Radiation dose index evaluation method and measurement phantom system applied to microscopic CT (Computed Tomography)

Abstract

The invention discloses a radiation dose index evaluation method and a measurement phantom system applied to micro-CT, and relates to the technical field of micro-CT system optimization research, the radiation dose index evaluation method comprises the following steps: setting a system structure corresponding to dose measurement, setting an imaging protocol to scan positioning imaging, and reading a reading; introducing a conversion coefficient and combining with the reading of a dose detector to obtain a radiation dose value index; factors influencing the system output dose are analyzed, and effective tube current is defined to be used for normalizing the radiation dose; performing a simulation experiment consistent with a real condition, obtaining a conversion coefficient, and providing a dose evaluation system combining experimental measurement and simulation; standardized application of microscopic CT in biomedical research is promoted, and scientificity of small animal experiments is improved; the cost of dose measurement equipment is reduced, and the quality control capability of a microscopic CT imaging system is improved; a unified microscopic CT radiation dose measurement standard is established, and the data comparability among different laboratories is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of micro-CT system optimization research, and in particular to a radiation dose index evaluation method and a measurement phantom system applied to micro-CT. Background Art

[0002] The measurement of CT radiation dose is crucial in clinical and preclinical studies. Clinical CT usually uses the CT dose index (CTDI) as a measure of radiation dose. This index is defined by the International Commission on Radiological Protection (ICRP) and the U.S. Food and Drug Administration (FDA) and is measured using a standard phantom (acrylic head or torso phantom) and a pencil ionization chamber. However, existing CTDI measurement methods are mainly targeted at clinical CT and are not suitable for small-aperture micro-CT (Micro-CT). The tube voltage, focal spot size, and scanning mode of Micro-CT are different from those of clinical CT, resulting in significant differences in radiation dose distribution and organ absorbed dose calculation. In addition, there is a size mismatch problem in current technology. The diameter of the clinical CTDI phantom is usually 16 cm or 32 cm. m, while the imaging aperture of micro-CT is small (usually in the range of 3-10 cm), and standard CTDI phantoms cannot be used directly for dose measurement; there is also the problem of incompatibility of dose measurement equipment. Traditional CTDI measurement uses a 100 mm long pencil ionization chamber, but the focal size and beam collimation width of micro-CT are small, resulting in the measurement range of the ionization chamber being unsuitable; there is also a lack of standardized methods. For example, current dose measurement of micro-CT mostly uses empirical calculations or Monte Carlo simulations, and there is a lack of unified experimental measurement standards, resulting in incomparable dose measurement results between different devices; and it cannot accurately characterize the dose of small animal organs: the size of experimental animals is much smaller than that of humans, and the existing clinical CT dose measurement methods cannot accurately reflect the radiation dose of various organs of experimental animals under micro-CT scanning. Summary of the Invention

[0003] The object of the present invention is to provide a radiation dose index evaluation method and a measurement phantom system for micro-CT, so as to solve the problems raised in the prior art.

[0004] To achieve the above object, the present invention provides the following technical solution: a radiation dose index evaluation method applied to micro-CT, comprising the following steps:

[0005] S1. Set up the system structure corresponding to the dose measurement, set up the imaging protocol for scanning the positioning imaging, and read the readings on the dose detector;

[0006] S2. Introducing a conversion coefficient and combining it with the reading of the dose detector to obtain a radiation dose value index;

[0007] S3. Analyze the factors that affect the system output dose and define the effective tube current based on the influencing factors to normalize the radiation dose;

[0008] S4. Conduct simulation experiments consistent with real-world conditions, obtain the conversion coefficient between simulation and reality, and provide a dose assessment system that combines experimental measurement and simulation.

[0009] Furthermore, in step S1: a system structure corresponding to dose measurement is set, including the distance from the X-ray source to the imaging center, the position of the dose detector, the placement of the dose detector for radiation dose detection, and readings on the dose detector; a system imaging protocol is set and then a positioning imaging scan is performed. The combination of tube voltage and additional filter type is an imaging protocol. The imaging protocol affects the distribution of the output X-ray spectrum and is not proportional to the radiation dose. Therefore, an imaging protocol is set before performing radiation dose measurement, and then a radiation dose index is measured based on the set imaging protocol;

[0010] Micro CT uses spiral scanning to perform X-ray scanning and detection. The dose detector is placed at the center of the rotation trajectory of the detector and the X-ray source to ensure that the dose detector is fully covered during each scan; and the dose detector reading is read during the scan.

[0011] Furthermore, in step S2: a conversion coefficient is introduced, and a radiation dose value index is defined by combining the conversion coefficient and the dose detector reading; the radiation dose value index definition formula is as follows:

[0012]

[0013] in, represents the dose detector reading; f represents the conversion coefficient obtained by calibration with a standard source; taking the mobileMOSFET model TN-RD-70-W (Best Medical Canada Ltd.) as an example, the dose conversion coefficient of this dose measurement instrument is derived from the calibration results previously conducted by the research team under the secondary standard X-ray radiation field conditions of the Shanghai Institute of Metrology and Testing Technology.

[0014] Furthermore, in step S3: under the same mechanical structure conditions, different tube voltages, additional filter types, single exposure currents, scanning times per revolution, number of images collected per revolution, and pitch sizes will affect the output radiation dose of the system and the absorbed dose of the subject; wherein the combination of tube voltage and additional filter type is called an imaging protocol, and the imaging protocol affects the distribution of the output X-ray spectrum and is not proportional to the radiation dose, so MCTDI is measured for each imaging protocol; the single exposure current size, scanning time per revolution, number of images collected per revolution, and pitch are proportional to the radiation dose, and the effective tube current I is defined based on the influencing factors proportional to the radiation dose. eff Used to normalize MCTDI; effective tube current I eff The definition is as follows:

[0015]

[0016] Among them, I Source Indicates the current size of a single exposure; T indicates the scanning time per circle; N indicates the number of images collected per circle; pitch indicates the screw pitch.

[0017] Further, in step S3: using the defined effective tube current I eff Normalize MCTDI. The definition of normalized MCTDI is as follows:

[0018]

[0019] Among them, MCTDI air Indicates the output of the Micro-CT system in air, reflecting the radiation output level of the equipment. It is the measurement result obtained when the MCTDI phantom is not placed during measurement. phantom The measurement results obtained by placing the MCTDI phantom represent the equivalent absorbed dose of the experimental animals, thereby realizing the calculation of the absorption amount of the experimental subjects, which can be close to the biological dose assessment needs in actual research.

[0020] Furthermore, in step S4, a simulation experiment is performed under the same conditions as the actual imaging conditions in a Monte Carlo simulation to obtain a conversion coefficient STM between the simulation and the actual. The conversion coefficient is expressed as follows:

[0021]

[0022] in, represents the MCTDI measured under actual conditions, It represents the normalized MCTDI on the simulation platform; based on the obtained conversion coefficient STM between simulation and reality, it can provide a dose assessment system that combines experimental measurement with simulation; the radiation dose index assessment method adjusts the traditional CTDI formula to make it suitable for micro-CT, filling the gap in micro-CT dose measurement standards.

[0023] A radiation dose index measurement phantom system for micro-CT includes a phantom structure, a standard measurement slot, and a dose measurement sensor with strong compatibility; the phantom structure is used to provide n measurement positions along the z-axis direction for measuring radiation dose profile distribution numbers.

[0024] Furthermore, the phantom in the phantom structure is made of polymethyl methacrylate material, and phantoms of different sizes are provided for use in micro-CT systems of different specifications; for example, phantoms of two sizes, 25 mm and 50 mm, are provided, which solves the problem that traditional CTDI phantoms cannot be used for micro-CT.

[0025] Furthermore, the standard dose measurement slot is provided inside the phantom for placing the ionization chamber, the MOSFET dose detector and the thermoluminescent dosimeter.

[0026] Furthermore, the dose measurement sensor with strong compatibility can be compatible with a small-sized ionization chamber, a MOSFET sensor, and a film dose measurement system for dose measurement, thereby improving measurement flexibility.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The present invention designs a small-sized dose measurement phantom suitable for micro-CT: it provides two sizes, 25 mm and 50 mm, which solves the problem that traditional CTDI phantoms cannot be used for micro-CT. It also adopts the MCTDI calculation method to adjust the traditional CTDI formula to make it suitable for micro-CT, filling the gap in micro-CT dose measurement standards. It is compatible with a variety of dose measurement equipment and can use different methods such as ionization chambers, MOSFET dose detectors, and TLDs for dose measurement, improving measurement flexibility. The present invention promotes the standardized application of micro-CT in biomedical research and improves the scientific nature of small animal experiments. It reduces the cost of dose measurement equipment and improves the quality control capability of micro-CT imaging systems. It establishes a unified micro-CT radiation dose measurement standard and improves the comparability of data between different laboratories. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the method flow of the radiation dose index evaluation method applied to micro-CT according to the present invention;

[0030] Figure 2Schematic diagram of the rotation trajectory of the detector and source of the radiation dose index measurement phantom system applied to micro-CT in the present invention in the xy plane;

[0031] Figure 3 Schematic diagram of the z-axis plane scanning of the radiation dose index measurement phantom system applied to micro-CT of the present invention;

[0032] Figure 4 A line graph showing the calibration results of the dose conversion coefficient of the radiation dose index evaluation method applied to micro-CT according to the present invention;

[0033] Figure 5 Schematic diagram of the MCTDI measurement phantom structure of the radiation dose index measurement phantom system applied to micro-CT of the present invention;

[0034] Figure 6 Schematic diagram of the dose measurement slot inside the phantom of the radiation dose index measurement phantom system applied to micro-CT of the present invention. DETAILED DESCRIPTION

[0035] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0036] Example: Figures 1-6 As shown, the present invention provides a technical solution for a radiation dose index evaluation method for micro-CT, such as Figure 1 As shown, the following steps are included:

[0037] S1. Set up the system structure corresponding to the dose measurement, set up the imaging protocol for scanning the positioning imaging, and read the readings on the dose detector;

[0038] S2. Introducing a conversion coefficient and combining it with the reading of the dose detector to obtain a radiation dose value index;

[0039] S3. Analyze the factors that affect the system output dose and define the effective tube current based on the influencing factors to normalize the radiation dose;

[0040] S4. Conduct simulation experiments consistent with real-world conditions, obtain the conversion coefficient between simulation and reality, and provide a dose assessment system that combines experimental measurement and simulation.

[0041] In step S1: setting the system structure corresponding to the dose measurement, including the distance from the X-ray source to the imaging center, the position of the dose detector, placing the dose detector for radiation dose detection, and reading the reading on the dose detector; setting a system imaging protocol and then performing a positioning imaging scan. The combination of tube voltage and additional filter type is an imaging protocol. The imaging protocol affects the distribution of the output X-ray spectrum and is not proportional to the radiation dose. Therefore, before performing the radiation dose measurement, an imaging protocol is set, and then the radiation dose index is measured based on the set imaging protocol.

[0042] Micro CT uses spiral scanning to perform X-ray scanning detection, such as Figure 2 and Figure 3 As shown, the dose detector is placed at the center of the rotation trajectory of the detector and the X-ray source to ensure that the dose detector is completely covered during each scan; and the dose detector reading is read during the scan.

[0043] In step S2: a conversion coefficient is introduced, and the radiation dose value index is defined by combining the conversion coefficient and the dose detector reading; the radiation dose value index definition formula is as follows:

[0044]

[0045] in, represents the dose detector reading; f represents the conversion coefficient obtained by calibration with a standard source; taking the mobileMOSFET model TN-RD-70-W (Best Medical Canada Ltd.) as an example, the dose conversion coefficient of this dose measurement instrument is derived from the calibration results previously conducted by the research team under the secondary standard X-ray radiation field conditions of the Shanghai Institute of Metrology and Testing Technology, such as Figure 4 As shown in Figure 1, the calibration result is shown, and the f value is 1.282.

[0046] In step S3: under the same mechanical structure conditions, different tube voltages, additional filter types, single exposure currents, scanning times per revolution, number of images collected per revolution, and pitch sizes will affect the output radiation dose of the system and the absorbed dose of the subject. The combination of tube voltage and additional filter type is called an imaging protocol, which affects the distribution of the output X-ray spectrum and is not proportional to the radiation dose. Therefore, MCTDI is measured for each imaging protocol. The single exposure current, scanning time per revolution, number of images collected per revolution, and pitch are proportional to the radiation dose. The effective tube current I is defined based on the influencing factors proportional to the radiation dose. eff Used to normalize MCTDI; effective tube current I eff The definition is as follows:

[0047]

[0048] Among them, I Source Indicates the current size of a single exposure; T indicates the scanning time per circle; N indicates the number of images collected per circle; pitch indicates the screw pitch.

[0049] In step S3: using the defined effective tube current I eff Normalize MCTDI. The definition of normalized MCTDI is as follows:

[0050]

[0051] Among them, MCTDI air Indicates the output of the Micro-CT system in air, reflecting the radiation output level of the equipment. It is the measurement result obtained when the MCTDI phantom is not placed during measurement. phantom The measurement results obtained by placing the MCTDI phantom represent the equivalent absorbed dose of experimental animals, which is close to the biological dose assessment needs in actual research.

[0052] In step S4: a simulation experiment is performed under the same conditions as the actual imaging conditions in a Monte Carlo simulation to obtain a conversion coefficient STM between the simulation and the actual imaging conditions. The conversion coefficient is expressed as follows:

[0053]

[0054] in, represents the MCTDI measured under actual conditions, It represents the normalized MCTDI on the simulation platform, thereby realizing the calculation of the absorption amount of the experimental object and providing a dose assessment system combining experimental measurement and simulation.

[0055] A radiation dose index measurement phantom system for micro-CT includes a phantom structure, a standard measurement slot, and a dose measurement sensor with strong compatibility; the phantom structure is used to provide n measurement positions along the z-axis direction for measuring radiation dose profile distribution numbers.

[0056] The phantom in the phantom structure is made of polymethyl methacrylate, and phantoms of different sizes are set for micro-CT systems of different specifications, such as phantoms with a diameter of 25 mm or a diameter of 50 mm, such as Figure 5 shown.

[0057] The standard dose measurement slot is set inside the phantom, such as Figure 6 As shown, it is used to place the ionization chamber, MOSFET dose detector and thermoluminescent dosimeter.

[0058] The dose measurement sensor with strong compatibility can be compatible with small-size ionization chambers, MOSFET sensors and film dosimetry systems for dose measurement.

[0059] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

Claims

1. A radiation dose index assessment method for micro-CT, characterized by: The following steps are involved: S1. Set up the system structure corresponding to the dose measurement, set up the imaging protocol for scanning the positioning imaging, and read the readings on the dose detector; S2. Introducing a conversion coefficient and combining it with the reading of the dose detector to obtain a radiation dose value index; S3. Analyze the factors that affect the system output dose and define the effective tube current based on the influencing factors to normalize the radiation dose; S4. Conduct simulation experiments consistent with real-world conditions, obtain the conversion coefficient between simulation and reality, and provide a dose assessment system that combines experimental measurement and simulation.

2. The radiation dose index evaluation method for micro-CT according to claim 1, characterized in that: In step S1: setting the system structure corresponding to the dose measurement, including the distance from the X-ray source to the imaging center, the position of the dose detector, placing the dose detector for radiation dose detection, and reading the reading on the dose detector; setting a system imaging protocol and then performing a positioning imaging scan. The combination of tube voltage and additional filter type is an imaging protocol, and the radiation dose index is measured based on the set imaging protocol; Micro CT uses spiral scanning to perform X-ray scanning and detection. The dose detector is placed at the center of the rotation trajectory of the detector and the X-ray source to ensure that the dose detector is fully covered during each scan; and the dose detector reading is read during the scan.

3. The radiation dose index evaluation method for micro-CT according to claim 1, characterized in that: In step S2: a conversion coefficient is introduced, and the radiation dose value index is defined by combining the conversion coefficient and the dose detector reading; the radiation dose value index definition formula is as follows: in, represents the dose detector reading; f represents the conversion factor obtained by calibration with a standard source.

4. The radiation dose index evaluation method for micro-CT according to claim 1, wherein: In step S3, the single exposure current, scanning time per circle, number of images collected per circle, and pitch are proportional to the radiation dose. The effective tube current I is defined based on the factors that are proportional to the radiation dose. eff Used to normalize MCTDI; effective tube current I eff The definition is as follows: Among them, I Source Indicates the current size of a single exposure; T indicates the scanning time per circle; N indicates the number of images collected per circle; pitch indicates the screw pitch.

5. The radiation dose index evaluation method for micro-CT according to claim 4, characterized in that: In step S3: using the defined effective tube current I eff Normalize MCTDI. The definition of normalized MCTDI is as follows: Among them, MCTDI air / phantom represents the normalized MCTDI.

6. The radiation dose index evaluation method for micro-CT according to claim 1, characterized in that: In step S4: a simulation experiment is performed under the same conditions as the actual imaging conditions in a Monte Carlo simulation to obtain a conversion coefficient STM between the simulation and the actual imaging conditions. The conversion coefficient is expressed as follows: in, represents the MCTDI measured under actual conditions, It represents the normalized MCTDI on the simulation platform; based on the conversion coefficient STM between simulation and reality, a dose evaluation system combining experimental measurement and simulation can be provided.

7. A radiation dose index measurement phantom system for micro-CT, characterized by: The measurement phantom system includes a phantom structure, a standard measurement slot and a dose measurement sensor; the phantom structure is used to provide n measurement positions along the z-axis direction for measuring radiation dose profile distribution numbers.

8. The radiation dose index measurement phantom system for micro-CT according to claim 7, characterized in that: The phantom in the phantom structure is made of polymethyl methacrylate material, and phantoms of different sizes are provided for micro-CT systems of different specifications.

9. The radiation dose index measurement phantom system for micro-CT according to claim 7, characterized in that: The standard dose measurement slot is arranged inside the phantom and is used for placing an ionization chamber, a MOSFET dose detector and a thermoluminescent dose meter.

10. The radiation dose index measurement phantom system for micro-CT according to claim 7, characterized in that: The dose measurement sensor is compatible with a small-sized ionization chamber, a MOSFET sensor, and a film dose measurement system for dose measurement.

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