An iterative block-shifting approach to retention time alignment that preserves the shape and area of gas chromatography-mass spectrometry peaks

<p>Abstract</p> <p>Background</p> <p>Metabolomics, petroleum and biodiesel chemistry, biomarker discovery, and other fields which rely on high-resolution profiling of complex chemical mixtures generate datasets which contain millions of detector intensity readings, each uniquely addressed along dimensions of <it>time </it>(<it>e.g.</it>, <it>retention time </it>of chemicals on a chromatographic column), a <it>spectral value </it>(<it>e.g., mass-to-charge ratio </it>of ions derived from chemicals), and the <it>analytical run number</it>. They also must rely on data preprocessing techniques. In particular, inter-run variance in the retention time of chemical species poses a significant hurdle that must be cleared before feature extraction, data reduction, and knowledge discovery can ensue. <it>Alignment methods</it>, for calibrating retention reportedly (and in our experience) can misalign matching chemicals, falsely align distinct ones, be unduly sensitive to chosen values of input parameters, and result in distortions of peak shape and area.</p> <p>Results</p> <p>We present an iterative block-shifting approach for retention-time calibration that detects chromatographic features and qualifies them by retention time, spectrum, and the effect of their inclusion on the quality of alignment itself. Mass chromatograms are aligned pairwise to one selected as a reference. In tests using a 45-run GC-MS experiment, block-shifting reduced the absolute deviation of retention by greater than 30-fold. It compared favourably to COW and XCMS with respect to alignment, and was markedly superior in preservation of peak area.</p> <p>Conclusion</p> <p>Iterative block-shifting is an attractive method to align GC-MS mass chromatograms that is also generalizable to other two-dimensional techniques such as HPLC-MS.</p

2017 HRS/EHRA/ECAS/APHRS/SOLAECE expert consensus statement on catheter and surgical ablation of atrial fibrillation: executive summary.

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Resident knowledge acquisition during a block conference series.

OBJECTIVE: This study\u27s objective was to determine whether attendance at lectures in a block conference format improves residents\u27 knowledge. METHODS: Seventeen family medicine residents were tested on the content of 27 lectures delivered in a block conference format over a 6-month period. For each lecture, residents completed a pretest, a short-term posttest, and a long-term posttest (1--3 weeks and 1.5--6 months after each lecture, respectively). RESULTS: Mean short-term posttest scores were 10.3 points higher for lecture attendees than nonattendees. Mean long-term posttest scores did not differ significantly for attendees (62.2) versus nonattendees (60.0). CONCLUSIONS: Attendance at didactic lectures in a block conference format did not improve resident knowledge over the long term. These results lead us to question the value of a block conference format and raise the possibility that resident learning might be better served by maximizing clinical experiences and minimizing time in conferences