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Search Results: 1 - 10 of 8059 matches for " 正弦图 "
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x射线ct环形伪影去除方法
马继明,宋岩,王群书,宋顾周,张建奇,夏惊涛,韩长材,段宝军,杜继业,周鸣
强激光与粒子束 , 2014,
Abstract: ?为去除x射线ct图像中的环形伪影,建立了一种投影数据预处理方法。该方法通过对各角度投影数据逐一进行分段多项式拟合的方式建立异常探元的备选校正因子集合,再根据备选校正因子的概率密度分布确定最可几校正因子。介绍了方法的物理依据、原理及其实现步骤,并分析了其在复杂条件下的适应性。结果表明:该方法对稀疏环形伪影、密集环形伪影以及伴随强噪声污染的ct图像环形伪影均可去除;与中值滤波等方法相比,可以更好地保持图像的空间分辨率。该方法可用于多材质检测对象ct图像的处理。
70kV结合正弦图迭代重建在腹部CTA扫描中的应用价值
张琳琳,于凤凯,赵红军,张瑞,苏炜
- , 2016, DOI: 10.13609/j.cnki.1000-0313.2016.09.017
Abstract: 【摘要】目的:探讨70kV结合正弦图迭代重建(SAFIRE)技术在腹部CTA扫描中的应用价值。方法:110例患者(低kV组)采用70kV、SAFIRE技术、欧乃派克(300mg I/mL)的CTA扫描方案,87例患者(对照组)采用120kV、滤波反投影(FBP)技术、欧乃派克(350mg I/mL)的扫描方案。对比两组的CT剂量指数(CTDIvol)、CT值、SD、对比噪声比(CNR)、图像灵敏度(FOM)、图像质量主观评分。结果:低kV组和对照组的CTDIvol分别为(3.08±0.15)mGy、(6.08±0.57)mGy,两组差异有统计学意义(P<0.05);低kV组腹主动脉、肾动脉、肠系膜上动脉的CT值分别为(431.45±27.42)HU、(415.44±16.51 )HU、(311.85±17.75)HU,对照组分别为(334.91±14.41)HU、(335.51±13.76)HU、(312.63±18.59)HU;低kV组腹主动脉、肾动脉、肠系膜上动脉的SD分别为(15.96±1.75)、(18.63±3.01)、(26.99±2.65),对照组分别为(23.21±2.91)、(25.34±2.67)、(29.8±3.04),两组差异均具有统计学意义(P<0.05);低kV组腹主动脉、肾动脉、肠系膜上动脉的CNR分别为(26.58±2.93)、(25.77±2.52)、(20.31±1.74),对照组分别为(20.79±1.87)、(20.82±1.92)、(19.98±1.63);低kV组腹主动脉、肾动脉、肠系膜上动脉的FOM分别为(233.32±55.35)、(218.46±45.44)、(135.51±24.74),对照组分别为(72.34±15.45)、(72.57±15.62)、(66.71±12.86),两组差异均具有统计学意义(P<0.05);低kV组的图像质量评分为(4.56±0.65),对照组为(4.55±0.73),两组差异无统计学意义(P>0.05)。结论:70kV结合SAFIRE技术在腹部CTA扫描中,不仅可以大幅度降低辐射剂量,而且改善了腹部CTA的图像质量,减少了碘对比剂的相对含量,具有较高的临床应用价值
基于正弦图平移匹配的投影旋转中心校正
Correction of the projection center of rotation based on the sinogram using translation matching method

赵琦,赵雨晴,丛长虹,冀东江,秦莉莉,陈晓冬,胡春红
- , 2018, DOI: 10.7507/1001-5515.201707065
Abstract: 投影旋转中心(COR)精准定位是确保计算机断层成像(CT)重建图像质量的关键要素,经典的互相关匹配算法在投影角度为 0~180° 时难以满足高质量 CT 成像要求,需进行改进创新。本文根据正弦图上 0° 与 180° 投影数据翻转后有对应性的特点提出基于这两行数据平移匹配的 COR 校正算法,该算法利用 OTSU 进行阈值分割以减少背景噪声影响,通过 L1 范数量化 COR 最小偏移得到准确校正值后进行 CT 重建。分别采用加入随机梯度噪声和高斯噪声的 Sheep-Logan 模型和雄性 SD 大鼠样本的同质肝脏与异质牙齿图像验证新算法的有效性,并将新算法与互相关匹配算法做性能对比。结果表明:新算法运算量少、简便快速且具有良好的抗噪鲁棒性,校正精度高(稀疏采样投影数据在 10%~50% 时也能很好地校正 COR 值),CT 重建图像质量有显著改进,效果优于互相关算法。
The accurate position of the center of rotation (COR) is a key factor to ensure the quality of computed tomography (CT) reconstructed images. The classic cross-correlation matching algorithm can not satisfy the requirements of high-quality CT imaging when the projection angle is 0 and 180°, and thus needs to be improved and innovated. In this study, considering the symmetric characteristic of the 0° and flipped 180° projection data in sinogram, a novel COR correction algorithm based on the translation and match of the 0° and 180° projection data was proposed. The OTSU method was applied to reduce noise on the background, and the minimum offset of COR was quantified using the L1-norm, and then a precise COR was obtained for the image correction and reconstruction. The Sheep-Logan simulation model with random gradients and Gaussian noise and the real male SD rats samples which contained the heterogenous tooth image and the homogenous liver image, were adopted to verify the performance of the new algorithm and the cross-correlation matching algorithm. The results show that the proposed algorithm has better robustness and higher accuracy of the correction (when the sampled data is from 10% to 50% of the full projection data, the COR value can still be measured accurately using the proposed algorithm) with less computational burden compared with the cross-correlation matching algorithm, and it is able to significantly improve the quality of the reconstructed images.
矩形光栅正弦象生成的研究
程堂郭,袁祥辉
重庆大学学报 , 1989,
Abstract: 不相干衍射受限成象系统的OTF,等效为强度频谱线性滤波器,当系统含有十分严重聚焦误差时,我们推导出公式,计算结果与实验数据吻合,从而给予矩形光栅正弦象以正确的解释。
PWM波形的等面积控制法
王学勤
重庆大学学报 , 1988,
Abstract: 本文提出了正弦波电压对时间积分与PWM波形电压对时间积分相等原理,使用作图法、逐次积分比较法计算PWM波形的换相点。并以PWM电流型逆变器为例探讨了微机控制问题。该方法简单、有效。特别适用PWM逆变器的工程控制。
FFT-Based Moving Average Maximum Likelihood Single-tone Frequency Estimation
基于FFT滑动平均极大似然法的正弦信号频率估计

Huang Yu-chun,Huang Zai-lu,Huang Ben-xiong,Xu Shu-hua,
黄玉春
,黄载禄,黄本雄,徐书华

电子与信息学报 , 2008,
Abstract: Based on the FFT of a single-tone sequence, this paper presents a novel Moving Average Maximum Likelihood (MAML) frequency estimator, which develops a Moving Average (MA) model by the real part relationship between different significant FFT coefficients firstly and a MA model-based maximum likelihood estimation technique. Simulation results show that the algorithm is effective and the proposed estimator outperforms the traditional Rife’s and Quinn’s estimator in both accuracy and the CRLB approximate RMSE of estimation. It is also shown that MAML has the merit of little computation effort and as lower SNR threshold as to -9dB.
Multi-Camera Calibration by FTP Technique
基于傅里叶条纹分析的多摄像机标定方法

LIU Yuan-kun,SU Xian-yu,WU Qing-yang,
刘元坤
,苏显渝,吴庆阳

光子学报 , 2007,
Abstract: A novel camera calibration technique has been proposed,which is based on plane-based camera calibration technique and precise control points extracted by Fourier Transform Profilometry. The higher 2D image coordinates of those control points could be got with respect to the wrapped phase distributions of the crossed sinusoid fringe model plane with previously-known 2D reference coordinates. And then the calibration procedure will be done by plane-based camera calibration technique after measuring the wrapped phase distributions of the model plane at several different orientations. The higher accuracy of phase measuring will provide the control points with higher precision and could lead to a better calibration result. Experimental data has confirmed the proposed technique is easy to use, reliable, high accurate and high-speed.
PHASE TRANSITION OF A PERIODICALLY DILUTED ISING MAGNET
周期性调制稀释Ising体系的相变

高红,王选章,吕树臣
物理学报 , 1996,
Abstract: Applying the effective-field theory with correlations, we study the phase transition of a periodically diluted Ising system in the presence or absence of a transverse field. We focus on the dependence of the critical temperature of the system on the modulation amplitude and transverse field. The interesting result is: the inhomogeneity of the concentration of magnetic atoms can cause an increase in the critical temperature of the system. However, as the modulation amplitude is increased, the bulk magnetic order of the system may change to a partial magnetic order.
一种基于状态空间实现的频率估计与频率时延联合估计算法的研究
吴云韬,廖桂生,陈建峰
自然科学进展 , 2003,
Abstract: 提出了一种基于状态空间实现的正弦信号的频率、时延联合估计新方法,其频率估计由状态过渡矩阵的特征值获得,同时时延估计则由观测矩阵和估计的频率给出,用正弦信号验证了该方法的性能.
昆虫发育速率与温度关系的正弦模型
周以俭 , 祝树德 , 戴志一
扬州大学学报(农业与生命科学版) , 1992,
Abstract: ????提出了昆虫发育速率与温度关系的一个新模型――正弦模型.这个模型适用性强,拟合精度高,计算方便,且能估计发育起点温度.
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