1,721,026 research outputs found
Effect of inversion-recovery fat suppression on hepatic R2* quantitation in transfusional siderosis
No full textOBJECTIVE. The purpose of this study is to evaluate whether the application of spectral presaturation
inversion recovery (SPIR) fat suppression in standard multiecho gradient-echo sequences
has a significant effect on hepatic R2* quantitation in patients with iron overload syndromes.
MATERIALS AND METHODS. Eighty patients were scanned with a multiecho gradient-
echo sequence without and with the application of SPIR. Six different postprocessing
approaches were used to extract R2* values for maximum generality.
RESULTS. SPIR fat suppression lowered R2* values by 3.9–7.0% (p < 0.0001 in all pairwise
comparisons), independently of the postprocessing algorithm. Coefficients of variation
for R2* ranged from 4.5% to 10.0%. Regardless of the size of the ROI (area of homogeneous
tissue or entire liver profile in the slice), pixelwise approaches combined with an exponential-
plus-constant fitting model yielded the lowest coefficients of variation (4.5% and 5.1%),
whereas truncated exponential fits of the averaged signals produced the highest coefficients
of variation (7.8% and 10%). For R2* values exceeding 200 Hz, a Bland-Altman analysis
showed a bias that grew linearly for all postprocessing methods.
CONCLUSION. SPIR fat suppression resulted in systematically lower hepatic R2* estimates.
Because calibration curves were derived using images without fat suppression, these
biases should be corrected when reporting liver iron concentrations estimated from fat-suppressed
multiecho T2*-weighted images
Robust estimation of pulse wave transit time using group delay
No full textPurpose: To evaluate the efficiency of a novel transit
time (Dt) estimation method from cardiovascular magnetic
resonance flow curves.
Materials and Methods: Flow curves were estimated
from phase contrast images of 30 patients. Our method
(TT-GD: transit time group delay) operates in the
frequency domain and models the ascending aortic waveform
as an input passing through a discrete-component
“filter,” producing the observed descending aortic waveform.
The GD of the filter represents the average time
delay (Dt) across individual frequency bands of the input.
This method was compared with two previously described
time-domain methods: TT-point using the half-maximum
of the curves and TT-wave using cross-correlation. High
temporal resolution flow images were studied at multiple
downsampling rates to study the impact of differences in
temporal resolution.
Results: Mean Dts obtained with the three methods
were comparable. The TT-GD method was the most
robust to reduced temporal resolution. While the TT-GD
and the TT-wave produced comparable results for velocity
and flow waveforms, the TT-point resulted in significant
shorter Dts when calculated from velocity waveforms (difference:
1.862.7 msec; coefficient of variability: 8.7%).
The TT-GD method was the most reproducible, with an
intraobserver variability of 3.4% and an interobserver variability
of 3.7%.
Conclusion: Compared to the traditional TT-point and
TT-wave methods, the TT-GD approach was more robust
to the choice of temporal resolution, waveform type, and
observer
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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