阅读说明：本技术 一种时间同步方式采集端口图像方法 (Method for acquiring port images in time synchronization mode ) 是由 戴建荣 王宏凯 于 2021-07-02 设计创作，主要内容包括：一种时间同步方式采集端口图像方法,属于影像技术领域。测量光子从X射线源中的靶到探测器之间的飞行时间,通过设置数据获取电子学中的时间窗口,在接收原射光子信号的同时剔除散射光子信号,在硬件层级消除散射光子的干扰。本发明的优点是区别于目前现有的基于X射线装置的成像设备上消除散射光子信号的相关技术。创新的采用了测量光子通过不同路径后的飞行时间的方法,对信号光子与散射光子进行鉴别以达到消除散射信号的干扰。无需在原有设备上进行大规模改造,仅通过信号引出的方式将所需的信号引出至外部数据处理系统,成本较低,测量设备占用空间小。(A method for acquiring port images in a time synchronization mode belongs to the technical field of images. Measuring the flight time of photons from a target in an X-ray source to a detector, acquiring a time window in electronics by setting data, receiving a primary photon signal and rejecting a scattered photon signal at the same time, and eliminating the interference of the scattered photons at a hardware level. The advantage of the present invention is distinguished from the related art of eliminating scattered photon signals on currently existing imaging devices based on X-ray apparatus. The method for measuring the flight time of photons passing through different paths is innovatively adopted, and the signal photons and the scattered photons are identified so as to eliminate the interference of scattered signals. The method does not need to carry out large-scale transformation on the original equipment, only leads out the required signal to an external data processing system in a signal leading-out mode, and has the advantages of low cost and small occupied space of measuring equipment.)

1. A method for acquiring port images in a time synchronization mode is characterized by comprising the following steps: measuring the flight time of photons from a target in an X-ray source to a detector, acquiring a time window in electronics by setting data, receiving a primary photon signal and rejecting a scattered photon signal at the same time, and eliminating the interference of the scattered photons at a hardware level.

2. The method for acquiring port images in a time-synchronous manner as claimed in claim 1, wherein the influence of scattered photons on image signal collection is reduced by setting different time-of-flight discrimination thresholds to effectively distinguish the primary photon signals from the scattered photon signals, thereby improving the quality of reconstructed images on hardware.

3. The method of claim 1, wherein the time of arrival of the primary photon signal at the detector plate is expressed by the following equation:

t_p＝TDD/c

wherein TDD is the distance from the X-ray target to a certain imaging unit of the detector, and c is the speed of light;

the scattered photon signal arrival time at the detector plate is expressed by:

t_s＝(TSD+SDD)/c

wherein TSD is the distance from the X-ray target to the position where Compton scattering occurs, SDD is the distance from the position where the scattering occurs to the same imaging unit of the detector, and c is the speed of light;

the resulting time difference is:

Δt＝t_s-t_p

and setting a proper time-of-flight truncation threshold value by analyzing the time difference, and distinguishing primary photons from scattered photons.

4. The method of claim 1, wherein photons are generated by bremsstrahlung after electrons generated in the X-ray source impact the target material, and photon time-of-flight start timing signals are provided while photons are generated at the target;

after a certain flight distance, the photons generate signals on a detector for detecting the photons, wherein the signals comprise detected real photon signals and noise signals;

after the signal output by the detector passes through the amplifying and forming circuit, the generated signal enters the data acquisition circuit, and meanwhile, the time of the photon received by the detector is recorded through an electronic circuit;

by analyzing the time of flight of the recorded photons, a certain threshold can be set and primary and scattered photons can be discriminated by the threshold.

5. The method of claim 1, wherein the selecting the primary photon signal and the scattered photon signal comprises: after a photon flight time starting timing signal is obtained from an X-ray source, a coincidence circuit for distinguishing primary photons from scattered photons is opened for a certain timing window width, the timing window width is determined according to the flight time of the primary photons on a fixed path and is adjusted according to actual requirements, if a photon flight time ending timing signal given by a detector is within the range of the timing window width, the photon flight time ending timing signal is judged as the primary photons, otherwise, the photon flight time ending timing signal is defined as the scattered photons.

6. A method for acquiring port images in a time synchronization mode is characterized by comprising an initial signal acquisition step, a conversion step and a signal acquisition and processing step;

an initial signal acquisition step: providing a photon start timing signal representative of the photon's start time of flight, wherein the rising edge of the pulse pickup signal can be on the order of picoseconds, the photon start signal providing a start timing signal for calibrating the emission of photons to the timing electronics in a manner that employs constant ratio timing or leading edge timing,

a conversion step: generating an output signal in response to the received photons when the signal generated by the detector is greater than a signal generation threshold; the amplifying and forming circuit is responsible for outputting the amplified, formed and converted model,

signal acquisition and processing steps: when X-ray passes through the detector, a photocurrent signal proportional to the photon number is generated, the photocurrent signal is amplified and shaped by a signal processing circuit and then sent into a corresponding multi-channel analysis circuit to obtain photon signal intensity in a certain beam pulse period, while photon intensity information is obtained, the flight time information of photons is recorded, an initial timing signal is given by an X-ray source and is used for generating an end timing signal which is output from the detector, a dual-threshold trigger mechanism is adopted for triggering, the end signal of photon flight is provided by the detector and a timing circuit connected with the detector, the signal output by the detector outputs an effective signal after passing through a coincidence system, the coincidence system receives the signal output by the dual-threshold discriminator, the signal in the low-threshold discriminator is delayed for a certain degree, and the delayed low-threshold signal and the high-threshold signal pass through the coincidence system, and forming a final effective signal output within a certain time window.

7. The method of claim 6, wherein the terminating signal timing acquisition: when the low-threshold discriminator receives a signal and triggers, the coincidence circuit opens a coincidence time window with a certain width (the width of the coincidence time window is adjusted in a certain range according to different types of detectors and electronic characteristics), and the coincidence circuit indicates that the rising edge of the signal is detected in the time window range, and meanwhile, a timestamp signal for recording the start of an event is also generated when the low-threshold signal is finished; because a certain time interval is usually arranged between the low threshold signal and the high threshold signal, in order to shorten the fit time window width as much as possible and reduce the influence of noise signals, the low threshold signal is delayed for a certain time; if the signal from the high threshold trigger is not received within the range of the receiving time window, the signal is not a valid signal, the signal source is the fluctuation, dark count or other noise of the signal in the detector, and the timing signal is discarded; if the coincidence discrimination circuit receives the signal from the high-threshold discriminator within the time receiving window range, the coincidence circuit outputs a valid signal, the signal is judged to be a valid signal, and a timing signal of the termination time is sent to a lower circuit;

after the time and intensity signals of photons are obtained, the two signals are sent to a photon signal selection and judgment circuit based on an FPGA to judge and process primary/scattered photons; after passing through the selection circuit, the time information of the primary photons is retained and transmitted to the computer together with the photon intensity information related to the time information for image reconstruction.

Technical Field

The invention relates to a method for acquiring port images in a time synchronization mode, and belongs to the technical field of images.

Background

The image technology is a technology for clearly, accurately and visually qualitatively or quantitatively displaying the internal structure, composition, material and other conditions of the detected object in a non-invasive way. The imaging technology relates to the fields of medical treatment, industry and the like. Taking the medical field as an example, various types of apparatuses such as medical X-ray Imaging apparatuses, X-ray-based Computed Tomography (CT) apparatuses, Magnetic Resonance Imaging (MRI) apparatuses using Magnetic Resonance technology, ultrasound Imaging apparatuses using the ultrasonic principle, nuclear medicine Imaging and Positron Emission Tomography (PET) apparatuses assisted by isotopes, and the like have been developed.

Among X-ray based imaging apparatuses, there are two main types, one is an X-ray based imaging device, and is mainly classified into an analog X-ray imaging apparatus and a digital X-ray imaging apparatus. The former is mainly a screen type X-ray photographic equipment using film, which is the first generation radiographic equipment, and the latter is mainly computer X-ray photography (CR) and digital X-ray photography (DR); the second category is X-ray based CT techniques. The fan-beam and cone-beam CT devices widely used at present are based on the principle of single-energy X-ray imaging, namely, the absorption difference of substances to single-energy X-rays is utilized for imaging. In order to improve the ability of CT images to distinguish substances, the use of two or more sets of energy or spectral data has also been gradually brought into human vision in recent years. And material information richer than that of the traditional CT image is obtained through a special reconstruction method. In addition, phase CT imaging methods developed in the last decade can improve the contrast of soft tissue imaging by imaging using phase change information when X-rays and a substance act on each other.

The basic principle of the device is that an X-ray source generates X-rays, a detector array sensitive to the X-rays collects photons, and a data acquisition system analyzes and calculates the photons to form an image. In the imaging process using an X-ray apparatus, the X-rays reaching the detector consist essentially of two parts, the first part being the primary X-rays generated by the source; and the other part is the secondary ray generated by the primary ray after Compton scattering equivalent to the substance, which is also called the scattered ray. Since the angle of the scattered ray is greatly different from that of the primary ray, the detector is easily interfered. Since the X-ray device usually adopts an area array type detector, scattered rays contribute to signals when large-field imaging is carried out, but the scattered rays do not reflect the attenuation of substances to the rays, and image resolution and signal-to-noise ratio are easy to reduce. Therefore, the method effectively removes the scattered ray signal contribution and is an important method for improving the image quality of the X-ray device.

Limitations of existing methods:

the X-ray imaging device has the greatest advantages of fast imaging, namely, the image blurring caused by the movement of the body of a patient and the image distortion caused by the movement of internal organs of the patient are reduced by using shorter scanning time, and the utilization efficiency of the X-ray source is improved. However, the main disadvantage is that the probability of scattering is increased due to the complex internal structure of the X-ray generating device and the interaction of photons with various substances in the path of travel. When the detection board receives a large amount of scattered photon signals, image quality related to noise, Contrast Resolution (Contrast Resolution), and the like, is greatly affected, which is more remarkable in the case of a large field. For a long time, researchers at home and abroad have made many studies on improvement of image quality of an X-ray device, and the elimination is mainly divided into two aspects of hardware and image reconstruction software according to the elimination type.

At present, there are several methods for eliminating scattering by using hardware, which are: scattering grids (Anti-scatter Grid), Air gaps (Air-Grid), collimating holes (collimater), or filters (Filter), Filter plates, etc., which mainly reduce the influence of scattered photons by adding a back scattering device at the receiving end of the detector. In addition, the method of improving the material of the flat panel detector, installing a beam compensation filter on the ray source and the like can also achieve the effect of reducing the number of scattered photons.

The scattering elimination method based on the hardware technology can effectively reduce the scattered rays in the rays to a certain extent, but due to the problems of operation space in a machine room, frame counterweight and the like, large-area use is difficult to realize by adding hardware equipment such as a filter and the like, so that the method cannot be applied to large-field treatment.

In the aspect of software, the estimation of the scattering distribution is realized through a computer tool by combining an image processing method, and the scattering correction is carried out on the acquired image. The scatter correction method based on software technology can be roughly divided into three types according to different image processing stages:

improving an image reconstruction mode:

the method comprises the steps of correcting an FDK cone beam reconstruction algorithm, improving a reconstruction width method, improving image quality by using two-dimensional and three-dimensional filtering, reducing metal artifacts by using forward projection reconstruction, performing four-dimensional reconstruction on anatomical deformation of respiration and organ motion and the like.

The evaluation method based on the model scattering distribution comprises the following steps:

such methods include a scatter estimation algorithm using polynomial interpolation, a Beam Stop Array (BSA) based scatter elimination plate, a Moving block-based (Moving block-based) based method, a method of establishing a scatter mathematical model, and the like.

The projection image denoising and three-dimensional reconstruction post-processing method comprises the following steps:

the method comprises the steps of carrying out multi-scale singularity detection on an image before reconstruction, carrying out global denoising on an acquired image by using a method of combining a wavelet with a digital reconstruction filter, removing Gaussian noise and impulse noise by using an adaptive filtering algorithm, carrying out an image denoising algorithm based on coefficient classification and the like.

In addition to the above methods, combining software and hardware technologies for scattering cancellation has been a hot research focus in the last 10 years. Such as a scatter-elimination plate method, a beam attenuation grid method, a primary ray modulation method, a frequency modulation and filtering method, and the like. Different methods have certain effects on the aspect of scattering elimination, but the methods have to be further researched on the aspects of denoising and image information retention.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides a method for acquiring port images in a time synchronization mode.

A method for acquiring port images in a time synchronization mode comprises the following steps:

measuring the flight time of photons from a target in an X-ray source to a detector, acquiring a time window in electronics by setting data, receiving a primary photon signal and rejecting a scattered photon signal at the same time, and eliminating the interference of the scattered photons at a hardware level.

The primary photon signals and the scattered photon signals are effectively distinguished by setting different flight time discrimination thresholds, and the influence of scattered photons on image signal collection is reduced, so that the quality of reconstructed images is improved on hardware.

A method for acquiring port images in a time synchronization mode comprises an initial signal acquisition step, a conversion step and a signal acquisition and processing step;

an initial signal acquisition step: providing a photon start timing signal representative of the photon's start time of flight, wherein the rising edge of the pulse pickup signal can be on the order of picoseconds, the photon start signal providing a start timing signal for calibrating the emission of photons to the timing electronics, in a manner that can be constant ratio timing or leading edge timing,

a conversion step: generating an output signal in response to the received photons when the signal generated by the detector is greater than a signal generation threshold; the amplifying and forming circuit is responsible for outputting the amplified, formed and converted model,

signal acquisition and processing steps: when X-ray passes through the detector, a photocurrent signal proportional to the photon number is generated, the photocurrent signal is amplified and shaped by a signal processing circuit and then sent into a corresponding multi-channel analysis circuit to obtain photon signal intensity in a certain beam pulse period, while photon intensity information is obtained, the flight time information of photons is recorded, an initial timing signal is given by an X-ray source and is used for generating an end timing signal which is output from the detector, a dual-threshold trigger mechanism is adopted for triggering, the end signal of photon flight is provided by the detector and a timing circuit connected with the detector, the signal output by the detector outputs an effective signal after passing through a coincidence system, the coincidence system receives the signal output by the dual-threshold discriminator, the signal in the low-threshold discriminator is delayed for a certain degree, and the delayed low-threshold signal and the high-threshold signal pass through the coincidence system, and forming a final effective signal output within a certain time window.

End signal timing acquisition: when the low-threshold discriminator receives a signal and triggers, the coincidence circuit opens a coincidence time window with a certain width (the width of the coincidence time window can be adjusted in a certain range according to different types of detectors and electronic characteristics), which indicates that the rising edge of the signal is detected in the time window range, and meanwhile, a timestamp signal for recording the start of an event is also generated when the low-threshold signal is finished; because a certain time interval is usually arranged between the low threshold signal and the high threshold signal, in order to shorten the fit time window width as much as possible and reduce the influence of noise signals, the low threshold signal is delayed for a certain time; if a signal from the high threshold trigger is not received within the acceptance time window, indicating that the signal is not a valid signal, the signal may be derived from fluctuations in the signal in the detector, dark counts or other noise, and the timing signal is discarded; if the coincidence discrimination circuit receives the signal from the high-threshold discriminator within the time acceptance window range, the coincidence circuit outputs a valid signal, the signal is judged as a valid signal, and an end time timing signal is sent to a lower circuit.

After the time and intensity signals of photons are obtained, the two signals are sent to a photon signal selection and judgment circuit based on an FPGA to judge and process primary/scattered photons; after passing through the selection circuit, the time information of the primary photons is retained and transmitted to the computer together with the photon intensity information related to the time information for image reconstruction.

The advantage of the present invention is distinguished from the related art of eliminating scattered photon signals on currently existing imaging devices based on X-ray apparatus. The method for measuring the flight time of photons passing through different paths is innovatively adopted, and the signal photons and the scattered photons are identified so as to eliminate the interference of scattered signals. The method does not need to carry out large-scale transformation on the original equipment, only leads out the required signal to an external data processing system in a signal leading-out mode, and has the advantages of low cost and small occupied space of measuring equipment.

By adopting the detector with high time resolution and the electronic equipment, the flight time of photons can be controllably selected and judged, the threshold value can be judged by adjusting the flight time, and scattered photons in a certain range are eliminated, so that the problem of image quality reduction caused by scattering effect is solved to different degrees, the image quality in image guidance is improved, and the precision of radiation diagnosis and treatment is improved.

After the scattered photons are eliminated, the influence of the scattered photons on the image can be obviously reduced, the image reconstruction steps can be simplified, and the image reconstruction efficiency is improved.

Compared with other hardware methods, the device adopted by the invention does not need to add hardware equipment with larger volume on the original device, so that the original operation space of a machine room is not occupied, mechanical changes such as counterweight and the like on a rack are not caused, and the scattered photons can be effectively identified only by a signal leading-out mode and external electronic equipment.

Drawings

A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein the accompanying drawings are included to provide a further understanding of the invention and form a part of this specification, and wherein the illustrated embodiments of the invention and the description thereof are intended to illustrate and not limit the invention, as illustrated in the accompanying drawings, in which:

fig. 1 is a diagram of a route employed by the present invention.

Fig. 2 is a signal acquisition flow chart of the present invention.

Fig. 3 is a timing diagram of the dual-threshold discrimination signal of the present invention.

Figure 4 is a timing diagram of TDC time measurement according to the present invention.

FIG. 5 is a timing diagram for photon signal discrimination according to the present invention.

FIG. 6 is a flow chart of the present invention.

The invention is further illustrated with reference to the following figures and examples.

Detailed Description

It will be apparent that those skilled in the art can make many modifications and variations based on the spirit of the present invention.

The terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description, "plurality" means two or more unless specifically limited otherwise.

Unless expressly stated or limited otherwise, the terms "mounted," "connected," "secured," and the like are intended to be inclusive and mean, for example, that they may be fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

It will be understood by those skilled in the art that, unless otherwise defined, all terms including technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art.

The following examples are further illustrative in combination for ease of understanding the examples and are not intended to limit the embodiments of the invention.

Example 1: as shown in fig. 1, fig. 2, fig. 3, fig. 4 and fig. 5, a method for acquiring a port image in a time synchronization manner includes the following steps:

measuring the flight time of photon signals from a target in an X-ray source to a detector, acquiring a time window in electronics by setting data, receiving the primary photon signals and rejecting scattered photon signals, and eliminating the interference of scattered photons at a hardware level.

The primary photon signals and the scattered photon signals are effectively distinguished by setting different flight time discrimination thresholds, and the influence of scattered photons on image signal collection is reduced, so that the quality of reconstructed images is improved on hardware.

The time of arrival of the primary photon signal at the detector plate can be expressed by the following equation:

t_p＝TDD/c

where TDD is the distance of the X-ray target to a certain imaging unit of the detector and c is the speed of light.

The scattered photon signal arrival time at the detector plate can be expressed by:

t_s＝(TSD+SDD)/c

where TSD is the distance from the X-ray target to the location where Compton scatter occurs, SDD is the distance from the location where scatter occurs to the same imaging unit of the detector, and c is the speed of light.

The resulting time difference is:

Δt＝t_s-t_p

by analyzing the time difference and setting a proper time-of-flight cutoff threshold, primary photons and scattered photons can be distinguished.

As shown in FIG. 1, a method for acquiring port images in a time synchronization manner mainly measures the flight time of photons from an X-ray target end to a detector end, effectively distinguishes primary photons from scattered photons by setting different flight time discrimination thresholds, reduces the influence of the scattered photons on image signal collection, and accordingly improves the quality of reconstructed images on hardware.

A method for acquiring port images in a time synchronization mode reduces the influence of scattered rays on the imaging quality of an X-ray device by measuring the flight time of photons.

The method comprises the following main steps:

after electrons generated in the X-ray source strike the target material, photons are generated by bremsstrahlung radiation, which provides a photon flight time start timing signal while the photons are generated at the target.

After a certain flight distance of the photon, a signal is generated at the detector for detecting the photon, which may include a detected true photon signal and a noise signal.

After the signal output by the detector passes through circuits such as amplification and molding, the generated signal enters a data acquisition circuit, and meanwhile, the time of the photon received by the detector is recorded through an electronic circuit.

By analyzing the time of flight of the recorded photons, a certain threshold can be set and primary and scattered photons can be discriminated by the threshold.

Example 2: as shown in fig. 1, fig. 2, fig. 3, fig. 4, fig. 5 and fig. 6, a method for acquiring a port image in a time synchronization manner includes a start signal acquiring step, a converting step, and a signal acquiring and processing step.

An initial signal acquisition step: a photon start timing signal is provided that represents the start time of flight of the photon. Where the rising edge of the pulse pick-up signal can reach the picosecond scale. The photon start signal will provide the electronics for timing with a start timing signal for calibrating the emission of photons, which may be timed in a constant ratio or leading edge timing technique.

A conversion step: generating an output signal in response to the received photons when the signal generated by the detector is greater than a signal generation threshold; the amplifying and forming circuit is responsible for outputting the amplified, formed and converted model.

The detector mainly comprises a photon sensitive detector and an amplifying and shaping circuit coupled with the photon sensitive detector. The timing circuitry in the data acquisition system provides an end signal for the time of flight of the photons, which is determined by the rising edge of the pulse generated when the photons deposit energy on the detector, and therefore the detector needs to have a fast signal rise time.

On this basis, the detector should also have a lower detection lower threshold and a higher detection efficiency. The detector may use scintillator materials including, but not limited to, crystal materials such as LSO, LYSO, LaBr, GSO, and BGO. Semiconductor and other types of detectors that meet performance requirements may also be used as desired.

Signal acquisition and processing steps: as shown in fig. 2, which is a signal acquisition flow diagram of the system, when X-rays pass through the detector, a photocurrent signal proportional to the number of photons is generated. The photocurrent signal is amplified and shaped by the signal processing circuit and then sent to a corresponding multi-channel analysis circuit to obtain the photon signal intensity in a certain beam pulse period.

At the same time as obtaining photon intensity information, the time-of-flight information that the photons have is also recorded. The start timing signal is given by the X-ray source. The trigger is triggered by a double-threshold trigger mechanism after the termination timing signal is generated and output from the detector. The circuit structure comprises a low-threshold discriminator and a high-threshold discriminator. When the two discriminator input conditions are met, respective outputs will be produced. The dual-threshold discrimination circuit composed of the two discriminators can effectively reduce the interference of noise on signals.

The termination signal for the photon flight is provided by the detector and the timing circuit connected thereto. The signal output by the detector outputs an effective signal after passing through the coincidence system. The coincidence system receives the signal output from the dual-threshold discriminator and delays the signal in the low-threshold discriminator to a certain extent. And forming final effective signal output in a certain time window after the delayed low-threshold signal and the delayed high-threshold signal pass through a coincidence system.

FIG. 3 shows a timing diagram of the termination signal timing acquisition logic at the detector. When the low threshold discriminator receives a signal and triggers, the coincidence circuit opens a coincidence time window of a certain width (the width of the coincidence time window can be adjusted within a certain range according to different types of detectors and electronic characteristics), indicating that within the time window range, the rising edge of the signal is detected, and at the same time, a timestamp signal for recording the start of the event is also generated at the end of the low threshold signal. Since there is usually a certain time interval between the low threshold signal and the high threshold signal, the low threshold signal may be delayed to shorten the fitting time window width as much as possible and reduce the influence of noise signals. If a signal from the high threshold trigger is not received within the acceptance time window, it is an indication that the signal is not a valid signal, which may result from fluctuations in the signal in the detector, dark counts or other noise, and the timing signal is discarded accordingly. If the coincidence discrimination circuit receives the signal from the high-threshold discriminator within the time acceptance window range, the coincidence circuit outputs a valid signal, the signal is judged as a valid signal, and an end time timing signal is sent to a lower circuit.

After the time and intensity signals of the photons are obtained, the two signals are sent to a photon signal selection and judgment circuit based on an FPGA to judge and process primary/scattered photons. After passing through the selection circuit, the time information of the primary photons is retained and transmitted to the computer together with the photon intensity information related to the time information for image reconstruction.

Time-of-flight Time signal measurements are generated by a Time-to-Digital Converter (DC), TDC has a multi-hit response capability that enables simultaneous measurement of a beam of photon signals.

The TDC measurement time is composed of a coarse counting part and a fine counting part. Wherein the coarse count is used to generate a base clock count while increasing the measurement range. The reference clock frequency used by the coarse counting module is generally hundreds of MHz, and the time precision of a plurality of ns can be achieved. The fine counting module adopts a Time delay Interpolation technology (Time Interpolation) to perform Time Interpolation in one clock period, and can achieve the Time resolution of tens of ps so as to realize the high-precision Time measurement capability. The TDC measurement module comprises a PLL phase-locked loop, a high-speed DLL clock, a latch, a decoder and the like.

The TDC measurement time is described below, comprising the following steps:

the time T to be measured is defined as the time interval between two rising edge signals of the TDC start and stop signal pulses. FIG. 4 shows a timing diagram of the measurement of the time intervals, respectively defining the coarse count measurement time period T_cWhich is an integer multiple of the measurement clock period. Defining the clock period as T_clkWhen the time length between the starting timing signal input into the TDC and the rising edge M of the next clock cycle is T₁The time between the termination timing signal and the next adjacent clock signal rising edge N is T₂Then the length of time measured by the counter is:

T_c＝(N-M)×T_clk

the measurement time interval obtained by the above process can be represented by the following formula:

T＝(N-M)×T_clk+T₁-T₂

according to the above process, the interval between the start and end timing signals is divided into three parts, the coarse measurement time interval is determined by the clock count, T₁And T₂The time interval is usually less than one unit clock cycle and a delay interpolation method is used for fine measurement. The delay interpolation method adopts a time-to-digital conversion method based on gate delay, and the number of signals passing through logic gates is calculated. The circuit structure of the delay line can adopt one of a basic delay chain, a vernier differential delay chain, a delay chain with DLL or two-stage delay.

Observing the propagation of the signal on the delay line when the rising edge of the start timing signal arrives, when N passes₁After each delay unit, the start signal is inverted, which means that the start signal passes through n delay units and coincides with the rising edge of the nearest clock signal clk, and at this time:

T₁＝T_clk-N₁τ where τ is the delay of one delay unit. Similarly, when the termination signal is inputted to the input terminal of the flip-flop, the termination signal passes through N₂After the delay unit, signal jump occurs, which includes:

T₂＝T_clk-N₂τ

when the TDC receives a valid detector time signal from the coincidence system, the latch latches the current clock value. The decoder decodes the clock value to generate a photon time stamp and transmits the signal to the memory.

The method for selecting and judging the primary photon signal and the scattered photon signal comprises the following steps:

FIG. 5 shows a timing diagram of photon signal discrimination logic, and when a photon time-of-flight start timing signal is obtained from the X-ray source, the coincidence circuit for discriminating the primary photon from the scattered photon opens a certain timing window width. The determination of the timing window width can be determined according to the flight time of the primary photon on the fixed path, and can be adjusted according to actual requirements. If the photon flight time ending timing signal given by the detector is within the range of the timing window width, the photon is judged as the primary photon, otherwise, the photon is defined as the scattered photon.

As described above, although the embodiments of the present invention have been described in detail, it will be apparent to those skilled in the art that many modifications are possible without substantially departing from the spirit and scope of the present invention. Therefore, such modifications are also all included in the scope of protection of the present invention.