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Session: Poster Session 1 (Even numbers)
Session starts: Thursday 26 January, 16:00
Presentation starts: 16:00

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Hadi Mirgolbabaee (Multi-Modality Medical Imaging (M3I) group, TechMed Center, University of Twente; Physics of Fluids (PoF) group, TechMed Center, University of Twente)
Guillaume Lajoinie (Physics of Fluids (PoF) group, TechMed Center, University of Twente )
Bob Geelkerken (Multi-Modality Medical Imaging (M3I) Group, Technical Medical Centre, University of Twente; Section of Vascular Surgery, Department of Surgery, Medisch Spectrum Twente, Enschede)
Michel Versluis (Physics of Fluids (PoF) group, TechMed Center, University of Twente )
Erik Groot Jebbink (Multi-Modality Medical Imaging (M3I) group, TechMed Center, University of Twente; Department of Vascular Surgery, Rijnstate Hospital, Arnhem)
Michel Reijnen (Multi-Modality Medical Imaging (M3I) group, TechMed Center, University of Twente; Department of Vascular Surgery, Rijnstate Hospital, Arnhem)

Abstract:
Background: Endovascular aneurysm repair (EVAR) has become the primary treatment option for abdominal aortic aneurysms (AAA). Although EVAR has excellent short and mid-term outcomes concerning mortality rates and hospitalization, its long-term results showed a similar survival rate as open surgical repair1,2. Moreover, 20-30% of EVAR-treated patients develop post-operative complications such as endoleaks, endograft migration, or limb occlusion, requiring reinterventions2. The latter is a major complication as it causes claudication and acute limb ischemia, which often requires reintervention3. The Anaconda endograft (Terumo Aortic, Inchinnan, Scotland, UK) has been related to higher limb occlusion rates, despite its kink-preventing and multiple independent ring design4. This may be an unforeseen side effect of the Anaconda's flexibility crib/valley ring design which can be expected to disturb the blood flow dynamics (e.g., fluid stasis and recirculation zones); the so-called Concertina effect4. These unfavourable hemodynamic parameters may increase the platelet activation potential (PAP), which could eventually promote limb occlusion. Method: A thin-walled AAA flow phantom was fabricated based on a patient's anatomy, who was treated by an Anaconda endograft. This phantom was designed using the latest post-operative computed tomography angiography (CTA) scan of the patient just before an occlusion occurred in the left graft limb. We performed contrast-enhanced ultrasound particle image velocimetry (echoPIV) measurements to quantify the velocity fields. The echoPIV measurements were performed in the same phantom with and without Anaconda endograft to investigate the rings' effects over the local flow field. Finally, vector complexity (VC), vortices, and particle residence time were calculated. Results: The iliac velocity fields obtained from the pre-operative measurements had low VC values (below 0.2). On the contrary, the post-operative measurements showed locally high VC values, especially near the stent ring. Furthermore, we observed flow complexity zones (e.g., vortices and flow stasis), mainly in the left graft limb, which may justify the detected patient limb occlusion. Conclusion: In this feasibility study, we identify and define unfavorable hemodynamic parameters that might promote PAP, and therefore carry a great potential as prognostic value for limb occlusion. Future studies must be done to further generalize the hypothesis and evaluate the defined hemodynamic norms.