WO2018090901A1

WO2018090901A1 - Device and method for measuring time information of photon

Info

Publication number: WO2018090901A1
Application number: PCT/CN2017/110865
Authority: WO
Inventors: 赵指向; 龚政; 黄秋; 许剑锋
Original assignee: 武汉中派科技有限责任公司
Priority date: 2016-11-15
Filing date: 2017-11-14
Publication date: 2018-05-24
Also published as: CN106656390B; CN106656390A

Abstract

Provided in the present invention are a device and method for measuring time information of a photon. The device comprises a current detection circuit and a processing circuit, wherein the current detection circuit is used to be connected to a photoelectric sensor to detect an initial signal output by the photoelectric sensor and generate a corresponding detection signal; an input end of the processing circuit is connected to an output end of the current detection circuit; and the processing circuit is used for determining the arrival time of a high-energy photon detected by the photoelectric sensor according to the detection signal, estimating the time drift according to the detection signal, and correcting the arrival time based on the time drift. According to the device and method in an embodiment of the present invention, estimating the time drift and correcting the arrival time based on the time drift can correct a time measurement error brought about by a dark event, and simply and conveniently obtain a time measurement result with high accuracy.

Description

Apparatus and method for measuring photon time information

Technical field

The present invention relates to the field of circuits, and in particular to an apparatus and method for measuring photon time information.

Background technique

The front-end detection device of the high-energy photon (X-ray, gamma photon, etc.) measurement system generally includes a scintillation crystal, a photodetector (or photosensor), and a photon measurement front-end circuit. High-energy photons interact with scintillation crystals to produce a lower energy subset of visible light. The photoelectric sensor converts the optical signal carried by the visible light subgroup into an electrical signal. The main purpose of the photon measurement front-end circuit is to obtain the energy and arrival time of high-energy photons by measuring the electrical signals generated by the photosensors. For example, in positron emission tomography (PET) and single photon emission imaging (SPECT) systems, gamma photons interact with scintillation crystals, such as yttrium silicate (LYSO) crystals, to produce a lower energy subset of visible light. A photoelectric sensor, such as a photomultiplier tube (PMT) or a silicon photomultiplier tube (SiPM), converts an optical signal carried by the visible light subgroup into an electrical signal. The photon measurement front-end circuit measures the electrical signal generated by the photosensor to obtain the energy and arrival time of the gamma photon.

In order to avoid the problem that the energy calculated by the analog-to-digital converter (ADC) sampling in the conventional technology is affected by the start time of the electrical signal output by the photosensor, an improved photon measurement front-end circuit is proposed, which utilizes an integration module. The electrical signal output by the photoelectric sensor is integrated, and when the accumulated charge in the integrating module reaches a certain amount, the pulse signal can be triggered. Information such as energy and arrival time of high energy photons can then be obtained based on the pulse signal.

When using an improved photon measurement front-end circuit to measure the arrival time of high-energy photons, the following problems exist. Studies have shown that the best time resolution can be achieved by measuring the time of the first few photons generated when high-energy photons act on the scintillation crystal. Therefore, in the improved photon measurement front-end circuit, it is desirable to generate a pulse signal usable for time measurement by setting system parameters such that after the integration module accumulates charges generated by n (for example, five) photons. However, this method does not necessarily achieve the best time resolution for the following reasons: Under the current technical conditions, the dark event rate in a photoelectric sensor such as SiPM is high. Dark event The charge will accumulate in the integration module. When high-energy photons act on the scintillation crystal, if the integration module has accumulated the charge generated by m dark events, the trigger theoretically occurs after the integration module accumulates the charge generated by the n-mth photon, instead of the nth. Since dark events and high-energy photons are randomly present, the value of m may be evenly distributed in the range of 0 to n-1. Therefore, when generating a pulse signal usable for time measurement, the charge accumulated in the integration module caused by high-energy photons is not necessarily the charge generated by n photons, but may be any number in the range of 1 to n. The charge produced by the visible light. That is to say, the baseline of the charge used to determine the arrival time of the high-energy photon may drift, so the measured arrival time may also drift as compared to the actual arrival time. For the above reasons, measurement accuracy may be affected when using an improved photon measurement front-end circuit to measure the arrival time of high-energy photons.

Accordingly, it is desirable to provide an apparatus for measuring photon time information to at least partially address the above-discussed problems in the prior art.

Summary of the invention

In order to at least partially solve the problems in the prior art, in accordance with an aspect of the present invention, an apparatus for measuring photon time information is provided. The device includes a current detection circuit and a processing circuit. The current detecting circuit is used for connecting the photoelectric sensor, detecting the initial signal output by the photoelectric sensor and generating a corresponding detecting signal. The input end of the processing circuit is connected to the output end of the current detecting circuit, and the processing circuit is configured to determine the arrival time of the high-energy photon detected by the photosensor according to the detection signal, estimate the time drift amount according to the detection signal, and correct the arrival time based on the time drift amount. .

According to another aspect of the present invention, a method for measuring photon time information includes: detecting an initial signal output by a photosensor and generating a corresponding detection signal; determining an arrival time of a high energy photon detected by the photosensor according to the detection signal Estimating the amount of time drift based on the detected signal; and correcting the arrival time based on the amount of time drift.

According to the apparatus and method of the embodiment of the present invention, the amount of time drift is estimated and the arrival time is corrected based on the amount of time drift, which can correct the time measurement error caused by the dark event, and obtain the high-precision time measurement result simply and conveniently.

A series of simplified concepts are introduced in the Summary of the Invention, which are further described in detail in the Detailed Description section. This Summary is not intended to be an attempt to define the key features and essential technical features of the claimed embodiments. The scope of protection of the technical solutions.

Advantages and features of the present invention are described in detail below with reference to the accompanying drawings.

DRAWINGS

The following drawings of the invention are hereby incorporated by reference in their entirety in their entirety. The embodiments of the invention and the description thereof are shown in the drawings In the drawing,

1 shows a schematic block diagram of an improved photon measurement front end circuit in accordance with one example;

2 shows a schematic block diagram of an apparatus for measuring photon time information, in accordance with one embodiment of the present invention;

3 shows a schematic block diagram of an apparatus for measuring photon time information, in accordance with one embodiment of the present invention;

4 is a waveform diagram showing a digital signal generated by a current detecting circuit according to an embodiment of the present invention;

Figure 5a shows an analysis diagram of measurement error of arrival time without correction, in accordance with one embodiment of the present invention;

Figure 5b is a graph showing an analysis of the measurement error of the arrival time in the case of correction using means for measuring photon time information, in accordance with one embodiment of the present invention;

6 is an analysis diagram showing measurement errors of arrival time in the case where correction is not performed and correction is performed using a device for measuring photon time information, according to an embodiment of the present invention;

FIG. 7 shows a flow diagram of a method for measuring photon time information, in accordance with one embodiment of the present invention.

detailed description

In the following description, numerous details are provided in order to provide a thorough understanding of the invention. However, those skilled in the art will appreciate that the following description is directed to the preferred embodiments of the invention, and that the invention may be practiced without one or more such details. Moreover, in order to avoid confusion with the present invention, some of the technical features well known in the art are not described.

As described above, in order to avoid the problem that the energy calculated by the ADC sampling in the conventional art is affected by the start time of the electrical signal output from the photosensor, an improved photon measurement front end circuit is currently proposed. FIG. 1 shows a schematic block diagram of an improved photon measurement front end circuit 100 in accordance with one example. It should be noted that the direction of the arrow shown in the figures herein is the transmission of the signal. Direction, not necessarily the direction of flow of the signal.

As shown in FIG. 1, the improved photon measurement front end circuit 100 includes an integration module 110, a comparator 120, a transmission controller 130, a negative feedback module 140, and a measurement module 150.

The integration module 110 is for connecting an output of a photosensor (not shown) and an output of the negative feedback module 140. The integration module 110 can receive an initial signal from the photosensor and a feedback signal from the negative feedback module 140, integrate the difference between the initial signal and the feedback signal, and output an integrated signal.

One input of comparator 120 is coupled to the output of integration module 110 and the other input of comparator 120 is coupled to a reference level. Comparator 120 can compare the integrated signal to a reference level and generate a comparison signal. For example, when the level value of the integrated signal is higher than the reference level, the comparator 120 may output a high level, and when the level value of the integrated signal is equal to or smaller than the reference level, the comparator 120 may output a low level. Therefore, only the high level and low level states can exist in the comparison signal output by the comparator 120.

The input of the transmission controller 130 is coupled to the output of the comparator 120. The transmission controller 130 can control the transmission of the comparison signal to output a digital signal using a clock signal. A high level in the digital signal having a duration equal to the period of the clock signal represents a first logic level, and a low level in the digital signal having a duration equal to the period of the clock signal represents a second logic level. In one example, the first logic level may be a logic level "1", the second logic level may be a logic level "0", and the digital signal is composed of logic levels "1" and "0" sequence.

The input of the negative feedback module 140 is coupled to the output of the transmission controller 130, and the negative feedback module 140 can convert the digital signal to a feedback signal and feed back the feedback signal to the integration module 110. The feedback signal is opposite to the flow direction of the initial signal.

It can be understood that when an effective event or a dark event occurs, the integrated signal obtained at the beginning is relatively small, and the comparison signal and the digital signal can always be in a low state. When the level value of the integrated signal is greater than the reference level, a high level appears in the comparison signal. Subsequently, a high level also appears in the digital signal. The time at which the first high level in the comparison signal or digital signal occurs when the valid event occurs can be taken as the arrival time of the high energy photon. The effective event described herein refers to an event in which a high-energy photon (such as a gamma photon, etc.) acts in a scintillation crystal connected to a photosensor to generate a current signal in a photosensor, and a dark event refers to noise (usually a hot electron) An event that causes a current signal to be generated in the photosensor. The photosensor can output a pulsed current signal (ie, the initial signal) when a valid event or a dark event occurs. Electricity generated by an effective event The energy of the stream signal is much larger than the energy of the current signal generated by the dark event, the former usually being tens to thousands of times the latter. Therefore, by analyzing the energy of the current signal output by the photosensor, it can be determined whether the event that occurred is a valid event or a dark event.

The measurement module 150 can measure various information such as energy, arrival time, and the like of high-energy photons using digital signals.

As described above, the best temporal resolution can be achieved by measuring the time at which the first few photons generated by the energetic photons acting on the scintillation crystal (i.e., when an effective event occurs). According to the operation of the improved photon measurement front end circuit 100, the charge that needs to be accumulated in the integration module 110 when the first high level of the comparison signal or digital signal occurs can be controlled by setting the reference level of the comparator 120. Therefore, it is desirable that the optimum time resolution can be obtained by setting the reference level to a level value of the integrated signal obtained by integrating the electric signal generated by the n visible light sub-integrals in the integration module 110. However, due to the dark event caused by the dark event as described above, it may be difficult to obtain the desired time measurement accuracy in this manner.

It should be understood that FIG. 1 and the related description are merely illustrative of the structure of the improved photon measurement front end circuit, which does not indicate that the apparatus provided by the embodiment of the present invention is only applicable to the photon measurement front end circuit shown in FIG. The device provided by the embodiment of the invention can be applied to other photon measurement front-end circuits adopting similar structures and principles.

In order to solve the above problems, according to an aspect of the present invention, an apparatus for measuring photon time information is provided. 2 shows a schematic block diagram of an apparatus 200 for measuring photon time information, in accordance with one embodiment of the present invention.

As shown in FIG. 2, device 200 includes current detection circuit 210 and processing circuit 220. The current detecting circuit 210 is configured to connect the photosensor, detect an initial signal output by the photosensor, and generate a corresponding detection signal. An input end of the processing circuit 220 is connected to an output end of the current detecting circuit 210, and the processing circuit 220 is configured to determine an arrival time of the high-energy photon detected by the photosensor according to the detection signal, estimate a time drift amount according to the detection signal, and arrive at the time drift amount based on the Time to correct.

Alternatively, the photosensors described herein can be any suitable photosensor, such as SiPM, PMT, avalanche photodiode (APD), and the like. In addition, the photosensors described herein may be photodetection devices of various scales such as sensor micro-elements, sensor units, and sensor arrays, and are not limited to a complete independent sensor. Those skilled in the art will appreciate that in a PET system, when positron annihilation occurs, a pair of gamma photons are generated. Sparkling crystals are gamma When a photon strikes, the photosensor outputs an initial signal, which is typically a pulsed current signal. The photosensor may output the initial signal to the device 200 such that the device 200 obtains time information of the gamma photon by measuring the initial signal, and obtains information about the positron annihilation event in combination with information such as energy information of the gamma photon.

The current detecting circuit 210 is configured to detect an initial signal output by the photosensor, which may be implemented using a circuit portion other than the measuring module 150 as shown in FIG. It can be understood that the current detecting circuit 210 detects an initial signal that the photosensor outputs during a certain period of time. During this time period, a valid event or a dark event may or may not occur. In the period in which no event occurs, the initial signal output by the photosensor is 0, and the detection signal generated by the current detecting circuit 210 may also be 0.

The processing circuit 220 can be implemented in any suitable hardware, software, and/or firmware, such as a field programmable gate array (FPGA), a digital signal processor (DSP), a complex programmable logic device (CPLD), a micro control unit. (MCU) or central processing unit (CPU) implementation. The processing circuit 220 can determine the arrival time of the high energy photons based on the detection signal. For example, a time-to-digital converter (TDC) can be used to measure the rising edge of the detected signal to determine the time of arrival. The processing circuit 220 can also estimate the amount of time drift based on the detected signal. As described above, the charge generated by the dark event can be accumulated in the integration module of the photon measurement front end circuit 100 such that the charge baseline drifts. The level value of the detection signal may reflect whether an active event and/or a dark event occurs and the amount of energy produced by the active event and/or the dark event. Therefore, the amount of charge accumulated in the integration module at the time of occurrence of the effective event can be estimated based on the detection signal, so that the amount of time drift can be estimated. The arrival time can then be corrected based on the amount of time drift.

The device 200 can be implemented by a hardware structure similar to the improved photon measurement front end circuit 100, which has a simple hardware structure and low cost. The apparatus 200 can solve the problem of a charge baseline shift due to a dark event occurring in the photon measurement front end circuit of the photon measurement front end circuit 100 and thereby causing inaccurate time measurement.

According to the apparatus of the embodiment of the present invention, the amount of time drift is estimated and the arrival time is corrected based on the amount of time drift, which can correct the time measurement error caused by the dark event, and obtain a highly accurate time measurement result simply and conveniently.

Alternatively, the detection signal can be a digital signal. The digital signal consists of a high level and a low level of equal duration. The sum of all high levels in the digital signal is proportional to the integral of the initial signal versus time. In one example, the current sensing circuit can be implemented as circuit 310 of FIG. Form to generate the above digital signal. FIG. 3 shows a schematic block diagram of an apparatus 300 for measuring photon time information, in accordance with one embodiment of the present invention.

As shown in FIG. 3, the integration module 311 is configured to connect the output of the photosensor and the output of the negative feedback module 314, and receive an initial signal from the photosensor and a feedback signal from the negative feedback module 314, for the initial signal and the feedback signal. The difference is integrated and the integrated signal is output.

The current detecting circuit 310 is a circuit including a negative feedback link, and the feedback signal is input to the integrating module 311. At the same time, the integration module 311 also receives an initial signal output by the photosensor. Both the initial signal and the feedback signal are current signals, and their flow directions are opposite. For example, if the initial signal is flowing from the integration module 311, the feedback signal can be set to flow from the negative feedback module 314 to the integration module 311. Therefore, for the integration module 311, the difference between the initial signal and the feedback signal is actually finally input, and the integration module 311 can integrate the difference. The integration module 311 can be implemented by an analog integration circuit, for example, by a circuit composed of components such as a resistor, a capacitor, and an operational amplifier.

One input of comparator 312 is coupled to the output of integration module 311 and the other input of comparator 312 is coupled to a reference level. Comparator 312 is operative to compare the integrated signal to a reference level and generate a comparison signal.

For example, when the level value of the integrated signal is higher than the reference level, the comparator 312 can output a high level, and when the level value of the integrated signal is equal to or smaller than the reference level, the comparator 312 can output a low level. Therefore, only the high level and low level states can exist in the comparison signal output from the comparator 312. That is, the comparison signal output by the comparator 312 may be a signal that switches between the high level and the low state over time. Alternatively, the reference level can be a ground level. The reference level can have any suitable level value. The reference level is the implementation of the ground level is relatively simple, and the final measurement results are more accurate.

The input end of the transmission controller 313 is connected to the output of the comparator 312 for controlling the transmission of the comparison signal by the clock signal to output a digital signal, wherein the duration of the digital signal is equal to the period of the clock signal. The level represents the first logic level, and the low level in the digital signal having a duration equal to the period of the clock signal represents the second logic level.

The comparison signal can be a signal that switches between a high level and a low state over time. In the comparison signal, the duration of the high and low levels may be changed in real time and cannot be determined. Therefore, the comparison signal can be time-quantized by the transmission controller 313 such that the duration of each successive high level or low level is the period of the clock signal. Integer multiple. This temporal quantization corresponds to the time discretization in the analog-to-digital conversion process, and therefore, from the viewpoint of function, both the comparator 312 and the transmission controller 313 can be regarded as a 1-bit ADC. In the digital signal output from the transmission controller 313, a high level having a duration equal to a period of the clock signal represents a first logic level, and a low level having a duration equal to a period of the clock signal represents a second logic level. In one example, the first logic level may be a logic level "1", the second logic level may be a logic level "0", and the digital signal is composed of logic levels "1" and "0" sequence. Assuming that the frequency of the clock signal is 100 Hz, that is, the period is 0.01 s, the duration of a single "1" or "0" in the digital signal is 0.01 s. In addition, it can be understood that when a plurality of "1"s or a plurality of "0"s appear consecutively, the duration of the plurality of "1"s or a plurality of "0"s is an integer multiple of 0.01 s. The transmission controller 313 may be a register or a switching circuit controlled by a clock signal or the like.

The input of the negative feedback module 314 is connected to the output of the transmission controller 313, and the negative feedback module 314 is used to convert the digital signal into a feedback signal and feed back the feedback signal to the integration module 311.

The negative feedback module 314 can include a digital to analog converter (DAC) for digital to analog conversion of the digital signal to convert it to an analog signal. Specifically, the DAC may be a 1-bit DAC to convert a sequence consisting of "1" and "0" output from the transmission controller 313 into an analog signal, for example, a voltage signal whose amplitude changes with time. The negative feedback module 314 can further include a current output circuit (which can be considered a "controlled current source"), such as a current output circuit composed of a resistor. The DAC is connected to the input of the integration module 311 via a current output circuit. The current output circuit generates a current signal, that is, a feedback signal, based on the voltage signal described above. The DAC and current output circuit can also be implemented simply by a resistor. The digital signal outputted by the transmission controller 313 is a voltage signal that can be converted into a current signal, that is, a feedback signal, through the resistor. The feedback signal is opposite to the initial signal direction, and the cumulative effect of the initial signal on the integration module 311 cancels each other, and the integral signal output by the integration module 311 can be prevented from being excessively large to keep the circuit stable. Optionally, the negative feedback module 314 is coupled to the processing circuit 320. The processing circuit 320 can be further configured to adjust the amplitude of the feedback signal output by the negative feedback module 314.

Since the feedback signal is positively and negatively depleted from the cumulative effect of the initial signal on the integration module 311, when the pulse duration of the initial signal has ended and the amplitude of the feedback signal stabilizes at zero (ie, the negative feedback action for the initial signal has ceased) The accumulated value of the feedback signal caused by the initial signal can be regarded as the accumulated value of the initial signal. Also, the accumulated value of the feedback signal is proportional to the number of "1"s in the digital signal. Therefore, digital signals can be utilized to calculate the energy of high energy photons. Of course, the comparison signal output by the comparator 312 can also be used to calculate the energy of the high energy photon, and only the same circuit as the transmission controller 313 is added to the subsequent processing circuit 320.

The input of the processing circuit 320 is coupled to the output of the transmission controller 313, and the processing circuit 320 can measure the arrival time of the high energy photons based on the digital signal. According to another example, the input of the processing circuit 320 can also be coupled to the output of the comparator 312 for measuring the arrival time of the high energy photons based on the comparison signal.

In particular, processing circuit 320 can include a time measurement module. The input of the time measuring module can be connected to the output of the transmission controller 313 for measuring the arrival time of the high energy photons using digital signals. The time at which the rising edge of the digital signal occurs can reflect the arrival time of the high energy photon. The time measurement module can measure the time at which the rising edge of the digital signal from the transmission controller 313 occurs. The method is to use the clock of the digital system to directly record the time when the rising edge occurs. This method is simple, quick and easy to implement. The time measurement module can also use a high-precision analog TDC or digital TDC (such as digital TDC based on FPGA delay line) to make accurate time measurements on the rising edge of the digital signal. This method can improve the accuracy of time measurement.

Optionally, the input of the time measuring module can also be connected to the output of the comparator 312 for measuring the arrival time of the high energy photon by using the comparison signal. The comparison signal is a signal that has not been quantized in time by the transmission controller 313. Therefore, by directly measuring the time information of the comparison signal, more accurate time information of the high-energy photon can be obtained. The time measurement module can measure the time at which the rising edge of the comparison signal from comparator 312 occurs. The method is to directly record the rise time of the rising edge using the clock of the FPGA digital system. The time measurement module can also use a high precision analog TDC or digital TDC (eg digital TDC based on FPGA delay line) to make accurate time measurements of the rising edge of the comparison signal.

In addition to the time measurement, the processing circuit 320 can also perform other desired measurements based on the digital signal, such as energy measurements, dark current measurements, waveform measurements, gain measurements, and the like.

The device 300 according to an embodiment of the present invention has a simple circuit structure, and active devices such as amplifiers and ADCs may not be used or used less. Therefore, such a device is low in cost and low in power consumption.

Generating a digital detection signal facilitates subsequent calculation of information such as energy or time of high energy photons.

Illustratively, the reference level received by the comparator 312 is equal to the level value of the integrated signal obtained by integrating the initial signal output when the photosensor detects a certain number of visible light sub-integrators. The specific number can be any suitable number, which can be determined as needed, The invention does not limit this. For example, a particular number can be equal to 10. In the case where the specific number is equal to 10, triggering the pulse signal available for time measurement (ie, triggering a high level in the digital signal) may occur when the charge of the first to tenth photons generated by the active event is collected by the integration module. time. On average, it can be considered that triggering a pulse signal that can be used for time measurement occurs at the moment when the charge of the fifth photon generated by the active event is collected by the integration module. This configuration allows for a higher time resolution.

Exemplarily, the processing circuit 120 can determine the arrival time of the high-energy photon by determining the effective trigger time according to the occurrence rule of the high level and the low level in the digital signal and using the effective trigger time as the arrival time, wherein the effective trigger time Is the time at which the active event triggers a high level in the digital signal. In one example, the effective trigger time may be the time that is triggered by a valid event to transition from a low level to a high level in the digital signal, ie, a rising edge. In another example, the effective trigger time may be a time that is triggered by a valid event to transition from a high level to a low level in the digital signal, ie, a falling edge. In yet another example, the effective trigger time can be any of the durations of the high level triggered by the active event.

As described above, the digital signal can be a sequence consisting of logic levels "1" and "0". In this case, it can be considered that the occurrence of the first logic level "1" in the digital signal is triggered by a valid event or a dark event. The following is an example.

The initial signal generated by a photon and a dark event in the photosensor is the same, so the level of the integrated signal obtained by integration in the integration module is also the same, assuming 0.1V. In addition, it is assumed that the reference level of the comparator is equal to 1V, which is equivalent to the total level value of the integrated signal obtained by integrating the initial signal generated in the photosensor by 10 visible pixels or 10 dark events in the integration module. Since a high-energy photon can induce a large number of visible light, each effective event produces much more energy than each dark event produces. However, dark events occur more frequently than they occur.

4 is a waveform diagram showing a digital signal generated by a current detecting circuit according to an embodiment of the present invention. Figure 4 is for illustrative purposes only and is not drawn to scale. The time axis of Fig. 4 gradually changes in order from left to right. As shown in FIG. 4, the digital signal includes four high levels (i.e., the first logic level "1"), which are represented by 410, 420, 430, and 440, respectively. There are 98 low levels (ie, the second logic level "0") between the high level 410 and the high level 420, and there are 101 low levels between the high level 420 and the high level 430. There are 50 low levels between the high level 430 and the high level 440. Assuming that a dark event occurs once every 10 nanoseconds, it occurs every 1 microsecond. 100 times, that is, the integrated signal obtained by integrating the initial signal generated by the 1 microsecond dark event in the integration module reaches the reference level, and the digital signal outputs "1" once, and between the two "1"s. It can be 99 "0"s. The above describes the ideal state. In fact, the number of "0"s appearing between two dark events is usually not constant, but can float up and down within a certain range, as shown in FIG.

As described above, the energy of the current signal generated by the effective event is much greater than the energy of the current signal generated by the dark event. Therefore, when the effective event does not occur, a scattered "1" may occur in the digital signal due to the presence of a dark event. When a valid event occurs, a large number of "1"s can appear in the digital signal in a short period of time. Therefore, it can be determined whether an effective event occurs according to the occurrence rule of the high level and the low level in the digital signal. In the case where it is determined that the valid event has not occurred, the time at which each "1" occurs or the time at which it ends or at any time during its appearance and end period can be regarded as the time at which the dark event triggers a high level in the digital signal, that is, Dark trigger time. In the case where it is determined that a valid event occurs, the time or end time of the first "1" caused by the valid event or any time during its occurrence and end may be regarded as a high level in the valid event trigger digital signal. Time, which is the effective trigger time. Referring to FIG. 4, the time corresponding to the rising edge of the

high level

410, 420, and 430 is the dark trigger time, and the time corresponding to the rising edge of the high level 440 is the effective trigger time.

Thus, the effective trigger time and/or the dark trigger time can be determined according to the occurrence rule of the high level and the low level in the digital signal. The occurrence of each valid event corresponds to the generation of a high-energy photon. When it is desired to know the arrival time of a high-energy photon, it can be determined by the effective trigger time of its corresponding valid event. That is, the effective trigger time can be regarded as high energy. The arrival time of the photon.

Illustratively, the processing circuit 120 can estimate the amount of time drift by determining the previous dark trigger time before the effective trigger time according to the occurrence rule of the high level and the low level in the digital signal, wherein the dark trigger time is dark The time at which the event triggers a high level in the digital signal; the time interval between the effective trigger time and the previous dark trigger time is calculated; the amount of dark events occurring during the time interval is estimated; and the dark event occurs according to the time interval The amount of time is estimated by the amount of time drift. In one example, the dark trigger time may be the time that is triggered by a dark event to transition from a low level to a high level in the digital signal, ie, a rising edge. In another example, the dark trigger time may be the time that is triggered by a dark event to transition from a high level to a low level in the digital signal, ie, a falling edge. In yet another example, the dark trigger time may be in the duration of a high level triggered by a dark event Any time.

The amount of dark events can be any indicator that measures how many dark events occur, such as the number of dark events, the amount of charge in a dark event, or the energy of a dark event. With continued reference to FIG. 4, in the case where it is determined that the occurrence of the high level 440 represents the occurrence of an active event, if it is desired to know the arrival time of the high energy photon corresponding to the effective event, the time drift corresponding to the arrival time can be determined by the following manner. the amount. It can be seen from the digital signal that the highest level that occurred last time was a high level 430 before the high level 440 occurred. The dark trigger time corresponding to the high level 430 can be regarded as the previous dark trigger time of the effective trigger time. Then, the time interval between the effective trigger time and the previous dark trigger time can be calculated. There are 50 "0"s between the high level 430 and the high level 440. Assuming that the duration of each "0" is equal to 10 nanoseconds, the time interval between the effective trigger time and the previous dark trigger time is 50. Nanoseconds. As described above, assuming that dark events occur on average every 10 nanoseconds, 50 dark events can occur within 50 nanoseconds. Then, based on empirical or theoretical calculations, it is possible to estimate how much charge accumulation generated by 50 dark events in the integration module will cause the arrival time to drift (ie, estimate the amount of time drift). In the above example, the duration of each high level and each low level in the digital signal is equal to the time interval between two consecutive dark events, however, this is merely an example and not a limitation of the present invention.

Figure 5a shows an analysis of the measurement error of the arrival time without correction, in accordance with one embodiment of the present invention; Figure 5b shows the correction using the means for measuring photon time information, in accordance with one embodiment of the present invention. An analysis of the measurement error of the arrival time in the case. In Figures 5a and 5b, the abscissa indicates that the error corresponds to the difference between the determined arrival time and the actual arrival time, and the ordinate indicates the difference between the determined arrival time and the actual arrival time. The number of times the number of visible light sub-shots indicated by the coordinates.

The embodiment shown in Figures 5a and 5b is implemented under the condition that the reference level is equal to the level value of the integrated signal obtained by integrating the initial signal output from the 10 visible light sub-integration modules. As described above, in the case where the specific number is equal to 10, triggering the pulse signal usable for time measurement (ie, triggering a high level in the digital signal) may occur in the first to ten photons generated by the effective event. The moment the integration module collects. On average, it can be considered that triggering a pulse signal that can be used for time measurement occurs at the moment when the charge of the fifth photon generated by the active event is collected by the integration module. When estimating the occurrence time of a pulse signal usable for time measurement in this manner, if the correction of the device provided by the embodiment of the present invention is not performed, the time of occurrence error The difference, that is, the arrival time of high-energy photons is -5 to +4 occurrences of visible light. As shown in the simulation results of Fig. 5a, the distribution of the cases where the error is -5 to +4 photons is not completely uniform due to statistical fluctuations. The root mean square (RMS) error for this case is 2.9144.

As shown in Fig. 5b, in the case of correction using a device for measuring photon time information, the distribution of errors changes from an approximately uniform distribution to an approximately normal distribution, and the RMS error is reduced from 2.9144 to 1.8943. Therefore, estimating the time drift amount by using the apparatus provided by the embodiment of the present invention and correcting the arrival time based on the time drift amount can effectively reduce the time measurement error.

Further, referring to FIG. 6, there is shown an analysis diagram of measurement error of arrival time in the case where correction is not performed and correction is performed using an apparatus for measuring photon time information, according to an embodiment of the present invention. The abscissa of Fig. 6 indicates the specific number of visible photons, and the ordinate indicates the root mean square error under the setting conditions of the specific number of photons indicated by the corresponding abscissa. The specific number represented by the abscissa of FIG. 6 is obtained by integrating the set reference level described above to be equal to the initial signal output when the photosensor detects a certain number of visible light sub-integrated in the integration module. The particular number described in the embodiment of the level value of the integrated signal.

In Fig. 6, the upper curve is a curve of the measurement error of the arrival time without correction, and the lower curve is the curve of the measurement error of the arrival time in the case of correction using the means for measuring the photon time information. .

A specific number can be represented by n. According to Fig. 6, the RMS error under the setting conditions of different n values (2 to 20 in the abscissa axis) can be compared. It can be seen from FIG. 6 that estimating the time drift amount by using the apparatus provided by the embodiment of the present invention and correcting the arrival time based on the time drift amount can reduce the time measurement error, and when n is larger, in the case of uncorrected and corrected The more obvious the error gap.

Illustratively, the processing circuit may estimate the amount of time drift based on the amount of dark events occurring during the time interval by estimating the amount of time drift using a lookup table and an amount of dark events occurring within the time interval, wherein The lookup table is used to record the relationship between the amount of dark events and the amount of time drift.

The relationship between the amount of dark events and the amount of time drift can be predetermined and recorded in a look-up table by any suitable means. For example, the amount of dark events and the amount of time drift can be predetermined by theoretical calculations, computer simulations, or experiments. Relationship between. For example, an oscilloscope can be used to measure the waveform of the integrated signal output by the integration module to determine the drift of the charge baseline each time an active event occurs, and the amount of time drift can be determined. Then, it can be caused by the current dark event The amount of charge drift is found in the lookup table for the corresponding amount of time drift. The contents of the lookup table record may differ depending on the design of the photosensor, so it can be determined in advance by experiments or the like.

For example, the lookup table can record: charge baseline drift 1 dark event corresponding to the amount of charge caused by time drift 0.1 nanoseconds, charge baseline drift 2 dark events corresponding to the amount of charge caused by time drift 0.22 nanoseconds, charge baseline drift 5 dark The amount of charge corresponding to the event causes a time drift of 0.6 nanoseconds, and so on. Then, in the case where it is known that the charge baseline drifts by the amount of charge corresponding to five dark events, it can be determined that the arrival time has drifted by 0.6 nanoseconds. That is to say, the actual arrival time of the high-energy photon can be considered to be 0.6 nanoseconds later than the effective trigger time. In this way, the arrival time of the high-energy photons can be corrected based on the above principle.

There may not be a linear relationship between the amount of dark events and the amount of time drift, so a lookup table can be used to determine how much the arrival time drifts. Of course, in the case where there is a linear relationship between the amount of dark events and the amount of time drift, the amount of time drift can be calculated directly from the amount of dark events.

In one embodiment, the processing circuit may include a time measurement module for determining an arrival time of the high-energy photon detected by the photosensor according to the detection signal, and a time correction module for estimating the arrival time of the high-energy photon. The amount of drift, and the arrival time is corrected based on the amount of drift. Two circuit modules can be used to determine the arrival time and the arrival time respectively. As can be seen from the above description, the processing circuit can be a digital circuit with data processing capability. Therefore, both the time measurement module and the time correction module can be implemented by using digital circuits. For example, by way of programming, the functions of the time measurement module and the time correction module can be implemented using digital circuits such as FPGAs. The time measurement module and the time correction module are implemented by separate circuit modules to facilitate management and maintenance of the circuit.

Optionally, the processing circuit can include one or more of an energy measurement module, a dark current measurement module, and a waveform measurement module. In one example, the processing circuit includes an energy measurement module for determining the energy of the high energy photons detected by the photosensor based on the detection signal. In another example, the processing circuit can include a dark current measurement module for measuring a dark current detected by the photosensor based on the detection signal, the dark current being representative of the amount of dark events. In yet another example, the processing circuit can include a waveform measurement module for performing waveform reconstruction and waveform measurement on the initial signal based on the detection signal.

For example, the processing circuit can include an energy measurement module. The energy measurement module can be coupled to the output of the transmission controller 313 described above and utilizes digital signals to measure the energy of the high energy photons. The digital signal contains energy information, which can reflect the high level detected by the photoelectric sensor The amount of energy that can be a photon. The energy measurement module can calculate or estimate the energy level of high-energy photons by performing certain operations on the digital signal (such as summation). It can be understood that the energy measurement module can obtain the relative value of the energy of the high energy photon through the digital signal, and the relative value can represent the exact value of the energy of the high energy photon. Additionally, the energy measurement module can include the same circuitry as the transmission controller 313 and connect the circuit to the output of the comparator 312 described above, which, after processing the comparison signal, will output the same output as the digital signal. The signal and energy measurement module reuses the signal to measure the energy of the high-energy photon, and the calculation process is the same as the process of directly calculating the digital signal, and will not be described again.

Alternatively, the energy measurement module can include a counter (not shown) for energy measurement of high energy photons by counting the first logic level. That is to say, the energy measurement can be performed by accumulating the number of "1"s in the digital signal. Alternatively, the energy measurement module can include an adder (not shown) for performing energy measurements on the high energy photons by summing the first logic levels. That is to say, the "1" in the digital signal can be directly added, and the sum obtained last is the energy of the high-energy photon. The method of performing energy measurement by counting or summing the first logic levels is simple, fast, and efficient.

The processing circuit can include a dark current measurement module. Similar to the energy measurement module, the dark current measurement module can be coupled to the output of comparator 312 or transmission controller 313 for dark current measurement using a comparison signal or a digital signal. For example, the dark current measurement module can perform dark current measurements by computing a digital signal from the transmission controller 313. For example, the magnitude of the dark current can be measured by calculating the number of "1"s in the digital signal per unit time when no valid event occurs. The magnitude of the dark current is proportional to the number of "1"s in the digital signal per unit time.

The processing circuit can include a waveform measurement module. Similar to the energy measurement module and the dark current measurement module, the waveform measurement module can be coupled to the output of the comparator 312 or the transmission controller 313 to perform waveform reconstruction and waveform measurement on the initial signal using the comparison signal or digital signal. For example, the waveform measurement module can perform waveform reconstruction on the initial signal by digital low-pass filtering. In some applications, reconstructed waveforms can be used to implement advanced measurements.

Additionally, the processing circuitry can include circuit modules for performing gain measurements.

According to another aspect of the present invention, a method for measuring photon time information is provided. FIG. 7 shows a flow diagram of a method 700 for measuring photon time information, in accordance with one embodiment of the present invention.

As shown in FIG. 7, method 700 includes the following steps.

In step S710, an initial signal output by the photosensor is detected and a corresponding detection signal is generated.

At step S720, the arrival time of the high-energy photon detected by the photosensor is determined based on the detection signal.

At step S730, the amount of time drift is estimated based on the detection signal.

At step S740, the arrival time is corrected based on the amount of time drift.

Alternatively, the detection signal may be a digital signal consisting of a high level and a low level of equal duration, and the sum of all high levels in the digital signal is proportional to the integral of the initial signal versus time.

Optionally, step S720 may include: determining an effective trigger time according to an occurrence rule of a high level and a low level in the digital signal, and using the effective trigger time as an arrival time, wherein the effective trigger time is a valid event trigger digital signal. The high level of time.

Optionally, step S730 may include: determining a previous dark trigger time before the effective trigger time according to an occurrence rule of a high level and a low level in the digital signal, wherein the dark trigger time is a dark event trigger digital signal High-level time; calculate the time interval between the effective trigger time and the previous dark trigger time; estimate the amount of dark events that occur during the time interval; and estimate the time drift based on the amount of dark events that occur during the time interval the amount.

Optionally, estimating the amount of time drift based on the amount of dark events occurring during the time interval may include estimating the amount of time drift using a lookup table and an amount of dark events occurring within the time interval, wherein the lookup table is The relationship between the amount of dark events and the amount of time drift is recorded.

Those skilled in the art can understand the embodiments of the method 700 for measuring photon time information and its advantages and the like disclosed herein based on the above description of the apparatus for measuring photon time information and FIGS. 1 to 6, for the sake of brevity, This article does not repeat this.

The present invention has been described by the above-described embodiments, but it should be understood that the above-described embodiments are only for the purpose of illustration and description. Further, those skilled in the art can understand that the present invention is not limited to the above embodiments, and various modifications and changes can be made according to the teachings of the present invention. These modifications and modifications are all claimed in the present invention. Within the scope. The scope of the invention is defined by the appended claims and their equivalents.

Claims

An apparatus for measuring photon time information, comprising:

a current detecting circuit for connecting a photosensor, detecting an initial signal output by the photosensor and generating a corresponding detection signal;

a processing circuit, an input end of the processing circuit is connected to an output end of the current detecting circuit, and the processing circuit is configured to determine, according to the detection signal, an arrival time of the high-energy photon detected by the photoelectric sensor, according to the detection signal The amount of time drift is estimated, and the arrival time is corrected based on the amount of time drift.
The apparatus according to claim 1, wherein said detection signal is a digital signal, said digital signal being composed of a high level and a low level of equal duration, a sum of all high levels in said digital signal It is proportional to the integral of the initial signal versus time.
The apparatus of claim 2 wherein said processing circuit determines said arrival time by:

Determining an effective trigger time according to an occurrence rule of a high level and a low level in the digital signal, and using the effective trigger time as the arrival time, wherein the effective trigger time is an effective event triggering in the digital signal High time.
The apparatus of claim 3 wherein said processing circuit estimates said amount of time drift by:

Determining a previous dark trigger time before the effective trigger time according to an occurrence rule of a high level and a low level in the digital signal, wherein the dark trigger time is a dark event triggering a high power in the digital signal Flat time

Calculating a time interval between the effective trigger time and the previous dark trigger time;

Estimating the amount of dark events that occur during the time interval;

The amount of time drift is estimated based on the amount of dark events that occur during the time interval.
The apparatus of claim 4 wherein the amount of dark events comprises the number of dark events, the amount of charge of a dark event, or the energy of a dark event.
The apparatus of claim 4 wherein said processing circuit estimates said amount of time drift based on an amount of dark events occurring during said time interval by:

The amount of time drift is estimated using a lookup table and an amount of dark events occurring during the time interval, wherein the lookup table is used to record a relationship between the amount of dark events and the amount of time drift.
Apparatus according to any one of claims 2 to 6 wherein said current check The measuring circuit comprises an integrating module, a comparator, a transmission controller and a negative feedback module, wherein

The integration module is configured to connect an output end of the photosensor and an output end of the negative feedback module, and receive the initial signal from the photosensor and a feedback signal from the negative feedback module, for the initial Integrating the difference between the signal and the feedback signal and outputting the integrated signal;

One input of the comparator is coupled to an output of the integration module and another input of the comparator is coupled to a reference level, the comparator is configured to compare the integrated signal to the reference level And generating a comparison signal;

An input of the transmission controller is coupled to an output of the comparator, the transmission controller is configured to control transmission of the comparison signal to output the digital signal with a clock signal, wherein duration of the digital signal a high level equal to a period of the clock signal represents a first logic level, and a low level of the digital signal having a duration equal to a period of the clock signal represents a second logic level;

An input end of the negative feedback module is connected to an output end of the transmission controller, and the negative feedback module is configured to convert the digital signal into the feedback signal and feed back the feedback signal to the integration module;

The input end of the processing circuit is connected to the output end of the transmission controller.
The apparatus according to claim 7, wherein said reference level is equal to an integral signal obtained by integrating an initial signal outputted by said photosensor when a specific number of visible light sub-senses are integrated in said integration module Level value.
The apparatus of claim 8 wherein said specified number is equal to ten.
The apparatus of claim 1 wherein said processing circuit further comprises an energy measurement module for determining an energy of said high energy photon detected by said photosensor based on said detection signal.
A method for measuring photon time information, comprising:

Detecting an initial signal output by the photosensor and generating a corresponding detection signal;

Determining, according to the detection signal, an arrival time of the high-energy photon detected by the photosensor;

Estimating a time drift amount based on the detection signal;

The arrival time is corrected based on the amount of time drift.
The method of claim 11 wherein said detection signal is a number A signal consisting of a high level and a low level of equal duration, the sum of all high levels in the digital signal being proportional to the integral of the initial signal versus time.
The method according to claim 12, wherein the determining, according to the detection signal, the arrival time of the high-energy photon detected by the photosensor comprises:

Determining an effective trigger time according to an occurrence rule of a high level and a low level in the digital signal, and using the effective trigger time as the arrival time, wherein the effective trigger time is an effective event triggering in the digital signal High time.
The method according to claim 13, wherein said estimating a time drift amount according to said detection signal comprises:

Determining a previous dark trigger time before the effective trigger time according to an occurrence rule of a high level and a low level in the digital signal, wherein the dark trigger time is a dark event triggering a high power in the digital signal Flat time

Calculating a time interval between the effective trigger time and the previous dark trigger time;

Estimating the amount of dark events that occur during the time interval;

The amount of time drift is estimated based on the amount of dark events that occur during the time interval.
The method of claim 14 wherein said estimating said amount of time drift based on an amount of dark events occurring during said time interval comprises:

The amount of time drift is estimated using a lookup table and an amount of dark events occurring during the time interval, wherein the lookup table is used to record a relationship between the amount of dark events and the amount of time drift.