Crystal position encoding method and system based on time threshold

Abstract

The present invention provides a crystal position encoding method and system based on time-crossing threshold, and the measurement method includes: configuring a detector module; configuring a position encoding module, including a resistor network circuit, a comparator, and a pulse width measurement module; the resistor network circuit superimposes the first sum signal of N X directions and the second sum signal of M Y directions output by the SiPM array, the comparator receives the first sum signal and the second sum signal, and compares them with a voltage threshold respectively to form a time-crossing threshold pulse signal; the phase-locked loop generates a sampling clock, and encodes the time-crossing threshold pulse signal to form a position code, and the pulse width measurement module collects the position of the rising edge and the falling edge in the position code to calculate the pulse width. After adopting the above technical solution, the resources of the FPGA chip itself are used to encode the excited crystal position, and the recognition accuracy is high.

Description

Technical Field

[0001] The present invention relates to the field of medical equipment, and in particular to a crystal position encoding method and system based on time threshold crossing. Background Art

[0002] At present, silicon photomultiplier (SiPM) detectors are increasingly used in positron emission tomography (PET) systems due to their good energy and time resolution and magnetic compatibility. The principle is to use the high-energy Gamma photons captured by the detector crystal module to convert them into low-energy visible light signals, which are then converted into electrical signals through SiPM, and then the energy and arrival time information of the electrical signals are obtained using energy measurement devices and time measurement devices (Time-Digital Converter, TDC). Then, the effective signals are screened out using methods such as coincidence judgment at the back end, and the precise location of the photon generation is obtained through image reconstruction algorithms.

[0003] In the implementation process, in order to control the system cost and complexity, a SiPM detector is generally used to couple multiple crystals, and then the position, energy and time are detected through a multiplexed row and column readout circuit. Among them, the position detection circuit based on the center of gravity method is widely used due to its good detection efficiency and position resolution performance. Most of the center of gravity position detection circuits that have been invented use a resistor-capacitor coding network and a medium- and high-speed analog-digital converter (ADC) to digitize the energy output at different positions of the coding network, and then further calculate the excited crystal position code. These methods basically require a large number of commercial ADC chips, which increases system complexity, cost and power consumption.

[0004] Therefore, a new crystal position encoding method and system is needed, which eliminates the need for commercial ADC chips and greatly reduces system complexity, cost and power consumption. Summary of the invention

[0005] In order to overcome the above technical defects, the purpose of the present invention is to provide a crystal position encoding method and system based on time threshold, which uses the resources of the FPGA chip itself to encode the excited crystal position with high recognition accuracy.

[0006] The present invention discloses a crystal position encoding method based on time thresholding, which is used in a spectroscopic PET device and comprises the following steps:

[0007] The detector module of the PET device is configured based on the following settings, the detector module includes a SiPM array and a LYSO crystal array, and the SiPM units in the SiPM array and the LYSO units in the LYSO crystal array are coupled in a 2:3 arrangement;

[0008] The position encoding module is configured based on the following settings, and the position encoding module includes a resistor network circuit, a comparator, and a pulse width measurement module;

[0009] The resistor network circuit is superimposed to form N first sum signals in the X direction and M second sum signals in the Y direction output by the SiPM array. The comparator receives the first sum signal and the second sum signal, and compares them with a voltage threshold respectively, and forms a time-over-threshold pulse signal based on the comparison result.

[0010] The phase-locked loop in the FPGA chip included in the pulse width measurement module generates a sampling clock, and encodes each first sum signal and each second sum signal at each sampling moment in the sampling clock to form a position code corresponding to each first sum signal and each second sum signal. The pulse width measurement module collects the position of the rising edge and falling edge of any pulse in each time-crossing threshold pulse signal in the position code to calculate the pulse width between the rising edge and the falling edge.

[0011] Preferably, the resistor network circuit superimposes N first sum signals in the X direction and M second sum signals in the Y direction output by the SiPM array, the comparator receives the first sum signal and the second sum signal, and compares them with a voltage threshold respectively, and the step of forming a time-over-threshold pulse signal based on the comparison result includes:

[0012] The resistor network circuit receives the output signals of 8*8 SiPM units, and sums the first signals in the same X direction to form 8 first sum signals, and sums the second signals in the same Y direction to form 8 second sum signals;

[0013] The comparator compares each first sum signal and the second sum signal with a voltage threshold. When the first sum signal or the second sum signal is less than the voltage threshold, the comparator outputs a low level signal. When the first sum signal or the second sum signal is greater than the voltage threshold, the comparator outputs a high level signal. The high level signal and the low level signal are continuously formed into a time-overthreshold pulse signal.

[0014] Preferably, the phase-locked loop in the FPGA chip included in the pulse width measurement module generates a sampling clock, and encodes each first sum signal and each second sum signal at each sampling time in the sampling clock to form a position code corresponding to each first sum signal and each second sum signal, and the pulse width measurement module collects the position of the rising edge and the falling edge of any pulse in each time-crossing threshold pulse signal in the position code to calculate the pulse width between the rising edge and the falling edge. The steps include:

[0015] The phase-locked loop generates a 400MHz sampling clock in eight phases to sample the time-over-threshold pulse signal. When the time-over-threshold pulse signal is at a low level, the phase-locked loop encodes each sampling moment as 0, and when the time-over-threshold pulse signal is at a high level, the phase-locked loop encodes each sampling moment as 1.

[0016] The encoding module of the pulse width measurement module records the first jump moment of each phase-locked loop encoding from 0 to 1, and the second jump moment of the first phase-locked loop encoding from 1 to 0 after the first jump moment, and represents the first jump moment and the second jump moment in binary numbers as a first binary moment and a second binary moment;

[0017] The encoding module of the pulse width measurement module calculates the difference between the first binary time and the second binary time, and records it as the pulse width.

[0018] Preferably, the pulse width measurement module collects the positions of the rising edge and the falling edge of any pulse in each time-crossing threshold pulse signal in the position code to calculate the pulse width between the rising edge and the falling edge, including:

[0019] A position calculation module calculates the position code P of each excited LYSO unit in the X direction and / or the Y direction based on the following formula:

[0020]

[0021]

[0022] Where T is the pulse width in the i-th X direction or Y direction, and w is the energy weight of the SiPM unit.

[0023] Preferably, the method further comprises the following steps:

[0024] The energy measurement module calculates the sum of all signals in the X direction or the Y direction as a first total signal or a second total signal, and digitally integrates the first total signal or the second total signal after digitization to deposit it as energy information;

[0025] The energy measurement module packages the energy information and the position code P to form an energy spectrum for each LYSO unit.

[0026] The present invention also discloses a crystal position encoding system based on time threshold crossing, which is used in a PET device and includes:

[0027] The detector module includes a SiPM array and a LYSO crystal array, and the SiPM units in the SiPM array and the LYSO units in the LYSO crystal array are coupled in a 2:3 arrangement;

[0028] Position coding module, the position coding module includes a resistor network circuit, a comparator, and a pulse width measurement module;

[0029] The resistor network circuit is superimposed to form N first sum signals in the X direction and M second sum signals in the Y direction output by the SiPM array. The comparator receives the first sum signal and the second sum signal, and compares them with a voltage threshold respectively, and forms a time-over-threshold pulse signal based on the comparison result.

[0030] The phase-locked loop in the FPGA chip included in the pulse width measurement module generates a sampling clock, and encodes each first sum signal and each second sum signal at each sampling moment in the sampling clock to form a position code corresponding to each first sum signal and each second sum signal. The pulse width measurement module collects the position of the rising edge and falling edge of any pulse in each time-crossing threshold pulse signal in the position code to calculate the pulse width between the rising edge and the falling edge.

[0031] Preferably, the resistor network circuit receives output signals of 8*8 SiPM units, and sums the first signals in the same X direction to form 8 first sum signals, and sums the second signals in the same Y direction to form 8 second sum signals;

[0032] The comparator compares each first sum signal and the second sum signal with a voltage threshold. When the first sum signal or the second sum signal is less than the voltage threshold, the comparator outputs a low level signal. When the first sum signal or the second sum signal is greater than the voltage threshold, the comparator outputs a high level signal. The high level signal and the low level signal are continuously formed into a time-overthreshold pulse signal.

[0033] Preferably, the phase-locked loop generates a 400MHz sampling clock in eight phases to sample the time-over-threshold pulse signal. When the time-over-threshold pulse signal is at a low level, the phase-locked loop encodes each sampling moment as 0, and when the time-over-threshold pulse signal is at a high level, the phase-locked loop encodes each sampling moment as 1.

[0034] The encoding module of the pulse width measurement module records the first jump moment of each phase-locked loop encoding from 0 to 1, and the second jump moment of the first phase-locked loop encoding from 1 to 0 after the first jump moment, and represents the first jump moment and the second jump moment in binary numbers as a first binary moment and a second binary moment;

[0035] The encoding module of the pulse width measurement module calculates the difference between the first binary time and the second binary time, and records it as the pulse width.

[0036] Preferably, the crystal position encoding system further comprises:

[0037] The position calculation module calculates the position code P of each excited LYSO unit in the X direction and / or the Y direction based on the following formula:

[0038]

[0039]

[0040] Where T is the pulse width in the i-th X direction or Y direction, and w is the energy weight of the SiPM unit.

[0041] Preferably, it also includes:

[0042] An energy measurement module calculates the sum of all signals in the X direction or the Y direction as a first total signal or a second total signal, and digitally integrates the first total signal or the second total signal after digitization to deposit energy information;

[0043] The energy measurement module packages the energy information and the position code P to form an energy spectrum for each LYSO unit.

[0044] Compared with the prior art, the above technical solution has the following beneficial effects:

[0045] 1. The system complexity is low, and the equipment success and power consumption are also reduced accordingly;

[0046] 2. The position of the excited crystal is accurately identified. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 A schematic diagram of the structure of a crystal position encoding system in accordance with a preferred embodiment of the present invention;

[0048] Figure 2 A schematic diagram of the structure of a detector module in accordance with a preferred embodiment of the present invention;

[0049] Figure 3 A schematic diagram of the structure of a pulse width measurement module in accordance with a preferred embodiment of the present invention;

[0050] Figure 4 A countmap of the count values ​​of each crystal unit of the crystal array in accordance with a preferred embodiment of the present invention;

[0051] Figure 5 To meet the deposition energy spectrum test results of the crystal array in a preferred embodiment of the present invention;

[0052] Figure 6a A schematic diagram of the test results of the bit error rate of the SiPM array and the crystal unit facing each other in accordance with a preferred embodiment of the present invention;

[0053] Figure 6b This is a schematic diagram of the test results of the bit error rate of the overlap position of the SiPM array and the crystal unit in accordance with a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0054] The advantages of the present invention are further described below in conjunction with the accompanying drawings and specific embodiments.

[0055] Exemplary embodiments will be described in detail herein, examples of which are shown in the accompanying drawings. When the following description refers to the drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present disclosure. Instead, they are merely examples of devices and methods consistent with some aspects of the present disclosure as detailed in the appended claims.

[0056] The terms used in this disclosure are for the purpose of describing specific embodiments only and are not intended to limit the disclosure. The singular forms of "a", "said" and "the" used in this disclosure and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0057] It should be understood that although the terms first, second, third, etc. may be used in the present disclosure to describe various information, such information should not be limited to these terms. These terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of the present disclosure, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Depending on the context, the word "if" as used herein may be interpreted as "at the time of" or "when" or "in response to determining".

[0058] In the description of the present invention, it is necessary to understand that the terms "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0059] In the description of the present invention, unless otherwise specified and limited, it should be noted that the terms "installed", "connected" and "connected" should be understood in a broad sense. For example, it can be a mechanical connection or an electrical connection, or it can be the internal connection between two components. It can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to the specific circumstances.

[0060] In the following description, the suffixes such as "module", "component" or "unit" used to represent elements are only used to facilitate the description of the present invention, and have no specific meanings. Therefore, "module" and "component" can be used interchangeably.

[0061] See also Figure 1 , Figure 2 and Figure 3 In one embodiment, in order to realize the new position coding based on time-over-threshold (TOT) and further the crystal position coding method, it is first necessary to configure the detector module, position coding module, pulse width measurement module and energy measurement module for the PET device to respectively receive the radiation energy, detect the irradiation position, measure the threshold time and determine the energy spectrum size. Therefore, the crystal position coding method includes the following steps:

[0062] S100: configuring a detector module in the PET device, the detector module comprising a SiPM array and a LYSO crystal array, and the SiPM units in the SiPM array and the LYSO units in the LYSO crystal array are coupled in a 2:3 arrangement

[0063] Silicon photomultiplier (SiPM) is a new type of photodetector device, which consists of an avalanche diode array working in Geiger mode. It has the characteristics of high gain, high sensitivity, low bias voltage, insensitivity to magnetic field, and compact structure. It was invented in the late 1990s and is widely used in high energy physics and nuclear medicine (PET) and other fields. Lutetium yttrium silicate scintillation crystal (LYSO) has attracted great attention from the international scintillation crystal community for its high light output, fast luminescence decay, large effective atomic number, and high density. It is also considered to be the best inorganic scintillation crystal material with the best comprehensive performance due to its stable physicochemical properties, non-deliquescent, and high efficiency in detecting gamma rays. It is an ideal scintillation crystal for SPECT and PET in the future to replace NaI (Tl) and BGO. The SiPM unit size is 3.92*3.92mm, with a spacing of 4mm. The LYSO unit size is 2.65mm*2.65mm, with a spacing of 2.66mm. Therefore, the SiPM unit and the LYSO unit are precisely coupled 2:3. In actual operation, a single SiPM unit or adjacent SiPM units may detect the irradiation of energy. Preferably, the size of the SiPM array is 8*8, and the size of the LYSO crystal array is 12*12.

[0064] S200: The position encoding module includes a resistor network circuit, a comparator, and a pulse width measurement module. The resistor network circuit is used to form a voltage according to the energy irradiation, the comparator is used to determine whether the formed voltage exceeds the threshold, and the pulse width measurement module determines the TOT time.

[0065] S300: The resistor network circuit is superimposed to form N first sum signals in the X direction and M second sum signals in the Y direction output by the SiPM array, the comparator receives the first sum signal and the second sum signal, and compares them with a voltage threshold respectively, and forms a time-overthreshold pulse signal based on the comparison result

[0066] Since the SiPM array and the LYSO crystal array are distributed in a square, each SiPM unit will output a voltage signal in two mutually perpendicular directions (X direction and Y direction). In order to save resources, the voltage acquisition of the resistor network circuit will be integrated, that is, a column in the X direction or a row in the Y direction is accumulated to form N first sum signals in the X direction and M second sum signals in the Y direction. Taking the 8*8 SiPM array as an example, the original 64 output signals will be simplified to 8 first sum signals in the X direction and 8 second sum signals in the Y direction.

[0067] The comparator compares each of the input first sum signal and second sum signal with a preset voltage threshold based on the IBUF resources in the PET device (configured in LVDS mode) to obtain a time-over-threshold (TOT) pulse of the input first sum signal and second sum signal (i.e., when the voltage is greater than the voltage threshold, a pulse signal will be formed, and when the voltage is less than the voltage threshold, no pulse signal will be formed).

[0068] S400: The phase-locked loop in the FPGA chip included in the pulse width measurement module generates a sampling clock, and encodes each of the first sum signal and each of the second sum signal's time-crossing threshold pulse signals at each sampling moment in the sampling clock to form a position code corresponding to each of the first sum signal and each of the second sum signal's time-crossing threshold pulse signals, and the pulse width measurement module collects the position of the rising edge and the falling edge of any pulse in each time-crossing threshold pulse signal in the position code to calculate the pulse width between the rising edge and the falling edge;

[0069] Based on the threshold-crossing pulse signal formed by the comparator, the phase-locked loop (PLL) based on the time-to-digital conversion (TDC) of the FPGA chip will generate a sampling clock, and the time-crossing pulse signals of the first and second sum signals are sampled and encoded at each sampling moment, that is, when the position where the pulse is formed is encoded as "1", and when the position where there is no pulse is encoded as "0", thereby forming a position encoding of the time-crossing pulse signal corresponding to each first and second sum signal. It can be understood that when the code jumps from 0 to 1 at a certain position, it means that the pulse begins to form, and conversely, the code jumps from 1 to 0, which means that the pulse ends. Since the pulse width measurement module will collect the rising edge and falling edge of any pulse in each time-crossing pulse signal in the position code, the pulse width between the rising edge and the falling edge is calculated. And using this TDC, the encoding has time information at the same time, and the position where the pulse width is generated and the time it is maintained can be calculated.

[0070] In a preferred embodiment, S300 includes:

[0071] S310: The resistor network circuit receives output signals of 8*8 SiPM units, and sums the first signals in the same X direction to form 8 first sum signals, and sums the second signals in the same Y direction to form 8 second sum signals;

[0072] S320: The comparator compares each of the first sum signal and the second sum signal with a voltage threshold. When the first sum signal or the second sum signal is less than the voltage threshold, the comparator outputs a low level signal. When the first sum signal or the second sum signal is greater than the voltage threshold, the comparator outputs a high level signal. The high level signal and the low level signal are continuously formed into a time-over-threshold pulse signal. The width of the TOT pulse can be used to characterize the energy of the input signal.

[0073] Further, step S400 includes:

[0074] S410: The phase-locked loop generates a 400 MHz sampling clock at eight phases (0° / 45° / 90° / 135° / 180° / 225° / 270° / 315°) to sample the time-over-threshold pulse signal. When the time-over-threshold pulse signal is at a low level, the phase-locked loop encodes each sampling moment as 0. When the time-over-threshold pulse signal is at a high level, the phase-locked loop encodes each sampling moment as 1.

[0075] With the above eight phases and 400MHZ sampling frequency settings, the sampling clock can increase the amount of sampled data to 32 times the original 100MHZ sampling frequency, so as to more accurately determine the position of the code jump. The code format is such as: 000..011..11, indicating that a jump occurs on the leading edge of the signal, or such as: 111..100..00, indicating that a jump occurs on the trailing edge of the signal.

[0076] S420: The encoding module of the pulse width measurement module records the first jump time of each phase-locked loop encoding from 0 to 1, and the second jump time of the first phase-locked loop encoding from 1 to 0 after the first jump time, and represents the first jump time and the second jump time in binary numbers as a first binary time and a second binary time;

[0077] When the code jumps from 0 to 1, the first jump time will be recorded as the starting time of the pulse width. Similarly, when the code jumps from 1 to 0, the second jump time will be recorded as the end time of the pulse width. It is understandable that due to the non-full-process sampling, the recorded jump time may not be the most real jump time, but under the eight-phase setting, the resolution of TOT pulse width measurement is 0.3125ns, and the TOT pulse width generated by gamma rays is about 200ns. This measurement resolution is better than 1%, which meets the application requirements.

[0078] S430: The encoding module of the pulse width measurement module calculates the difference between the first binary time and the second binary time, and records it as the pulse width

[0079] Finally, the difference between the first binary moment and the second binary moment is represented in the form of a binary number and recorded as a pulse width for later use.

[0080] In a further preferred embodiment, step S400 further includes:

[0081] S440: A position calculation module calculates the position code P of each excited LYSO unit in the X direction and / or the Y direction based on the following formula:

[0082]

[0083]

[0084] Wherein T is the pulse width in the i-th X direction or Y direction, w is the energy weight of the SiPM unit, and the energy weights w of the eight SiPM units in the X or Y direction are (0, 2, 3, 5, 6, 8, 9, 11), respectively. It can be understood that the position code P of the excited LYSO unit can be calculated according to the position and time correspondence of the pulse width.

[0085] More preferably, the method further comprises the following steps:

[0086] S500: The energy measurement module calculates the energy information of the LYSO crystal array based on the pulse width

[0087] Finally, the energy measurement module calculates the energy information received by the LYSO crystal array based on the pulse width (i.e., the time it takes for the voltage to cross the threshold) and expresses it in the form of an energy spectrum, which is used to determine the irradiation position and intensity of the gamma rays in the PET device.

[0088] Specifically, step S500 may include:

[0089] S510: The energy measurement module calculates the sum of all signals in the X direction or the Y direction as a first total signal or a second total signal, and digitally integrates the first total signal or the second total signal after digitization to deposit an energy information

[0090] That is, the energy measurement module calculates the sum of all signals in the X direction (or Y direction), and records them as the first total signal (or the second total signal), and digitizes the first total signal or the second total signal using an analog-digital converter (ADC), and then performs digital integration inside the FPGA chip to obtain energy information deposited in the crystal;

[0091] S520: The energy measurement module packages the energy information and the position code P to form an energy spectrum of each LYSO unit;

[0092] Finally, the energy information is packaged with the position code P to obtain the energy of each γ-ray excited LYSO unit.

[0093] See also Figure 4 , Figure 5 , Figure 6a and Figure 6b With the above configuration, after testing, a point source 22Na was placed 10 cm in front of the detector module to collect crystal position code and energy information. The test results show that each statistical distribution is basically uniform. According to the measured crystal position and energy information, the following can be obtained: Figure 5The energy spectrum of each LYSO crystal unit shows that the energy spectrum of each crystal unit is clear, and the energy resolution at 511keV is about 13%. In addition, the bit error rate of position coding was tested. A single crystal was installed at different positions of the SiPM array, and the other crystal units were covered with shading materials for optical isolation. Then the statistical distribution of the module was tested, as shown in Figure 6. The bit error rates of crystals in two positions, one completely corresponding to the SiPM and one bridging two SiPMs, were tested. The test results show that for the case where the crystal completely corresponds to one SiPM, the bit error rate is about 1%. For the crystal bridging two SiPMs, the bit error rate is about 10%, which can meet the application requirements.

[0094] The present invention also discloses a crystal position encoding system based on time threshold crossing, which is used in a PET device and includes:

[0095] The detector module includes a SiPM array and a LYSO crystal array, and the SiPM units in the SiPM array and the LYSO units in the LYSO crystal array are coupled in a 2:3 arrangement;

[0096] Position coding module, the position coding module includes a resistor network circuit, a comparator, and a pulse width measurement module;

[0097] The resistor network circuit is superimposed to form N first sum signals in the X direction and M second sum signals in the Y direction output by the SiPM array. The comparator receives the first sum signal and the second sum signal, and compares them with a voltage threshold respectively, and forms a time-over-threshold pulse signal based on the comparison result.

[0098] The phase-locked loop in the FPGA chip included in the pulse width measurement module generates a sampling clock, and encodes each first sum signal and each second sum signal at each sampling moment in the sampling clock to form a position code corresponding to each first sum signal and each second sum signal. The pulse width measurement module collects the position of the rising edge and falling edge of any pulse in each time-crossing threshold pulse signal in the position code to calculate the pulse width between the rising edge and the falling edge.

[0099] Preferably, the resistor network circuit receives output signals of 8*8 SiPM units, and sums the first signals in the same X direction to form 8 first sum signals, and sums the second signals in the same Y direction to form 8 second sum signals;

[0100] The comparator compares each first sum signal and the second sum signal with a voltage threshold. When the first sum signal or the second sum signal is less than the voltage threshold, the comparator outputs a low level signal. When the first sum signal or the second sum signal is greater than the voltage threshold, the comparator outputs a high level signal. The high level signal and the low level signal are continuously formed into a time-overthreshold pulse signal.

[0101] Preferably, the phase-locked loop generates a 400MHz sampling clock in eight phases to sample the time-over-threshold pulse signal. When the time-over-threshold pulse signal is at a low level, the phase-locked loop encodes each sampling moment as 0, and when the time-over-threshold pulse signal is at a high level, the phase-locked loop encodes each sampling moment as 1.

[0102] The encoding module of the pulse width measurement module records the first jump moment of each phase-locked loop encoding from 0 to 1, and the second jump moment of the first phase-locked loop encoding from 1 to 0 after the first jump moment, and represents the first jump moment and the second jump moment in binary numbers as a first binary moment and a second binary moment;

[0103] The encoding module of the pulse width measurement module calculates the difference between the first binary time and the second binary time, and records it as the pulse width.

[0104] Preferably, the crystal position encoding system further comprises:

[0105] The position calculation module calculates the position code P of each excited LYSO unit in the X direction and / or the Y direction based on the following formula:

[0106]

[0107]

[0108] Wherein T is the pulse width in the i-th X direction or Y direction, and w is the energy weight of the SiPM unit.

[0109] Preferably, it also includes: an energy measurement module, calculating all signals in the X direction or the Y direction or the first total signal and the second total signal, and digitally integrating the first total signal or the second total signal after digitization to deposit energy information;

[0110] The energy measurement module packages the energy information and the position code P to form an energy spectrum for each LYSO unit.

[0111] It should be noted that the embodiments of the present invention have better practicability and do not impose any form of limitation on the present invention. Any technician familiar with the field may use the technical content disclosed above to change or modify it into an equivalent effective embodiment. However, any modification or equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A crystal position encoding method based on time thresholding, used in PET equipment, characterized in that: The steps include: The detector module of the PET device is configured based on the following settings, wherein the detector module includes a SiPM array and a LYSO crystal array, and the SiPM units in the SiPM array and the LYSO units in the LYSO crystal array are coupled in a 2:3 arrangement; A position encoding module is configured based on the following settings, wherein the position encoding module includes a resistor network circuit, a comparator, and a pulse width measurement module; The resistor network circuit is superimposed to form N first sum signals in the X direction and M second sum signals in the Y direction output by the SiPM array, the comparator receives the first sum signal and the second sum signal, and compares them with a voltage threshold respectively, and forms a time-overthreshold pulse signal based on the comparison result; The phase-locked loop in the FPGA chip included in the pulse width measurement module generates a sampling clock, and encodes each of the first and second sum signals at each sampling moment in the sampling clock to form a position code corresponding to the time-crossing threshold pulse signal of each first and second sum signal. The pulse width measurement module collects the position of the rising edge and falling edge of any pulse in each time-crossing threshold pulse signal in the position code to calculate the pulse width between the rising edge and the falling edge.

2. The crystal position encoding method according to claim 1, characterized in that: The resistor network circuit is superimposed to form N first sum signals in the X direction and M second sum signals in the Y direction output by the SiPM array, the comparator receives the first sum signal and the second sum signal, and compares them with a voltage threshold respectively, and the steps of forming a time-over-threshold pulse signal based on the comparison result include: The resistor network circuit receives the output signals of 8*8 SiPM units, and sums the first signals in the same X direction to form 8 first sum signals, and sums the second signals in the same Y direction to form 8 second sum signals; The comparator compares each of the first sum signal and the second sum signal with a voltage threshold. When the first sum signal or the second sum signal is less than the voltage threshold, the comparator outputs a low level signal. When the first sum signal or the second sum signal is greater than the voltage threshold, the comparator outputs a high level signal. The high level signal and the low level signal are continuously formed into a time-overthreshold pulse signal.

3. The crystal position encoding method according to claim 2, characterized in that: The phase-locked loop in the FPGA chip included in the pulse width measurement module generates a sampling clock, and encodes each of the first sum signal and each of the second sum signal's time-crossing threshold pulse signals at each sampling moment in the sampling clock to form a position code corresponding to each of the first sum signal and each of the second sum signal's time-crossing threshold pulse signals, and the pulse width measurement module collects the position of the rising edge and the falling edge of any pulse in each time-crossing threshold pulse signal in the position code to calculate the pulse width between the rising edge and the falling edge, including the following steps: The phase-locked loop generates a 400 MHz sampling clock in eight phases to sample the time-crossing threshold pulse signal. When the time-crossing threshold pulse signal is at a low level, the phase-locked loop encodes each sampling moment as 0, and when the time-crossing threshold pulse signal is at a high level, the phase-locked loop encodes each sampling moment as 1; The encoding module of the pulse width measurement module records the first jump moment of each phase-locked loop encoding from 0 to 1, and the second jump moment of the first phase-locked loop encoding from 1 to 0 after the first jump moment, and represents the first jump moment and the second jump moment in binary numbers as a first binary moment and a second binary moment; The encoding module of the pulse width measurement module calculates the difference between the first binary moment and the second binary moment, and records it as the pulse width.

4. The crystal position encoding method according to claim 3, characterized in that: The pulse width measurement module collects the positions of the rising edge and the falling edge of any pulse in each time-crossing threshold pulse signal in the position code to calculate the pulse width between the rising edge and the falling edge, including: The position calculation module calculates the position code P of each excited LYSO unit in the X direction and / or Y direction based on the following formula: Where T is the pulse width in the i-th X direction or Y direction, and w is the energy weight of the SiPM unit.

5. The crystal position encoding method according to claim 4, characterized in that: The following steps are also included: The energy measurement module calculates the sum of all signals in the X direction or the Y direction as a first total signal or a second total signal, and digitally integrates the first total signal or the second total signal after digitization to deposit it as energy information; The energy measurement module packages the energy information and the position code P to form an energy spectrum of each LYSO unit.

6. A crystal position encoding system based on time thresholding, used in PET equipment, characterized in that: include: A detector module, wherein the detector module includes a SiPM array and a LYSO crystal array, and the SiPM units in the SiPM array and the LYSO units in the LYSO crystal array are coupled in a 2:3 arrangement; a position encoding module, wherein the position encoding module includes a resistor network circuit, a comparator, and a pulse width measurement module; The resistor network circuit is superimposed to form N first sum signals in the X direction and M second sum signals in the Y direction output by the SiPM array, the comparator receives the first sum signal and the second sum signal, and compares them with a voltage threshold respectively, and forms a time-overthreshold pulse signal based on the comparison result; The phase-locked loop in the FPGA chip included in the pulse width measurement module generates a sampling clock, and encodes each of the first sum signal and each of the second sum signal at each sampling moment in the sampling clock to form a position code corresponding to each of the first sum signal and each of the second sum signal. The pulse width measurement module collects the position of the rising edge and the falling edge of any pulse in each time-crossing threshold pulse signal in the position code to calculate the pulse width between the rising edge and the falling edge.

7. The crystal position encoding system according to claim 6, characterized in that: The resistor network circuit receives the output signals of 8*8 SiPM units, and sums the first signals in the same X direction to form 8 first sum signals, and sums the second signals in the same Y direction to form 8 second sum signals; The comparator compares each of the first sum signal and the second sum signal with a voltage threshold. When the first sum signal or the second sum signal is less than the voltage threshold, the comparator outputs a low level signal. When the first sum signal or the second sum signal is greater than the voltage threshold, the comparator outputs a high level signal. The high level signal and the low level signal are continuously formed into a time-overthreshold pulse signal.

8. The crystal position encoding system according to claim 6, characterized in that: The phase-locked loop generates a 400 MHz sampling clock in eight phases to sample the time-crossing threshold pulse signal. When the time-crossing threshold pulse signal is at a low level, the phase-locked loop encodes each sampling moment as 0, and when the time-crossing threshold pulse signal is at a high level, the phase-locked loop encodes each sampling moment as 1; The encoding module of the pulse width measurement module records the first jump moment of each phase-locked loop encoding from 0 to 1, and the second jump moment of the first phase-locked loop encoding from 1 to 0 after the first jump moment, and represents the first jump moment and the second jump moment in binary numbers as a first binary moment and a second binary moment; The encoding module of the pulse width measurement module calculates the difference between the first binary moment and the second binary moment, and records it as the pulse width.

9. The crystal position encoding system according to claim 7, characterized in that: The crystal position encoding system also includes: The position calculation module calculates the position code P of each excited LYSO unit in the X direction and / or the Y direction based on the following formula: Where T is the pulse width in the i-th X direction or Y direction, and w is the energy weight of the SiPM unit.

10. The crystal position encoding system according to claim 9, characterized in that: Also includes: An energy measurement module calculates the sum of all signals in the X direction or the Y direction as a first total signal or a second total signal, and digitally integrates the first total signal or the second total signal after digitization to deposit it as energy information; The energy measurement module packages the energy information and the position code P to form an energy spectrum of each LYSO unit.

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