自动管电流调制技术在双源CT冠状动脉成像中降低辐射剂量的价值

目的：探讨双源CT自动管电流调制（ATCM）技术在冠状动脉成像中降低辐射剂量的价值。方法：回顾性分析134例双源CT冠脉成像资料,根据体重指数（BMI〈18.5,18.5≤BMI≤24,BMI〉24）将受试者分三组,每组分别为28例,50例及56例。每组各随机抽取一半受试者为实验组,根据体重指数手动调节管电流,同时使用ACTM技术（勾选Care Dose 4D）进行扫描;另一半为对照组,仅根据体重指数手动调节管电流。计算所有患者CTA检查的辐射剂量,对冠脉节段进行图像质量评分。结果：实验组及对照组图像质量和图像噪声无显著差异。三组中CTDIvol、DLP、ED值之间差异有统计学意义,实验组比对照组均下降约50%（详细数据见表1）;体重指数偏大组SD值实验组略大于对照组。结论：在图像质量无明显下降的情况下,双源CT冠状动脉成像中使用ATCM能明显降低患者检查的剂量。     

非洲城市二元社会空间结构模式

以城市中心变迁和阶层居住分化为研究视角,探究了非洲近代、现代2个时期的城市二元社会空间结构特征与模式。结果表明：不同时期,非洲城市内部的二元社会空间结构存在显著差异。随着欧洲殖民进程的结束,社会空间结构从旧二元向新二元转变。近代时期,非洲城市空间形态表现出典型的双城模式,殖民者与本地人的居住空间被严格区分;现代时期,非洲城市表现出新旧中心并存模式,中上阶层与贫民居住空间存在明显分异。政治、经济、人口与社会等因素是城市二元社会空间结构形成的重要驱动力。最后,为促进非洲城市社会空间的可持续发展提出了建议。     

双频激电法在澳大利亚Charity Well金矿寻找隐伏矿体的应用

澳大利亚Charity Well金矿地表被第四系覆盖,地表未见明显的找矿标志,本次研究引入了在该矿区较少使用的双频激电地球物理勘查方法。测试数据显示矿区金矿石与围岩视幅频率Fs值具有明显差异,矿石的视幅频率Fs一般都在3.3%以上,而非矿岩石的视幅频率一般小于1.9%,岩石Au品位越高,幅频率一般也越高;赋矿位置与金属硫化物分布范围基本一致,矿区具有开展双频激电法找矿的基础;使用双频激电法在矿区内划分了一个重点找矿靶区和三个一般找矿靶区,利用激电测深展示了异常体在深部的延伸情况,同时也间接地展现了矿化体在深部可能的延伸方向和规模。双频激电法在该区的成功使用为西澳大利亚地区的找矿工作提供了新的思路。     

A novel RANSAC approach to robustly solve the 3D similarity transformation problem

A novel RANSAC robust estimation technique is presented as an effiecient method for solving the seven-parameter datum transformation problem in the presence of outliers. RANSAC method, which is frequently employed in geodesy, has two sensitive features: (i) the user adjusts some parameters of the algorithm, making it subjective and a rather difficult procedure, and (ii) in its shell, a nonlinear system of equation should be solved repeatedly. In this contribution, we suggest an automatic adjustment strategy for the most important parameter, ‘the threshold value’, based on the ‘early stopping’ principle of the machine-learning technology. Instead of using iterative numerical methods, we propose the use of an algebraic polynomial system developed via a dual-quaternion technique and solved by a non-iterative homotophy method, thereby reducing the computation time considerably. The novelty of the proposed approach lies in three major contributions: (i) the provision for automatically finding the proper error limit parameter for RANSAC method, which has until now been a trial-and-error technique; (ii) employing the algebraic polynomial form of the dual-quaternion solution in the RANSAC shell, thereby accelerating the repeatedly requested solution process; and (iii) avoiding iterations via a heuristic approach of the scaling parameter. To illustrate the proposed method, the transformation parameters of the Western Australian Geodetic Datum (AGD 84) to Geocentric Datum Australia (GDA 94) are computed.     

FLASH扫描在冠状动脉CTA双低中的应用研究

目的:探讨在100kV管电压条件下应用碘克沙醇低碘浓度(270mgI/mL)对比剂,结合大螺距前瞻性心电门控螺旋扫描(FLASH spiral)模式和正弦波迭代重建技术(SAFIRE)行冠状动脉CT成像(CCTA)的可行性。方法:收集接受CCTA检查且心率≤70次/min的患者60例,随机分为A、B两组。A组患者采用FLASH spiral扫描模式,扫描管电压100kV,碘对比剂浓度为270mgI/mL,应用迭代重建技术(SAFIRE),重建卷积核I26f;B组患者采用前瞻性心电门控序列扫描模式,扫描管电压为120kV,碘对比剂浓度为370mgI/mL,采用滤波反投影重建(FBP),重建卷积核B26f,比较两组患者CCTA图像质量与有效射线剂量的差异性。结果:①两组患者年龄、心率和BMI比较,差异无统计学意义(P>0.05)。②图像质量:两组图像质量主观评价比较,差异无统计学意义(P>0.05)。两组图像质量客观评价比较,A、B两组在左冠状动脉主干的SD和SNR数值差异有统计学意义外(P<0.05),其他指标差异均无统计学意义(P>0.05)。③辐射剂量:A组平均有效射线剂量为(0.94±0.05)mSv,B组(4.31±1.21)mSv,两组的差异有统计学意义(P<0.05)。A组有效剂量较B组大幅减低,降幅约达78.2%。结论:100kV管电压条件下应用碘克沙醇低碘浓度(270mgI/mL)对比剂,结合FLASH扫描模式和SAFIRE行CCTA检查,图像质量可以满足临床诊断需要,与一般前瞻性心电门控序列扫描相比,有效剂量降低约78.2%。      

基于行政区划调整的合肥-芜湖双核空间整合

行政区划的调整导致城市地域的空间结构发生变化, 对整个区域的发展产生重大影响。2011年7月, 国务院批准了安徽省撤销巢湖市, 将其一分为三, 分别划归合肥、芜湖、马鞍山三市管辖, 合肥、芜湖两个核心城市从此相互毗邻, 合肥-芜湖双核结构是安徽省具有代表性的地域空间结构形式, 其空间整合面临着新的机遇、模式与路径。运用城市空间相互作用理论和方法, 以及双核结构原理对行政区划调整后的合肥-芜湖双核空间整合进行分析。提出在不同时期可以分别采用轴线模式、双核模式、“T”型模式和扇面模式, 采取打破行政区界限的刚性约束、加强双核轴线整体规划、扩大产业整合力度、发挥双核中间城市的比较优势、整体推进合肥-芜湖发展轴建设等措施。     

一种用于非饱和黄土钻探的双管螺旋钻

为了满足非饱和黄土连续原状取芯的要求,参考美国已成熟的螺旋空心钻技术,设计了一种双管螺旋钻具。该钻具结合双管单动岩芯钻和螺旋钻的双重功能,通过螺旋叶片旋进土中,外围土体顺叶片上涌,贴在叶片间的外壁上;里面的空心部分则可以套取土样,使其免受扰动。钻具提出后,清除掉外壁上的土体,卸下钻头,取出里面的土样,不仅可用于土的鉴定,也可用于室内试验。试验表明其钻探取样效果良好,但对钻机动力和工艺要求较高。该钻探技术主要用于黄土滑坡钻探,通过连续取得原状土芯,从中识别和鉴定滑动带。     

车载移动测量系统方位角对比与分析

方位计算对移动测量计算具有重要的意义,本文通过移动测量系统的实测数据,分别在静态环境与动态环境下比较车载移动测量系统的惯性测量单元（IMU）、双天线及轨迹拟合方位角。结果表明：在静态环境下,双天线方位角精度高于IMU方位角的精度;在动态环境下,IMU方位角与拟合方位角在直线段处的表现较好,而在转弯处,双天线方位角的绝对精度更高。     

Surface roughness signatures of summer arctic snow-covered sea ice in X-band dual-polarimetric SAR

ABSTRACT

Surface roughness of sea ice is primary information for understanding sea ice dynamics and air–ice–ocean interactions. Synthetic aperture radar (SAR) is a powerful tool for investigating sea ice surface roughness owing to the high sensitivity of its signal to surface structures. In this study, we explored the surface roughness signatures of the summer Arctic snow-covered first-year sea ice in X-band dual-polarimetric SAR in terms of the root mean square (RMS) height. Two ice campaigns were conducted for the first-year sea ice with dry snow cover in the marginal ice zone of the Chukchi Sea in August 2017 and August 2018, from which high-resolution (4 cm) digital surface models (DSMs) of the sea ice were derived with the help of a terrestrial laser scanner to obtain the in situ RMS height. X-band dual-polarimetric (HH and VV) SAR data (3 m spatial resolution) were obtained for the 2017 campaign, at a high incidence angle (49.5°) of TerraSAR-X, and for the 2018 campaign, at a mid-incidence angle (36.1°) of TanDEM-X 1–2 days after the acquisition of the DSMs. The sea ice drifted during the time between the SAR and DSM acquisitions. As it is difficult to directly co-register the DSM to SAR owing to the difference in spatial resolution, the two datasets were geometrically matched using unmanned aerial vehicle (4 cm resolution) and helicopter-borne (30 cm resolution) photographs acquired as part of the ice campaigns. A total of five dual-polarimetric SAR features―backscattering coefficients at HH and VV polarizations, co-polarization ratio, co-polarization phase difference, and co-polarization correlation coefficient ―were computed from the dual-polarimetric SAR data and compared to the RMS height of the sea ice, which showed macroscale surface roughness. All the SAR features obtained at the high incidence angle were statistically weakly correlated with the RMS height of the sea ice, possibly influenced by the low backscattering close to the noise level that is attributed to the high incidence angle. The SAR features at the mid-incidence angle showed a statistically significant correlation with the RMS height of the sea ice, with Spearman’s correlation coefficient being higher than 0.7, except for the co-polarization ratio. Among the intensity-based and polarimetry-based SAR features, HH-polarized backscattering and co-polarization phase difference were analyzed to be the most sensitive to the macroscale RMS height of the sea ice. Our results show that the X-band dual-polarimetric SAR at mid-incidence angle exhibits potential for estimation of the macroscale surface roughness of the first-year sea ice with dry snow cover in summer.     

基于双立体同步摄影的面部三维重建与量测

介绍了利用多台数码相机基于双立体同步摄影的面部三维模型重建与量测系统 ,提出了一种半自动提取格网点的有效方法。实现了无接触、无伤害、快速地获取面部三维数据和面部特征数据 ,为临床诊治提供依据。实验表明 ,系统达到了 0 .5 m m的量测精度 ,完全能满足实际的精度需求。