A dual-layer detector-based thyroid i-131 activity measurement system

Abstract

The application provides a kind of thyroid I-131 activity measurement system based on double-layer detector, for measuring I-131 activity in human thyroid, comprising: double-layer detector, for receiving the gamma ray emitted by I-131 to outside the body and converting the gamma ray into optical signal, with front and rear end CsI (TI) crystal and rear end CsI (TI) crystal arranged in front and rear adhesion;Nuclear electronics equipment, used with double-layer detector, for converting optical signal into electrical signal;Annular band, for fixing adhesion in human neck, with double-layer detector and nuclear electronics equipment arranged inside;Spectrum analysis module, for analyzing according to electrical signal, to obtain the energy spectrum of gamma ray;Detection efficiency calibration module, for calibrating the detection efficiency of double-layer detector, including OTT calibration unit and detection efficiency calibration unit;Energy spectrum analysis module, for analyzing the energy spectrum of gamma ray received by double-layer detector after calibration to obtain I-131 activity.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of radio diagnosis and treatment, and particularly relates to a thyroid I-131 activity measurement system based on a double-layer detector. BACKGROUND

[0002] The clinical nuclear medicine in China has developed very rapidly, and radioisotopes have played an indispensable important role in medical diagnosis and treatment. The frequency and dosage of radionuclides are also increasing. Compared with other radiation-related medical applications, the internal exposure risk of patients and staff in the nuclear medicine department cannot be ignored. In addition, in recent years, the concept of precision medicine has been widely recognized and promoted worldwide, and the importance of modern personalized radio diagnosis and treatment technology has become increasingly prominent, and the radiation protection of seeking benefits and avoiding harm has also put forward the requirements of precision and individualization.

[0003] In addition, China is in the strategic transition period from a "nuclear power" to a "nuclear power", and the radiation emergency management and disposal under the condition of nuclear accident involves national security, and has the strategic significance of "training soldiers for a long time and using soldiers for a short time". However, in sharp contrast to the urgent strategic demand, I-131, as one of the most commonly used medical radioisotopes in the nuclear medicine department, and the main nuclide in the gaseous effluent of nuclear power accidents, its measurement technology and dose evaluation related research are relatively lacking. Especially the precision of thyroid I-131 activity measurement, the individualization of internal exposure dose evaluation and the on-site adaptability of detection means are important technical problems that need to be solved.

[0004] Since the 1980s, researchers have carried out research work on the measurement of I-131 activity in the thyroid and the evaluation of internal exposure dose. The commonly used I-131 activity measurement methods include three categories: in-vivo direct measurement, biological sample analysis and air sampling analysis. Among them, biological sample analysis uses the excretion of urine, feces and other waste samples to analyze the in-vivo nuclide activity and internal exposure dose. The air sampling analysis method is based on the environmental source term and the biological kinetic model to evaluate the internal exposure dose. In practice, considering the convenience of operation and the accuracy of measurement, the thyroid I-131 activity monitoring is the preferred in-vivo direct measurement method and the most mainstream monitoring method.

[0005] The in-vivo quantitative measurement methods of I-131 activity include the following categories:

[0006] (1) Using ECT, gamma camera and whole-body counter, combined with calibration source and related efficiency correction for measurement. The disadvantages of this method are as follows: 1. The measurement accuracy is high, but it will occupy valuable equipment time, the training period of the operator is long, and the cost of starting and instrument is high; 2. For large-scale measurement equipment represented by whole-body counter, high atomic number shielding layer and low background measurement environment make it have high sensitivity and nuclide resolution capability, however, strong shielding capability also means that high measurement load will make the system face the risk of radioactive contamination; 3. Due to high cost, small number of instruments, it is not suitable for large-scale population screening, only suitable for scientific research of individual cases.

[0007] (2) Using portable gamma spectrometer to directly measure I-131 emitted gamma rays outside the body is the most common technical solution in practice. Thyroid I-131 measurement instrument based on NaI(Tl) scintillator and portable gamma spectrometer belong to this kind of measurement method. The measurement accuracy of this method is limited.

[0008] (3) Film and Image Plate (IP) system are used for research, most of which are experimental attempts. The disadvantages of this method are as follows: 1. Based on IP system, a complete measurement needs to go through four steps of erasing, exposing, transporting and reading, the measurement process is complex and time-consuming; 2. The reading of IP system needs to be carried out in a professional laboratory, and on-site data reading cannot be realized. In the data transportation process, the image plate will read extra background noise information affected by factors such as fading effect, temperature and background noise. In a long data reading time, part of the radiation will be emitted in advance, resulting in the loss of radioactive information; 3. The back-end analysis instrument is expensive; 4. IP system is difficult to simulate by Monte Carlo simulation, and related research is lacking due to the limitation of the types of experimental phantoms; 5. Film is not sensitive to small dose irradiation effect, and the application scene is limited.

[0009] Overall, the above three methods are affected by the equivalence of phantom and human body in quantity traceability, and there are different measurement short boards in the adaptability of different human body structures. In practice, they can only be used as a qualitative or semi-quantitative measurement method. The specific performance is as follows:

[0010] (1) Common error factors: the measurement accuracy of any activity evaluation tool will be affected by environmental background radiation, nuclear electronics noise, measurement condition variation and gamma spectrum analysis algorithm. Due to the working characteristics of the measurement tool itself, the anti-interference energy is inconsistent.

[0011] (ii) Measurement cannot be personalized: inter-individual anatomical differences, scale phantom distortion, and geometric offset of the measurement system are factors contributing to thyroid problems. 131 The main factors contributing to I activity measurement errors are anatomical differences, including overlaying tissue thickness (OTT), thyroid volume, and thyroid shape, as well as system geometric differences, such as neck-detector distance (NDD), detector angle offset, and detector position offset. These raw parameters of the efficiency scale are often difficult to fully reproduce in actual measurements. Summary of the Invention

[0012] The present invention was made to solve the above-mentioned problems, and its purpose is to provide a thyroid I-131 activity measurement system based on a dual-layer detector.

[0013] The application provides a kind of based on double-layer detector's thyroid I-131 activity measurement system, for the measurement of I-131 activity in human thyroid, with such characteristics, including: double-layer detector, for receiving I-131 emitted to the outside of the body γ ray and converting γ ray into optical signal, with front and rear end CsI (TI) crystal and rear end CsI (TI) crystal of front end fit setting;Nuclear electronics equipment, used with double-layer detector, for converting optical signal into electrical signal;Annular band, for fixing fit in human neck, internally provided with double-layer detector and nuclear electronics equipment;Spectrum analysis module, for analysis according to electrical signal, obtain the energy spectrum of γ ray;Detection efficiency calibration module, for calibrating the detection efficiency of double-layer detector, reduce the measurement error caused by the difference of the thickness of the covering tissue from thyroid to the ventral surface of neck, including OTT calibration unit for calculating the thickness of covering tissue and detection efficiency calibration unit for calculating detection efficiency;Spectrum analysis module, for analyzing the energy spectrum of γ ray received by double-layer detector after calibration to obtain I-131 activity, wherein OTT calibration unit establishes the relationship function between correction factor and covering tissue thickness by changing the thickness of covering tissue from thyroid to neck phantom according to energy spectrum, correction factor is based on the double-layer crystal structure of double-layer detector, and is obtained by the count ratio of front end CsI (TI) crystal and rear end CsI (TI) crystal at 365keV full energy peak, detection efficiency calibration unit establishes the relationship function between covering tissue thickness and detection efficiency by changing the thickness of covering tissue from thyroid to neck phantom according to energy spectrum, detection efficiency calibration module obtains correction factor by double-layer detector measurement, to bring into OTT calibration unit to obtain the relationship function between correction factor and covering tissue thickness, calculate the numerical value of covering tissue thickness, and bring the numerical value of covering tissue thickness into the relationship function between covering tissue thickness and detection efficiency obtained by detection efficiency calibration unit to obtain detection efficiency, spectrum analysis module analyzes the energy spectrum of γ ray received by double-layer detector after detection efficiency calibration, and calculates to obtain the accurate measurement value of I-131 activity in thyroid.

[0014] In the double-layer detector-based thyroid I-131 activity measurement system provided by the application, the thickness of the front end CsI (TI) crystal can be 6-10 mm, the length can be 30-45 mm, and the height can be 30-45 mm, the thickness of the rear end CsI (TI) crystal can be 15-25 mm, the length can be 30-45 mm, and the height can be 30-45 mm, and the surface area ratio of the front end CsI (TI) crystal to the rear end CsI (TI) crystal can be distributed as 0.5-2.

[0015] In the thyroid I-131 activity measurement system based on the double-layer detector provided by the application, the double-layer detector can be a detection structure in which a front-end CsI(TI) crystal and a rear-end CsI(TI) crystal are arranged in front of and behind each other, and the front-to-rear spacing is 1mm-5mm.

[0016] In the thyroid I-131 activity measurement system based on the double-layer detector provided by the application, the circumference of the ring-shaped belt can be adjusted adaptively according to the neck circumference of the human body.

[0017] Effects of the application

[0018] According to the thyroid I-131 activity measurement system based on the double-layer detector provided by the application, the square double-layer detector with a volume close to that of a conventional 2-inch detector is used under the premise of fully ensuring the detection efficiency, and the double-layer detector does not need to be used in cooperation with calibration and fixing equipment such as a jack, and is more lightweight and portable. The close-fitting measurement structure realized by the ring-shaped belt can eliminate the error influence caused by the distance between the neck and the surface of the detector. The application obtains the functional relationship between the ratio of the front and rear CsI(TI) crystals at 365keV photoelectric peaks and the covered tissue thickness, and the functional relationship between the covered tissue thickness and the detection efficiency, and estimates the covered tissue thickness of the measured person individually, performs efficiency correction, and realizes accurate measurement. In addition, the double-layer detector algorithm used by the application reduces the demand for environmental background radiation shielding of the instrument due to the use of the characteristic peak of 365keV which is easy to identify and analyze, and thus can evaluate I-131 with low activity. Therefore, the thyroid I-131 activity measurement system based on the double-layer detector of the application adopts a close-fitting measurement structure and a double-layer CsI(TI) crystal structure with high quantum efficiency, so the detection efficiency is high, the measurement time is short, and the demand for rapid screening and batch measurement in a short time can be met, and the lower detection limit is low. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a system block diagram of a thyroid I-131 activity measurement system based on a double-layer detector in an embodiment of the application;

[0020] Figure 2 is a structural schematic diagram of a thyroid I-131 activity measurement system based on a double-layer detector in an embodiment of the application;

[0021] Figure 3 is a working flowchart of a thyroid I-131 activity measurement system based on a double-layer detector in an embodiment of the application. DETAILED DESCRIPTION

[0022] In order to make the technical means and effects of the present application easy to understand, the present application is specifically described below in combination with embodiments and drawings.

[0023] <Embodiment>

[0024] Figure 1 is a system block diagram of a thyroid I-131 activity measurement system based on a double-layer detector in an embodiment of the present application.

[0025] As shown in Figure 1 , a thyroid I-131 activity measurement system 100 based on a double-layer detector in the embodiment is used to measure the I-131 activity in the human thyroid, and includes a double-layer detector 10, a nuclear electronics device 20, a ring-shaped belt 30, a spectral analysis module 40, a detection efficiency calibration module 50, and a spectrum analysis module 60.

[0026] Figure 2 is a structural schematic diagram of a thyroid I-131 activity measurement system based on a double-layer detector in an embodiment of the present application.

[0027] As shown in Figure 2 , the double-layer detector 10 is used to receive the I-131 emitted γ-rays to the outside of the body and convert the γ-rays into optical signals, and has a front-end CsI(TI) crystal 11 and a rear-end CsI(TI) crystal 12 arranged in front and back.

[0028] The double-layer detector is a detection structure with the front-end CsI(TI) crystal 11 and the rear-end CsI(TI) crystal 12 arranged in front and back, and the front and back spacing is 1mm-5mm.

[0029] The front-end CsI(TI) crystal 11 is closer to the surface of the human neck, and the rear-end Cs(TI) crystal 12 is farther from the surface of the human neck,

[0030] The thickness of the front-end CsI(TI) crystal 11 is 6mm-10mm, the length is 30mm-45mm, and the height is 30mm-45mm,

[0031] The thickness of the rear-end CsI(TI) crystal 12 is 15mm-25mm, the length is 30mm-45mm, and the height is 30mm-45mm,

[0032] The surface area ratio of the front-end Cs(TI) crystal 11 to the rear-end Cs(TI) crystal 12 is distributed as 0.5-2.

[0033] In the embodiment, the size of the front-end CsI(TI) crystal 11 is 37mm*8mm*37mm, and the size of the rear-end CsI(TI) crystal 12 is 37mm*20mm*36mm.

[0034] In this embodiment, the material used by the double-layer detector 10 can also be NaI(TI) crystal.

[0035] The nuclear electronics device 20 is used in conjunction with the double-layer detector 10 to convert the optical signal into an electrical signal.

[0036] The annular band 30 is used to fix the double-layer detector 10 and the nuclear electronics device 20 to the neck of a human body.

[0037] The circumference of the annular band 30 can be adjusted according to the neck circumference of the human body.

[0038] The spectrum analysis module 40 is used to analyze the electrical signal to obtain the energy spectrum of the gamma rays.

[0039] In this embodiment, the spectrum analysis module 40 is GammaAnt.

[0040] The detection efficiency calibration module 50 is used to calibrate the detection efficiency of the double-layer detector 10 to reduce the measurement error caused by the difference in the thickness of the covering tissue from the thyroid to the ventral surface of the neck, and includes an OTT calibration unit for calculating the thickness of the covering tissue and a detection efficiency calibration unit for calculating the detection efficiency.

[0041] The OTT calibration unit establishes a relationship function between the correction factor and the thickness of the covering tissue by changing the thickness of the covering tissue of the thyroid-neck phantom according to the energy spectrum.

[0042] The correction factor is obtained based on the double-layer crystal structure of the double-layer detector 10 by the count ratio of the front-end CsI(TI) crystal 11 and the rear-end CsI(TI) crystal 12 at 365keV full-energy peak.

[0043] The detection efficiency calibration unit establishes a relationship function between the thickness of the covering tissue and the detection efficiency by changing the thickness of the covering tissue of the thyroid-neck phantom according to the energy spectrum.

[0044] The detection efficiency calibration module 50 obtains the correction factor by measuring the double-layer detector 10, and uses the correction factor to bring the relationship function between the correction factor and the thickness of the covering tissue obtained by the OTT calibration unit to calculate the value of the thickness of the covering tissue, and brings the value of the thickness of the covering tissue into the relationship function between the thickness of the covering tissue and the detection efficiency obtained by the detection efficiency calibration unit to obtain the detection efficiency. The energy spectrum analysis module 60 analyzes the energy spectrum of the gamma rays received by the double-layer detector 10 after the detection efficiency calibration, and calculates the accurate measurement value of the I-131 activity in the thyroid.

[0045] Figure 3 is the working flowchart of the thyroid I-131 activity measurement system based on the double-layer detector in the embodiment of the present application.

[0046] As shown in Figure 3 The working process of the thyroid I-131 activity measurement system 100 based on a double-layer detector according to the embodiment includes the following steps:

[0047] Step 1, the double-layer detector 10 and the nuclear electronics device 20 are fixed and attached to the neck of the tester through the annular belt 30, the double-layer detector 10 receives the gamma rays emitted by I-131 to the outside of the body and converts them into optical signals, the optical signals are converted into electrical signals by the nuclear electronics device 20, and the energy spectrum analysis module 40 analyzes the electrical signals to obtain the energy spectrum of the gamma rays;

[0048] Step 2, the OTT calibration unit changes the thickness of the covered tissue of the thyroid-neck phantom according to the energy spectrum, establishes a function relationship between the correction factor (the count ratio of the front-end CsI(TI) crystal 11 and the rear-end CsI(TI) crystal 12 at 365keV full-energy peak) and the thickness of the covered tissue, and the detection efficiency calibration unit changes the thickness of the covered tissue of the thyroid-neck phantom according to the energy spectrum, establishes a function relationship between the thickness of the covered tissue and the detection efficiency, and calculates the detection efficiency;

[0049] Step 3, after the detection efficiency calibration of the double-layer detector 10 is completed, the measurement is started, and the energy spectrum analysis module 60 analyzes the energy spectrum of the gamma rays received by the double-layer detector 10 to obtain the I-131 activity.

[0050] Effects of the embodiment

[0051] According to the thyroid I-131 activity measurement system based on a double-layer detector according to the embodiment, on the premise of fully ensuring the detection efficiency, a square double-layer detector with a volume close to 2 inches of a conventional detector is used, without the need to cooperate with calibration and fixing equipment such as a jack, and it is more lightweight and portable. The close-to-body measurement structure realized by the annular belt can eliminate the error influence caused by the neck-detector surface distance. The embodiment obtains the function relationship between the ratio of the front and rear CsI(TI) crystals at 365keV photoelectric peak and the thickness of the covered tissue, and the function relationship between the thickness of the covered tissue and the detection efficiency, estimates the thickness of the covered tissue of the tester individually, corrects the efficiency, and realizes accurate measurement. In addition, the double-layer detector algorithm used in the embodiment reduces the demand for environmental background radiation shielding of the instrument due to the use of a characteristic peak of 365keV that is easy to identify and analyze, so it can evaluate low-activity I-131. Therefore, the thyroid I-131 activity measurement system based on a double-layer detector according to the embodiment adopts a close-to-body measurement structure and a double-layer CsI(TI) crystal structure with high quantum efficiency, so the detection efficiency is high, the measurement time is short, and it can meet the demand for rapid screening and batch measurement in a short time, and has a low lower detection limit.

[0052] The above embodiments are preferred cases of the present application and are not intended to limit the scope of protection of the present application.

Claims

1. A thyroid I-131 activity measurement system based on a dual-layer detector, used to measure the I-131 activity in the human thyroid gland, characterized in that, The system comprises: a double-layer detector for receiving I-131 emitted gamma rays outside the body and converting the gamma rays into optical signals, having a front-end CsI(TI) crystal and a rear-end CsI(TI) crystal arranged in a front-to-back manner; a nuclear electronics device used in conjunction with the double-layer detector for converting the optical signals into electrical signals; a circular bandage for fixing the double-layer detector and the nuclear electronics device to the neck of a human body; a spectrum analysis module for analyzing the electrical signals to obtain the energy spectrum of the gamma rays; a detection efficiency calibration module for calibrating the detection efficiency of the double-layer detector to reduce measurement errors caused by differences in the thickness of the covering tissue from the thyroid to the ventral surface of the neck, comprising an OTT calibration unit for calculating the thickness of the covering tissue and a detection efficiency calibration unit for calculating the detection efficiency; an energy spectrum analysis module for analyzing the energy spectrum of the gamma rays received by the double-layer detector after calibration to obtain the I-131 activity, wherein the OTT calibration unit establishes a relationship function between the correction factor and the thickness of the covering tissue by changing the thickness of the covering tissue from the thyroid to the neck phantom based on the energy spectrum, the correction factor is obtained based on the double-layer crystal structure of the double-layer detector by the count ratio of the front-end CsI(TI) crystal and the rear-end CsI(TI) crystal at 365keV full-energy peak, the detection efficiency calibration unit establishes a relationship function between the thickness of the covering tissue and the detection efficiency by changing the thickness of the covering tissue from the thyroid to the neck phantom based on the energy spectrum, the detection efficiency calibration module measures the correction factor by the double-layer detector, which is used to bring the relationship function between the correction factor and the thickness of the covering tissue obtained by the OTT calibration unit to calculate the numerical value of the thickness of the covering tissue, and the numerical value of the thickness of the covering tissue is brought into the relationship function between the thickness of the covering tissue and the detection efficiency obtained by the detection efficiency calibration unit to obtain the detection efficiency, and the energy spectrum analysis module analyzes the energy spectrum of the gamma rays received by the double-layer detector after the detection efficiency calibration to calculate the accurate measurement value of the I-131 activity in the thyroid.

2. The double-layer detector-based thyroid I-131 activity measurement system according to claim 1, wherein: wherein the thickness of the front-end CsI(TI) crystal is 6mm-10mm, the length is 30mm-45mm, and the height is 30mm-45mm, the thickness of the rear-end CsI(TI) crystal is 15mm-25mm, the length is 30mm-45mm, and the height is 30mm-45mm, the surface area ratio of the front-end CsI(TI) crystal to the rear-end CsI(TI) crystal is distributed in the range of 0.5-2.

3. The double-layer detector-based thyroid I-131 activity measurement system according to claim 1, wherein: wherein The double-layer detector is a detection structure in which the front-end CsI(TI) crystal and the rear-end CsI(TI) crystal are arranged in front and behind, and the front and rear spacing is 1mm-5mm.

4. The double-layer detector based thyroid I-131 activity measurement system according to claim 1, characterized in that: wherein The circumference of the annular belt can be adjusted adaptively according to the neck circumference of the human body.

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