Browsing by Author "Mutlu, Onur"
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Item Evaluating the effect of the number of wire of flow diverter stents on the nonstagnated region formation in an aneurysm sac using lagrangian coherent structure and hyperbolic time analysis(Elsevier Science, 2020-01) Mutlu, Onur; Olcay, Ali Bahadır; Bilgin, Cem; Hakyemez, Bahattin; Bursa Uludağ Üniversitesi/Tıp Fakültesi/Radyoloji Anabilim Dalı.; 0000-0002-3425-0740; HHS-7433-2022; AAI-2318-2021; 57200617643; 6602527239Background: Giant aneurysms at carotid arteries are typically treated with flow diverter (FD) stents in the clinic. Although the goal of an FD stent is to direct most of the blood flow into the main artery, not much is known regarding the effects of wire number an FD possesses on the hemodynamics inside the aneurysm. Methods: In this study, 48-, 72-, and 96-wire FD stents were separately implanted into the site of aneurysm of a 45-year-old woman to evaluate the effects of the FD's number of wires on fluid flow behavior in the aneurysm sac. Time evolution of both finite-time Lyapunov exponent (FTLE) and hyperbolic time fields in the aneurysm sac were calculated by using computational fluid dynamics along with Lagrangian coherent structure (LCS) methods. Results: The computations reveal that a 48-wire FD stent allows a large amount of blood to enter inside the aneurysm sac revealing scattered nonstagnant flow zones formation. Besides, time-dependent results of LCS analysis show that most of the blood flow is diverted into the main artery when 72- and 96-wire number Surpass brand FD stents are separately implanted into the site of the aneurysm, yielding a small amount of blood flow to penetrate into the aneurysm sac. Conclusions: Furthermore, FTLE and hyperbolic time field plots are in good agreement with the patient's digital subtraction angiography image captured 3.5 minutes after 72-wire Surpass brand FD stent implantation.Item Evaluating the effectiveness of 2 different flow diverter stents based on the stagnation region formation in an aneurysm sac using lagrangian coherent structure(Elsevier Science Inc, 2019-07) Mutlu, Onur; Olcay, Ali Bahadır; Hakyemez, Bahattin; Bilgin, Cem; Uludağ Üniversitesi/Tıp Fakültesi/Radyoloji Anabilim Dalı.; 0000-0002-3425-0740; AAI-2318-2021; HHS-7433-2022; 57200617643; 6602527239BACKGROUND: Flow diverter stents are often used in the treatment of giant aneurysms at carotid arteries. Although these stents promise to decrease blood flow into the aneurysm sac, little is known about hemodynamics inside the aneurysm once the stent is planted into the aneurysm neck. To further explore this, computational fluid dynamics and Lagrangian coherent structure (LCS) techniques were used to evaluate the time evolution mechanism of stagnation regions inside an aneurysm. The purpose of this work is to provide a quantitative effectiveness comparison of 2 different flow diverter stents placed into the aneurysm neck based on their stagnation zone formations in the sac.METHODS: In numerical modeling, Womersley function, and fluidsolid interaction were defined as the 3 cardiac cycles for blood velocity and the aneurysm wall, respectively. Moreover, blood was accepted as a non-Newtonian fluid, and mean arterial blood pressure of the patient was entered into the computational domain to accurately mimic the hemodynamics inside the aneurysm sac accurately.RESULTS: The numerical analyses revealed that the use of a Fred-type stent in the aneurysm neck causes fluid flow zone formations yielding to sequenced stagnated regions. Time evolution of stagnation regions in an aneurysm sac was shown just after a flow diverter stent was employed at a patient's aneurysm neck. Furthermore, the stagnation field in the Fred stent-fitted aneurysm was nearly 4.8 times the stagnation area of the Surpass brand stent-attached aneurysm.CONCLUSIONS: Finite time Lyapunov exponent fields obtained from the LCS techniques demonstrated a good agreement with the patient's digital subtraction angiography images obtained just after treatment.Publication Numerical study of a simplified cerebral aneurysm using a two different flow diverter stent modeling(Ieee, 2019-01-01) Tercanlı, Muhammed Furkan; Mutlu, Onur; Olcay, Ali Bahadır; Bilgin, Cem; Hakyemez, Bahattin; BİLGİN, CEM; HAKYEMEZ, BAHATTİN; Bursa Uludağ Üniversitesi/Tıp Fakültesi/Radyoloji Anabilim Dalı.; 0000-0002-3425-0740 ; HHS-7433-2022; AAI-2318-2021The effectiveness of clinical treatments in-stent modeling have been recently started to be analyzed using Computational Fluid Dynamics (CFD) technique. Particularly, variation of pressure loss with flow velocity is used to evaluate permeability and internal resistance coefficients of the flow diverter stents to describe the stent properties to CFD model. The velocity profile is described as pulsatile parabolic at the inlet, the pressure is described at the outlet to be 93 mmHg as a mean arterial pressure (MAP) in the present study. The results implied that there was no significant difference found between porous media and stent implantation of a flow diverter stent modelings based on the studied cases. However, fluid flow simulations indicated that use of 48 wires stent allows more blood flow passing into the aneurysm sac compared to the 72 and 96 wires stents for the studied geometry. Effect of pressure change in the vessel and shape factor of the artery was neglected.Publication Understanding the effect of effective metal surface area of flow diverter stent's on the patient-specific intracranial aneurysm numerical model using lagrangian coherent structures(Elsevier, 2020-10-01) Mutlu, Onur; Olcay, Ali Bahadır; Bilgin, Cem; Hakyemez, Bahattin; BİLGİN, CEM; HAKYEMEZ, BAHATTİN; Bursa Uludağ Üniversitesi/Tıp Fakültesi/Radyoloji Anabilim Dalı; 0000-0002-3425-0740; AAI-2318-2021; HHS-7433-2022The effective metal surface area (EMSA) of flow diversions plays an essential role in the occlusion mechanism inside the aneurysm since the value of EMSA determines the amount of blood flow into the aneurysm sac. In the present study, three different models of a flow diverter stent, namely FRED 4017, FRED 4038, and FRED 4539, were virtually placed at the aneurysm neck of a 52-years-old female patient to identify the effect of EMSA on stagnation region formation inside the aneurysm sac. Lagrangian coherent structures (LCSs), hyperbolic time, and particle tracking analysis were employed to the velocity vectors obtained from computational fluid dynamics (CFD). It is noticed that use of FRED 4017 stent with 0.42 EMSA value caused nearly 40% of the weightless blood flow particles (more than FRED 4038 and FRED 4539) to stay inside the aneurysm while only 0.35% of the blood flow was remaining inside the aneurysm sac when no stent was placed into the aneurysm site. Furthermore, hyperbolic time computations illustrated the formation of stagnation fluid flow zones that can be associated with the residence time of the blood flow particles. Lastly, the results of hyperbolic time analysis are in good agreement with digital subtraction angiography (DSA) images taken in the clinic a few minutes after a FRED 4017 implantation. (C) 2020 Elsevier Ltd. All rights reserved.