CN100563575C - Meet system in a kind of position emissron tomography and meet method - Google Patents

Abstract

The invention relates to the fields of medical tomography and nuclear imaging, in particular to a first set of boards, a signal buffer unit, a second set of receiving boards, a data buffer unit, and a reference system used in positron emission tomography equipment. Clock 17, a clock adjustment unit, field programmable gate array; method: use field programmable gate array to judge the time, position and energy between events, and two events that pass these selection rules become a matching case. By introducing field-programmable gate arrays, the hardware description language is used to quickly and efficiently process the event information captured by the front-end detector module of the PET instrument to determine the occurrence of coincident events. The present invention is an improvement over existing PET compliance systems. The invention can efficiently and quickly complete system-compliant processing by using one FPGA, and does not introduce dead time into the system while obtaining high system sensitivity.

Description

A coinciding system and coinciding method in positron emission tomography

technical field

The invention relates to the fields of medical tomography and nuclear imaging, in particular to a method for designing coincident systems in Positron Emission Tomography (PET) equipment.

Background technique

Coincidence detection is the essence of positron emission tomography (PET), and its design directly affects the performance of the entire system. The positrons produced by the decay of radiopharmaceuticals injected into the living body undergo an annihilation reaction with the electrons in the living body to produce two gamma photon pairs with opposite directions and an energy of 511keV. If they are captured by the detector at the same time within a certain time window, it is called A match was detected. 1 in Fig. 1 indicates that positron annihilation produces two gamma photons 2a and 2b with equal energy and opposite directions, which can be detected by two oppositely placed detectors 3a and 3b. 1 means that substances containing radioactive isotopes such as ¹⁸ F, ²² Na, and ¹¹ C undergo beta decay to produce positrons, which undergo annihilation reactions with surrounding electrons. 2a and 2b represent two gamma photons with equal energy and opposite directions produced after positron annihilation. 3a, 3b represent detectors that can detect gamma photons (in PET, scintillation crystals are often combined with position-sensitive photomultiplier tubes, and other detector combinations that can detect gamma photons can also be used.)

4a and 4b in FIG. 2 represent the time t1 and t2 when the two gamma photons 2a and 2b respectively arrive at the two detectors 3a and 3b in FIG. 1 . If the difference between them is smaller than the pre-set time window 5, the two gamma photons are considered to be generated by the same annihilation event, and this process is called coincidence detection.

Due to the effects of scattering and accidental coincidence, after detecting a time coincident event, the coincidence system needs to further judge whether the two photon signals are generated by the same event. In order to reduce the system dead time of the circuit part, the PET instrument requires a compliance system to make a fast judgment on these photons.

In the traditional PET design, the compliance system circuit is made of separate devices, which is complex, difficult to detect, and expensive; there are also some PET compliance system circuits that are made of Application Specific Integrated Circuit (ASIC). The compliance system circuit is greatly simplified, but the cost is still high, and the production cycle is long.

Contents of the invention

In order to solve the problems of high cost and long production cycle in the prior art, the present invention adopts FPGA as the core to realize PET coincidence system processing, the hardware circuit is simple to realize, the cost is low, and a kind of coincidence system in positron emission tomography that can be realized quickly and design methods.

In order to achieve the above object, one aspect of the present invention is to provide a coincidence system in positron emission tomography, and the technical solution includes:

The first group of boards is used to receive and process the time signal indicating that each detector block detects a single case;

A signal buffer unit, which is used to temporarily store and output the time signal conforming to the single case of the first group of boards;

The second group of receiving boards is used to receive and process data representing the position and energy of each single instance;

A data cache unit, which is used to temporarily store the data of each single instance position and energy output by the second group of boards;

A reference clock 17, used to provide a reference clock for the system;

A clock adjustment unit, which adjusts the input reference clock to generate a clock signal with the same phase as the system reference clock;

The field programmable gate array will receive the synchronous digital signal representing case information and the analog signal representing time collected by all the detectors in the front end of the PET system, and is used to match the synchronous digital signal representing case information and the analog signal representing time Comprehensive treatment of judgment;

According to a preferred embodiment, the field programmable gate array adopts one or several field programmable gate arrays, and uses hardware description language HDL to realize the core coincidence algorithm.

According to a preferred embodiment, the chip includes a single-chip microcomputer or a chip with a CPU function.

According to a preferred embodiment, the hardware description language HDL adopts Verilog HDL, VHDL or AHDL, and is used for configuring and realizing the function of the field programmable gate array.

In order to achieve the above object, another aspect of the present invention is to provide a coincident method in positron emission tomography, the technical scheme is as follows:

The field programmable gate array is used to judge the time, position and energy between various events, and two events that pass these selection rules become a coincidence case.

According to a preferred embodiment, the matching steps are as follows:

Step 24: start;

Step 25: First load the required data;

Step 26: Judging the loaded data in terms of time, that is, by judging whether the difference between the occurrence times of two events is smaller than the set time window:

If there are two single cases in the same time window, go to step 27; if not, go to step 30;

Step 27: perform table lookup operation;

Step 28: Check the table in step 27 to determine whether the two single cases fall within the set field of view, if yes, execute step 29; if not, execute step 30;

Step 29: package and transmit the two events;

Step 30: Then judge whether the scanning is over, to determine whether to load the data of the next cycle for judgment, if yes, then perform step 31; if not, then perform step 25;

Step 31: until the end.

According to a preferred embodiment, the table look-up operation in step 27 pre-sets the coincidence results of each position according to the set field of view, and directly judges whether two events match in position by looking up the table.

According to a preferred embodiment, by configuring corresponding delays in the same field programmable gate array, the delay compliance is completed, and the specific steps are as follows:

The field programmable gate array is used to realize the multiplexing of the matching judging units 34a, 34b:

Carrying out one path of the input signal unit 32 to meet the selection process of the selection unit 34a;

The other path of the input signal unit 32 is carried out to the corresponding delay unit 33, and the delayed signal is passed through a same coincidence selection process of the selection selection unit 34b;

The case unit 36 and the real case unit 35 obtained by accidental coincidence are passed through the multiplexer 37 to transmit the occasional coincidence and real case data 38 .

According to a preferred embodiment, the delay unit 33 is located outside the FPGA; or inside the FPGA, implemented by means of register buffering.

The purpose of the present invention is to provide a design method that can be widely used in a coincidence system in a multi-parameter measurement system, especially a design method for a coincidence system in a positron emission tomography (Positron Emission Tomography, PET) device. By introducing a field-programmable gate array (FPGA), the hardware description language (HDL) is used to quickly and efficiently process the case information captured by the front-end detector module of the PET instrument to determine the occurrence of coincident events. The present invention is an improvement over existing PET compliance systems. The invention can efficiently and quickly complete system-compliant processing by using one FPGA, and does not introduce dead time into the system while obtaining high system sensitivity.

1. The working method of the assembly line of the present invention is to judge the input data once in each cycle, so as to avoid introducing dead time into the system during processing;

2. In the design of the present invention, the hardware circuit is simple to implement, and all coincidence processing is completed inside an FPGA. If the processing content needs to be modified, only the reprogrammed program needs to be inserted into the FPGA again, without changing the hardware.

3. The design of the present invention adopts FPGA as the core, has fast realization speed, and has the feature of online programming. It is only necessary to modify the software programs and re-download them into the FPGA to make corresponding modifications, which can be quickly changed online.

4. The cost of the design of the present invention is greatly reduced compared with the conventional coinciding circuit or the coinciding circuit with ASIC as the core.

5. The present invention is convenient and flexible in design, and besides the PET system, it can also be used in a data acquisition system for multi-parameter coincidence measurement of related events in nuclear spectroscopy.

6. The present invention is different from the traditional step-by-step processing method, that is, the signals of several modules (Modual) are first processed by a processor, and then aggregated to a processor for final judgment. The method of the present invention collects all detectors The received synchronous digital signals representing case information and the analog signals representing time all enter this coincidence system for unified processing.

The invention is used in a high-speed parallel multi-channel data acquisition system for nuclear spectroscopy and nuclear electronics, especially a data acquisition system for multi-parameter coincidence measurement of related events in nuclear spectroscopy.

Description of drawings

Fig. 1 Existing technology coincidence detection hardware block diagram

Fig. 2 Schematic diagram of the prior art compliance judgment principle

Fig. 3 is a schematic diagram of the crystal structure of the detector ring of the present invention

Fig. 4 is the design diagram of FOV and position of the present invention

Fig. 5 is that the present invention conforms to system hardware structural diagram

Fig. 6 is that the present invention conforms to circuit board FPGA internal program flowchart

Fig. 7 is a schematic diagram of the position of the detector ring composed of 6 probes according to the table in the present invention

Fig. 8 is a functional block diagram for the present invention to complete occasional coincidence and true case selection

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings. It should be noted that the described embodiments are only intended to facilitate the understanding of the present invention, rather than limiting it in any way.

According to the design of the front-end detector, each detector crystal bar on the detector ring is numbered, and the way of looking up the table is used to determine whether it is a real response event. The events that come in the cycle can be judged according to the requirements.

As shown in Figure 3, the entire detector ring 9 is composed of 16 modules 8 (modules), each module 8 contains two blocks 7 (blocks), and each block is composed of a 1.9mm×1.9mm×10mm strip LYSO crystals 6 are formed in a 16×16 array, so that 8192 LYSO crystal strips form a detector array with 32 rings and 256 crystal strips in each ring.

Figure 3 shows the composition of the detector crystal ring 9 in PET. 6 represents the scintillation crystal strip used, and a block 7 is formed by many such scintillation crystal strips 6 in a certain arrangement (such as 16×16, or other numbers); a module is formed by two or more blocks 7 8. The entire PET detector crystal ring 9 is formed by 16 (or other numbers) modules 8 .

Fig. 4 shows a PET detector ring composed of multiple detectors 12a to 12p. According to different detection fields of view (dotted lines 11a, 11b), the coincidence judgment among the detectors is performed, and the coincidence detection among the detectors is represented by the response line 10 . Comply with the system requirements and judge whether two detector blocks 7 are consistent (Fig. 1).

Fig. 5 shows the composition block diagram of conforming to the system hardware board 22, it receives the time signal that each detector block 7 detects conforming to a single case and sends these signals after being processed by the first group of boards 13a-13z Temporarily stored in the input signal buffer unit 15; the conforming system hardware board 22 also receives the data indicating the position and energy of each single instance sent by the second group of boards 14a-14m after processing, and puts them into the data buffer unit 16 At the same time, a reference clock 17 is also required for the system to work, which can be generated by devices such as crystal oscillators, or special boards, etc., and this working clock is preferably used after being conditioned by the clock conditioning unit 18; The work also requires the provision of power 19 . Then a field programmable gate array FPGA20 (or a few chips) performs the main coincidence judging task. The processed data is transferred to the back-end computer 23 for further processing under the control of a chip 21 with a CPU function such as a single-chip microcomputer.

The program flow used inside FPGA20 is shown in Figure 6. The field programmable gate array is used to judge the time, position and energy between events, and two events that pass these judgment rules become a coincidence case. After the program starts at 24, the required data is first loaded into 25, and then the data is judged 26 in time, that is, by judging whether the difference between the occurrence times of two events is smaller than the set time window (such as 6ns, 10ns, etc.) , if there are and only two single cases in the same time window, the operation of table lookup 27 is performed; otherwise, it is judged whether the scan ends 30 . Check the table 27 to judge whether the two single cases fall within the set field of view 28, if so, pack and transmit the two events 29, and then judge whether the scan is over 30, to decide whether to load the next cycle The data is judged until the end 31.

Fig. 7 shows the operation of the look-up table 27 in Fig. 6, the operation of the look-up table is to pre-set the matching results of each position according to the set field of view, and directly judge whether the two events match in the position by looking up the table.

Taking a ring composed of six detectors as an example, according to the set FOV size, a detector module needs to make a coincidence judgment with the three opposite modules. Judgment results are shown in Figure 7. The 'pair' in the figure means it is within the FOV of the field of view, and the 'cross' means it is not in the field of view. For example, if one event is detected by detector 2 and the other is detected by detector 5, the table (2, 5) in the figure shows that the two events match in position and are valid events within the field of view FOV, which can be Continue to step 29 in FIG. 6 . The method of table look-up not only simplifies the operation, but also can be completed in one cycle, so that the whole program can smoothly use the pipeline for data processing, and no dead time is introduced into the whole system in the matching judgment stage.

Another problem that needs attention is that when designing the table in Figure 7, it should be carried out in units of modules. If it is designed according to crystal strips, the table will be very large. Take a detector ring composed of 16 modules as an example. Each block consists of 16×16 crystal strips. If so many crystal positions are all put into the table, then the table matrix will be 8192×8192, which is not very easy to realize. And if the module is used as the unit, the matrix will become 32×32, which can be realized by using the internal storage resources of the FPGA, without the need for external memory and at high speed.

In addition, since the FPGA is mainly used to realize the match judgment in the present invention, it can be multiplexed conveniently. Fig. 8 shows that the input signal unit 32 is directly carried out the coincidence judgment process of the above-mentioned coincidence judgment unit 34a, and another one is separated out to carry out the corresponding delay unit 33, and the delayed signal is passed through the coincidence of the same coincidence judgment unit 34b. The judging process will obtain the incidental case unit 36, which will pass through a multi-way switch 37 together with the real case unit 35 to transmit the occasional coincidence and real case data 38. Since the delay unit 33 can be implemented externally or within the FPGA through register buffering, the entire function in Figure 8 can be completed through a single FPGA. At this time, the entire PET system can easily obtain accidental coincidence and real cases. data. It greatly simplifies the complexity of conforming to the hardware implementation of the system.

The above is only a specific implementation mode in the present invention, but the scope of protection of the present invention is not limited thereto. Anyone familiar with the technology can understand the conceivable transformation or replacement within the technical scope disclosed in the present invention. All should be covered within the scope of the present invention, therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims (8)

1, meet system in a kind of position emissron tomography, it is characterized in that, comprising:

First group of integrated circuit board is used to receive and handle each detector chunk of expression and detects the time signal that meets single example;

A signal buffer unit is used for temporary and exports the time signal that meets single example of first group of integrated circuit board;

Second group of integrated circuit board is used to receive and handle the data of representing each single example position, energy;

A data buffer unit is used for each single example position of temporary second group of integrated circuit board output, the data of energy;

A reference clock is used to system that reference clock is provided;

A clock adjustment unit is nursed one's health the reference clock of input, generates and the synchronous clock signal of system reference clock;

Field programmable gate array, to receive the synchronous digital signal of the expression example information that all detectors of front end collect in the PET system and the analogue signal of express time, be used for the synchronous digital signal of expression example information and the analogue signal of express time are met the integrated treatment of declaring choosing; In with a slice field programmable gate array, postpone, finish and postpone to meet by configuration is corresponding, utilize field programmable gate array realize to meet declare select unitary multiplexing: input signal unit one tunnel is carried out above-mentioned meeting declares choosing; Another road, input signal unit is postponed accordingly, the signal after postponing is declared the process of selecting by same meeting; With obtaining accidental example unit that meets and true example unit together,, meet and the transfer of data of true example is gone out accidental by variable connector.

2, the system that meets according to claim 1 is characterized in that, described field programmable gate array adopts a slice or several field programmable gate arrays, adopts hardware description language HDL to realize that core meets algorithm.

3, the system that meets according to claim 1 is characterized in that, described field programmable gate array comprises single-chip microcomputer or has the chip of cpu function.

4, the system that meets according to claim 2 is characterized in that, described hardware description language HDL adopts Verilog HDL, VHDL or AHDL, is used for disposing the function that realizes field programmable gate array.

5, a kind ofly realize meeting the method for declaring choosing, it is characterized in that, utilize field programmable gate array to carry out the judgement of time, position and energy between each incident, become one by these two incidents declaring the choosing rule and meet example; Postpone by configuration is corresponding in a slice field programmable gate array, finish delay and meet, concrete steps are as follows:

Utilize field programmable gate array to realize declaring the multiplexing of menu unit (34a, 34b) to meeting:

Input signal unit (32) one tunnel is carried out the above-mentioned process (34a) of declaring choosing that meets;

Corresponding delay cell (33) is carried out on another road, input signal unit (32), the signal after postponing is declared the process (34b) of selecting by same meeting;

With obtaining accidental example unit (36) that meets and true example unit (35) together,, meet and the data (38) of true example transfer out accidental by variable connector (37).

6, according to claim 5 meeting declared choosing method, it is characterized in that, meets example and declares and select step as follows:

Step 24: beginning;

Step 25: at first required data are written into;

Step 26: these data that are written into are judged in time promptly the difference by judging two Time To Events is whether less than set time window:

If two incidents are arranged in window at the same time, then execution in step 27; If not, execution in step 30 then;

Step 27: the operation of tabling look-up;

Step 28: table look-up to judge whether these two incidents drop within the set visual field by step 27, if then execution in step 29; If not, execution in step 30 then;

Step 29: with the transmission of packing of these two incidents;

Step 30: judge then whether scanning finishes, and whether is written into the data of following one-period with decision and judges, if then execution in step 31; If not, execution in step 25 then;

Step 31: until end.

7, according to claim 6 meeting declared choosing method, it is characterized in that, the operation that described step 27 is tabled look-up preestablishes the result that meets of each position according to the field range of setting, and directly judges whether two incidents meet on the position by tabling look-up.

8, according to claim 5 meeting declared choosing method, it is characterized in that, delay cell (33) is positioned at the field programmable gate array outside; Or programmable gate array internal at the scene, realize by the buffered method of depositor.

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