针对低剂量计算机断层扫描(CT)重建图像时出现明显条形伪影的现象,提出一种自适应广义总变分(ATGV)降噪算法。该算法考虑了传统广义总变分(TGV)算法在降噪时模糊图像边缘信息的缺点,把可以有效区分图像平滑区和细节区的直觉模糊熵应用到传统TGV中,对图像的不同区域进行不同强度的去噪,从而达到保护图像细节的效果。该算法首先采用滤波反投影(FBP)算法得到低剂量CT重建图像;然后利用基于直觉模糊熵的边缘指示函数对传统TGV模型进行改进;最后用改进后的模型对重建图像进行降噪处理。采用Shepp-Logan模型和数字胸腔模型(thorax phantom)仿真低剂量CT重建图像来验证算法的有效性。实验结果表明,所提算法的归一化均方距离(NMSD)和归一化平均绝对距离(NAAD)均比总变分(TV)降噪算法和广义总变分(TGV)降噪算法小,且可分别获得26.90 d B和44.58 d B的峰值信噪比(PSNR)。该算法在去除条形伪影的同时可以较好地保持图像的边缘和细节信息。
The mean path length(MPL)of photons is a critical parameter to calculate tissue absorption coefficient as well as blood oxygenation using modified Beer-Lambert law,where in the differential path factor(DPF)is often as...
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The mean path length(MPL)of photons is a critical parameter to calculate tissue absorption coefficient as well as blood oxygenation using modified Beer-Lambert law,where in the differential path factor(DPF)is often assumed as constant over range of tissue *** utilizing the Monte Carlo(MC)simulation of photon migrations in the leg,this study used four approaches to estimate MPL,and compared them with that determined by the MPL *** simulation results indicate that the DPF is remarkably affected by tissue absorption,at approximate 10% variation.A linear model is suggested to calculate MPL for measurements of tissue absorption as well as blood oxygenation using modified Beer-Lambert law.
MEMS gyroscope is a new inertial navigation sensor,which can measure the input angular rate of sensitive axis using Coriolis *** to the conventional gyroscope,it owns many unique advantages.A novel structure of vibrat...
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MEMS gyroscope is a new inertial navigation sensor,which can measure the input angular rate of sensitive axis using Coriolis *** to the conventional gyroscope,it owns many unique advantages.A novel structure of vibrating ring gyroscope is proposed and the finite element model of the oscillator is established based on MEMS *** the modal analysis,the natural frequency and mode shapes of the oscillator are *** analyzing the effects of the structural parameters on the mode shapes and frequency of the harmonic oscillator,the optimal design parameters are *** frequency difference between the operating mode and the other modes is greater than 1kHz after optimization,which can avoid the frequency coupling of the operating mode and other vibrating modes of the *** simulation results show that the performance parameters of the ring structure meet the design requirements and have obvious advantages.
为提高SOI压阻式压力传感器的灵敏度,对传感器敏感结构的弹性膜片和压敏电阻的形状、尺寸等结构参数进行了优化设计。利用COMSOL Multiphysics多物理场耦合分析软件对优化后的敏感结构进行了静力学仿真与分析,完成了敏感芯片的制备和加压测试,测试结果表明:优化后的传感器输出灵敏度为5.98 m V/(V·bar),较原结构输出灵敏度提高了1倍,非线性误差小于0.096%。
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