188 research outputs found
Power density spectrum of nonstationary short-lived light curves
The power density spectrum of a light curve is often calculated as the
average of a number of spectra derived on individual time intervals the light
curve is divided into. This procedure implicitly assumes that each time
interval is a different sample function of the same stochastic ergodic process.
While this assumption can be applied to many astrophysical sources, there
remains a class of transient, highly nonstationary and short-lived events, such
as gamma-ray bursts, for which this approach is often inadequate. The power
spectrum statistics of a constant signal affected by statistical (Poisson)
noise is known to be a chi2(2) in the Leahy normalisation. However, this is no
more the case when a nonstationary signal is also present. As a consequence,
the uncertainties on the power spectrum cannot be calculated based on the
chi2(2) properties, as assumed by tools such as XRONOS powspec. We generalise
the result in the case of a nonstationary signal affected by uncorrelated white
noise and show that the new distribution is a non-central chi2(2,lambda), whose
non-central value lambda is the power spectrum of the deterministic function
describing the nonstationary signal. Finally, we test these results in the case
of synthetic curves of gamma-ray bursts. We end up with a new formula for
calculating the power spectrum uncertainties. This is crucial in the case of
nonstationary short-lived processes affected by uncorrelated statistical noise,
for which ensemble averaging does not make any physical sense.Comment: 11 pages, 5 figures, accepted to MNRA
Colon capsule versus CT colonography in patients with incomplete colonoscopy: a prospective, comparative trial.
Quality performance measures for small capsule endoscopy: Are the ESGE quality standards met?
Background and study aims The European Society of Gastrointestinal Endoscopy (ESGE) recently issued a quality performance measures document for small bowel capsule endoscopy (SBCE). The aim of this nationwide survey was to explore SBCE practice with ESGE quality measures as a benchmark.
Patients and methods A dedicated per-center semiquantitative questionnaire based on ESGE performance measures for SBCE was created by a group of SBCE experts. One-hundred-eighty-one centers were invited to participate and were asked to calculate performance measures for SBCE performed in 2018. Data were compared with 10 ESGE quality standards for both key and minor performance measures.
Results Ninety-one centers (50.3 %) participated in the data collection. Overall in the last 5 years (2014–2018), 26,615 SBCEs were performed, 5917 of which were done in 2018. Eighty percent or more of the participating centers reached the minimum standard established by the ESGE Small Bowel Working Group (ESBWG) for four performance measures (indications for SBCE, complete small bowel evaluation, diagnostic yield and retention rate). Conversely, compliance with six minimum standards established by ESBWG concerning adequate bowel preparation, patient selection, timing of SBCE in overt bleeding, appropriate reporting,
reading protocols and referral to device-assisted enteroscopy was met by only 15.5%, 10.9%, 31.1%, 67.7%, 53.4%, and 32.2% of centers, respectively.
Conclusions The present survey shows significant variability across SBCE centers; only four (4/10: 40 %) SBCE procedural minimum standards were met by a relevant proportion of the centers ( ≥ 80 %). Our data should help in identifying target areas for quality improvement programs in SBCE
Revising the European Society of Gastrointestinal Endoscopy (ESGE) research priorities: a research progress update
AbstractBackground One of the aims of the European Society of Gastrointestinal Endoscopy (ESGE) is to encourage high quality endoscopic research at a European level. In 2016, the ESGE research committee published a set of research priorities. As endoscopic research is flourishing, we aimed to review the literature and determine whether endoscopic research over the last 4 years had managed to address any of our previously published priorities.Methods As the previously published priorities were grouped under seven different domains, a working party with at least two European experts was created for each domain to review all the priorities under that domain. A structured review form was developed to standardize the review process. The group conducted an extensive literature search relevant to each of the priorities and then graded the priorities into three categories: (1) no longer a priority (well-designed trial, incorporated in national/international guidelines or adopted in routine clinical practice); (2) remains a priority (i. e. the above criterion was not met); (3) redefine the existing priority (i. e. the priority was too vague with the research question not clearly defined).Results The previous ESGE research priorities document published in 2016 had 26 research priorities under seven domains. Our review of these priorities has resulted in seven priorities being removed from the list, one priority being partially removed, another seven being redefined to make them more precise, with eleven priorities remaining unchanged. This is a reflection of a rapid surge in endoscopic research, resulting in 27 % of research questions having already been answered and another 27 % requiring redefinition.Conclusions Our extensive review process has led to the removal of seven research priorities from the previous (2016) list, leaving 19 research priorities that have been redefined to make them more precise and relevant for researchers and funding bodies to target
Second-generation colon capsule endoscopy compared with colonoscopy
Colon capsule endoscopy (CCE) represents a noninvasive technology
that allows visualization of the colon without requiring sedation and air
insufflation. A second-generation colon capsule endoscopy system (PillCam Colon
2) (CCE-2) was developed to increase sensitivity for colorectal polyp detection
compared with the first-generation system. OBJECTIVE: To assess the feasibility,
accuracy, and safety of CCE-2 in a head-to-head comparison with colonoscopy.
DESIGN AND SETTING: Prospective, multicenter trial including 8 European sites.
PATIENTS: This study involved 117 patients (mean age 60 years). Data from 109
patients were analyzed. INTERVENTION: CCE-2 was prospectively compared with
conventional colonoscopy as the criterion standard for the detection of
colorectal polyps that are >/=6 mm or masses in a cohort of patients at average
or increased risk of colorectal neoplasia. Colonoscopy was independently
performed within 10 hours after capsule ingestion or on the next day. MAIN
OUTCOME MEASUREMENTS: CCE-2 sensitivity and specificity for detecting patients
with polyps >/=6 mm and >/=10 mm were assessed. Capsule-positive but
colonoscopy-negative cases were counted as false positive. Capsule excretion
rate, level of bowel preparation, and rate of adverse events also were assessed.
RESULTS: Per-patient CCE-2 sensitivity for polyps >/=6 mm and >/=10 mm was 84%
and 88%, with specificities of 64% and 95%, respectively. All 3 invasive
carcinomas were detected by CCE-2. The capsule excretion rate was 88% within 10
hours. Overall colon cleanliness for CCE-2 was adequate in 81% of patients.
LIMITATIONS: Not unblinding the CCE-2 results at colonoscopy; heterogenous
patient population; nonconsecutive patients. CONCLUSION: In this European,
multicenter study, CCE-2 appeared to have a high sensitivity for the detection of
clinically relevant polypoid lesions, and it might be considered an adequate tool
for colorectal imaging
Colonoscopy quality across Europe : a report of the European Colonoscopy Quality Investigation (ECQI) Group
publishedVersionPeer reviewe
Efficacy and Tolerability of High- vs Low-Volume Split-Dose Bowel Cleansing Regimens for Colonoscopy: A Systematic Review and Meta-analysis
Background & Aims
Efficacy of bowel preparation is an important determinant of outcomes of colonoscopy. It is not clear whether approved low-volume polyethylene glycol (PEG) and non-PEG regimens are as effective as high-volume PEG regimens when taken in a split dose.
Methods
In a systematic review of multiple electronic databases through January 31, 2019 with a registered protocol (PROSPERO: CRD42019128067), we identified randomized controlled trials that compared low- vs high-volume bowel cleansing regimens, administered in a split dose, for colonoscopy. The primary efficacy outcome was rate of adequate bowel cleansing, and the secondary efficacy outcome was adenoma detection rate. Primary tolerability outcomes were compliance, tolerability, and willingness to repeat. We calculated relative risk (RR) and 95% CI values and assessed heterogeneity among studies by using the I2 statistic. The overall quality of evidence was assessed using the GRADE framework.
Results
In an analysis of data from 17 randomized controlled trials, comprising 7528 patients, we found no significant differences in adequacy of bowel cleansing between the low- vs high-volume split-dose regimens (86.1% vs 87.4%; RR, 1.00; 95% CI, 0.98–1.02) and there was minimal heterogeneity (I2 = 17%). There was no significant difference in adenoma detection rate (RR, 0.96; 95% CI, 0.87–1.08) among 4 randomized controlled trials. Compared with high-volume, split-dose regimens, low-volume split-dose regimens had higher odds for compliance or completion (RR, 1.06; 95% CI, 1.02–1.10), tolerability (RR, 1.39; 95% CI, 1.12–1.74), and willingness to repeat bowel preparation (RR, 1.41; 95% CI, 1.20–1.66). The overall quality of evidence was moderate.
Conclusions
Based on a systematic review of 17 randomized controlled trials, low-volume, split-dose regimens appear to be as effective as high-volume, split-dose regimens in bowel cleansing and are better tolerated, with superior compliance
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