Photon counting detector and energy calibration method thereof
By measuring the energy spectrum at different set voltages in a photon counting detector, the energy threshold range where the number of photons is zero was found. The characteristic peaks of the X-ray tube target were used for calibration, which solved the problems of difficult and costly nuclide acquisition and achieved safe and low-cost energy calibration.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-11
- Publication Date
- 2026-04-03
AI Technical Summary
Among the existing energy calibration methods for photon counting detectors, it is difficult to obtain nuclides when using radionuclide sources for calibration, and the cost of calibration using X-ray tube characteristic peaks is relatively high.
By measuring the energy spectrum of the photon counting detector under different set voltages, the energy threshold range where the number of photons is zero is found. The relationship between the maximum photon energy and the energy threshold range is fitted, and the characteristic peaks of the X-ray tube target are used for calibration to achieve energy calibration.
Energy calibration of photon counting detectors can be performed safely and at low cost without the need for nuclides, various target tubes, or special filter materials.
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Figure CN121784818A_ABST
Abstract
Description
Technical Field
[0001] This application belongs to the field of photon counting detector technology, and in particular relates to a photon counting detector and its energy calibration method. Background Technology
[0002] Currently, photon counting detectors typically employ two energy calibration methods:
[0003] 1) Radionuclide source calibration, the radioactive nuclide sources used include: 57 Co 122keV, 137 Cs 662keV, 241 Am 59.5keV, 99m Tc 140keV, 133 Ba 80keV, 109 Cd 22.1keV, 153 Gd 41.5keV, 55 Fe 5.9keV. Besides... 241 Am is commonly used in smoke detectors because it is relatively easy to obtain. Other nuclides are subject to strict control and are difficult to obtain. Furthermore, laboratory personnel must take protective measures when handling nuclides.
[0004] 2) The characteristic peaks of the X-ray tube / filtration are used for calibration. The disadvantage is that it requires a variety of target X-ray tubes or special filtration materials, and the research and development costs are high. Summary of the Invention
[0005] This application provides a photon counting detector and its energy calibration method to solve the problems of difficulty in obtaining nuclides when using radionuclide sources for calibration and high cost of calibration using X-ray tube characteristic peaks in the prior art.
[0006] In a first aspect, this application provides an energy calibration method for a photon counting detector, comprising the following steps: under several different set voltage values, the X-ray tube finds the energy threshold interval corresponding to the zero photon count on the energy spectrum measured by the photon counting detector, so as to determine the maximum photon energy generated by the X-ray tube under the set voltage value; based on the maximum photon energy generated by the corresponding X-ray tube under different set voltage values, a relationship between the maximum photon energy generated by the X-ray tube under the set voltage value and the energy threshold interval is fitted; the relationship is calibrated according to the characteristic peak of the X-ray tube target material to complete the energy calibration of the photon detector.
[0007] In this application, when the X-ray tube is illuminated at several preset voltage values, the energy threshold intervals corresponding to zero photon counts on the horizontal axis are found on the energy spectrum measured by the photon counting detector. Based on these energy threshold intervals, the maximum photon energy generated by the X-ray tube at a certain preset voltage value is determined. Then, a series of point coordinates formed by different preset voltage values and the corresponding maximum photon energy generated by the X-ray tube are fitted to obtain the relationship between the maximum photon energy generated by the X-ray tube at different preset voltage values and the energy threshold intervals. Furthermore, since the characteristic peaks of the X-ray tube target are usually very accurate, the characteristic peaks are used to calibrate the relationship, thereby completing the energy calibration of the photon detector. This technical solution allows for the energy calibration of a small photon counting detector device without the need for nuclides, multiple target X-ray tubes, or special filter materials, while maintaining safety and low cost.
[0008] In one implementation of the first aspect, the step of calibrating the relation based on the characteristic peak of the X-ray tube target to complete the energy calibration of the photon detector includes: finding the energy threshold interval corresponding to the characteristic peak on the energy spectrum measured by the photon counting detector at a certain set voltage value; substituting the energy threshold interval into the relation to obtain the maximum photon energy; and if there is a difference between the energy value corresponding to the characteristic peak of the X-ray tube target and the maximum photon energy, then calibrating the relation based on the difference.
[0009] In one implementation of the first aspect, the process of finding the energy threshold interval corresponding to the photon count being zero on the energy spectrum measured by the photon counting detector under several different set voltage values includes: dividing the energy range that the photon counting detector can respond to into multiple consecutive energy threshold intervals based on energy resolution, with each energy threshold interval corresponding to an energy box number on the energy spectrum; and determining the corresponding energy threshold interval on the energy spectrum based on the energy box number corresponding to the photon count being zero.
[0010] In one implementation of the first aspect, the sensitive material of the photon counting detector is cadmium telluride (CdTe) or cadmium zinc telluride (CdZnTe).
[0011] Secondly, this application provides a photon counting detector that uses the energy calibration method provided in the above embodiments to achieve energy calibration.
[0012] Thirdly, this application provides a computer-readable storage medium having a computer program stored thereon, which, when executed, implements the above-described energy calibration method.
[0013] As described above, the photon counting detector and its energy calibration method described in this application have the following beneficial effects:
[0014] When the X-ray tube illuminates at several preset voltage values, the energy threshold intervals corresponding to zero photon counts on the horizontal axis are found on the energy spectrum measured by the photon counting detector. Based on these energy threshold intervals, the maximum photon energy generated by the X-ray tube at a given voltage value is determined. Then, by fitting a series of point coordinates formed by different preset voltage values and the corresponding maximum photon energies generated by the X-ray tube, a relationship between the maximum photon energy generated by the X-ray tube at different preset voltage values and the energy threshold intervals is obtained. Furthermore, since the characteristic peaks of the X-ray tube target are usually very accurate, these characteristic peaks can be used to calibrate the relationship, thereby completing the energy calibration of the photon detector. This technical solution allows for the energy calibration of small photon counting detector devices without the need for nuclides, multiple target X-ray tubes, or special filter materials, while maintaining safety and low cost. Attached Figure Description
[0015] Figure 1 The diagram shown is a flowchart illustrating an energy calibration method for a photon counting detector as described in an embodiment of this application.
[0016] Figure 2 The image shown is a schematic diagram of the energy spectrum of a X-ray tube at a set voltage of 85 kV in an energy calibration method for a photon counting detector as described in an embodiment of this application.
[0017] Figure 3 The diagram shows the distribution of X-ray photon counts per unit area under different set voltage values in the X-ray tube of the photon counting detector energy calibration method described in this application embodiment. Detailed Implementation
[0018] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. This application can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, unless otherwise specified, the following embodiments and features in the embodiments can be combined with each other.
[0019] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of this application. Therefore, the drawings only show the components related to this application and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.
[0020] The technical solutions in the embodiments of this application will be described in detail below with reference to the accompanying drawings.
[0021] like Figure 1 The diagram shown is a flowchart illustrating an energy calibration method for a photon counting detector provided in this embodiment.
[0022] refer to Figure 1 The energy calibration method includes the following steps:
[0023] Step S101: Under several different set voltage values, the X-ray tube finds the energy threshold interval corresponding to the zero photon count on the energy spectrum measured by the photon counting detector, so as to determine the maximum photon energy generated by the X-ray tube under the set voltage value.
[0024] Step S102: Based on different set voltage values and the maximum photon energy generated by the corresponding X-ray tube, fit the relationship between the maximum photon energy generated by the X-ray tube and the energy threshold range under different set voltage values.
[0025] Step S103: The relationship is calibrated according to the characteristic peak of the X-ray tube target to complete the energy calibration of the photon detector.
[0026] This embodiment is applied to a direct X-ray detector, in which the sensitive material can directly absorb X-ray photons and immediately generate collectable charge carriers such as electron-hole pairs. These charges are then collected under the action of an external electric field, directly forming an electrical signal.
[0027] The main technical principles include:
[0028] 1) Photoconductive effect: The working principle of direct detectors is the photoconductive effect. When X-ray photons with energy higher than the bandgap of the sensitive material are incident, they excite electrons in the valence band to the conduction band, leaving a hole in the valence band, thus creating an electron-hole pair.
[0029] 2) Charge collection: A high-voltage electric field is applied to both sides of the detector to drive electrons to move towards the anode and holes to move towards the cathode. The movement of charges forms a current pulse.
[0030] 3) Signal readout: The current pulse is amplified and shaped by subsequent readout circuits (such as preamplifiers and shaping amplifiers) to finally form a voltage pulse whose amplitude is proportional to the energy of the incident X-ray photons.
[0031] Photon counting detectors are a more advanced form of X-ray direct detectors. The fundamental difference between the two lies in "how to read out the electrical signals converted from X-ray photons." X-ray direct detectors use an integration / current mode, where the signal magnitude depends only on the total energy of the received X-rays, making it impossible to distinguish individual photons and their energies. In contrast, photon counting detectors process the electrical pulses generated by each incident photon individually. By setting an energy threshold, they count only pulses with amplitudes exceeding the threshold and can classify them by energy, enabling energy spectrum imaging.
[0032] The purpose of energy calibration is to establish a precise mapping between the "channel number" (the position of a characteristic peak on the detector's energy spectrum) read from the detector and the energy of the incident X-ray photons. The unit of photon energy is keV (kiloelectron volt), which is the unit of energy produced by electrons under voltage acceleration. Simply put, energy calibration is determining the actual photon energy value (keV) represented by each energy threshold (corresponding to a digital channel number).
[0033] In step S101 above, the X-ray tube finds the energy threshold interval corresponding to the number of photons being zero on the energy spectrum measured by the photon counting detector under several different set voltage values, so as to determine the maximum photon energy generated by the X-ray tube under the set voltage value.
[0034] Specifically, several preset voltage values are used to put the X-ray tube into a working state (i.e., bright field) at different preset voltage values. The energy spectrum at each preset voltage value is measured by a photon counting detector. In this embodiment, the sensitive material of the photon counting detector is cadmium telluride (CdTe) or cadmium zinc telluride (CdZnTe).
[0035] like Figure 2 The diagram shown is a schematic of the energy spectrum of a X-ray tube at a set voltage of 85 kV, as described in the energy calibration method for a photon counting detector according to an embodiment of this application. (Reference) Figure 2 The horizontal axis represents the threshold, corresponding to 256 energy bins with a bit depth of 8 bits. The vertical axis represents the counts (number of photons). The curves of different colors represent the energy spectrum curves measured by the photon counting detector under different currents at a set voltage value of 85KV.
[0036] Those skilled in the art will understand that an energy bin refers to a pre-defined continuous energy range within the energy response range of a photon counting detector. An energy bin acts like an energy filter; the detector only counts photons whose energy falls within this specified range. Each energy bin is defined by a lower threshold and an upper threshold. For example, an energy bin set to [20 keV, 35 keV] will only count photons with energy between 20 keV and 35 keV. Therefore, the horizontal axis 'th' is a numerical value (called the energy bin number) corresponding to an energy threshold range.
[0037] Then, locate the energy threshold interval corresponding to zero photon count on the energy spectrum. Specifically, this includes the following steps:
[0038] Step S1011: Based on the energy resolution, the energy range that the photon counting detector can respond to is divided into multiple consecutive energy threshold intervals. Each energy threshold interval corresponds to an energy box number on the energy spectrum. The energy resolution is related to the bit depth.
[0039] Step S1012: Determine the corresponding energy threshold range on the energy spectrum based on the energy box number corresponding to the photon count being zero.
[0040] As mentioned above, an 8-bit bit depth corresponds to 256 energy bins, representing 256 energy threshold intervals. In practice, the bit depth can be extended to 16-bit, 32-bit, etc. (i.e., higher energy resolution), resulting in a larger number of energy bins. This prevents two photons with similar energies from being reshaped into a single photon with a higher energy, leading to inaccurate photon counting within different energy bins. Therefore, increasing the bit depth allows for more accurate counting across different energy bins. For example, in the medical field, similar soft tissue images can be distinguished more clearly (e.g., blood vessels and joints, etc.).
[0041] like Figure 3 The diagram shows the distribution of X-ray photon numbers per unit area with different photon energies under different set voltage values in the X-ray tube. (Reference) Figure 3As shown in the figure, under the conditions of set voltage values (60kV, 80kV, 90kV, 120kV, and 140kV), the maximum photon energies of the X-rays are 60keV at point a, 80keV at point b, 90keV at point c, 120keV at point d, and 140keV at point e, respectively. It is evident that the set voltage value of the X-ray tube is numerically equal to the maximum photon energy that the tube can produce at that set voltage value. Therefore, the th value (energy box number) X0 corresponding to zero photon count on the energy spectrum can be approximated as the set voltage value or the maximum photon energy that the X-ray tube can produce.
[0042] Then, for different set voltage values (e.g., 60KV, 70KV, 90KV, 100KV, ..., 140KV), a photon counting detector was used to measure values similar to those obtained from other voltage settings. Figure 2 The energy spectrum is shown, and the energy threshold range corresponding to zero photon count at the set voltage value is found to determine the maximum photon energy generated by the X-ray tube at the set voltage value. Further details are omitted here.
[0043] In step S102, a relationship between the maximum photon energy generated by the X-ray tube and the energy threshold range under different set voltage values is fitted based on different set voltage values and the maximum photon energy generated by the corresponding X-ray tube.
[0044] According to the implementation of step S101 above, the maximum photon energy generated by the corresponding X-ray tube under different set voltage values can be obtained, thereby obtaining a series of points with the set voltage value as the abscissa and the th value (i.e. the maximum photon energy generated by the corresponding X-ray tube) corresponding to the photon number being zero as the ordinate, such as: (85, X0), (60, X1), (70, X2), (90, X3), (100, X5), (110, X6), (120, X7), (130, X8) and (140, X9), etc.
[0045] Furthermore, by fitting these points, the relationship between the maximum photon energy produced by the X-ray tube and the energy threshold range under different set voltage values can be obtained, i.e., the relationship between Kev and th. This embodiment does not impose specific limitations on the relationship; in practice, it can be determined based on the fitting results between the different set voltage values and the th value corresponding to zero photon count. Therefore, based on the fitted relationship, the th value corresponding to zero photon count (corresponding to the maximum photon energy produced by the X-ray tube) can be obtained for any set voltage value.
[0046] In step S103, the relationship is calibrated according to the characteristic peak of the X-ray tube target to complete the energy calibration of the photon detector.
[0047] Specifically, this step includes:
[0048] Step S1031: Under a certain set voltage value, the X-ray tube finds the energy threshold range corresponding to the characteristic peak on the energy spectrum measured by the photon counting detector;
[0049] Step S1032: Substitute the energy threshold range into the relational expression to obtain the maximum photon energy;
[0050] Step S1033: If there is a difference between the energy value corresponding to the characteristic peak of the X-ray tube target and the maximum photon energy, then the relationship is calibrated based on the difference.
[0051] Those skilled in the art will understand that the relationship between the maximum photon energy produced by the X-ray tube and the energy threshold range under different set voltage values obtained by fitting may contain errors, but the energy values corresponding to the characteristic peaks of the X-ray tube target material (e.g., Rhenium-tungsten alloy wire material) are generally quite accurate. Therefore, in this embodiment, the characteristic peaks of the X-ray tube target material can be used to calibrate the relationship.
[0052] For example, if the X-ray tube is in a bright field at a set voltage of 140kV, and the energy spectrum is measured by a photon counting detector, a relatively obvious characteristic peak of tungsten Kα1 (electron transition from the L layer to the K layer) will appear on the energy spectrum, such as W. Kα1 =59.3keV. Then, the x-coordinate of this characteristic peak can be found on the energy spectrum. wα1 Value (based on th) wα1 The value can determine the energy threshold range), and this th wα1 Substitute the value into the above keV-th relationship to calculate the keV value. Compare the keV value with the energy value of 59.3 keV corresponding to the tungsten Kα1 characteristic peak, using the difference ∆. If the difference ∆ = 0 (i.e., no difference), it indicates that the above-obtained keV-th relationship is accurate and does not require calibration. If the difference ∆ is not 0, it indicates that the above-obtained keV-th relationship needs calibration, which can be done by adding or subtracting the difference ∆.
[0053] Based on the above method embodiments, this application also provides a photon counting detector, which uses the energy calibration method described above for energy calibration.
[0054] The scope of protection for the energy calibration method of the photon counting detector described in this application is not limited to the execution order of the steps listed in this embodiment. Any solution implemented by adding, subtracting, or replacing steps in the prior art based on the principles of this application is included within the scope of protection of this application.
[0055] In the embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, or methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative. For instance, the division of modules / units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple modules or units may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection of apparatuses or modules or units may be electrical, mechanical, or other forms.
[0056] The modules / units described as separate components may or may not be physically separate. The components shown as modules / units may or may not be physical modules; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules / units can be selected to achieve the objectives of the embodiments of this application, depending on actual needs. For example, the functional modules / units in the various embodiments of this application may be integrated into one processing module, or each module / unit may exist physically separately, or two or more modules / units may be integrated into one module / unit.
[0057] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.
[0058] This application also provides a computer-readable storage medium storing a computer program that, when executed, implements the energy calibration method described in the above embodiments. Those skilled in the art will understand that all or part of the steps in the methods of the above embodiments can be implemented by a program instructing a processor. The program can be stored in a computer-readable storage medium, which is a non-transitory medium, such as random access memory, read-only memory, flash memory, hard disk, solid-state drive, magnetic tape, floppy disk, optical disk, and any combination thereof. The storage medium can be any available medium accessible to a computer or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., digital video disc (DVD)), or a semiconductor medium (e.g., solid-state disk (SSD)).
[0059] The descriptions of the processes or structures corresponding to the above figures each have their own emphasis. For parts of a process or structure that are not described in detail, please refer to the relevant descriptions of other processes or structures.
[0060] The above embodiments are merely illustrative of the principles and effects of this application and are not intended to limit this application. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of this application. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in this application should still be covered by the claims of this application.
Claims
1. A method for energy calibration of a photon counting detector, characterized in that, The energy calibration method includes: Under several different set voltage values, the X-ray tube finds the energy threshold interval corresponding to the zero photon count on the energy spectrum measured by the photon counting detector, so as to determine the maximum photon energy generated by the X-ray tube under the set voltage value. Based on different set voltage values and the maximum photon energy generated by the corresponding X-ray tube, a relationship between the maximum photon energy generated by the X-ray tube and the energy threshold range under different set voltage values is fitted. The relationship is calibrated based on the characteristic peaks of the X-ray tube target to complete the energy calibration of the photon detector.
2. The energy calibration method according to claim 1, characterized in that, The step of calibrating the relationship based on the characteristic peaks of the X-ray tube target to complete the energy calibration of the photon detector includes: When the X-ray tube is at a certain set voltage value, the energy threshold range corresponding to the characteristic peak is found on the energy spectrum measured by the photon counting detector. Substitute the energy threshold range into the relation to obtain the maximum photon energy; If there is a difference between the energy value corresponding to the characteristic peak of the X-ray tube target and the maximum photon energy, the relationship is calibrated based on the difference.
3. The energy calibration method as described in claim 1, characterized in that, The X-ray tube, under several different set voltage values, identifies energy threshold intervals on the energy spectrum measured by the photon counting detector where the number of photons is zero, including: Based on the energy resolution, the energy range that the photon counting detector can respond to is divided into multiple consecutive energy threshold intervals, and each energy threshold interval corresponds to an energy box number on the energy spectrum. The corresponding energy threshold range is determined on the energy spectrum based on the energy box number corresponding to the zero photon count.
4. The energy calibration method as described in claim 1, characterized in that, The sensitive material of the photon counting detector is cadmium telluride (CdTe) or cadmium zinc telluride (CdZnTe).
5. A photon counting detector, characterized in that, The photon counting detector is calibrated using the energy calibration method described in any one of claims 1 to 4.
6. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed, it implements the energy calibration method as described in any one of claims 1 to 4.