阅读说明：本技术 一种用于x射线探测器的光生电荷的快速计算方法 (Rapid calculation method for photo-generated charge of X-ray detector ) 是由 史再峰 黄泳嘉 曹清洁 高静 罗韬 于 2019-09-20 设计创作，主要内容包括：一种用于X射线探测器的光生电荷的快速计算方法,包括：通过入射能谱得到入射光子的个数与能量分布；将单个入射光子与探测器的原子发生光电效应；对所有成像电子数进行求和得到单个入射光子作用时成像电子总数；对光子数进行累加。本发明对探测和收集过程中的系统噪声进行了修正,并对输出电子进行了统计,本发明克服了传统分析方法中的只适用于低能量X射线的缺点,在减少整个能谱的能量解析计算过程的同时,进一步减少了高能量段因为散射噪声造成的统计噪声和随机噪声等误差,提高级联分析模型的测试效率和准确程度。(A method for fast calculation of photo-generated charge for an X-ray detector, comprising: obtaining the number and energy distribution of incident photons through an incident energy spectrum; generating photoelectric effect between single incident photon and atom of detector; summing all the imaging electron numbers to obtain the total number of imaging electrons under the action of single incident photons; the number of photons is accumulated. The invention corrects the system noise in the detection and collection process, and counts the output electrons, overcomes the defect that the traditional analysis method is only suitable for low-energy X-rays, reduces the energy analysis calculation process of the whole energy spectrum, further reduces errors such as statistical noise, random noise and the like caused by scattering noise in a high-energy section, and improves the test efficiency and the accuracy of a cascade analysis model.)

1. A method for rapidly calculating photo-generated charge of an X-ray detector is characterized by comprising the following steps:

1) obtaining the number and energy distribution of incident photons through an incident energy spectrum;

2) bringing a single incident photon into a photoelectric effect with the atoms of the detector, wherein: the probability of a single incident photon interacting with the atomic K layer of the detector is P_kThe probability of a single incident photon interacting with the atomic L layer of the detector is P_LThe probability of a single incident photon interacting with the atomic M layer of the detector is P_MAnd P is_k+P_L+P_M＝1；

3) Summing all the imaging electron numbers obtained in the step 2) to obtain the total number q of imaging electrons under the action of single incident photon_outExpressed as:

wherein q is_iRepresenting the ith imaging electron number obtained in the step 2);

4) accumulating the number of photons

By accumulating photons of different energies, the total number of imaging electrons generated by the action of all photons entering the detector is obtained:

wherein N represents the total number of incident photons, E_iRepresenting the incident energy of the ith photon.

2. The method for fast calculation of photo-generated charge for an X-ray detector according to claim 1, wherein step 2) comprises:

(1) a single incident photon interacts with the atomic K layer:

the probability of transition of an electron in the atomic L layer to the atomic K layer is set as a_KLThe probability of the transition of the electron of the atomic M layer to the electron of the atomic K layer is 1-a_KLGain by electron-hole pairs produced by single photon interaction at energy E

(2) the electrons on the atom L layer interact with the atom K layer

When the electrons in the atomic L layer jump to the atomic K layer, Auger electrons and fluorescent X rays are generated, and the probability of generating the fluorescent X rays is set as b_KLWith a probability of generating Auger electrons of 1-b_KLWhen the fluorescent X-ray is generated, let the probability of reabsorption of the fluorescent X-ray be f_KLAccording toGain of fluorescent X-ray excited electron-hole pairsNumber q of fluorescent X-ray excited imaging electrons₂Expressed as:

number q of imaging electrons formed by Auger electrons₃Expressed as:

wherein the content of the first and second substances,

when the transition of the atomic L layer electron generates fluorescent X-ray, the imaging electrons formed by fluorescent X-ray and auger electron emission acting at the atomic M layer are respectively represented as:

wherein q is₄And q is₅Respectively representing imaging electrons formed by fluorescent X-rays and auger electron emission;

(3) m layer electron to K layer transition

The imaging electrons formed by the interaction between the electrons of atom K and the layer of atom M are represented as:

wherein q is₆And q is₇Respectively representing imaging electrons formed by fluorescent X-rays and auger electron emission;

(4) Single incident photon interacts with atomic L layer

A single incident photon directly interacts with the atomic L layer, and the probability of generating fluorescent x-ray by the transition of the atomic M layer electrons to the atomic L layer is set as b_LM(ii) a The probability of generating Auger electrons is 1-b_LM(ii) a The imaging electrons generated by the photoelectric effect on the layer of atoms L are then:

the imaging electrons formed by the fluorescent X-ray and auger electron emission are then represented as:

wherein q is₉And q is₁₀Respectively represent imaging electrons formed by the interaction of the atomic L layer and the atomic M layer and formed by fluorescent X-ray and Auger electron emission;

(5) a single incident photon interacts with the atomic M layer and the remaining atomic layers

When energy interaction occurs between a single incident photon and the atomic M layer, the number of imaging electrons generated by the rest atomic layers is set asThe atomic M layer and the remaining atomic layers produce imaging electrons in the number of

Wherein the content of the first and second substances,

Technical Field

The invention relates to a method for calculating photo-generated charges. In particular to a method for quickly calculating photo-generated charges for an X-ray detector in the process of energy interaction and electron transition between photons and extra-nuclear electrons under any shell layer outside an atomic core.

Background

In recent years, the computed tomography technology is rapidly developed and widely applied to the fields of clinical medical treatment, industrial diagnosis, security detection and the like. In clinical medicine, CT techniques are often used to obtain images of internal structures of the human body in a non-invasive manner. The detector is an important component in a CT system, and the precision of the detector has great influence on the imaging quality. Compared with the traditional CT, the energy spectrum CT has higher imaging precision and quality, better soft tissue contrast and lower ray dose. Meanwhile, the energy spectrum CT reduces artifacts caused by the motion of a scanned object and beam hardening, and can divide energy intervals to achieve the purpose of fully utilizing energy spectrum information.

The value of the Detector Quantum Efficiency (DQE), which is a characteristic parameter of the detector performance, indicates the level of the detection capability of the detector. Since the noise introduced into the photon counting detector can cause the reduction of DQE and affect the performance of the detector, the physical characteristics of the interaction between X-rays and the detector, such as the photoelectric effect, Compton effect and the influence of K fluorescence reabsorption on the performance of the photoelectric conductor X-ray detector, need to be analyzed comprehensively. At the present stage, a Monte Carlo method is adopted to research the influence of the physical characteristics of the particles on the DQE and accurately design the relevant parameters of the detector. However, the simulation speed of the method is slow, which seriously affects the design efficiency of the detector.

Therefore, a cascade system theory analysis method is introduced for counting the imaging electron quantity of the detector imaging system. By this approach, the imaging system is clearly modeled as a cascade of fundamental physical processes, where the "transfer" of signal and noise is described by the input-output relationship of each process of the cascade, reducing the impact of noise on the detector detection performance. However, the current cascade analysis model is simple and is only used for describing the influence of average fluorescence x-rays generated when photons interact with atoms on the imaging process, and statistics of reabsorption efficiency of the fluorescence x-rays are ignored. The application range of the current cascade analysis model is relatively limited because the reabsorption effect of the fluorescence x-ray has a relatively large influence on the detector material with a relatively high atomic number.

In order to adapt to a more complex image forming process, complex parallel cascades are introduced to describe signal and noise transfer from a plurality of serial cascades, and a cascade analysis model is utilized to carry out analog calculation on the quantum collection efficiency of a detector, so that more accurate photo-generated charge number can be obtained. Therefore, a rapid calculation method for the statistical properties of the energy absorption of atomic K and L layer fluorescent X rays and Auger (Auger) electrons under the photoelectric effect is provided, so that the simulation precision of a cascade analysis model is improved, the application range of the method is expanded, and the operation speed is improved.

Disclosure of Invention

The invention aims to solve the technical problem of providing a quick calculation method for photo-generated charges of an X-ray detector, which can improve the test efficiency and accuracy of a cascade analysis model.

The technical scheme adopted by the invention is as follows: a method for fast calculation of photo-generated charge for an X-ray detector, comprising the steps of:

1) obtaining the number and energy distribution of incident photons through an incident energy spectrum;

2) bringing a single incident photon into a photoelectric effect with the atoms of the detector, wherein: the probability of a single incident photon interacting with the atomic K layer of the detector is P_kThe probability of a single incident photon interacting with the atomic L layer of the detector is P_LThe probability of a single incident photon interacting with the atomic M layer of the detector is P_MAnd P is_k+P_L+P_M＝1；

3) Summing all the imaging electron numbers obtained in the step 2) to obtain the total number q of imaging electrons under the action of single incident photon_outExpressed as:

wherein q is_iRepresenting the ith imaging electron number obtained in the step 2);

4) accumulating the number of photons

By accumulating photons of different energies, the total number of imaging electrons generated by the action of all photons entering the detector is obtained:

wherein N represents the total number of incident photons, E_iRepresenting the incident energy of the ith photon.

The step 2) comprises the following steps:

(1) a single incident photon interacts with the atomic K layer:

the probability of transition of an electron in the atomic L layer to the atomic K layer is set as a_KLThe probability of the transition of the electron of the atomic M layer to the electron of the atomic K layer is 1-a_KLGain by electron-hole pairs produced by single photon interaction at energy EThe number of imaging electrons generated in the atomic K layer due to the photoelectric effect is represented as:

(2) the electrons on the atom L layer interact with the atom K layer

When the electrons in the atomic L layer jump to the atomic K layer, Auger electrons and fluorescent X rays are generated, and the probability of generating the fluorescent X rays is set as b_KLWith a probability of generating Auger electrons of 1-b_KLWhen the fluorescent X-ray is generated, let the probability of reabsorption of the fluorescent X-ray be f_KLGain of electron-hole pairs based on fluorescent X-ray excitationNumber q of fluorescent X-ray excited imaging electrons₂Expressed as:

number q of imaging electrons formed by Auger electrons₃Expressed as:

wherein the content of the first and second substances,

expressed as the gain when auger electrons are emitted;

when the transition of the atomic L layer electron generates fluorescent X-ray, the imaging electrons formed by fluorescent X-ray and auger electron emission acting at the atomic M layer are respectively represented as:

wherein q is₄And q is₅Respectively representing imaging electrons formed by fluorescent X-rays and auger electron emission;and

respectively representing gains generated when electrons generate fluorescent X-rays at the atomic M layer and emit Auger electrons; b_LMRepresents the probability of the fluorescent X-ray being absorbed at the atomic M layer; f. of_LMRepresenting the reabsorption probability of the fluorescent X-rays;

(3) m layer electron to K layer transition

The imaging electrons formed by the interaction between the electrons of atom K and the layer of atom M are represented as:

wherein q is₆And q is₇Respectively representing imaging electrons formed by fluorescent X-rays and auger electron emission;

and

respectively representing gains generated when atomic K layer electrons generate fluorescence X-rays at the M layer and emit Auger electrons; b_KMRepresents the probability of the fluorescent X-ray being absorbed at the atomic M layer; f. of_KMIndicating the probability of reabsorption of fluorescent X-rays.

(4) Single incident photon interacts with atomic L layer

A single incident photon directly interacts with the atomic L layer, and the probability of generating fluorescent x-ray by the transition of the atomic M layer electrons to the atomic L layer is set as b_LM(ii) a The probability of generating Auger electrons is 1-b_LM(ii) a The imaging electrons generated by the photoelectric effect on the layer of atoms L are then:

the imaging electrons formed by the fluorescent X-ray and auger electron emission are then represented as:

wherein q is₉And q is₁₀Respectively represent imaging electrons formed by the interaction of the atomic L layer and the atomic M layer and formed by fluorescent X-ray and Auger electron emission;

andrespectively representing gains generated when electrons of the atomic L layer generate fluorescence X rays at the atomic M layer and emit Auger electrons; f. of_LMRepresenting the reabsorption probability of the fluorescent X-rays;

(5) a single incident photon interacts with the atomic M layer and the remaining atomic layers

When energy interaction occurs between a single incident photon and the atomic M layer, the number of imaging electrons generated by the rest atomic layers is set as

The atomic M layer and the remaining atomic layers produce imaging electrons in the number of

Wherein the content of the first and second substances,

representing the gain of the photon on the atomic M layer for the photoelectric effect to occur.

The invention relates to a method for quickly calculating photo-generated charges for an X-ray detector, which corrects system noise in the detection and collection processes and counts output electrons.

Drawings

FIG. 1 is a block diagram of a method of the present invention for fast calculation of photo-generated charge for an X-ray detector;

FIG. 2 is a flow chart of a method of the present invention for fast calculation of photo-generated charge for an X-ray detector;

FIG. 3 is a schematic diagram of the interaction of photons and electrons between the atomic K layer and the atomic L layer in the present invention;

FIG. 4 is a schematic diagram of the interaction of photons and electrons between the atomic K layer and the atomic M layer in the present invention;

FIG. 5 is a schematic diagram of the interaction of photons and electrons in the atomic L layer of the present invention;

FIG. 6 is a schematic diagram of the interaction of photons and electrons between the layer of atom L and the layer of atom M in the present invention.

Detailed Description

The following provides a detailed description of a method for fast calculation of photo-generated charge for an X-ray detector according to the present invention with reference to the accompanying drawings.

The invention discloses a method for quickly calculating photo-generated charges of an X-ray detector, which mainly aims at cascading various events on a shell layer of an atomic layer in a photoelectric effect, establishes a corresponding model without considering secondary scattering and explains each path in the model in detail. Because the probability of interaction between photons and electrons under a shell layer close to an atomic nucleus is higher under the photoelectric effect, the method mainly analyzes the action mechanisms of the photons and the atomic K layer, the atomic L layer and the atomic M layer on the outer layer of the atomic nucleus.

As shown in fig. 1 and fig. 2, a method for fast calculating photo-generated charge for an X-ray detector of the present invention includes the following steps:

1) obtaining the number and energy distribution of incident photons through an incident energy spectrum; the incident energy spectrum is input to a matlab or gate simulation program in a simulated real detection process, and the number and the energy distribution of incident photons are obtained.

2) Bringing a single incident photon into a photoelectric effect with the atoms of the detector, wherein: the probability of a single incident photon interacting with the atomic K layer of the detector is P_kThe probability of a single incident photon interacting with the atomic L layer of the detector is P_LThe probability of a single incident photon interacting with the atomic M layer of the detector is P_MAnd P is_k+P_L+P_M1 is ═ 1; the method comprises the following steps:

(1) a single incident photon interacts with the atomic K layer:

the probability of transition of an electron in the atomic L layer to the atomic K layer is set as a_KLThe probability of the transition of the electron of the atomic M layer to the electron of the atomic K layer is 1-a_KLGain by electron-hole (E-h) pairs produced by single photon interaction at energy E

The number of imaging electrons generated in the atomic K layer due to the photoelectric effect is represented as:

(2) the electrons on the atom L layer interact with the atom K layer

When the atomic L layer electrons transit to the atomic K layer, auger electrons and fluorescent X-rays are generated, as shown in fig. 3. Setting the probability of generating fluorescent X-rays to b_KLWith a probability of generating Auger electrons of 1-b_KLWhen the fluorescent X-ray is generated, let the probability of reabsorption of the fluorescent X-ray be f_KLGain of electron-hole (e-h) pairs based on fluorescent X-ray excitation

Number q of fluorescent X-ray excited imaging electrons₂Expressed as:

number q of imaging electrons formed by Auger electrons₃Expressed as:

wherein the content of the first and second substances,

expressed as the gain when auger electrons are emitted;

when the transition of the atomic L layer electron generates fluorescent X-ray, the imaging electrons formed by fluorescent X-ray and auger electron emission acting at the atomic M layer are respectively represented as:

wherein q is₄And q is₅Respectively representing imaging electrons formed by fluorescent X-rays and auger electron emission;

and

respectively representing gains generated when electrons generate fluorescent X-rays at the atomic M layer and emit Auger electrons; b_LMRepresents the probability of the fluorescent X-ray being absorbed at the atomic M layer; f. of_LMRepresenting the reabsorption probability of the fluorescent X-rays;

(3) m layer electron to K layer transition

As shown in fig. 4, the imaging electrons formed by the interaction between the atom K and the electrons of the atom M layer are represented as:

wherein q is₆And q is₇Respectively representing imaging electrons formed by fluorescent X-rays and auger electron emission;

and

respectively representing gains generated when atomic K layer electrons generate fluorescence X-rays at the M layer and emit Auger electrons; b_KMRepresents the probability of the fluorescent X-ray being absorbed at the atomic M layer; f. of_KMIndicating the probability of reabsorption of fluorescent X-rays.

(4) Single incident photon interacts with atomic L layer

As shown in FIG. 5, a single incident photon interacts directly with the atomic L layer, setting the probability b that an electron in the atomic M layer will generate a fluorescent x-ray as it transitions to the atomic L layer_LM(ii) a The probability of generating Auger electrons is 1-b_LM(ii) a The imaging electrons generated by the photoelectric effect on the layer of atoms L are then:

as shown in fig. 6, the imaging electrons formed by the fluorescent X-ray and auger electron emission are represented as:

wherein q is₉And q is₁₀Respectively represent imaging electrons formed by the interaction of the atomic L layer and the atomic M layer and formed by fluorescent X-ray and Auger electron emission;andrespectively representing gains generated when electrons of the atomic L layer generate fluorescence X rays at the atomic M layer and emit Auger electrons; f. of_LMIndicating reabsorption of fluorescent X-raysProbability;

(5) a single incident photon interacts with the atomic M layer and the remaining atomic layers

When energy interaction occurs between a single incident photon and the atom M layer, because the probability of photoelectric effect between the photon and other atom layers except the atom K layer, the atom M layer and the atom L layer is very small, the number of imaging electrons generated by the other atom layers is set as

The atomic M layer and the remaining atomic layers produce imaging electrons in the number of

Wherein the content of the first and second substances,

representing the gain of the photon on the atomic M layer for the photoelectric effect to occur.

3) Summing all the imaging electron numbers obtained in the step 2) to obtain the total number q of imaging electrons under the action of single incident photon_outExpressed as:

wherein q is_iRepresenting the ith imaging electron number obtained in the step 2);

4) accumulating the number of photons

By accumulating photons of different energies, the total number of imaging electrons generated by the action of all photons entering the detector is obtained:

wherein N represents the total number of incident photons, E_iRepresenting the incident energy of the ith photon.

The quick calculation method for the photo-generated charges of the X-ray detector improves the calculation speed and further improves the accuracy of simulation test. The implementation of the method of the invention needs to meet the following four points: 1. the probability of energy interaction occurring in each atomic nucleus outer electronic layer under a single incident photon with 1kev energy needs to be tested, and the silicon material is accurately measured in the industry at present, so that the method can have higher accuracy when being applied to a silicon material detector; 2. in the detector simulation process, a small electron pair effect and relevant scattering are needed, the action process of secondary scattering can be ignored, and the interaction probability of the first three shells on the atom is generally analyzed because incident photons generally interact with the first three shells of the atom; 3. because only the photoelectric effect is considered and the known incident energy spectrum is needed, the method is suitable for simulating the detection process with the ray range below 60 kev; 4. the method firstly calculates the imaging electrons of the photoelectric effect of single incident photon with 1kev energy, and then accumulates according to the particle energy, and because the number of the imaging electrons increases linearly along with the increase of the incident energy, the Fano factor shadow response of the detector material is relatively small, thereby meeting the requirement of calculation precision.