Quantification issues of in vivo 1H NMR spectroscopy of the rat brain investigated at 16.4 T

The accuracy and precision of the quantification of metabolite concentrations in in vivo ¹H NMR spectroscopy are affected by linewidth and signal‐to‐noise ratio (SNR). To study the effect of both factors in in vivo ¹H NMR spectra acquired at ultrahigh field, a reference spectrum was generated by summing nine in vivo ¹H NMR spectra obtained in rat brain with a STEAM sequence at 16.4 T. By progressive deterioration of linewidth and SNR, 6400 single spectra were generated. In an accuracy study, the variation in the mean concentrations of five metabolites was mainly dependent on SNR, whereas 11 metabolites were predominantly susceptible to the linewidth. However, the standard deviations of the concentrations obtained were dependent almost exclusively on the SNR. An insignificant correlation was found between most of the heavily overlapping metabolite peaks, indicating independent and reliable quantification. Two different approaches for the consideration of macromolecular signals were evaluated. The use of prior knowledge derived by parameterization of a metabolite‐nulled spectrum demonstrated improved fitting quality, with reduced Cramér–Rao lower bounds, compared to the calculation of a regularized spline baseline. Copyright © 2012 John Wiley & Sons, Ltd.     

A PREFRONTAL ERP INVOLVED IN DECISION MAKING DURING VISUAL DURATION AND SIZE DISCRIMINATION TASKS

Recently, a late positive component (LPCt) with prefrontal dominance was identified in a duration discrimination task as a marker of decision-making processes (Paul et al., 2003). In the present study, LPCt amplitudes and latencies were measured in visual and size discrimination tasks for the purpose of determining the selectivity of this phenomenon. LPCt amplitudes were larger and latencies shorter for longer stimulus pairs, at a time of maximal behavioral performances. Wave amplitudes were also larger for smaller stimuli, but were not directly related to behavioral performances. These results indicate that the LPCt is not specific to temporal discrimination but can reflect more general decision-making processes.     

牙冠延长术应用于磨牙缺损修复的临床评价

目的:比较两种不同治疗方法修复磨牙缺损的临床效果。方法:选取86例缺损位于龈下的患牙,分别采用牙冠延长术和牙龈切除术暴露断面,修复后6个月观察临床疗效。结果:牙冠延长组总有效率明显高于牙龈切除组,差异有统计学意义。结论:牙冠延长术能有效恢复患牙生物学宽度,是磨牙缺损的最佳选择。     

A systematic review classifies sources of bias and variation in diagnostic test accuracy studies

ObjectiveTo classify the sources of bias and variation and to provide an updated summary of the evidence of the effects of each source of bias and variation.Study Design and SettingWe conducted a systematic review of studies of any design with the main objective of addressing bias or variation in the results of diagnostic accuracy studies. We searched MEDLINE, EMBASE, BIOSIS, the Cochrane Methodology Register, and Database of Abstracts of Reviews of Effects (DARE) from 2001 to October 2011. Citation searches based on three key papers were conducted, and studies from our previous review (search to 2001) were eligible. One reviewer extracted data on the study design, objective, sources of bias and/or variation, and results. A second reviewer checked the extraction.ResultsWe summarized the number of studies providing evidence of an effect arising from each source of bias and variation on the estimates of sensitivity, specificity, and overall accuracy.ConclusionsWe found consistent evidence for the effects of case–control design, observer variability, availability of clinical information, reference standard, partial and differential verification bias, demographic features, and disease prevalence and severity. Effects were generally stronger for sensitivity than for specificity. Evidence for other sources of bias and variation was limited.