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排序方式: 共有962条查询结果,搜索用时 15 毫秒
1.
Maria Drangova Yudong Zhu Norbert J. Pelc 《Journal of magnetic resonance imaging : JMRI》1997,7(4):664-668
The reproducibility of myocardial motion trajectories calculated from cine phase-contrast (PC) velocity data is reduced by artifacts due to the inconsistent motion of intracardiac blood. Spatial presaturation reduces these artifacts but requires a longer sequence TR, with a potentially negative effect on trajectory accuracy and reproducibility. We investigated the effect of spatial presaturation on trajectory reproducibility. A midventricular transaxial slice was imaged in five normal volunteers. The same slice was imaged three times each with sequences using spatial presaturation or not. Because the most serious artifacts originate in the heart chambers and propagate in the phase-encoded direction, myocardial regions that were in line with the heart chambers (in the phase-encode direction) had the highest artifact level in the scans without spatial presaturation. The reproducibility of trajectories for regions placed in these areas (the anterior wall, septum and posterior wall in the transaxial scans with phase encoding in the anterior-posterior direction) improved by a factor of two when presaturation was used (P < .001). In areas that were not in line with the heart chambers (eg, the anterior aspect of the lateral wall in the transaxial scans), the effect of presaturation was not significant. These results correlate well with the measured reduction in artifact level. The reproducibility of myocardial motion trajectories over large areas of the heart is improved to approximately 1 mm when presaturation is used. Therefore, use of presaturation is recommended for myocardial motion studies using cine PC velocity data. 相似文献
2.
Hana Illner John A. S. McGuigan Daniel Lüthi 《Pflügers Archiv : European journal of physiology》1992,422(2):179-184
The new fluorescent indicator, mag-fura-5, was evaluated for its ability to measure accurately physiological changes in cytosolic free magnesium. The apparent dissociation constants (K
d) of the fluorochrome for Mg2+, Mg2+/EGTA and Ca2+/EGTA solutions were 14.7 mM, 15.4 mM, and 1.8 mM respectively. The calculated difference in the fluorescence ratios and in the resulting pMg between the standards with low-Ca2+ or low H+ backgrounds and the corresponding samples with approximately physiological levels were not significant. In contrast, the changes due to an increased Ca2+ or H+ content were statistically significant, with mean pMg differences of 0.10±0.09 (P<0.02) and 0.33±0.26 (P<0.01) respectively. Repetitive measurements on 3 consecutive days yielded comparable data with differences not exceeding 4%. Because of the good reproducibility, it is suggested that the new fluoresecent probe may be suitable for free cytosolic magnesium determinations in isolated cells. 相似文献
3.
T. A. Larnach S. J. Boyd R. C. Smart S. P. Butler P. G. Rohl T. H. Diamond 《Calcified tissue international》1992,51(4):255-258
Summary Reproducibility of lateral spine dual energy X-ray absorptiometry (LAT DEXA) scans using a Lunar DPX-L scanner was assessed in a cadaveric phantom and in patients. One hundred phantom measurements over 7 months demonstrated a longitudinal stability of 1.7% (coefficient of variation, CV). Additional scans were performed with the phantom rotated by up to 20° in each of the three orthogonal planes to assess the effects of variable patient positioning. Horizontal and vertical rotation of the spine had little effect on the estimated bone mineral density (BMD), however, axial rotation of greater than 8° led to errors in the BMD measurement. One hundred consecutive patients had two lateral scans performed within 1 month. BMD (range 0.10–1.6 g/cm2) was determined for each scan by one operator. Significant overlap from ribs and pelvis was often seen with L2 and L4 vertebrae but one vertebra (L3) could be measured in every case. Intraoperator and interoperator variability was assessed by three experienced operators, each analyzing 10 patients' scans on five separate occasions, and was found to be less than 1.1% for a single vertebra. BMD estimation of vertebral bodies and midslices by lateral DEXA scans (CV% of 3.8% and 4.6%) have a 95% confidence interval of 0.074 g/cm2 and 0.096 g/cm2, respectively for two vertebrae. This variability is due mainly to axial rotation, with operator variability, horizontal rotation, and vertical rotation having little effect on BMD estimation. 相似文献
4.
Prof. Dr. J. Köbberling A. Kerlin W. Creutzfeldt 《Journal of molecular medicine (Berlin, Germany)》1980,58(10):527-530
Summary Three oral glucose tolerance tests (oGTT) have been performed in 312 non-diabetic relatives of diabetics over a period of 10 years. In a second study 6 identical oGTT's have been performed at weekly intervals in 55 individuals. In this study the variance, calculated from the logarithmic values, increased in the following order: fasting (0.026), 1 h (0.035), 2 h (0.044) and 3 h values (0.047). The sum of the 1 h and 2 h values showed the lowest variance (0.024). No significant difference of the variances was found in the 43 individuals in whom both the long-term and the short-term studies have been performed. Thus, a great proportion of the total variance of glucose observed over longer periods only represents a random variation. This random variation is much higher than most other factors which might influence the result of an oGTT. A diagnosis based on a single oGTT is of only limited value.Supported by a grant from Deutsche Forschungsgemeinschaft (Ko 457/8) 相似文献
5.
K. B. Veiersted 《European journal of applied physiology》1991,62(2):91-98
Summary The main purpose of this study was to evaluate the reproducibility of electromyographic (EMG) measurements and specifically to test a calibration procedure with submaximal test contractions. Bipolar surface electrodes (20 mm fixed distance) were repositioned by a tracing sheet on both trapezius muscles, halfway between acromion and processus prominens. Submaximal test contractions were performed by keeping both arms straight abducted 90° and forward flexed 10° for 15-s periods. The arm position could be precisely reproduced in the frontal plane, but deviated forwards by 4° in the horizontal plane, where the sensitivity of the EMG response to arm position was lowest. The electrodes were repositioned within a radius of 3 mm with a probability of 90%. Large deviations in the EMG response were found within this radius and a significant depression of the EMG response was recorded over the middle part of the muscle (the innervation zone?). This change in sensitivity of the EMG response with electrode position occurred in parallel for the test and maximal contractions. The total coefficient of variation was estimated to be 23% for recurrent EMG measurements using the calibration procedure described. 相似文献
6.
《Journal of the Academy of Nutrition and Dietetics》2022,122(9):1665-1676.e2
BackgroundDietary supplement use is common, particularly among cancer survivors and those at increased risk for cancer.ObjectiveThe objectives of this study were to assess 1-year test–retest reproducibility of dietary supplement use reported via food frequency questionnaire (FFQ-1 vs FFQ-2) and relative validity in comparison to repeated 24-hour dietary recalls (FFQ-2 vs DRs).DesignThis ancillary study was conducted within a large prospective cohort, the American Cancer Society’s Cancer Prevention Study-3.Participants/settingBetween 2015 and 2016, 684 participants in the United States (64% women; 62% non-Hispanic White, 23% non-Hispanic Black, and 15% Hispanic) completed two FFQs and up to six unannounced telephone interviewer-administered DRs over 1 year as part of the Cancer Prevention Study-3 Diet Assessment Substudy.Primary outcome measuresFFQs queried current multivitamin-mineral supplement (≥10 components) use, frequency and dose (range) for seven supplements taken individually or as part of a complex (individual/complex) including calcium, vitamins D, C, and E, folic acid, fish oil, and glucosamine. DRs allowed exact reporting of supplement frequency and dose.Statistical analysesWeighted κ statistics were used to evaluate reproducibility between FFQ-1 and FFQ-2 and Spearman correlation coefficients assessed agreement between supplemental nutrient amounts assessed by FFQ-2 and the average of DRs.ResultsJust more than half of the participants reported taking multivitamin-mineral supplements on the baseline FFQ. Kappa statistics for the comparison of categorical responses between FFQ-1 and FFQ-2 were 0.67 for multivitamin-mineral supplements. Kappas for individual/complex supplements ranged from 0.47 for folic acid to 0.74 for vitamin D, with a mean of 0.64. Results were similar between men and women. Spearman correlation coefficients comparing FFQ-2 with the average of DRs (validity) for nutrient intakes from all sources ranged from 0.65 (fish oil for women) to 0.77 (vitamin D for men and calcium for women); results were similar among men and women.ConclusionsThese findings suggest the FFQ used in Cancer Prevention Study-3 has good reproducibility over 1 year and yields estimates comparable to a more detailed assessment for commonly consumed dietary supplements. 相似文献
7.
Reproducibility of the signal-averaged electrocardiogram using individual lead analysis 总被引:1,自引:0,他引:1
AGANAUSKIENE J.; SORNMO L.; ATARIUS R.; BLOMSTROM-LUNDQVIST C. 《European heart journal》1995,16(9):1244-1254
The aim of the study was to evaluate the immediate reproducibilityof time domain parameters in the signal averaged electrocardiogramusing a new method for endpoint determination in individualFrank leads. The method is based on a statistical model of theelectrocardiogram (ECG) in which maximum likelihood (ML) estimationis employed. The reproducibility of the ML method was comparedto that of conventional time domain analysis using the vectormagnitude (VM) of Frank leads. Fifty-nine patients were includedin the study and two consecutive ECGs were recorded for signalaveraging. The results showed that the mean of the absolutedifference of the filtered QRS duration (QRSD) between two consecutiverecordings was significantly lower for the ML method than theconventional method when employing 60 Hz highpass filtering(2.1 ± 2.2 ms vs 5.9 ± 10.2 ms, P < 0.05).Moreover, the ML method resulted in a significantly longer QRSDcompared to the VM-based method (P < 0.05). The terminalamplitude of the QRS complex (RMS40) showed a greater variabilitythan the QRSD for both methods, although the ML method was associatedwith a higher reproducibility than the VM method for the 60Hz filter. These findings may contribute to a better identificationof patients at high risk of ventricular arrhythmias. A reductionin the number of measurement errors has important implicationswhen QRS changes are analysed over time. 相似文献
8.
In contrast to other reliability estimates, test-retest reliability (or reproducibility) captures not only the measurement error of an assessment instrument, but also the stability of the construct measured. Consequently, one would expect any departure from identity (Y = X) of measurement pairs (X first, and Y second measurement) to be treated as 'error' by the respective reproducibility statistic, even if 'true' changes happened, e.g. worsening of a disease due to its natural course. The Pearson correlation, still often advocated for continuous measures in test-retest reliability studies, however captures the degree of linearity (Y = bX + a): perfect relationship can be computed, even if the measurement pairs differ not only by a additive constant 'a', but also because of a multiplication of the X-values with the slope 'b'. Therefore, intraclass correlation coefficients (ICCs) have been proposed as alternative statistics for reproducibility. However, only ICCs with absolute agreement definition of concordance capture the degree of identity. ICCs with a consistency definition of concordance measure the degree of additivity (Y = X + a). ICCs are calculated from repeated measures analyses of variance (ANOVAs), and a common population variance must be is assumed for the different measurements. Given this assumption, an ICC computed from a one-way ANOVA seems to be the best choice for this purpose. Otherwise, Lin's concordance correlation coefficient is recommended as identity measure. 相似文献
9.
宫颈细胞学的临床价值 总被引:3,自引:2,他引:3
目的:探讨宫颈细胞学筛查的准确性和对临床的指导意义。方法:收集2003年四川大学附属华西第二医院筛查出382例宫颈细胞为ASC/AGC及以上病变患者的阴道镜检查、病理诊断等资料和同期住院1 147例宫颈细胞学为阴性患者的组织学结果,并将部分细胞学标本进行再次诊断,比较二次细胞学诊断结果。结果:细胞学异常的患者中,年轻患者(<35岁)占30.6%,宫颈细胞学诊断的一致性不够理想(k=0.39);ASC、LSIL和HSIL对于C INⅡ及以上病变的阳性预测值分别为40.1%、36.2%和72.0%,宫颈细胞学阴性预测值为98.9%。结论:应重视年轻女性的宫颈细胞学筛查,包括ASC在内的异常细胞学均应行阴道镜检查和组织学诊断。 相似文献
10.