Apparatus, systems and methods for precise time measurement of PET using lasers

Abstract

This invention discloses a device, system, and method for precise time measurement of PET using lasers. The device for precise time measurement of PET using lasers includes a PET detector module, a PET digital electronics board, and a laser. The PET detector module detects gamma photons emitted by the target and sends the generated detection signal to the PET digital electronics board. The PET digital electronics board is equipped with an optoelectronic device for receiving light pulse signals and converting them into a clock reference signal. The laser generates light pulse signals and sends them to the optoelectronic device. The PET digital electronics board digitizes the received detection signal according to the clock reference signal and measures the time. This device improves upon traditional PET systems, fully leveraging the time performance advantages of the detector, electronics, and other components.

Description

Technical Field

[0001] This invention relates to the field of positron emission tomography (PET) imaging technology, and more particularly to an apparatus, system, and method for achieving precise time measurement of PET using lasers. Background Technology

[0002] Positron emission tomography (PET), as a high-end medical imaging device, can realize the early diagnosis of tumors and use molecular probes to perform brain imaging for Alzheimer's disease, playing an important role in the early diagnosis of diseases and pathological and pharmacological research.

[0003] The basic principle of PET is to introduce drugs labeled with positron-emitting radionuclides into the body. These drugs can typically bind specifically to tumors or certain receptors, and have the ability to perform functional imaging that reflects metabolism. Radionuclides that accumulate at lesions or target receptors undergo β-transformation. + After decaying and emitting positrons, the radionuclide undergoes an annihilation reaction, releasing a pair of back-to-back gamma rays with an energy of 511 keV. The PET detector can obtain the spatial distribution of the radionuclide within the tested object by combining coincidence detection with image reconstruction algorithms.

[0004] To meet the demands of high-precision molecular imaging and dynamic imaging, higher requirements have been placed on the temporal resolution, energy resolution, positional resolution, and dynamic range of PET imaging systems. Among these, further improvement in temporal resolution remains a key challenge in current PET technology. Figure 1 As shown, improving the time resolution of the PET system allows for more accurate measurement of the time difference of flight of positron-annihilated gamma photon pairs. This can further refine the range and even the specific location of gamma photon pair generation, reduce back-projection noise during reconstruction, improve the system's signal-to-noise ratio and imaging accuracy, significantly reduce the amount of data required for image reconstruction, reduce the radiation dose required for imaging, and simplify the reconstruction process. These are also advantages of Time-of-Flight (TOF) PET over traditional PET.

[0005] Currently, with the continuous optimization of PET technology, the optimal PET system-level resolution has reached <200ps (FWHM), which has brought about a certain effect on improving the signal-to-noise ratio, but further improvement is still needed. In recent years, after years of research on materials and devices, the time performance of each component of the PET system has been further improved.

[0006] In the field of detectors, the successful fabrication and application of scintillation crystals, which emit light faster and have higher light yields, and silicon photomultiplier tubes (SiPMs) with superior single-photon time resolution (SPTR) have significantly improved the temporal performance of detectors based on scintillation emission mechanisms. Currently, the use of lutetium silicate crystals (LSO) combined with non-commercial SiPMs has achieved a coincidence time resolution (CTR) of 60 ps (FWHM). Furthermore, Cherenkov light, as a transient luminescent particle generated by the polarization and depolarization of atoms or molecules in a medium, has an emission time on the order of ps. Therefore, using the Cherenkov emission mechanism to replace the scintillation mechanism can fundamentally improve the temporal performance of detectors. Currently, pure Cherenkov radiators such as lead fluoride and lead glass are also finding some application. Microchannel plate photomultiplier tubes (MCP-PMTs), as a novel photodetector, utilize microchannel plates (MCPs) to replace traditional darad structures to achieve electron multiplication. They possess inherent advantages such as high gain and fast response, excellent temporal performance, and good single-photon resolution. They are suitable for detecting transient Cherenkov light signals with few or even single photons. Currently, the single-photon transit time dispersion (TTS) of commercially available MCP-PMTs has reached 25 ps (FWHM), far superior to the approximately 100 ps (FWHM) SPTR of SiPM devices. By integrating the Cherenkov radiator and the MCP-PMT photocathode into an integrated optical window, a coincidence time resolution of 27 ps (FWHM) has been achieved, fully demonstrating the improvement in the detector's temporal performance.

[0007] In the field of readout electronics, with the development of the semiconductor industry and the improvement of integrated circuit technology, application-specific integrated circuits (ASICs) with advantages such as high integration, high speed, and low power consumption have begun to be used in PET systems. Currently, some organizations have developed multi-purpose ASIC chips, including front-end amplification, shaping, digitization, and timing control, which have been applied in the TOF-PET field, greatly improving the time measurement accuracy of PET systems. At present, analog ASIC chips and dedicated time-to-digital converter (TDC) chips used for signal amplification and shaping have reached a time resolution of <10ps (FWHM). In addition, with the continuous improvement of FPGA performance and application level, high-precision TDC based on FPGA has now reduced the time resolution to <20ps (FWHM), and with the continuous improvement of process and technology, the time resolution capability of readout electronics will continue to improve.

[0008] As mentioned above, the timing performance of PET detectors and related readout electronics has been significantly improved. At the PET system level, the key is to fully utilize the timing performance of each part of the system. When the total time resolution contributed by each part of the system is less than 50 ps or even reaches ~10 ps, ​​higher demands are placed on the structure of the PET system, the jitter level of the reference clock signals between various modules, and the time calibration accuracy of the system. Currently, the clock reference signals commonly used in PET systems are distributed and transmitted to various electronic boards through circuits. Affected by various factors, there is a certain amount of time jitter between different clock signals, and the level of jitter is difficult to meet the requirements of PET systems when the time resolution reaches a high level (<50 ps or even <30 ps). Moreover, with the further improvement of the time resolution level of related devices, the time resolution of the PET system will be further improved. At that time, the jitter between different clock signals will become the main factor affecting the time resolution of the PET system. In addition, with the continuous improvement of the system time resolution, the accuracy of PET system time correction must also be improved. Semiconductor pulsed lasers can play a role in these aspects by leveraging their advantages, breaking through the limitations of clock signal jitter and time calibration accuracy on the time resolution of PET systems.

[0009] Solid-state and semiconductor lasers have become research hotspots in recent years. Lasers based on solid-state and semiconductor laser theory have been widely used in high-precision machining, laser medicine, and other fields. However, high-power lasers are mostly used. With the special requirements of emerging fields such as quantum communication and other technologies for lasers, lasers with characteristics such as low pulse power, narrow pulse width, low time jitter, and high stability have been widely developed. At present, this type of commercial laser can cover a wide range of modulation bandwidth and wavelength, with pulse widths as narrow as ps or even fs. The time jitter between the optical pulse and the laser modulation signal is less than 1 ps or even tens of fs. The peak power range of the optical pulse is also from tens to hundreds of mW, and the corresponding photon number level can meet the requirements for detection using optoelectronic devices.

[0010] Furthermore, based on statistical principles and experimental results, when using photoelectric devices to detect light pulse signals, the time jitter between the output signal and the light pulse signal, and the number of photons received by the photoelectric device, follow the following rules:

[0011]

[0012] Where, N pe It refers to the number of light (photoelectrons) received by an optoelectronic device. When the number of photons reaches 10... 5 -10 6At the level of [missing information], taking SiPM as an example, the introduced time jitter will be reduced from approximately 100 ps (FWHM) of SPTR to the order of fs (FWHM), which is negligible compared to the jitter of the laser itself. Therefore, the time jitter of the pulse signal obtained by combining a laser with optoelectronic devices relative to the modulation signal can be considered to be determined by the time jitter of the laser itself, thus achieving a time jitter of <1 ps or even <tens of fs. Furthermore, using beam splitting to distribute the optical pulses can eliminate many influences of traditional electrical signal distribution methods, reducing the time jitter between signals to ~1 ps or even better. Therefore, the time accuracy of the pulse signal obtained by combining a laser with optoelectronic devices and optical distribution is far superior to the accuracy achievable by the clock distribution method and time correction method currently used in PET systems.

[0013] Therefore, lasers, with their excellent timing performance, can play a role in both replacing the PET clock signal and performing PET time correction. The relevant implementation methods in PET are as follows:

[0014] In current PET systems, to provide a unified reference clock signal for each channel and module, the clock module needs to generate signals of different frequencies using multiple crystal oscillators. These signals are then converted into clock signals and distributed to various digital electronics for time measurement. This clock signal is affected by factors such as differences in crystal oscillator performance, jitter during clock distribution, and differences in signal propagation paths, resulting in jitter of approximately 10 ps or even tens of ps between different clock signals. While this has a relatively small impact on the current time resolution of PET systems, as the time resolution of PET systems improves to the tens of ps level, this clock signal reference method becomes insufficient to meet the requirements for precise time information measurement.

[0015] In PET systems, to achieve position resolution, each detector module has multiple detector units. Due to inconsistencies in the response delays between the output signals and received optical signals of different modules and detector units, and differences between different signal links, the time spectrum peaks of different detector units on each LOR line exhibit varying degrees of shift. Therefore, time correction is required for different modules and channels. Current PET system time correction methods mostly employ a point-source radiation source located at the center or a linear radiation source rotating around the center, combined with subsequent equation construction and iterative solutions to achieve time correction between different modules and detector units. Since the method of using coincidence detection of the radiation source for time correction needs to consider the influence of optical path difference, and when the linear source needs to be fixed on a transmission device for correction, the machining accuracy of the PET system and the precision and stability of the transmission device will affect the correction accuracy. The time correction accuracy achieved by the current PET time correction methods is insufficient to meet the requirements when the time resolution of PET systems reaches tens of ps or higher. Summary of the Invention

[0016] Addressing the problems existing in current PET (Pulse Detection and Reduction) technologies, and analyzing the advantages of applying lasers to PET, this invention aims to propose a device that utilizes lasers combined with optoelectronic devices to provide high-precision clock reference signals for various modules of a PET system. Based on this device, the traditional PET system is improved. Furthermore, this invention proposes a method for achieving precise time measurement in PET systems and for using lasers for time correction of the PET system. This device and method simplify the structure of the PET system, reduce the impact of system integration on time resolution, improve the accuracy of system correction, and fully leverage the time performance advantages of novel PET detectors and electronic components.

[0017] The present invention provides a device for precise time measurement of PET using laser, characterized in that it includes a PET detector module, a PET digital electronics board, and a laser; wherein the PET digital electronics board is connected to the detector module, and the PET digital electronics board is equipped with an optoelectronic device;

[0018] The laser is used to generate optical pulse signals and send them to the optoelectronic device;

[0019] The PET detector module is used to detect gamma photons emitted by the target to be detected and send the generated detection signal to the PET digital electronics board.

[0020] The PET digital electronics board is used to generate a clock reference signal based on the received optical pulse signal, and then digitize the received detection signal based on the clock reference signal.

[0021] Furthermore, an optoelectronic device is provided on the PET digital electronics board. The optoelectronic device is used to receive laser pulse signals and convert them into electrical signals, which are then sent to the time detection unit. The time detection unit uses the electrical signals as clock reference signals.

[0022] Furthermore, the optoelectronic device is matched with an optical fiber interface, and the optoelectronic device is connected to the laser through the optical fiber interface to receive the optical pulse signal of the semiconductor laser.

[0023] Furthermore, the method by which the PET digital electronics board digitizes the received detection signal according to the clock reference signal is as follows: wherein the i-th digital electronics board is connected to two detector modules T1 and T2 respectively struck by the same pair of gamma photons, and the current time t of the reference clock signal obtained by the i-th digital electronics board through the time detection chip is used. i1 ,t i2 And the times t1′ and t2′ of the output signals of detector modules T1 and T2 obtained by the time detection chip; then t1′-t i1 =t1,t2′-t i2 =t2, and then calculate the time difference ΔT = t1 - t2.

[0024] The present invention also provides a PET system, characterized in that it includes a laser, a laser beam splitter, and multiple detection devices; the multiple detection devices constitute a detection space; each detection device includes one or more PET detector modules and a PET digital electronics board, the PET digital electronics board being connected to each of the detector modules, and the PET digital electronics board being equipped with an optoelectronic device; wherein,

[0025] The semiconductor laser is used to generate optical pulse signals and send them to the laser beam splitter.

[0026] The laser beam splitter is used to split the received optical pulse signal to obtain multiple optical pulse signals and transmit each optical pulse signal to a corresponding optoelectronic device on a PET digital electronics board.

[0027] The PET detector module is used to detect gamma photons emitted by the target to be detected in the detection space and send the generated detection signal to the PET digital electronics board.

[0028] The PET digital electronics board is used to generate a clock reference signal based on the received optical pulse signal, and then digitize the received detection signal based on the clock reference signal.

[0029] Furthermore, the laser beam splitter is connected to the laser via an optical fiber to receive the optical pulse signal from the laser; the optoelectronic device is connected to an optical fiber interface, and the optoelectronic device is connected to a branch output optical fiber of the laser beam splitter via the optical fiber interface.

[0030] A device that uses lasers combined with optoelectronic devices to provide high-precision clock reference signals for various modules of a PET system, and the basic components of a PET system improved based on this device, as follows: Figure 2 As shown, the device mainly consists of four parts: a PET detector module, a PET digital electronics board, and a laser. In a PET system constructed using this device, a laser beam splitter is also required for beam splitting. More specifically, similar to a traditional PET system, the PET detector module detects gamma photons. The PET digital electronics board is directly connected to the detector module to receive the gamma photon detection signal and perform digitization. The improvement over a traditional PET system lies in the fact that each board is equipped with optoelectronic devices and a matching fiber optic interface to receive the optical pulse signal generated by the laser and split into multiple paths by the laser beam splitter, which provides a clock reference signal for the digital electronics.

[0031] The specific composition of the aforementioned electronic board is as follows: Figure 3 As shown, its function is similar to that of a traditional PET digital electronics board, but its improvement lies in the fact that each detector module in this device is directly connected to the digital electronics board, and an optoelectronic device is added to the digital electronics board. A light-shielding optical fiber interface is set on the surface of the optoelectronic device to receive the light pulses output by the laser after it is split by the beam splitter. The optoelectronic device converts the received light pulses into electrical signals and outputs them to a specific input port of the time detection chip located on the digital electronics board, which serves as the clock reference signal for the PET system.

[0032] The laser needs to be selected with a wavelength that matches the optimal photosensitive or photon-detecting efficiency of the optoelectronic device used. The optical pulse signal is then extracted via optical fiber and input to a laser beam splitter, such as... Figure 4 As shown, the split optical fibers are connected to the optical fiber interfaces of the optoelectronic devices on each digital electronics board.

[0033] like Figure 5Based on the aforementioned apparatus for providing a clock reference signal using laser combined with optoelectronic devices, this invention relates to a method for precise time measurement of PET using laser, comprising:

[0034] S1: Adjust the output power of the laser's optical pulses to a suitable level, and adjust the modulation signal used to control the generation of optical pulses by the laser according to the requirements of the PET system, thereby controlling the output frequency of the optical pulses.

[0035] S2: The light pulses output by the laser are split by a laser beam splitter and coupled to the optoelectronic devices of each digital electronics board to provide clock reference signals.

[0036] S3: During PET scanning, using a clock reference signal provided by a laser combined with optoelectronic devices as a reference, digital electronics are used to measure the time when a pair of gamma photons hit the detector's output signal. The time-of-flight (TOF) information of the two gamma photons is obtained from this time. Specifically, the i-th digital electronics board is connected to two detector modules T1 and T2 that are hit by the same pair of gamma photons. The current time t of the reference clock signal obtained by the time detection chip from the i-th digital electronics board is used. i1 t i2 And the times t1′ and t2′ of the output signals of detector modules T1 and T2 obtained by the time detection chip; then t1′-t i1 =t1, t1′-t i2 =t2, and then calculate the time difference ΔT = t1 - t2.

[0037] S4: Combine TOF information with location information to obtain TOF-PET data, and transmit it to the host computer for reconstruction to obtain a PET image of the target area.

[0038] like Figure 6 Based on the aforementioned laser and beam splitter, the present invention also relates to a method for time correction of a PET system using a laser, comprising:

[0039] S1: Adjust the output power and frequency of the laser's optical pulses, and split the modulation signal that controls the laser to generate optical pulses into one channel for connection to the digital electronics board.

[0040] S2: Increase the number of outputs of the laser beam splitter and couple the split laser beams to each detection unit of the detector module. Each detection unit converts the split laser pulse signal into an electrical signal.

[0041] S3: Measure the time delay between the detection signal output by the detection unit on the corresponding detector module and the laser modulation signal using the digital electronics board of each detector module, and perform statistical analysis to obtain the delay time between the signal output by each detection unit and the laser modulation signal.

[0042] S4: Based on the recorded delay time, the host computer corrects the consistency data between all detection units of the PET system.

[0043] The advantages of this invention are as follows:

[0044] Compared with existing technologies, this invention utilizes a laser combined with optoelectronic devices to provide a clock reference signal for the PET system. This simplifies the PET system structure and reduces its electronic complexity. Furthermore, leveraging the laser's excellent timing performance, it further reduces time jitter in the clock reference signal between different modules, improving the PET system's timing performance. Using a laser instead of a radiation source for PET system time correction improves the efficiency of time correction, simplifies the correction process, and eliminates the influence of radiation source movement mechanisms and system machining precision on system correction in traditional methods. It also utilizes the laser's low time jitter advantage to improve time correction accuracy. This invention proposes a device and method for using lasers for precise time measurement and correction in PET systems. It is suitable for TOF-PET imaging equipment with ultra-high time resolution and can be widely applied and promoted to improve the timing performance of PET systems. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of the time-of-flight (TOF) technology for PET.

[0046] Figure 2 A schematic diagram of a device and PET system that uses lasers combined with optoelectronic devices to provide clock reference signals.

[0047] Figure 3 A schematic diagram showing the addition of optoelectronic devices and fiber optic interfaces to a PET digital electronics board.

[0048] Figure 4 This is a schematic diagram of a laser beam splitter.

[0049] Figure 5 This is a flowchart illustrating a method for precise time measurement of PET using lasers.

[0050] Figure 6 This is a flowchart of a method for time correction of a PET system using laser. Detailed Implementation

[0051] The present invention will now be described in further detail with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0052] This invention relates to an apparatus and method for precise time measurement of PET (Physical Electrosurgical Unit) using lasers. The invention is characterized by the use of a device that combines a laser with optoelectronic devices to provide a clock reference signal. Based on this device, the traditional PET system is improved, and methods for precise time measurement and time correction of the PET system using lasers are proposed. The composition and implementation of the apparatus and method are as follows:

[0053] 1) A device that uses lasers combined with optoelectronic devices to provide high-precision clock reference signals for each module of a PET system, and the basic components of a PET system improved based on this device, such as... Figure 2 As shown, the device mainly consists of four parts: a PET detector module, a PET digital electronics board, and a laser. When using this device to construct a PET system, a laser beam splitter is also required for beam splitting. More specifically, similar to traditional PET systems, the PET detector module is used to detect gamma photons and generate detection signals. Its specific structure and composition depend on the requirements of different PET systems. The PET digital electronics board functions similarly to the digital electronics in traditional PET systems, used to receive the gamma photon detection signals for digitization to obtain position, energy, and time information. In this device, the digital electronics board is directly connected to the detector module and corresponds one-to-one. Based on the original components of the digital electronics, each digital electronics board is equipped with optoelectronic devices and a matching fiber optic interface to receive the optical pulse signals generated by the laser and split into multiple paths by the laser beam splitter, which are used to provide clock reference signals for each digital electronics module.

[0054] 2) The specific composition of the aforementioned electronic board is as follows: Figure 3 As shown, each detector module in this device is directly connected to the digital electronics board, and an optoelectronic device is added to the digital electronics board. The types of optoelectronic devices include, but are not limited to, silicon photomultiplier tubes (SiPM), avalanche photodiodes (APD), or photodiodes (PD). A light-shielding optical fiber interface is set on the surface of the optoelectronic device to receive the light pulses output by the laser. The optoelectronic device converts the received light pulses into electrical signals and outputs them, which are connected to a specific input port of the time detection chip (including but not limited to FPGA-based TDC, dedicated TDC, waveform sampling chip) located on the digital electronics board, as the clock reference signal of the PET system.

[0055] 3) Select the emission wavelength of the laser to match the wavelength corresponding to the optimal optical sensitivity (photodiode PD, avalanche photodiode APD) or photon detection efficiency (PDE, silicon photomultiplier tube SiPM) of the optoelectronic device used. Extract the optical pulse signal through an optical fiber and input it into the laser beam splitter, such as... Figure 4 As shown, multiple uniform and synchronized optical pulse signals are obtained. The number of beam splits will be determined by the number of detector modules and digital electronics boards. The split optical fibers are connected to the optical fiber interfaces of the optoelectronic devices on each digital electronics board. The size of the optical fiber output port needs to be smaller than the sensitive area of ​​the optoelectronic device to ensure sufficient light collection.

[0056] 4) such as Figure 5 Based on the aforementioned device that utilizes laser combined with optoelectronic devices to provide a clock reference signal, the method for precise time measurement of PET using laser is as follows:

[0057] S1: Adjust the output power of the laser to ensure that the number of photons in each beam output pulse is within a suitable range (10,000 to 20,000). According to the requirements of the corresponding PET system, adjust the output frequency of the laser pulse by setting the frequency of the modulation signal so that the frequency of the reference signal provided by each optoelectronic device is the frequency required by the system (10MHz to 100MHz), which facilitates subsequent data transmission and processing.

[0058] S2: The laser beam is split by a laser beam splitter, and the split laser beam is connected to the optoelectronic device in digital electronics through an optical fiber for optical pulse detection, providing the required clock reference signal.

[0059] S3: During PET scanning, the time-of-flight difference ΔT between the detected matching gamma photon pairs will be determined by the signals output from the two detector modules hit by the gamma photons, and by times t1 and t2 measured by digital electronics, based on a clock reference signal provided by a laser-coupled optoelectronic device.

[0060] The i-th digital electronics board is connected to two detector modules T1 and T2 struck by the same pair of gamma photons. The current time t of the reference clock signal obtained by the time detection chip from the i-th digital electronics board is used. i1 t i2 And the times t1′ and t2′ of the output signals of detector modules T1 and T2 obtained by the time detection chip; then t1′-t i1 =t1,t2-t i2 =t2, then calculate the time difference:

[0061] ΔT=t1-t2

[0062] S4: Combine the precise TOF information of each matching event measured under the condition of clock reference signal with the position information of gamma ray hitting the detector to obtain the TOF-PET data required for reconstruction, and transmit it to the host computer for reconstruction to obtain the PET scan image of the target area.

[0063] 5) such as Figure 6 Based on the aforementioned laser and beam splitter, the method for time correction of a PET system using laser is as follows:

[0064] S1: Adjust the output power and output laser pulse frequency of the laser, and split the modulation signal that controls the laser to generate light pulses into one channel, and connect it to the digital electronics connected to each detector module that needs time correction.

[0065] S2: Set a suitable laser interface in each detection unit and increase the output of the laser beam splitter to couple the split laser to each detection unit of the detector module.

[0066] S3: Utilize the digital electronics described above to measure the time delay between the output signal of all detection units in each module and the laser modulation signal. Statistically analyze the time delay between the output signal of the detection unit and the laser modulation signal in optical pulse events and obtain the distribution of the unit's time delay, i.e., the time delay spectrum. Find the peaks in the time delay spectrum to obtain the delay time of different detection units.

[0067] S4: Based on the delay time of different detection units obtained in step S3, the PET coincidence data is processed by the host computer to eliminate the influence of the different delay times of each detection unit on the time difference of flight measurement, and realize the time correction of all detection modules and detection units of the PET system.

[0068] Although specific embodiments of the invention have been disclosed for illustrative purposes to aid in understanding and implementing the invention, those skilled in the art will understand that various substitutions, variations, and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the invention should not be limited to the content disclosed in the preferred embodiments, and the scope of protection claimed by the invention is defined by the claims.

Claims

1. An apparatus for precise time measurement of PET using a laser, characterized in that, The PET system comprises a PET detector module, a PET digital electronics board card, and a laser; the PET digital electronics board card is connected with the detector module, and the PET digital electronics board card is provided with an optoelectronic device; The laser is configured to generate a light pulse signal and send the light pulse signal to the optoelectronic device; The PET detector module is configured to detect gamma photons emitted by a target to be detected and send a generated detection signal to the PET digital electronics board card; The PET digital electronics board card is configured to generate a clock reference signal according to the received light pulse signal, and then perform digital processing on the received detection signal according to the clock reference signal; A time detection unit is provided on the PET digital electronics board. The photoelectric device is used to receive laser pulse signals and convert them into electrical signals, which are then sent to the time detection unit. The time detection unit uses the electrical signals as clock reference signals. The method by which the PET digital electronics board digitizes the received detection signals based on the clock reference signals is as follows: The i1th and i2th digital electronics boards are respectively connected to two detector modules T1 and T2 struck by the same pair of gamma photons. The current time t of the reference clock signal obtained by the time detection chip from the i1th and i2th digital electronics boards is used. i1 ,t i2 And the times t1′ and t2′ of the output signals of detector modules T1 and T2 obtained by the time detection unit; then t1′-t i1 =t1,t2′-t i2 =t2, and then calculate the time difference ΔT = t1 - t2.

2. The apparatus of claim 1, wherein, The optoelectronic device is matched with a fiber interface, and the optoelectronic device is connected with the laser through the fiber interface and configured to receive the light pulse signal of the laser.

3. A PET system characterized by, The PET system comprises a laser, a laser beam splitting device, and a plurality of detection devices; the plurality of detection devices form a detection space; each detection device comprises one or more PET detector modules and a PET digital electronics board card, the PET digital electronics board card is connected with each PET detector module, and the PET digital electronics board card is provided with an optoelectronic device; wherein, The laser is configured to generate a light pulse signal and send the light pulse signal to the laser beam splitting device; The laser beam splitting device is configured to split the received light pulse signal to obtain a plurality of light pulse signals and transmit each light pulse signal to an optoelectronic device on a corresponding PET digital electronics board card; The PET detector module is configured to detect gamma photons emitted by a target to be detected in the detection space and send a generated detection signal to the PET digital electronics board card; The PET digital electronics board card is configured to generate a clock reference signal according to the received light pulse signal, and then perform digital processing on the received detection signal according to the clock reference signal; The PET digital electronics board card is provided with a time detection unit, the photoelectric device is used for receiving a laser pulse signal and converting the laser pulse signal into an electric signal and sending the electric signal to the time detection unit, and the time detection unit takes the electric signal as a clock reference signal; the method for the PET digital electronics board card to carry out digital processing on the received detection signal according to the clock reference signal is as follows: wherein the i1th and i2th digital electronics board cards are connected with two detector modules T1 and T2 hit by the same pair of gamma photons respectively, the current time t of the reference clock signal obtained by the i1th and i2th digital electronics board cards through the time detection chip is used, and the time t1' and t2' of the output signals of the detector modules T1 and T2 obtained through the time detection unit; then t1'-t i1 , i2 = t1 and t2'-t i1 = t2, and then the time difference ΔT = t1-t2 is calculated. i2 ​ 4. The PET system of claim 3, wherein, The laser beam splitting device is connected with the laser through an optical fiber and configured to receive the light pulse signal of the laser; the optoelectronic device is connected with a fiber interface, and the optoelectronic device is connected with an output optical fiber of the laser beam splitting device through the fiber interface.

5. A time measurement method based on the PET system of claim 3, comprising the following steps: 1) adjusting a modulation signal for controlling the laser to generate a light pulse according to the requirements of the PET system, to control the output frequency of the light pulse; 2) splitting the light pulse output by the laser through the laser beam splitting device, and coupling the light pulse to each PET digital electronics board card to generate a clock reference signal; 3) during PET scanning, each PET detector module detects gamma photons emitted by a target to be detected in the detection space and sends a generated detection signal to the PET digital electronics board card; the PET digital electronics board card measures the time-of-flight difference ΔT between each pair of gamma photons of a coincidence event detected, i.e., TOF information, based on the clock reference signal.

6. The method of claim 5, wherein, In step 3), the individual PET digital electronics board card calculates the two detection signal times t1 and t2 corresponding to the same coincidence event based on the clock reference signal, and then calculates ΔT = t1 - t2.

7. The method of claim 5, wherein, The TOF information of each coincidence event measured based on the clock reference signal is combined with the position information of the gamma ray hitting the detector module to obtain the TOF-PET data required for reconstruction and transmit to the upper computer for reconstruction to obtain the PET scan image of the target region.

8. A time correction method based on the PET system of claim 3, comprising: 1) adjusting the light pulse output power and frequency of the laser, and dividing a modulation signal for controlling the laser to generate light pulses into a branch for accessing the digital electronics board card; 2) splitting the light pulses output by the laser through a laser beam splitting device, and coupling them to each detection unit of the detector module to be corrected respectively; 3) using the connected digital electronics board card of each detector module to measure the time delay value between the detection signal output by the detection unit on the corresponding detector module and the laser modulation signal, and obtaining the time delay distribution, i.e. the time delay spectrum, of each detection unit by counting the time difference between the detection signal output by each detection unit and the semiconductor laser modulation signal in the light pulse event; peak searching is performed on the time delay spectrum to obtain the delay time of different detection units; 4) based on the delay time of different detection units, the coincidence data of the PET is processed by the upper computer to exclude the influence of the delay time difference of each detection unit on the time of flight difference measurement, and the time correction of all detector modules and detection units of the PET system is realized.

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