CN107767427A

CN107767427A - A kind of signal waveform restoration methods and device

Info

Publication number: CN107767427A
Application number: CN201710898283.XA
Authority: CN
Inventors: 贺亮; 杨龙; 高鹏; 张军; 宁鹏
Original assignee: Neusoft Medical Systems Co Ltd
Current assignee: Shenyang Zhihe Medical Technology Co ltd
Priority date: 2017-09-28
Filing date: 2017-09-28
Publication date: 2018-03-06
Anticipated expiration: 2037-09-28
Also published as: CN107767427B

Abstract

This application discloses a kind of signal waveform restoration methods and device, this method to include：The pulse signal of collection target photodetector output in real time, according to the signal amplitude for having gathered signal, it is determined that the initial time of signal pile-up occurs, the signal pile-up refers to accumulate at least one other pulse signal on the basis of target impulse signal, the purpose is to the signal amplitude for belonging to the target impulse signal for making to gather before the initial time directly to export, the signal amplitude for belonging to the target impulse signal need to be only extracted from the pileup signals and its collection signal afterwards that the initial time gathers, so as to complete the waveform recovery to the target impulse signal, without obtaining whole signal waveforms, waveform fitting is carried out respectively also without to whole rising edges and trailing edge, this mode can effectively improve the recovery efficiency of impulse waveform and real-time is higher.

Description

Signal waveform recovery method and device

Technical Field

The present application relates to the field of medical imaging technologies, and in particular, to a method and an apparatus for restoring a signal waveform.

Background

In medical imaging devices such as Positron Emission Tomography (PET), most of imaging data acquisition principles are that high-energy particles are converted into visible light after passing through a scintillation crystal, and then the visible light is detected and converted into an electrical signal in a pulse form through a photoelectric detector. However, under the excitation of a high-dose radioactive source, a large amount of high-energy particles can reach the photodetector in a short time, and at this time, a plurality of pulse signals are stacked on the photodetector, and a signal formed by stacking a plurality of pulse signals is referred to as a stacked (Pileup) signal, and a corresponding signal waveform is referred to as a Pileup signal waveform.

However, if the detection system does not perform the identification processing on the Pileup signal, the performance of the system is affected. Firstly, if a plurality of pulse signals are piled up, the pulse energy of other signals is wrongly accumulated on the pulse energy of the original signal, which brings error to the calculation of the original pulse energy, thereby affecting the position information calculated by the position calculation method for judging the actual hitting position of the particle by the gravity center method, i.e. the energy value, i.e. causing the position information to be calculated inaccurately, thereby causing deterioration influence to the generated energy diagram effect, as shown in fig. 1, the left side is a normal energy diagram, and the right side is a deteriorated pileup energy diagram; furthermore, errors in pulse energy calculation directly affect the energy spectrum and energy resolution, and, if the piled-up pulses are not distinguished, it is not beneficial to determine the rising edge of the original pulse signal, which can have an adverse effect on coincidence time resolution, which becomes increasingly severe as the radiation dose increases.

In the prior art, firstly, derivation is performed on a sampling signal of a whole signal waveform to determine a pulse rising edge region in the signal waveform, then whether an interval between two rising edges is smaller than a preset threshold value is judged, if so, the signal waveform is judged to be a pileup waveform, which indicates that waveform reconstruction is required; however, waveform reconstruction needs to segment rising edges and falling edges, and sequentially reconstruct a signal pulse waveform corresponding to a single event (i.e., an event that a single high-energy particle energy reaches a photodetector) by using the segmented waveform parameters. Therefore, in the prior art, it is determined whether the whole signal waveform is a pileup waveform only by obtaining the whole signal waveform, and each parameter of the pileup waveform needs to be obtained to perform waveform reconstruction, so that the processing speed in the process is low, and the real-time performance is poor.

Disclosure of Invention

The present application is directed to a method and an apparatus for recovering a signal waveform, which can improve a waveform recovery speed and have high real-time performance.

The application provides a signal waveform recovery method, which comprises the following steps:

acquiring an electric signal output by a target photoelectric detector in real time, wherein the target photoelectric detector is any one photoelectric detector in a detector ring of medical imaging equipment;

determining a starting moment of signal accumulation according to the signal amplitude of the collected signal, wherein the signal accumulation refers to accumulation of at least one other pulse signal on the basis of the target pulse signal;

keeping the signal amplitude belonging to the target pulse signal collected before the starting moment;

and separating the signal amplitude belonging to the target pulse signal from the signal amplitude of the collected signal from the starting moment.

Optionally, the determining a starting time of signal accumulation according to the signal amplitude of the acquired signal includes:

determining a differential absolute value of each signal amplitude from a first rising edge to a second rising edge based on an original waveform formed by the signal amplitudes at each acquisition time, and taking the maximum differential absolute value as a differential discrimination threshold, wherein the first rising edge is a rising edge of the target pulse signal, and the second rising edge is a rising edge appearing after the first rising edge;

determining a signal amplitude corresponding to the second rising edge;

if the differential absolute value of the signal amplitude corresponding to the second rising edge is greater than the differential discrimination threshold, determining the interval acquisition time between the first rising edge and the second rising edge;

and if the interval acquisition time is less than the attenuation time constant of the target pulse signal, determining the acquisition time corresponding to the second rising edge as the initial time for signal accumulation.

Optionally, the method further includes:

determining other photodetectors corresponding to the same crystal array as the target photodetector;

the electric signals output by the other photoelectric detectors are collected in real time while the electric signals output by the target photoelectric detector are collected in real time;

then, before the determining the interval acquisition time between the first rising edge and the second rising edge, further comprising:

for the target photoelectric detector and the other photoelectric detectors, calculating the average value of signal energy output by each photoelectric detector at N acquisition moments before the second rising edge, and taking the sum of the calculated average values as an energy discrimination threshold, wherein N is more than or equal to 1;

and calculating the signal energy value output by each photoelectric detector at the second rising edge moment, and if the sum of the calculated energy values is greater than the energy discrimination threshold, executing the determination of the interval acquisition time between the first rising edge and the second rising edge.

Optionally, the separating the signal amplitude belonging to the target pulse signal from the signal amplitude of the collected signal starting from the starting time includes:

taking each acquisition time starting from the starting time as the current acquisition time in sequence;

determining a signal amplitude value corresponding to the target pulse signal at the current acquisition time according to the attenuation time constant of the target pulse signal and the signal amplitude value corresponding to the target pulse signal at the previous acquisition time;

calculating a difference absolute value between a signal amplitude corresponding to the current acquisition time and a reference value, wherein the reference value is a direct-current component amplitude of the target pulse signal;

and if the absolute value of the difference is smaller than a preset threshold value, finishing the amplitude recovery of the target pulse signal.

Optionally, after the separating the signal amplitude belonging to the target pulse signal, the method further includes:

removing the signal amplitude belonging to the target pulse signal from the signal amplitude of the acquired signal to obtain a signal amplitude after the removal operation;

and taking the signal amplitude after the removal operation as the signal amplitude of the acquired signal, and determining the starting time of signal accumulation and subsequent steps according to the signal amplitude of the acquired signal until the starting time cannot be determined.

Optionally, after acquiring the electrical signal output by the target photodetector in real time, the method further includes:

and filtering the acquired signals to enable the original waveform formed by the signal amplitude values at all the acquisition moments to tend to be smooth or remove part of peak burrs in the original waveform.

The present application also provides a signal waveform recovery apparatus, including:

the system comprises a first signal acquisition unit, a second signal acquisition unit and a third signal acquisition unit, wherein the first signal acquisition unit is used for acquiring an electric signal output by a target photoelectric detector in real time, and the target photoelectric detector is any one photoelectric detector in a detector ring of medical imaging equipment;

the accumulation time determining unit is used for determining the starting time of signal accumulation according to the signal amplitude of the collected signal, wherein the signal accumulation refers to accumulation of at least one other pulse signal on the basis of the target pulse signal;

the signal amplitude holding unit is used for holding the signal amplitude which is acquired before the starting moment and belongs to the target pulse signal;

and the signal amplitude separation unit is used for separating the signal amplitude belonging to the target pulse signal from the signal amplitude of the collected signal from the starting moment.

Optionally, the accumulation time determining unit includes:

a differential threshold determining subunit, configured to determine, based on an original waveform formed by signal amplitudes at each acquisition time, a differential absolute value of each signal amplitude starting from a first rising edge to before a second rising edge, and use a maximum differential absolute value as a differential discrimination threshold, where the first rising edge is a rising edge of the target pulse signal, and the second rising edge is a rising edge occurring after the first rising edge;

a rising edge amplitude determining subunit, configured to determine a signal amplitude corresponding to the second rising edge;

an interval time determining subunit, configured to determine an interval acquisition time between the first rising edge and the second rising edge if a differential absolute value of the signal amplitude corresponding to the second rising edge is greater than the differential discrimination threshold;

and the accumulation time determining subunit is configured to determine, if the interval acquisition time is less than the decay time constant of the target pulse signal, that the acquisition time corresponding to the second rising edge is the start time at which signal accumulation occurs.

Optionally, the apparatus further comprises:

a detector determination unit for determining other photodetectors corresponding to the same crystal array as the target photodetector;

the second signal acquisition unit is used for acquiring the electric signals output by the target photoelectric detector in real time and acquiring the electric signals output by other photoelectric detectors in real time;

then, the accumulation timing determination unit further includes:

an energy threshold determining subunit, configured to, before the interval acquisition time between the first rising edge and the second rising edge is determined by the interval time determining subunit, calculate, for the target photodetector and the other photodetectors, signal energy mean values output by each photodetector at N acquisition times before the second rising edge, and use a sum of the calculated mean values as an energy discrimination threshold, where N is greater than or equal to 1;

and the energy value comparison subunit is used for calculating the signal energy value output by each photoelectric detector at the second rising edge moment, and if the sum of the calculated energy values is greater than the energy discrimination threshold, triggering the interval time determination subunit to determine the interval acquisition time between the first rising edge and the second rising edge.

The present application also provides a signal waveform recovery apparatus, including: a processor, a memory, a system bus;

the processor and the memory are connected through the system bus;

the memory is for storing one or more programs, the one or more programs comprising instructions, which when executed by the processor, cause the processor to carry out any of the method claims above.

The signal waveform recovery method and the signal waveform recovery device collect pulse signals output by a target photoelectric detector in real time, determining a starting moment at which a signal pile-up occurs, based on the signal amplitude of the acquired signal, said signal pile-up being a pile-up of at least one other pulse signal on the basis of the target pulse signal, the method aims to directly output the signal amplitude which is acquired before the starting time and belongs to the target pulse signal, only the signal amplitude which belongs to the target pulse signal is extracted from the pileup signal acquired at the starting time and the acquired signal after the pileup signal, therefore, the waveform recovery of the target pulse signal is completed without obtaining all signal waveforms or respectively performing waveform fitting on all rising edges and all falling edges, and the recovery efficiency of the pulse waveform can be effectively improved by the method, and the real-time performance is high.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.

FIG. 1 is a diagram of a normal energy diagram and a pileup energy diagram provided by the prior art;

fig. 2 is a schematic diagram of a dual Pileup signal waveform provided in an embodiment of the present application;

fig. 3 is a flowchart illustrating a signal waveform recovery method according to an embodiment of the present disclosure;

FIG. 4 is a schematic signal flow diagram provided in accordance with an embodiment of the present application;

fig. 5A is one of schematic flow diagrams of a pileup start time determining method provided in the embodiment of the present application;

fig. 5B is a second schematic flow chart of the pileup start time determining method according to the embodiment of the present application;

FIG. 6 is a schematic diagram of a pulse waveform provided by an embodiment of the present application;

fig. 7 is a second schematic flowchart of a signal waveform recovery method according to an embodiment of the present application;

FIG. 8 is a second schematic diagram of a pulse waveform provided by the present embodiment;

FIG. 9 is a diagrammatic illustration of an embodiment of the present application;

fig. 10 is a schematic diagram illustrating a signal waveform recovery apparatus according to an embodiment of the present application;

fig. 11 is a schematic hardware structure diagram of a signal waveform recovery apparatus according to an embodiment of the present disclosure.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some embodiments of the present application, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

To facilitate understanding of the background and the embodiments of the present application, the definition of the multiple pileup signal will be described first. Namely: the dual pileup signal refers to: accumulating another signal on one signal to form a double Pileup signal, wherein the corresponding signal waveform is called a double Pileup signal waveform; the triple pileup signal refers to: accumulating another signal on one signal, and accumulating another signal on the accumulated signal to obtain a triple Pileup signal, wherein the corresponding signal waveform is called a triple Pileup signal waveform; by analogy, a stacked signal in which n signals are stacked is an n-fold Pileup signal, and a corresponding signal waveform is referred to as an n-fold Pileup signal waveform.

For example, referring to the dual Pileup signal waveform diagram shown in fig. 2, the left pulse is formed by an exponential decay of a certain signal 1, a new signal 2 appears in the signal 1 during the decay, and the signal 2 is stacked on the signal 1 without the complete decay to form the right pulse in the figure, that is, the right pulse is formed by stacking the signal 2 on the basis of the signal 1 being decayed.

In the existing pileup signal waveform processing method, firstly, all electrical signals output by a photodetector are sampled to form a whole signal waveform, then, a derivative is carried out on the sampled signals, two rising edge areas in the signal waveform are determined according to the derivative result, and when the interval of the two rising edges is smaller than a preset threshold value, the signal waveform is determined as the pileup waveform, so that waveform reconstruction is required to reconstruct a signal pulse waveform corresponding to a single event (namely, an event that energy of a single high-energy particle reaches the photodetector). The waveform reconstruction needs to segment the rising edge and the falling edge, judge a rising edge region and a falling edge region, then fit corresponding parameters of corresponding waveform functions by using the segmented waveforms through a formula and the like, and reconstruct the pulse waveform of each single event in the pileup waveform in sequence through the obtained parameters.

However, in the above method, it is necessary to obtain all waveforms of rising edge and falling edge and to distinguish the waveforms of rising edge and falling edge, and it is also necessary to perform waveform fitting on the rising edge and falling edge respectively, and to reconstruct and restore the original waveform data after calculating corresponding parameters.

In order to solve the above problem, the present embodiment provides a signal waveform recovery method, and for convenience of distinction, the present embodiment defines any one of the photodetectors outputting the photoelectron pulse signal as a target photodetector, and defines a normal pulse signal that may be piled up by other pulse signals as a target pulse signal. When the waveform of the target pulse signal is recovered, the electric signal output by the target photoelectric detector needs to be collected in real time, whether other pulse signals are accumulated on the target pulse signal or not is determined according to the collected signal amplitude, the starting moment of signal accumulation is determined, the signal amplitude of the collected signal before the starting moment is directly output, and only the signal amplitudes of the collected signal before and after the starting moment are processed, so that the signal amplitude belonging to the target pulse signal is separated from the collected signals. It can be seen that, in the present embodiment, when the waveform identification of the pileup signal is performed, all signal waveforms do not need to be obtained, and waveform fitting does not need to be performed on all rising edges and all falling edges, but the first-appearing pileup signal can be determined based on the collected signal (i.e., a part of the signal waveform), so as to determine that the signal waveform is the pileup waveform, and only the signal amplitude of the target pulse signal needs to be extracted from the first-appearing pileup signal and the collected signals thereafter, so as to complete the waveform recovery of the target pulse signal, and this non-full-wave recovery mode can effectively improve the waveform recovery efficiency and has high real-time performance.

Referring to fig. 3, a schematic flow chart of a signal waveform recovery method provided in an embodiment of the present application is shown, where the method includes:

s301: and acquiring an electric signal output by a target photoelectric detector in real time, wherein the target photoelectric detector is any one photoelectric detector in a detector ring of the medical imaging equipment.

Referring to the signal flow schematic diagram shown in fig. 4, in this embodiment, after the real-time acquisition signal is preprocessed, two pipelines of signal discrimination and signal recovery are used to process the real-time acquisition signal in parallel, and the two pipelines respectively have the functions of pileup occurrence time judgment and pileup signal waveform recovery, so that the real-time performance of waveform recovery can be effectively improved. The present embodiment will be described later with reference to fig. 4.

In step S301, the electrical signal output by the target photodetector is collected in real time to obtain a signal amplitude corresponding to each collection time, and the signal amplitudes are arranged according to the collection sequence to form a signal waveform.

In an embodiment of the present application, after step S301, the method may further include: and filtering the acquired signals to enable the original waveform formed by the signal amplitude values at all the acquisition moments to tend to be smooth or remove part of peak burrs in the original waveform. In this embodiment, first, digital filtering is performed on each acquired signal, which may be implemented by the signal filtering module shown in fig. 4, and specifically, mean filtering or median filtering may be performed according to the noise characteristics of the acquired signals; the n-point mean filtering is adopted, so that the subsequent signal energy calculation result is not influenced essentially, the signal waveform can be smoother through the mean filtering, positive contribution can be brought to accurate judgment of the subsequent pileup occurrence time, and the peak burr pulse with high amplitude cannot be removed through the mean filtering; the n-point median filtering is a nonlinear filtering, and the median filtering is adopted, so that the subsequent signal energy calculation result is influenced (namely, the energy calculation result is inaccurate), but the median filtering can remove the spike and burr pulses with higher amplitude. Of course, other filtering methods or no filtering of the collected signal may be adopted in the present embodiment.

S302: and determining the starting moment of signal accumulation according to the signal amplitude of the acquired signal, wherein the signal accumulation refers to the accumulation of at least one other pulse signal on the basis of the target pulse signal.

In this embodiment, the signal recovery pipeline shown in fig. 4 is configured to output the signal waveform of the target pulse signal in real time, and specifically, in order to perform waveform recovery on the target pulse signal in real time, an actual acquisition signal is adopted to output when a pileup signal does not occur, and a fitting signal (i.e., the fitted target pulse signal) is used to replace the actual acquisition signal to output at and after a start time point of the pileup signal. For this reason, in this embodiment, it is necessary to determine a starting time point at which the pileup signal occurs based on a non-full signal waveform formed by the acquired signals, and then perform waveform fitting on the acquired signals after the starting time point based on parameters of the non-full signal waveform to fit the target pulse signal from the pileup signal.

The present embodiment may determine the starting point in time at which the pileup signal occurs in the following manner.

Referring to one of the flow diagrams of the pileup start time determining method shown in fig. 5A, step S302 may specifically include:

s501: determining the differential absolute value of each signal amplitude from the first rising edge to the second rising edge based on the original waveform formed by the signal amplitudes at each acquisition moment, and taking the maximum differential absolute value as a differential discrimination threshold; wherein the first rising edge is a rising edge of the target pulse signal, and the second rising edge is a rising edge occurring after the first rising edge.

For example, referring to fig. 2 (the following description of fig. 2 will be based on the upward reversal of the portion below the baseline), it is assumed that the waveform shown in fig. 2 is an original waveform formed based on the signal amplitudes at the respective acquisition moments, wherein the horizontal direction is a time axis and the vertical direction is the signal amplitude, and for the sake of convenience of distinction, the rising edge of the left-side pulse is defined as a first rising edge and the rising edge of the right-side pulse is defined as a second rising edge. Assuming that the left-side pulse is a pulse corresponding to the signal 1 (i.e., the target pulse signal), the signal 1 starts to decay from the first rising edge position, in the process of the decay, the signal 2 is stacked on the signal 1, the position where the signal starts to be stacked is the second rising edge, and the remaining decay energy of the signal 1 and the decay energy of the signal 2 are added together to form the right-side pulse.

In this embodiment, a signal amplitude y (n) corresponding to each acquisition time in a first pulse region (i.e., a waveform region from a first rising edge to a second rising edge) is obtained, an absolute value of a differential value of the signal amplitude y (n) is calculated, and a maximum differential absolute value obtained by calculation is used as a differential discrimination threshold.

Wherein, the differential value calculation formula may be:

wherein,_y[n]acquiring a signal amplitude corresponding to the moment n;_y′[n]is composed of_y[n]A differential value of (d);_y[n-Δ]the signal amplitude corresponding to the acquisition time n-delta; Δ is the time interval between acquisition instant n and acquisition instant n- Δ.

Of course, other digital differential calculation methods may be adopted, which is not limited in this embodiment.

This step may be implemented by the signal differentiation module shown in fig. 4.

S502: and determining the signal amplitude corresponding to the second rising edge.

S503: and if the differential absolute value of the signal amplitude corresponding to the second rising edge is greater than the differential discrimination threshold, determining the interval acquisition time between the first rising edge and the second rising edge.

In step S501, the maximum absolute value of the differential of the first pulse region is calculated as a differential discrimination threshold, which is used to determine whether the second rising edge is a rising edge corresponding to the effective photon signal or a glitch noise interference signal. Specifically, a specific proportional relationship K exists between a spike fluctuation amplitude on an exponential descent curve of the photoelectron signal and a differential value corresponding to the spike position, that is, the greater the spike fluctuation amplitude, the greater the differential absolute value of the signal amplitude corresponding to the spike position, based on which, if the second rising edge is an effective rising edge, the fluctuation amplitude is relatively large, then the differential absolute value corresponding to the second rising edge is also relatively large, and if the differential absolute value corresponding to the second rising edge is greater than the differential discrimination threshold, it is considered that the second rising edge may be the first pileup signal.

It should be noted that, in this embodiment, the differential discrimination threshold may be used as a unique criterion for determining whether the second rising edge is a valid rising edge; an energy discrimination threshold may be further introduced to determine whether the second rising edge is a valid rising edge by using a dual criterion, and the related content of the energy discrimination threshold is referred to in the following. The energy discrimination threshold may be determined by the signal energy module shown in fig. 4, and the validity of the second rising edge may be determined by the signal rising edge determination module shown in fig. 4.

Next, in order to further determine whether the second rising edge is a true pileup signal, it is further required to determine an interval acquisition time between the first rising edge and the second rising edge, and perform step S504. As shown in fig. 4, the real-time acquisition signal reaches the signal recovery pipeline and the signal discrimination pipeline after being preprocessed, and the pileup signal discrimination function can be realized by a signal rising edge decision module in the signal discrimination pipeline.

S504: and if the interval acquisition time is less than the attenuation time constant of the target pulse signal, determining the acquisition time corresponding to the second rising edge as the initial time for signal accumulation.

In this embodiment, the acquisition time corresponding to the first rising edge may be denoted as T1, the acquisition time corresponding to the second rising edge may be denoted as T2, and then an interval time between the second rising edge and the occurrence time of the first rising edge is determined, that is, T2-T1 ═ m, m may be obtained by timing with an internal clock of a Field-Programmable Gate Array (FPGA), and if the value of m is smaller than the decay time constant B of the target pulse signal, the time T2 is determined as the start time of the occurrence signal pileup. This is because the high-energy particle signal is in exponential form y ═ a · e^-BxThe attenuation time constant B is fixed, namely the signal attenuation time is fixed, so that if m is less than B, a new signal appears after a signal is not completely attenuated, and a pileup signal is considered to appear.

As shown in fig. 4, the starting occurrence time of the Pileup signal may be determined by the rising edge interval time determination module, which also feeds back the time to the Pileup occurrence time determination module in the Pileup signal recovery pipeline.

In step S503, the energy determination threshold is mentioned as a further criterion for determining whether the second rising edge is an effective rising edge, that is, the second rising edge signal is subjected to differential threshold determination and energy threshold determination, so that whether the second rising edge is a rising edge of an effective signal or other spike interference can be more accurately distinguished.

For this reason, in an embodiment of the present application, it is further required to determine other photodetectors corresponding to the same crystal array as the target photodetector, and acquire the electrical signals output by the other photodetectors in real time while acquiring the electrical signals output by the target photodetector in real time. For example, for a crystal array in a certain detector module, it is assumed that the crystal array corresponds to 4 photodetectors, such as 4 photomultiplier tubes (PMT), and if one of the photodetectors is the target photodetector, the electrical signals output by the 4 photodetectors are collected in real time.

Based on this, referring to the second flow chart of the pileup start time determination method shown in fig. 5B, the step S503 in fig. 5A may be replaced by the following steps S503a and S503B:

s503 a: if the absolute value of the differential of the signal amplitude corresponding to the second rising edge is greater than the differential discrimination threshold, calculating the average value of the signal energy output by each photoelectric detector at N acquisition moments before the second rising edge for the target photoelectric detector and the other photoelectric detectors, and taking the sum of the calculated average values as the energy discrimination threshold, wherein N is greater than or equal to 1.

For example, suppose that fig. 2 shows a signal waveform corresponding to the target photodetector, and a certain crystal array corresponds to 4 photodetectors including the target photodetector, which are now respectively named as detector 1, detector 2, detector 3, and detector 4, where detector 1 is the target photodetector. Then step S503a has the following two implementations:

mode 1: firstly, for N acquisition moments before the second rising edge, calculating a mean value 1 of N signal amplitudes output by a detector 1, calculating a mean value 2 of N signal amplitudes output by a detector 2, calculating a mean value 3 of N signal amplitudes output by a detector 3, and calculating a mean value 4 of N signal amplitudes output by a detector 4; then, the energy discrimination threshold, that is, the energy discrimination threshold reflecting the signal energy level before the second rising edge, is calculated as mean 1+ mean 2+ mean 3+ mean 4.

Mode 2: the baseline value (signal amplitude at baseline as shown in fig. 2) is subtracted from the energy discrimination threshold calculated in mode 1, and this value is used as the final energy discrimination threshold, which also reflects the signal energy level before the second rising edge, but reflects the signal alternating portion.

It should be noted that each collected electrical signal is composed of a dc portion and an ac portion, the dc portion of the signal is a reference level, and this reference level is the baseline value, and when the portion below the baseline shown in fig. 2 is turned upwards, the portion above the baseline reflects the fluctuation of the ac portion of the signal.

S503 b: and calculating the signal energy value output by each photoelectric detector at the second rising edge moment, and if the sum of the calculated energy values is greater than the energy discrimination threshold, executing the determination of the interval acquisition time between the first rising edge and the second rising edge.

If the energy discrimination threshold is calculated in the above-described mode 1 in S503a, in step S503b, for the acquisition time corresponding to the second rising edge position, the signal amplitude 1 output by the detector 1 at the acquisition time is calculated, the signal amplitude 2 output by the detector 2 at the acquisition time is calculated, the signal amplitude 3 output by the detector 3 at the acquisition time is calculated, the signal amplitude 4 output by the detector 4 at the acquisition time is calculated, and the sum of the amplitudes F is calculated as amplitude 1+ amplitude 2+ amplitude 3+ amplitude 4. When the sum F of the amplitudes is greater than the energy discrimination threshold calculated in the above manner 1, the second rising edge is considered to be an effective rising edge rather than spike interference.

It should be noted that, in this embodiment, when the steps S503a and S503b are adopted to determine whether the second rising edge is an effective rising edge, all photodetectors of the same crystal array are combined, because the detector module is composed of the crystal array and multiple photodetectors, a gamma photon hitting the crystal generates visible light, the visible light is received by the photodetectors to generate optoelectronic pulse signals, in this process, the multiple photodetectors corresponding to one crystal array all receive signal energy generated by the gamma photon to different degrees, so that when a photo detector generates a pileup signal, the other photodetectors also generate pileup signals, and the occurrence times of the pileup signals are also the same. Based on this, the energies of the multiple paths of signals are gathered together to be summed, that is, a total energy value at the second rising edge time is obtained, the total energy value is the actual energy corresponding to the output of the gamma photon signal, and the noise energy is much smaller than the actual energy, so that when the total energy value is larger than the energy discrimination threshold, it can be determined that the second rising edge is the rising edge of the photon signal and not the noise, and thus, it is more accurate to judge the effectiveness of the second rising edge. Thus, when the second rising edge signal is formed by stacking small signals on a large signal or stacking small signals on a small signal, the second rising edge signal is not mistaken for being noise although the second rising edge signal is low in amplitude and small in absolute value of its differential.

Next, when it is determined that the second rising edge is a valid rising edge, it can be determined whether the second rising edge time is a start time when signal accumulation occurs according to step S504, and if so, the following step S303 is executed.

S303: and keeping the signal amplitude belonging to the target pulse signal collected before the starting moment.

As shown in fig. 4, each real-time acquisition signal is output to the signal discrimination pipeline and the signal recovery pipeline through the preprocessing module, because the signal discrimination pipeline and the signal recovery pipeline are parallel pipelines, when the rising edge interval time determination module in the signal discrimination pipeline determines that the second rising edge signal is a pileup signal, if the acquisition time of the pileup signal is T2, the original acquisition signal is not processed before the time of T2, and is directly output, and meanwhile, the pileup signal delay module is required to perform signal delay buffering processing, that is, signal fitting is performed on the acquisition signals at T2 and later times, and the residual attenuation waveform belonging to the target pulse signal is separated therefrom, and if the pileup signal does not occur, the signal recovery pipeline always outputs the original acquisition signal, thereby maintaining the real-time output of the pulse attenuation signal.

It should be noted that, when the pileup initial occurrence signal is sent from the rising edge interval time determination module shown in fig. 4 to the pileup occurrence time determination module, the signal amplitude of each pileup signal is recorded in the module, so as to perform signal waveform fitting recovery by using each pileup signal amplitude. Since the pileup signal may be interfered by noise to affect the correct acquisition of the signal amplitude, the noise needs to be eliminated, for example, the true signal value can be more approximated by adopting a front n-point mean filtering method.

S304: and separating the signal amplitude belonging to the target pulse signal from the signal amplitude of the collected signal from the starting moment.

The embodiment adopts a non-full waveform fitting mode, namely, only the exponentially decaying part accumulated by other pulse signals in the target pulse signal is fitted. For example, as shown in fig. 2, signal waveform fitting recovery is performed starting from the second rising edge in order to remove all of the signal 2 stacked on the signal 1 to separate the attenuation waveform of the signal 1 from the signal stacked portion.

In an embodiment of the present application, step S304 may specifically include steps a-D:

step A: and taking each acquisition time at which the starting time starts as the current acquisition time in turn.

Firstly, taking the initial moment when signal accumulation occurs as the current acquisition moment, and separating signal amplitude values belonging to target pulse signals from signal amplitude values corresponding to the current acquisition moment; and taking the starting moment as the last acquisition moment and the next signal acquisition moment of the starting moment as the current moment, … …, and so on until all signal amplitudes belonging to the target pulse signal are fitted.

For each current acquisition signal, separating a signal amplitude belonging to the target pulse signal from signal amplitudes corresponding to the current acquisition time according to the following steps.

And B: and determining the signal amplitude value corresponding to the target pulse signal at the current acquisition time according to the attenuation time constant of the target pulse signal and the signal amplitude value corresponding to the target pulse signal at the previous acquisition time.

The exponential function equation of a single photon signal without pileup is y ═ A.e^-BxThe derivative is y ═ A.B.e^-BxSince the function equation y is equal to a · e^-BxIs a solution of its derivative equation y '═ B · y, so that if y' is to be obtained, it is not necessary to know the values of x and a, but only the value of B, which remains unchanged under certain attenuation characteristics.

Wherein y is the signal amplitude; x is the signal acquisition time; the signal amplitude when A is 0; and B is a decay time constant.

Since the signal amplitude of each acquired signal in this embodiment is in a discrete form, the signal amplitude corresponding to the current acquisition time may be recorded as y [ n +1], the signal amplitude corresponding to the previous acquisition time may be recorded as y [ n ], and the derivative value of y [ n ] may be recorded as y' n, which satisfy formula (1):

y[n+1]＝y[n]+y′[n](1)

in the discrete case, the previously derived formula y' ═ -B · y can be written as formula (2):

y′[n]＝-By[n](2)

wherein B is a decay time constant.

Substituting equation (2) into equation (1) can obtain the discrete point signal amplitude recurrence equation (3):

y[n+1]＝(1-B)×y[n](3)

next, if the corresponding signal amplitude at the acquisition time is recorded as y [ n +1]]Then will be from y [ n +1]]The signal amplitude after the pileup signal is removed is recorded as y₁[n+1]. Assuming that the acquisition time T2 is the starting time of the generation of the signal pileup, the previous acquisition time of T2 may be denoted as T2-1, and each acquisition time after T2 may be denoted as T1, T2, and T3 … … in sequencetn, then, at time T2, the corresponding target pulse signal amplitude is y₁[T₂]＝(1-B)×y[T₂-1]This is the 1 st recovered signal amplitude; then executing step C, if the execution result of step C does not satisfy step D, using formula y₁[t1]＝(1-B)×y₁[T₂]The signal amplitude at time t1 is recovered, and then the formula y is used₁[t2]＝(1-B)×y₁[t1]And D, restoring the signal amplitude at the time t2, and repeating … … until the currently restored signal amplitude meets the step D.

And C: and calculating a difference absolute value between a signal amplitude corresponding to the current acquisition time and a reference value, wherein the reference value is the direct-current component amplitude of the target pulse signal.

Step D: and if the absolute value of the difference is smaller than a preset threshold value, finishing the amplitude recovery of the target pulse signal.

Each acquired signal consists of a dc component and an ac component, the dc component of the signal is a reference level, and the reference level is a baseline value, for example, the approximate "straight line" on the left side of fig. 2 is a baseline. In this embodiment, signal amplitudes corresponding to M acquisition times before the first rising edge may be obtained, and an average value of the M signal amplitudes is used as a baseline value, where M is greater than or equal to 1, and the baseline value may be determined by the signal baseline module shown in fig. 4.

For each recovered signal amplitude y₁[n+1]When y is₁[n+1]The fit is completed when the baseline value is approached. This is because, since the photon signal is exponentially attenuated, when the current photon signal is not completely attenuated and the next photon signal is accumulated thereon, the un-attenuated part of the current photon signal will generate a level accumulation for the dc part (reference level) of the next photon signal, and at this time, the signal tail accumulation will bring the signal baseline to rise, because the rising baseline is not the true baseline of the current photon signal, and therefore, the baseline of the current photon signal, that is, the dc component of the signal, needs to be obtainedAnd comparing the currently recovered signal amplitude with a baseline value when the target pulse signal is recovered from the piled-up signal, and indicating that the signal recovery is finished when the target pulse signal is recovered to the baseline value.

It will be appreciated that, since the amplitude of the recovered signal that is closest to the baseline value may not be equal to the baseline value, an acceptable threshold may be set, and when the recovered amplitude is less than the predetermined threshold, signal recovery is terminated.

The above steps S303 and S304 can be implemented by the pileup restoration and reconstruction output module shown in fig. 4.

In summary, the signal waveform recovery method provided in this embodiment collects the pulse signal output by the target photodetector in real time, determining a starting moment at which a signal pile-up occurs, based on the signal amplitude of the acquired signal, said signal pile-up being a pile-up of at least one other pulse signal on the basis of the target pulse signal, the method aims to directly output the signal amplitude which is acquired before the starting time and belongs to the target pulse signal, only the signal amplitude which belongs to the target pulse signal is extracted from the pileup signal acquired at the starting time and the acquired signal after the pileup signal, therefore, the waveform recovery of the target pulse signal is completed without obtaining all signal waveforms or respectively performing waveform fitting on all rising edges and all falling edges, and the recovery efficiency of the pulse waveform can be effectively improved by the method, and the real-time performance is high.

Further, the following is a combination of the existing signal waveform recovery methods to analyze the advantages of the embodiments of the present application:

when the prior art is adopted for waveform recovery, reconstruction parameter estimation and waveform reconstruction of a rising edge and a falling edge are carried out, and system resource consumption is extremely large, so that the waveform recovery method is not suitable for a non-computer system such as an FPGA (field programmable gate array), and can not be rapidly finished if a recovery signal waveform needs to be output in real time. The reason is that from the practical engineering point of view, if the rising edge parameters need to be accurately recovered, the AD sampling rate is required to be high enough, but the cost is greatly increased, and if the low-cost AD is adopted, the sampling rate is low, so that data at 2 or more different moments cannot be acquired on the quick rising edge, and thus errors can occur in the recovery of the rising edge.

In each acquisition time of the embodiment of the application, the fitting point of the next acquisition time can be obtained by adding the derivative value of the current AD sampling value, and then the original signal waveform can be approximately recovered by repeatedly recursion of the fitting point by using a formula (3). Therefore, the formula (3) is adopted to recover the signal waveform, complex fitting parameter calculation or table lookup, variable multiplication operation and the like are not needed, and therefore, the signal can be output in real time by using few logic resources and operation resources, and the method can be better applied to embedded systems with relatively few resources, such as an FPGA (field programmable gate array) and the like. The B value is fixed, the FPGA only needs to use shift addition operation for multiplication of the fixed constant 1-B, and the calculation can be completed in a few clock beats, so that the operation time can be greatly shortened, the signal recovery real-time performance is increased, and the resource consumption is effectively reduced.

To illustrate the signal waveform recovery effect of this embodiment, a pulse waveform diagram shown in fig. 6 is taken as an example, where a curve 1 is a recovered signal waveform, a curve 2 is a theoretical signal waveform without pileup occurrence, and a curve 3 is an actual collected signal waveform with other signals accumulated on the curve 2. Therefore, the recovered curve 1 can well approach the waveform change condition of the curve 2, and the waveform recovery effect is good.

In addition, the existing signal waveform recovery method has the following defects:

in the prior art, two rising edges are determined by adopting a mode of carrying out derivation on signals, and whether a pileup signal exists in a current signal waveform is judged according to the interval of the two rising edges, however, the mode can only process a double pileup signal waveform, and cannot help the pileup signal waveform with more than two layers.

Referring to fig. 7, a second flowchart of a signal waveform recovery method provided in the embodiment of the present application can solve the above-mentioned drawback by the following steps, which may further include, after step S304 shown in fig. 3:

s305: and removing the signal amplitude belonging to the target pulse signal from the signal amplitude of the acquired signal to obtain the signal amplitude after the removal operation.

For each of the actually acquired signals before the pileup signal separation is achieved through step S304 (i.e. the real-time signals acquired through step S301, and these signals are the original signals before the pileup separation is performed), if the corresponding signal amplitude is recorded as y [ n +1]]From y [ n +1]]Removing the signal amplitude y of the target pulse signal₁[n+1]The resulting signal amplitude is then recorded as y₂[n+1]Namely:

y₂[n+1]＝y[n+1]-y₁[n+1]

next, let y₂[n+1]As the signal amplitude of the acquired signal in S301, the execution of step S302 and its subsequent steps is continued to determine y₂[n+1]Whether the formed signal waveform is a pileup signal waveform, and continuing the next round of signal separation in the case where it is a pileup signal waveform.

It should be noted that, for the original signal waveform corresponding to the previous round of signal separation, the second rising edge thereof is the signal waveform corresponding to the next round of signal separation (i.e. y)₂[n+1]The resulting signal waveform).

S306: and taking the signal amplitude after the removal operation as the signal amplitude of the acquired signal, and executing the step S302 again until the starting time can not be determined.

Since the signal waveform acquired in step S301 may be a double-level Pileup signal waveform or a triple or more-level Pileup signal waveform, in order to prevent it from being a triple or more-level Pileup signal waveform, it is preferable thatAfter the first round of waveform recovery is completed, the signal waveforms of the remaining individual signals need to be recovered by continuous iteration, and therefore, for each signal amplitude y obtained by step S305, the signal waveforms of the remaining individual signals need to be recovered₂[n+1]Taking the amplitude as the signal amplitude of the acquired signal in step S302, detecting whether the amplitude is a Pileup signal waveform, and performing waveform recovery to recover the pulse waveform corresponding to each single photon signal.

Thus, the pileup signal discrimination pipeline and the pileup signal recovery pipeline shown in fig. 4 can continuously identify the pileup signal, so that multiple pileup waveforms can be identified and recovered.

The treatment effect of the present application is described below in terms of experimental effects:

in practical application, when a pileup signal occurs in the PET/CT device, simulation analysis shows that 20% of useful data is lost if the pileup signal is not processed, but the pileup signal is not processed by the current PET/CT device. When the method is used for processing the pileup signal, for example, the pulse waveform schematic diagram shown in fig. 8 is adopted, wherein a smoother curve 1 is a restored signal waveform, and a curve 2 with more burrs and spikes is an actually acquired signal waveform with other signals accumulated.

After the pileup signal is processed by the embodiment of the present application, a simulation experiment analysis is performed on an energy diagram generated based on the processed signal, for example, as shown in fig. 9, the left side is an energy diagram generated based on an original signal waveform without pileup, the middle is an energy diagram generated based on the pileup signal waveform, and the right side is an energy diagram generated based on a recovery waveform without the pileup signal (by the method of the present application). From the perspective of macroscopic effect, the right graph can obviously restore the position calculation error (namely, the black area of the middle graph) caused by pileup stacking signals to the correct area, and the recovery accuracy can reach more than 70%, so that the embodiment of the application overcomes the defect that 70% of original data is lost or the particle position calculation error is caused by pileup.

Referring to fig. 10, a schematic diagram of a signal waveform recovering apparatus provided in an embodiment of the present application is shown, where the apparatus 1000 includes:

the system comprises a first signal acquisition unit 1001, a second signal acquisition unit and a third signal acquisition unit, wherein the first signal acquisition unit is used for acquiring an electric signal output by a target photoelectric detector in real time, and the target photoelectric detector is any one photoelectric detector in a detector ring of medical imaging equipment;

a pile-up time determining unit 1002, configured to determine a start time at which signal pile-up occurs according to a signal amplitude of an acquired signal, where the signal pile-up refers to pile-up of at least one other pulse signal on the basis of a target pulse signal;

a signal amplitude holding unit 1003, configured to hold a signal amplitude belonging to the target pulse signal acquired before the start time;

a signal amplitude separating unit 1004, configured to separate a signal amplitude belonging to the target pulse signal from signal amplitudes of the acquired signal starting at the starting time.

In one embodiment of the present application, the stacking time determining unit 1002 may include:

In one embodiment of the present application, the apparatus 1000 may further include:

then, the accumulation timing determination unit 1002 may further include:

In one embodiment of the present application, the signal amplitude separating unit 1004 may include:

the time definition subunit is used for sequentially taking each acquisition time at which the starting time starts as the current acquisition time;

the amplitude determining subunit is used for determining a signal amplitude corresponding to the target pulse signal at the current acquisition time according to the attenuation time constant of the target pulse signal and the signal amplitude corresponding to the target pulse signal at the previous acquisition time;

the difference value calculating subunit is configured to calculate an absolute value of a difference value between a signal amplitude corresponding to the current acquisition time and a reference value, where the reference value is a dc component amplitude of the target pulse signal;

and the amplitude separation subunit is used for finishing the amplitude recovery of the target pulse signal if the absolute value of the difference is smaller than a preset threshold value.

a signal removing unit, configured to remove the signal amplitude belonging to the target pulse signal from the signal amplitudes of the acquired signals after the signal amplitude separating unit 1004 separates the signal amplitude belonging to the target pulse signal, so as to obtain a signal amplitude after a removal operation;

and a signal re-separation unit, configured to use the signal amplitude after the removal operation as the signal amplitude of the acquired signal, and trigger the accumulation time determination unit 1002 to determine a starting time at which signal accumulation occurs according to the signal amplitude of the acquired signal until the starting time cannot be determined.

and a signal filtering unit, configured to filter the acquired signals after the first signal acquisition unit 1001 acquires the electrical signals output by the target photodetector in real time, so that an original waveform formed by signal amplitudes at each acquisition time tends to be smooth, or part of spike burrs in the original waveform are removed.

Referring to fig. 11, for a schematic diagram of a hardware structure of a signal waveform recovering apparatus provided in an embodiment of the present application, the display device 1100 includes a memory 1101, a receiver 1102, and a processor 1103 connected to the memory 1101 and the receiver 1102 respectively, where the memory 1101 is configured to store a set of program instructions, and the processor 1103 is configured to call the program instructions stored in the memory 1101 to perform the following operations:

In one embodiment of the present application, the processor 1103 is further configured to call the program instructions stored in the memory 1101 to perform the following operations:

determining a signal amplitude corresponding to the second rising edge;

before the interval acquisition time between the first rising edge and the second rising edge is determined, calculating the average value of signal energy output by each photoelectric detector at N acquisition moments before the second rising edge for the target photoelectric detector and other photoelectric detectors, and taking the sum of the calculated average values as an energy discrimination threshold, wherein N is more than or equal to 1;

after the signal amplitude belonging to the target pulse signal is separated, removing the signal amplitude belonging to the target pulse signal from the signal amplitudes of the acquired signals to obtain a signal amplitude after removal operation;

and after the electric signal output by the target photoelectric detector is collected in real time, filtering the collected signal so as to enable an original waveform formed by signal amplitudes at each collection moment to tend to be smooth or remove part of spike burrs in the original waveform.

In some embodiments, the processor 903 may be a Central Processing Unit (CPU), the Memory 901 may be a Random Access Memory (RAM) type internal Memory, and the receiver 902 may include a common physical interface, which may be an Ethernet (Ethernet) interface or an Asynchronous Transfer Mode (ATM) interface. The processor 903, receiver 902, and memory 901 may be integrated into one or more separate circuits or hardware, such as: application Specific Integrated Circuit (ASIC).

As can be seen from the above description of the embodiments, those skilled in the art can clearly understand that all or part of the steps in the above embodiment methods can be implemented by software plus a necessary general hardware platform. Based on such understanding, the technical solution of the present application may be essentially or partially implemented in the form of a software product, which may be stored in a storage medium, such as a ROM/RAM, a magnetic disk, an optical disk, etc., and includes several instructions for enabling a computer device (which may be a personal computer, a server, or a network communication device such as a media gateway, etc.) to execute the method according to the embodiments or some parts of the embodiments of the present application.

It should be noted that, in the present specification, the embodiments are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments may be referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.

It is further noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A signal waveform recovery method, comprising:

2. The method of claim 1, wherein determining a starting time for signal pile-up to occur based on the signal amplitude of the acquired signal comprises:

determining a signal amplitude corresponding to the second rising edge;

3. The method of claim 2, further comprising:

4. The method of claim 1, wherein the separating the signal amplitude belonging to the target pulse signal from the signal amplitude of the collected signal starting from the starting time comprises:

5. The method according to any one of claims 1 to 4, wherein after separating out the signal amplitude belonging to the target pulse signal, further comprising:

6. The method according to any one of claims 1 to 4, wherein after the acquiring the electrical signal output by the target photodetector in real time, the method further comprises:

7. A signal waveform recovery apparatus, comprising:

8. The apparatus according to claim 7, wherein the accumulation timing determining unit includes:

9. The apparatus of claim 7 or 8, further comprising:

then, the accumulation timing determination unit further includes:

10. A signal waveform recovery apparatus, comprising: a processor, a memory, a system bus;

the processor and the memory are connected through the system bus;

the memory is to store one or more programs, the one or more programs comprising instructions, which when executed by the processor, cause the processor to perform the method of any of claims 1-6.