Carotid geometry reconstruction: a comparison between MRI and 3D Ultrasound

Image-based Computational Fluid Dynamics (CFD) has become a popular tool for the prediction of in vivo flow profiles and hemodynamic wall parameters. Currently, Magnetic Resonance Imaging (MRI) is most widely used for in vivo geometry acquisition. For superficial arteries such as the carotids and the femoral artery, three-dimensional (3-D) extravascular ultrasound (3-DUS) could be a cost-effective alternative to MRI. In this study, nine healthy subjects were scanned both with MRI and 3-DUS. The reconstructed carotid artery geometries for each subject were compared by evaluating cross-sectional areas, centerlines, and carotid nonplanarity. Lumen areas agreed very well between the two different acquisition techniques, whereas centerlines and nonplanarity parameters showed measurable disagreement, possibly due to the different neck and head positions adopted for 3-DUS versus MRI. With the current level of agreement achieved, 3-DUS has the potential to become an inexpensive and fast alternative to MRI for image-based CFD modeling of superficial arteries. (C) 2003 American Association of Physicists in Medicine

Effect of Head Posture on the Healthy Human Carotid Bifurcation Hemodynamics

Head and neck postures may cause morphology changes to the geometry of the carotid bifurcation (CB) that alter the low and oscillating wall shear stress (WSS) regions previously reported as important in the development of atherosclerosis. Here the right and left CB were imaged by MRI in two healthy subjects in the neutral head posture with the subject in the supine position and in two other head postures with the subject in the prone position: (1) rightward rotation up to 80°, and (2) leftward rotation up to 80°. Image-based computational models were constructed to investigate the effect of posture on arterial geometry and local hemodynamics. The area exposure to unfavorable hemodynamics, based on thresholds set for oscillatory shear index (OSI), WSS and relative residence time, was used to quantify the hemodynamic impact on the wall. Torsion of the head was found to: (1) cause notable changes in the bifurcation and internal carotid artery angles and, in most cases, on cross-sectional area ratios for common, internal and external carotid artery, (2) change the spatial distribution of wall regions exposed to unfavorable hemodynamics, and (3) cause a marked change in the hemodynamic burden on the wall when the OSI was considered. These findings suggest that head posture may be associated with the genesis and development of atherosclerotic disease as well as complications in stenotic and stented vessels

Computational fluid dynamics application in reducing complications of patent ductus arteriosus stenting

In some cases, especially in neonates, ductus arteriosus needs to remain patent for multiple medical purposes. In order to achieve this, current practice involves inserting stent in the ductus arteriosus. This condition is called patent duc-tus arteriosus (PDA). For this process, stents such as coronary stent are commonly used due to unavailability of customized stent for PDA in neonates. The usage of coronary stent however, opens the possibility of acute stent thrombosis and other complications. Therefore, there is a high need of special and customized stents to be used for PDA in neonates. This customized stent has to be able to sustain the hemodynamic effects of the flow inside the PDA. The stent has to be able to support the ductus wall compression and contraction due to arterial compliance. What is more important is that the stent must properly fit into various morphologies of the ductus. There are several different morphologies of PDA identified and the stents must be able to sustain the various shapes and tortuosity. In addition, the stent has to be tested for biocompatibility and practicality. Therefore, the customized design of the PDA stents can be derived from the concept of coronary stents and in compliance with all the mentioned characteristics. However, further analysis has to be completed ensure proper compatibility with neonates. In conclusion, the biggest challenge is to customize a stent that fits all the PDA morphologies

The Effect of Head Rotation on the Geometry and Hemodynamics of Healthy Vertebral Arteries

The geometric and hemodynamic characteristics of the left and right vertebral arteries (LVA, RVA) of six healthy volunteers were investigated for the supine (S) and the prone position (P) a common sleeping posture with head rotation. MRI images were used to reconstruct the subject specific three-dimensional solid models of the LVA and RVA from the level of the carotid bifurcation to the vertebrobasilar junction (VJ). Geometric parameters such as cross sectional area ratio, curvature, tortuosity and branch angle were estimated. MR-PCA was used to obtain the blood flow waveforms for the two positions and computational fluid dynamics (CFD) were used to assess the flow field in terms of wall shear stress (WSS) relative residence times (RRT) and localized normalized helicity (LNH). Significant geometric changes but moderate flow changes were observed for both vertebral arteries with head rotation. The CFD results at the VJ show that head rotation causes changes in the WSS distribution, RRT and LNH. Further studies are warranted to assess the clinical significance of the results in terms of atherosclerosis development at the VJ and how the observed geometric changes may affect blood flow to the brain in healthy subjects and vertebral artery stenosis patients, and in terms of increased rapture susceptibility in vertebrobasilar aneurysm patients