Cerebral CT Venography Using a 320-MDCT Scanner With a Time-Density Curve Technique and Low Volume of Contrast Agent: Comparison With Fixed Time-Delay Technique

2015 ◽  
Vol 205 (6) ◽  
pp. 1269-1275 ◽  
Author(s):  
Shubhabrata Biswas ◽  
Arun Chandran ◽  
Sue Roughley ◽  
Maneesh Bhojak ◽  
Kumar Das
Keyword(s):  
Time Delay ◽  
Contrast Agent ◽  
Fixed Time ◽  
Ct Venography ◽  
Density Curve ◽  
Low Volume ◽  
Time Density ◽  
Mdct Scanner

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.

Optimum Active Vehicle Suspensions With Actuator Time Delay

2000 ◽  
Vol 123 (1) ◽  
pp. 54-61 ◽  
Author(s):  
Nader Jalili ◽  
Ebrahim Esmailzadeh
Keyword(s):  
Optimal Control ◽  
Time Delay ◽  
Wide Band ◽  
Fixed Time ◽  
Realistic Model ◽  
Vertical Acceleration ◽  
Band Frequency ◽  
The Road ◽  
Stability Chart ◽  
The Stability

A new approach to optimal control of vehicle suspension systems, incorporating actuator time delay, is presented. The inclusion of time delay provides a more realistic model for the actuators, and the problem is viewed from a different perspective rather than the conventional optimal control techniques. The objective here is to select a set of feedback gains such that the maximum vertical acceleration of the sprung mass is minimized, over a wide band frequency range and when subjected to certain constraints. The constraints are dictated by the vehicle stability characteristics and the physical bounds placed on the feedback gains. Utilizing a Simple Quarter Car model, the constrained optimization is then carried out in the frequency domain with the road irregularities described as random processes. Due to the presence of the actuator time delay, the characteristic equation is found to be transcendental rather than algebraic, which makes the stability analysis relatively complex. A new scheme for the stability chart strategy with fixed time delay is introduced in order to address the stability issue. The stability characteristics are also verified utilizing other conventional methods such as the Michailov technique. Results demonstrate that the suspension system, when considering the effect of the actuator time delay, exhibits a completely different behavior.

scholarly journals Dynamics of a Stage Structure Pest Control Model with Impulsive Effects at Different Fixed Time

2009 ◽  
Vol 2009 ◽  
pp. 1-15 ◽  
Author(s):  
Bing Liu ◽  
Ying Duan ◽  
Yinghui Gao
Keyword(s):  
Time Delay ◽  
Pest Control ◽  
Natural Enemies ◽  
Stage Structure ◽  
Threshold Level ◽  
Fixed Time ◽  
Control Model ◽  
Pest Population ◽  
Maturation Time ◽  
Maturation Time Delay

Many existing pest control models, which control pests by releasing natural enemies, neglect the effect that natural enemies may get killed. From this point of view, we formulate a pest control model with stage structure for the pest with constant maturation time delay (through-stage time delay) and periodic releasing natural enemies and natural enemies killed at different fixed time and perform a systematic mathematical and ecological study. By using the comparison theorem and analysis method, we obtain the conditions for the global attractivity of the pest-eradication periodic solution and permanence of the system. We also present a pest management strategy in which the pest population is kept under the economic threshold level (ETL) when the pest population is uniformly permanent. We show that maturation time delay, impulsive releasing, and killing natural enemies can bring great effects on the dynamics of the system. Numerical simulations confirm our theoretical results.

A reaction–diffusion epidemic model with incubation period in almost periodic environments

2020 ◽  
pp. 1-24
Author(s):  
LIZHONG QIANG ◽  
BIN-GUO WANG ◽  
ZHI-CHENG WANG
Keyword(s):  
Time Delay ◽  
Spatial Heterogeneity ◽  
Incubation Period ◽  
Epidemic Model ◽  
Reaction Diffusion ◽  
Fixed Time ◽  
Reaction Diffusion Equations ◽  
Threshold Dynamics ◽  
Almost Periodic ◽  
Periodic Reaction

In this paper, we propose and study an almost periodic reaction–diffusion epidemic model in which disease latency, spatial heterogeneity and general seasonal fluctuations are incorporated. The model is given by a spatially nonlocal reaction–diffusion system with a fixed time delay. We first characterise the upper Lyapunov exponent $${\lambda ^*}$$ for a class of almost periodic reaction–diffusion equations with a fixed time delay and provide a numerical method to compute it. On this basis, the global threshold dynamics of this model is established in terms of $${\lambda ^*}$$ . It is shown that the disease-free almost periodic solution is globally attractive if $${\lambda ^*} < 0$$ , while the disease is persistent if $${\lambda ^*} < 0$$ . By virtue of numerical simulations, we investigate the effects of diffusion rate, incubation period and spatial heterogeneity on disease transmission.

Correlation between dose rate and T1 in blood at gd-enhanced MR angiography

1998 ◽  
Vol 39 (5) ◽  
pp. 579-582 ◽  
Author(s):  
L. O. M. Johansson ◽  
H. K. Ahlström
Keyword(s):  
Time Delay ◽  
Contrast Agent ◽  
Dose Rate ◽  
Abdominal Aorta ◽  
Signal Intensity ◽  
Mr Angiography ◽  
Pulse Sequence ◽  
Test Dose ◽  
Contrast Enhanced ◽  
First Pass

Purpose: to determine the correlation between dose rate and T1 in blood at Gd-enhanced MR angiography (MRA) Material and Methods: A test dose of contrast agent was used to calculate the time delay between injection and arrival in the abdominal aorta. the dose rate was expressed as ml · kg b.w.−1 · s−1. the correlation between dose rate and T1 was determined by varying the dose rate while keeping the scanning and infusion times constant. the signal intensity in the abdominal aorta was measured during the first pass of Gd and compared with markers of known T1 values Results: A correlation between dose rate and T1 in blood was obtained Conclusion: A Gd dose rate of 0.01 ml · kg b.w.−1 · s−1 gives a T1 in blood of 100 ms. This can be used to calculate the optimal pulse sequence for contrast-enhanced MRA

Norepinephrine reuptake, baroreflex dynamics, and arterial pressure variability in rats

2000 ◽  
Vol 279 (4) ◽  
pp. R1257-R1267 ◽  
Author(s):  
Delphine Bertram ◽  
Christian Barrès ◽  
Yong Cheng ◽  
Claude Julien
Keyword(s):  
Time Delay ◽  
Transfer Function ◽  
Fixed Time ◽  
Baroreceptor Reflex ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Mayer Waves ◽  
Frequency Responses ◽  
Low Pass ◽  
Norepinephrine Reuptake

This study examined the effect of norepinephrine reuptake blockade with desipramine (DMI) on the spontaneous variability of the simultaneously recorded arterial pressure (AP) and renal sympathetic nerve activity (SNA) in conscious rats. Acute DMI administration (2 mg/kg iv) depressed AP Mayer waves (∼0.4 Hz) and increased low-frequency (<0.2 Hz) components of AP variability. DMI decreased renal SNA variability, especially due to the abolition of oscillations related to Mayer waves. To examine whether DMI-induced changes in AP and renal SNA variabilities could be explained by alterations in the dynamic characteristics of the baroreceptor reflex loop, the frequency responses of mean AP to aortic depressor nerve stimulation were studied in urethan-anesthetized rats. DMI accentuated the low-pass filter properties of the transfer function without significantly altering the fixed time delay. The frequency responses of iliac vascular conductance to stimulation of the lumbar sympathetic chain were studied in an additional group of anesthetized rats. DMI did not markedly alter the low-pass filter properties of the transfer function and slightly increased the fixed time delay. These results suggest that the DMI-induced decrease in the dynamic gain of the baroreceptor reflex is responsible for the decreased spontaneous renal SNA variability and the accompanying increased AP variability. The “slowing down” of baroreflex responses cannot be attributed to an effect of DMI at the vascular neuroeffector junction.

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