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排序方式: 共有95条查询结果,搜索用时 15 毫秒
91.
92.
切伦科夫光生物成像技术是目前分子影像学中的研究热点,具有成像时间短、探针无毒、成本低、灵敏度高等特点,同时为单一分子探针实现核素和光学显像的双模态成像提供了条件,在肿瘤诊断、监测基因表达、疗效评价和引导肿瘤外科手术等方面展现出巨大的应用潜力。本文详细介绍切伦科夫光生物成像在国际范围内的一些显著进展,对切伦科夫光生物断层成像中重建质量和重建速度优化的研究进行综述;同时针对切伦科夫光生物成像技术因切伦科夫光信号强度弱及组织穿透性差而所受的限制,归纳了国内外学者在成像优化方面所做的努力,讨论了向临床应用转化所需的进一步研究和改进。 相似文献
93.
Lianlin Li Fang Li 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
Two models of ionosphere tomography based on spaceborne SAR (Synthetic Aperture Radar) are proposed. For HF-SAR the signal with sweeping frequency lower than the characteristic frequency of ionosphere will be scatted during the ionosphere propagation and completely reflected at a corresponding height. The ionospheric electron density isolines looked as series of random surfaces can be reconstructed from the HF-SAR echoes by using the inverse scattering technique for layered rough surfaces and the method of moment (MoM). The numerical simulation show that due to the MoM can provide a full wave solution, the ionosphere tomography with high resolution can be obtained as long as enough sampling data of HF-SAR echoes are used. For VHF/UHF/P/L-band SAR the TEC (Total Electron Content) can be obtained from the SAR echoes scattered by some strong point targets (such as the calibrators, etc.) appeared in the SAR imaged ground region, and the ionosphere tomography can be performed by CT technique. 相似文献
94.
基于改进NL-means算法的显微CT图像降噪 总被引:1,自引:0,他引:1
显微CT(Computed Tomography)采用微焦点射线源,射线剂量低,CT图像噪声大,对其降噪十分必要.综述了现存主要CT图像降噪算法及其优缺点,介绍了NL(nonlocal)-means算法,根据实验结果分析了其会在图像平滑区域引入人工伪影的不足.根据NL-means算法的不足,在原算法中引入图像的梯度信息,提出了改进的降噪算法,改进算法保持了原算法优良的降噪功能,并能有效抑制人工伪影,且能够提高图像细节对比度,实验结果验证了改进算法的有效性. 相似文献
95.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2023,71(6):2818-2832
Electron density measurements obtained from China Seismo‐Electromagnetic Satellite (CSES) and Swarm-B can play an increasingly important role in the study of ionosphere above F2 peak height. This study presented a comprehensive comparison of electron density products obtained from Langmuir probe mounted on CSES and Swarm-B with ionospheric tomography for a whole year period of 2019. CSES was fully compared with Swarm-B on a global scale, including both absolute and relative differences, and a new index called NFI was developed to better quantify the similarity between two latitudinal profiles of electron density. CSES and Swarm-B were then compared with tomography respectively in four regions, roughly located in America, Europe, Australia and China. Results indicated that CSES data are consistent with Swarm-B, as NFI values exceed 0.6 for most of the analyses. Tomography and Swarm-B were found to have a good agreement as their biases are less than 0.2 × 105 el/cm3 in general. For the comparison between CSES and tomography, the bias increased to around 0.6 × 105 el/cm3 but the standard deviation changed slightly, validating the underestimation of electron density by CSES. The spatiotemporal comparisons of CSES and Swarm-B with tomography showed that: 1) the differences in electron density were relatively low in middle latitudes and increased rapidly in the regions of equatorial ionization anomaly; 2) Swarm-B has a better consistent with tomography than CSES, but both are capable of detecting ionosphere anomalies such as midlatitude arcs; and 3) CSES and Swarm-B both can capture the seasonal changes of electron density, while their values are basically smaller than those from tomography in Spring and Summer months. 相似文献