Analysis of morphological and hemodynamical indexes in abdominal aortic aneurysms as preliminary indicators of intraluminal thrombus deposition

Abstract

In this paper we study the correlation between the Wall Shear Stress (WSS), a haemodynamical index derived from numerical simulations, and an new index MFA-ILT for the characterisation of intraluminal thrombus (ILT) in presence of abdominal aortic aneurysms. Based on the processing of medical images, we define our index MFA-ILT by projecting onto lumen surface a measure of the ILT thickness. From the physical point of view, haemodynamical indexes describe the mechanical stimuli at which the luminal surface of the vessel wall is subject to, due to blood flow. Specifically, we consider the time-averaged wall shear stress and the oscillatory shear index. The first index provides a measurement of the averaged magnitude of the shear stress; the second index measures the rate of change of shear stress. To reconstruct the haemodynamical indexes, we build in silico three-dimensional models. We use the same physical parameters and boundary conditions for all the aneurysms in the sample. The computer simulations do not require any additional invasive patient examination.We consider eleven cases of abdominal aortic aneurysms spanning a wide range of different morphological features. All the cases are characterized by a thin intraluminal thrombus. We can, therefore, assume that the lumen we currently observe does not significantly differ from the one before the thrombus deposition. Our results suggest that the value of wall shear stresses and intraluminal thrombus deposition are correlated. Moreover, we conclude that in six cases time-averaged wall shear stress provides a preliminary indication of the area at risk of thrombus deposition.

Association of vortical structures and hemodynamic parameters for regional thrombus accumulation in abdominal aortic aneurysms

“…Previous studies had originally hypothesized that high values of OSI, which indicated a highly disturbed flow near wall, were related to the accumulation of thrombus 10 . Other studies have challenged this by showing that low OSI values could be an indicative of a persistent flow circulatory pattern, which could explain the no correlation reported among these parameters 7 . Our results, by identifying high and low OSI levels over regions where changes in ILT were observed agree with both mechanisms; which could explain the lack of correlation determined by our and other recent investigations.…”

“…In case of AAAs, low TAWSS values have also being associated to the formation of thrombus 9 . Specifically, the observation of low levels of TAWSS in regions where thrombus accumulation is high has led to the suggestion for a potential correlation among these two 7,21 . Biochemically, low values of WSS are related to a decrease in the production of prostacyclin, prostaglandins, 22 and nitric oxide (NO), 23 which are agents in charge of signaling multiple biological functions (e.g., vasodilation, remodeling; among others) and protecting the arterial wall against pro‐thrombotic activities.…”

“…Our current understanding indicates that flow conditions inside aneurysms are closely related to the formation of ILT. This has led many studies to propose some hemodynamic metrics related to the ILT accumulation process (e.g., the wall shear stress (WSS) and oscillatory shear index (OSI)), 6,7 and to suggest specific flow characteristics (e.g., formation of vortices and their dynamic) potentially modulating its formation 8 . For instance, previous computational analyses have shown that low time averaged WSS (TAWSS) 9 and high OSI 10 levels are common flow characteristics preceding an ILT accumulation.…”

Analysis of hemodynamic changes from aneurysm inception to large sizes

“…In the field of abdominal aortic aneurysms, although a different disease, aneurysm morphology and hemodynamics have been linked to intraluminal thrombus formation which has been identified as one of the drivers of aortic aneurysm progression. 20,21 Furthermore, hemodynamic and morphological factors, in combination with clinical data and shape of the intra-luminal thrombus, have been proposed as predictors of aortic aneurysm growth using data from longitudinally followed abdominal aortic aneurysms. 22 In contrast, intra-aneurysmal thrombus is rare in cerebral aneurysms and it mostly observed in large or giant aneurysms (>25 mm), and the mechanisms for their evolution remains unclear.…”

Computational Fluid Dynamics to Assess Hemodynamic Forces in Abdominal Aortic Aneurysm

“…Hemodynamics is indeed known to be related to abdominal aortic aneurysm (AAA) development, intraluminal thrombus deposition, and finally expansion till rupture. 2 Wall shear stresses (WSS) and blood pressure are confirmed to be major hemodynamic determinants of this expansion and rupture. Moreover, also the aortic blood impingement against the inner lumen could explain different rates of growth of AAA.…”