Flattening filter-free(FFF) beams generated by medical linear particle accelerators(linacs) have recently been used in radiotherapy clinical practice.FFF beams have fundamental physical parameter differences with resp...Flattening filter-free(FFF) beams generated by medical linear particle accelerators(linacs) have recently been used in radiotherapy clinical practice.FFF beams have fundamental physical parameter differences with respect to standard flattening filter(FF) beams,such that the generally used dosimetric parameters and definitions are not always viable.This study investigates dosimetric parameters for use in the quality assurance of FFF beams generated by medical linacs in radiotherapy.The main characteristics of the photon beams are analyzed using specific data generated by a Varian True Beam linac having both FFF and FF beams of 6 and 10 MV(megavolt) energy,respectively.Definitions for dose profile parameters are suggested,starting from the renormalization of the FFF with respect to the corresponding FF beam.From this point,the flatness concept is translated into one of "un-flatness",and other definitions are proposed,maintaining a strict parallelism between FFF and FF parameter concepts.The quality controls used in establishing a quality assurance program when introducing FFF beams into the clinical environment are given,maintaining similarity to those used for standard FF beams,and recommendations for the introduction of FFF beams into clinical radiotherapy application for breast cancer patients are provided as an example for comparison between FFF and FF for dose distribution and coverage for a target volume.Although there are many advantages of using a FFF beam,especially for advanced radiotherapy techniques,there are a few limitations(e.g.,using a relatively higher energy photon beam for stereotactic radiotherapy(SRT),limited speed of current multileaf collimators(MLCs),and off-axis distance-dependent modulation in intensitymodulated radiation therapy(IMRT)) as well as challenges(e.g.,criteria for beam quality evaluation and penumbra,establishment of dosimetry methods,and consequences of photon target burn-up) that need to be addressed for establishing the FFF beam as a viable alternative to the FF beam.展开更多
There is increasing interest in the clinical use of flattening filter-free(FFF) beams.In this study,we aimed to investigate the dosimetric characteristics of volumetric modulated arc radiotherapy(VMAT) with FFF beams ...There is increasing interest in the clinical use of flattening filter-free(FFF) beams.In this study,we aimed to investigate the dosimetric characteristics of volumetric modulated arc radiotherapy(VMAT) with FFF beams for nasopharyngeal carcinoma(NPC).Ten NPC patients were randomly selected to undergo a RapidArc plan with either FFF beams(RA-FFF) or conventional beams(RA-C).The doses to the planning target volumes(PTVs),organs at risk(OARs),and normal tissues were compared.The technical delivery parameters for RapidArc plans were also assessed to compare the characteristics of FFF and conventional beams.Both techniques delivered adequate doses to PTVs.For PTVs,RA-C delivered lower maximum and mean doses and improved conformity and homogeneity compared with RA-FFF.Both techniques provided similar maximum doses to the optic nerves and lenses.For the brain stem,spinal cord,larynx,parotid glands,oral cavity,and skin,RA-FFF showed significant dose increases compared to RA-C.The dose to normal tissue was lower in RA-FFF.The monitor units(MUs) were(536 ± 46) MU for RA-FFF and(501± 25) MU for RA-C.The treatment duration did not significantly differbetween plans.Although both treatment plans could meet clinical needs,RA-C is dosimetrically superior to RA-FFF for NPC radiotherapy.展开更多
To improve the efficiency of operating rooms, reduce the hospital＇ s costs and improve the level of service qualities, a scheduling method is presented based on a filtered-beam-search-based algo- rithm. Firstly, a sc...To improve the efficiency of operating rooms, reduce the hospital＇ s costs and improve the level of service qualities, a scheduling method is presented based on a filtered-beam-search-based algo- rithm. Firstly, a scheduling problem domain is described. Mathematical programming models are al- so set up with an objective function of minimizing related costs of the system. On the basis of the de= scriptions mentioned above, a solving policy of generating feasible scheduling solutions is estab- lished. Combining with the speeific constraints of operation theatres, a filtered-beam-search-based algorithm is put forward to solve scheduling problems. Finally, simulation experiments are designed. The performance of the proposed algorithm is evaluated and compared with that of other approaches through simulations. Results indicate that the proposed algorithm can reduce costs, and are of prac- ticality and effectiveness.展开更多
Piezoelectric actuators fundamentally possess hysteresis behavior. Estimation of the hysteresis is usually demanded for enhancing the performance of piezo-actuated systems. This paper presents an observer-based scheme...Piezoelectric actuators fundamentally possess hysteresis behavior. Estimation of the hysteresis is usually demanded for enhancing the performance of piezo-actuated systems. This paper presents an observer-based scheme to estimate the hysteresis in piezo—actuated flexible beams. The observer is based on a nonlinearity observer method. The discrete-time Kalman-filter algorithm is adopted for determination of the observer gains. The major advantages of the presented scheme include ease of implementation and robustness to uncertainty of hysteresis parameters. Simulation results demonstrate that the observer is able to estimate the hysteresis efficiently and has better robustness compared to the previous scheme existing in the literature. The present scheme was also successfully applied to a real-life system. Moreover, a control application example is included to demonstrate the effectiveness of the scheme.展开更多
In this article we introduce an exact backprojection filtered (BPF) type reconstruction algorithm for cone-beam scans based on Zou and Pan’s work. The algorithm can reconstruct images using only the projection data p...In this article we introduce an exact backprojection filtered (BPF) type reconstruction algorithm for cone-beam scans based on Zou and Pan’s work. The algorithm can reconstruct images using only the projection data passing through the parallel PI-line segments in reduced scans. Computer simulations and practical experiments are carried out to evaluate this algorithm. The BPF algorithm has a higher computational efficiency than the famous FDK algorithm. The BPF algorithm is evaluated using the practical CT projection data on a 450 keV X-ray CT system with a flat-panel detector (FPD). From the practical experiments, we get the spatial resolution of this CT system. The algo- rithm could achieve the spatial resolution of 2.4 lp/mm and satisfies the practical applications in industrial CT inspec- tion.展开更多
Motive of the study is to present quantitative and qualitative analysis and comparison of beam data measurement with FF (flattening filter) and FFF (flattening filter free) beam in a Varian TrueBeam<sup>TM</s...Motive of the study is to present quantitative and qualitative analysis and comparison of beam data measurement with FF (flattening filter) and FFF (flattening filter free) beam in a Varian TrueBeam<sup>TM</sup> Medical Linear Accelerator. Critique of beam characterization and evolution of dosimetric properties for 6 MV, 10 MV, 15 MV FF beam and 6 MVFFF, 10 MVFFF FFF beam has been carried out. We performed the comparison of photon beam data for two standard FF photon energy 6 MV, 10 MV verses 6 MVFFF, and 10 MVFFF FFF beam. Determination and comparison of parameter involved PDD (Percentage depth dose), Depth dose profile, Symmetry, Flatness, Quality index, Relative output factor, Penumbra, Transmission factor, DLG (Dosimetric leaf gap), in addition to degree of Un-flatness and off-axis ratio of FFF beam. Outcomes of presenting study had shown that change of various parameters such as Percentage depth dose curves, Shape of the depth dose profile, Transmission, Value of quality index and significant rise in surface dose for FFF in comparison with FF beam. Differences in the output factor at lower and higher field sizes for FFF beam compared to that of FF beam were found. The maximum output factor deviation between 6 MV and 6 MVFFF was found to be 4.55%, whereas in 10 MV and 10 MVFFF was 5.71%. Beam quality TPR20/10 for FFF beam was found to be lesser in magnitude, 5.42% for 6 MVFFF whereas 4.50% for 10 MVFFF compared to 6 MV and 10 MV FF beam respectively. Jaw transmission and interleaf leakage for FFF beam were found to be lesser than FF beam. Also DLG for FFF beam was found to be lesser in magnitude comparable to that of flattened beam. This study is mainly inclined towards evaluation and comparison of the FF and FFF beam. It has been observed that, the outcome of a commissioning beam data generation fully complies with vendor specification and published literature.展开更多
Thanks to recent advances in manufacturing technology, aerospace system designers have many more options to fabricate high-quality, low-weight, high-capacity, cost-effective filters. Aside from traditional methods suc...Thanks to recent advances in manufacturing technology, aerospace system designers have many more options to fabricate high-quality, low-weight, high-capacity, cost-effective filters. Aside from traditional methods such as stamping, drilling and milling, many new approaches have been widely used in filter-manufacturing practices on account of their increased processing abilities. How- ever, the restrictions on costs, the need for studying under stricter conditions such as in aggressive fluids, the complicity in design, the workability of materials, and others have made it difficult to choose a satisfactory method from the newly developed processes, such as, photochemical machining （PCM）, photo electroforming （PEF） and laser beam machining （LBM） to produce small, inexpensive, lightweight aerospace filters. This article appraises the technical and economical viability of PCM, PEF, and LBM to help engineers choose the fittest approach to turn out aerospace filters.展开更多
A novel wideband beam-forming structure with constant beam width based on complex coefficients (FIR) digital filters used in underwater acoustic communication is proposed. First,the received signals are compensated wi...A novel wideband beam-forming structure with constant beam width based on complex coefficients (FIR) digital filters used in underwater acoustic communication is proposed. First,the received signals are compensated with integer sampling period by using delay line. Then their complex envelopes are calculated by using frequency shift method. Finally,the envelopes are weighted by using complex coefficients FIR digital filters whose coefficients are optimized. Simulation results show that,in the communication band,the maximum difference between the designed beam and desired beam is less than 0.3 dB when the ratio of communication band to carrier frequency is 0.85.展开更多
Utilizing the tool of beam propagation method (BPM) to calculate the zeroth order diffraction beam intensity, we find SVHG displays notched diffraction response as a function of the readout wavelength. Using the metho...Utilizing the tool of beam propagation method (BPM) to calculate the zeroth order diffraction beam intensity, we find SVHG displays notched diffraction response as a function of the readout wavelength. Using the method of SA and considering the variance of refractive index as the readout wavelength changes, a practiced notch filter can be designed and the period of the filter is discussed.展开更多
We have described a method of obtaining useful information from noisy seismic refraction data. The simple method, tagged beam-forming technique, is based on the basic time-distance equations of refraction seismology. ...We have described a method of obtaining useful information from noisy seismic refraction data. The simple method, tagged beam-forming technique, is based on the basic time-distance equations of refraction seismology. It involves basically of introducing relative time delays to individual seismic traces of seismic refraction spread to correct for the non-coincidence of the incidence seismic energy at different geophones, and averaging the traces to obtain the beam. The assumption here is that the signal is coherent between the geophones while the noise is random, and for groups of geophones corresponding to the same refraction segments of the travel time curve, this basic assumption is valid. The process of beam forming therefore leads to improvement in signal-to-noise ratio (SNR) and correct determination of the intercept times which are subsequently used to compute other geologic layer parameters. The ability of the applied technique to filter out or minimize random noise has been tested using a modified random number routine. The performance test on computation of geologic layer parameters using very noisy synthetic data reveals that the method is still very reliable even with very poor quality data having SNR as small as 0.05.展开更多
A cross-correlation detection method to process backscatter signals of multi-laser beams measuring （MLBM） is presented, which can be firstly filtered by the digital filter composed of average median filter and finit...A cross-correlation detection method to process backscatter signals of multi-laser beams measuring （MLBM） is presented, which can be firstly filtered by the digital filter composed of average median filter and finite impulse response （FIR） digital filter. The processing of backscatter signals using single-pulse and three-pulse cross-correlation detection methods is depicted in detail. From calculation results, the multi-pulse cross-correlation detection could effectively improve signal-to-noise ratio （SNR）. Finally, both wind velocity and direction are determined by the peak-delay method based on the correlation function which shows high measuring precision and high SNR of the MLBM system with the assistance of the digital cross- correlation detection.展开更多
This paper proposes a more inclusive statistical model for predicting image noise in Computed Tomography (CT), associated with scanning factors, considering the effect of beam hardening and image processing filters. I...This paper proposes a more inclusive statistical model for predicting image noise in Computed Tomography (CT), associated with scanning factors, considering the effect of beam hardening and image processing filters. It is based on power functions where the levels of the parameters will determine the rate of noise variation with respect to a given scanning factor. It includes the influence of tube potential, tube current, slice thickness, Field of View (FOV), reconstruction methods and post-processing filters. To validate the model, tomographic measurements were made by using a PMMA phantom that simulates paediatric head and adult abdomen, a PET bottle was used to simulate the head of the new-born. The influence of ROI (Region Of Interest) size over nonlinear model parameters was analysed, and high variations of powers of attenuation and FOV were found depending on ROI size. A nonlinear robust regression method was used. The validation was performed graphically by weighted residual analysis. A nonlinear noise model was obtained with an adjusted coefficient of determination for ROI sizes between 10% and 70% of the phantom diameter or FOV. The model confirms the significance of the tube current, slice thickness and beam hardening effect on image. The process of estimation of the parameters of the model by Nonlinear Robust Regression turned out to be optimal.展开更多
目的比较肺癌立体定向放射治疗有无均整器模式下容积旋转调强(VMAT)计划,评估两种模式计划的剂量学和计划执行效率差异。方法选择行立体定向放射治疗的非小细胞肺癌患者20例,其中男性14例,女性6例;年龄42~83岁,中位年龄62岁;TNM分期T_(1...目的比较肺癌立体定向放射治疗有无均整器模式下容积旋转调强(VMAT)计划,评估两种模式计划的剂量学和计划执行效率差异。方法选择行立体定向放射治疗的非小细胞肺癌患者20例,其中男性14例,女性6例;年龄42~83岁,中位年龄62岁;TNM分期T_(1)N0M0_(7)例,T2N0M013例;病理诊断类型,腺癌15例,鳞状细胞癌5例。基于Monte Carlo算法设计有均整器(FF)模式和无均整器(FFF)模式的VMAT计划,计划靶区(PTV)给予相同的处方剂量50 Gy/5F照射,在满足临床要求的情况下,比较两种计划在剂量学、机器跳数、出束时间及计划验证通过率的差异。结果FFF模式PTV的适形指数(CI)优于FF模式,差异有统计学意义(0.87±0.21 vs 0.84±0.04。P<0.05),梯度指数(GI)差异亦有统计学意义(5.22±0.09 vs 5.95±0.17。P<0.05),靶区D_(98%)、D2%、D_(2cm)两者比较,差异均无统计学意义(P>0.05);FFF模式在食管平均剂量保护上优于FF模式[(5.02±1.34)Gy vs(5.81±0.76)Gy。P<0.05],在脊髓的D0.25cc、心脏D150cc、双肺D1000cc、D1500cc、Dmean及皮肤D10cc两者比较,差异无统计学意义(P>0.05);FFF模式的机器总跳数相对于FF模式增加,出束总时间较FF模式缩短,两种模式间差异均有统计学意义[4072.72±273.04 vs 3638.79±255.35、(303.52±137.20)s vs(429.95±158.04)s。P<0.05]。两种模式基于TH=10%、3%/2 mm的条件下伽马分析,验证率均大于95%,差异无统计学意义(P>0.05)。结论基于Monte Carlo算法下有无均整器模式肺癌立体定向放射治疗均能满足临床需求,FFF模式的肺癌立体定向放射治疗能提升靶区的适形度并降低靶区GI,较FF模式有一定的剂量优势;FFF模式下,计划执行效率有所提升。展开更多
In a dynamic CT, the acquired projections are corrupted due to strong dynamic nature of the object, for example: lungs, heart etc. In this paper, we present fan-beam reconstruction algorithm without position-dependent...In a dynamic CT, the acquired projections are corrupted due to strong dynamic nature of the object, for example: lungs, heart etc. In this paper, we present fan-beam reconstruction algorithm without position-dependent backprojection weight which compensates for the time-dependent translational, uniform scaling and rotational deformations occurring in the object of interest during the data acquisition process. We shall also compare the computational cost of the proposed reconstruction algorithm with the existing one which has position-dependent weight. To accomplish the objective listed above, we first formulate admissibility conditions on deformations that is required to exactly reconstruct the object from acquired sequential deformed projections and then derive the reconstruction algorithm to compensate the above listed deformations satisfying the admissibility conditions. For this, 2-D time-dependent deformation model is incorporated in the fan-beam FBP reconstruction algorithm with no backprojection weight, assuming the motion parameters being known. Finally the proposed reconstruction algorithm is evaluated with the motion corrupted projection data simulated on the computer.展开更多
国际原子能机构(International Atomic Energy Agency,IAEA)与美国医学物理学家协会(American Association of Physicists in Medicine,AAPM)联合制定的外照射光子束小野静态射野剂量学操作规程(TRS-483)中提供的小野射野输出修正因子(k...国际原子能机构(International Atomic Energy Agency,IAEA)与美国医学物理学家协会(American Association of Physicists in Medicine,AAPM)联合制定的外照射光子束小野静态射野剂量学操作规程(TRS-483)中提供的小野射野输出修正因子(k_(Qclin,Qref)^(fclin,fref))未考虑均整模式(Flattening Filter,FF)、非均整模式(Flattening Filter Free,FFF)束流间差异,对于电离室在相同射野条件下测量的小野射野输出因子(Ω^(fclin,fref) _(Qclin,Qref))给出相同修正系数,可能引入超过1%的偏差。据此,提出利用蒙特卡罗模拟细化电离室k_(Qclin,Qref)^(fclin,fref)的方法,对FF、FFF束流下电离室小野测量数据进行分别修正,进一步提升临床小野剂量测量准确性。基于EGSnrc构建Elekta Synergy加速器机头模型,建立电离室k_(Qclin,Qref)^(fclin,fref)模拟方法。通过电离室在FF束流不同射野条件下Ω^(fclin,fref)_(Qclin,Qref)的测量及修正,验证蒙特卡罗计算模型,并分别计算了6款小灵敏体积电离室在FF、FFF束流不同射野范围(0.8 cm×0.8 cm~10 cm×10 cm)的k_(Qclin,Qref)^(fclin,fref)。研究发现,同一电离室在FF、FFF束流不同射野条件下计算的k_(Qclin,Qref)^(fclin,fref)存在明显差异,其中PTW 31015在FFF模式下计算的k_(Qclin,Qref)^(fclin,fref)与FF模式计算结果相比最大偏差超过1.02%。因此,通过细化电离室k_(Qclin,Qref)^(fclin,fref)的方法能够有效提升临床小野水吸收剂量测量准确性。展开更多
文摘Flattening filter-free(FFF) beams generated by medical linear particle accelerators(linacs) have recently been used in radiotherapy clinical practice.FFF beams have fundamental physical parameter differences with respect to standard flattening filter(FF) beams,such that the generally used dosimetric parameters and definitions are not always viable.This study investigates dosimetric parameters for use in the quality assurance of FFF beams generated by medical linacs in radiotherapy.The main characteristics of the photon beams are analyzed using specific data generated by a Varian True Beam linac having both FFF and FF beams of 6 and 10 MV(megavolt) energy,respectively.Definitions for dose profile parameters are suggested,starting from the renormalization of the FFF with respect to the corresponding FF beam.From this point,the flatness concept is translated into one of "un-flatness",and other definitions are proposed,maintaining a strict parallelism between FFF and FF parameter concepts.The quality controls used in establishing a quality assurance program when introducing FFF beams into the clinical environment are given,maintaining similarity to those used for standard FF beams,and recommendations for the introduction of FFF beams into clinical radiotherapy application for breast cancer patients are provided as an example for comparison between FFF and FF for dose distribution and coverage for a target volume.Although there are many advantages of using a FFF beam,especially for advanced radiotherapy techniques,there are a few limitations(e.g.,using a relatively higher energy photon beam for stereotactic radiotherapy(SRT),limited speed of current multileaf collimators(MLCs),and off-axis distance-dependent modulation in intensitymodulated radiation therapy(IMRT)) as well as challenges(e.g.,criteria for beam quality evaluation and penumbra,establishment of dosimetry methods,and consequences of photon target burn-up) that need to be addressed for establishing the FFF beam as a viable alternative to the FF beam.
文摘There is increasing interest in the clinical use of flattening filter-free(FFF) beams.In this study,we aimed to investigate the dosimetric characteristics of volumetric modulated arc radiotherapy(VMAT) with FFF beams for nasopharyngeal carcinoma(NPC).Ten NPC patients were randomly selected to undergo a RapidArc plan with either FFF beams(RA-FFF) or conventional beams(RA-C).The doses to the planning target volumes(PTVs),organs at risk(OARs),and normal tissues were compared.The technical delivery parameters for RapidArc plans were also assessed to compare the characteristics of FFF and conventional beams.Both techniques delivered adequate doses to PTVs.For PTVs,RA-C delivered lower maximum and mean doses and improved conformity and homogeneity compared with RA-FFF.Both techniques provided similar maximum doses to the optic nerves and lenses.For the brain stem,spinal cord,larynx,parotid glands,oral cavity,and skin,RA-FFF showed significant dose increases compared to RA-C.The dose to normal tissue was lower in RA-FFF.The monitor units(MUs) were(536 ± 46) MU for RA-FFF and(501± 25) MU for RA-C.The treatment duration did not significantly differbetween plans.Although both treatment plans could meet clinical needs,RA-C is dosimetrically superior to RA-FFF for NPC radiotherapy.
基金Supported by the National Natural Science Foundation of China(No.61273035,71471135)
文摘To improve the efficiency of operating rooms, reduce the hospital＇ s costs and improve the level of service qualities, a scheduling method is presented based on a filtered-beam-search-based algo- rithm. Firstly, a scheduling problem domain is described. Mathematical programming models are al- so set up with an objective function of minimizing related costs of the system. On the basis of the de= scriptions mentioned above, a solving policy of generating feasible scheduling solutions is estab- lished. Combining with the speeific constraints of operation theatres, a filtered-beam-search-based algorithm is put forward to solve scheduling problems. Finally, simulation experiments are designed. The performance of the proposed algorithm is evaluated and compared with that of other approaches through simulations. Results indicate that the proposed algorithm can reduce costs, and are of prac- ticality and effectiveness.
基金supported by Royal Golden Jubilee Ph.D.Programof the Thai Research Fund
文摘Piezoelectric actuators fundamentally possess hysteresis behavior. Estimation of the hysteresis is usually demanded for enhancing the performance of piezo-actuated systems. This paper presents an observer-based scheme to estimate the hysteresis in piezo—actuated flexible beams. The observer is based on a nonlinearity observer method. The discrete-time Kalman-filter algorithm is adopted for determination of the observer gains. The major advantages of the presented scheme include ease of implementation and robustness to uncertainty of hysteresis parameters. Simulation results demonstrate that the observer is able to estimate the hysteresis efficiently and has better robustness compared to the previous scheme existing in the literature. The present scheme was also successfully applied to a real-life system. Moreover, a control application example is included to demonstrate the effectiveness of the scheme.
基金Supported by a grant from the Ph.D. Programs Foundation of Ministry of Education of China (No. 20030003074) and the National Natural Science Founda-tion of China (No. 10575059).
文摘In this article we introduce an exact backprojection filtered (BPF) type reconstruction algorithm for cone-beam scans based on Zou and Pan’s work. The algorithm can reconstruct images using only the projection data passing through the parallel PI-line segments in reduced scans. Computer simulations and practical experiments are carried out to evaluate this algorithm. The BPF algorithm has a higher computational efficiency than the famous FDK algorithm. The BPF algorithm is evaluated using the practical CT projection data on a 450 keV X-ray CT system with a flat-panel detector (FPD). From the practical experiments, we get the spatial resolution of this CT system. The algo- rithm could achieve the spatial resolution of 2.4 lp/mm and satisfies the practical applications in industrial CT inspec- tion.
文摘Motive of the study is to present quantitative and qualitative analysis and comparison of beam data measurement with FF (flattening filter) and FFF (flattening filter free) beam in a Varian TrueBeam<sup>TM</sup> Medical Linear Accelerator. Critique of beam characterization and evolution of dosimetric properties for 6 MV, 10 MV, 15 MV FF beam and 6 MVFFF, 10 MVFFF FFF beam has been carried out. We performed the comparison of photon beam data for two standard FF photon energy 6 MV, 10 MV verses 6 MVFFF, and 10 MVFFF FFF beam. Determination and comparison of parameter involved PDD (Percentage depth dose), Depth dose profile, Symmetry, Flatness, Quality index, Relative output factor, Penumbra, Transmission factor, DLG (Dosimetric leaf gap), in addition to degree of Un-flatness and off-axis ratio of FFF beam. Outcomes of presenting study had shown that change of various parameters such as Percentage depth dose curves, Shape of the depth dose profile, Transmission, Value of quality index and significant rise in surface dose for FFF in comparison with FF beam. Differences in the output factor at lower and higher field sizes for FFF beam compared to that of FF beam were found. The maximum output factor deviation between 6 MV and 6 MVFFF was found to be 4.55%, whereas in 10 MV and 10 MVFFF was 5.71%. Beam quality TPR20/10 for FFF beam was found to be lesser in magnitude, 5.42% for 6 MVFFF whereas 4.50% for 10 MVFFF compared to 6 MV and 10 MV FF beam respectively. Jaw transmission and interleaf leakage for FFF beam were found to be lesser than FF beam. Also DLG for FFF beam was found to be lesser in magnitude comparable to that of flattened beam. This study is mainly inclined towards evaluation and comparison of the FF and FFF beam. It has been observed that, the outcome of a commissioning beam data generation fully complies with vendor specification and published literature.
基金Key National Natural Science Foundation of China(50635040)
文摘Thanks to recent advances in manufacturing technology, aerospace system designers have many more options to fabricate high-quality, low-weight, high-capacity, cost-effective filters. Aside from traditional methods such as stamping, drilling and milling, many new approaches have been widely used in filter-manufacturing practices on account of their increased processing abilities. How- ever, the restrictions on costs, the need for studying under stricter conditions such as in aggressive fluids, the complicity in design, the workability of materials, and others have made it difficult to choose a satisfactory method from the newly developed processes, such as, photochemical machining （PCM）, photo electroforming （PEF） and laser beam machining （LBM） to produce small, inexpensive, lightweight aerospace filters. This article appraises the technical and economical viability of PCM, PEF, and LBM to help engineers choose the fittest approach to turn out aerospace filters.
基金Sponsored by the project supported by the National Natural Science Foundation of China(60672046)the Natural Science Foundation of Fujian Province of China(2010J05139)
文摘A novel wideband beam-forming structure with constant beam width based on complex coefficients (FIR) digital filters used in underwater acoustic communication is proposed. First,the received signals are compensated with integer sampling period by using delay line. Then their complex envelopes are calculated by using frequency shift method. Finally,the envelopes are weighted by using complex coefficients FIR digital filters whose coefficients are optimized. Simulation results show that,in the communication band,the maximum difference between the designed beam and desired beam is less than 0.3 dB when the ratio of communication band to carrier frequency is 0.85.
基金Supported by the National Natural Science Foundation of China!696 07005)
文摘Utilizing the tool of beam propagation method (BPM) to calculate the zeroth order diffraction beam intensity, we find SVHG displays notched diffraction response as a function of the readout wavelength. Using the method of SA and considering the variance of refractive index as the readout wavelength changes, a practiced notch filter can be designed and the period of the filter is discussed.
文摘We have described a method of obtaining useful information from noisy seismic refraction data. The simple method, tagged beam-forming technique, is based on the basic time-distance equations of refraction seismology. It involves basically of introducing relative time delays to individual seismic traces of seismic refraction spread to correct for the non-coincidence of the incidence seismic energy at different geophones, and averaging the traces to obtain the beam. The assumption here is that the signal is coherent between the geophones while the noise is random, and for groups of geophones corresponding to the same refraction segments of the travel time curve, this basic assumption is valid. The process of beam forming therefore leads to improvement in signal-to-noise ratio (SNR) and correct determination of the intercept times which are subsequently used to compute other geologic layer parameters. The ability of the applied technique to filter out or minimize random noise has been tested using a modified random number routine. The performance test on computation of geologic layer parameters using very noisy synthetic data reveals that the method is still very reliable even with very poor quality data having SNR as small as 0.05.
基金supported by National Natural Science Foundation of China under Grant No. 60425101-1Foundation for Innovative Research Groups of NSFC under Grant No. 60721001
文摘A cross-correlation detection method to process backscatter signals of multi-laser beams measuring （MLBM） is presented, which can be firstly filtered by the digital filter composed of average median filter and finite impulse response （FIR） digital filter. The processing of backscatter signals using single-pulse and three-pulse cross-correlation detection methods is depicted in detail. From calculation results, the multi-pulse cross-correlation detection could effectively improve signal-to-noise ratio （SNR）. Finally, both wind velocity and direction are determined by the peak-delay method based on the correlation function which shows high measuring precision and high SNR of the MLBM system with the assistance of the digital cross- correlation detection.
文摘This paper proposes a more inclusive statistical model for predicting image noise in Computed Tomography (CT), associated with scanning factors, considering the effect of beam hardening and image processing filters. It is based on power functions where the levels of the parameters will determine the rate of noise variation with respect to a given scanning factor. It includes the influence of tube potential, tube current, slice thickness, Field of View (FOV), reconstruction methods and post-processing filters. To validate the model, tomographic measurements were made by using a PMMA phantom that simulates paediatric head and adult abdomen, a PET bottle was used to simulate the head of the new-born. The influence of ROI (Region Of Interest) size over nonlinear model parameters was analysed, and high variations of powers of attenuation and FOV were found depending on ROI size. A nonlinear robust regression method was used. The validation was performed graphically by weighted residual analysis. A nonlinear noise model was obtained with an adjusted coefficient of determination for ROI sizes between 10% and 70% of the phantom diameter or FOV. The model confirms the significance of the tube current, slice thickness and beam hardening effect on image. The process of estimation of the parameters of the model by Nonlinear Robust Regression turned out to be optimal.
文摘目的比较肺癌立体定向放射治疗有无均整器模式下容积旋转调强(VMAT)计划,评估两种模式计划的剂量学和计划执行效率差异。方法选择行立体定向放射治疗的非小细胞肺癌患者20例,其中男性14例,女性6例;年龄42~83岁,中位年龄62岁;TNM分期T_(1)N0M0_(7)例,T2N0M013例;病理诊断类型,腺癌15例,鳞状细胞癌5例。基于Monte Carlo算法设计有均整器(FF)模式和无均整器(FFF)模式的VMAT计划,计划靶区(PTV)给予相同的处方剂量50 Gy/5F照射,在满足临床要求的情况下,比较两种计划在剂量学、机器跳数、出束时间及计划验证通过率的差异。结果FFF模式PTV的适形指数(CI)优于FF模式,差异有统计学意义(0.87±0.21 vs 0.84±0.04。P<0.05),梯度指数(GI)差异亦有统计学意义(5.22±0.09 vs 5.95±0.17。P<0.05),靶区D_(98%)、D2%、D_(2cm)两者比较,差异均无统计学意义(P>0.05);FFF模式在食管平均剂量保护上优于FF模式[(5.02±1.34)Gy vs(5.81±0.76)Gy。P<0.05],在脊髓的D0.25cc、心脏D150cc、双肺D1000cc、D1500cc、Dmean及皮肤D10cc两者比较,差异无统计学意义(P>0.05);FFF模式的机器总跳数相对于FF模式增加,出束总时间较FF模式缩短,两种模式间差异均有统计学意义[4072.72±273.04 vs 3638.79±255.35、(303.52±137.20)s vs(429.95±158.04)s。P<0.05]。两种模式基于TH=10%、3%/2 mm的条件下伽马分析,验证率均大于95%,差异无统计学意义(P>0.05)。结论基于Monte Carlo算法下有无均整器模式肺癌立体定向放射治疗均能满足临床需求,FFF模式的肺癌立体定向放射治疗能提升靶区的适形度并降低靶区GI,较FF模式有一定的剂量优势;FFF模式下,计划执行效率有所提升。
文摘In a dynamic CT, the acquired projections are corrupted due to strong dynamic nature of the object, for example: lungs, heart etc. In this paper, we present fan-beam reconstruction algorithm without position-dependent backprojection weight which compensates for the time-dependent translational, uniform scaling and rotational deformations occurring in the object of interest during the data acquisition process. We shall also compare the computational cost of the proposed reconstruction algorithm with the existing one which has position-dependent weight. To accomplish the objective listed above, we first formulate admissibility conditions on deformations that is required to exactly reconstruct the object from acquired sequential deformed projections and then derive the reconstruction algorithm to compensate the above listed deformations satisfying the admissibility conditions. For this, 2-D time-dependent deformation model is incorporated in the fan-beam FBP reconstruction algorithm with no backprojection weight, assuming the motion parameters being known. Finally the proposed reconstruction algorithm is evaluated with the motion corrupted projection data simulated on the computer.
文摘国际原子能机构(International Atomic Energy Agency,IAEA)与美国医学物理学家协会(American Association of Physicists in Medicine,AAPM)联合制定的外照射光子束小野静态射野剂量学操作规程(TRS-483)中提供的小野射野输出修正因子(k_(Qclin,Qref)^(fclin,fref))未考虑均整模式(Flattening Filter,FF)、非均整模式(Flattening Filter Free,FFF)束流间差异,对于电离室在相同射野条件下测量的小野射野输出因子(Ω^(fclin,fref) _(Qclin,Qref))给出相同修正系数,可能引入超过1%的偏差。据此,提出利用蒙特卡罗模拟细化电离室k_(Qclin,Qref)^(fclin,fref)的方法,对FF、FFF束流下电离室小野测量数据进行分别修正,进一步提升临床小野剂量测量准确性。基于EGSnrc构建Elekta Synergy加速器机头模型,建立电离室k_(Qclin,Qref)^(fclin,fref)模拟方法。通过电离室在FF束流不同射野条件下Ω^(fclin,fref)_(Qclin,Qref)的测量及修正,验证蒙特卡罗计算模型,并分别计算了6款小灵敏体积电离室在FF、FFF束流不同射野范围(0.8 cm×0.8 cm~10 cm×10 cm)的k_(Qclin,Qref)^(fclin,fref)。研究发现,同一电离室在FF、FFF束流不同射野条件下计算的k_(Qclin,Qref)^(fclin,fref)存在明显差异,其中PTW 31015在FFF模式下计算的k_(Qclin,Qref)^(fclin,fref)与FF模式计算结果相比最大偏差超过1.02%。因此,通过细化电离室k_(Qclin,Qref)^(fclin,fref)的方法能够有效提升临床小野水吸收剂量测量准确性。
