scholarly journals Time density curve analysis for C-arm FDCT PBV imaging

2016 ◽  
Vol 22 (2) ◽  
pp. 176-186 ◽  
Author(s):  
Mudassar Kamran ◽  
James V Byrne
Keyword(s):  
Steady State ◽  
Goodness Of Fit ◽  
Contrast Material ◽  
Horizontal Line ◽  
Cerebral Vasculature ◽  
Line Model ◽  
Density Curve ◽  
Injection Protocol ◽  
The Individual ◽  
Time Density

Introduction Parenchymal blood volume (PBV) estimation using C-arm flat detector computed tomography (FDCT) assumes a steady-state contrast concentration in cerebral vasculature for the scan duration. Using time density curve (TDC) analysis, we explored if the steady-state assumption is met for C-arm CT PBV scans, and how consistent the contrast-material dynamics in cerebral vasculature are across patients. Methods Thirty C-arm FDCT datasets of 26 patients with aneurysmal-SAH, acquired as part of a prospective study comparing C-arm CT PBV with MR-PWI, were analysed. TDCs were extracted from the 2D rotational projections. Goodness-of-fit of TDCs to a steady-state horizontal-line-model and the statistical similarity among the individual TDCs were tested. Influence of the differences in TDC characteristics on the agreement of resulting PBV measurements with MR-CBV was calculated. Results Despite identical scan parameters and contrast-injection-protocol, the individual TDCs were statistically non-identical ( p < 0.01). Using Dunn's multiple comparisons test, of the total 435 individual comparisons among the 30 TDCs, 330 comparisons (62%) reached statistical significance for difference. All TDCs deviated significantly ( p < 0.01) from the steady-state horizontal-line-model. PBV values of those datasets for which the TDCs showed largest deviations from the steady-state model demonstrated poor agreement and correlation with MR-CBV, compared with the PBV values of those datasets for which the TDCs were closer to steady-state. Conclusion For clinical C-arm CT PBV examinations, the administered contrast material does not reach the assumed ‘ideal steady-state’ for the duration of scan. Using a prolonged injection protocol, the degree to which the TDCs approximate the ideal steady-state influences the agreement of resulting PBV measurements with MR-CBV.

scholarly journals Carotid webs produce greater hemodynamic disturbances than atherosclerotic disease: a DSA time–density curve study

2021 ◽  
pp. neurintsurg-2021-017588
Author(s):  
Charlie C Park ◽  
Retta El Sayed ◽  
Benjamin B Risk ◽  
Diogo C Haussen ◽  
Raul G Nogueira ◽  
...  
Keyword(s):  
Logistic Regression ◽  
Carotid Artery ◽  
Carotid Arteries ◽  
Region Of Interest ◽  
Hemodynamic Parameters ◽  
Density Curve ◽  
Atherosclerotic Lesions ◽  
Clinically Significant ◽  
Flow Stasis ◽  
Time Density

BackgroundCarotid webs (CaWs) are associated with ischemic strokes in younger patients without degrees of stenosis that are traditionally considered clinically significant.ObjectiveTo compare the hemodynamic parameters in the internal carotid artery (ICA) bulbar segment in patients with CaW with those in patients with atherosclerotic lesions using time–density curve (TDC) analysis of digital subtraction angiography (DSA) images.MethodsWe retrospectively assessed DSA images of 47 carotid arteries in 41 adult patients who underwent ICA catheter angiography for evaluation after ischemic stroke. Hemodynamic parameters, including full width at half maximum (FWHM) and area under the time–density curve (AUC) as proxies for increased flow stasis, were calculated using TDC analyses of a region of interest (ROI) in the ICA bulb immediately rostral to the web/atherosclerotic plaque, relative to a standardized ROI in the ipsilateral distal common carotid artery (eg, relative FWHM (rFWHM)). Hemodynamic parameters were compared using non-parametric Kruskal-Wallis tests. Logistic regression was used to predict CaW versus mild/moderate atherosclerosis for each hemodynamic parameter, adjusting for degree of stenosis.ResultsMean age of patients was 56.0±13 years, with 22 (53.7%) women. 17 CaWs, 22 atherosclerotic plaques (15 mild/moderate and 7 severe), and eight normal carotid arteries were assessed. Significant between-group differences were present in the relative total AUC (p<0.001), relative AUC at wash out (p=0.031), and relative FWHM (p=0.001). Logistic regression to predict CaW versus mild/moderate atherosclerosis showed that rAUC total had the highest predictive value (pAUC=0.96, 95% CI 0.90 to 1.00), followed by rFWHM (0.87, 95% CI 0.74 to 1.00), and rAUC WO (0.74, 95% CI (0.57 to 0.91).ConclusionCaW results in larger local hemodynamic disruption, characterized by flow stasis, than mild/moderate carotid atherosclerotic lesions, suggesting that CaWs may produce larger regions of thrombogenic flow stasis.

scholarly journals INHERITED TASTES AND ENDOGENOUS LONGEVITY

2017 ◽  
Vol 23 (2) ◽  
pp. 674-698 ◽  
Author(s):  
Luciano Fanti ◽  
Luca Gori ◽  
Cristiana Mammana ◽  
Elisabetta Michetti
Keyword(s):  
Steady State ◽  
Overlapping Generations ◽  
Standard Of Living ◽  
Poverty Trap ◽  
Individual State ◽  
State Of Health ◽  
Tax Rate ◽  
Public Investments ◽  
The Individual ◽  
Endogenous Longevity

This article aims at studying a general equilibrium model with overlapping generations that incorporates inherited tastes (aspirations) and endogenous longevity. The existence of standard-of-living aspirations transmitted between two subsequent generations in a context where the individual state of health depends on public investments in health has some remarkable consequences at the macroeconomic level. First, aspirations allow escaping from the well-known poverty trap scenario described by Chakraborty (2004). Second, the steady-state equilibrium may be destabilized through a super-critical Neimark–Sacker bifurcation when the health tax rate is set at too high or too low a level. This causes endogenous fluctuations in income and longevity.

scholarly journals Levitation of non-magnetizable droplet inside ferrofluid

2018 ◽  
Vol 857 ◽  
pp. 398-448 ◽  
Author(s):  
Chamkor Singh ◽  
Arup K. Das ◽  
Prasanta K. Das
Keyword(s):  
Magnetic Field ◽  
Steady State ◽  
Viscosity Ratio ◽  
Temporal Dynamics ◽  
Liquid Droplet ◽  
Droplet Surface ◽  
Two Dimensions ◽  
Projection Algorithm ◽  
The Stability ◽  
The Individual

The central theme of this work is that a stable levitation of a denser non-magnetizable liquid droplet, against gravity, inside a relatively lighter ferrofluid – a system barely considered in ferrohydrodynamics – is possible, and exhibits unique interfacial features; the stability of the levitation trajectory, however, is subject to an appropriate magnetic field modulation. We explore the shapes and the temporal dynamics of a plane non-magnetizable droplet levitating inside a ferrofluid against gravity due to a spatially complex, but systematically generated, magnetic field in two dimensions. The coupled set of Maxwell’s magnetostatic equations and the flow dynamic equations is integrated computationally, utilizing a conservative finite-volume-based second-order pressure projection algorithm combined with the front-tracking algorithm for the advection of the interface of the droplet. The dynamics of the droplet is studied under both the constant ferrofluid magnetic permeability assumption as well as for more realistic field-dependent permeability described by Langevin’s nonlinear magnetization model. Due to the non-homogeneous nature of the magnetic field, unique shapes of the droplet during its levitation, and at its steady state, are realized. The complete spatio-temporal response of the droplet is a function of the Laplace number $La$ , the magnetic Laplace number $La_{m}$ and the Galilei number $Ga$ ; through detailed simulations we separate out the individual roles played by these non-dimensional parameters. The effect of the viscosity ratio, the stability of the levitation path and the possibility of existence of multiple stable equilibrium states is investigated. We find, for certain conditions on the viscosity ratio, that there can be developments of cusps and singularities at the droplet surface; we also observe this phenomenon experimentally and compare with the simulations. Our simulations closely replicate the singular projection on the surface of the levitating droplet. Finally, we present a dynamical model for the vertical trajectory of the droplet. This model reveals a condition for the onset of levitation and the relation for the equilibrium levitation height. The linearization of the model around the steady state captures that the nature of the equilibrium point goes under a transition from being a spiral to a node depending upon the control parameters, which essentially means that the temporal route to the equilibrium can be either monotonic or undulating. The analytical model for the droplet trajectory is in close agreement with the detailed simulations.

scholarly journals Estimates of Michaelis-Menten Constants for the Two Membranes of the Brain Endothelium

1984 ◽  
Vol 4 (2) ◽  
pp. 241-249 ◽  
Author(s):  
Albert Gjedde ◽  
Ove Christensen
Keyword(s):  
Steady State ◽  
Endothelial Cell ◽  
Transport Properties ◽  
Glucose Transport ◽  
Cell Membranes ◽  
Experimental Studies ◽  
Facilitated Diffusion ◽  
Capillary Endothelial Cells ◽  
The Individual ◽  
Tracer Experiments

Tracer studies on facilitated diffusion across the blood–brain barrier lead to the calculation of Michaelis-Menten constants that describe the rate of transport. However, the barrier consists of two endothelial cell membranes, and the relevance of single Michaelis-Menten constants in relation to the two cell membranes is unknown. We have formulated a model of two endothelial cell membranes and show that the measured Michaelis-Menten constants are simple functions of the properties of the individual membranes when transport across the endothelium is rapid ( P1 > 10−6 cm s−1). We also show that the Michaelis-Menten constants determined in tracer experiments describe facilitated diffusion in the steady state only if the two membranes have similar transport properties. As an application of this observation, we have examined three experimental studies that measure glucose transport in the steady state and show that the Michaelis-Menten constants for glucose transport calculated from the tracer experiments are equal to the constants calculated from the steady-state experiments. We conclude that the luminal and abluminal membranes of brain capillary endothelial cells have equal glucose transport properties.

scholarly journals Overall efficacies of combined measures for controlling grape bunch rot can be estimated by multiplicative consideration of individual effects

OENO One ◽  
2017 ◽  
Vol 51 (4) ◽  
pp. 401-407 ◽  
Author(s):  
Daniel Molitor ◽  
Lucien Hoffmann ◽  
Marco Beyer
Keyword(s):  
Disease Severity ◽  
Goodness Of Fit ◽  
Control Measures ◽  
Average Absolute Deviation ◽  
Absolute Deviation ◽  
Additional Measure ◽  
Severity Level ◽  
Bunch Rot ◽  
The Individual ◽  
Disease Severity Level

Aims: The present analyses aimed at evaluating the performance of two models for estimating the overall effect of combining two or more measures (leaf removal, cluster division, late shoot topping, botryticide application, bioregulator application) for controlling grape bunch rot based on the efficacy of the individual measures.Methods and results: Field trials with the white Vitis vinifera cultivars Pinot gris and Riesling on the efficacy of three bunch rot control measures applied either alone or in combination were analyzed. Bunch rot disease severities prior to harvest were assessed and efficacies were calculated for each treatment. Observed efficacies of single measures were used to estimate the overall efficacies of all possible measure combinations. Calculated efficacies matched observed efficacies more accurately when assuming multiplicative interaction among the individual measures (R2 = 0.8574, p < 0.0001; average absolute deviation: 7.9%) than in case of assuming additive effects (R2 = 0.8280; average absolute deviation: 14.7%).Conclusions: The multiplicative approach assumes that each additional measure is affecting (in case of efficient measures: reducing) the disease severity level as the result of the additional treatments rather than compared to the disease severity level in the untreated control.Significance and impact of the study: The high goodness of fit as well as the observed low deviations between the estimated and the observed efficacies suggest that the multiplicative approach is appropriate for estimating the efficacy of combined viticultural measures in a complex practical bunch rot control strategy assembled of different modules.

Lower Extremity Joint Work During Acceleration, Deceleration, and Steady State Running

2017 ◽  
Vol 33 (1) ◽  
pp. 56-63 ◽  
Author(s):  
D.S. Blaise Williams ◽  
Jonathan H. Cole ◽  
Douglas W. Powell
Keyword(s):  
Steady State ◽  
Lower Extremity ◽  
Sagittal Plane ◽  
Three Dimensional ◽  
Joint Work ◽  
Negative Work ◽  
Relative Contribution ◽  
Acceleration And Deceleration ◽  
The Individual ◽  
Positive Work

Running during sports and for physical activity often requires changes in velocity through acceleration and deceleration. While it is clear that lower extremity biomechanics vary during these accelerations and decelerations, the work requirements of the individual joints are not well understood. The purpose of this investigation was to measure the sagittal plane mechanical work of the individual lower extremity joints during acceleration, deceleration, and steady-state running. Ten runners were compared during acceleration, deceleration, and steady-state running using three-dimensional kinematics and kinetics measures. Total positive and negative joint work, and relative joint contributions to total work were compared between conditions. Total positive work progressively increased from deceleration to acceleration. This was due to greater ankle joint work during acceleration. While there was no significant change in total negative work during deceleration, there was a greater relative contribution of the knee to total negative work with a subsequent lower relative ankle negative work. Each lower extremity joint exhibits distinct functional roles in acceleration compared with deceleration during level running. Deceleration is dominated by greater contributions of the knee to negative work while acceleration is associated with a greater ankle contribution to positive work.

scholarly journals Population Pharmacokinetics and Dosage Optimization of Linezolid in Patients with Liver Dysfunction

2020 ◽  
Vol 64 (6) ◽  
Author(s):  
Su-hua Zhang ◽  
Zhen-yu Zhu ◽  
Zi Chen ◽  
Ying Li ◽  
Yang Zou ◽  
...  
Keyword(s):  
Steady State ◽  
Population Pharmacokinetics ◽  
Liver Dysfunction ◽  
Goodness Of Fit ◽  
Standard Dose ◽  
Visual Predictive Check ◽  
Therapeutic Drug ◽  
Optimal Dosage ◽  
Clinical Trial Registry ◽  
Bootstrap Analysis

ABSTRACT Linezolid is the first synthetic oxazolidone agent to treat infections caused by Gram-positive pathogens. Infected patients with liver dysfunction (LD) are more likely to suffer from adverse reactions, such as thrombocytopenia, when standard-dose linezolid is used than patients with LD who did not use linezolid. Currently, pharmacokinetics data of linezolid in patients with LD are limited. This study aimed to characterize pharmacokinetics parameters of linezolid in patients with LD, identify the factors influencing the pharmacokinetics, and propose an optimal dosage regimen. We conducted a prospective study and established a population pharmacokinetics model with the Phoenix NLME software. The final model was evaluated by goodness-of-fit plots, bootstrap analysis, and prediction corrected-visual predictive check. A total of 163 concentration samples from 45 patients with LD were adequately described by a one-compartment model with first-order elimination along with prothrombin activity (PTA) and creatinine clearance as significant covariates. Linezolid clearance (CL) was 2.68 liters/h (95% confidence interval [CI], 2.34 to 3.03 liters/h); the volume of distribution (V) was 58.34 liters (95% CI, 48.00 to 68.68 liters). Model-based simulation indicated that the conventional dose was at risk for overexposure in patients with LD or severe renal dysfunction; reduced dosage (300 mg/12 h) would be appropriate to achieve safe (minimum steady-state concentration [Cmin,ss] at 2 to 8 μg/ml) and effective targets (the ratio of area under the concentration-time curve from 0 to 24 h [AUC0–24] at steady state to MIC, 80 to 100). In addition, for patients with severe LD (PTA, ≤20%), the dosage (400 mg/24 h) was sufficient at an MIC of ≤2 μg/ml. This study recommended therapeutic drug monitoring for patients with LD. (This study has been registered in the Chinese Clinical Trial Registry under no. ChiCTR1900022118.)

scholarly journals Small-Signal Stability Analysis of Multi-Terminal DC Grids

Electronics ◽  
2019 ◽  
Vol 8 (2) ◽  
pp. 130
Author(s):  
Amr Radwan
Keyword(s):  
Steady State ◽  
State Space ◽  
State Space Model ◽  
Operation Time ◽  
Power Sharing ◽  
Voltage Source ◽  
Small Signal ◽  
Small Signal Stability ◽  
Steady State Operation ◽  
The Individual

This paper presents a detailed small-signal analysis and an improved dc power sharing scheme for a six terminal dc grid. The multi-terminal DC (MTDC) system is composed of (1) two voltage-source converters (VSCs) entities operating as rectification stations; (2) two VSCs operating as inverting stations; (3) two dc/dc conversion stations; and (4) an interconnected dc networking infrastructure. The small-signal state-space sub-models of the individual entities are developed and integrated to formulate the state-space model of the entire system. Using the modal analysis, it is shown that the most critical modes are associated with the power sharing droop coefficients of the rectification stations, which are constrained by the steady-state operational requirements. Therefore, a second degree-of-freedom compensation scheme is proposed to improve the dynamic response of the MTDC system without influencing the steady-state operation. Time domain simulation results are presented to validate the analysis and show the effectiveness of the proposed techniques.

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