Showing papers by "Raffaele Ponzini published in 2014"

A Survey of Quantitative Descriptors of Arterial Flows

Abstract: Knowledge of blood flow mechanics is a critical issue (1) for an in depth understanding of the relationships between hemodynamic factors and arterial homeostasis and (2) for the identification of those flow features that lead to changes in the function and health of vessels. While from one side there is clear evidence that regions of disrupted flow are correlated to, e.g., the localization of atherosclerosis, the development of aneurysms and non-physiological transport of species, on the opposite cause-effect links still do not emerge clearly. To allow for a more effective and valuable understanding of blood flow structures and mechanisms in complex four-dimensional cardiovascular flows, in recent years a large number of hemodynamic parameters have surfaced in the literature, enabling the understanding of arterial hemodynamics and of the role of streaming blood in the development of pathological events. In this work, a survey of the currently adopted methods to characterize blood flow structures in arteries is presented and open questions (1) on their clinical utility and (2) on the inherent limitations in their in silico and in vivo application are discussed.

Mapping aortic hemodynamics using 3D cine phase contrast magnetic resonance parallel imaging: Evaluation of an anisotropic diffusion filter

Abstract: Purpose To propose and evaluate an anisotropic diffusion filter to improve visualization and analysis of the thoracic aorta local hemodynamics from phase-contrast MRI sensitivity encoding imaging. Methods The filter parameters were tailored to the phase-contrast MRI sensitivity encoding data, using a simple calibration procedure. The filter was applied to 20 phase-contrast MR image studies (five subjects acquired with four different sensitivity encoding reduction factors). The filter effect was estimated with respect to image quality (noise in velocity images, σn), regularity of the velocity fields (divergence; relative error in velocity magnitude, and absolute error in flow direction), aorta flow pattern visualization (streamlines, secondary flows) and flow rate quantification. Results σn decreased up to three times, divergence, error in velocity magnitude, and absolute error in flow direction decreased (by at least 313, 40, and 10%, respectively), indicating less noisy and more regular velocity fields after filtering. Streamline analysis confirmed the beneficial effect of anisotropic diffusion filter, both visually and quantitatively (streamline numbers increased by 207% in whole cardiac cycle and by 180% in systolic phase). A high correlation (r = 0.99) between the prefiltering and postfiltering aortic flow rate values was found. Conclusion The anisotropic diffusion filter approach can be considered effective in improving the visualization and analysis of the thoracic aorta hemodynamics from phase-contrast MRI sensitivity encoding images. Magn Reson Med 71:1621–1631, 2014. © 2013 Wiley Periodicals, Inc.

A virtual test bench for hemodynamic evaluation of aortic cannulation in cardiopulmonary bypass

Abstract: Introduction Cardiopulmonary bypass (CPB) is a common practice in cardiac surgery. In this technique, venous blood is directed from the venous system to a heart-lung machine and then returned to the aorta through an inserted arterial cannula. Among the perioperative and postoperative complications, a reduction of cerebral perfusion, resulting in neurological complications, is observed, linked to the reduction of blood flow from the aortic arch to the carotid artery. Related to the altered flow conditions induced by the arterial cannula, a second major complication is an increased risk of thromboembolic events, caused by the mechanical activation of platelet aggregation pathways, induced by the highly disturbed flow patterns. Thus, the study of the effect of cannulation and its influence on the described mechanisms is of high clinical relevance and could allow the optimization of therapeutic performances. Currently, there is very little guidance for the surgeons regarding optimal clinical use parameters. In this study, we implemented a computational fluid dynamics (CFD) model to numerically assess the fluid dynamics generated by the arterial cannula. Mesh morphing techniques based on radial basis functions (RBF) are used to explore clinical use parameters that influence surgery performances. As an example of the parameters that can be analysed with the developed benchmark, the cannula insertion angle is considered and its effect on flow dynamics-related thromboembolic risk and supra-aortic arteries perfusion is evaluated.