Many scientific domains use gamma-ray spectrometry, but non-destructive gamma scanning and gamma emission tomography of radioactive fuel in particular. In the experimental setting, a collimator is frequently employed ...Many scientific domains use gamma-ray spectrometry, but non-destructive gamma scanning and gamma emission tomography of radioactive fuel in particular. In the experimental setting, a collimator is frequently employed to focus on a particular location of interest in the fuel. Predictive models for the transmitted gamma-ray intensity through the collimator are required for both the optimization of instrument design and the planning of measurement campaigns. Gamma-ray transport accuracy is frequently predicted using Monte Carlo radiation transport methods, but using these tools in low-efficiency experimental setups is challenging due to the lengthy computation times needed. This study focused on the full-energy peak intensity that was transmitted through several collimator designs, including rectangle and cylinder. The rate of photons arriving at a detector on the other side of the collimator was calculated for anisotropic source of SNM (U<sub>3</sub>O<sub>8</sub>). Some geometrical assumptions that depended on the source-to-collimator distance and collimator dimensions (length, radius or length, height, and width) were applied to achieve precise findings.展开更多
The world's first full Experimental Advanced Superconducting Tokamak(EAST) is designed with the auxiliary heating method of neutral beam injection(NBI)system. Beam collimators are arranged on both sides of the bea...The world's first full Experimental Advanced Superconducting Tokamak(EAST) is designed with the auxiliary heating method of neutral beam injection(NBI)system. Beam collimators are arranged on both sides of the beam channel for absorbing the divergence beam during the beam transmission process in the EAST-NBI system.The gas baffle entrance collimator(GBEC) is a typical high-heat-flux component located at the entrance of gas baffle. An efficient and accurate analysis of its thermodynamic performance is of great significance to explore the working limit and to ensure safe operation of the system under a high-parameter steady-state condition. Based on the thermo-fluid coupled method, thermodynamic analysis and simulation of GBEC is performed to get the working states and corresponding operating limits at different beam extraction conditions. This study provides a theoretical guidance for the next step to achieve long pulse with highpower experimental operation and has an important reference to ensure the safe operation of the system.展开更多
Objective Radiotherapy combined with conservative surgery plays an important role in the treatment of early-stage breast cancer. Volumetric modulated arc therapy(VMAT) has been introduced into clinical practice. The p...Objective Radiotherapy combined with conservative surgery plays an important role in the treatment of early-stage breast cancer. Volumetric modulated arc therapy(VMAT) has been introduced into clinical practice. The purpose of this study was to investigate the dosimetric effects of different multileaf collimators(MLC) on VMAT radiotherapy plans for treating breast cancer.Methods Fifteen breast cancer patients who were treated using a conventional technique in our department were selected to participate in this retrospective analysis. VMAT plans based on three types of Elekta MLCs [Beam Modulator(BM) with 4-mm leaf width, Agility with 5-mm leaf width and MLCi2 with 10-mm leaf width] were independently generated for each patient. Plan comparisons were performed based on dose-volume histogram(DVH) analysis including dosimetric parameters such as the homogeneity index(HI), conformity index(CI), Dmax, Dmin, and Dmean for the planning treatment volume(PTV), in addition to dose-volume parameters for the organs at risk(OARs). The delivery efficiency of the three types of MLCs was compared in terms of the beam delivery time and the monitor units(MUs) per fraction for each plan. Results Both target uniformity and conformity were improved in plans for Agility and BM MLC compared with the plan using MLCi2. The mean HI decreased from 1.14 for MLCi2 to 1.13 for BM and 1.10 for Agility, while the mean CI increased from 0.68 for MLCi2 to 0.73 for BM and 0.75 for Agility. Furthermore, at both low and high dose levels, smaller volumes of ipsilateral lung, heart, contralateral lung, and breast were irradiated with Agility MLC than with the other two types of MLCs. The delivery time with Agility MLC was reduced by 10.8% and 32.1%, respectively, compared with that for MLCi2 and BM.Conclusion Our results indicate that the Agility MLC exhibits a dosimetric advantage and a significant improvement in delivery efficiency for the treatment of breast cancer using VMAT.展开更多
A space-borne hard X-ray collimator,comprising 91 pairs of grids,has been developed for the Hard X-ray Imager(HXI).The HXI is one of the three scientific instruments onboard the first Chinese solar mission:the Advance...A space-borne hard X-ray collimator,comprising 91 pairs of grids,has been developed for the Hard X-ray Imager(HXI).The HXI is one of the three scientific instruments onboard the first Chinese solar mission:the Advanced Space-based Solar Observatory(ASO-S).The HXI collimator(HXI-C)is a spatial modulation X-ray telescope designed to observe hard X-rays emitted by energetic electrons in solar flares.This paper presents the detailed design of the HXI-C for the qualification model that will be inherited by the flight model.Series tests on the HXI-C qualification model are reported to verify the ability of the HXI-C to survive the launch and to operate normally in on-orbit environments.Furthermore,results of the X-ray beam test for the HXI-C are presented to indirectly identify the working performance of the HXI-C.展开更多
The Adaptive Quality Control Phantom (AQCP) is a computer-controlled phantom which positions and moves a radioactive source in the Field of View (FOV) of an imaging nuclear medicine device on a definite path to produc...The Adaptive Quality Control Phantom (AQCP) is a computer-controlled phantom which positions and moves a radioactive source in the Field of View (FOV) of an imaging nuclear medicine device on a definite path to produce a spatial distribution of gamma rays to perform QC Tests such as the Collimator Hole Angulation (CHA) and the Center of Rotation (COR) of Single Photon Emission Computer Tomography (SPECT). The collimator hole angulation for six collimators was measured using a point source and a computer-controlled cylindrical positioning system. In this method, the displacement of the image of a point source was examined as the AQCP was moving point source vertically away from the collimator face. The results of the high-accuracy measurement method of CHA show that the measurement accuracy for absolute angulation errors is better than ±0.024°. The Root Mean Square (RMS) of CHA for LEHR, LEHS and LEUHR collimators of SMV dual heads camera and LEGP, MEGP and HEGP of GE Millennium MG were evaluated to be 0.290°, 0.292°, 0.208°, 0.154°, 0.220° and 0.202°, respectively. It is to be added in this connection that the evaluated RMS of CHA for LEHR collimator with the distance variation from the collimator’s surface ±1 mm has been varied ±0.04 degree. A new method for the center of rotation assessment by AQCP is introduced and the results of this proposed method as compared with the routine QC test and their differences are discussed in detail. We defined and measured a new parameter called Dynamic Mechanical Error (DME) for applying the gantry motion correction.展开更多
To obtain a small-angle monoenergetic neutron source,a shielding collimator device is designed for the neutron source generated by a neutron tube.The device is divided into the collimator and the capture cave.The coll...To obtain a small-angle monoenergetic neutron source,a shielding collimator device is designed for the neutron source generated by a neutron tube.The device is divided into the collimator and the capture cave.The collimator is made of three layers of stainless steel and borated polyethylene and is used to constrain neutrons in a small angle.The capture cave is used to increase the number of times neutron inelastic scattering occurs in the opposite direction of the radiation field,thereby reducing the proportion of scattered neutrons in the radiation field.Material thickness,aperture size,and the optimum structure of the capture cave were simulated using MCNP.The design features a neutron emission angle within a range of 3° and neutron fluxes in the radiation field,which are higher by two orders of magnitude than those outside the radiation field.This research has practical value for the generation of monoenergetic small-angle neutron sources and neutron applications.展开更多
The flow properties and substrate deposition rate profile, which are the important parameters in electron beam physical vapor deposition, are investigated computationally in this article.Collimators are used to achiev...The flow properties and substrate deposition rate profile, which are the important parameters in electron beam physical vapor deposition, are investigated computationally in this article.Collimators are used to achieve the desired vapor beam and deposition rate profile in some applications.This increases the difficulty measuring boundary conditions and the size of the liquid metal pool inside the collimators.It is accordingly hard to obtain accurate results from numerical calculations.In this article, two-dimensional direct simulation Monte Carlo(DSMC) codes are executed to quantify the influence of uncertainties of boundary conditions and pool sizes.Then, three-dimensional DSMC simulations are established to simulate cerium and neodymium evaporation with the collimator.Experimental and computational results of substrate deposition rate profile are in excellent agreement at various evaporation rates and substrate heights.The results show that the DSMC method can assist in metal evaporation with a collimator.展开更多
Needs in scintimammography applications,especially for small animal cardiac imaging,lead to develop a small field of view,high spatial resolution gamma camera with a pinhole collimator.However the ideal pinhole collim...Needs in scintimammography applications,especially for small animal cardiac imaging,lead to develop a small field of view,high spatial resolution gamma camera with a pinhole collimator.However the ideal pinhole collimator must keep a compromise between spatial resolution and sensitivity.In order to design a pinhole collimator with an optimized sensitivity and spatial resolution,the spatial resolution and the geometric sensitivity response as a function of the source to collimator distance has been obtained by means of Monte-Carlo simulation for a small field of view gamma camera with a pinhole collimator of various-hole diameters.The results show that the camera with pinhole of 1 mm,1.5 mm and 2 mm diameter has respectively spatial resolution of 1.5 mm,2.25 mm and 3 mm and geometric sensitivity of 0.016%,0.022%and 0.036%,while the source to collimator distance is 3 cm.We chose the pinhole collimator with hole diameter size of 1.2 mm for our the gamma camera designed based on the trade-off between sensitivity and resolution.展开更多
A compact terahertz （THz） wave collimator is proposed, which works under the frequency from 2.4 THz to 2.7 THz with a photonic crystal （PC） slab based on the self-collimation effect. The plane wave expansion （PWE...A compact terahertz （THz） wave collimator is proposed, which works under the frequency from 2.4 THz to 2.7 THz with a photonic crystal （PC） slab based on the self-collimation effect. The plane wave expansion （PWE） method is used to calculate the dispersion surfaces and the equal-frequency contours （EFCs） and optimize the structure. The propagation of the THz waves in the structure is simulated and the normalized transmission is calculated by using the finite-difference time-domain （FDTD） method with perfectly matched layer （PML） absorbing boundary conditions. Numerical simulations show that the designed collimator has a good collimation property and a high transmittance.展开更多
To the transverse beam collimation system in a rapid cycling synchrotron,an important component is the primary collimator,which improves emittance of the beam halo particles such that the particles outside the predefi...To the transverse beam collimation system in a rapid cycling synchrotron,an important component is the primary collimator,which improves emittance of the beam halo particles such that the particles outside the predefined trajectory can be absorbed by the secondary collimators.Given the material properties and power deposition distribution,the beam scraper of the primary collimator is a0.17 mm tungsten foil on a double face-wedged copper block of 121.5 mm x 20 mm.The heat is transferred to the outside by a φ34 mm copper rod.In this paper,for minimizing brazing thermal stress,we report our theoretical analysis and tests on brazing the tungsten and copper materials which differ greatly in size.We show that the thermal stress effect can be controlled effectively by creating stress relief grooves on the copper block and inserting a tungsten transition layer into the copper block.This innovation contributes to the successful R&D of the primary collimator.And this study may be of help for working out a brazing plan of similar structures.展开更多
A new compact gamma camera for small object imaging has been developed.It consists of a pixelized Nal(T1) scintillator array coupled to a position sensitive photomultiplier tube (Hamamatsu R2486) with a parallel-hole ...A new compact gamma camera for small object imaging has been developed.It consists of a pixelized Nal(T1) scintillator array coupled to a position sensitive photomultiplier tube (Hamamatsu R2486) with a parallel-hole lead collimator.The compact camera has better spatial resolution than Anger camera.The average value of intrinsic spatial resolutions is 2.3 mm (FWHM).The overall spatial resolution (FWHM) is 3,5 and 6 mm at 0,2.5 and 3 mm SCD (source-to-collimator distance),respectively.The phantom studies with the compact camera have demonstrated that parallel-hole collimator gamma camera is a practical technique for nuclear medicine application.展开更多
A set of point spread functions (PSF) has been obtained by means of Monte-Carlo simulation for asmall gamma camera with a pinhole collimator of various hole diameters. The FOV (field of view) of the camera isexpended ...A set of point spread functions (PSF) has been obtained by means of Monte-Carlo simulation for asmall gamma camera with a pinhole collimator of various hole diameters. The FOV (field of view) of the camera isexpended from 45 mm to 70 mm in diameter. The position dependence of the variances of PSF is presented, and theacceptance for the 140 kev gamma rays is explored. A phantom of 70 mm in diameter was experimentally imaged inthe camera with effective FOV of only 45 mm in diameter.展开更多
The Adaptive Quality Control Phantom (AQCP) is the computer-controlled phantom which positions and moves a radioactive source in the Field of View (FOV) of an imaging nuclear medicine device on a definite path to prod...The Adaptive Quality Control Phantom (AQCP) is the computer-controlled phantom which positions and moves a radioactive source in the Field of View (FOV) of an imaging nuclear medicine device on a definite path to produce any spatial distribution of gamma rays to perform the QC Tests such as the Collimator Hole Angulation (CHA) of Single Photon Emission Computer Tomography (SPECT). The collimator hole angulation for seven collimators were measured with the method by using a point source and computer-controlled cylindrical positioning. In this method the displacement of the image of a point source examined as the AQCP move point source vertically away from the collimator face. The results of the high-accuracy measurement method of CHA show that the measurement accuracy for absolute angulation errors is better than ±0.024°. The Root Mean Square (RMS) of CHA for LEHR, LEHS, LEUHR, MEGP-250, MEGP-300, MEGP-360 and HEPH collimators of SMV dual heads camera were measured to be 0.290°, 0.292°, 0.208°, 0.194°, 0.181°, 0.177°, 0.150°, respectively. The Root Mean Square (RMS) of CHA for LEGP, MEGP and HEGP collimators of GE Millennium MG were measured to be 0.154°, 0.220° and 0.202° respectively. It is to be added in this connection that the measured RMS of CHA for LEHR collimator with the distance variation from the collimator’s surface +/– 1 mm has been varied +/– 0.04 degree.展开更多
Gradient-index rod lens (GRIN-lens) whose pitch is ordinary value with bevel ferrule coupling system is analyzed, an equivalent method which can be used to analyze this system is put forward, and a general formula for...Gradient-index rod lens (GRIN-lens) whose pitch is ordinary value with bevel ferrule coupling system is analyzed, an equivalent method which can be used to analyze this system is put forward, and a general formula for determining the coupling loss with axes mismatch, radial mismatch, and angular mismatch is derived by use of the Gaussian field approximation and mode-field coupling theory. The experimental results are in good agreement with the theory prediction. It indicates that these formulas are suitable to analyze the gradient-index rod lens coupling system with pigtail fiber.展开更多
Objective The aiom of the study was to compare the impacts of two types of multileaf collimators （MLC） [standard MLC with a width of 10 mm （sMLC） and micro-MLC with a width of 5 mm （mMLC）] on volumetric modulate...Objective The aiom of the study was to compare the impacts of two types of multileaf collimators （MLC） [standard MLC with a width of 10 mm （sMLC） and micro-MLC with a width of 5 mm （mMLC）] on volumetric modulated arc therapy （VMAT） planning for malignant pleural mesothelioma. Methods VMAT for ten patients with inoperable malignant pleural mesotheliomas was retrospectively planned with the sMLC and mMLC. Histogram-based dose-volume parameters of the planning target vol- ume （PTV） [conformity index （CI） and homogeneous index （HI）] and organs-at-risk were compared for VMAT plans with sMLC （sMLC-VMAT） and mMLC （mMLC-VMAT）. Results The mMLC-VMAT plans were more efficient （average delivery time： 2.67±1.49 min） than the sMLC-VMAT plans （average delivery time： 4.21 ± 2.03 min; P 〈 0.05）. Moreover, compared to the sMLC plans, the mMLC plans demonstrated advantages in the dose coverage of the PTV （CI 0.75 ± 0.08 vs 0.73± 0.09; HI 1.09 ±0.02 vs 1.10± 0.02）, although the difference was not statistically significant （P 〉 0.05）. In addition, significant dose sparing in the fraction of the ipsilateral lung volume receiving 〉 20 Gy （V20; 54.72± 27.08 vs 58.52 ± 29.30） and 〉 30 Gy （V30; 42.74 ± 27.86 vs 46.86± 31.49） radiation, respectively, was observed for the mMLC plans （P 〈 0.05）. Conclusion Comparing sMLC-VMAT and mMLC-VMAT not only demonstrated the higher efficiency and better optimal target coverage of mMLC-VMAT, but also considerably improved the dose sparing of the ipsilateral lung in the VMAT plans for mali qnant pleural mesothelioma.展开更多
In gamma camera and single-photon emission computerized tomography, the collimator removes most photons. Here, a gamma camera without collimator utilizes a specific arrangement of detectors. Instead of bending beams(l...In gamma camera and single-photon emission computerized tomography, the collimator removes most photons. Here, a gamma camera without collimator utilizes a specific arrangement of detectors. Instead of bending beams(like a lens) or directing beams(by parallel hole collimator), changes are created in detectors' field of view(FOV), so that each detector's FOV looks different from others. Simulation proved this theory, with 98 detectors(2 cm 9 1.41 cm) arranged in a zigzag manner for Monte Carlo simulation. A radioactive source with energy of140 ke V was situated on the detectors' faces. Sixty projections, each 3(0 –179) apart, were simulated by Monte Carlo N-Particle(MCNP) 4C code, rotating detectors around a radioactive point. The band containing the radioactive source is clearly visible in each projection.Counts obtained after simulation in different projections were reconstructed, and point source location emerged correctly. Simulation of gamma camera with zigzag arrangement of detectors and MCNP-4C code demonstrated that one could string the space and determine radioactive source by image reconstruction without using collimators, solely through these special detectors' distribution.展开更多
In this paper,the spatial resolution and geometry sensitivity of parallel- and pin-hole collimators in compact gamma camera are presented,and quantitatively compared by GEANT4 code in Monte-Carlo library.The results s...In this paper,the spatial resolution and geometry sensitivity of parallel- and pin-hole collimators in compact gamma camera are presented,and quantitatively compared by GEANT4 code in Monte-Carlo library.The results show that the geometry sensitivity for pinhole collimator rapidly drops with increasing the gamma source-to- collimator distance(SCD);and for parallel-hole collimator,mildly.Meanwhile,the spatial resolution for pin-hole collimator mildly deteriorates;and for parallel-hole collimator,severely.The pin-hole collimator for close imaging objects has higher geometry sensitivity than parallel-hole collimator.Our findings are helpful for setting compact gamma camera collimators in nuclear medicine imaging.展开更多
文摘Many scientific domains use gamma-ray spectrometry, but non-destructive gamma scanning and gamma emission tomography of radioactive fuel in particular. In the experimental setting, a collimator is frequently employed to focus on a particular location of interest in the fuel. Predictive models for the transmitted gamma-ray intensity through the collimator are required for both the optimization of instrument design and the planning of measurement campaigns. Gamma-ray transport accuracy is frequently predicted using Monte Carlo radiation transport methods, but using these tools in low-efficiency experimental setups is challenging due to the lengthy computation times needed. This study focused on the full-energy peak intensity that was transmitted through several collimator designs, including rectangle and cylinder. The rate of photons arriving at a detector on the other side of the collimator was calculated for anisotropic source of SNM (U<sub>3</sub>O<sub>8</sub>). Some geometrical assumptions that depended on the source-to-collimator distance and collimator dimensions (length, radius or length, height, and width) were applied to achieve precise findings.
基金supported by the National Natural Science Foundation of China(No.11605234)the Foundation of ASIPP(No.DSJJ-15-GC02)
文摘The world's first full Experimental Advanced Superconducting Tokamak(EAST) is designed with the auxiliary heating method of neutral beam injection(NBI)system. Beam collimators are arranged on both sides of the beam channel for absorbing the divergence beam during the beam transmission process in the EAST-NBI system.The gas baffle entrance collimator(GBEC) is a typical high-heat-flux component located at the entrance of gas baffle. An efficient and accurate analysis of its thermodynamic performance is of great significance to explore the working limit and to ensure safe operation of the system under a high-parameter steady-state condition. Based on the thermo-fluid coupled method, thermodynamic analysis and simulation of GBEC is performed to get the working states and corresponding operating limits at different beam extraction conditions. This study provides a theoretical guidance for the next step to achieve long pulse with highpower experimental operation and has an important reference to ensure the safe operation of the system.
文摘Objective Radiotherapy combined with conservative surgery plays an important role in the treatment of early-stage breast cancer. Volumetric modulated arc therapy(VMAT) has been introduced into clinical practice. The purpose of this study was to investigate the dosimetric effects of different multileaf collimators(MLC) on VMAT radiotherapy plans for treating breast cancer.Methods Fifteen breast cancer patients who were treated using a conventional technique in our department were selected to participate in this retrospective analysis. VMAT plans based on three types of Elekta MLCs [Beam Modulator(BM) with 4-mm leaf width, Agility with 5-mm leaf width and MLCi2 with 10-mm leaf width] were independently generated for each patient. Plan comparisons were performed based on dose-volume histogram(DVH) analysis including dosimetric parameters such as the homogeneity index(HI), conformity index(CI), Dmax, Dmin, and Dmean for the planning treatment volume(PTV), in addition to dose-volume parameters for the organs at risk(OARs). The delivery efficiency of the three types of MLCs was compared in terms of the beam delivery time and the monitor units(MUs) per fraction for each plan. Results Both target uniformity and conformity were improved in plans for Agility and BM MLC compared with the plan using MLCi2. The mean HI decreased from 1.14 for MLCi2 to 1.13 for BM and 1.10 for Agility, while the mean CI increased from 0.68 for MLCi2 to 0.73 for BM and 0.75 for Agility. Furthermore, at both low and high dose levels, smaller volumes of ipsilateral lung, heart, contralateral lung, and breast were irradiated with Agility MLC than with the other two types of MLCs. The delivery time with Agility MLC was reduced by 10.8% and 32.1%, respectively, compared with that for MLCi2 and BM.Conclusion Our results indicate that the Agility MLC exhibits a dosimetric advantage and a significant improvement in delivery efficiency for the treatment of breast cancer using VMAT.
基金supported by the Strategic Priority Research Program on Space Science,Chinese Academy of Sciences(No.XDA 15320104)the National Natural Science Foundation of China(Grant Nos.11803093,11973097 and 12022302)the Scientific Instrument Developing Project of the CAS(No.20200077)。
文摘A space-borne hard X-ray collimator,comprising 91 pairs of grids,has been developed for the Hard X-ray Imager(HXI).The HXI is one of the three scientific instruments onboard the first Chinese solar mission:the Advanced Space-based Solar Observatory(ASO-S).The HXI collimator(HXI-C)is a spatial modulation X-ray telescope designed to observe hard X-rays emitted by energetic electrons in solar flares.This paper presents the detailed design of the HXI-C for the qualification model that will be inherited by the flight model.Series tests on the HXI-C qualification model are reported to verify the ability of the HXI-C to survive the launch and to operate normally in on-orbit environments.Furthermore,results of the X-ray beam test for the HXI-C are presented to indirectly identify the working performance of the HXI-C.
文摘The Adaptive Quality Control Phantom (AQCP) is a computer-controlled phantom which positions and moves a radioactive source in the Field of View (FOV) of an imaging nuclear medicine device on a definite path to produce a spatial distribution of gamma rays to perform QC Tests such as the Collimator Hole Angulation (CHA) and the Center of Rotation (COR) of Single Photon Emission Computer Tomography (SPECT). The collimator hole angulation for six collimators was measured using a point source and a computer-controlled cylindrical positioning system. In this method, the displacement of the image of a point source was examined as the AQCP was moving point source vertically away from the collimator face. The results of the high-accuracy measurement method of CHA show that the measurement accuracy for absolute angulation errors is better than ±0.024°. The Root Mean Square (RMS) of CHA for LEHR, LEHS and LEUHR collimators of SMV dual heads camera and LEGP, MEGP and HEGP of GE Millennium MG were evaluated to be 0.290°, 0.292°, 0.208°, 0.154°, 0.220° and 0.202°, respectively. It is to be added in this connection that the evaluated RMS of CHA for LEHR collimator with the distance variation from the collimator’s surface ±1 mm has been varied ±0.04 degree. A new method for the center of rotation assessment by AQCP is introduced and the results of this proposed method as compared with the routine QC test and their differences are discussed in detail. We defined and measured a new parameter called Dynamic Mechanical Error (DME) for applying the gantry motion correction.
文摘To obtain a small-angle monoenergetic neutron source,a shielding collimator device is designed for the neutron source generated by a neutron tube.The device is divided into the collimator and the capture cave.The collimator is made of three layers of stainless steel and borated polyethylene and is used to constrain neutrons in a small angle.The capture cave is used to increase the number of times neutron inelastic scattering occurs in the opposite direction of the radiation field,thereby reducing the proportion of scattered neutrons in the radiation field.Material thickness,aperture size,and the optimum structure of the capture cave were simulated using MCNP.The design features a neutron emission angle within a range of 3° and neutron fluxes in the radiation field,which are higher by two orders of magnitude than those outside the radiation field.This research has practical value for the generation of monoenergetic small-angle neutron sources and neutron applications.
文摘The flow properties and substrate deposition rate profile, which are the important parameters in electron beam physical vapor deposition, are investigated computationally in this article.Collimators are used to achieve the desired vapor beam and deposition rate profile in some applications.This increases the difficulty measuring boundary conditions and the size of the liquid metal pool inside the collimators.It is accordingly hard to obtain accurate results from numerical calculations.In this article, two-dimensional direct simulation Monte Carlo(DSMC) codes are executed to quantify the influence of uncertainties of boundary conditions and pool sizes.Then, three-dimensional DSMC simulations are established to simulate cerium and neodymium evaporation with the collimator.Experimental and computational results of substrate deposition rate profile are in excellent agreement at various evaporation rates and substrate heights.The results show that the DSMC method can assist in metal evaporation with a collimator.
基金Supported by National Foundation of Nature Science of China(No.10275063)
文摘Needs in scintimammography applications,especially for small animal cardiac imaging,lead to develop a small field of view,high spatial resolution gamma camera with a pinhole collimator.However the ideal pinhole collimator must keep a compromise between spatial resolution and sensitivity.In order to design a pinhole collimator with an optimized sensitivity and spatial resolution,the spatial resolution and the geometric sensitivity response as a function of the source to collimator distance has been obtained by means of Monte-Carlo simulation for a small field of view gamma camera with a pinhole collimator of various-hole diameters.The results show that the camera with pinhole of 1 mm,1.5 mm and 2 mm diameter has respectively spatial resolution of 1.5 mm,2.25 mm and 3 mm and geometric sensitivity of 0.016%,0.022%and 0.036%,while the source to collimator distance is 3 cm.We chose the pinhole collimator with hole diameter size of 1.2 mm for our the gamma camera designed based on the trade-off between sensitivity and resolution.
基金supported by the National Natural Science Foundation of China under Grant No.60588502
文摘A compact terahertz （THz） wave collimator is proposed, which works under the frequency from 2.4 THz to 2.7 THz with a photonic crystal （PC） slab based on the self-collimation effect. The plane wave expansion （PWE） method is used to calculate the dispersion surfaces and the equal-frequency contours （EFCs） and optimize the structure. The propagation of the THz waves in the structure is simulated and the normalized transmission is calculated by using the finite-difference time-domain （FDTD） method with perfectly matched layer （PML） absorbing boundary conditions. Numerical simulations show that the designed collimator has a good collimation property and a high transmittance.
基金supported by the National Natural Science Foundation of China(No.11375217)
文摘To the transverse beam collimation system in a rapid cycling synchrotron,an important component is the primary collimator,which improves emittance of the beam halo particles such that the particles outside the predefined trajectory can be absorbed by the secondary collimators.Given the material properties and power deposition distribution,the beam scraper of the primary collimator is a0.17 mm tungsten foil on a double face-wedged copper block of 121.5 mm x 20 mm.The heat is transferred to the outside by a φ34 mm copper rod.In this paper,for minimizing brazing thermal stress,we report our theoretical analysis and tests on brazing the tungsten and copper materials which differ greatly in size.We show that the thermal stress effect can be controlled effectively by creating stress relief grooves on the copper block and inserting a tungsten transition layer into the copper block.This innovation contributes to the successful R&D of the primary collimator.And this study may be of help for working out a brazing plan of similar structures.
基金Supported by National Natural Science Foundation of China (No.10275063)
文摘A new compact gamma camera for small object imaging has been developed.It consists of a pixelized Nal(T1) scintillator array coupled to a position sensitive photomultiplier tube (Hamamatsu R2486) with a parallel-hole lead collimator.The compact camera has better spatial resolution than Anger camera.The average value of intrinsic spatial resolutions is 2.3 mm (FWHM).The overall spatial resolution (FWHM) is 3,5 and 6 mm at 0,2.5 and 3 mm SCD (source-to-collimator distance),respectively.The phantom studies with the compact camera have demonstrated that parallel-hole collimator gamma camera is a practical technique for nuclear medicine application.
基金Supported by the National Natural Science Foundation of China(10275063)
文摘A set of point spread functions (PSF) has been obtained by means of Monte-Carlo simulation for asmall gamma camera with a pinhole collimator of various hole diameters. The FOV (field of view) of the camera isexpended from 45 mm to 70 mm in diameter. The position dependence of the variances of PSF is presented, and theacceptance for the 140 kev gamma rays is explored. A phantom of 70 mm in diameter was experimentally imaged inthe camera with effective FOV of only 45 mm in diameter.
文摘The Adaptive Quality Control Phantom (AQCP) is the computer-controlled phantom which positions and moves a radioactive source in the Field of View (FOV) of an imaging nuclear medicine device on a definite path to produce any spatial distribution of gamma rays to perform the QC Tests such as the Collimator Hole Angulation (CHA) of Single Photon Emission Computer Tomography (SPECT). The collimator hole angulation for seven collimators were measured with the method by using a point source and computer-controlled cylindrical positioning. In this method the displacement of the image of a point source examined as the AQCP move point source vertically away from the collimator face. The results of the high-accuracy measurement method of CHA show that the measurement accuracy for absolute angulation errors is better than ±0.024°. The Root Mean Square (RMS) of CHA for LEHR, LEHS, LEUHR, MEGP-250, MEGP-300, MEGP-360 and HEPH collimators of SMV dual heads camera were measured to be 0.290°, 0.292°, 0.208°, 0.194°, 0.181°, 0.177°, 0.150°, respectively. The Root Mean Square (RMS) of CHA for LEGP, MEGP and HEGP collimators of GE Millennium MG were measured to be 0.154°, 0.220° and 0.202° respectively. It is to be added in this connection that the measured RMS of CHA for LEHR collimator with the distance variation from the collimator’s surface +/– 1 mm has been varied +/– 0.04 degree.
文摘Gradient-index rod lens (GRIN-lens) whose pitch is ordinary value with bevel ferrule coupling system is analyzed, an equivalent method which can be used to analyze this system is put forward, and a general formula for determining the coupling loss with axes mismatch, radial mismatch, and angular mismatch is derived by use of the Gaussian field approximation and mode-field coupling theory. The experimental results are in good agreement with the theory prediction. It indicates that these formulas are suitable to analyze the gradient-index rod lens coupling system with pigtail fiber.
文摘Objective The aiom of the study was to compare the impacts of two types of multileaf collimators （MLC） [standard MLC with a width of 10 mm （sMLC） and micro-MLC with a width of 5 mm （mMLC）] on volumetric modulated arc therapy （VMAT） planning for malignant pleural mesothelioma. Methods VMAT for ten patients with inoperable malignant pleural mesotheliomas was retrospectively planned with the sMLC and mMLC. Histogram-based dose-volume parameters of the planning target vol- ume （PTV） [conformity index （CI） and homogeneous index （HI）] and organs-at-risk were compared for VMAT plans with sMLC （sMLC-VMAT） and mMLC （mMLC-VMAT）. Results The mMLC-VMAT plans were more efficient （average delivery time： 2.67±1.49 min） than the sMLC-VMAT plans （average delivery time： 4.21 ± 2.03 min; P 〈 0.05）. Moreover, compared to the sMLC plans, the mMLC plans demonstrated advantages in the dose coverage of the PTV （CI 0.75 ± 0.08 vs 0.73± 0.09; HI 1.09 ±0.02 vs 1.10± 0.02）, although the difference was not statistically significant （P 〉 0.05）. In addition, significant dose sparing in the fraction of the ipsilateral lung volume receiving 〉 20 Gy （V20; 54.72± 27.08 vs 58.52 ± 29.30） and 〉 30 Gy （V30; 42.74 ± 27.86 vs 46.86± 31.49） radiation, respectively, was observed for the mMLC plans （P 〈 0.05）. Conclusion Comparing sMLC-VMAT and mMLC-VMAT not only demonstrated the higher efficiency and better optimal target coverage of mMLC-VMAT, but also considerably improved the dose sparing of the ipsilateral lung in the VMAT plans for mali qnant pleural mesothelioma.
基金supported by grants from Rafsanjan University of Medical Sciences,Rafsanjan,Iran
文摘In gamma camera and single-photon emission computerized tomography, the collimator removes most photons. Here, a gamma camera without collimator utilizes a specific arrangement of detectors. Instead of bending beams(like a lens) or directing beams(by parallel hole collimator), changes are created in detectors' field of view(FOV), so that each detector's FOV looks different from others. Simulation proved this theory, with 98 detectors(2 cm 9 1.41 cm) arranged in a zigzag manner for Monte Carlo simulation. A radioactive source with energy of140 ke V was situated on the detectors' faces. Sixty projections, each 3(0 –179) apart, were simulated by Monte Carlo N-Particle(MCNP) 4C code, rotating detectors around a radioactive point. The band containing the radioactive source is clearly visible in each projection.Counts obtained after simulation in different projections were reconstructed, and point source location emerged correctly. Simulation of gamma camera with zigzag arrangement of detectors and MCNP-4C code demonstrated that one could string the space and determine radioactive source by image reconstruction without using collimators, solely through these special detectors' distribution.
文摘In this paper,the spatial resolution and geometry sensitivity of parallel- and pin-hole collimators in compact gamma camera are presented,and quantitatively compared by GEANT4 code in Monte-Carlo library.The results show that the geometry sensitivity for pinhole collimator rapidly drops with increasing the gamma source-to- collimator distance(SCD);and for parallel-hole collimator,mildly.Meanwhile,the spatial resolution for pin-hole collimator mildly deteriorates;and for parallel-hole collimator,severely.The pin-hole collimator for close imaging objects has higher geometry sensitivity than parallel-hole collimator.Our findings are helpful for setting compact gamma camera collimators in nuclear medicine imaging.
