1,721,425 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Late gadolinium enhancement as a potential marker of increased perioperative risk in aortic valve replacement
No full textOBJECTIVES: Risk assessment of patients with aortic stenosis (AS) undergoing aortic valve replacement (AVR) is challenging. We set out to determine the impact of myocardial late gadolinium enhancement (LGE), as detected by cardiovascular magnetic resonance (CMR), on postoperative outcomes following AVR.METHODS: A prospective observational study was conducted on patients undergoing CMR using the LGE technique within 1 year of subsequent AVR. Patients were categorized into absent, mid-wall or infarct patterns of LGE by independent observers blinded to all clinical data, and data were collected with regard to 30-day mortality, major adverse cardiac and cerebrovascular events (MACCE) and postoperative complications.RESULTS: A total of 63 patients were studied. Twenty-five patients had no LGE; 20 had mid-wall LGE and 18 had an infarct pattern. The incidence of MACCE, cerebrovascular accident (CVA) and heart block were significantly higher in the mid-wall group compared with the other two groups (MACCE: 25 vs. 0 vs. 5%, P = 0.014; CVA: 20 vs. 0 vs. 0%, P = 0.013; heart block: 30 vs. 4 vs. 12%, P = 0.050). Patients with no LGE had no 30-day MACCE events and no deaths up to 2 years of follow-up.CONCLUSIONS: The myocardial LGE holds promise as a means of predicting risk prior to AVR for AS
Cardiovascular magnetic resonance and positron emission tomography in the assessment of aortic stenosis
Full text linkBackground
Aortic stenosis is not only characterized by progressive valve narrowing but also by
the hypertrophic response of the left ventricle that ensues. In this most common
valvular condition novel imaging approaches (cardiovascular magnetic resonance
[CMR] and positron emission tomography [PET]) have shown promise in the
assessment of disease progression and risk stratification. The central aim of this
thesis was to investigate the potential of CMR imaging to refine risk prediction and to
improve the imaging protocol of 18F-sodium fluoride PET for aortic stenosis.
Methods and Results
Asymmetric wall thickening in aortic stenosis
In a prospective observational cohort study, 166 patients with aortic stenosis (age 69,
69% males, mean aortic valve area 1.0±0.4cm2) and 37 age and sex-matched
healthy volunteers underwent phenotypic characterisation with comprehensive
clinical, imaging and biomarker evaluation. Asymmetric wall thickening on both
echocardiography and cardiovascular magnetic resonance was defined as regional
wall thickening ≥13 mm and >1.5-fold the thickness of the opposing myocardial
segment.
Asymmetric wall thickening was observed in 26% (n=43) of patients with aortic
stenosis using magnetic resonance and 17% (n=29) using echocardiography. Despite
similar demographics, co-morbidities, valve narrowing, myocardial hypertrophy and
fibrosis, patients with asymmetric wall thickening had increased cardiac troponin I and
brain natriuretic peptide concentrations (both p<0.001). Over 28 [22, 33] months of
follow-up, asymmetric wall thickening was an independent predictor of aortic valve
replacement or death whether detected by magnetic resonance (HR=2.15; 95 CI 1.29
to 3.59; p=0.003) or echocardiography (HR=1.79; 95 CI 1.08 to 3.69; p=0.021).
Animal model of pressure overload
We performed serial Cardiac Magnetic Resonance (CMR) imaging every 2-week in
31 mice subjected to pressure overload (continuous angiotensin II infusion) for 6
weeks and investigated reverse remodelling by repeating CMR 1 month following
normalization of afterload (n=9). Cine CMR was used to measure left ventricular
volumes, mass, and systolic function whilst myocardial fibrosis was assessed using
indexed ECV (iECV) calculated from T1-relaxation times acquired with a small animal
modified look-locker inversion recovery sequence.
During the initial phase of increased pressure afterload indices of left ventricular
hypertrophy (0.091 [0.083, 0.105] vs 0.123 [0.111, 0.138] g) and myocardial fibrosis
(iECV: 0.022 [0.019, 0.024] vs 0.022 [0.019, 0.024] mL) increased in line with blood
pressure measurements (65.1±12.0 vs 84.7±9.2 mmHg) whilst left ventricular ejection
fraction (LVEF, 59.3 [57.6, 59.9] vs 46.9 [38.5, 49.6] %) deteriorated significantly (all
p≤0.01 compared to baseline).
During the reverse remodelling phase blood pressure normalized (68.8±5.4 vs
65.1±12.0 mmHg, p=0.42 compared to baseline). Whilst LV mass (0.108 [0.098,
0.116] vs 0.091 [0.083, 0.105] g) and iECV (0.034 [0.032, 0.036] vs 0.022 [0.019,
0.024] mL) improved both remained elevated compared to baseline (p<0.05).
Similarly, the LVEF remained impaired 51.1 [42.9, 52.8] vs 59.3 [57.6, 59.9] %,
p=0.03. There was a strong association between LVEF and iECV values during
pressure overload (r=-0.88, p<0.001).
Gender differences in aortic stenosis
Two hundred forty-nine patients (66±13 years, 30% women) with at least mild AS
were recruited from two prospective observational cohort studies and underwent
comprehensive Doppler echocardiography and CMR exams. On CMR, T1 mapping
was used to quantify extracellular volume (ECV) fraction as a marker of diffuse
fibrosis, and late gadolinium enhancement (LGE) was used to assess focal fibrosis.
There was no difference in age between women and men (66±15 vs 66±12 years,
p=0.78). However, women presented a better cardiovascular risk profile than men
with less hypertension, dyslipidemia, diabetes, and coronary artery disease (all
p≤0.10). As expected, LV mass index measured by CMR was smaller in women than
in men (p<0.0001). Despite fewer comorbidities, women presented larger ECV
fraction [29.0 (27.4-30.6) vs. 26.8 (25.1-28.7) %, p<0.0001] and similar LGE [4.5 (2.3-
7.0) vs. 2.8 (0.6-6.8) %, p=0.20] than men. In multivariable analysis, female sex
remained an independent determinant of higher ECV fraction and LGE (both p≤0.05).
Prior CT angiography for PET
Forty-five patients (age 67.1±6.9 years, 76% males) underwent CTA (CTA1) and
combined 18F-NaF PET/CTA (CTA2) imaging within 14 [10,21] days. We fused CTA1
from visit one with 18F-NaF PET from the second visit (PET) and compared visual
pattern of activity, maximal standard uptake values (SUVmax) and target to
background (TBR) measurements on (PET/CTA1) fused versus hybrid (PET/CTA2)
data.
On PET/CTA2, 226 coronary plaques were identified. Fifty-eight coronary segments
from 28 (62%) patients had high 18F-NaF uptake (TBR>1.25), whilst 168 segments
had lesions with 18F-NaF TBR ≤1.25. Uptake in all lesions was categorized identically
on co-registered PET/CTA1. There was no significant difference in 18F-NaF uptake
values between PET/CTA1 and PET/CTA2 (SUVmax: 1.16±0.40 vs. 1.15±0.39,
p=0.53; TBR:1.10±0.45 vs. 1.09±0.46, p=0.55). The intraclass correlation coefficient
for SUVmax and TBR was 0.987 (95%CI 0.983 to 0.991) and 0.986 (95%CI 0.981 to
0.992). There was no fixed or proportional bias between PET/CTA1 and PET/CTA2
for SUVmax and TBR. Cardiac motion correction of PET scans improved
reproducibility with tighter 95% limits of agreement (±0.14 for SUVmax and ±0.15 for
TBR vs. ±0.20 and ±0.20 on diastolic imaging; p<0.001).
Delayed PET imaging
Twenty patients (67±7years old, 55% male) with stable coronary artery disease
underwent coronary CT angiography and PET/CT both 1 h and 3 h after the injection
of 266.2±13.3 MBq of 18F-NaF. We compared the visual pattern of coronary uptake,
maximal background (blood pool) activity, noise, standard uptake values (SUVmax),
corrected SUV (cSUVmax) and target to background (TBR) measurements in lesions
defined by CTA on 1h vs 3h post injection 18F-NaF PET.
On 1h PET 26 CTA lesions with 18F-NaF PET uptake were identified in 12 (60%)
patients. On 3h PET we detected 18F-NaF PET uptake in 7 lesions which were not
identified on the 1h PET. The median cSUVmax and TBR values of these lesions
were 0.48 [interquartile range (IQR) 0.44-0.51] and 1.45 [IQR, 1.39-1.52] compared
to -0.01 [IQR, -0.03-0.001] and 0.95 [IQR, 0.90-0.98] on 1h PET, both p<0.001.
Across the entire cohort 3h PET SUVmax values were similar to 1h PET
measurements 1.63 [IQR, 1.37-1.98] vs. 1.55 [IQR, 1.43-1.89], p=0.30 and the
background activity was lower 0.71 [IQR, 0.65-0.81] vs. 1.24 [IQR, 1.05-1.31],
p<0.001. On 3h PET, the TBR values, cSUVmax and the noise were significantly
higher (2.30 [IQR, 1.70-2.68] vs 1.28 [IQR, 0.98-1.56], p<0.001; 0.38 [IQR, 0.27-0.70]
vs 0.90 [IQR, 0.64-1.17], p<0.001 and 0.10 [IQR, 0.09-0.12] vs. 0.07 [IQR, 0.06-0.09],
p=0.02). The median cSUVmax and TBR values increased by 92% (range: 33-225%)
and 80% (range: 20-177%).
Conclusions
In aortic stenosis, asymmetric wall thickening is associated with adverse prognosis,
in this condition there are significant differences in the fibrosis burden between male
and female patients and the adverse remodeling of the ventricle can be reproduced
in a simple animal model of pressure overload. For 18F-NaF PET utilizing a CT
angiography acquired before the PET acquisition enables adequate uptake
quantification and delayed emission scanning facilitates image analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
Computed tomography and positron emission tomography in the assessment of aortic valve disease
Full text linkIntroduction
Native and bioprosthetic aortic valve diseases are an increasingly common clinical challenge as a consequence of the ageing demographic and the expansion of new valve technology. In both conditions, there remains substantial scope to broaden our understanding of the pathophysiology, improve diagnostic sensitivity and accuracy, and develop new markers of disease activity with which to measure therapeutic effect. Computed tomography (CT) and positron emission tomography (PET) are non-invasive imaging assessments that combine high resolution anatomical detail with real-time functional information about disease activity, and as such are ideally suited to complement echocardiography in the investigation of native and bioprosthetic aortic valve diseases.
Methods
Aortic Stenosis
Volunteers with aortic stenosis (n=143) across a range of severity underwent echocardiography, CT aortic valve calcium scoring and contrast-enhanced CT angiography. Aortic valve fibrosis and calcification were quantified to produce two novel measures: the fibro-calcific ratio and fibro-calcific burden. From the same study population, a subset of 15 volunteers underwent hybrid 18F-fluoride PET/CT on two separate occasions and we investigated different methods of image analysis to optimise accuracy and reproducibility.
Bioprosthetic Valves
Explanted degenerated bioprosthetic valves (n=16) were examined ex vivo using histopathology and preclinical 18F-fluoride PET/CT. Patients with bioprosthetic aortic valves (n=78) were then recruited into two cohorts, with and without prosthetic valve dysfunction, and underwent in-vivo contrast-enhanced CT angiography, 18F-fluoride PET, and serial echocardiography over 2 years of follow-up.
Results
Aortic Stenosis
Contrast-enhanced CT calcium volume correlated closely with conventional CT calcium score in the aortic valve (r=0.86, p=<0.001). Fibrosis dominated in mild aortic stenosis while calcification dominated in severe stenosis (fibro-calcific ratio: 1.33 [0.91-2.4]) versus 0.53 [0.35-1.05] respectively; p=0.001). Males exhibited more calcium than fibrosis, with the reverse true for females (fibro-calcific ratio: 0.89 [0.45-1.54] versus 1.49 [0.82-5.74] respectively; p=0.001). The fibro-calcific burden demonstrated the strongest correlation with peak aortic-jet velocity (r=0.71, p<0.001), especially in women (r=0.77, p=0.001) where it outperformed CT calcium score (p=0.027). In our investigation of 18F-fluoride-PET/CT, contrast-enhanced, ECG-gated PET/CT provided superior spatial localisation of 18F-fluoride uptake. Scan-rescan reproducibility was markedly improved using enhanced analysis techniques leading to a reduction in variability from 25% to <10%.
Bioprosthetic Valves
In degenerated bioprosthetic valves ex vivo, calcification was the most prevalent pathological feature (87%), whilst thrombus (40%) and pannus overgrowth (47%) were other common findings. All valves exhibited 18F-fluoride uptake on PET, with a strong positive correlation between 18F-fluoride uptake and calcium volume (r=0.73, p=0.0031). 18F-Fluoride uptake was highest in regions of leaflet calcification but also localised to regions of organised thrombus, fibrosis and features of matrix degradation on histopathology.
In the cohort study of patients with bioprosthetic aortic valves, all those with recognised valve dysfunction exhibited abnormalities on CT and high 18F-fluoride uptake. In the 71 patients without valve dysfunction, 20% had leaflet pathology on CT and 34% had increased 18F-fluoride uptake (target-to-background ratio 1.55 [1.44-1.88]). Patients with increased 18F-fluoride uptake exhibited more rapid deterioration in valve function than those without (annualised change in peak transvalvular velocity: 0.30 [0.13-0.61] versus 0.01 [-0.05-0.16] ms-1/year, p<0.001). 18F-Fluoride uptake correlated with deterioration in all echocardiographic measures of valve function (e.g. change in peak velocity, r=0.72; p<0.001) and, on multivariable analysis, was the only independent predictor of future bioprosthetic dysfunction.
Conclusions
In both native aortic valve disease and bioprosthetic valve disease, CT and 18F-fluoride PET afford valuable insights into disease mechanisms, inform patient risk stratification and prognosis, and provide biomarkers of disease activity that may be used for the development of future therapeutic interventions
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