A system and method for boosting count rate in a TOF-PET system

Abstract

The application discloses a kind of system and method for promoting TOF-PET system counting rate.The system includes a data processing module and multiple acquisition units, each acquisition unit includes a detector module and an electronics module;Detector module is used to detect the gamma photon pair generated by positron annihilation in the detected object, and the nuclear signal generated according to the detected gamma photon pair is converted into electrical signal input electronics module;Electronics module selects the input electrical signal to obtain real coincidence event for acquisition;Data processing module is used to receive the same coincidence time window as a pair of real coincidence events with two real coincidence events, calculate the time difference of two real coincidence events in each pair of real coincidence events to its corresponding detector module, and determine the position of the detected object according to the statistical result of the time difference of each pair of real coincidence events.Theoretical effective counting rate can be improved several times or even an order of magnitude, which greatly improves the sensitivity of the system.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of positron emission computed tomography (PET) imaging technology, and in particular to a system and method for realizing count rate improvement of a TOF-PET system using an electronics hardware level pre-coincidence trigger. BACKGROUND

[0002] Positron emission tomography (PET) is an advanced medical imaging technology that utilizes the physical properties of positron radioactive isotopes to enable dynamic imaging of molecular interactions and metabolic activities within the body. PET has been widely applied in the diagnosis, monitoring and research of diseases, including cancer, cardiovascular disease and nervous system diseases. In addition to improving sensitivity, the introduction of time-of-flight (TOF) information can significantly improve the performance of a PET system. This is because the temporal distribution of annihilation photons is directly proportional to the spatial uncertainty of the annihilation position. Therefore, higher time resolution means more accurate annihilation point localization and better image signal-to-noise ratio. The requirements of a PET system for high sensitivity and high time resolution impose strict requirements on the channel number, count rate and time precision of the readout electronics.

[0003] With the advantages of short dead time, low power consumption and high integration, the time measurement technology based on a timing discriminator circuit combined with a high-precision TDC has become the first choice for readout electronics design in a TOF-PET system. After the amplified nuclear signal is converted to a fast front pulse signal by a discriminator (comparator), the time information of the pulse arrival is obtained by inputting the TDC. However, the time performance of this technical solution is mainly limited by the discrimination module. The timing precision is related to the amplitude and time of the rising edge, and there is a time walk effect. The timing precision is usually about 20 ps, and the count rate is in the order of tens to hundreds of kcps.

[0004] Another high-precision time measurement scheme is implemented based on waveform digitization technology. Compared with a high-speed ADC (sampling rate > 1 GSPS), the waveform sampling scheme based on a switched capacitor array (SCA) technology combined with an ADC reduces power consumption by combining high-speed analog sampling with slow readout while preserving the time, energy and other physical information in the original nuclear signal. The timing precision can be less than 10 ps. However, the slow readout process results in a long dead time, and the count rate is usually in the order of several to tens of kcps, which limits its application in high count rate scenarios such as TOF-PET. Currently, there are few studies on improving the count rate of this technical solution. Only some research teams have improved the count rate to twice the original by using a ping-pong architecture, but this also doubles the hardware cost. SUMMARY

[0005] To address the problems existing in the prior art, the present invention aims to provide a system and method for improving the count rate of a TOF-PET system using electronic pre-coincidence triggering. By employing an electronic hardware-level pre-coincidence triggering design, the effective count rate of the SCA+ADC waveform sampling electronics is increased.

[0006] The technical solution of the present invention is:

[0007] A method for improving the count rate of a TOF-PET system, wherein the TOF-PET system includes a data processing module and multiple acquisition units, each of which includes a TOF-PET detector module and a TOF-PET electronics module. The method comprises the following steps:

[0008] 1) Using the TOF-PET detector module to detect gamma photon pairs generated by positron annihilation in the object being detected, and converting the nuclear signals generated by the detected gamma photon pairs into electrical signals that are input into the TOF-PET electronics module of the acquisition unit;

[0009] 2) Each of the TOF-PET electronic modules screens the input electrical signals, and when the energy of the nuclear signal meets the set energy screening conditions, generates a trigger signal and sends it to each of the acquisition units; when the i-th acquisition unit receives the trigger signal generated by the TOF-PET electronic module in the i-th acquisition unit and the trigger signal generated by the TOF-PET electronic module in other acquisition units within the t-th coincidence time window, the TOF-PET electronic module in the i-th acquisition unit collects the nuclear signal within the t-th coincidence time window as a true coincidence event;

[0010] 3) The data processing module receives the true coincidence events collected by the TOF-PET electronics module, and regards two true coincidence events within the same coincidence time window as a pair of true coincidence events; extracts the time and energy information from each pair of true coincidence events, and calculates the time difference between the two true coincidence events in each pair of true coincidence events arriving at their corresponding TOF-PET detector modules, counts the time differences between each pair of true coincidence events, and determines the position of the detected object based on the statistical results.

[0011] Furthermore, each of the TOF-PET detector modules is connected in series, and the last-level TOF-PET detector module is connected to the data processing module; each of the TOF-PET electronics modules includes a comparator, a waveform sampling circuit and an FPGA; the comparator is used to perform energy screening on the input nuclear signal, and when the energy of the nuclear signal meets the set energy screening condition, a trigger signal is generated and sent to the FPGA in each acquisition unit; the waveform sampling circuit is used to acquire the input nuclear signal to obtain a coincidence signal and send it to the FPGA; when the FPGA receives the trigger signal generated by the comparator in its acquisition unit and the trigger signal generated by other acquisition units within the i-th coincidence time window, it retains the coincidence signal within the i-th coincidence time window and sends it as a true coincidence event to the next-level TOF-PET electronics module; the last-level TOF-PET detector module sends the received true coincidence event to the data processing module.

[0012] Furthermore, the waveform sampling circuit includes a DRS4 chip and an ADC; the DRS4 chip is used to perform high-speed analog sampling on the input nuclear signal and then input it into the ADC; the ADC is used to digitize the input analog signal to obtain a digitized waveform.

[0013] Furthermore, adjacent acquisition units are connected via high-bandwidth cables for transmitting the trigger signal; and the FPGA determines whether the received trigger signals are within the same coincidence time window through an AND gate.

[0014] Furthermore, the data processing module calculates the position of positron annihilation based on the time t1 when one gamma photon arrives at the TOF-PET detector module and the time t2 when the other gamma photon arrives at the TOF-PET detector module in each pair of true coincidence events. where c is the speed of light.

[0015] A system for improving the count rate of a TOF-PET system, characterized by comprising a data processing module and a plurality of acquisition units, each of the acquisition units comprising a TOF-PET detector module and a TOF-PET electronics module;

[0016] The TOF-PET detector module is used to detect gamma photon pairs generated by positron annihilation in the detected object, and convert the nuclear signals generated by the detected gamma photon pairs into electrical signals and input them into the TOF-PET electronics module of the acquisition unit;

[0017] The TOF-PET electronics module is used for screening the input electrical signal, and a trigger signal is generated and sent to each of the collection units when the energy of the nuclear signal meets the set energy screening condition; wherein when the i-th collection unit receives the trigger signal generated by the TOF-PET electronics module in the i-th collection unit and the trigger signal generated by the TOF-PET electronics module in other collection units in the t-th coincidence time window, the TOF-PET electronics module of the i-th collection unit collects the nuclear signal in the t-th coincidence time window as a real coincidence event;

[0018] The data processing module is used for receiving the real coincidence events collected by the TOF-PET electronics module, taking two real coincidence events in the same coincidence time window as a pair of real coincidence events, extracting the time and energy information in each pair of real coincidence events, calculating the time difference between the two real coincidence events in each pair of real coincidence events, and calculating the time difference of each pair of real coincidence events, and determining the position of the detected object according to the statistical result.

[0019] The advantages of the present application are as follows:

[0020] The effective events are efficiently screened and read out through the design of the pre-coincidence trigger of the electronics hardware level, and the collected events are all real events that have been coincided, so that the readout and processing of invalid events in the time measurement route based on SCA+ADC are avoided, the pressure of the host computer for processing data is greatly reduced. Compared with the traditional system without integrated pre-coincidence trigger design, the theoretical effective count rate can be increased by several times or even an order of magnitude, and the sensitivity of the system is greatly improved. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The figure is a system structure diagram of the present application.

[0022] Figure 2 The figure is a structure principle diagram of the TOF-PET electronics module. DETAILED DESCRIPTION

[0023] The present application will be further described in detail below with reference to the accompanying drawings, and the examples are only used to explain the present application, and are not used to limit the scope of the present application.

[0024] The present application relates to a method for improving the count rate and realizing high sensitivity of TOF-PET based on the pre-coincidence trigger design of electronics. The embodiments of the present application are as follows:

[0025] 1) The whole TOF-PET system is composed of three parts, which are TOF-PET detector module, TOF-PET electronics module and data processing module. Among them, the TOF-PET electronics module is a waveform sampling electronics board card, Figure 2 The connection relationship of two detector modules and the data processing module of the electronics module is shown, the TOF-PET detector module is used for detecting the gamma photons generated by positron annihilation, and generating the corresponding detection signal, the specific structure and composition thereof are determined according to the requirements of different PET systems.

[0026] 2) The waveform sampling electronics board card is directly connected with the detector module, which is used for receiving and extracting the physical information in the nuclear signal generated by the gamma photons, including time, energy, etc. In addition, the electronics system is also responsible for selecting the coincidence signal. As shown in Figure 2 The whole waveform sampling electronics board card is composed of three parts: comparator, waveform sampling circuit and data processing unit FPGA. The waveform sampling circuit is composed of DRS4 chip based on SCA technology and ADC, which can provide several to hundreds of analog sampling channels, and the sampling rate is in the order of GSPS. The signal output by the front-end detector is first amplified and shaped by the front-end electronics, and then enters the DRS4 chip for high-speed analog sampling. After the sampling process is completed, the holding charge of the internal sampling unit is read out to the external ADC at a rate of 33MHz to complete digitization. After digitization, the waveform enters the FPGA to extract the time, energy and other physical information, and finally the data is summarized and transmitted to the next board card Figure 2 Waveform sampling board 1 transmits data to waveform sampling board 2), and the last board card collects the data of all board cards and transmits them to the data processing module through Gigabit Ethernet. In addition, the FPGA is also responsible for the logic control of DRS4 and ADC, and provides the clock required by DRS4 and ADC.

[0027] 3) Figure 2 The specific design and method of using electronics hardware level pre-coincidence trigger to improve the sensitivity of the system are shown as follows:

[0028] S1: The detector nuclear signal is sampled into the waveform sampling electronics board card, and also input into the threshold comparator. When the amplitude of the nuclear signal is higher than the threshold value of the comparator, that is, the energy selection condition is met, the over-threshold pulse signal generated will be input into the FPGA as a trigger signal. In this process, the threshold value of the comparator can be adjusted online by the FPGA.

[0029] S2: If the coincidence signal of the two detectors and the coincidence signal of the two electronics modules are both triggered and the two trigger signals are in the same coincidence time window, then the coincidence signal is a true coincidence event. The time window is determined by the AND gate of the FPGA. The trigger signal is transmitted by the cable between the waveform sampling electronics board and the detector.

[0030] S3: The true coincidence event that meets the time and energy selection requirements will generate a trigger signal. The trigger signal is transmitted by the cable between the board cards, and the corresponding electronics board of the coincidence detector uses the FPGA to control the DRS4 chip to collect the coincidence event. In this process, scattered events, uncoincidence events, etc. are eliminated, and the electronics board card collects only coincidence events. The improvement of the counting rate is mainly due to the improvement of the effective coincidence events:

[0031] Assuming that the detection efficiency of a pair of coincidence detector modules is DE1 and DE2, respectively, when the dead time of the electronics is fixed and the network bandwidth of data transmission reaches the peak value, the number of events transmitted to the data processing module per unit time is SE. Without the design of electronic pre-coincidence trigger,

[0032] SE = SA x (DE1 + DE2) (1)

[0033] Where SA is the number of SA pairs of gamma rays produced by the annihilation of the radioactive source within the solid angle of a pair of coincidence detection modules. At this time, the theoretical coincidence counting rate is

[0034] CR1 = SA x DE1 x DE2 (2)

[0035] From formulas (1) and (2), we can see that:

[0036]

[0037] After adding the pre-coincidence trigger design, since the coincidence detection module collects only coincidence events, the theoretical coincidence event rate CR2 is:

[0038]

[0039] Compared with the system without the pre-coincidence trigger design, the coincidence counting rate of the system with the pre-coincidence trigger design is theoretically improved by:

[0040]

[0041] The detection efficiency DE1 and DE2 are mainly related to the type and length of the scintillation crystal in the detector module, and the value is less than 1.

[0042] S4: The collected digitized coincidence signals are transmitted to the data processing module after being packed by the gigabit Ethernet module of the waveform sampling electronic board. The data processing module performs statistical calculation on the time difference information of the coincidence events, and finally obtains the positioning of the object to be measured. The improvement of the count rate ensures the rapid implementation of the statistics and improves the sensitivity of the system.

[0043] Although specific embodiments of the application are disclosed herein for illustrative purposes, and are to be considered merely illustrative and not restrictive of the scope of the application, it will be readily apparent to those of ordinary skill in the art that other embodiments and variations of the present application can be made without departing from the spirit and scope of the application as defined by the claims. Therefore, the application is not to be limited to the specific embodiments disclosed herein, but only to the scope of the claims.

Claims

1. A method for improving the count rate of a TOF-PET system, the TOF-PET system comprising a data processing module and multiple acquisition units, each of the acquisition units comprising a TOF-PET detector module and a TOF-PET electronics module; the method comprising: 1) Using the TOF-PET detector module to detect gamma photon pairs generated by positron annihilation in the object being detected, and converting the nuclear signals generated by the detected gamma photon pairs into electrical signals that are input into the TOF-PET electronics module of the acquisition unit; 2) Each of the TOF-PET electronic modules screens the input electrical signals, and when the energy of the nuclear signal meets the set energy screening conditions, generates a trigger signal and sends it to each of the acquisition units; when the i-th acquisition unit receives the trigger signal generated by the TOF-PET electronic module in the i-th acquisition unit and the trigger signal generated by the TOF-PET electronic module in other acquisition units within the coincidence time window, the TOF-PET electronic module in the i-th acquisition unit collects the nuclear signal within the t-th coincidence time window as a true coincidence event; 3) The data processing module receives the true coincidence events collected by the TOF-PET electronics module, and regards two true coincidence events within the same coincidence time window as a pair of true coincidence events; extracts the time and energy information from each pair of true coincidence events, and calculates the time difference between the two true coincidence events in each pair of true coincidence events arriving at their corresponding TOF-PET detector modules, counts the time differences between each pair of true coincidence events, and determines the position of the detected object based on the statistical results.

2. The method according to claim 1, characterized in that The TOF-PET detector modules are connected in series, and the last-level TOF-PET detector module is connected to the data processing module; each TOF-PET electronics module includes a comparator, a waveform sampling circuit and an FPGA; the comparator is used to perform energy screening on the input nuclear signal, and when the energy of the nuclear signal meets the set energy screening condition, a trigger signal is generated and sent to the FPGA in each acquisition unit; the waveform sampling circuit is used to acquire the input nuclear signal to obtain a coincidence signal and send it to the FPGA; when the FPGA receives the trigger signal generated by the comparator in its acquisition unit and the trigger signal generated by other acquisition units in the i-th coincidence time window, it retains the coincidence signal in the i-th coincidence time window and sends it as a true coincidence event to the next-level TOF-PET electronics module; the last-level TOF-PET detector module sends the received true coincidence event to the data processing module.

3. The method according to claim 2, characterized in that The waveform sampling circuit includes a DRS4 chip and an ADC; the DRS4 chip is used to perform high-speed analog sampling on the input nuclear signal and then input it into the ADC; the ADC is used to digitize the input analog signal to obtain a digitized waveform.

4. The method according to claim 2, characterized in that The adjacent acquisition units are connected via high-bandwidth cables for transmitting the trigger signal; the FPGA determines whether the received trigger signal is within the same coincidence time window through an AND gate.

5. The method according to claim 1, wherein The data processing module calculates the position of positron annihilation based on the time t1 when one gamma photon arrives at the TOF-PET detector module and the time t2 when the other gamma photon arrives at the TOF-PET detector module in each pair of true coincidence events. where c is the speed of light.

6. A system for improving the count rate of a TOF-PET system, characterized in that: It includes a data processing module and a plurality of acquisition units, each of which includes a TOF-PET detector module and a TOF-PET electronics module; The TOF-PET detector module is used to detect gamma photon pairs generated by positron annihilation in the detected object, and convert the nuclear signals generated by the detected gamma photon pairs into electrical signals and input them into the TOF-PET electronics module of the acquisition unit; The TOF-PET electronics module is configured to screen the input electrical signals and generate a trigger signal when the energy of the nuclear signal meets a set energy screening condition and send the trigger signal to each of the acquisition units; wherein when the i-th acquisition unit receives the trigger signal generated by the TOF-PET electronics module in the i-th acquisition unit and the trigger signal generated by the TOF-PET electronics module in other acquisition units within the t-th coincidence time window, the TOF-PET electronics module in the i-th acquisition unit acquires the nuclear signal within the t-th coincidence time window as a true coincidence event; The data processing module is used to receive true coincidence events collected by the TOF-PET electronics module, and treat two true coincidence events within the same coincidence time window as a pair of true coincidence events; extract the time and energy information from each pair of true coincidence events, and calculate the time difference between the two true coincidence events in each pair of true coincidence events when they reach their corresponding TOF-PET detector modules, count the time differences of each pair of true coincidence events, and determine the position of the detected object based on the statistical results.

7. The system according to claim 6, characterized in that The TOF-PET detector modules are connected in series, and the last-level TOF-PET detector module is connected to the data processing module; each TOF-PET electronics module includes a comparator, a waveform sampling circuit and an FPGA; the comparator is used to perform energy screening on the input nuclear signal, and when the energy of the nuclear signal meets the set energy screening condition, a trigger signal is generated and sent to the FPGA in each acquisition unit; the waveform sampling circuit is used to acquire the input nuclear signal to obtain a coincidence signal and send it to the FPGA; when the FPGA receives the trigger signal generated by the comparator in its acquisition unit and the trigger signal generated by other acquisition units in the i-th coincidence time window, it retains the coincidence signal in the i-th coincidence time window and sends it as a true coincidence event to the next-level TOF-PET electronics module; the last-level TOF-PET detector module sends the received true coincidence event to the data processing module.

8. The system according to claim 7, characterized in that The waveform sampling circuit includes a DRS4 chip and an ADC; the DRS4 chip is used to perform high-speed analog sampling on the input nuclear signal and then input it into the ADC; the ADC is used to digitize the input analog signal to obtain a digitized waveform.

9. The system according to claim 7, wherein: The adjacent acquisition units are connected via high-bandwidth cables for transmitting the trigger signal; the FPGA determines whether the received trigger signal is within the same coincidence time window through an AND gate.

10. The system according to claim 6, wherein: The data processing module calculates the position of positron annihilation based on the time t1 when one gamma photon arrives at the TOF-PET detector module and the time t2 when the other gamma photon arrives at the TOF-PET detector module in each pair of true coincidence events. where c is the speed of light.

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