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Jesse I. Hamilton Yun Jiang Brendan Eck Mark Griswold Nicole Seiberlich 《NMR in biomedicine》2020,33(8)
This study introduces a technique called cine magnetic resonance fingerprinting (cine‐MRF) for simultaneous T1, T2 and ejection fraction (EF) quantification. Data acquired with a free‐running MRF sequence are retrospectively sorted into different cardiac phases using an external electrocardiogram (ECG) signal. A low‐rank reconstruction with a finite difference sparsity constraint along the cardiac motion dimension yields images resolved by cardiac phase. To improve SNR and precision in the parameter maps, these images are nonrigidly registered to the same phase and matched to a dictionary to generate T1 and T2 maps. Cine images for computing left ventricular volumes and EF are also derived from the same data. Cine‐MRF was tested in simulations using a numerical relaxation phantom. Phantom and in vivo scans of 19 subjects were performed at 3 T during a 10.9 seconds breath‐hold with an in‐plane resolution of 1.6 x 1.6 mm2 and 24 cardiac phases. Left ventricular EF values obtained with cine‐MRF agreed with the conventional cine images (mean bias ?1.0%). Average myocardial T1 times in diastole/systole were 1398/1391 ms with cine‐MRF, 1394/1378 ms with ECG‐triggered cardiac MRF (cMRF) and 1234/1212 ms with MOLLI; and T2 values were 30.7/30.3 ms with cine‐MRF, 32.6/32.9 ms with ECG‐triggered cMRF and 37.6/41.0 ms with T2‐prepared FLASH. Cine‐MRF and ECG‐triggered cMRF relaxation times were in good agreement. Cine‐MRF T1 values were significantly longer than MOLLI, and cine‐MRF T2 values were significantly shorter than T2‐prepared FLASH. In summary, cine‐MRF can potentially streamline cardiac MRI exams by combining left ventricle functional assessment and T1‐T2 mapping into one time‐efficient acquisition. 相似文献
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目的 通过对某省29家三级综合医院住院医疗服务进行综合评价,为医院管理决策提供参考依据。方法 运用Saaty权重法确定各指标权重,采用非整秩次RSR法围绕医疗服务能力、医疗服务效率、医疗服务质量三方面进行住院医疗服务综合评价与排序。结果 将29家医院划分为好、较好、中等、较差、差五个档次,各档次分别有2家、6家、14家、6家、1家医院。结论 加权非整秩次RSR法结合DRGs指标,能够科学、客观、有效地综合评价住院医疗服务情况,可助力卫生主管部门和医院管理决策。 相似文献
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David Epstein 《Health economics》2019,28(6):801-807
The cost‐effectiveness acceptability curve (CEAC) shows the probability that an option ranks first for net benefit. Where more than two options are under consideration, the CEAC offers only a partial picture of the decision uncertainty. This paper discusses the appropriateness of showing the full set of rank probabilities for reporting the results of economic evaluation in multiple technology appraisal (MTA). A case study is used to illustrate the calculation of rank probabilities and associated metrics, based on Monte Carlo simulations from a decision model. Rank probabilities are often used to show uncertainty in the results of network meta‐analysis, but until now have not been used for economic evaluation. They may be useful decision‐making tools to complement the CEAC in specific MTA contexts. 相似文献
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《Journal of the American College of Radiology》2020,17(10):1337-1343
ObjectiveTo evaluate gender and racial profiles of US academic radiology faculty.Materials and MethodsThis is a retrospective analysis of the American Association of Medical College database of radiology faculty members from 2006 to 2017 by academic rank, chair position, race or ethnicity, and gender. The data were described with annual proportions and average annual counts and fit to a Poisson regression model. Comparison data were taken from American Association of Medical College on matriculants at US medical schools and from ACGME on radiology residents.ResultsWomen increased significantly in the ranks of professor by 4.5%, associate professor by 4.8%, and assistant professor by 4.8% (P < .05). Asian and multiple race non-Hispanic radiologists increased in the rank of professor by 5.9% and 3.1%, respectively (P < .05). Among department chairs, only women and Asian faculty increased by 6.4% and 7.5%, respectively (P < .05). The proportion of women chairs increased from 10.0% (19 of 191) in 2006 to 17.4% (39 of 224) in 2017. Black and Hispanic chairs collectively represented less than 10% of the total chairs every year.DiscussionThe significant percent annual increase in women faculty in academic ranks and chair positions suggests that the radiology faculty is becoming more diverse. However, the decreasing proportion of women with increasing academic ranks within each year of the study period suggests attrition or lack of promotion of women radiology faculty. The disparity in black and Hispanic faculty members and chairs suggests that emphasis should continue to be placed on tailored recruitment. 相似文献
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A marginal rank‐based inverse normal transformation approach to comparing multiple clinical trial endpoints 下载免费PDF全文
The increase in incidence of obesity and chronic diseases and their health care costs have raised the importance of quality diet on the health policy agendas. The healthy eating index is an important measure for diet quality which consists of 12 components derived from ratios of dependent variables with distributions hard to specify, measurement errors and excessive zero observations difficult to model parametrically. Hypothesis testing involving data of such nature poses challenges because the widely used multiple comparison procedures such as Hotelling's T2 test and Bonferroni correction may suffer from substantial loss of efficiency. We propose a marginal rank‐based inverse normal transformation approach to normalizing the marginal distribution of the data before employing a multivariate test procedure. Extensive simulation was conducted to demonstrate the ability of the proposed approach to adequately control the type I error rate as well as increase the power of the test, with data particularly from non‐symmetric or heavy‐tailed distributions. The methods are exemplified with data from a dietary intervention study for type I diabetic children. Published 2016. This article is a U.S. Government work and is in the public domain in the USA 相似文献
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Power and sample size calculations for the Wilcoxon–Mann–Whitney test in the presence of death‐censored observations 下载免费PDF全文
We consider a clinical trial of a potentially lethal disease in which patients are randomly assigned to two treatment groups and are followed for a fixed period of time; a continuous endpoint is measured at the end of follow‐up. For some patients; however, death (or severe disease progression) may preclude measurement of the endpoint. A statistical analysis that includes only patients with endpoint measurements may be biased. An alternative analysis includes all randomized patients, with rank scores assigned to the patients who are available for the endpoint measurement on the basis of the magnitude of their responses and with ‘worst‐rank’ scores assigned to those patients whose death precluded the measurement of the continuous endpoint. The worst‐rank scores are worse than all observed rank scores. The treatment effect is then evaluated using the Wilcoxon–Mann–Whitney test. In this paper, we derive closed‐form formulae for the power and sample size of the Wilcoxon–Mann–Whitney test when missing measurements of the continuous endpoints because of death are replaced by worst‐rank scores. We distinguish two approaches for assigning the worst‐rank scores. In the tied worst‐rank approach, all deaths are weighted equally, and the worst‐rank scores are set to a single value that is worse than all measured responses. In the untied worst‐rank approach, the worst‐rank scores further rank patients according to their time of death, so that an earlier death is considered worse than a later death, which in turn is worse than all measured responses. In addition, we propose four methods for the implementation of the sample size formulae for a trial with expected early death. We conduct Monte Carlo simulation studies to evaluate the accuracy of our power and sample size formulae and to compare the four sample size estimation methods. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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Alexander B. Chase Claudia Weihe Jennifer B. H. Martiny 《Proceedings of the National Academy of Sciences of the United States of America》2021,118(18)
Microbial community responses to environmental change are largely associated with ecological processes; however, the potential for microbes to rapidly evolve and adapt remains relatively unexplored in natural environments. To assess how ecological and evolutionary processes simultaneously alter the genetic diversity of a microbiome, we conducted two concurrent experiments in the leaf litter layer of soil over 18 mo across a climate gradient in Southern California. In the first experiment, we reciprocally transplanted microbial communities from five sites to test whether ecological shifts in ecotypes of the abundant bacterium, Curtobacterium, corresponded to past adaptive differentiation. In the transplanted communities, ecotypes converged toward that of the native communities growing on a common litter substrate. Moreover, these shifts were correlated with community-weighted mean trait values of the Curtobacterium ecotypes, indicating that some of the trait variation among ecotypes could be explained by local adaptation to climate conditions. In the second experiment, we transplanted an isogenic Curtobacterium strain and tracked genomic mutations associated with the sites across the same climate gradient. Using a combination of genomic and metagenomic approaches, we identified a variety of nonrandom, parallel mutations associated with transplantation, including mutations in genes related to nutrient acquisition, stress response, and exopolysaccharide production. Together, the field experiments demonstrate how both demographic shifts of previously adapted ecotypes and contemporary evolution can alter the diversity of a soil microbiome on the same timescale.Microbial communities respond quickly to environmental change (1, 2). These responses are typically associated with ecological processes; however, the potential for microbes to evolve and adapt to changes in the environment on ecological timescales remains largely unexplored in natural ecosystems. While evolutionary processes are typically considered over longer timescales, the short generation times, large populations, and high mutation rates indicative of microorganisms may allow for rapid adaptation. Laboratory studies have repeatedly demonstrated rapid evolution of bacterial populations (3) with consequences for organismal physiology (4), yet it remains unclear how these in vitro studies extend to in situ communities (5).Both ecological and evolutionary processes likely contribute simultaneously (6, 7) to the response of a microbiome to changing environmental conditions (8). However, separating these processes for bacteria can be difficult as they occur along a continuum of temporal and genetic scales. In terms of ecological processes, microbiome composition can respond demographically, as selective forces promote the growth and survival of differentially adapted taxa within the bacterial community. Certainly, many studies have observed such shifts in taxonomic composition of 16S ribosomal RNA (rRNA)–defined taxa in response to simulated global changes (9), and these responses are considered an ecological process (e.g., species sorting). Few examples, however, link these responses to trait differences among bacterial taxa (10–13), precluding direct insights into whether these ecological shifts are due to adaptive differentiation among taxa as a result of past evolutionary divergence. Concurrently, the same selective forces can also shift the abundance of conspecific strains and alter the allele frequencies of preexisting genetic variation, which at this genetic scale is defined as an evolutionary process (14). Finally, evolution through de novo mutation can provide a new source of genetic variation that may allow for further adaptation to environmental change.In this study, we aimed to capture this continuum of ecological and evolutionary processes that together produce the response of a microbiome’s diversity to environmental change (Fig. 1A). Studying evolution in microbial communities in situ, however, is challenging. For one, variation in highly conserved marker genes used in many microbiome studies (e.g., 16S rRNA) represents distant evolutionary divergences, and thus these regions are too conserved to detect locally adapted lineages (11, 12, 15), let alone recent evolutionary change within communities (16). To overcome this limitation, studies have leveraged shotgun metagenomic data (17, 18) and genome sequences of co-occurring, closely related strains (19, 20) to characterize evolutionary processes (e.g., recombination and gene flow) structuring the genetic diversity of bacterial lineages. However, these studies are also limited by an inherent challenge in microbiome research: delineating population boundaries, the fundamental unit of evolution. While progress has been made in defining microbial species (21–23), the high genetic heterogeneity within diverse microbial communities, such as soils, convolute the boundaries of the fine-scale patterns of genetic diversity within microbial taxonomic units (12). For instance, metagenome-assembled genomes are often composed of a composite of strains forming a large population of mosaic genomes (24) that may not fully capture the diversity of the local population (25). As such, it remains difficult to study evolutionary rates within microbial communities (however, see refs. 26, 27), and the extent and time scale at which evolutionary processes contribute to both standing and new genetic variation relative to ecological processes.Open in a separate windowFig. 1.Microbial community transplant experiment. (A) Changes in microbial community composition can be due to a continuum of ecological and evolutionary processes. For instance, shifts in standing genetic variation can be attributed to both ecological and evolutionary processes depending on the level of biological resolution, while de novo mutations can be a result from evolutionary adaptation. (B) A schematic of the two parallel transplant experiments at the community and strain level. Inoculated litterbags were transplanted to all sites along an elevation gradient that covaried in temperature and precipitation. Site codes: D=Desert; Sc=Scrubland; G=Grassland; P=Pine-Oak; S=Subalpine.Here, we asked the following question: can we characterize the ecological and evolutionary processes that are contributing concurrently to the response of a soil bacterial community to a changing environment? To answer this question, we utilized a field-based experimental approach to quantify the influence of both ecological and evolutionary processes on one focal soil bacterium in its natural environment, the genus Curtobacterium (28). Specifically, we transplanted the bacterium across an elevation gradient on a common resource (leaf litter) substrate (29) to assess its response to new climates in two parallel experiments over the same 18 mo time period (Fig. 1B). In both experiments, we used microbial cages [nylon mesh bags that allow for nutrient transport (30)] to manipulate microbial composition while restricting microbial migration to eliminate the introduction of new alleles and/or variants from dispersal (31). A reciprocal transplant design allowed for direct testing of microbial adaptation to abiotic conditions (i.e., moisture and temperature) in a natural setting.In the first experiment, we conducted a reciprocal transplant of the entire microbial community (32) and tracked the ecological response of Curtobacterium ecotypes (33). A bacterial ecotype is defined as highly clustered genotypic and phenotypic strains occupying the same ecological niche, somewhat equivalent to a eukaryotic species (34). To test the hypothesis that Curtobacterium ecotypes are locally adapted to their climate conditions, we assessed the convergence of ecotype composition in the transplanted communities to that of control communities (those that remained in their native environment; Fig. 1B). We further hypothesized that the demographic shifts were due to differential adaptation to local climates as a result of trait variation among the ecotypes. Thus, we expected that the climate gradient would select for a strong trait–environment relationship (assessed by community-weighted mean (CWM) trait values) as typically observed in plant communities (35, 36).In parallel, we conducted an in situ evolution experiment by transplanting an isogenic Curtobacterium strain across the same gradient to investigate the potential for rapid evolution on the same timescales. We hypothesized that a variety of genomic mutations would be associated with adaptation to local climate conditions. Therefore, we expected fewer genetic changes when the strain was transplanted to its original environment, the midelevation Grassland site, while the extreme sites of the gradient would impose stronger selective pressures resulting in greater genetic changes. We further expected to observe parallel mutations among replicates within a site, which would be indicative of adaptive events (37). Variation in such mutations across sites would suggest selection differences across the climate gradient. Together, the two experiments capture the simultaneous effects of both ecological and evolutionary processes on the response of a soil bacterium to new climates in the field. 相似文献