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Regional documentation --- Caucasus --- Russia --- Ukraine --- Georgia --- Finland

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Initiation and progression of thoracic aortic aneurysms is closely related with the vascular growth and remodelling process. It is understood that the hemodynamics of the blood flow mechanically stimulate the arterial tissue and in this way affect this mechano-biological process. In the light of development of models for prediction of thoracic aneurysm initiation and progression, it is therefore crucial that blood hemodynamics can reliably be estimated in both healthy as aneurysmal thoracic aortas based on in vivo acquired data. This study presents the construction of a robust, patient-specific computational fluid dynamics (CFD) model based on in vivo acquired MRI data of a surgically induced aneurysm in the descending part of the thoracic sheep aorta. MRI data was acquired at three time points after surgery over a six months study period which enabled a longitudinal comparison of the hemodynamic quantities and geometrical progression of the aneurysmal region. The wall shear stress (WSS) and its dynamic variation throughout the cardiac cycle are known to have an important impact on vascular remodelling and are therefore considered as the main hemodynamic quantities of interest. Velocity fields obtained with CFD modelling showed great correspondence with the velocity fields obtained from PC-MRI measurements in and around the thoracic aortic aneurysm (TAA), a good indication for trustworthy WSS quantification. The presence of the aneurysm clearly disturbs the blood flow. This flow disturbance becomes more important as the size of the aneurysm increases and is observed to have a big impact on the dynamical behaviour of the WSS vector throughout the cardiac cycle, characterised by the oscillatory shear index. Regions of high WSS values are observed especially near the distal neck of the TAA right after surgery, with time-averaged WSS values reaching 7.92 Pa and peak WSS values reaching 33.91 Pa, almost three times higher as in the healthy aorta. Interestingly, these regions of high WSS seem to be associated with accelerated aneurysm progression. To enable a more quantitative comparison of the hemodynamic changes over time, physiological variation of the blood flow between the CFD models should be eliminated in the future. For a more accurate quantification of the WSS in and around the TAA, deformation of the arterial wall could be considered in a more complete fluid structure interaction (FSI) model as a possible improvement of the presented CFD model.