闪光照相系统成像重复性的测量

为了更直观利用照像图像信息考察照相系统的重复性,提出了利用等光程条件下的黑密度分布曲线对成像重复性进行测量的方法,通过两次成像的黑密度分布曲线的线性拟合参数来评估成像系统的成像重复性。实验测量了有无后锥条件下的闪光照相系统的重复性以及底片接收系统的成像重复性,实验结果表明:后锥的存在对成像重复性没有明显影响,底片接收时闪光照相系统的成像重复性约为5%,底片本身引入的成像重复误差约为1.6%。     

闪光照相系统成像重复性的测量

为了更直观利用照像图像信息考察照相系统的重复性,提出了利用等光程条件下的黑密度分布曲线对成像重复性进行测量的方法,通过两次成像的黑密度分布曲线的线性拟合参数来评估成像系统的成像重复性。实验测量了有无后锥条件下的闪光照相系统的重复性以及底片接收系统的成像重复性,实验结果表明:后锥的存在对成像重复性没有明显影响,底片接收时闪光照相系统的成像重复性约为5％,底片本身引入的成像重复误差约为1.6％。     

Examiner repeatability of patellar cartilage T2 values

Aim

The purpose of this study was to evaluate the intra- and interexaminer resegmentation precision of patellar cartilage T₂ mapping measurements in healthy subjects.

Materials and Methods

T₂-weighted images of patellar cartilage for 10 subjects were acquired. Two individuals manually segmented patellar cartilage at each slice location twice, once on each of two separate days. Bulk average and zonal T₂ values for the superficial, middle, and deep layers of cartilage were calculated. The root mean square (RMS) and coefficient of variation (COV) were calculated using the repeated measurements of each slice of each subject by each examiner.

Results

The intraexaminer bulk T₂ differences were 0.2±1.0 ms, with an RMS error of 0.7 ms and a COV of 1.9%. The differences of interexaminer bulk T₂ values was 1.0±1.4 ms, with an RMS error of 1.2 ms and a COV of 3.3%. The superficial zone of cartilage had the highest zonal variability of T₂ values. The average interexaminer T₂ values for the superficial, middle and deep zones were 42.2±5.6, 38.1±5.3 and 31.9±4.6 ms, respectively.

Conclusion

The interexaminer variability of calculated T₂ values highlights the difficulty of interpreting significant differences of T₂ values which are similar in magnitude. The repeatability measurements of patellar cartilage T₂ values were less than reported intersession T₂ repeatability.     

丝阵内爆实验条件重复性控制

在丝阵负载Z箍缩实验中实施了电流加载前真空下负载初始状态的监测,并分别采用新旧结构的电极进行了对比性实验研究,利用十分幅纳秒分幅相机成功获取了不同内爆阶段的实验图像。通过对实验结果的分析,讨论了电极结构和负载初始状态对实验结果的影响程度。实验结果表明：采用新装配方式的负载电极结构具有安装时间短、同轴性容易控制、负载现场安装就位精度高等优点;新研制电极和实施真空下负载状态的检测,有效减少了实验数据分散性,为实验负载参数优化设计提供了技术支持。     

丝阵内爆实验条件重复性控制

在丝阵负载Z箍缩实验中实施了电流加载前真空下负载初始状态的监测,并分别采用新旧结构的电极进行了对比性实验研究,利用十分幅纳秒分幅相机成功获取了不同内爆阶段的实验图像。通过对实验结果的分析,讨论了电极结构和负载初始状态对实验结果的影响程度。实验结果表明:采用新装配方式的负载电极结构具有安装时间短、同轴性容易控制、负载现场安装就位精度高等优点;新研制电极和实施真空下负载状态的检测,有效减少了实验数据分散性,为实验负载参数优化设计提供了技术支持。     

On the improvement of signal repeatability in laser-induced air plasmas

The relatively low repeatability of laser-induced breakdown spectroscopy (LIBS) severely hinders its wide commercialization. In the present work, we investigate the optimization of LIBS system for repeatability improvement for both signal generation (plasma evolution) and signal collection. Timeintegrated spectra and images were obtained under different laser energies and focal lengths to investigate the optimum configuration for stable plasmas and repeatable signals. Using our experimental setup, the optimum conditions were found to be a laser energy of 250 mJ and a focus length of 100 mm. A stable and homogeneous plasma with the largest hot core area in the optimum condition yielded the most stable LIBS signal. Time-resolved images showed that the rebounding processes through the air plasma evolution caused the relative standard deviation (RSD) to increase with laser energies of > 250 mJ. In addition, the emission collection was improved by using a concave spherical mirror. The line intensities doubled as their RSDs decreased by approximately 25%. When the signal generation and collection were optimized simultaneously, the pulse-to-pulse RSDs were reduced to approximately 3% for O(I), N(I), and H(I) lines, which are better than the RSDs reported for solid samples and showed great potential for LIBS quantitative analysis by gasifying the solid or liquid samples.     

灵敏度、分辨率和精度

详细解释大学物理实验中用到的灵敏度、分辨率以及精度的概念,帮助学生认识仪器参数,更好地完成实验内容及误差处理。     

Accuracy of trace formulas

Using quantum maps, we study the accuracy of semiclassical trace formulas. The role of chaos in improving the semiclassical accuracy in some systems is demonstrated quantitatively. However, our study of the standard map cautions that this may not be most general. While studying a sawtooth map we demonstrate the rather remarkable fact that at the level of the time one trace even in the presence of fixed points on singularities the trace formula may be exact, and in any case has no logarithmic divergences observed for the quantum bakers map. As a byproduct we introduce fantastic periodic curves akin to curlicues.     

子孔径拼接干涉检测及其精度分析

介绍了利用小口径干涉仪检测大口径光学元件的方法，从统计的角度出发，详细地推导了子孔径拼接干涉检测技术中拼接参量的具体求解过程，以及使用统计回归方法分析了拼接检测系统精度。并通过实验对该理论进行了实际分析运算。     

Influence of laser diode wavelength tunability on the range, resolution and repeatability of interferometric distance measurement

The coherence length of a single mode laser diode (LD) can reach more than 10 m. It allows the application of this source of light to interferometric distance measurement, with a measurement range of several meters. However, the LD's wavelength tunability, which is a result of the dependence of the lasing wavelength on the injection current, prevents the realization of the theoretically possible metrological parameters of the interferometer. In this study, we analyze the influence of a low-frequency signal disturbance, e.g., noise or disturbing modulation inherent to the injection current of the LD, on the repeatability and measurement range of an LD interferometer used for displacement measurements. Both the measurement range and the resolution of the interferometer are found to be highly limited by this factor.     

Quantitative MRI: Defining repeatability,reproducibility and accuracy for prostate cancer imaging biomarker development

IntroductionQuantitative MRI (qMRI) parameters have been increasingly used to develop predictive models to accurately monitor treatment response in prostate cancer after radiotherapy. To reliably detect changes in signal due to treatment response, predictive models require qMRI parameters with high repeatability and reproducibility. The purpose of this study was to measure qMRI parameter uncertainties in both commercial and in-house developed phantoms to guide the development of robust predictive models for monitoring treatment response.Materials and methodsADC, T1, and R2* values were acquired across three 3 T scanners with a prostate-specific qMRI protocol using the NIST/ISMRM system phantom, RSNA/NIST diffusion phantom, and an in-house phantom. A B1 field map was acquired to correct for flip angle inhomogeneity in T1 maps. All sequences were repeated in each scan to assess within-session repeatability. Weekly scans were acquired on one scanner for three months with the in-house phantom. Between-session repeatability was measured with test-retest scans 6-months apart on all scanners with all phantoms. Accuracy, defined as percentage deviation from reference value for ADC and T1, was evaluated using the system and diffusion phantoms. Repeatability and reproducibility coefficients of variation (%CV) were calculated for all qMRI parameters on all phantoms.ResultsOverall, repeatability CV of ADC was <2.40%, reproducibility CV was <3.98%, and accuracy ranged between −8.0% to 2.7% across all scanners. Applying B1 correction on T1 measurements significantly improved the repeatability and reproducibility (p<0.05) but increased error in accuracy (p<0.001). Repeatability and reproducibility of R2* was <4.5% and <7.3% respectively in the system phantom across all scanners.ConclusionRepeatability, reproducibility, and accuracy in qMRI parameters from a prostate-specific protocol was estimated using both commercial and in-house phantoms. Results from this work will be used to identify robust qMRI parameters for use in the development of predictive models to longitudinally monitor treatment response for prostate cancer in current and future clinical trials.     

用低精度CCD获得高精度测量方法的研究

为了大幅提高线阵CCD的测量精度,提出了一种全新的CCD使用方法。该方法是将N个像元间距为H的线阵CCD器件许排组合住一起,并沿像元线性分布方向以距离为H/N依次均匀错开排列。多个线阵CCD的感光电信号经多通道模一数同步采集,保存到存储器中指定位置。然后,通过对所有CCD测量数据的分析计算来获得精确的测量值。分别采用单CCD和双CCD错排对长为30mm,直径为5．000mm、8．000mm、12．000mm的三个标准杆件的直径进行了测量。结果表明,蚁CCD错排可获得两倍于单CCD的测量精度。该方法可从理论上彻底打破CCD像元问距的限制,并使线阵CCD的测量精度大幅度地提高。     

高精度的光学传递函数计算

直接从基尔霍夫衍射积分理论出发，在数学模型上考虑了瞳面振幅分布的不均匀性和倾斜因子，并采取一系列改进数值计算方法的措施，力求光学传递函数计算的高精度。通过对多个同类软件和多个典型镜头进行比对计算和分析的结果表明，本软件适用于为光学传递函数标准镜头准确定值，也适用于各种大相对孔径和广角光学系统的设计与计算。     

Accuracy of finite element eigenproblems

The accuracy of the eigenvalues λ_r, and eigenvectors u_r of the elliptic eigenproblem of the 2mth order discretized by an arbitrary mesh of simplex finite elements has been studied. It is established as a function of r, of m, of the order of the elements and of the geometrical characteristics of the elements. Comparison with other theoretical results and with experimental results shows the present estimates to be realistic.     

耦合器分光比的精确控制

利用矩形近似理论对用熔锥法制作的耦合器分光比进行了分析。结果表明,影响分光比的主要因素为耦合区长度。给出了两者间变化的理论公式,并在实验中得到了证实。CorningSMF28光纤耦合器分光比随耦合区长度变化的实验值为0 04%/μm,实验值与理论值基本一致。通过调节耦合区长度,得到了精确的50∶50分光比的光纤耦合器。     

焦度计的精度设计

本文讨论了在焦度计的具体技术设计中,如何决定各透镜的焦距、口径和相互位置,以及附加透镜的焦距范围。     

Short- and midterm repeatability of magnetic resonance elastography in healthy volunteers at 3.0 T

The purpose of this study was to evaluate the short- and midterm repeatability of liver stiffness measurements with magnetic resonance elastography (MRE) in healthy subjects at 3.0 T. Twenty-two healthy volunteers were enrolled in this prospective study. The stiffness measurements were obtained from three slices with three repeated acquisitions for each slice (session 1) by two independent raters. After a mean period of 7 ± 2 days (session 2) and 195 ± 15 days (session 3), each subject was scanned again using the same protocol and MR system. The liver stiffness differences were calculated between sessions or raters. The intraclass correlation coefficient (ICC) was calculated to assess interrater agreement and intersession agreement. The stiffness differences over the short- and midterm intervals was (− 0.004 ± 0.086) kPa for sessions 1–2, lower than (− 0.055 ± 0.150) kPa for sessions 1–3 and (− 0.051 ± 0.173) kPa for sessions 2–3. The liver stiffness was more repeatable for the short-term interval with the mean overall ICC of 0.96 (sessions 1–2) (95% confidence interval [CI]: 0.90–0.98) compared with 0.91 (sessions 1–3) (95% CI: 0.78–0.96) and 0.87 (sessions 2–3) (95% CI: 0.69–0.95) for the midterm intervals. The overall ICC of interrater agreement was excellent at 0.987 (95% CI: 0.983 to 0.990). These results confirm that MRE is a reproducible technique for liver stiffness quantification over short- and midterm intervals up to 6 months in a healthy population at 3.0 T.