CN207020320U - A kind of gain correcting device of scintillation detector - Google Patents

Abstract

The utility model provides a gain correction device for a scintillation detector. The device includes a calibration radiation source and at least two comparators, a counting module, a temperature sensor and a single-chip microcomputer. Each comparator is connected with a photoelectric device for communication. The analog voltage signals of different energy segments are converted into digital pulse signals; the counting module communicates with each comparator and simultaneously measures the counting rate of the digital pulse signal; the temperature sensor measures the surface temperature data of the scintillation detector; the single-chip microcomputer and the counting module The communication is connected and the target gain and correction voltage are calculated according to the counting rate and the measured temperature data; the high-voltage power supply is connected to the single-chip microcomputer to receive the correction voltage, and the high-voltage power supply is also connected to the photoelectric device to realize the gain correction of the photoelectric device according to the correction voltage. The utility model can directly adjust the gain according to the temperature, can avoid information loss, speed up the calibration speed, and improve the efficiency of gain correction.

Description

A Gain Correction Device for Scintillation Detector

technical field

The utility model relates to a signal correction device and method in the field of nuclear medical imaging and ionizing radiation measurement, more particularly to a gain correction device of a scintillation detector.

Background technique

Scintillation detectors are widely used in the fields of nuclear medical imaging and ionizing radiation measurement, and are the core devices for imaging or radiation measurement. The scintillation detector includes mutually coupled scintillation crystals and photoelectric devices. The scintillation crystals are used to convert ionizing radiation rays (including X-rays, gamma photons, neutrons, alpha photons and beta photons, etc.) The optical signal is converted into an electrical signal, and after the electrical signal is processed by the corresponding electronic design, information such as the corresponding arrival time, arrival position, and energy of the gamma photons can be obtained. Currently commonly used scintillation crystals include sodium iodide (NaI) crystals, yttrium lutetium silicate (LYSO) crystals, lutetium silicate (LSO) crystals, yttrium silicate (YSO) crystals, and cesium iodide (CsI) crystals. Optoelectronic devices include photodiodes (APDs), photomultiplier tubes (PMTs) and emerging silicon photomultipliers (SiPMs).

Since the scintillation detector is the core device for imaging or radiation measurement, its gain parameters will directly affect the accuracy of radiation measurement. However, due to differences in the individual light output of scintillation crystals (light output refers to the number of ionizing rays absorbed by scintillation crystals per unit energy and converted into photons), this difference will cause changes in the gain of scintillation detectors, especially in silicon The photomultiplier is the scintillation detector of the photoelectric device, its gain is extremely sensitive to temperature, and the gain can vary by more than 56% in the temperature range of -20 to 50°C, which seriously affects the accuracy of the system. Therefore, it is necessary to correct the gain of the scintillation detector in actual use.

At present, the method of correcting the gain of the scintillation detector is mostly to add an amplifier at the back end of the scintillation detector, and use multi-channel analysis equipment to measure the energy spectrum of the scintillation detector, so as to obtain the photoelectric peak position of the test source, and then use the photoelectric The peak position is used as the gain of the scintillation detector. By adjusting the gain of the amplifier to compensate for the influence caused by the gain change of the scintillation detector, the photoelectric peak position remains unchanged to achieve gain calibration.

Although the existing technology can add an amplifier at the back end of the scintillation detector to amplify the output signal twice to achieve gain correction, however, since the scintillation detector using a silicon photomultiplier itself has a relatively fixed amplitude noise floor Signal, when the gain of the silicon photomultiplier decreases, part of the output signal will be submerged in the background noise signal. Even if an amplifier is added at the back end, the signal-to-noise ratio will not be improved, resulting in the loss of signal information. Secondly, after the amplifier is used, it is necessary to measure the complete energy spectrum of the calibration radiation source and obtain its photoelectric peak position to achieve calibration. Usually, the data acquisition amount is not less than 5000 events, which will cause slow system calibration speed and increase hardware cost. big. Thirdly, after the amplifier is used, the calibration measurement process needs to be repeated when the temperature changes, and the calibration efficiency is reduced.

Utility model content

The purpose of the utility model is to provide a gain correction device of a scintillation detector, so as to solve the problems of slow gain correction speed, low calibration efficiency and high cost of the scintillation detector in the prior art.

In order to solve the above-mentioned technical problems, the technical solution of the utility model is to provide a kind of gain correction device of scintillation detector, the gain G of the scintillation detector, temperature t and voltage x satisfy the gain temperature-voltage equation G(x, t)= at+bx+c, wherein parameters a, b, c are constants; the gain correction method comprises the following steps:

The first step is to determine the gain temperature voltage equation of the standard scintillation detector, the specific steps are:

Step S1: Take a standard scintillation detector, measure the gain G ₀ of the standard scintillation detector when the temperature T ₀ and the voltage X ₀ are fixed, and use the gain G ₀ of the standard scintillation detector as the scintillation detector to be tested The target gain of the device;

Step S2: Fix the temperature as T ₀ , adjust the voltage as X ₂ , measure the gain G ₂ of the standard scintillation detector, substitute it into the gain temperature-voltage equation, and calculate the parameters k ₂ and p ₂ , where k ₂ = b,p ₂ =at ₀ +c;

Step S3: Fix the voltage to X ₀ , adjust the temperature to T ₁ , measure the gain G ₁ of the standard scintillation detector, substitute it into the gain temperature voltage equation, and calculate the parameters k ₁ and p ₁ , where k ₁ =a , p ₁ =bx ₀ +c;

Step S4 _: Substituting the parameters _k1 , k2, p1 and _p2 into the gain temperature-voltage equation, calculating the parameters a, b and c of the standard scintillation detector, thereby determining the gain temperature-voltage equation of the standard scintillation detector as:

G(x,t)=at+bx+c

Step S5: When the target gain is G0, the relationship between the voltage _x and the temperature t of the scintillation detector can be determined according to the gain temperature voltage equation as:

x=(G ₀ -at-c)/b

The second step is to measure the gain difference between the scintillation detector to be tested and the standard scintillation detector, and obtain the voltage temperature equation of the scintillation detector to be tested under the target gain condition;

The third step is to use the voltage-temperature equation obtained in the second step as a reference for correction, calculate the corresponding correction voltage according to the measured temperature of the scintillation detector to be tested, and change the voltage of the scintillation detector according to the correction voltage In order to realize the gain correction of the scintillation detector under test.

The specific steps of the second step are as follows:

Step S6: Adjust the temperature to T ₀ and the voltage to X ₀ , measure the gain G' of the scintillation detector to be tested, then the gain temperature-voltage equation of the scintillation detector to be tested is:

G(x,t)=at+bx+c+(G'-G ₀ );

Step S7: When the target gain is G0, the voltage-temperature equation of the scintillation detector to be tested is _:

x=(-at-c+2G ₀ -G')/b.

According to an embodiment of the present invention, a temperature sensor is used to obtain the measured temperature on the surface of the scintillation detector to be tested, and a single-chip microcomputer is used to calculate and obtain the corresponding correction voltage.

For scintillation detectors with the same size and specifications, the first step only needs to be performed once, and other scintillation detectors to be tested perform the second step to obtain the voltage-temperature equation at the target gain.

The utility model provides a gain correction device for a scintillation detector. The scintillation detector includes a scintillation crystal and a photoelectric device coupled to each other. The gain correction device includes: a calibration radiation source, and the scintillation crystal receives the ionizing radiation emitted by the calibration radiation source And converting the ionizing radiation into visible light, the photoelectric device converts the visible light into an analog voltage signal; at least two comparators, each of which is connected to the photoelectric device in communication to convert different energy segments The analog voltage signal is converted into a digital pulse signal; a counting module, the counting module is respectively connected to the comparator of each road to receive the digital pulse signal sent by the comparator of each road, and the counting module measures the digital pulse signal at the same time The counting rate of the digital pulse signal; a temperature sensor, the temperature sensor is arranged on the outer surface of the photoelectric device to measure the temperature data; a single-chip microcomputer, the single-chip microcomputer communicates with the counting module to receive the counting rate, the single-chip microcomputer is also communicatively connected with the temperature sensor to receive the measured temperature data, and the single-chip microcomputer calculates a target gain and a correction voltage according to the counting rate and the measured temperature data; and A high-voltage power supply, the high-voltage power supply is connected to the single-chip microcomputer to receive the correction voltage, and the high-voltage power supply is also connected to the photoelectric device to realize gain correction of the photoelectric device according to the correction voltage.

The calibration radiation source adopts single-energy radiation source.

The radionuclide used in the calibration radioactive source is Cs-137, Co-60 or Eu-152.

When calibrating the scintillation detector of the same kind, the relative position between the calibration radiation source and the scintillation crystal remains fixed.

The multi-way comparator includes two-way comparators, and the two-way comparators are respectively connected in communication with the photoelectric device and the computing module.

The optoelectronic device is a silicon photomultiplier.

The gain calibration device of the scintillation detector provided by the utility model can directly perform gain calibration from the scintillation detector end, which solves the problem of missing information, uses a multi-channel comparator instead of a multi-channel analyzer, and simplifies the measurement equipment requirements in the calibration process , to speed up the calibration. At the same time, the utility model establishes a mathematical model of the gain, temperature and voltage of the scintillation detector, and the gain can be directly adjusted according to the temperature without re-measurement, thus improving the efficiency of gain correction.

Description of drawings

Fig. 1 is a schematic diagram of energy segmentation of a gain correction device of a scintillation detector according to an embodiment of the present invention;

2 is a schematic diagram of the relationship between the gain and temperature of the gain correction device of the scintillation detector according to an embodiment of the present invention;

Fig. 3 is a schematic diagram of the correction process of the gain correction device of the scintillation detector according to a preferred embodiment of the present invention;

Fig. 4 is a system schematic diagram of a gain correction device of a scintillation detector according to an embodiment of the present invention;

Fig. 5 is a schematic diagram of arrangement of multiple comparators of a gain correction device for a scintillation detector according to an embodiment of the present invention.

detailed description

Below in conjunction with specific embodiment, the utility model is described further. It should be understood that the following examples are only used to illustrate the utility model but not to limit the scope of the utility model.

The energy spectrum in the utility model refers to the energy distribution histogram drawn by energy segments by using the scintillation detector to obtain the energy and quantity information of the ionizing radiation rays. Each radiation source can emit several kinds of ionizing radiation rays with fixed energy, so each radiation source has a relatively fixed energy spectrum form. If n different energy limits E _n are used to divide the energy spectrum into several energy segments, then the ratio of all pulse count rates per unit time in each energy segment is the energy channel count rate ratio, for example, using 3 energy limits E ₁ , E ₂ , E ₃ divide the energy spectrum into three energy segments, and the intervals of these three energy segments are [E ₁ , E ₂ ), [E ₂ , E ₃ ), [E ₃ , +∞) , the counting rates in the three energy segments are CR ₁ , CR ₂ , and CR ₃ respectively, and the counting rate ratio of the energy channel is CR ₁ :CR ₂ :CR ₃ . For a scintillation crystal with a certain size, its energy spectrum form for the same radiation source is also relatively fixed, that is, the count rate ratio of each energy channel is stable, so the total count rate ratio of different energy segments is also stable. Based on the above principles, any two comparators with different reverse voltages can be used to record the count rate ratio of different energy segments as a reference standard for calibration, and the ratio of different count rates can be used as the gain of the photoelectric device of the scintillation detector . Specifically, as shown in Figure 1, the energy spectrum of Cs-137 can be divided into two energy segments, as shown in the dotted line division in the figure, the gain of the optoelectronic device of the scintillation detector can be determined by the above principle as:

G=CountRate2/CountRate1

Among them, CountRate refers to the counting rate recorded by the comparators of different channels, CountRate1 is the counting rate of comparator 1 with a lower energy limit, and CountRate2 is the counting rate of comparator 2 with a higher energy limit.

Further, Fig. 2 is a schematic diagram of the relationship between the gain and temperature of the scintillation detector according to a preferred embodiment of the present invention. It can be seen from Fig. 2 that, according to the actual measurement results, the gain and temperature of the photoelectric device are basically in a linear relationship, and the gain And the voltage also has a linear relationship, therefore, the following equation is satisfied between the gain G and the temperature t and the voltage x:

G(x,t)=at+bx+c (1)

Among them, a is the temperature coefficient, b is the voltage coefficient, and c is the gain deviation constant determined by the properties of the scintillation detector that is independent of voltage and temperature, such as the light loss caused by the coupling between the scintillation crystal and the optoelectronic device.

The correction within the temperature range can be realized by obtaining a, b, and c through the relationship measurement of formula (1), as follows:

First, when the temperature t ₀ is fixed, we can get

G(x,t ₀ )=k ₂ x+p ₂ (2)

where k ₂ =b, p ₂ =at ₀ +c;

Second, when the voltage x ₀ is fixed, we have

G(x ₀ ,t)=k ₁ t+p ₁ (3)

Wherein, k ₁ =a, p ₁ =bx ₀ +c.

According to the above relationship, in conjunction with Fig. 3, it can be seen that the steps of the utility model for gain correction are as follows:

The first step is to determine the gain temperature voltage equation of the standard scintillation detector in order to achieve gain correction at different temperatures, the specific steps are:

S1: Take a standard scintillation detector, measure the gain G ₀ of the standard scintillation detector when the temperature T ₀ and the voltage X ₀ are fixed, and use the gain G ₀ of the standard scintillation detector as the target gain of other scintillation detectors to be tested ;

S2: Fix the temperature as T ₀ , adjust the voltage as X ₂ , measure the gain G ₂ of the standard scintillation detector, substitute it into the formula (2) above, and calculate the parameters k ₂ and p ₂ ;

S3: Fix the voltage to X ₀ , adjust the temperature to T ₁ , measure the gain G ₁ of the standard scintillation detector, substitute it into the formula (3) above, and calculate the parameters k ₁ and p ₁ ;

S4: Substituting the parameters k1, k2, p1 and _p2 into the above _formula ( ₁ ) to calculate the parameters a, b and c of the standard scintillation detector, so as to determine the gain temperature voltage equation of the standard scintillation detector as:

G(x,t)=at+bx+c (1)

S5: When the target gain is G ₀ , according to the above formula, the relationship between the voltage x and the temperature t of the scintillation detector can be determined as:

x=(G ₀ -at-c)/b

The second step is to measure the gain difference between the scintillation detector to be tested and the standard scintillation detector under the sample conditions of the standard scintillation detector, and obtain the voltage temperature equation of the scintillation detector to be tested under the fixed target gain condition; the sample here The conditions refer to the fixed temperature T ₀ and voltage X ₀ in the first step, and the specific steps are as follows:

S6: Adjust the temperature to T ₀ and the voltage to X ₀ , measure the gain G' of the scintillation detector to be tested, then the gain temperature-voltage equation of the scintillation detector to be tested is:

G(x,t)=at+bx+c+(G'-G ₀ )

S7: When the target gain is G0, the voltage-temperature equation of the scintillation detector to be tested is _:

x=(-at-c+2G ₀ -G')/b

In the third step, according to the actual measurement of the gain difference between the scintillation detector to be tested and the standard scintillation detector, the voltage-temperature equation obtained in step S7 is used as a reference for correction, and the corresponding correction voltage is calculated by using the temperature actually measured by the temperature sensor. On-chip microcomputer (MCU) controls the high-voltage power supply to change the voltage according to the correction voltage to realize the correction of the scintillation detector to be tested.

For scintillation detectors with the same size and specifications, the first step only needs to be performed once, that is, steps S1-S5 only need to be performed once, and other scintillation detectors to be tested only need to perform subsequent steps (S6-S7) in sequence Obtain the voltage temperature equation at the target gain.

It should be noted that there may be errors between the actual measured gain and the target gain in actual use. After determining the relationship between the voltage and temperature of the scintillation detector to be tested through steps S6-S7, the correction voltage is calculated by the MCU and the high-voltage voltage is controlled. After the correction voltage output is calibrated, the gain can be continuously measured by performing step S6, and compared with the target gain by step S7. If the corrected gain does not meet the target gain, repeat steps S6-S7 and re-adjust until it reaches The required range; if the corrected gain meets the target gain, then the gain calibration of the next scintillation detector to be tested will be automatically performed.

Therefore, according to the above principles, the system schematic diagram of the gain correction device of the scintillation detector provided by the present invention is shown in Figure 4, as can be seen from Figure 4, the gain correction device of the scintillation detector 10 of the present invention includes a calibration radiation source 20, Multi-way comparator 30, counting module 40, single-chip microcomputer (MCU) 50, high-voltage power supply 60 and temperature sensor 70, wherein, scintillation detector 10 includes mutually coupled scintillation crystal 11 and photoelectric device 12; Calibration radiation source 20 adopts Single-energy radiation source, such as Cs-137, calibration radiation source 20 emits ionizing radiation rays, such as X-rays, gamma photons, neutrons, alpha photons and beta photons, etc.; scintillation crystal 11 receives the ionizing radiation radiation emitted by calibration radiation source 20 and convert the ionizing radiation into visible light, and the photoelectric device 12 coupled with the scintillation crystal 11 receives the visible light and converts the visible light into an analog voltage signal; The analog voltage signal of the multi-way comparator 30 is set to convert the analog voltage signal into a digital pulse signal according to different energy segments and sends it to the counting module 40; the counting module 40 is connected with the multi-way comparator 30 to receive the digital pulse signal, count The module 40 simultaneously measures the number of digital pulse signals sent by the multi-channel comparator 30 per unit time, that is, the count rate, and then sends the count rate to the MCU50; the temperature sensor 70 is arranged on the surface of the optoelectronic device 12 so as to accurately measure the optoelectronic device 12 the real-time temperature of the surface, the temperature sensor 70 sends the real-time temperature data measured to the MCU50; The real-time temperature data calculates the correction voltage, and after the MCU 50 determines the correction voltage, it sends an adjustment command to the high-voltage power supply 60 to adjust the voltage to the voltage required for calibration, thereby completing the calibration and controlling the calibration operation.

More specifically, FIG. 5 is a schematic diagram of the layout of the multiple comparators of the gain correction device of the scintillation detector according to an embodiment of the present invention, wherein there are n comparators in total, and the optoelectronic devices 12 communicate with the multiple comparators 30 respectively. connection, that is, the optoelectronic device 12 is respectively connected to the first comparator 31, the second comparator 32, ..., and the nth comparator, and the first comparator 31, the second comparator 32, ..., and the nth comparator The devices are respectively connected to the counting module 40 in communication. Since the energy spectrum is divided into several energy segments by n different energy limits, each comparator correspondingly converts the analog digital signal in each energy segment into a digital pulse signal, and the counting module 40 simultaneously measures the energy of each comparator in a unit time. The number of digital pulse signals sent by the detector and the count rate data of each channel are sent to the MCU50, and the MCU determines the count rate ratio of the energy channel, and then determines the target gain.

According to a preferred embodiment of the utility model, the multi-way comparator 30 only uses two comparators 31 and 32 with different reverse voltages, and the counting rate ratio of different energy segments is recorded by the counting module 40, as a reference standard for calibration , and the ratio of the different count rates is corrected by the MCU as the gain of the scintillation detector.

It should be noted that since the ionizing radiation emitted by the calibration radiation source 20 is easily reflected and refracted by surrounding objects, this will affect the form of the energy spectrum measured by the scintillation crystal. There is a dense object in between, such as a metal plate. At the same time, it should also be noted that the relative position between the calibration radiation source 20 and the scintillation crystal 11 should be kept fixed. When calibrating the same kind of scintillation detector, the relative position between the calibration radiation source 20 and the scintillation crystal 11 should also be consistent. Failure to do so will cause calibration errors.

According to an embodiment of the present invention, the calibration radiation source 20 adopts a single-energy radiation source, such as Cs-137, Co-60 or Eu-152, not necessarily Cs-137, because the energy spectrum of the single-energy radiation source is relatively simple , a relatively stable channel count ratio can be obtained. It should be understood that the calibration radiation source of the present invention is not limited to a single-energy radiation source, and may also be other types of radiation sources.

According to a preferred embodiment of the present utility model, optoelectronic device 12 adopts silicon photomultiplier (SiPM), and temperature sensor 70 is installed close to SiPM; side.

The gain correction device of the scintillation detector provided by the utility model can realize the gain correction from the scintillation detector end, which ensures that the signal-to-noise ratio of the scintillation detector remains unchanged under the conditions of different temperatures and scintillation crystals with different performances, and makes the scintillation detector The lower limit of energy detection after calibration remains unchanged, maintaining the integrity of information. The utility model adopts two-way or multi-way comparators and counters instead of multi-channel analyzers, and the measurement of the gain can be realized without measuring the complete energy spectrum, and the accurate gain can be measured only by 1000 events. Compared with the energy spectrum method Get the gain, the number of measurement events drops by 80%, and the calibration is faster. At the same time, the utility model establishes a mathematical model of the gain of the photoelectric device to temperature and voltage, and only needs to measure the data at two temperatures to realize the correction of the complete temperature range, and the calibration efficiency is higher.

The above are only preferred embodiments of the present utility model, and are not intended to limit the scope of the present utility model. Various changes can also be made to the above-mentioned embodiments of the present utility model, such as the gain, temperature , Voltage Models can be fitted using quadratic or higher order functions. That is to say, all simple and equivalent changes and modifications made according to the claims of the utility model application and the contents of the description all fall within the protection scope of the claims of the utility model patent. What the utility model does not describe in detail is conventional technical contents.

Claims (6)

1. A gain correction device for a scintillation detector, said scintillation detector comprising scintillation crystals and optoelectronic devices coupled to each other, characterized in that said gain correction device comprises: a calibration radiation source, the scintillation crystal receives the ionizing radiation emitted by the calibration radiation source and converts the ionizing radiation into visible light, and the photoelectric device converts the visible light into an analog voltage signal; At least two comparators, each of which is communicatively connected to the optoelectronic device to convert the analog voltage signals of different energy segments into digital pulse signals; A counting module, the counting module is connected in communication with each of the comparators to receive the digital pulse signal sent by each of the comparators, and the counting module simultaneously measures the count rate of the digital pulse signal; A temperature sensor, the temperature sensor is arranged outside the photoelectric device to measure temperature data; A single-chip microcomputer, the single-chip microcomputer communicates with the counting module to receive the count rate, and the single-chip microcomputer communicates with the temperature sensor to receive the measured temperature data, the single-chip microcomputer The on-chip microcomputer calculates a target gain and a correction voltage according to the count rate and the measured temperature data; and A high-voltage power supply, the high-voltage power supply is connected to the single-chip microcomputer to receive the correction voltage, and the high-voltage power supply is also connected to the photoelectric device to realize gain correction of the photoelectric device according to the correction voltage. 2 . The gain correction device for a scintillation detector according to claim 1 , wherein the calibration radiation source is a single-energy radiation source. 3 . 3. The gain correction device of scintillation detector according to claim 2, characterized in that the radionuclide used in the calibration radiation source is Cs-137, Co-60 or Eu-152. 4 . The gain correction device for scintillation detectors according to claim 1 , wherein when calibrating the scintillation detectors of the same type, the relative position between the calibration radiation source and the scintillation crystal remains fixed. 5. The gain correction device of the scintillation detector according to claim 1, wherein the comparator comprises two comparators, and the two comparators are connected in communication with the photoelectric device and the counting module respectively . 6. The gain correction device of scintillation detector according to claim 1, characterized in that, the photoelectric device is a silicon photomultiplier.