WO2018090901A1 - Dispositif et procédé de mesure d'informations temporelles de photon - Google Patents

Dispositif et procédé de mesure d'informations temporelles de photon Download PDF

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Publication number
WO2018090901A1
WO2018090901A1 PCT/CN2017/110865 CN2017110865W WO2018090901A1 WO 2018090901 A1 WO2018090901 A1 WO 2018090901A1 CN 2017110865 W CN2017110865 W CN 2017110865W WO 2018090901 A1 WO2018090901 A1 WO 2018090901A1
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time
signal
amount
dark
digital signal
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PCT/CN2017/110865
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English (en)
Chinese (zh)
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赵指向
龚政
黄秋
许剑锋
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武汉中派科技有限责任公司
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Publication of WO2018090901A1 publication Critical patent/WO2018090901A1/fr

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J3/00—Time-division multiplex systems
    • H04J3/02—Details
    • H04J3/06—Synchronising arrangements
    • H04J3/0635—Clock or time synchronisation in a network
    • H04J3/0638—Clock or time synchronisation among nodes; Internode synchronisation
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M1/00—Analogue/digital conversion; Digital/analogue conversion
    • H03M1/12—Analogue/digital converters
    • H03M1/50—Analogue/digital converters with intermediate conversion to time interval
    • H03M1/52—Input signal integrated with linear return to datum

Definitions

  • the present invention relates to the field of circuits, and in particular to an apparatus and method for measuring photon time information.
  • 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.
  • 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.
  • an improved photon measurement front-end circuit 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.
  • the improved photon measurement front-end circuit 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.
  • 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.
  • 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.
  • measurement accuracy may be affected when using an improved photon measurement front-end circuit to measure the arrival time of high-energy photons.
  • an apparatus for measuring photon time information 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. .
  • 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.
  • 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.
  • FIG. 1 shows a schematic block diagram of an improved photon measurement front end circuit in accordance with one example
  • FIG. 2 shows a schematic block diagram of an apparatus for measuring photon time information, in accordance with one embodiment of the present invention
  • FIG. 3 shows a schematic block diagram of an apparatus for measuring photon time information, in accordance with one embodiment of the present invention
  • FIG. 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
  • FIG. 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.
  • 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.
  • 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.
  • 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
  • a low level in the digital signal having a duration equal to the period of the clock signal represents a second logic level.
  • the first logic level may be a logic level "1”
  • the second logic level may be a logic level "0”
  • 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.
  • 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.
  • the level value of the integrated signal is greater than the reference level, a high level appears in the comparison signal.
  • 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.
  • 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).
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • the photosensors described herein can be any suitable photosensor, such as SiPM, PMT, avalanche photodiode (APD), and the like.
  • 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.
  • 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.
  • TDC time-to-digital converter
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • comparator 312 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.
  • the comparator 312 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.
  • 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.
  • 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.
  • a high level having a duration equal to a period of the clock signal represents a first logic level
  • a low level having a duration equal to a period of the clock signal represents a second logic level
  • the first logic level may be a logic level "1”
  • the second logic level may be a logic level "0”
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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 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.
  • 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.
  • triggering the pulse signal available for time measurement ie, triggering a high level in the digital signal
  • 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.
  • 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.
  • 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.
  • 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.
  • the effective trigger time can be any of the durations of the high level triggered by the active event.
  • 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.
  • a valid event or a dark event.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • the effective trigger time of its corresponding valid event 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 is not limited to know the arrival time of a high-energy photon.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • the time interval between the effective trigger time and the previous dark trigger time can be calculated.
  • 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.
  • the abscissa indicates that the error corresponds to the difference between the determined arrival time and the actual arrival time
  • 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.
  • the specific number is equal to 10
  • triggering the pulse signal usable for time measurement ie, triggering a high level in the digital signal
  • 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.
  • the time of occurrence error The difference, that is, the arrival time of high-energy photons is -5 to +4 occurrences of visible light.
  • the root mean square (RMS) error for this case is 2.9144.
  • 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.
  • 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.
  • the upper curve is a curve of the measurement error of the arrival time without correction
  • 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.
  • n A specific number can be represented by n.
  • 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.
  • 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.
  • the amount of dark events and the amount of time drift can be predetermined by theoretical calculations, computer simulations, or experiments. Relationship between.
  • 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.
  • 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.
  • 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.
  • the amount of time drift can be calculated directly from the amount of dark events.
  • 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.
  • 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.
  • the processing circuit can include one or more of an energy measurement module, a dark current measurement module, and a waveform measurement module.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • processing circuitry can include circuit modules for performing gain measurements.
  • FIG. 7 shows a flow diagram of a method 700 for measuring photon time information, in accordance with one embodiment of the present invention.
  • method 700 includes the following steps.
  • step S710 an initial signal output by the photosensor is detected and a corresponding detection signal is generated.
  • the arrival time of the high-energy photon detected by the photosensor is determined based on the detection signal.
  • the amount of time drift is estimated based on the detection signal.
  • the arrival time is corrected based on the amount of time drift.
  • 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.
  • 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 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.
  • 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.
  • 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.

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Abstract

La présente invention concerne un dispositif et un procédé de mesure d'informations temporelles d'un photon. Le dispositif comprend un circuit de détection actuel et un circuit de traitement, le circuit de détection actuel étant utilisé afin d'être connecté à un capteur photoélectrique afin de détecter un signal initial émis par le capteur photoélectrique et de générer un signal de détection correspondant; une extrémité d'entrée du circuit de traitement est connectée à une extrémité de sortie du circuit de détection actuel; et le circuit de traitement est utilisé de manière à déterminer le temps d'arrivée d'un photon à énergie élevée détecté par le capteur photoélectrique conformément au signal de détection, estimer la dérive temporelle conformément au signal de détection et corriger le temps d'arrivée sur la base de la dérive temporelle. Conformément au dispositif et au procédé dans un mode de réalisation de la présente invention, l'estimation de la dérive temporelle et la correction du temps d'arrivée sur la base de la dérive temporelle peuvent corriger une erreur de mesure temporelle provoquée par un événement sombre, et obtenir simplement et commodément un résultat de mesure de temps avec une grande précision.
PCT/CN2017/110865 2016-11-15 2017-11-14 Dispositif et procédé de mesure d'informations temporelles de photon WO2018090901A1 (fr)

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CN107450092B (zh) * 2017-08-23 2019-07-26 中派科技（深圳）有限责任公司 用于测量光子信息的装置
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