Impact of hemodynamics on lumen boundary displacements in abdominal aortic aneurysms by means of dynamic computed tomography and computational fluid dynamics

Objective. The aim of the present work is to quantitatively assess the three dimensional (3D)distributions of the displacements experienced during the cardiac cycle by the luminal boundary of abdominal aortic aneurysm (AAA) in vivo and to correlate it with the local bulk hemodynamics. Methods. Ten patients were acquired by means of time resolved computed tomography (4DCT) and each patient-specific morphology of the abdominal aorta and aneurysmal sac was reconstructed for all available time frames. The AAA lumen boundary motion was successively tracked over the cardiac cycle and the lumen boundary displacement (LBD) computed for each time frame to a reference position selected at the mid-diastolic phase. The intra-aneurysm hemodynamic quantities, such as wall shear stress (WSS), were evaluated with a computational fluid dynamics (CFD) simulation performed on the reference geometry of each patient. The co-localization of LBD and WSS distributions was evaluated by means of Pearson correlation coefficient. Results. A clear anisotropic distribution of LBD was evidenced in both space and time. AAA lumen boundary exhibited a combination of inward- and outward-directed motions throughout the cardiac cycle and specifically at time frames close to the systolic peak. For almost all the analyzed cases a co-localization between largest outward LBD and high WSS, taken as a surrogate of flow impingement, was demonstrated supporting our hypothesis of a mechanistic relationship between anisotropic displacement and hemodynamic forces related to the impingement of the blood on the lumen boundary. Conclusions. The assessment of AAA lumen boundary anisotropic displacements may represent a promising direction for patient risk stratification and investigation of AAA progression. Four dimensional CT and patient-specific CFD may become valuable tools in research and clinical environments for patient management and pre-surgical evaluation.