Electrogram analysis and pacing are complimentary for recognition of abnormal conduction and far-field potentials during substrate mapping of infarct-related ventricular tachycardia.

BACKGROUND Mapping to identify scar-related ventricular tachycardia re-entry circuits during sinus rhythm focuses on sites with abnormal electrograms or pace-mapping findings of QRS morphology and long stimulus to QRS intervals. We hypothesized that (1) these methods do not necessarily identify the same sites and (2) some electrograms are far-field potentials that can be recognized by pacing. METHODS AND RESULTS From 12 patients with coronary disease and recurrent ventricular tachycardia undergoing catheter ablation, we retrospectively analyzed electrograms and pacing at 546 separate low bipolar voltage (<1.5 mV) sites. Electrograms were characterized as showing evidence of slow conduction if late potentials (56%) or fractionated potentials (76%) were present. Neither was present at (13%) sites. Pacing from the ablation catheter captured 70% of all electrograms. Higher bipolar voltage and fractionation were independent predictors for pace capture. There was a linear correlation between the stimulus to QRS duration during pacing and the lateness of a capturing electrogram (P<0.001), but electrogram and pacing markers of slow conduction were discordant at 40% of sites. Sites with far-field potentials, defined as those that remained visible and not captured by pacing stimuli, were identified at 48% of all pacing sites, especially in areas of low bipolar voltage and late potentials. Initial radiofrequency energy application rendered 74% of targeted sites electrically unexcitable. CONCLUSIONS Far-field potentials are common in scar areas. Combining analysis of electrogram characteristics and assessment of pace capture may refine identification of substrate targets for radiofrequency ablation.

On ANOVA Decompositions of Kernels and Gaussian Random Field Paths

The FANOVA (or “Sobol’-Hoeffding”) decomposition of multivariate functions has been used for high-dimensional model representation and global sensitivity analysis. When the objective function f has no simple analytic form and is costly to evaluate, computing FANOVA terms may be unaffordable due to numerical integration costs. Several approximate approaches relying on Gaussian random field (GRF) models have been proposed to alleviate these costs, where f is substituted by a (kriging) predictor or by conditional simulations. Here we focus on FANOVA decompositions of GRF sample paths, and we notably introduce an associated kernel decomposition into 4 d 4d terms called KANOVA. An interpretation in terms of tensor product projections is obtained, and it is shown that projected kernels control both the sparsity of GRF sample paths and the dependence structure between FANOVA effects. Applications on simulated data show the relevance of the approach for designing new classes of covariance kernels dedicated to high-dimensional kriging.

Beryllium sampling methods: Comparison of two personal sample collection methods with the AEC sample collection method as used for one year in a beryllium production facility. /

Item 499-F-2

Field test plan for evaluating the cooperative breath analyzer. Technical report.

National Highway Traffic Safety Administration, Washington, D.C.

Field research planning for driver's license law enforcement. Final report.

National Highway Traffic Safety Administration, Washington, D.C.

Handbook for a field research program for driver's license law enforcement. User guidelines and handbook.

National Highway Traffic Safety Administration, Washington, D.C.

A comparison of lighting, signing, and pavement marking methods for detecting rural intersections at night. Final report.

Ohio Department of Transportation, Columbus

An historical review of the National Highway Traffic Safety Administration's field accident investigation activities. NHTSA technical report.

Mode of access: Internet.

Field research planning for driver's license law enforcement. Interim report.

National Highway Traffic Safety Administration, Washington, D.C.

Design of field passive restraint evaluation. Final report.

National Highway Traffic Safety Administration, Washington, D.C.

Hydrographical surveying : a description of means and methods employed in constructing marine charts /

Mode of access: Internet.

An isotopic analysis of geothermal brine and calcite scaling from the Blue Mountain geothermal field, Winnemucca, Nevada

Understanding, and controlling, the conditions under which calcite precipitates within geothermal energy production systems is a key step in maintaining production efficiency. In this study, I apply methods of bulk and clumped isotope thermometry to an operating geothermal energy facility in northern Nevada to see how those methods can better inform the facility owner, AltaRock Energy, Inc., about the occurrence of calcite scale in their power plant. I have taken water samples from five production wells, the combined generator effluent, shallow cold-water wells, monitoring wells, and surface water. I also collected calcite scale samples from within the production system. Water samples were analyzed for stable oxygen isotope composition (d18O). Calcite samples were analyzed for stable oxygen and carbon (d13C) composition, and clumped isotope composition (D47). With two exceptions, the water compositions are very similar, likely indicating common origin and a well-mixed hydrothermal system. The calcite samples are likewise similar to one another. Apparent temperatures calculated from d18O values of water and calcite are lower than those recorded for the system. Apparent temperatures calculated from D47 are several degrees higher than the recorded well temperatures. The lower temperatures from the bulk isotope data are consistent with temperatures that could be expected during a de-pressurization of the production system, which would cause boiling in the pipes, a reduction in system temperature, and rapid precipitation of calcite scale. However, the high apparent temperature indicated by the D47 data suggests that the calcite is depleted in clumped isotopes given the known temperature of the system, which is inconsistent with this hypothesis. This depletion could instead result from disequilibrium isotopic fractionation during the aforementioned boil events, which would make both the apparent d18O-based and D47-based temperatures unrepresentative of the actual water temperature. This research can help improve our understanding of how isotopic analyses can better inform us about the movement of water through geothermal systems of the past and how it now moves through modern systems. Increased understanding of water movement in these systems could potentially allow for more efficient utilization of geothermal energy as a renewable resource.

An Exploratory Assessment of Parklet Usage in Seattle: Methods and Findings

Thesis (Master's)--University of Washington, 2016-06

Electromagnetic fields inside a lossy, multilayered spherical head phantom excited by MRI coils: models and methods

The precise evaluation of electromagnetic field (EMF) distributions inside biological samples is becoming an increasingly important design requirement for high field MRI systems. In evaluating the induced fields caused by magnetic field gradients and RF transmitter coils, a multilayered dielectric spherical head model is proposed to provide a better understanding of electromagnetic interactions when compared to a traditional homogeneous head phantom. This paper presents Debye potential (DP) and Dyadic Green's function (DGF)-based solutions of the EMFs inside a head-sized, stratified sphere with similar radial conductivity and permittivity profiles as a human head. The DP approach is formulated for the symmetric case in which the source is a circular loop carrying a harmonic-formed current over a wide frequency range. The DGF method is developed for generic cases in which the source may be any kind of RF coil whose current distribution can be evaluated using the method of moments. The calculated EMFs can then be used to deduce MRI imaging parameters. The proposed methods, while not representing the full complexity of a head model, offer advantages in rapid prototyping as the computation times are much lower than a full finite difference time domain calculation using a complex head model. Test examples demonstrate the capability of the proposed models/methods. It is anticipated that this model will be of particular value for high field MRI applications, especially the rapid evaluation of RF resonator (surface and volume coils) and high performance gradient set designs.

Winding patterns for biplanar MRI shim coils with rectangular and circular target-field regions

A method is presented for calculating the winding patterns required to design independent zonal and tesseral biplanar shim coils for magnetic resonance imaging. Streamline, target-field, Fourier integral and Fourier series methods are utilized. For both Fourier-based methods, the desired target field is specified on the surface of the conducting plates. For the Fourier series method it is possible to specify the target field at additional depths interior to the two conducting plates. The conducting plates are confined symmetrically in the xy plane with dimensions 2a x 2b, and are separated by 2d in the z direction. The specification of the target field is symmetric for the Fourier integral method, but can be over some asymmetric portion pa < x < qa and sb < y < tb of the coil dimensions (-1 < p < q < 1 and -1 < s < t < 1) for the Fourier series method. Arbitrary functions are used in the outer sections to ensure continuity of the magnetic field across the entire coil face. For the Fourier series case, the entire field is periodically extended as double half-range sine or cosine series. The resultant Fourier coefficients are substituted into the Fourier series and integral expressions for the internal and external magnetic fields, and stream functions on both the conducting surfaces. A contour plot of the stream function directly gives the required coil winding patterns. Spherical harmonic analysis of field calculations from a ZX shim coil indicates that example designs and theory are well matched.