彩色多普勒超声帧差伪像的成因与特征探讨

本文目的在于探讨超声帧差伪像的形成原因与声像图特征。通过分析医用超声诊断仪器所采用的设计模型与人体组织声学特性之间存在的矛盾、探头振元数与物理通道数之间的匹配关系、2D图像与彩色多普勒图像在显示屏上的“实时”复合方式,揭示出在图像复合显示过程中,因帧频不同而导致的人体解剖结构与血流信号在时间、空间上“错位”而导致的伪像,阐明它具有的必然性、复合性、隐蔽性、低关注度特点,为仪器设计开发和超声医生在工作中及时识别帧差伪像,减少误诊,提供思路。     

Spatially robust estimates of biological nitrogen (N) fixation imply substantial human alteration of the tropical N cycle

Biological nitrogen fixation (BNF) is the largest natural source of exogenous nitrogen (N) to unmanaged ecosystems and also the primary baseline against which anthropogenic changes to the N cycle are measured. Rates of BNF in tropical rainforest are thought to be among the highest on Earth, but they are notoriously difficult to quantify and are based on little empirical data. We adapted a sampling strategy from community ecology to generate spatial estimates of symbiotic and free-living BNF in secondary and primary forest sites that span a typical range of tropical forest legume abundance. Although total BNF was higher in secondary than primary forest, overall rates were roughly five times lower than previous estimates for the tropical forest biome. We found strong correlations between symbiotic BNF and legume abundance, but we also show that spatially free-living BNF often exceeds symbiotic inputs. Our results suggest that BNF in tropical forest has been overestimated, and our data are consistent with a recent top-down estimate of global BNF that implied but did not measure low tropical BNF rates. Finally, comparing tropical BNF within the historical area of tropical rainforest with current anthropogenic N inputs indicates that humans have already at least doubled reactive N inputs to the tropical forest biome, a far greater change than previously thought. Because N inputs are increasing faster in the tropics than anywhere on Earth, both the proportion and the effects of human N enrichment are likely to grow in the future.Over the last few decades, humans have dramatically altered the global nitrogen (N) cycle (1–3). Three main processes—Haber–Bosch fixation of atmospheric N₂, widespread cultivation of leguminous N-fixing crops, and incidental N fixation during fossil fuel combustion—collectively add more reactive N to the biosphere each year than all natural processes combined (2). Although human perturbation of the N cycle has brought substantial benefits to society (most notably, an increase in crop production) (4), it has also had a number of negative effects on both ecosystems (5, 6) and people (7).Although humanity’s large imprint on the global N cycle is clear, quantifying the extent of anthropogenic changes depends, in large part, on establishing baseline estimates of nonanthropogenic N inputs (1, 8, 9). Before recent human activities, biological N fixation (BNF) was the largest source of new N to the biosphere (9). Terrestrial BNF has been particularly challenging to quantify, because it displays high spatial and temporal heterogeneity at local scales, it arises from both symbiotic associations between bacteria and plants as well as free-living microorganisms (e.g., in leaf litter and soil) (10), and high atmospheric concentrations of N₂ make direct flux measurements unfeasible. Consequently, spatial estimates of BNF have always been highly uncertain (11), and global rate estimates have fallen precipitously in the last 15 y (from 100–290 to ∼44 Tg N y⁻¹) (9). This decline in BNF implies an increase in the relative magnitude of anthropogenic N inputs from 100–150% to 190–470% of BNF (9).Historically, the largest anthropogenic changes to the N cycle have occurred in the northern temperate zone: first throughout the United States and western Europe and more recently, in China (12, 13). Large-scale estimates of BNF in natural ecosystems in these regions are consistently low (11), leading some to conclude that anthropogenic N inputs in the northern temperate zone exceed naturally occurring BNF and preindustrial atmospheric N deposition by an order of magnitude or more (1, 14). By contrast, the highest rates of naturally occurring BNF have been thought to occur in the evergreen lowland tropical rainforest biome (11), implying that, on a regional basis, human alteration of the tropical N cycle has been comparatively modest. However, in recent years, the tropics have seen some of the most dramatic increases in anthropogenic N inputs of any region on Earth—a trend that is likely to continue (2, 6, 13). Anthropogenic N inputs are increasing in tropical regions, primarily because of increasing fossil fuel combustion (13) and expanding high-N-input agriculture for both food and biofuels (6). These anthropogenic N inputs are having a measurable effect on tropical ecosystems (15). However, understanding and forecasting the effects of anthropogenic N depend, in part, on accurate estimates of BNF in lowland tropical rainforest.Unfortunately, the paradigm that the tropics have high rates of BNF is based on a paucity of evidence and several tenuous assumptions. For example, an early global synthesis of terrestrial BNF (11)—which included contributions from both symbiotic and free-living sources—included only one measured estimate of symbiotic BNF from tropical forest (16 kg N ha⁻¹ y⁻¹) (16). That single estimate, scaled over thousands of square kilometers, represented the only direct evidence of high tropical BNF rates available at that time (Fig. 1). Subsequent modeled estimates (17) that indirectly estimated BNF have reinforced the notion that tropical BNF rates are high and dominated by the symbiotic form of fixation (Fig. 1). Such high estimates of symbiotic BNF are consistent with the large number of leguminous trees in tropical forest (18–20). However, many legume species do not form N-fixing nodules (21), and of those species that do, nodulation in individuals varies with soil nutrient status, N demand, and tree age (22). Several recent analyses (10, 22–24) indicate lower tropical forest BNF and suggest that symbiotic BNF may not be as important to total BNF as previously thought (Fig. 1), although few studies have simultaneously measured symbiotic and free-living BNF.Open in a separate windowFig. 1.Previous estimates of BNF in tropical rainforest and BNF measured in this study. Percentages indicate the proportion of total BNF from symbiotic BNF. Cleveland et al. 1999 A (11) is a literature database-derived estimate of tropical forest BNF; Cleveland et al. 1999 B (11) is a modeled estimate of BNF based on the correlation between net primary productivity (NPP) and BNF derived with remotely sensed NPP and evergreen broadleaved forest (EBF) land cover classification. Central estimates and variance for Cleveland et al., 1999 A (11) and Reed et al. 2011 (10) represent the low, central, and high data-based estimates of BNF assuming 5%, 15%, and 15% legume cover, respectively. Central estimates and variance for Wang and Houlton 2009 (17) represent the modeled mean and SD of BNF predicted for the EBF biome. Central estimates and variance for Cleveland et al. 2010 (23) represent the low, central, and high estimates of symbiotic BNF plus free-living BNF or modeled BNF plus free-living BNF. Central estimates and variance for BNF in the four forest ages measured here (primary, 5–15 y, 15–30 y, and 30–50 y) represent means ± 1 SD (n = 3). Our estimate of BNF in a dynamic primary forest (gap dynamics) lacks SD, because it consisted of only two measurements: low and high estimates of forest turnover times equal to 150 and 75 y, respectively.There is also a sound theoretical basis for questioning high estimates of BNF in tropical forest. Namely, high concentrations of soil N in the legume-rich tropics create something of a paradox. Although BNF could create N-rich conditions, the substantial energetic cost of BNF means—and some data show—that BNF should be suppressed under high N availability in primary forests (25). Because of high rates of net primary productivity and high N demand in secondary forests (26, 27), regenerating canopy gaps or abandoned agricultural land may have higher rates of BNF than late-successional forest ecosystems (26).Resolving the uncertainty in the tropical (and global) N cycle requires that we overcome the enduring challenge of quantifying BNF in any ecosystem. How do we estimate large-scale rates of a process that displays extreme spatial heterogeneity at local scales? Whether using acetylene reduction assays, ¹⁵N tracer incubations, or the ¹⁵N natural abundance method, most past approaches to empirically estimate symbiotic BNF have relied on spatial extrapolations of BNF rates measured at the level of individual trees. Typically, such extrapolations are based on legume abundance (e.g., percent cover) and make species- or genera-level assumptions about nodulation status of putative N fixers. Here, we applied a method commonly used by community ecologists to measure rare species abundances—stratified adaptive cluster sampling (SACS) (28)—to measure symbiotic BNF. This approach could be used in any ecosystem, and in contrast to other methods, SACS generates unbiased estimates of mean symbiotic BNF (independent of legume abundance) and can more robustly capture the irregular distribution of nodules on the landscape. We simultaneously measured symbiotic and free-living BNF multiple times over the course of 1 y to generate spatially explicit rates of BNF inputs in primary and secondary (5–50 y old) lowland tropical forest in Costa Rica and then used the understanding gained from those estimates to revisit estimates of BNF and anthropogenic N inputs in the tropical forest biome.     

新形势下医疗器械抽查检验管理规定的修订

目的：探讨医疗器械抽检有关规定的修订要点。方法：对医疗器械监管特别是抽检所面临的新形势进行整理,对现行医疗器械抽检有关规定的不足和问题进行归纳,对修订要点的可行性和影响进行分析。结果：提出了修订《医疗器械抽查检验管理办法》的若干建议。结论：监管机构应当充分认识当前医疗器械监管形势的变化,及时总结经验教训,调整定位并主动作为,将修订医疗器械抽检有关规定提上日程。     

2017-2018年国家医疗器械抽检产品质量状况分析

目的：从国家医疗器械抽检结果出发,总结抽检品种质量状况特点,探讨如何进一步加强医疗器械监督管理。方法：通过对监督抽检发现的医疗器械质量状况存在的问题进行分析研究,提出相应的措施和意见建议。结果：有源医疗器械不合格检出率较高,无源医疗器械的原料选购和工艺存在一定问题,医疗器械领域贯彻执行国家标准、行业标准存在隐忧及一些问题企业。结论：应从落实企业主体责任并强化质量体系建设、严格处理问题产品和企业、提高审核查验针对性和力度、加大审评指导、加强国家标准和行业标准宣贯等角度入手,加强医疗器械监管。     

A seven day actigraphy-based study of rumination and sleep disturbance among young adults with depressive symptoms

Objectives

Trait ruminators exhibit significantly higher levels of sleep disturbance than those without this cognitive vulnerability. However, support for the sleep disruptive effects of state rumination, especially in the pre-sleep period, is rare, and hindered by methodological drawbacks such as self-report and single night assays of sleep. Finally, despite the pervasiveness of the ruminative response style among individuals with depression, the association between rumination and sleep disturbance has not been explored in this population. The present study employed a week-long daily sampling approach to examine the effects of naturally occurring pre-sleep rumination on self-reported and actigraphy-based sleep among individuals with high depressive symptomatology.

Methods

Forty-two university students (19.6 ± 3.2 yo;73.8% female), all of whom reported at least moderate levels of depressive symptoms, completed a short questionnaire after waking each morning for seven days. On this questionnaire, they self-reported sleep indices from the previous night and levels of engagement in pre-sleep rumination. Sleep was also monitored throughout this period via wrist actigraphy. Hierarchical-linear-modeling was used to examine the association between nightly rumination and sleep.

Results

Nightly variations in pre-sleep rumination were predictive of significantly longer actigraphy- and diary-based sleep onset latency (SOL). Notably, a 1 SD increase on the pre-sleep rumination scale was associated with an approximately 7 minute increase in actigraphy-based SOL, even after controlling for baseline sleep disturbance and depressive symptoms.

Conclusions

These data offer compelling evidence for the impact of pre-sleep rumination on sleep onset, providing insight into one potential mechanism that triggers sleep disturbance among individuals with depressive symptoms.     

Non-clinical pharmacokinetics and pharmacodynamics of rVIII-SingleChain,a novel recombinant single-chain factor VIII

Introduction

rVIII-SingleChain (CSL627), a novel recombinant coagulation factor VIII (FVIII), is under investigation in a phase I/III clinical programme (AFFINITY) for the treatment of haemophilia A. Non-clinical studies were conducted to investigate the pharmacokinetic/pharmacodynamic profile of rVIII-SingleChain in comparison with full-length recombinant FVIII.

Materials and Methods

Binding affinity of rVIII-SingleChain for von Willebrand factor was investigated by surface plasmon resonance analysis. The pharmacokinetic profile of rVIII-SingleChain was compared with a marketed full-length recombinant FVIII concentrate (Advate^®) in haemophilia A mice, von Willebrand factor knock-out mice, Crl:CD (SD) rats, rabbits and cynomolgus monkeys. Systemic FVIII activity or antigen levels were recorded. Procoagulant activity was measured in an FeCl₃-induced arterial occlusion model and by recording thrombin generation activity (ex vivo) after administration of 200–250 IU/kg rVIII-SingleChain or full-length FVIII to haemophilia A mice.

Results

rVIII-SingleChain displayed a high affinity for von Willebrand factor (K_D = 44 pM vs. 139 pM for full-length recombinant FVIII). In all animal species tested, rVIII-SingleChain had more favourable pharmacokinetic properties than full-length recombinant FVIII: clearance was decreased and area under the curve and terminal half-life were enhanced vs. full-length recombinant FVIII, while in vivo recovery and volume of distribution were equivalent. rVIII-SingleChain showed a prolonged thrombin generation potential and prolonged procoagulant activity vs. full-length recombinant FVIII in an FeCl₃-induced arterial occlusion model.

Conclusions

rVIII-SingleChain had a higher affinity for von Willebrand factor than full-length recombinant FVIII and displayed favourable pharmacokinetic/pharmacodynamic properties in non-clinical models.     

Compressive fluorescence microscopy for biological and hyperspectral imaging

The mathematical theory of compressed sensing (CS) asserts that one can acquire signals from measurements whose rate is much lower than the total bandwidth. Whereas the CS theory is now well developed, challenges concerning hardware implementations of CS-based acquisition devices--especially in optics--have only started being addressed. This paper presents an implementation of compressive sensing in fluorescence microscopy and its applications to biomedical imaging. Our CS microscope combines a dynamic structured wide-field illumination and a fast and sensitive single-point fluorescence detection to enable reconstructions of images of fluorescent beads, cells, and tissues with undersampling ratios (between the number of pixels and number of measurements) up to 32. We further demonstrate a hyperspectral mode and record images with 128 spectral channels and undersampling ratios up to 64, illustrating the potential benefits of CS acquisition for higher-dimensional signals, which typically exhibits extreme redundancy. Altogether, our results emphasize the interest of CS schemes for acquisition at a significantly reduced rate and point to some remaining challenges for CS fluorescence microscopy.     

The antimicrobial effect of apical box versus apical cone preparation using iodine potassium iodide as root canal dressing: A pilot study

Abstract

Purpose. The purpose was to study the reduction of intra-canal microflora in premolars with apical periodontitis instrumented with either apical box or apical cone preparation and to provide measurements of intervention effects to allow proper power calculation in future clinical trials. Methods. Twenty-four patients were centrally randomized to apical box preparation (size #60) or cone preparation (apical size #25). The groups were comparable regarding the presence of primary caries and type of coronal restoration. In the course of canal preparation each tooth was irrigated with 2.5% NaOCl (12 ml). Lastly, the canals were filled with 17% EDTA (2 × 30 s) and 5% iodine potassium iodide (IKI) for 10 min. The canals were sampled for micro-organisms on four occasions: before instrumentation, after instrumentation, after application of IKI dressing and at the beginning of the second appointment 1 week later. Between the treatment sessions, the root canals were sealed with IRM cement. In the laboratory, culture techniques were used to measure microbial growth, which was classified as: none, very sparse, sparse, moderate, heavy or very heavy. Results. Initially, microbes were recovered in 88% of the teeth. Growth was classified as none in 35% of the teeth after instrumentation and in 50% after the application of IKI. Irrespective of the time of sampling, no significant difference in microbial growth reduction was observed between the two types of apical preparation. Based on the 1-week post-sampling, a power calculation revealed that over 900 patients are needed to show a difference of 9% between the two protocols tested. Conclusions. Future trials should be conducted using stringent protocols and as multi-centre trials for reaching the required information size.     

Laterality of central venous sampling: lack of effect on the accuracy of intraoperative parathyroid hormone monitoring

Background

The purpose of this study was to determine if laterality of internal jugular vein (IJV) sampling affects the accuracy of intraoperative parathyroid hormone (PTH) monitoring during parathyroidectomy for primary hyperparathyroidism.

Methods

In this study, 109 patients underwent parathyroidectomy (82 with unilateral disease, 27 with multigland disease). PTH samples were taken from both the left and the right IJV at these time points: preincision (baseline) and then at 5, 10, and, in selected patients, 20 minutes after excision. The Miami criterion was used to determine operative success.

Results

In all 109 patients combined, the mean decreases in intraoperative PTH levels were 73.8 ± 22.2% for the left IJV and 71.9 ± 23.0% for the right IJV (P = .22). The Miami criterion was met in 105 patients: in 100 (95%) left IJV samples and 99 (94%) right IJV samples (P = 1.00).

Conclusions

No difference was found in the accuracy of intraoperative PTH monitoring between patients' left and right IJV samples. Central venous laterality did not affect fulfillment of the Miami criterion.