filtering unit (not specifically shown in the figure) may be further provided between the photoelectric conversion unit 510 and the comparator, for rectifying and filtering the first electrical signal before inputting it into each comparator.

[0023] Specifically, the photoelectric conversion unit 510 may be a crystal made of a semiconductor material, such as a crystal made of a semiconductor material such as CdZnTe (cadmium zinc telluride), CdTe (cadmium antimonide) or GaAs (gallium arsenide). When a photon is incident on a crystal made of a semiconductor material, the crystal directly converts the photon into an electron, thereby generating a first electrical signal. It should be noted that a reverse bias voltage can also be applied to the crystal by an external power supply to deplete the junction interface region of the crystal and generate an electric field inside. When the incident photon is converted into an electron-hole pair, under the action of the electric field, the electron drifts toward the positive pole of the external power supply and the hole drifts toward the negative pole of the external power supply, thereby generating a first electrical signal. Among them, the magnitude of the reverse bias voltage depends on many factors, such as the type of semiconductor material, the doping concentration, and the thickness of the crystal produced.

[0024] The n pixels in the readout unit 520 are arranged at equal intervals to form a pixel array. Each pixel can be connected to the voltage conversion unit 510 via a connector to achieve pixelization. The comparator and counter in each pixel can be implemented in hardware or software. The specific implementation method is not limited here, as long as the first electrical signal can be compared with the second electrical signal corresponding to the corresponding threshold code, and photon counting can be achieved when the first electrical signal is greater than the second electrical signal.

[0025] The energy correction subunit and digital-to-analog converter in the given unit 530 can be implemented by hardware or software. The specific implementation method is not limited here, as long as it can convert the energy threshold setting value into a threshold code based on the target correspondence between the photon energy corresponding to each pixel and the threshold code, convert the threshold code into a second electrical signal, and provide the second electrical signal to each comparator in the readout unit 520. Of course, the given unit 530 also needs to be able to directly provide the threshold code to facilitate the acquisition of the target correspondence between the photon energy corresponding to each pixel and the threshold code, that is, energy correction.

[0026] When the energy spectrum curve is scanned by the above-mentioned device 500, an energy spectrum curve with the energy threshold as the independent variable and the photon count value as the dependent variable can be obtained. Specifically, taking the energy spectrum curve of an object scanned by X-rays as an example, when the X-ray photons pass through the object and enter the photoelectric conversion unit 510, the photoelectric conversion unit 510 converts the photons into first electrical signals and inputs them into each pixel of the readout unit 520; the comparator in each pixel compares the first electrical signal with its corresponding energy threshold, and when the comparison result meets the conditions, the corresponding counter increments the photon count value by one. For example, comparator 1 in pixel 1 compares the first electrical signal with the energy threshold corresponding to pixel 1, and when the comparison result meets the conditions, the photon count value of counter 1 is incremented by one. At the same time, comparator 2 in pixel 2 compares the first electrical signal with the energy threshold corresponding to pixel 2, and when the comparison result meets the conditions, the photon count value of counter 2 is incremented by one, and so on, ultimately obtaining a material energy spectrum curve with the energy threshold as the independent variable and the photon count value as the dependent variable.

[0027] When the comparator in the above-mentioned device 500 compares the first electrical signal with the energy threshold, since the units of the first electrical signal are mV and the units of the energy threshold are keV, the two units are different and cannot be directly compared. Therefore, in order to achieve the comparison between the two, it is necessary to convert the set energy threshold, i.e., the energy threshold setting value, into an electrical signal. The entire conversion process can be implemented by the setting unit 530. The specific conversion process is: the target correspondence between the photon energy corresponding to each pixel obtained by energy correction of the energy threshold setting value and the threshold code is converted into a digital threshold code. The digital threshold code is converted by an analog-to-digital converter to obtain a second electrical signal. The magnitude of the second electrical signal can represent the magnitude of the energy threshold setting value. The unit is mV, the same as the unit of the first electrical signal. Therefore, when the comparator performs the comparison, it actually compares the first electrical signal and the second electrical signal. For example, when the first electrical signal is greater than the second electrical signal, it indicates that the comparison result meets the conditions, and the photon count value of the corresponding counter is increased by one.

[0028] It should be noted that energy correction is to solve the correspondence between energy threshold and threshold coding, that is, the correspondence between photon energy and threshold coding. However, the energy correction in related technologies is performed pixel by pixel. Due to the inherent systematic errors of the energy correction method and the inherent differences between pixels, there is a certain energy spectrum inconsistency between each pixel after energy correction.

[0029] To address this technical problem, an embodiment of the present invention provides an energy correction method that can reduce energy spectrum inconsistency between pixels while achieving the original energy correction purpose.

[0030] Figure 2 FIG. 4 is a flow chart of an energy correction method according to an embodiment of the present invention.

[0031] like Figure 2 As shown, the energy correction method may include:

[0032] S101, obtaining a corresponding relationship between a photon energy corresponding to each pixel in a plurality of pixels and a threshold code.

[0033] Specifically, energy correction can be performed on each pixel based on the k-edge (also known as k-edge) characteristics of the calibration object to obtain the corresponding relationship between the photon energy corresponding to each pixel and the threshold code. By correcting the energy of each pixel, the original purpose of energy correction can be guaranteed. It should be noted that the calibration object can be a single substance or a compound, specifically a metal element or a compound containing the target metal element, such as the metal element tungsten or the compound CeO2 (cerium oxide) containing Ce (cerium). In practical applications, there is no restriction on the specific substance used, as long as the substance has k-edge characteristics.

[0034] S102: Determine a reference correspondence relationship between multiple pixels.

[0035] It should be noted that the reference correspondence, as a target of energy spectrum consistency between pixels, can be obtained by averaging the energy spectrum curves of all pixels.

[0036] S103 , optimizing the correspondence between the photon energy and the threshold code corresponding to each pixel according to the reference correspondence, and obtaining a target correspondence between the photon energy and the threshold code for each pixel.

[0037] That is to say, with the goal of energy spectrum consistency between pixels, the correspondence between the photon energy corresponding to each pixel and the threshold code is optimized, so that when the energy spectrum curve is obtained by scanning based on the optimized target correspondence between the photon energy of each pixel and the threshold code, the energy spectrum consistency between pixels can be guaranteed.

[0038] In the above embodiment, the correspondence between the photon energy corresponding to each pixel and the threshold code is optimized according to the reference correspondence, which can reduce the energy spectrum inconsistency between pixels, and the correspondence between the photon energy corresponding to each pixel and the threshold code can be corrected based on the original energy correction purpose, thereby reducing the energy spectrum inconsistency between pixels while achieving the original energy correction purpose.

[0039] The following describes how to obtain the corresponding relationship between the photon energy corresponding to each pixel in a plurality of pixels and the threshold code with reference to a specific example.

[0040] As an implementation method, the correspondence between the photon energy corresponding to each pixel in a plurality of pixels and the threshold code is obtained, including: for each pixel, obtaining the threshold code corresponding to the k-edge value of each calibration object in a plurality of calibration objects, and fitting the k-edge values ​​of the plurality of calibration objects and the corresponding threshold codes to obtain the correspondence between the photon energy corresponding to each pixel and the threshold code.

[0041] It should be noted that the calibration object can be any substance with k-edge characteristics. The k-edge characteristics of a substance refer to the physical phenomenon that the attenuation coefficient of the substance suddenly increases under a certain photon energy, such as Figure 3 As shown, the attenuation coefficient of metallic gadolinium (Gd) exhibits a significant sudden increase at a photon energy of 50.2 keV, which is the k-edge value of Gd. Because a material's attenuation coefficient significantly increases at the k-edge value, according to the Lambert-Beer law, the photon count value of its energy spectrum curve will exhibit a significant sudden drop at the k-edge value. Since the energy spectrum curve represents the relationship between photon counts and threshold codes, the threshold code corresponding to this sudden drop in photon count value is the threshold code corresponding to the material's k-edge value. Using the material's k-edge properties, a correspondence between k-edge values ​​and threshold codes can be established. Since k-edge values ​​correspond to photon energy, a correspondence between the photon energy and threshold code for each pixel can be established.

[0042] Specifically, if Figure 1 As shown, for pixel 1, the threshold code corresponding to the k-edge value of each calibration object in the multiple calibration objects is obtained, thereby obtaining multiple groups of k-edge values ​​and corresponding threshold codes, and then fitting the multiple groups of k-edge values ​​and corresponding threshold codes is performed. For example, the threshold code corresponding to the k-edge value is used as the independent variable and the k-edge value is used as the dependent variable. Fitting is performed according to a preset fitting method to obtain the correspondence between the k-edge value and the threshold code corresponding to pixel 1. Since the k-edge value is the photon energy, the correspondence between the photon energy and the threshold code corresponding to pixel 1 is obtained; similarly, the correspondence between the photon energy and the threshold code of each remaining pixel can be obtained.

[0043] It should be noted that the preset fitting methods include but are not limited to linear fitting, polynomial fitting, Gaussian fitting, Fourier fitting, etc., which are determined according to actual conditions. However, the number of calibration objects needs to be greater than or equal to the number of coefficients of the fitting function to ensure that the fitting results can be obtained.

[0044] Therefore, based on the k-edge characteristics of the calibration object, the corresponding relationship between the photon energy and threshold coding corresponding to each pixel can be obtained. In addition, this method only requires adding calibration objects in hardware without changing the original hardware structure of the equipment, which greatly reduces the energy correction cost and is conducive to industrial productization.

[0045] In some embodiments, as Figure 4 As shown, the threshold encoding corresponding to the k-edge value of each calibration object in multiple calibration objects is obtained, including:

[0046] S201 , for each calibration object, obtain an energy spectrum curve of the corresponding calibration object based on a plurality of preset threshold coding scans, wherein the energy spectrum curve of the calibration object is a discrete curve of photon count values ​​with respect to the threshold coding.

[0047] like Figure 1 As shown, since the threshold code is a digital quantity, its size can be set by a given unit. Therefore, a plurality of different threshold codes can be directly given by the given unit to scan and obtain the energy spectrum curve of each calibration object. There are many ways to give the threshold code. For example, multiple threshold codes can be set in advance, and then a threshold code is given at a certain interval until all threshold codes are given; or a threshold code range can be set in advance, and then within the threshold code range, a threshold code is given at a certain interval according to a preset given step size.

[0048] Taking pixel 1 as an example, the first calibration object is first placed between the detector and the tube. X-ray photons emitted by the tube pass through the calibration object and are incident on the photoelectric conversion unit. After conversion by the photoelectric conversion unit, a first electrical signal is obtained, which eventually enters comparator 1. At the same time, the setting unit sets a threshold code at a preset time. This threshold code is converted by the digital-to-analog converter to obtain a second electrical signal, which enters comparator 1. Comparator 1 compares the first electrical signal and the second electrical signal. Counter 1 adds one to the photon count value based on the comparison result, thereby obtaining the photon count value corresponding to each preset threshold code. This further obtains the energy spectrum curve of the first calibration object corresponding to pixel 1, that is, a discrete curve with the threshold code as the independent variable and the photon count value as the dependent variable. Using the same method, the energy spectrum curve of each of the other calibration objects corresponding to pixel 1 can be obtained.

[0049] For other pixels, the same method as that for pixel 1 is adopted to obtain the energy spectrum curve of each calibration object corresponding to each pixel in the other pixels.

[0050] It is understood that when obtaining the energy spectrum curve of each calibration object corresponding to each pixel in the plurality of pixels, the process can be performed simultaneously. For example, a first calibration object is first placed between the detector and the tube. X-ray photons emitted by the tube pass through the calibration object and are incident on the photoelectric conversion unit. After conversion by the photoelectric conversion unit, a first electrical signal is obtained, which ultimately enters comparator 1, comparator 2, ..., and comparator n. A setting unit sets a threshold code at a preset time interval. The threshold code is converted by a digital-to-analog converter to obtain a second electrical signal, which enters comparator 1, comparator 2, ..., and comparator n. Comparator 1 compares the first electrical signal with the second electrical signal, and counter 1 increments the photon count value based on the comparison result. Simultaneously, comparator 2 compares the first electrical signal with the second electrical signal, and counter 2 increments the photon count value based on the comparison result. ... Simultaneously, comparator n compares the first electrical signal with the second electrical signal, and counter n increments the photon count value based on the comparison result. Ultimately, each pixel obtains the photon count value corresponding to each threshold code, thereby obtaining the energy spectrum curve of the first calibration object. In the same way, each pixel can obtain the energy spectrum curve of each of the other calibration objects.

[0051] S202, obtaining a threshold coding range of a k-edge value of a corresponding calibration object.

[0052] S203 , obtaining the threshold code corresponding to the mutation value of the energy spectrum curve of the corresponding calibration object within the threshold code range, and obtaining the threshold code corresponding to the k-edge value of each calibration object.

[0053] Specifically, since the energy spectrum curve is a relationship curve of the photon count value with respect to the threshold code, and based on the k-edge characteristics of the calibration object, it can be known that in the energy spectrum curve of the calibration object, the photon count value at the k-edge value of the calibration object will undergo a mutation. Therefore, based on the mutation of the photon count value, the threshold code corresponding to the k-edge value of the calibration object can be determined. For example, the threshold code corresponding to the photon count value with obvious mutation is used as the threshold code corresponding to the k-edge value of the calibration object. Therefore, based on the energy spectrum curve, the threshold code corresponding to the k-edge value of each calibration object corresponding to each pixel can be obtained.

[0054] It is understood that when the calibration object is determined, the threshold code range corresponding to its k-edge value can be determined. Therefore, when determining the threshold code corresponding to its k-edge value based on the energy spectrum curve of the calibration object, the threshold code range can be determined based on the threshold code range, thereby improving the accuracy of the threshold code determination. As an implementation method, the threshold code range within which the k-edge value of the calibration object falls can be predetermined, and the threshold code range and the calibration object name can be stored in correspondence, so that it can be directly called in actual use.

[0055] After obtaining the threshold coding range, the energy spectrum curve of the corresponding calibration object within the threshold coding range can be fitted to obtain a fitting curve, and the threshold coding corresponding to the photon count mutation value in the fitting curve can be obtained to obtain the threshold coding corresponding to the k-edge value of each calibration object.

[0056] Specifically, taking the first type of calibration object as an example, the threshold coding range of the k-edge value of the calibration object can be read from the system. Then, after obtaining the energy spectrum curve of the calibration object, since the energy spectrum curve is a discrete curve with the threshold coding as the independent variable and the photon count value as the dependent variable, the energy spectrum curve of the calibration object within the threshold coding range can be fitted to obtain a fitting curve. Then, the photon count value that has undergone a mutation, that is, the photon count mutation value, is obtained from the fitting curve, and the threshold coding corresponding to the photon count mutation value is used as the threshold coding corresponding to the k-edge value of the calibration object. In the same way, the threshold coding corresponding to the k-edge value of other calibration objects can be obtained. Since the threshold coding corresponding to the k-edge value of the calibration object is obtained within the threshold coding range where the k-edge value of the calibration object is located, noise interference can be reduced, thereby ensuring the accuracy of the threshold coding acquisition.

[0057] It should be noted that the fitting methods in the above process include but are not limited to polynomial fitting method, Gaussian fitting method, Fourier fitting method, etc.

[0058] Therefore, confirming the threshold code corresponding to the k-edge value from the energy spectrum curve based on the threshold code range of the k-edge value of the calibration object can effectively improve the accuracy of the threshold code corresponding to the k-edge value of the calibration object, thereby helping to improve the accuracy of energy correction.

[0059] It is understandable that the k-edge characteristics of some calibration objects are not particularly obvious or are affected by factors such as the inherent differences between pixels, which may make the accuracy of the threshold encoding corresponding to the k-edge value of the calibration object low. Therefore, the k-edge characteristics of the calibration object can be highlighted from the curve in a certain way, thereby improving the accuracy of the threshold encoding corresponding to the k-edge value.

[0060] As a way to implement Figure 5 As shown, the threshold encoding corresponding to the k-edge value of each calibration object in multiple calibration objects is obtained, including:

[0061] S301 , for each calibration object, obtain an energy spectrum curve and an air energy spectrum curve of the corresponding calibration object based on multiple preset threshold coding scans, wherein the energy spectrum curve of the calibration object and the air energy spectrum curve are both discrete curves of photon count values ​​with respect to the threshold coding.

[0062] It should be noted that the air energy spectrum curve is the energy spectrum curve obtained by scanning when there is only air, no additional material between the detector and the tube. Taking pixel 1 as an example, the X-ray photons emitted by the tube pass through the air and are incident on the photoelectric conversion unit. After conversion by the photoelectric conversion unit, a first electrical signal is generated, which ultimately enters comparator 1. At the same time, the setting unit sets a threshold code at a preset time. This threshold code is converted by the digital-to-analog converter to a second electrical signal, which enters comparator 1. Comparator 1 compares the first and second electrical signals. Counter 1 increments the photon count value based on the comparison result, thereby obtaining the photon count value corresponding to each preset threshold code. This further generates the air energy spectrum curve corresponding to pixel 1, i.e., a discrete curve with the threshold code as the independent variable and the photon count value as the dependent variable.

[0063] For other pixels, the same method as for pixel 1 is used to obtain the air energy spectrum curve corresponding to each of the other pixels. It is understood that when obtaining the air energy spectrum curve corresponding to each of the multiple pixels, it can be performed simultaneously. The specific process can be referred to the aforementioned description of simultaneously obtaining the energy spectrum curve of each calibration object for multiple pixels, and will not be repeated here.

[0064] S302 , processing the energy spectrum curve of the corresponding calibration object using the air energy spectrum curve to obtain a discrete curve of the attenuation value parameter and the threshold code corresponding to each calibration object.

[0065] Specifically, the energy spectrum curve of each calibration object can be corrected using the air energy spectrum curve, so that the k-edge characteristics of the calibration object can be highlighted from the corresponding discrete curve after correction, so as to obtain a more accurate threshold encoding corresponding to the k-edge value of the calibration object.

[0066] As an example, the energy spectrum curve of the corresponding calibration object is processed using the air energy spectrum curve to obtain a discrete curve of the attenuation value parameter and the threshold code corresponding to each calibration object, including: obtaining the ratio relationship between the air energy spectrum curve and the energy spectrum curve of the corresponding calibration object; taking the logarithm and derivative calculation of the ratio relationship in turn to obtain a discrete curve of the attenuation value derivative and the threshold code corresponding to each calibration object. That is, the discrete curve of the attenuation value derivative and the threshold code corresponding to each calibration object is shown in the following formula (1):

[0067]

[0068] Among them, P(Th) represents the discrete curve of the attenuation value derivative and threshold encoding corresponding to a certain calibration object, I Air (Th) represents the air energy spectrum curve, I Metal(Th) represents the energy spectrum curve of a calibration object, and Th represents the threshold code. This formula primarily performs air correction on the energy spectrum curve of the calibration object to obtain an attenuation value, and then derives the attenuation value to obtain a corresponding discrete curve. This discrete curve can highlight the characteristics of the calibration object near the k-edge value, thereby obtaining a more accurate threshold code corresponding to the k-edge value based on this discrete curve.

[0069] As another example, the energy spectrum curve of the corresponding calibration object is processed using the air energy spectrum curve to obtain a discrete curve of the attenuation value parameter and the threshold code corresponding to each calibration object, including: obtaining the ratio relationship between the air energy spectrum curve and the energy spectrum curve of the corresponding calibration object; and sequentially differentiating and taking the inverse of the ratio relationship to obtain a discrete curve of the attenuation value differential and the threshold code corresponding to each calibration object. That is, the discrete curve of the attenuation value differential and the threshold code corresponding to each calibration object is shown in the following formula (2):

[0070]

[0071] Among them, P'(Th) represents the discrete curve of the attenuation value differential and threshold encoding corresponding to a certain calibration object, I Air (Th) represents the air energy spectrum curve, I Metal (Th) represents the energy spectrum curve of a calibration object, and Th represents the threshold code. This formula primarily performs air correction on the energy spectrum curve of the calibration object to obtain an attenuation value, and then differentiates the attenuation value to obtain a corresponding discrete curve. This discrete curve can highlight the characteristics of the calibration object near the k-edge value, thereby obtaining a more accurate threshold code corresponding to the k-edge value based on this discrete curve.

[0072] Therefore, the characteristics of the calibration object near the k-edge value can be highlighted from the curve in different ways, so as to obtain a more accurate threshold encoding corresponding to the k-edge value of the calibration object.

[0073] S303: Obtain the threshold coding range of the k-edge value of the corresponding calibration object.

[0074] S304 , obtaining the threshold code corresponding to the mutation value of the discrete curve of the attenuation value parameter of the corresponding calibration object and the threshold code within the threshold code range, and obtaining the threshold code corresponding to the k-edge value of each calibration object.

[0075] Specifically, because the discrete curve of the attenuation value parameter and the threshold code obtained based on air correction can highlight the characteristics of the calibration object at the k-edge value, the threshold code corresponding to the k-edge value of the calibration object can be determined based on this discrete curve. As an implementation method, the threshold code range of the k-edge value of the corresponding calibration object can be first obtained. Then, the discrete curve of the attenuation value parameter and the threshold code within the threshold code range is fitted to obtain a fitting curve. The threshold code corresponding to the extreme value of the attenuation value parameter in the fitting curve is obtained to obtain the threshold code corresponding to the k-edge value of each calibration object.

[0076] Specifically, taking the first type of calibration object as an example, the threshold coding range of the k-edge value of the calibration object can be read from the system. Then, after obtaining the discrete curve of the attenuation value parameter and threshold coding of the calibration object, the discrete curve of the attenuation value parameter and threshold coding of the calibration object within the threshold coding range is fitted to obtain a fitting curve. Then, the extreme value of the attenuation value parameter is obtained from the fitting curve, and the threshold coding corresponding to the extreme value is used as the threshold coding corresponding to the k-edge value of the calibration object. For example, when the discrete curve is a discrete curve of the attenuation value derivative and the threshold code, the fitting curve obtained by fitting the discrete curve within the threshold code range will present a valley of a Gaussian curve near the k-edge value of the calibration object, so the extreme value obtained is the minimum value of the attenuation value derivative within the threshold code range, and the threshold code corresponding to the minimum value is the threshold code corresponding to the k-edge value of the calibration object; when the discrete curve is a discrete curve of the attenuation value differential and the threshold code, the fitting curve obtained by fitting the discrete curve within the threshold code range will present a peak of a Gaussian curve near the k-edge value of the calibration object, so the extreme value obtained is the maximum value of the attenuation value differential within the threshold code range, and the threshold code corresponding to the maximum value is the threshold code corresponding to the k-edge value of the calibration object.

[0077] In the same way, the threshold code corresponding to the k-edge value of each calibration object in other calibration objects can be obtained. It should be noted that the fitting method in the above process includes but is not limited to polynomial fitting method, Gaussian fitting method, Fourier fitting method, etc.

[0078] Therefore, by correcting, deriving or differentiating the energy spectrum curve of the calibration object through the air energy spectrum curve, not only can the k-edge characteristics of the calibration object be highlighted from the curve to improve the accuracy of obtaining the threshold code corresponding to the k-edge value of the calibration object, but also the influence of the tube output energy spectrum on the energy correction can be eliminated; at the same time, the threshold code corresponding to the k-edge value can be confirmed from the fitting curve in combination with the threshold code range of the k-edge value of the calibration object, which can further improve the accuracy of the threshold code corresponding to the k-edge value, thereby facilitating improving the accuracy of energy correction.

[0079] It should be noted that when performing air correction on the energy spectrum curve of the calibration object, the first voltage when scanning each calibration object and the second voltage when scanning the air must be the same, while the first current when scanning each calibration object and the second current when scanning the air can be the same or different, that is, Figure 1 The voltage applied to both ends of the bulb is the same, but the current flowing through the bulb can be the same or different. When the first current and the second current are different, current correction can be performed.

[0080] As an implementation method, obtaining the threshold code corresponding to the k-edge value of each calibration object among multiple calibration objects also includes: obtaining a first current when scanning the corresponding calibration object and a second current when scanning the air; when the first current and the second current are different, calculating the ratio of the first current to the second current to obtain a ratio coefficient, and correcting the discrete curve of the attenuation value parameter corresponding to the corresponding calibration object and the threshold code according to the ratio coefficient.

[0081] For example, the discrete curve of the attenuation value parameter and threshold encoding corresponding to each calibration object is shown in the following formula (3) or formula (4):

[0082]

[0083]

[0084] Among them, P(Th) represents the discrete curve of the attenuation value derivative and threshold encoding corresponding to a certain calibration object, I Air (Th) represents the air energy spectrum curve, I Metal (Th) represents the energy spectrum curve of a certain calibration object, Th represents the threshold code, P'(Th) represents the discrete curve of the attenuation value differential and threshold code corresponding to a certain calibration object, C Metal Indicates the first current when scanning the calibration object, C Air It should be noted that when the first current and the second current are the same, the ratio between the two is 1.

[0085] Therefore, when the currents for scanning the calibration object and the air are different, the calculated attenuation value can be made consistent with its physical meaning through current correction.

[0086] In the above embodiment, the threshold code corresponding to the k-edge value of each calibration object can be obtained based on a variety of methods, and when obtaining the threshold code corresponding to the k-edge value of each calibration object, the accuracy of the threshold code acquisition can be improved according to the threshold code range in which the k-edge value of the calibration object is located. At the same time, based on air correction and derivation or differentiation, the k-edge characteristics of the calibration object can be highlighted from the curve, thereby further improving the accuracy of the threshold code acquisition, which is conducive to improving the accuracy of energy correction.

[0087] The following describes how to determine the reference correspondence between multiple pixels with reference to specific examples.

[0088] As a way to implement Figure 6 As shown, determining a reference correspondence relationship of multiple pixels includes:

[0089] S401 , obtaining an energy spectrum curve of each pixel based on a plurality of preset threshold coding scans, wherein the energy spectrum curve is a discrete curve of photon count values ​​with respect to the threshold coding.

[0090] It should be noted that the energy spectrum curve of each pixel can be obtained by scanning any substance such as air, metal, or other substances. The specific process can be referred to above and will not be repeated here. After scanning and obtaining the energy spectrum curve of each pixel, the energy spectrum curve of each pixel can be normalized. The normalization process can eliminate the impact of the longitudinal inconsistency of the energy spectrum curves of multiple pixels on the energy spectrum consistency correction.

[0091] S402 , using the correspondence between the photon energy corresponding to each pixel and the threshold code, convert the energy spectrum curve of the corresponding pixel to obtain an energy spectrum conversion curve of the corresponding pixel, wherein the energy spectrum conversion curve is a discrete curve of the photon count value with respect to the photon energy.

[0092] Specifically, since the energy spectrum curve defines the relationship between the photon count value and the threshold code, and the correspondence between the photon energy and the threshold code defines the relationship between the photon energy and the threshold code, the energy spectrum curve can be converted using the correspondence between the photon energy and the threshold code to obtain a discrete curve between the photon energy and the photon count value, namely the energy conversion curve, so that the energy spectrum conversion curve of each pixel can be obtained, and then the reference correspondence can be determined based on the energy spectrum conversion curves of multiple pixels.

[0093] S403 , performing an average or weighted calculation on the energy spectrum conversion curves of the plurality of pixels to obtain a reference corresponding relationship, wherein the reference corresponding relationship is a curve of the relationship between the photon count value and the photon energy.

[0094] It should be noted that the energy spectrum curve for each pixel can be obtained by scanning at least one arbitrary substance. Different substances correspond to different energy spectrum curves. When multiple arbitrary substances are present, each arbitrary substance corresponds to a reference correspondence relationship. In other words, when scanning a single substance, a corresponding energy spectrum curve is obtained for each pixel, and ultimately a reference correspondence relationship is obtained. When scanning multiple substances, multiple corresponding energy spectrum curves are obtained for each pixel, and ultimately multiple reference correspondence relationships are obtained.

[0095] For example, when Figure 1 When the device is used only to scan a specific metal, the metal can be placed between the detector and the tube. A threshold code is assigned at preset intervals by a given unit, so that each pixel can obtain an energy spectrum curve of the metal. Then, the energy spectrum curve of the corresponding pixel is converted using the corresponding relationship between the photon energy corresponding to each pixel and the threshold code to obtain an energy spectrum conversion curve for the corresponding pixel. The energy spectrum conversion curves of multiple pixels are averaged or weighted to obtain a reference correspondence relationship for the metal for the multiple pixels. When performing the weighted calculation, assuming that five energy spectrum conversion curves are obtained, if one energy spectrum conversion curve differs significantly from the other four energy spectrum conversion curves, the weights of the other four energy spectrum conversion curves can be set larger, while the weight of the one energy spectrum conversion curve can be set smaller, thereby making the reference correspondence relationship more accurate.

[0096] For example, when Figure 1 When the device is used to scan a human body, since the human body is composed of water, flesh, bone, and the scanning is performed in air, it can scan a variety of substances, thereby making the obtained reference correspondence more consistent with actual conditions. The specific acquisition process may include: first, placing water between the detector and the tube, and using a given unit to assign a threshold code at preset intervals so that each pixel can obtain a water energy spectrum curve. Then, using the correspondence between the photon energy corresponding to each pixel and the threshold code, the water energy spectrum curve of the corresponding pixel is converted to obtain a water energy spectrum conversion curve for the corresponding pixel. The water energy spectrum conversion curves of multiple pixels are averaged or weighted to obtain reference correspondences for multiple pixels for water. Using the same method, reference correspondences for multiple pixels for flesh, bone, and air can be obtained in sequence.

[0097] In the above embodiment, a reference correspondence can be obtained by averaging or weighting the energy spectrum conversion curves of all pixels, and the energy spectrum conversion curve is obtained by converting the energy spectrum curve of each pixel by the correspondence between the photon energy corresponding to each pixel and the threshold encoding. Therefore, the obtained reference correspondence does not affect the original energy correction purpose of each pixel, so that the reference correspondence can meet the purpose of energy correction of each pixel, thereby reducing the energy spectrum inconsistency between pixels while achieving the original energy correction purpose, and the obtained reference correspondence is more in line with the actual characteristics of the equipment, and the energy correction result is more accurate.

[0098] The following describes how to optimize the correspondence between the photon energy corresponding to each pixel and the threshold code based on the reference correspondence relationship with reference examples.

[0099] As an implementation method, the correspondence between the photon energy corresponding to each pixel and the threshold code is optimized according to the reference correspondence, including: adjusting the coefficients in the correspondence between the photon energy corresponding to each pixel and the threshold code, until the energy spectrum conversion curve of each pixel obtained by converting the energy spectrum curve of the corresponding pixel using the adjusted correspondence between the photon energy and the threshold code is consistent with the reference correspondence. It should be noted that the curve consistency can be the shape consistency of the curve. Since the influence of the longitudinal inconsistency of the energy spectrum curves of multiple pixels on the energy spectrum consistency correction is eliminated by normalization processing, it is sufficient to ensure the horizontal consistency of the energy spectrum curves of multiple pixels based on the reference correspondence.

[0100] Specifically, it is assumed that the correspondence between the photon energy corresponding to each pixel and the threshold code is a linear relationship, which is expressed as E=k*Th+b, where E represents the photon energy, Th represents the threshold code, and k and b are coefficients. When optimizing the correspondence between the photon energy corresponding to each pixel and the threshold code, the energy spectrum curve of each pixel can be first converted using this correspondence to obtain a corresponding energy spectrum conversion curve, which is then compared with the reference correspondence to determine whether the energy spectrum conversion curve of each pixel is consistent with the reference correspondence, that is, whether the shapes of the energy spectrum conversion curves of multiple pixels are relatively consistent. If not, the coefficients k and b corresponding to the multiple pixels are adjusted (the specific adjustment method is not limited here), and then the energy spectrum curve of each pixel is converted using the adjusted correspondence to obtain a corresponding energy spectrum conversion curve, which is then compared with the reference correspondence to determine whether the energy spectrum conversion curve of each pixel is consistent with the reference correspondence. If not, the adjustment is continued until it is determined that the energy spectrum conversion curve of each pixel is consistent with the reference correspondence.

[0101] It should be noted that there are multiple ways to determine whether the energy spectrum conversion curve of each pixel is consistent with the reference correspondence. As an implementation method, determining whether the energy spectrum conversion curve of each pixel is consistent with the reference correspondence includes: obtaining the deviation between the energy spectrum conversion curve of each pixel and the reference correspondence; determining the total deviation of multiple pixels based on the deviation of each pixel; and when the total deviation is the minimum value, determining that the energy spectrum conversion curve of each pixel is consistent with the reference correspondence.

[0102] Optionally, the total deviation of multiple pixels is determined based on the deviation of each pixel, including: adding the squares of the deviations corresponding to each pixel to obtain the total deviation; or adding the absolute values ​​of the deviations corresponding to each pixel to obtain the total deviation.

[0103] That is, by adjusting the coefficients in the correspondence between the photon energy and the threshold code corresponding to each pixel, such as k and b, the deviation between the energy spectrum conversion curve obtained by converting the energy spectrum curve of the corresponding pixel based on the adjusted correspondence between the photon energy and the threshold code and the reference correspondence is obtained. is the minimum value, or When I is the minimum value, the energy spectrum conversion curve of each pixel is determined to be consistent with the reference corresponding relationship, thereby optimizing the corresponding relationship between the photon energy and the threshold code corresponding to each pixel, and obtaining the target corresponding relationship between the photon energy and the threshold code of each pixel, that is, the optimal energy correction result. i (E) represents the energy spectrum conversion curve corresponding to the i-th pixel, Indicates the reference correspondence.

[0104] It should be noted that or The objective function is only used to evaluate the consistency between the energy spectrum conversion curves of multiple pixels and the reference correspondence, and the expression of the objective function is not limited to this. For example, it can also be the average value of the deviation between the energy spectrum conversion curves of multiple pixels and the reference correspondence, etc. There is no specific restriction here.

[0105] It should be noted that the above example is used as an example when there is only one reference correspondence relationship. Based on the above analysis, it can be seen that the reference correspondence relationship can also include multiple ones. At this time, judging whether the energy spectrum conversion curve of each pixel is consistent with the reference correspondence relationship also includes: obtaining the total deviation corresponding to each arbitrary substance; summing the total deviations corresponding to multiple arbitrary substances, and when the sum result is the minimum value, determining that the energy spectrum conversion curve of each pixel is consistent with the reference correspondence relationship.

[0106] Specifically, taking water, meat, bones and air as examples, the reference correspondences obtained based on the four substances are recorded as When optimizing the relationship between the photon energy and threshold coding for each pixel, the objective function can be:

[0107] , where I Wai (E) represents the energy spectrum conversion curve of the i-th pixel for water, which is obtained by converting the energy spectrum curve of the i-th pixel for water using the corresponding relationship between its photon energy and the threshold code; I Mei (E) represents the energy spectrum conversion curve of the i-th pixel for meat, specifically, the energy spectrum curve of the i-th pixel for meat is converted using the corresponding relationship between its photon energy and the threshold code; I Boi (E) represents the energy spectrum curve of the i-th pixel for the bone, which is obtained by converting the energy spectrum curve of the i-th pixel for the bone using the corresponding relationship between its photon energy and the threshold code; I Airi (E) represents the energy spectrum curve for the i-th pixel relative to air. Specifically, it is obtained by converting the energy spectrum curve for the i-th pixel relative to air using the correspondence between its photon energy and threshold code. By adjusting the coefficients in the correspondence between the photon energy and threshold code of multiple pixels until the reference correspondence reaches a minimum value, the coefficients are stopped from being adjusted. At this point, the coefficients are optimized.

[0108] It should be noted that, since the proportions of various substances in the human body are different, when determining the objective function, corresponding weights can also be set for the total deviation corresponding to each substance. For example, the objective function can be set to Among them, K1, K2, K3 and K4 are weights, and the specific sizes can be determined based on the proportions of various substances, and K1+K2+K3+K4=1, so that the objective function is more in line with the actual situation.

[0109] Therefore, by optimizing the correspondence between the photon energy and the threshold coding of multiple pixels based on one or more reference correspondences corresponding to one or more substances, not only can the energy spectrum consistency of multiple pixels be ensured, but it can also be more in line with actual conditions.

[0110] In the above embodiment, by optimizing the correspondence between the photon energy corresponding to each pixel and the threshold code based on the reference correspondence, the energy spectrum consistency between pixels can be ensured.

[0111] The following describes how to perform energy correction in general with reference to specific examples.

[0112] First, the corresponding relationship between the photon energy corresponding to each pixel in the plurality of pixels and the threshold code is obtained.

[0113] like Figure 1As shown, the first calibration object is placed between the detector and the tube, and then multiple preset threshold codes are traversed to obtain the energy spectrum curve of each pixel for the first calibration object. Next, the second calibration object is placed between the detector and the tube, and multiple preset threshold codes are traversed to obtain the energy spectrum curve of each pixel for the second calibration object. This process is repeated until the energy spectrum curve of each pixel for the mth calibration object is obtained. Then, when there is only air between the detector and the tube, multiple preset threshold codes are traversed to obtain the energy spectrum curve of each pixel for air.

[0114] Next, for pixel 1, the air energy spectrum curve of pixel 1 is first used to correct and take the logarithmic derivative of the energy spectrum curve of the first calibration object corresponding to pixel 1 according to the above formula (1) or formula (3), and the discrete curve P(Th) of the attenuation value derivative and threshold encoding corresponding to the first calibration object is obtained. Metal11 , and according to the threshold coding range of the estimated k-edge value of the first calibration object, fit the discrete curve P(Th) of the attenuation value derivative and threshold coding within the range Metal11 , and the threshold code corresponding to the minimum value of the fitting curve is used as the threshold code corresponding to the k-edge value of the first calibration object; at the same time, using the air energy spectrum curve of pixel 1, the energy spectrum curve of the second calibration object corresponding to pixel 1 is corrected and logarithmically derived according to the above formula (1) or formula (3), and the discrete curve P(Th) of the attenuation value derivative and threshold code corresponding to the second calibration object is obtained. Metal12 Then, according to the threshold coding range of the estimated k-edge value of the second calibration object, the discrete curve P(Th) of the attenuation value derivative and threshold coding in the range is fitted. Metal12 The threshold code corresponding to the minimum value of the fitted curve is used as the threshold code corresponding to the k-edge value of the second calibration object; and so on, until the threshold code corresponding to the k-edge value of the m-th calibration object is obtained. It should be noted that the method of fitting the relationship curve includes but is not limited to polynomial fitting, Gaussian fitting, and Fourier fitting.

[0115] Then, using the threshold code corresponding to the k-edge value of each calibration object as the independent variable and the k-edge value of the calibration object as the dependent variable, the corresponding relationship between the k-edge value and the threshold code of pixel 1 is fitted, that is, the corresponding relationship between the photon energy of pixel 1 and the threshold code is E1=f(Th), where E represents the photon energy and Th represents the threshold code. It should be noted that the method of fitting the functional relationship includes but is not limited to linear fitting, polynomial fitting, Gaussian fitting, and Fourier fitting.

[0116] Next, for pixel 2, the same method as pixel 1 is used to obtain the corresponding relationship between the photon energy and the threshold code corresponding to pixel 2, E2 = f(Th). And so on, until the corresponding relationship between the photon energy and the threshold code corresponding to the nth pixel, E n =f(Th).

[0117] Second, the reference correspondence of multiple pixels is determined, and the correspondence between the photon energy and the threshold code corresponding to each pixel is optimized according to the reference correspondence to obtain the target correspondence between the photon energy and the threshold code of each pixel, that is, the energy correction result.

[0118] Let’s take the reference correspondence relationship as an example. Figure 1 As shown, when there is only air between the detector and the tube, the air energy spectrum curve of each pixel is obtained by traversing multiple preset threshold codes, which are respectively denoted as I Air1 (Th), I Air2 (Th),...,I Airn (Th), and then normalize the air energy spectrum curve of each pixel to obtain the normalized air energy spectrum curve, which is recorded as I Air-Nor1 (Th), I Air-Nor2 (Th),...,I Air-Norn (Th).

[0119] Next, for pixel 1, the normalized air energy spectrum curve I is calculated using the corresponding relationship between photon energy and threshold code E1 = f(Th). Air-Nor1 (Th) is converted to obtain the energy spectrum conversion curve I Air-Nor1 (E); For pixel 2, the normalized air energy spectrum curve I is obtained by using the corresponding relationship between photon energy and threshold coding E2 = f(Th) Air-Nor2 (Th) is converted to obtain the energy spectrum conversion curve I Air-Nor2 (E); and so on, until the energy spectrum conversion curve I of pixel n is obtained Air-Norn (E). Then, the energy spectrum conversion curve I Air-Nor1 (E), I Air-Nor2 (Th),...,I Air-Norn (E) Calculate the average value to obtain the reference correspondence

[0120] Next, the functional form of the correspondence between the photon energy and the threshold code of each pixel is kept unchanged, and its coefficients are optimized. For example, when the correspondence between the photon energy and the threshold code is a linear relationship and the expression is E=k*Th+b, the coefficients k and b are optimized so that the air energy spectrum curve I of each pixel is Airi (Th) is converted into energy spectrum conversion curve I based on the corresponding relationship between the corresponding photon energy and threshold codingAiri (E) Correspondence between the back and reference As consistent as possible, for example, the objective function can be set to or When the value of the objective function is the minimum, it means that the air energy spectrum curve of each pixel is consistent with the reference correspondence after being converted into the energy spectrum conversion curve. At this time, the correspondence between the photon energy corresponding to each pixel and the threshold code is the optimal function relationship.

[0121] Let’s take the case where the reference correspondence includes two. Figure 1 As shown, when there is only air between the detector and the tube, the air energy spectrum curve of each pixel is obtained by traversing multiple preset threshold codes, which are respectively denoted as I Air1 (Th), I Air2 (Th),...,I Airn (Th), and then normalize the air energy spectrum curve of each pixel to obtain the normalized air energy spectrum curve, which is recorded as I Air-Nor1 (Th), I Air-Nor2 (Th),...,I Air-Norn (Th); When there is metal material A between the detector and the tube, the energy spectrum curve of the metal material corresponding to each pixel is obtained by traversing multiple preset threshold codes, which are respectively recorded as I MetalA1 (Th), I MetalA2 (Th),...,I MetalAn (Th), and then the energy spectrum curve of the metal substance corresponding to each pixel is normalized to obtain the normalized energy spectrum curve of the metal substance, which is recorded as I MetalA-Nor1 (Th), I MetalA-Nor2 (Th),...,I MetalA-Norn (Th).

[0122] Next, for pixel 1, the normalized air energy spectrum curve I is calculated using the corresponding relationship between photon energy and threshold code E1 = f(Th). Air-Nor1 (Th) is converted to obtain the energy spectrum conversion curve I Air-Nor1 (E); For pixel 2, the normalized air energy spectrum curve I is obtained by using the corresponding relationship between photon energy and threshold coding E2 = f(Th) Air-Nor2 (Th) is converted to obtain the energy spectrum conversion curve I Air-Nor2 (E); and so on, until the energy spectrum conversion curve I of pixel n is obtained Air-Norn (E). Then, the energy spectrum conversion curve I Air-Nor1 (E), I Air-Nor2 (Th),...,I Air-Norn (E) Calculate the average value to obtain the reference correspondence

[0123] Similarly, for pixel 1, the normalized energy spectrum curve of the metal material I is obtained by using the corresponding relationship between photon energy and threshold code E1 = f(Th). MetalA-Nor1 (Th) is converted to obtain the energy spectrum conversion curve I MetalA-Nor1 (E); For pixel 2, the normalized energy spectrum curve of the metal material I is obtained by using the corresponding relationship between photon energy and threshold coding E2 = f(Th) MetalA-Nor2 (Th) is converted to obtain the energy spectrum conversion curve I MetalA-Nor2 (E); and so on, until the energy spectrum conversion curve I of pixel n is obtained MetalA-Norn (E). Then, the energy spectrum conversion curve I MetalA-Nor1 (E), I MetalA-Nor2 (E), ..., I MetalA-Norn (E) Calculate the average value to obtain the reference correspondence

[0124] Next, the functional form of the correspondence between the photon energy and the threshold code of each pixel is kept unchanged, and its coefficients are optimized. For example, when the correspondence between the photon energy and the threshold code is a linear relationship and the expression is E=k*Th+b, the coefficients k and b are optimized so that the air energy spectrum curve I of each pixel is Airi (Th) is converted into energy spectrum conversion curve I based on the corresponding relationship between the corresponding photon energy and threshold coding Airi (E) Correspondence between the back and reference As consistent as possible, and make the energy spectrum curve of the metal material corresponding to each pixel I Metali (Th) is converted into energy spectrum conversion curve I based on the corresponding relationship between the corresponding photon energy and threshold coding Metali (E) Correspondence between the back and reference As consistent as possible. For example, the objective function can be set to or When the value of the objective function is the minimum, it means that the air energy spectrum curve of each pixel is consistent with the reference correspondence after being converted into the energy spectrum conversion curve. At this time, the correspondence between the photon energy corresponding to each pixel and the threshold code is the optimal function relationship.

[0125] In the above embodiment, with the goal of energy spectrum consistency between pixels, the correspondence between the photon energy corresponding to each pixel and the threshold code is optimized, which can ensure the consistency of the energy spectrum between pixels; the correspondence between the photon energy corresponding to each pixel and the threshold code is obtained based on the k-edge characteristics of the material, which can achieve the purpose of correcting each pixel, and during optimization, the reference correspondence is obtained based on the correspondence between the photon energy corresponding to each pixel and the threshold code, so that the energy spectrum inconsistency between pixels can be reduced while ensuring the purpose of correcting each pixel; when obtaining the correspondence between the photon energy corresponding to each pixel and the threshold code, the energy spectrum curve of the metal material is also corrected using the air energy spectrum curve, etc., thereby ensuring the accuracy of the functional relationship and thus ensuring the accuracy of the energy correction.

[0126] To sum up, according to the energy correction method of an embodiment of the present invention, the correspondence between the photon energy corresponding to each pixel and the threshold code is optimized according to the reference correspondence, which can reduce the energy spectrum inconsistency between pixels, and the correspondence between the photon energy corresponding to each pixel and the threshold code can be corrected based on the original energy correction purpose, thereby reducing the energy spectrum inconsistency between pixels while achieving the original energy correction purpose.

[0127] Corresponding to the above embodiment, an embodiment of the present invention further provides a computer-readable storage medium.

[0128] Figure 7 FIG. 1 is a schematic diagram of a computer-readable storage medium according to an embodiment of the present invention.

[0129] like Figure 7 As shown, the computer-readable storage medium 100 stores an energy correction program 110 , which implements the aforementioned energy correction method when executed by a processor.

[0130] According to the computer-readable storage medium of the embodiment of the present invention, based on the aforementioned energy correction method, it is possible to reduce the energy spectrum inconsistency between pixels while achieving the original energy correction purpose.

[0131] Corresponding to the above embodiment, an embodiment of the present invention further provides a photon counting CT device.

[0132] like Figure 1 As shown, the photon counting CT device 500 includes: a photoelectric conversion unit 510, a readout unit 520 and a setting unit 530, wherein:

[0133] The photoelectric conversion unit 510 is used to convert photons into a first electrical signal. Optionally, the device 500 further includes a rectification and filtering unit (not specifically shown in the figure) for performing rectification and filtering on the first electrical signal.

[0134] The readout unit 520 includes multiple pixels (such as pixel 1, pixel 2,..., pixel n), each pixel includes a comparator and a counter (such as pixel 1 includes comparator 1 and counter 1, pixel 2 includes comparator 2 and counter 2,..., pixel n includes comparator n and counter n), the comparator is used to compare the first electrical signal with the second electrical signal corresponding to the corresponding threshold code, and the counter is used to increase the photon count value by one when the first electrical signal is greater than the second electrical signal.

[0135] The given unit 530 is used to convert the energy threshold setting value of the corresponding pixel into the threshold code of the corresponding pixel based on the energy correction result of each pixel, and convert the threshold code of the corresponding pixel into a second electrical signal, wherein the energy correction result is obtained by the energy correction method of an embodiment of the present invention.

[0136] As an implementation method, the photon counting CT device also includes an energy correction result acquisition unit for obtaining energy correction results. Specifically, the energy correction result acquisition unit is used to: obtain, for each pixel, the threshold code corresponding to the k-edge value of each of the multiple calibration objects, and fit the k-edge values ​​of the multiple calibration objects and the corresponding threshold codes to obtain the corresponding relationship between the photon energy corresponding to each pixel and the threshold code.

[0137] As an implementation method, the energy correction result acquisition unit is used to: for each calibration object, obtain the energy spectrum curve of the corresponding calibration object based on multiple preset threshold coding scans, or the energy spectrum curve of the corresponding calibration object and the air energy spectrum curve, wherein the energy spectrum curve of the calibration object and the air energy spectrum curve are both discrete curves of the photon counting value with respect to the threshold coding; use the air energy spectrum curve to process the energy spectrum curve of the corresponding calibration object to obtain a discrete curve of the attenuation value parameter and the threshold coding corresponding to each calibration object; obtain the threshold coding corresponding to the mutation value of the energy spectrum curve of the corresponding calibration object within the threshold coding range, or the threshold coding corresponding to the mutation value of the discrete curve of the attenuation value parameter of the corresponding calibration object and the threshold coding, to obtain the threshold coding corresponding to the k-edge value of each calibration object.

[0138] As an implementation method, the energy correction result acquisition unit is used to: obtain the first current when scanning the corresponding calibration object and the second current when scanning the air; when the first current and the second current are different, calculate the ratio of the first current to the second current to obtain a ratio coefficient; and correct the discrete curve of the attenuation value parameter corresponding to the corresponding calibration object and the threshold encoding according to the ratio coefficient.

[0139] As an implementation method, in the correspondence between the photon energy corresponding to each pixel and the threshold code, the threshold code corresponding to the photon energy is the independent variable and the photon energy is the dependent variable.

[0140] As an implementation method, the energy correction result acquisition unit is used to: obtain an energy spectrum curve of each pixel based on multiple preset threshold coding scans, wherein the energy spectrum curve is a discrete curve of the photon count value with respect to the threshold coding; use the correspondence between the photon energy corresponding to each pixel and the threshold coding to convert the energy spectrum curve of the corresponding pixel to obtain an energy spectrum conversion curve of the corresponding pixel, wherein the energy spectrum conversion curve is a discrete curve of the photon count value with respect to the photon energy; average or weightedly calculate the energy spectrum conversion curves of multiple pixels to obtain a reference correspondence, wherein the reference correspondence is a curve of the relationship between the photon count value and the photon energy.

[0141] As an implementation method, the energy correction result acquisition unit is used to adjust the coefficients in the correspondence between the photon energy corresponding to each pixel and the threshold code until the energy spectrum conversion curve of each pixel obtained by converting the energy spectrum curve of the corresponding pixel using the adjusted correspondence between the photon energy and the threshold code is consistent with the reference correspondence.

[0142] As an implementation method, the energy correction result acquisition unit is used to: obtain the deviation between the energy spectrum conversion curve of each pixel and the reference corresponding relationship; determine the total deviation of multiple pixels based on the deviation of each pixel; when the total deviation is the minimum value, determine that the energy spectrum conversion curve of each pixel is consistent with the reference corresponding relationship.

[0143] As an implementation method, the energy spectrum curve of each pixel is obtained by scanning at least one arbitrary substance, wherein, when the arbitrary substances include multiple substances, each arbitrary substance corresponds to a reference correspondence relationship. As an implementation method, the energy correction result acquisition unit is used to: obtain the total deviation corresponding to each arbitrary substance; sum the total deviations corresponding to multiple arbitrary substances, and when the sum result is a minimum value, determine that the energy spectrum conversion curve of each pixel is consistent with the reference correspondence relationship.

[0144] According to the photon counting CT device of an embodiment of the present invention, a corresponding relationship between the photon energy corresponding to each pixel of a plurality of pixels and a threshold code is obtained through a given unit, a reference corresponding relationship of the plurality of pixels is determined, and the corresponding relationship between the photon energy corresponding to each pixel and the threshold code is optimized based on the reference corresponding relationship to obtain a target corresponding relationship between the photon energy and the threshold code of each pixel. This can reduce the energy spectrum inconsistency between pixels while achieving the original energy correction purpose.

[0145] It should be noted that the logic and / or steps represented in the flowcharts or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing the logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (e.g., a computer-based system, a system including a processor, or other system that can fetch and execute instructions from an instruction execution system, apparatus, or device). For purposes of this specification, a "computer-readable medium" can be any device that can contain, store, communicate, propagate, or transport a program for use by, or in conjunction with, an instruction execution system, apparatus, or device. More specific examples (non-exhaustive list) of computer-readable media include the following: an electrical connection with one or more wires (electronic device), a portable computer disk cartridge (magnetic device), random access memory (RAM), read-only memory (ROM), erasable and programmable read-only memory (EPROM or flash memory), fiber optic devices, and portable compact disc read-only memory (CDROM). Furthermore, the computer-readable medium may even be paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium and then editing, interpreting or processing it in another suitable manner if necessary, and then storing it in a computer memory.

[0146] It should be understood that various parts of the present invention can be implemented using hardware, software, firmware, or a combination thereof. In the above-described embodiments, multiple steps or methods can be implemented using software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented using hardware, as in another embodiment, any one of the following technologies known in the art or a combination thereof can be used: a discrete logic circuit having a logic gate circuit for implementing a logic function on a data signal, an application-specific integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0147] Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "examples," "specific examples," or "some examples" means that a specific feature, structure, material, or characteristic described in conjunction with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0148] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0149] In the present invention, unless otherwise specified or limited, the terms "installed," "connected," "connect," "fixed," etc. should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integration; mechanical connection, electrical connection; direct connection, or indirect connection through an intermediate medium; internal communication between two components, or interaction between two components, unless otherwise specified. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0150] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. An energy correction method, applied to a photon counting CT device, wherein the photon counting CT device includes a readout unit, the readout unit includes a plurality of pixels, and is characterized in that: The method comprises: Obtaining a corresponding relationship between a photon energy corresponding to each pixel in the plurality of pixels and a threshold code; determining a reference correspondence relationship of the plurality of pixels; The corresponding relationship between the photon energy corresponding to each pixel and the threshold code is optimized according to the reference corresponding relationship to obtain a target corresponding relationship between the photon energy of each pixel and the threshold code.

2. The energy correction method according to claim 1, wherein: The obtaining of a corresponding relationship between a photon energy corresponding to each pixel in a plurality of pixels and a threshold code includes: For each pixel, the threshold code corresponding to the k-edge value of each calibration object in the multiple calibration objects is obtained, and the k-edge values ​​of the multiple calibration objects and the corresponding threshold codes are fitted to obtain the corresponding relationship between the photon energy corresponding to each pixel and the threshold code.

3. The energy correction method according to claim 2, characterized in that: The step of obtaining a threshold value encoding corresponding to a k-edge value of each calibration object in the plurality of calibration objects includes: For each calibration object, an energy spectrum curve of the corresponding calibration object, or an energy spectrum curve of the corresponding calibration object and an energy spectrum curve of air are obtained based on a plurality of preset threshold coding scans, wherein the energy spectrum curve of the calibration object and the energy spectrum curve of air are both discrete curves of photon count values ​​with respect to the threshold coding; Processing the energy spectrum curve of the corresponding calibration object using the air energy spectrum curve to obtain a discrete curve of the attenuation value parameter and threshold coding corresponding to each calibration object; Obtain the threshold code corresponding to the mutation value of the energy spectrum curve of the corresponding calibration object within the threshold code range, or the threshold code corresponding to the mutation value of the discrete curve of the attenuation value parameter of the corresponding calibration object and the threshold code, and obtain the threshold code corresponding to the k-edge value of each calibration object.

4. The energy correction method according to claim 3, characterized in that: The step of obtaining a threshold value encoding corresponding to a k-edge value of each calibration object in the plurality of calibration objects further includes: acquiring a first current when scanning a corresponding calibration object and a second current when scanning air; When the first current and the second current are different, calculating a ratio of the first current to the second current to obtain a ratio coefficient; The discrete curve of the attenuation value parameter and the threshold encoding corresponding to the corresponding calibration object is corrected according to the ratio coefficient.

5. The energy correction method according to claim 1, wherein: In the correspondence between the photon energy corresponding to each pixel and the threshold code, the threshold code corresponding to the photon energy is the independent variable, and the photon energy is the dependent variable.

6. The energy correction method according to claim 1, wherein: The determining of the reference correspondence relationship of the plurality of pixels includes: Obtaining an energy spectrum curve for each pixel based on a plurality of preset threshold coding scans, wherein the energy spectrum curve is a discrete curve of photon count values ​​with respect to the threshold coding; Using the correspondence between the photon energy corresponding to each pixel and the threshold code, the energy spectrum curve of the corresponding pixel is converted to obtain an energy spectrum conversion curve of the corresponding pixel, wherein the energy spectrum conversion curve is a discrete curve of the photon count value with respect to the photon energy; The reference corresponding relationship is obtained by averaging or weighted calculation of the energy spectrum conversion curves of the multiple pixels, wherein the reference corresponding relationship is a relationship curve of photon count value with respect to photon energy.

7. The energy correction method according to claim 6, characterized in that: Optimizing the correspondence between the photon energy corresponding to each pixel and the threshold code according to the reference correspondence includes: Adjust the coefficients in the correspondence between the photon energy and the threshold code corresponding to each pixel until the energy spectrum conversion curve of each pixel obtained by converting the energy spectrum curve of the corresponding pixel using the adjusted correspondence between the photon energy and the threshold code is consistent with the reference correspondence.

8. The energy correction method according to claim 7, characterized in that: Determining whether the energy spectrum conversion curve of each pixel is consistent with the reference corresponding relationship includes: Obtaining a deviation between the energy spectrum conversion curve of each pixel and the reference corresponding relationship; determining a total deviation of the plurality of pixels according to the deviation of each pixel; When the total deviation is a minimum value, it is determined that the energy spectrum conversion curve of each pixel is consistent with the reference corresponding relationship.

9. The energy correction method according to claim 8, characterized in that: The energy spectrum curve of each pixel is obtained by scanning at least one arbitrary substance, wherein when the arbitrary substances include multiple substances, each arbitrary substance corresponds to a reference correspondence relationship, and determining that the energy spectrum conversion curve of each pixel is consistent with the reference correspondence relationship further includes: Obtaining a total deviation corresponding to each arbitrary substance; The total deviations corresponding to the plurality of arbitrary substances are summed, and when the sum is a minimum value, it is determined that the energy spectrum conversion curve of each pixel is consistent with the reference corresponding relationship.

10. A computer-readable storage medium, characterized in that An energy correction program is stored thereon, and when the energy correction program is executed by a processor, the energy correction method according to any one of claims 1 to 9 is implemented.

11. A photon counting CT device, characterized in that: include: a photoelectric conversion unit, configured to convert photons into a first electrical signal; a readout unit, the readout unit comprising a plurality of pixels, each pixel comprising a comparator and a counter, the comparator being configured to compare the first electrical signal with a second electrical signal corresponding to a corresponding threshold code, the counter being configured to increment a photon count value by one when the first electrical signal is greater than the second electrical signal; A given unit is used to convert the energy threshold setting value of the corresponding pixel into the threshold code of the corresponding pixel based on the energy correction result of each pixel, and convert the threshold code of the corresponding pixel into the second electrical signal, wherein the energy correction result is obtained by the energy correction method described in any one of claims 1 to 9.

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