Estimates Of Vp Research Articles

The Effect of Polymorphisms and Other Biomarkers on Infliximab Exposure in Paediatric Inflammatory Bowel Disease: Development of a Population Pharmacokinetic Model.

Therapeutic drug monitoring (TDM) of infliximab has been shown to be a effective strategy for inflammatory bowel disease (IBD). Population pharmacokinetic (PopPK) modeling can predict trough concentrations for individualized dosing. The aim of this study was to develop a PopPK model of infliximab in a paediatric population with IBD, assessing the effect of single nucleotide polymorphisms (SNPs) and other biomarkers on infliximab clearance. This observational and ambispective single-centre study was conducted in paediatric patients with IBD treated with infliximab between July 2016 and July 2022 in the Paediatric Gastroenterology Service of the Hospital Universitari Vall d'Hebron (HUVH) (Spain). Demographic, clinical, and analytical variables were collected. Twenty SNPs potentially associated with variations in the response to infliximab plasma concentrations were analysed. infliximab serum concentrations and antibodies to infliximab (ATI) were determined by ELISA. PopPK modelling was performed using nonlinear mixed-effects analysis (NONMEM). Thirty patients (21 males) were included. The median age (range) at the start of infliximab treatment was 13 years (16 months to 16 years). A total of 190 samples were obtained for model development (49 [25.8%] during the induction phase). The pharmacokinetics (PK) of infliximab were described using a two-compartment model. Weight, erythrocyte sedimentation rate (ESR), faecal calprotectin (FC), and the SNP rs1048610 (ADAM17) showed statistical significance for clearance (CL), and albumin for inter-compartmental clearance (Q). Estimates of CL1 (genotype 1-AA), CL2 (genotype 2-AG), CL3 (genotype 3-GG), Q, Vc, and Vp (central and peripheral distribution volumes) were 0.0066L/h/46.4kg, 0.0055L/h/46.4kg, 0.0081L/h/46.4kg, 0.0029L/h/46.4kg, 0.6750L/46.4kg, and 1.19L/46.4kg, respectively. The interindividual variability (IIV) estimates for clearance, Vc, and Vp were 19.33, 16.42, and 36.02%, respectively. A popPK model utilising weight, albumin, FC, ESR, and the SNP rs1048610 accurately predicted infliximab trough concentrations in children with IBD.

Sound Velocities of Superhydrous Phase B up to 21 GPa and 900 K

AbstractSound velocities and density of Mg10Si3H4O18 superhydrous phase B (SuB) were investigated by synchrotron X‐rays combined with ultrasonic interferometry techniques in a multi‐anvil apparatus, up to 21 GPa and 900 K. Our data show that SuB has compressional (VP) and shear velocities (VS) lower than major anhydrous minerals but higher than majorite garnet. Our data combined with those of other mantle minerals allowed estimation of VP and VS of hydrated mantle regions at depths of the mantle transition zone and upper lower mantle. The local hydration of pyrolitic mantle with SuB as the main water host could explain low VP and low VS anomalies near cold subduction zones while it would be associated with low VP and high VS anomalies in hot mantle regions. The anomalies may be particularly strong in the ∼30 km beneath the 660 km discontinuity, due to the discrepancy of post‐spinel transition between hydrous and dry pyrolite lithologies.

Estimation of shallow VP and VS models in La Reforma Caldera, Baja California Sur, Mexico, using H/V ratios. Preliminary results

We evaluate the subsoil conditions at La Reforma caldera, located inside the Tres Virgenes Volcanic Complex in Baja California Sur, Mexico, using the Horizontal to Vertical Spectral Ratios (HVSR) method. The spatial distribution of the dominant frequencies has a complex pattern, which could be related to the heterogeneities of the zone. There is a good correlation between the inverted velocity models and the caldera lithology proposed in early studies. Our results show significant contrast between VP and VS, resulting in high VP/VS ratios. These high VP/VS ratios suggest a water-saturated material and define a possible water central pathway in La Reforma caldera. The VP/VS values obtained for La Reforma caldera are different from those found in the rest of the Tres Virgenes volcanic complex.

Site characterization at Treasure Island and Delaney Park downhole arrays by heterogeneous data assimilation

This article extends a recently proposed heterogeneous data assimilation technique for site characterization to estimate compression and shear wave velocity ( Vp and Vs, respectively) and damping at Treasure Island and Delaney Park downhole arrays. The adopted method is based on the joint inversion of earthquake acceleration time series and experimental surface wave dispersion data and includes physical constraints to improve the inverse problem’s well-posedness. We first use synthetic data at these two sites to refine the proposed approach and then apply the refined algorithm to real datasets available at the Treasure Island and Delaney Park downhole arrays. The joint inversion results show that the estimated Vs and Vp profiles are in very good agreement with measured profiles at these two sites. Our synthetic and real data experiment results suggest that Vp estimation from inversion at downhole arrays can be improved by integrating the water table depth information or the higher modes of the Rayleigh wave dispersion data. In the last part of this article, we compare the performance of the inverted profiles to other methods used to incorporate spatial variability and wave scattering effects in one-dimensional (1D) ground response analysis (GRA). The comparisons show that the joint inversion-based Vs and Vp profiles and damping ratios estimated in this article can better integrate the effects of spatial variability and wave scattering into 1D GRAs, especially at the Delaney Park downhole array, which is classified as a poorly modeled site using traditional 1D GRA.

Dynamic contrast-enhanced MRI parametric mapping using high spatiotemporal resolution Golden-angle RAdial Sparse Parallel MRI and iterative joint estimation of the arterial input function and pharmacokinetic parameters.

The aim of this work is to develop a data-driven quantitative dynamic contrast-enhanced (DCE) MRI technique using Golden-angle RAdial Sparse Parallel (GRASP) MRI with high spatial resolution and high flexible temporal resolution and pharmacokinetic (PK) analysis with an arterial input function (AIF) estimated directly from the data obtained from each patient. DCE-MRI was performed on 13 patients with gynecological malignancy using a 3-T MRI scanner with a single continuous golden-angle stack-of-stars acquisition and image reconstruction with two temporal resolutions, by exploiting a unique feature in GRASP that reconstructs acquired data with user-defined temporal resolution. Joint estimation of the AIF (both AIF shape and delay) and PK parameters was performed with an iterative algorithm that alternates between AIF and PK estimation. Computer simulations were performed to determine the accuracy (expressed as percentage error [PE]) and precision of the estimated parameters. PK parameters (volume transfer constant [Ktrans ], fractional volume of the extravascular extracellular space [ve ], and blood plasma volume fraction [vp ]) and normalized root-mean-square error [nRMSE] (%) of the fitting errors for the tumor contrast kinetic data were measured both with population-averaged and data-driven AIFs. On patient data, the Wilcoxon signed-rank test was performed to compare nRMSE. Simulations demonstrated that GRASP image reconstruction with a temporal resolution of 1 s/frame for AIF estimation and 5 s/frame for PK analysis resulted in an absolute PE of less than 5% in the estimation of Ktrans and ve , and less than 11% in the estimation of vp . The nRMSE (mean ± SD) for the dual temporal resolution image reconstruction and data-driven AIF was 0.16 ± 0.04 compared with 0.27 ± 0.10 (p< 0.001) with 1 s/frame using population-averaged AIF, and 0.23 ± 0.07 with 5 s/frame using population-averaged AIF (p< 0.001). We conclude that DCE-MRI data acquired and reconstructed with the GRASP technique at dual temporal resolution can successfully be applied to jointly estimate the AIF and PK parameters from a single acquisition resulting in data-driven AIFs and voxelwise PK parametric maps.

Micromechanical modeling of ultrasonic velocity for pore-structure and porosity characterization considering anisotropy in carbonate samples

This work presents an approach to characterize the pore-structure and anisotropy in carbonate samples based on the Effective Medium Method (EMM). It considers a matrix with spheroidal inclusions which induce a transverse anisotropy. The compressional wave (VP), vertical (VSV) and horizontal (VSH) shear wave velocities are estimated taking into account parameters as characteristic length, frequency, angle of wave incidence, aspect ratio, mineralogy, and pore-filling fluid to predict pore shape in carbonates. Ranges of aspect ratios are shown to discriminate different pore types: intercrystalline, intergranular, moldic, and vuggy. The angle of wave incidence is a determinant parameter in the estimation of VP(0º, 45º, 90º), VSV(0º) and VSH(90º) to calculate dynamic anisotropic Young’s modulus (E33) and Poisson’s ratio (v31), as well as the Thomsen parameters, Epsilon, Gamma and Delta for quantification of the anisotropic pore-structure. The obtained results establish that the size, as well as the pore-structure, have a more significant impact on the elastic properties when the porosity takes values greater than 4% for the three frequencies, ultrasonic, sonic, and seismic. This investigation predicts the pore-structure and pore-size to improve characterization and elastic properties modeling of carbonate reservoirs. Validation of results includes porosity measurements and ultrasonic velocity data for different carbonate samples.

A novel algorithm to estimate mineral elastic properties and pore aspect ratio in the carbonate reservoirs

Rock physics models provide a link between the interior structure of rocks and seismic, petrophysics and geological data. Despite considerable advancements in reservoir rock physics, most models are developed to study the sandstone reservoirs, hence their application in the carbonate reservoirs probably needs further discussions. This might be due to the nature of sedimentation, existence of multiple pore types, and the diversity in their packing and sorting. The rock physics models utilizing effective medium theory provide a more accurate estimation by introducing the pore aspect ratio to such methods. However, the pore aspect ratio and the remaining input parameters, including the elastic moduli of minerals, are mostly derived from references and do not necessarily represent the actual rock matrix. In this study an algorithm is provided to simultaneously estimate the bulk and shear moduli of minerals and pore aspect ratio. The algorithm uses the velocity logs along with Kuster-Toksӧz model to derive an equation in terms of mineral elastic moduli and aspect ratio. This equation is then solved using Newton-Raphson method. The results are used to calculate the compressional- and shear- velocities in a carbonate gas reservoir that exhibit a reasonable match with the measured logs with mean absolute errors of 10−4% and 2.97%, respectively. The estimated elastic parameters are then averaged over different lithologies. Application of averaged input parameters resulted in estimation of Vp and Vs with mean absolute errors of 3.54% and 3.88%, respectively. The outcome of this study would also assist on determining the rock forming minerals and the number of pore systems available in the matrix.

Semi-global inversion of vp to vs ratio for elastic wavefield inversion

We introduce an approach to estimate the ratio between P- and S-wave velocities, vp/vs, in the scope of elastic full waveform inversion (FWI). Elastic FWI is generally implemented with local optimization methods relying on initial estimates of the long wavelengths of P- and S-wave models. However, successful inversions can be hindered if an accurate enough relation between vp and vs velocities is not used as a constraint. This relation can be estimated from empirical relations. Herein, we introduce an alternative approach based upon a semi-global inversion scheme. We observe that for a large number of cases, and particularly in the context of FWI, vp/vs can be represented on a sparse basis. This sparse basis has a much smaller dimension than that of the typical model space in elastic FWI. This creates the possibility of using global optimization methods. The optimal estimate of vp/vs is obtained with quantum particle swarm optimization (QPSO). This method probes a population of possible models. The assessment of each model of vp/vs in the population is obtained with nested local iterations updating for vp only. Conventional elastic FWI is then carried out for jointly estimating high-resolution models of vp and vs. We demonstrate with synthetic examples that the estimates of vp are relatively robust to errors in the estimated vp/vs, and that effectively a sparse representation of the model of vp/vs is feasible for the reconstruction of a model of vs. We also demonstrate that the proposed approach performs better than constraining elastic FWI with an empirical relation between vp and vs, leading to improved estimates of models of vp and vs from seismic data.

Abstract W P256: Voxel-by-Voxel Distribution Pattern of Estimates of Vascular Volume and that of Blood-to-brain Forward Volume Transfer Constant are different in Experimental Embolic Stroke

Background and Purpose: Changes in vascular indices such as blood-to-brain forward volume transfer constant (Ktrans) and plasma distribution volume (vp) are considered as potential predictors of impending hemorrhage in acute stroke. However, few studies have reported their spatial distributions and variability within a given stroke lesion. This study examined the voxel-by-voxel distributions of vp and Ktrans within a region of interest (ROI) and the overall mean for the entire ROI to investigate their possible inherent variability. Methods: Male Wistar rats (~300 g; N=6) were subjected to embolic occlusion of the middle cerebral artery for 2 h followed by treatment with recombinant tissue plasminogen activator (rTPA) treatment for thrombolysis. Measurements of vp and Ktrans were made in the ischemic lesion after rTPA infusion using dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). Data were generated using two approaches. In the first, voxel-by-voxel values of moments about the mean viz., median and skewness. In the second, values were summed across the ROI producing a mean and standard deviation. Differences between the two means were assessed by t-tests and significance inferred at p≤0.05. Results: The voxel-by-voxel estimates of vp were larger (0.025+0.008) than the summed mean (0.016+0.005), the difference being marginally significant (p=0.05). A positive skew value of 1.88 was obtained for the data and accordingly the median value (0.019) was lower than the mean. In contrast, voxel -based estimate of Ktrans (0.002+0.001) was not different from the summed mean (0.002+0.001; p&gt;0.05). The median value for Ktrans (0.002) was not significantly different from the mean (p&gt;0.05) suggesting a more uniform distribution of the data across the voxels with a very low skewness (0.05). Conclusions: These observations suggest that the voxel-by-voxel distributions can be dissimilar for the different indices of vascular injury within a given ischemic lesion. Such variations may be representative of varying degrees of damage and, consequently, may also represent the effects of a putative treatment. Understanding the tissue pathology determining these variations can assist in employing them as biomarkers of injury and response to treatment.

Bias in seismic estimates of crustal properties

SUMMARY It has come to our attention that the least-squares estimator we proposed in a recent paper to recover bulk crustal P velocity, VP, and P velocity/S velocity ratio, R, of the crust from traveltimes of scattered teleseismic phases, is inconsistent. That is, in the presence of errors, estimates of R will be biased downwards and estimates of VP will be biased upwards from their true values. In this note we supply bias corrections for both quantities that depend upon an estimate of the variance in a ratio of traveltime sums, and demonstrate their validity through comparison with estimates based on a two-parameter grid search. Application to station HYB yields R = 1.756 ± 0.005, VP = 6.2 ± 0.1 km s −1 , after correction of a systematic traveltime picking error that had affected our previous results. In addition, we provide an alternative waveform-stacking approach that involves a 2-D grid search over R and VP followed by a 1-D line search over crustal thickness H. An estimate of the direct Ps conversion time is required, and results from station HYB are consistent with those produced using traveltimes alone.

Quantitative assessment of volcanic ash hazards for health and infrastructure at Mt. Etna (Italy) by numerical simulation

We performed a quantitative hazard assessment to determine the potential impacts of volcanic tephra fall on human health and infrastructure in the vicinity of Mt. Etna (Italy). Using the numerical model VOL-CALPUFF, we explored the dynamics of long-lasting weak plume eruptions and their effects on the surrounding region. Input data are based on credible estimates of the main parameters characterising the expected events as derived from the historically observed and reconstructed explosive record of Mt. Etna. Monte Carlo techniques are used to capture the effects on estimates of finer ash concentration and total ground deposition due to volcanological uncertainties and meteorological variability. Numerical simulations compute the likelihoods of experiencing critical 10-μm volcanic particle (VP 10) concentrations in ambient air and tephra ground deposition at various populated locations around the volcano, including the city of Catania, and at key infrastructure, such as airports and main roads. Results show how the towns and infrastructure on the east side of the volcano are significantly more exposed to ash-related hazards than those on the west side, in accordance with wind statistics. Simulation outcomes also illustrate how, at the sites analysed, the amount of deposited particulate matter is proportional to the intensity (i.e. mass flow rate) of the event whereas predicted values of VP 10 concentrations are significantly larger for smaller events due to the reduced dispersal of low altitude plumes. The use of a simple re-mobilization model highlights the fact that particle re-suspension needs to be considered in the estimation of VP 10 values. Our findings can be used to inform civil protection agencies responsible for mitigating tephra fall impacts to human health, road transport and aviation safety.

Prestack full waveform inversion for estimating elastic properties of marine sediments

Prestack seismic waveform inversion is a highly challenging task. The nonlinearity and nonuniqueness together with computed intensive forward modeling make the problem intractable. Here we report on a new approach to seismic waveform inversion based on a gradient descent scheme that makes use of innovative gradient calculation, adaptive regularization, and an efficient conjugate gradient algorithm. We exploit sparsity of the gradient matrix based on physics in designing an algorithm that is computationally very efficient. The results from our approach are highly encouraging in that we are able to invert large 3‐D dataset with nearly 1,000 model parameters fairly rapidly. Not only that, because of the use of adaptive regularization, we are able to track smooth as well as sharp variations in the impedance, Vp and Vs profiles when realistic starting solutions are used. We have applied the technique successfully to numerous 3‐D exploration and academic datasets. Of particular interest is our ability to estimate density from seismic data that can be used to map porosity in an effective manner. Application to seismic data collected over offshore Oregon resulted in estimates of Vp and Vs that could be used in estimating hydrate concentration in the shallow sediment.

Comparative study of methods for determining vascular permeability and blood volume in human gliomas

To characterize human gliomas using T1-weighted dynamic contrast-enhanced MRI (DCE-MRI), and directly compare three pharmacokinetic analysis techniques: a conventional established technique and two novel techniques that aim to reduce erroneous overestimation of the volume transfer constant between plasma and the extravascular extracellular space (EES) (Ktrans) in areas of high blood volume. Eighteen patients with high-grade gliomas underwent DCE-MRI. Three kinetic models were applied to estimate Ktrans and fractional blood plasma volume (vp). We applied the Tofts and Kermode (TK) model without arterial input function (AIF) estimation, the TK model modified to include vp and AIF estimation (mTK), and a "first pass" variant of the TK model (FP). KTK values were considerably higher than KmTK and KFP values (P <0.001). KmTK and KFP were more comparable and closely correlated (rho=0.744), with KmTK generally higher than KFP (P <0.001). Estimates of vp(mTK) and vp(FP) also showed a significant difference (P <0.001); however, these values were very closely correlated (rho=0.901). KTK parameter maps showed "pseudopermeability" effects displaying numerous vessels. These were not visualized on KmTK and KFP maps but appeared on the corresponding vp maps, indicating a failure of the TK model in commonly occurring vascular regions. Both of the methods that incorporate a measured AIF and an estimate of vp provide similar pathophysiological information and avoid erroneous overestimation of Ktrans in areas of significant vessel density, and thus allow a more accurate estimation of endothelial permeability.

Parallel conductance estimation by hypertonic dilution method with conductance catheter: effects of the bolus concentration and temperature.

The conductance catheter has gained momentum since its introduction in cardiovascular dynamics back in 1980. However, measuring errors are still blurring its clinical acceptance. The main objective here was to study the effects of the injected saline concentration and temperature on the evaluation of the parallel conductance, Gp, and thus, on the correction volume Vp. That conductance, Gp, and its associated volume, Vp, were computed using 167 saline dilution curves obtained with boluses at different concentrations and temperatures, injected in seven anesthetized closed-chest dogs. The excursion of the total conductance relative to the steady-state value during a saline maneuver showed good correlation with the injected concentration at both studied temperatures. The reference parallel volume (one reference per dog) was defined as the average value obtained with three successive maneuvers, at 6-M concentration and at body temperature; therefore, the method acted as its own reference. The variation of Vp relative to the reference value was clearly dependent on the injected concentration and on its temperature; dispersion was greater at 22 degrees C than at 40 degrees C. The variability would recognize also other causes, such as uncertainty of the extrapolation procedure and the thoracic redistribution of electrical field lines. As conclusion, it is recommended to characterize each maneuver by its concentration and temperature. Body temperature and 6-M concentration appear as the most recommendable combination for the injectate in most animals. Finally, these results intend to characterize the Vp estimation procedure in order to minimize errors. The variability of Vp, in different experimental conditions, demonstrated that both concentration and temperature are additional parameters that may modify the Gp estimate.

Genetics of cleft lip and palate: S. N. BhatiaBr. Dent. J.132: 95–103, Feb. 1, 1972

The time course of RNA synthesis in vitro commonly starts with a lag followed by a linear phase. Differing from the earlier interpretation we have previously proposed that, under conditions where the initiation rate is low, the lag represents the time taken for the first RNA polymerase molecule to reach a termination site. During the linear phase, initiation is balanced by termination (Mahon, G.A.T., McWilliam, P., Gordon, R.L. and McConnell, D.J. (1980) J. Theor. Biol. 87, 483–515). We report the use of rifampicin as a further test of this new model. We show that it does apply under conditions of high ionic strength (0.3 M KCl), and under these conditions time courses may be analyzed to yield unbiased estimates of the initiation (Vi) and chain elongation (Vp) rates. We illustrate the application of the method of time course analysis and confirm some of its features by examining the effect of variation in the concentrations of RNA polymerase and nucleoside triphosphate on the estimates of Vi and Vp. The alternative interpretation of the time course applies under conditions of low ionic strength, where the initiation rate is high. (Chamberlin, M.J., Nierman, W.C., Wiggs, J. and Neff, N. (1979) J. Biol. Chem. 254, 10061–10069.) The advantages of each model in measuring Vi and Vp (the major parameters of the transcription reaction) are discussed.