CN117075175A - SiPM-based time correction method and system for inter-crystal scattering events of PET detector - Google Patents
SiPM-based time correction method and system for inter-crystal scattering events of PET detector Download PDFInfo
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- BPQQTUXANYXVAA-UHFFFAOYSA-N Orthosilicate Chemical compound [O-][Si]([O-])([O-])[O-] BPQQTUXANYXVAA-UHFFFAOYSA-N 0.000 description 1
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Abstract
The invention provides a time correction method and a system for scattering events among crystals of a PET detector based on SiPM. During correction, firstly, general correction is carried out on the amorphous scattering events, then, further, off-line statistics is carried out on time differences of the amorphous scattering events on each crystal and the amorphous scattering events on the response line, so that extra time differences of each amorphous scattering event due to time migration effect are obtained, then, secondary time correction is carried out on the amorphous scattering events on line, and the time resolution of the system is improved.
Description
Technical Field
The invention relates to the technical field of medical imaging equipment, in particular to a time correction method and a system for inter-crystal scattering events of a PET detector based on SiPM.
Background
A positron emission computed tomography imaging system (PET, positron Emission Tomography) is a nuclear medicine imaging device, consisting essentially of a detector system, an electronics system, a data acquisition system, and a reconstruction system. Wherein the detector system is composed of a scintillation crystal, a photoelectric conversion device and front-end electronics. Currently, detection devices based on silicon photomultipliers (Silicon Photomultiplier, siPM) are increasingly being used in PET systems due to their good energy and time resolution and magnetic compatibility. The main working principle is that high-energy Gamma photons captured by a scintillation crystal are converted into low-energy visible light by utilizing SiPM, the low-energy visible light is converted into analog electric signals by utilizing photoelectric effect, the analog electric signals are amplified and formed by utilizing an analog conditioning circuit and then sent into an energy, time and position measuring device to obtain energy, time and position information of the electric signals, and effective signals are screened out by utilizing methods such as coincidence judgment and the like at the rear end.
Currently, a Time of flight (TOF) PET (positron emission tomography) detector based on lutetium yttrium silicate scintillation (LYSO) crystals and SiPM (Silicon photomultiplier) is one of the most prominent devices for early detection of cancer.
The principle is that a visible light signal converted from high-energy Gamma photons captured by a crystal module is converted into an analog electric signal through a photoelectric effect by utilizing SiPM, the analog electric signal is amplified and formed by utilizing an analog conditioning circuit, the energy and the reaching time of the analog electric signal are obtained by utilizing an energy measuring device and a time measuring device, and then effective data are obtained by methods of coincidence judgment and selection and the like.
The data contains gamma photon energy information, reaction crystal position information and time information, and the gamma radioactive source position and shape information can be reconstructed through the information. And obtaining the nuclide reaction position through a back-end reconstruction system, and further reconstructing a cancer image.
Because of the variability of Gamma photons in different crystals, the transmission paths of visible light in the crystals, the responses of different sipms to generate electrical signals, and different channel electronic delays, alignment is generally required by back-end correction of the time delay of events hitting different crystals. In a general time correction scheme, a set of correction coefficients is obtained by counting time delays of different crystal events hit, and correction is performed in a digital processor at the back end.
However, many times, gamma photons undergo Inter-crystal Compton scattering (ICS) in a crystal, that is, some Gamma photons are scattered by electrons in the crystal into adjacent crystals, and visible light is generated again in the adjacent crystals, so that two crystals generate signals simultaneously.
For this case, the first problem is that the crystal position determination is error-prone, and furthermore, since the two scattered signals are relatively small, there is an additional time delay due to the time walk effect (time walk) compared to the non-scattered signal (non-ICS). If the general time correction scheme is still adopted, the time correction error of the ICS event is larger, and the system conforming time resolution (Coincidence time resolution, CTR) is further affected.
In the prior art, ICS events are randomly selected in position, so that larger judgment errors are caused. And obtaining a group of correction coefficients by counting the time delay of the event hitting different crystals, and carrying out online correction in the digital processor. The method does not perform special processing on ICS events, and because two ICS signals are smaller, compared with a non-scattering signal, an extra time delay occurs due to a time walk effect (timewealk), so that the time correction of the ICS events is inaccurate.
Disclosure of Invention
In order to overcome the technical defects, the invention aims to provide a time correction method and a system for inter-crystal scattering events of an SiPM-based PET detector, which are used for further time correction of inter-crystal scattering events on the basis of a general time correction scheme.
The invention discloses a time correction method of inter-crystal scattering events of a SiPM-based PET detector, which comprises the following steps: comparing all row and column signals of the SiPM detector array with a fixed voltage threshold under a differential signal mode to obtain time threshold crossing pulses of the signals; the time measurement is carried out on the front edge and the rear edge of the time threshold passing pulse through a time digital converter based on clock phase separation, so that the time threshold passing pulse width is obtained; judging whether an event in a crystal of the SiPM detector is an amorphous scattering event or an inter-crystal scattering event according to the time threshold pulse width; counting the time difference between the amorphous scattering event in each crystal and the amorphous scattering event on the response line, and obtaining a first time correction lookup table through multiple iterations; counting the time difference between the inter-crystal scattering event in each crystal and the non-crystal scattering event on the response line, and obtaining a second time correction lookup table through multiple iterations; the addresses of the first time correction lookup table and the second time correction lookup table are crystal coding positions, and the content is time difference information; and storing the first time correction lookup table and the second time correction lookup table, and carrying out real-time online correction on the time of the inter-crystal scattering event through the first time correction lookup table and the second time correction lookup table.
Preferably, said determining whether an event in a crystal of the SiPM detector is an amorphous scattering event or an inter-crystal scattering event by said time-passing threshold pulse width comprises: for non-crystal scattering events, determining unique code information hitting the crystal location; and for inter-crystal scattering events, taking a crystal code corresponding to the time threshold pulse width which is larger than a preset threshold value in the time threshold pulse width information of all signals as hit crystal position code information.
Preferably, the real-time online correction of the time of the inter-crystal scattering event by the first time correction lookup table and the second time correction lookup table includes: for the inter-crystal scattering event, according to the determined position coding information of the hit crystal and the inter-crystal scattering mark, searching the content corresponding to the address through the address of the first time correction lookup table, so as to obtain time difference information corresponding to the position coding information, and correcting a time measurement result based on the time difference information; and searching the content corresponding to the address through the address of the second time correction lookup table, so as to obtain time difference information corresponding to the position coding information, and carrying out secondary correction on a time measurement result based on the time difference information.
Preferably, the real-time online correction of the time of the inter-crystal scattering event by the first time correction lookup table and the second time correction lookup table includes: and for the amorphous scattering event, searching the content corresponding to the address through the address of the first time correction lookup table according to the determined position coding information of the hit crystal, so as to obtain time difference information corresponding to the position coding information, and correcting a time measurement result based on the time difference information.
Preferably, the method further comprises: summing signals of the SiPM detector array, and measuring the summed signals through a high-speed comparator and a time-to-digital converter based on a carry chain, so as to obtain the arrival time of the signals received by the SiPM detector array; and performing time correction on the arrival time based on the time difference information.
Preferably, the method further comprises: the SiPM detector arrays are added through resistor network rows and columns respectively, and the channel number of a position reading circuit is changed from n 2 Reduced to 2n and the position of the fired SiPM detector element is determined by determining the trigger position of the column sum signal.
Preferably, the SiPM detector array is coupled to the LYSO crystals in a 1:1 manner.
Preferably, the method further comprises: the signals of the SiPM detector array are summed, the analog signal is converted to a digitized signal by an analog-to-digital converter, and then the digitized signal is integrated to obtain the number of ADC channels characterizing the energy of the analog signal.
The invention also discloses a time correction system of the inter-crystal scattering event of the SiPM-based PET detector, which comprises a time measurement module, a position pulse width measurement and calculation module arranged in the field programmable gate array, an off-line time correction table generation module and an on-line time correction module;
the position pulse width measuring and calculating module comprises a comparator unit, a position pulse width measuring unit and a position calculating unit; the comparator unit compares all row-column signals of the SiPM detector array with a fixed voltage threshold under a differential signal mode to obtain time threshold passing pulses of the signals; the position pulse width measuring unit performs time measurement on the front edge and the rear edge of the time threshold passing pulse through a time digital converter based on clock phase separation so as to obtain a time threshold passing pulse width; the position calculation unit determines whether an event in a crystal of the SiPM detector is an amorphous scattering event or an inter-crystal scattering event by the time threshold pulse width, and: for non-crystal scattering events, determining unique code information hitting the crystal location; for inter-crystal scattering events, taking a crystal code corresponding to a time threshold pulse width greater than a preset threshold value in the time threshold pulse width information of all signals as hit crystal position code information;
the off-line time correction table generation module counts the time difference between the amorphous scattering event in each crystal and the amorphous scattering event on the response line, and a first time correction lookup table is obtained through multiple iterations; counting the time difference between the inter-crystal scattering event in each crystal and the non-crystal scattering event on the response line, and obtaining a second time correction lookup table through multiple iterations; the addresses of the first time correction lookup table and the second time correction lookup table are crystal coding positions, and the content is time difference information;
the time measurement module sums the signals of the SiPM detector array, and the summed signals are measured through a high-speed comparator and a time-to-digital converter based on a carry chain, so that the arrival time of the signals received by the SiPM detector array is obtained;
the online time correction module stores the first time correction lookup table and the second time correction lookup table through a random access memory; and carrying out real-time online correction on the arrival time acquired by the time measurement module through the first time correction lookup table and the second time correction lookup table.
Preferably, the system further comprises a front end position coding circuit and an energy measuring module; the front end position coding circuit adds SiPM detector arrays through resistor network rows and columns respectively, and the number of channels of the position reading circuit is n 2 Reducing the number to 2n, and judging the positions of the excited SiPM detector units by judging the triggering positions of the row and column summation signals; the energy measurement module sums the signals of the SiPM detector array, converts the analog signals into digital signals through an analog-to-digital converter, and integrates the digital signals to obtain the ADC channel number representing the energy of the analog signals.
After the technical scheme is adopted, compared with the prior art, the method has the following beneficial effects:
1. the invention carries out pulse width measurement on the electric signal output by each SiPM detector by instantiating a plurality of time-to-digital converters in a field programmable gate array device, and can judge the non-crystal scattering event and the inter-crystal scattering event according to the pulse width and the energy of the signal because the pulse width is positively correlated, and judge the position of the inter-crystal scattering event so as to reduce the position selection error;
2. in the correction part, firstly, general correction is carried out on the amorphous scattering events, then, further, the time difference between the amorphous scattering events occurring in each crystal and the amorphous scattering events on the response line is counted in an off-line mode, the extra time difference of each amorphous scattering event due to the time migration effect is obtained, then, secondary time correction is carried out on the amorphous scattering events on line, and the time resolution of the system is improved.
Drawings
FIG. 1 is a schematic diagram of a preferred embodiment of a system for time correction of inter-crystal scatter events for an SiPM-based PET detector provided by the present invention;
FIG. 2 is a graph showing time delay differences between inter-crystal scattering events and non-inter-crystal scattering events;
FIG. 3 is a graph of the results of the test before and after correction of the inter-crystal scattering event time spectrum provided by the invention;
FIG. 4 is a graph showing the results of a test prior to correction of the time spectrum of inter-crystalline and non-crystalline scattering events provided by the present invention;
FIG. 5 is a graph showing the results of the test after the time spectrum correction of the inter-crystalline scattering events and the non-crystalline scattering events provided by the present invention.
Detailed Description
Advantages of the invention are further illustrated in the following description, taken in conjunction with the accompanying drawings and detailed description.
Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, the same numbers in different drawings refer to the same or similar elements, unless otherwise indicated. The implementations described in the following exemplary examples are not representative of all implementations consistent with the present disclosure. Rather, they are merely examples of apparatus and methods consistent with some aspects of the present disclosure as detailed in the accompanying claims.
The terminology used in the present disclosure is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used in this disclosure and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should also be understood that the term "and/or" as used herein refers to and encompasses any or all possible combinations of one or more of the associated listed items.
It should be understood that although the terms first, second, third, etc. may be used in this disclosure to describe various information, these information should not be limited to these terms. These terms are only used to distinguish one type of information from another. For example, first information may also be referred to as second information, and similarly, second information may also be referred to as first information, without departing from the scope of the present disclosure. The word "if" as used herein may be interpreted as "at … …" or "at … …" or "responsive to a determination", depending on the context.
In the description of the present invention, it should be understood that the terms "longitudinal," "transverse," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like indicate orientations or positional relationships based on the orientation or positional relationships shown in the drawings, merely to facilitate describing the present invention and simplify the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and therefore should not be construed as limiting the present invention.
In the description of the present invention, unless otherwise specified and defined, it should be noted that the terms "mounted," "connected," and "coupled" are to be construed broadly, and may be, for example, mechanical or electrical, or may be in communication with each other between two elements, directly or indirectly through intermediaries, as would be understood by those skilled in the art, in view of the specific meaning of the terms described above.
In the following description, suffixes such as "module", "component", or "unit" for representing elements are used only for facilitating the description of the present invention, and are not of specific significance per se. Thus, "module" and "component" may be used in combination.
The invention discloses a time correction method of inter-crystal scattering events of a PET detector based on SiPM, which comprises the steps of carrying out pulse width measurement on an electric signal output by each SiPM detector by instantiating a plurality of time-to-digital converters in a field programmable gate array device, judging an amorphous scattering event and an inter-crystal scattering event according to pulse width and energy positive correlation of the signal, and judging the positions of the inter-crystal scattering events so as to reduce position selection errors; and then in the correction part, firstly, carrying out general correction on the amorphous scattering events, and then, further, carrying out off-line statistics on the time difference between the amorphous scattering events occurring in each crystal and the amorphous scattering events on the response line to obtain the extra time difference of each amorphous scattering event due to the time migration effect, and then, carrying out secondary time correction on the amorphous scattering events on line to improve the time resolution of the system.
Specifically, first, the amorphous scattering events and the crystalline scattering events are distinguished. In the differential signal mode, all row and column signals of the SiPM detector array are compared to a fixed voltage threshold to obtain a time-over-threshold (TOT) pulse of the signal. The time measurement is then performed on the front and back edges of the time-critical TOT pulse by a clock-phase-based time-to-digital converter (multi-phase TDC), resulting in a time-critical pulse width. Since pulse width is positively correlated with the energy of the signal, then the event in the crystal of the SiPM detector is judged by the time-to-threshold TOT pulse width as being an amorphous scattering event or an inter-crystal scattering event.
Then time correction is performed, specifically by a time correction lookup table. The time correction lookup table is obtained by the following steps: counting the time difference between the amorphous scattering event in each crystal and the amorphous scattering event on the response line, and obtaining a first time correction lookup table through multiple iterations; and counting the time difference between the inter-crystal scattering event in each crystal and the non-crystal scattering event on the response line, and obtaining a second time correction lookup table through multiple iterations. The addresses of the first time correction lookup table and the second time correction lookup table are crystal coding positions, the content is time difference information, the addresses and the content are in one-to-one correspondence, and it can be understood that each address corresponds to one time difference information. The first time correction lookup table and the second time correction lookup table are stored. And in the subsequent correction stage, based on the first time correction lookup table and the second time correction lookup table, the time difference information corresponding to the crystal coding position can be known by knowing the crystal coding position, so that correction is performed.
The time based on correction is obtained through time measurement, specifically, signals of the SiPM detector array are added, the added signals are measured through a high-speed comparator and a carry chain-based time-to-digital converter (carrchain FPGA-TDC), so that the arrival time of the signals received by the SiPM detector array is obtained, and the arrival time can be corrected through combining the obtained time difference information.
Preferably, the position of the detector array is also known before, and specifically, the SiPM detector array is usedThe channel numbers of the position reading circuit are respectively added from n through resistor network rows and columns 2 Reduced to 2n and the position of the fired SiPM detector element is determined by determining the trigger position of the column sum signal. The SiPM detector array is coupled to the LYSO crystals in a 1:1 manner.
The signals of the SiPM detector array are then summed, the analog signal is converted to a digitized signal by an analog-to-digital converter, and the digitized signal is then integrated to obtain the number of ADC channels characterizing the energy of the analog signal.
Referring to fig. 1-2, the invention also discloses a time correction system for scattering events among crystals of the SiPM-based PET detector, which comprises a front end position coding circuit, an energy measuring module, a time measuring module, a position pulse width measuring and calculating module arranged in a Field Programmable Gate Array (FPGA), an off-line time correction table generating module and an on-line time correction module.
1) The front end position coding circuit adds the SiPM detector arrays through resistor network rows and columns respectively, and the number of channels of the position reading circuit is n 2 Reduced to 2n and the position of the fired SiPM detector element is determined by determining the trigger position of the column sum signal.
2) The energy measurement module is used for summing signals of the SiPM detector array, converting the Analog signals into digital signals through a middle-high speed Analog-to-digital converter (Analog-digital Converter, ADC), and integrating the digital signals to obtain the ADC channel number used for representing energy of the Analog signals.
3) The time measurement module is used for measuring the signal arrival time, and the subsequent time correction is based on the time known by the module. Specifically, signals of the SiPM detector array are summed, and the summed signals are measured by a high-speed comparator and a carry chain-based time-to-digital converter, so that the arrival time of the signals received by the SiPM detector array is obtained.
4) The position pulse width measurement and calculation module then determines whether an event in the crystal of the SiPM detector is an amorphous scattering event or an inter-crystal scattering event. The position pulse width measuring and calculating module comprises a comparator unit, a position pulse width measuring unit and a position calculating unit.
4.1 Firstly, the comparator unit utilizes IBUF resources in the FPGA to configure a differential signal LVDS mode, and compares all (2 n) row and column signals of the SiPM detector array with a fixed voltage threshold value to obtain time-over-threshold (TOT) pulses of the signals. The width (pulse width) of the time-over-threshold TOT pulse can be used to characterize the energy of the input signal.
4.2 Next, the position pulse width measuring unit performs time measurement on the front and rear edges of the time threshold-crossing TOT pulse by using a clock-split-based time-to-digital converter (multi-phase TDC) inside the FPGA, thereby obtaining the time threshold-crossing TOT pulse width.
4.3 Finally, the position calculation unit judges whether the event in the crystal of the SiPM detector is an amorphous scattering event or an inter-crystal scattering event through the information of (2 n) time threshold passing pulse widths, because the pulse widths are positively correlated with the energy of the signal. And: for non-crystal scattering events, determining unique code information hitting the crystal location; for inter-crystal scattering events, the crystal code corresponding to the time-to-threshold pulse width greater than the preset threshold (i.e., relatively greater) in the information of the time-to-threshold pulse width of all signals is used as the hit crystal position code information. The preset threshold value can be selected according to the requirement, and is not limited to the maximum value or the range within which the preset threshold value is controlled.
5) Next, two time correction look-up tables are obtained by an offline time correction table generation module. The off-line time correction table generation module may include two off-line time correction table generation units, i.e., a first off-line time correction table generation unit that generates a correction for the inter-crystal scattering event and a second off-line time correction table generation unit that generates a correction for the inter-crystal scattering event. The principle is shown in fig. 2, where the energy (about 511 keV) is deposited entirely within one crystal for gamma events, which are amorphous inter-scatter events. While for inter-crystal scattering events, its energy is deposited within both crystals. Since the time measurement section measures the first signal time to cross the threshold, the cross-threshold time of the inter-crystalline scattering event will be a time delay difference from the non-crystalline scattering event due to the time walk effect. The inter-crystal scattering event time correction table generated by the second off-line time correction table generation unit is used for saving the time delay difference for further correction.
5.1 The first off-line time correction table (inter-amorphous scattering event time correction table) generating unit counts time differences between the inter-amorphous scattering events in each crystal and the inter-amorphous scattering events on the response line, and obtains a first time correction lookup table LUT1 through a plurality of iterations.
5.2 The second off-line time correction table (inter-crystal scattering event time correction table) generating unit counts time differences between inter-crystal scattering events in each crystal and non-crystal scattering events on the response line, and obtains the second time correction lookup table LUT2 through a plurality of iterations.
The addresses of the first time correction lookup table and the second time correction lookup table are crystal coding positions, the content is time difference information, the addresses and the content are in one-to-one correspondence, and it is understood that each address corresponds to one time difference information.
6) The on-line time correction module stores a first time correction lookup table and a second time correction lookup table through a random access memory, specifically stores the first time correction lookup table through a first random access memory RAM1 and stores the second time correction lookup table through a second random access memory RAM 2. And carrying out real-time online correction on the arrival time acquired by the time measuring module based on the first time correction lookup table and the second time correction lookup table.
6.1 For the amorphous scattering event, searching the content corresponding to the address through the address of the first time correction lookup table according to the determined position coding information of the hit crystal, thereby obtaining time difference information corresponding to the position coding information, and correcting a time measurement result based on the time difference information.
6.2 For inter-crystal scattering events, based on the determined position-coding information of the hit crystal and inter-crystal scattering markers, first correcting the ground of the lookup table by the first timeSearching the content corresponding to the address, thereby obtaining time difference information corresponding to the position coding information, and correcting a time measurement result based on the time difference information; and searching the content corresponding to the address through the address of the second time correction lookup table, so as to obtain time difference information corresponding to the position coding information, and carrying out secondary correction on a time measurement result based on the time difference information. See the formula:where t is the original time measurement (i.e., the arrival time output by the time measurement module), and t' is the corrected time measurement. Pos is a crystal position code, LUT1 is a first time correction lookup table (amorphous inter-crystal scattering event time correction table), and LUT2 is a second time correction lookup table (inter-crystal scattering event time correction table).
The scheme of the invention carries out verification test on a model PET scanner, the test result is shown in figures 3-5, for inter-crystal scattering events, the CTR can be improved by 134ps through the scheme, and for all events of the whole system, the CTR can be improved by 46ps, so that a better result is obtained.
It should be noted that the embodiments of the present invention are preferred and not limited in any way, and any person skilled in the art may make use of the above-disclosed technical content to change or modify the same into equivalent effective embodiments without departing from the technical scope of the present invention, and any modification or equivalent change and modification of the above-described embodiments according to the technical substance of the present invention still falls within the scope of the technical scope of the present invention.
Claims (10)
1. A method for time correction of inter-crystal scatter events for SiPM-based PET detectors, comprising:
comparing all row and column signals of the SiPM detector array with a fixed voltage threshold under a differential signal mode to obtain time threshold crossing pulses of the signals; the time measurement is carried out on the front edge and the rear edge of the time threshold passing pulse through a time digital converter based on clock phase separation, so that the time threshold passing pulse width is obtained; judging whether an event in a crystal of the SiPM detector is an amorphous scattering event or an inter-crystal scattering event according to the time threshold pulse width;
counting the time difference between the amorphous scattering event in each crystal and the amorphous scattering event on the response line, and obtaining a first time correction lookup table through multiple iterations; counting the time difference between the inter-crystal scattering event in each crystal and the non-crystal scattering event on the response line, and obtaining a second time correction lookup table through multiple iterations; the addresses of the first time correction lookup table and the second time correction lookup table are crystal coding positions, and the content is time difference information;
and storing the first time correction lookup table and the second time correction lookup table, and carrying out real-time online correction on the time of the inter-crystal scattering event through the first time correction lookup table and the second time correction lookup table.
2. The method of claim 1, wherein determining whether an event in a crystal of an SiPM detector is an amorphous scattering event or an inter-crystal scattering event by the time-to-threshold pulse width comprises:
for non-crystal scattering events, determining unique code information hitting the crystal location;
and for inter-crystal scattering events, taking a crystal code corresponding to the time threshold pulse width which is larger than a preset threshold value in the time threshold pulse width information of all signals as hit crystal position code information.
3. The method of claim 2, wherein the real-time online correction of the time of the inter-crystal scattering event by the first time correction lookup table and the second time correction lookup table comprises:
for the inter-crystal scattering event, according to the determined position coding information of the hit crystal and the inter-crystal scattering mark, searching the content corresponding to the address through the address of the first time correction lookup table, so as to obtain time difference information corresponding to the position coding information, and correcting a time measurement result based on the time difference information; and searching the content corresponding to the address through the address of the second time correction lookup table, so as to obtain time difference information corresponding to the position coding information, and carrying out secondary correction on a time measurement result based on the time difference information.
4. The method of claim 2, wherein the real-time online correction of the time of the inter-crystal scattering event by the first time correction lookup table and the second time correction lookup table comprises:
and for the amorphous scattering event, searching the content corresponding to the address through the address of the first time correction lookup table according to the determined position coding information of the hit crystal, so as to obtain time difference information corresponding to the position coding information, and correcting a time measurement result based on the time difference information.
5. The method for time correction of inter-crystal scattering events of claim 1, further comprising:
summing signals of the SiPM detector array, and measuring the summed signals through a high-speed comparator and a time-to-digital converter based on a carry chain, so as to obtain the arrival time of the signals received by the SiPM detector array;
and performing time correction on the arrival time based on the time difference information.
6. The method for time correction of inter-crystal scattering events of claim 1, further comprising:
separate phases of SiPM detector arrays through resistor network rows and columnsAdding the number of the position reading circuit channels from n 2 Reduced to 2n and the position of the fired SiPM detector element is determined by determining the trigger position of the column sum signal.
7. The method of claim 6, wherein the SiPM detector array is coupled to the LYSO crystals in a 1:1 manner.
8. The method for time correction of inter-crystal scattering events of claim 1, further comprising:
the signals of the SiPM detector array are summed, the analog signal is converted to a digitized signal by an analog-to-digital converter, and then the digitized signal is integrated to obtain the number of ADC channels characterizing the energy of the analog signal.
9. The time correction system for the inter-crystal scattering event of the SiPM-based PET detector is characterized by comprising a time measurement module, a position pulse width measurement and calculation module, an off-line time correction table generation module and an on-line time correction module, wherein the position pulse width measurement and calculation module is arranged in a field programmable gate array;
the position pulse width measuring and calculating module comprises a comparator unit, a position pulse width measuring unit and a position calculating unit; the comparator unit compares all row-column signals of the SiPM detector array with a fixed voltage threshold under a differential signal mode to obtain time threshold passing pulses of the signals; the position pulse width measuring unit performs time measurement on the front edge and the rear edge of the time threshold passing pulse through a time digital converter based on clock phase separation so as to obtain a time threshold passing pulse width; the position calculation unit determines whether an event in a crystal of the SiPM detector is an amorphous scattering event or an inter-crystal scattering event by the time threshold pulse width, and: for non-crystal scattering events, determining unique code information hitting the crystal location; for inter-crystal scattering events, taking a crystal code corresponding to a time threshold pulse width greater than a preset threshold value in the time threshold pulse width information of all signals as hit crystal position code information;
the off-line time correction table generation module counts the time difference between the amorphous scattering event in each crystal and the amorphous scattering event on the response line, and a first time correction lookup table is obtained through multiple iterations; counting the time difference between the inter-crystal scattering event in each crystal and the non-crystal scattering event on the response line, and obtaining a second time correction lookup table through multiple iterations; the addresses of the first time correction lookup table and the second time correction lookup table are crystal coding positions, and the content is time difference information;
the time measurement module sums the signals of the SiPM detector array, and the summed signals are measured through a high-speed comparator and a time-to-digital converter based on a carry chain, so that the arrival time of the signals received by the SiPM detector array is obtained;
the online time correction module stores the first time correction lookup table and the second time correction lookup table through a random access memory; and carrying out real-time online correction on the arrival time acquired by the time measurement module through the first time correction lookup table and the second time correction lookup table.
10. The system for time correction of inter-crystal scattering events of claim 9, further comprising a front end position encoding circuit and an energy measurement module;
the front end position coding circuit adds SiPM detector arrays through resistor network rows and columns respectively, and the number of channels of the position reading circuit is n 2 Reducing the number to 2n, and judging the positions of the excited SiPM detector units by judging the triggering positions of the row and column summation signals;
the energy measurement module sums the signals of the SiPM detector array, converts the analog signals into digital signals through an analog-to-digital converter, and integrates the digital signals to obtain the ADC channel number representing the energy of the analog signals.
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