Standardized MR protocol for the evaluation of MRA sequences and/or contrast agents effects in high-degree arterial stenosis analysis

Purpose To investigate the relative role of high resolution (spatial or temporal) magnetic resonance angiography (MRA) sequence and of contrast agent properties in the evaluation of high-degree arterial stenosis. Methods We qualitatively and quantitatively studied both 50 and 95% (300 μm diameter) stenosis of a 6 mm arterial phantom with two contrast agents (CA), Gd-DOTA (r₁ =2.9 mM⁻¹ s⁻¹) versus P760 (r₁ =25 mM⁻¹ s⁻¹) at several CA concentrations, including arterial peak concentration after injection of either a single or double dose of CA, using either a high temporal (booster) or high spatial (HR) resolution 3D MRA sequences. Experimental data were then compared to theoretical data. Results With the 3D HR sequence, both visual and quantitative analysis were significantly better compared to the 3D booster sequence, at each phantom diameter. Quantitative analysis was significantly improved by injection of a double versus a single dose of each CA (Gd-DOTA or P760), primarily in high degree stenosis. Conclusion Combined MRA spatial resolution and high CA efficiency are mandatory to correctly evaluate high degree stenosis.     

Coronary Artery Stenosis Quantification for Computed Tomography Angiography Based on Modified Student's t‐Mixture Model

Coronary artery disease (CAD) is a major cause of death in the world. As a non‐invasive imaging modality, computed tomography angiography (CTA) is now usually used in clinical practice for CAD diagnosis. Precise quantification of coronary stenosis is of great interest for diagnosis and treatment planning. In this paper, a novel cluster method based on a Modified Student's t‐Mixture Model is applied to separate the region of vessel lumen from other tissues. Then, the area of the vessel lumen in each slice is computed and the estimated value of it is fitted with a curve. Finally, the location and the level of the most stenoses are captured by comparing the calculated and fitted areas of the vessel. The proposed method has been applied to 17 clinical CTA datasets and the results have been compared with reference standard degrees of stenosis defined by an expert. The results of the experiment indicate that the proposed method can accurately quantify the stenosis of the coronary artery in CTA.     

Two-layered micropolar fluid flow through stenosed artery: Effect of peripheral layer thickness

An unsteady analysis of a two-layered blood flow through a flexible artery under stenotic conditions has been carried out in the present study where the flowing blood is represented by the two-fluid model, consisting of a core region of suspension of all erythrocytes assumed to be Eringen’s micropolar fluid and a plasma layer free from cells of any kind as a Newtonian fluid. The artery has been treated as an elastic (moving wall) cylindrical tube. The equations governing the unsteady flow mechanism subject to pulsatile pressure gradient, has been solved numerically using finite difference scheme by exploiting the appropriate physically realistic prescribed conditions. An extensive quantitative analysis has been performed through numerical computations in order to estimate the effect of different micropolar fluid parameters and the Reynolds number on the flow velocity, the flux, the resistive impedance and the wall shear stress together with their dependencies with time, the input pressure gradient and the severity of the stenosis. The graphical representations of these results do illustrate the flow characteristics of blood under stenotic conditions with proper scientific reasoning and hence validate the applicability of the model under consideration. Special emphasis has duly been made to compare the present theoretical results with the existing ones including experimental results and good agreement between them has been achieved both qualitatively and quantitatively.     

Real-time volume rendering of MRCP: clinical applications

MR-cholangiopancreatography (Signa Contour 0.5T; GE/Medical Systems, Milwaukee, WI) data sets of 156 patients, obtained with a 2D T2-weighted FSE sequence, in the coronal plane, were volume rendered (Advantage Windows 3.1; GEMS) independently by two radiologists, that were asked to define the range of signal intensitics in which the signal of the pancreaticobiliary system was included and to rank the quality of native images and volume renderings. Patients had biliary stones (n=47), inflammatory ampullary stenoses (n=18), pancreaic tumors (n=12), surgical bilio-enteric anastomoses (n=19), ampullary carcinomas (n=2), pancreatic duct stone (n=1), cholangiocarcinoma (n=3) and normal pancreaticobiliary tree (n=54). Good quality volume renderings of the bile ducts were obtained for at least a maximum diameter of 1.5 mm. The quality rank agreement between volume rendering and native images was excellent (k=0.94). The correlation between the observers for the setting the signal intensity range was excellent and statistically significant (p<0.001). The correlation between the observers for the time of volume rendering was not statistically significant. Bilary stones could be displayed in 32/47 (68%) cases. The pancreatic duct stones was displayed as well. Inflammatory ampullary stenoses were detected in all cases (100%). In case of pancreatic tumors, cholangiocarcinomas and ampullary carcinomas volume rendering allowed to identify the site of stenosis. In surgical bilio-enteric anastomoses volume rendering was helpful to display the residual bilary tract, the site of anastomosis and the enteric tract. Volume rendering could be a reliable and efficient tool for the study of the anatomy and pathological changes of the pancreaticobiliary tract. Note: keywords have been selected from the Index to imaging literature (January 1999), of the RSNA (Supplement to Radiology).     

UNSTEADY ANALYSIS OF VISCOELASTIC BLOOD FLOW THROUGH ARTERIAL STENOSIS

A mathematical model of unsteady non-Newtonian blood flow in an artery under stenotic condition has been developed. The flowing blood is considered to be a viscoelastic fluid characterized by the Oldroyd-B model and the arterial wall is considered to be rigid, having cosine-shaped stenosis. The governing equations of motion accompanied by appropriate choice of the initial and boundary conditions are solved numerically by the MAC (marker and cell) method, and the results are checked, for numerical stability with desired degree of accuracy. The key factors like the wall shear stress, resistive impedance, and the other viscoelastic parameters are also examined for further qualitative insight into the flow through arterial stenosis. Comparison of the results reveals that dimensionless pressure drop for the viscoelastic model increases while it diminishes for the shear-thinning power law model over that of the Newtonian model. Moreover, the possibility of flow separation increases with increasing relaxation time (Deborah number), and in case of Newtonian fluid, delayed separation is observed. The grid independence study has also been performed successfully in order to validate the applicability of the methodology as well as the model used under consideration. Special emphasis has duly been made to compare the present theoretical results with the existing ones, and good agreement between them has been achieved both qualitatively and quantitatively.     

The preliminary studies on prevention of TIPSS shunt stenosis with 103pd stents

1 Introduction Transjugular intrahepatic portosystemic stentshunt (TIPSS) is a new interventional techniquewidely used in clinical practice in recent decade. Themetal stent is placed between hepatic vein and portalvein to make an artificial shunt a…     

Numerical simulation of fluid–structure interaction in stenotic arteries considering two layer nonlinear anisotropic structural model

The unsteady non-Newtonian blood flow in symmetric stenotic arteries is numerically simulated considering fluid–structure interaction (FSI) using the code ADINA. A two layer hyperelastic anisotropic structural model is used for the compliant arterial wall. The pressure used as outlet boundary condition was obtained running a CFD simulation for each stenosis with a physiologically-realistic time variation of pressure at inlet for different velocities. The obtained pressure drop increases in potential form with the inlet velocity for a fixed stenosis severity. The FSI results show that the maxima velocity and WSS at throat increase in exponential form with stenosis severity. The minimum and maximum effective stress at throat for stenosis severity of S = 70% ranged between 47 kPa and 96 kPa at diastole and systole, respectively.     

A study of pulsatile blood flow modeled as a power law fluid in a constricted tube

A mathematical model for the pulsatile blood flow in a small vessel in the cardiovascular system with a mild stenosis is analyzed. Blood is modeled as a power law fluid and the differential approximation for the heat flux is invoked in the energy equation. The effect of heat transfer on the velocity is computed and discussed.     

Absolute quantification of high energy phosphate metabolites in normal, hypertrophied and failing human myocardium

2. Conclusion For definitive conclusions, larger numbers of patients will have to be studied, but our preliminary results indicate that (1) ATP levels decline in heart failure but not in left ventricular hypertrophy and (2) phosphocreatine/ATP ratios underestimate the true changes in myocardial high-energy phosphate concentrations in chronically injured human myocardium.     

A numerical model on pulsatile flow of magnetic nanoparticles as drug carrier suspended in Herschel–Bulkley fluid through an arterial stenosis under external magnetic field and body force

ABSTRACT

A theoretical model for blood flow through an artery with stenosis carrying magnetic particles in the presence of magnetic field and periodic body acceleration is analysed. In the present study, blood is assumed to be Herschel–Bulkley fluid carrying iron oxide nanoparticles. The governing equations are highly non-linear and were solved numerically. The effects of model parameters are investigated and the results are represented graphically. The shear stress at the arterial wall and resistive impedance increases with enhancing values of stenotic height, yield stress, flow behaviour index, consistency index, pulsatile Reynolds number, amplitude of body acceleration, particle concentration and particle mass parameters. In order to treat the circulation disorders, control of the parameters involved in blood flow is necessary. The present model is useful in normalizing the parameter values and hence it can be applied in the field of medicine. The study has significant applications in drug delivery for treating cancer.