Current output dose measurement in CT is based on (CTDI). The conventional methodology of CT dosimetric performance characterization is not appropriate to modern CT scanners with helical scanning modes, dose modulatio...Current output dose measurement in CT is based on (CTDI). The conventional methodology of CT dosimetric performance characterization is not appropriate to modern CT scanners with helical scanning modes, dose modulation, array detectors and multiple slice planes or cone-beam irradiation geometries. AAPM TG 111 report recognizes the shortfall of the CTDI methods and recommends a new technique that more accurately characterizes the dose profile from modern CT scanners, which utilizes a short conventional ion chamber rather than a pencil chamber. We developed and characterize a in-house phantom design using a three separate anatomical regions of clinical scan sequences (Head, chest and abdomen), and determined the equilibrium dose in our dose equilibrium phantom, measured if the attenuation of the beam is the equal to that of CTDI Perspex phantom and compare CTDI dose estimations using a standard pencil chamber to the dose equilibrium phantom measurements. This methodology allows measurements of the accumulated dose for any clinical scan length and allowing measurement of the equilibrium dose. Using the new methodology, we determined that the CTDI approach can underestimate the dose by 25% to 35% and all of our dose values from the water phantom and farmer chamber were independently verified with TLD measurements.展开更多
To overcome the disadvantages of the location algorithm based on received signal strength indication(RSSI) in the existing wireless sensor networks(WSNs),a novel adaptive cooperative location algorithm is proposed.To ...To overcome the disadvantages of the location algorithm based on received signal strength indication(RSSI) in the existing wireless sensor networks(WSNs),a novel adaptive cooperative location algorithm is proposed.To tolerate some minor errors in the information of node position,a reference anchor node is employed.On the other hand,Dixon method is used to remove the outliers of RSSI,the standard deviation threshold of RSSI and the learning model are put forward to reduce the ranging error of RSSI and improve the positioning precision effectively.Simulations are run to evaluate the performance of the algorithm.The results show that the proposed algorithm offers more precise location and better stability and robustness.展开更多
针对接收信号强度指示(Received Signal Strength Indication,RSSI)测距定位算法存在定位结果不稳定且精度低的问题,本文分析了一种基于狄克逊检验法滤波RSSI的高斯牛顿定位(Dixon test filter RSSI Gauss-Newton,DF-RSSI-GN)算法。采...针对接收信号强度指示(Received Signal Strength Indication,RSSI)测距定位算法存在定位结果不稳定且精度低的问题,本文分析了一种基于狄克逊检验法滤波RSSI的高斯牛顿定位(Dixon test filter RSSI Gauss-Newton,DF-RSSI-GN)算法。采用狄克逊(Dixon)检验法滤波剔除观测信号异常值使得观测数据偏度降低,根据偏态程度对观测信号进行高斯均值滤波并通过非线性回归模型拟合RSSI衰减模型参数,在目标点坐标求解阶段利用滤波后的观测信号确定不同方向上的权值进行高斯牛顿(Gauss-Newton)迭代定位。实验结果表明,DF-RSSI-GN算法定位平均精度在1.5 m左右,相比RSSI定位算法和最小二乘定位算法,精度提高1倍以上。展开更多
文摘Current output dose measurement in CT is based on (CTDI). The conventional methodology of CT dosimetric performance characterization is not appropriate to modern CT scanners with helical scanning modes, dose modulation, array detectors and multiple slice planes or cone-beam irradiation geometries. AAPM TG 111 report recognizes the shortfall of the CTDI methods and recommends a new technique that more accurately characterizes the dose profile from modern CT scanners, which utilizes a short conventional ion chamber rather than a pencil chamber. We developed and characterize a in-house phantom design using a three separate anatomical regions of clinical scan sequences (Head, chest and abdomen), and determined the equilibrium dose in our dose equilibrium phantom, measured if the attenuation of the beam is the equal to that of CTDI Perspex phantom and compare CTDI dose estimations using a standard pencil chamber to the dose equilibrium phantom measurements. This methodology allows measurements of the accumulated dose for any clinical scan length and allowing measurement of the equilibrium dose. Using the new methodology, we determined that the CTDI approach can underestimate the dose by 25% to 35% and all of our dose values from the water phantom and farmer chamber were independently verified with TLD measurements.
基金supported by National Natural Science Foundation of China (No.60872038)Natural Science Foundation of Chongqing(CSTC2009BA2064)
文摘To overcome the disadvantages of the location algorithm based on received signal strength indication(RSSI) in the existing wireless sensor networks(WSNs),a novel adaptive cooperative location algorithm is proposed.To tolerate some minor errors in the information of node position,a reference anchor node is employed.On the other hand,Dixon method is used to remove the outliers of RSSI,the standard deviation threshold of RSSI and the learning model are put forward to reduce the ranging error of RSSI and improve the positioning precision effectively.Simulations are run to evaluate the performance of the algorithm.The results show that the proposed algorithm offers more precise location and better stability and robustness.
文摘针对接收信号强度指示(Received Signal Strength Indication,RSSI)测距定位算法存在定位结果不稳定且精度低的问题,本文分析了一种基于狄克逊检验法滤波RSSI的高斯牛顿定位(Dixon test filter RSSI Gauss-Newton,DF-RSSI-GN)算法。采用狄克逊(Dixon)检验法滤波剔除观测信号异常值使得观测数据偏度降低,根据偏态程度对观测信号进行高斯均值滤波并通过非线性回归模型拟合RSSI衰减模型参数,在目标点坐标求解阶段利用滤波后的观测信号确定不同方向上的权值进行高斯牛顿(Gauss-Newton)迭代定位。实验结果表明,DF-RSSI-GN算法定位平均精度在1.5 m左右,相比RSSI定位算法和最小二乘定位算法,精度提高1倍以上。
