Comparison of diametric and volumetric changes in Stanford type B aortic dissection patients in assessing aortic remodeling post-stent graft treatment

Background: The study aims to analyze the correlation between the maximal diameter (both axial and orthogonal) and volume changes in the true (TL) and false lumens (FL) after stent-grafting for Stanford type B aortic dissection. Method: Computed tomography angiography was performed on 13 type B aortic dissection patients before and after procedure, and at 6 and 12 months follow-up. The lumens were divided into three regions: the stented area (Region 1), distal to the stent graft to the celiac artery (Region 2), and between the celiac artery and the iliac bifurcation (Region 3). Changes in aortic morphology were quantified by the increase or decrease of diametric and volumetric percentages from baseline measurements. Results: At Region 1, the TL diameter and volume increased (pre-treatment: volume =51.4±41.9 mL, maximal axial diameter =22.4±6.8 mm, maximal orthogonal diameter =21.6±7.2 mm; follow-up: volume =130.7±69.2 mL, maximal axial diameter =40.1±8.1 mm, maximal orthogonal diameter =31.9+2.6 mm, P<0.05 for all comparisons), while FL decreased (pre-treatment: volume =129.6±150.5 mL; maximal axial diameter =43.0±15.8 mm; maximal orthogonal diameter =28.3±12.6 mm; follow-up: volume =66.6±95.0 mL, maximal axial diameter =24.5±19.9 mm, maximal orthogonal diameter =16.9±13.7, P<0.05 for all comparisons). Due to the uniformity in size throughout the vessel, high concordance was observed between diametric and volumetric measurements in the stented region with 93% and 92% between maximal axial diameter and volume for the true/false lumens, and 90% and 92% between maximal orthogonal diameter and volume for the true/false lumens. Large discrepancies were observed between the different measurement methods at regions distal to the stent graft, with up to 46% differences between maximal orthogonal diameter and volume. Conclusions: Volume measurement was shown to be a much more sensitive indicator in identifying lumen expansion/shrinkage at the distal stented region

Development of an image-based model for capillary vasculature of retina

The paper presents a method of development of a detailed network model to represent retinal capillary vasculature. The capillary model is a circular mesh consisting of concentric rings with an increasing diameter. Each of the rings has uniformly distributed bifurcation nodes to represent capillary vessels. The model is customized using the data that has been measured from confocal microscopic images of a mouse retina. The capillary model developed can be connected to networks of larger vessels of the vasculature such as arterial and venous networks to form a complete model of the retinal network. A method to automate such interface connections between capillary and other vascular networks using connecting vessels (i.e., pre-capillary and post-capillary) is also presented in the paper. Such a detailed image-based capillary model together with the arterial and venular networks can be used for various circulation simulations to obtain accurate information on hemodynamic quantities such as the spatial distribution of pressure and flow in the vasculature for both physiological and pathological conditions. The method presented for the development of the capillary model can also be adopted for vasculatures of other organs

Prediction of thrombus formation using vortical structures presentation in Stanford type B aortic dissection: A preliminary study using CFD approach

False lumen patency has been recognized as the key determinant of aneurismal dilatation and rupture, whereas complete thrombosis has been proven clinically to improve disease outcomes. However, to date, there is no definitive method that could predict false lumen thrombosis in Stanford type B aortic dissection patient. The present study aims to use the evolution of vortical structures throughout a cardiac cycle and its interaction with the wall shear stress (WSS) to illustrate the potential mechanism behind the formation of thrombus and predict its highly possible location in an aortic dissection patient. A three-dimensional (3D) patient-specific Stanford type B aortic dissection domain was generated from computed tomography (CT) angiographic images. The effects of false lumen size on vortical structures and the subsequent risk of thrombus formation were investigated. The Carreau–Yasuda model, representing non-Newtonian fluid property was used to study the difference between Newtonian and non-Newtonian fluid settings on vortical structures. Based on our analysis, we predicted that the formation and thickening of thrombus is very much likely to occur at the posterior false lumen wall, distal to the entry tear region, in the patient. Higher λ2 intensity, associated with a higher maximum WSS and a lower minimum WSS, was achieved with an increase in the false lumen size, and we believed that this increases the risk of thrombus formation and thus aneurismal dilatation. On the other hand, percentage of flow entering the false lumen increased with an increase in the false lumen size, leading to a downward shift of the areas of thrombus formation along the false lumen wall