Numerical Modeling of the Sound Generated on an Intracranial Aneurysm Using Computational Fluid Dynamics

Intracranial aneurysm is the enlargement of an artery in the brain which may lead to rupture and result in serious health disorders. The exact mechanism of aneurysm formation is still unclear; however, the disturbed hemodynamics take part in the initiation of the vessel enlargement. In this study, a simplified intracranial aneurysm is numerically investigated to elucidate the disturbed flow conditions and the generated sound on the aneurysm wall. In order to determine the generated sound, the pressure fluctuations on the inner wall are obtained using computational fluid dynamics simulations. Large eddy simulation model is employed to find the unsteady flow pressures. The results indicate that the sound levels increase at the proximity of the intracranial aneurysm. The sound levels on the aneurysm are compared to the sound levels on the sites with normal vessel diameter, and it is seen that the aneurysm results in about 10 dB increase in the sound generation. This relative increase in the flow-generated sound is important in terms of the diagnosis of the intracranial aneurysms, which can be used as a diagnostic tool for the early detection of the aneurysm before facing with the serious symptoms

Damar hastalıklarına girişimsel olmayan akustik metotlarla tanı koymanın katı-sıvı etkileşimli sayısal teknikler kullanılarak incelenmesi.

Atherosclerosis is a cardiovascular disease in which arterial occlusion adversely affects blood circulation. Because of the narrowing of the artery, the blood flow is disturbed and a recirculating flow occurs at the downstream of the stenosis exit. The dynamic pressure fluctuations on the inner arterial wall cause the blood vessel wall to vibrate and the resulting acoustic energy propagates through the surrounding soft tissue and reaches the skin surface. To understand the problem in more detail, computational analyses and experimental studies have been carried out. Vein, blood, muscle, fat and bones are modeled by means of computational analysis. The turbulence-induced dynamic pressure fluctuations are applied to the inner wall of the artery and the radial displacement, velocity and acceleration responses on the skin surface are investigated considering various flow rates, stenosis severities and structural material properties. The computational results show good agreement with the experimental findings. Vibration of the phantom tissue used in the experimental studies is determined using a contact microphone, an electronic stethoscope and a laser Doppler vibrometer. 70% stenosis is an important threshold value, because severities higher than 70% lead to significant increase in vibration amplitudes. If the severity of stenosis is increased from 70% to 90%, the arterial vibration amplitudes increase by more than ten times. Arterial vibration is approximately proportional to the third power of the Reynolds number. When thickness of the tissue surrounding the artery is increased from 6.5 to 16.5 mm, the amplitudes are reduced by about 35%. The highest excitation is obtained about 20 mm downstream of the stenosis exit for a tissue thickness of 16.5 mm. The first two highly excited frequencies are determined as 30 and 60 Hz for the thigh, 100 and 200 Hz for the upper arm, 120 and 190 Hz for the neck. The optimum range for stenosis detection is between 200 and 500 Hz.Ph.D. - Doctoral Progra

Dolaşım sistemindeki kan akışı ile damarlar arasındaki etkileşimlerin patolojik ve tanısal yönlerden incelenmesi.

Atherosclerosis is a disease of the cardiovascular system where a stenosis may develop in an artery which is an abnormal narrowing in the blood vessel that adversely affects the blood flow. Due to the constriction of the blood vessel, the flow is disturbed, forming a jet and recirculation downstream of the stenosis. Dynamic pressure fluctuations on the inner wall of the blood vessel leads to the vibration of the vessel structure and acoustic energy is propagated through the surrounding tissue that can be detected on the skin surface. Acoustic energy radiating from the interaction of blood flow and stenotic blood vessel carries valuable information from a diagnostic perspective. In this study, a constricted blood flow is modeled by using ADINA finite element analysis software together with the blood vessel in the form of a thin cylindrical shell with an idealized blunt constriction. The flow is considered as incompressible and Newtonian. Water properties at indoor temperature are used for the fluid model. The diameter of the modeled vessel is 6.4 mm with 87% area reduction at the throat of the stenosis. The flow is investigated for Reynolds numbers 1000 and 2000. The problem is handled in three parts which are rigid wall Computational Fluid Dynamics (CFD) solution, structural analysis of fluid filled cylindrical shell, and Fluid Structure Interaction (FSI) solutions of fluid flow and vessel structure. The pressure fluctuations and consequential vessel wall vibrations display broadband spectral content over a range of several hundred Hz with strong fluid-structural coupling. Maximum dynamic pressure and vibration amplitudes are observed around the reattachment point of the flow near the exit of the stenosis and this effect gradually decreases along downstream of flow. Results obtained by the numerical simulations are compared with relevant studies in the literature and it is concluded that ADINA can be used to investigate these types of problems involving high frequency pressure fluctuations of the fluid and the resulting vibratory motion of the surrounding blood vessel structure.M.S. - Master of Scienc

SKIN SURFACE RESPONSE DUE TO ACOUSTIC RADIATION FROM STENOSED FEMORAL ARTERY

Arterial stenosis leads to serious health problems such as stroke and heart attack. For a clinician, it is of critical importance to diagnose the stenosis at an early stage to prevent serious damage. Peripheral artery diseases observed in the arms and legs can be a sign of serious cardiovascular disorders. For a stenosed artery, turbulence is observed downstream of constriction exit. Turbulent flow generates sound and vibration on artery wall. Vibro-acoustic radiation propagates through surrounding tissues and reaches skin surface. In this study, skin surface response of thigh due to acoustic generation from a stenosed femoral artery is investigated which may provide important information for diagnostic purposes. Human thigh is modelled using commercial finite element analysis software ADINA. Modal analyses are performed for thigh model. Realistic material properties and model geometry are employed. Acoustic generation due to arterial stenosis is modelled using empirical relations provided in literature. Harmonic acoustic pressures are applied on the inner surface of the artery wall. Radial velocity response and pressure response on thigh skin surface are obtained by considering different stenosis degrees and different stenosis locations. Results indicate that increasing stenosis degree leads to an increase in amplitudes of harmonic responses. Highest radial velocity and pressure amplitudes are obtained at locations closest to the arterial stenosis. Low frequency response between 0-50 Hz is found to be more useful to obtain information about the location of the stenosis

Damar tıkanıklığı hastalıklarında katı dokuya yayılan akustik enerjinin sayısal ve deneysel olarak incelenmesi

Tıkanıklık bulunan damarlardan yayılan geniş frekans bandına sahip seslerin damar etrafındaki dokular içinde yayılımı ve deri yüzeyine ulaşması sayısal ve deneysel olarak modellenip, deri yüzeyinden bu seslerin ölçülebilirliği ve elde edilen akustik verilerin damar sağlığı ile ilgili tanı koymada kullanılabilirliği araştırılacaktır.Daha önceki çalışmalarımızda damar tıkanıklıkları ile damar içinde oluşan seslerle ilgili sayısal ve deneysel araştırmalar yapılmıştı. Bu proje ile ortaya konulan problemin ikinci aşamasına geçmek mümkün olacaktır. Bu proje sonucu elde edilecek kazanımlara göre, bu alanda kullanılmakta olan mevcut prosedürlerin aksine, girişimsel olmayan, ucuz ve kısa süren, bu sayede çok sayıda insana uygulanabilecek bir metod geliştirilmesi hedeflenmektedir

Computational analysis of high frequency fluid–structure interactions in constricted flow

Constricted flow in a thin cylindrical shell with an idealized blunt constriction is modeled using ADINA. Highly disturbed recirculation region is observed at the constriction exit where pressure fluctuations and consequential vessel wall vibrations display broadband spectral content over a range of several hundred Hz. Maximum dynamic pressure and vibration amplitudes are observed around the reattachment point and they gradually decrease along downstream of flow. Results obtained by numerical simulations are compared with relevant studies in the literature and are in good agreement in terms of general spectral behavior. However, the amplitudes were significantly lower as compared to experimental results

Computational analysis of high frequency fluid-structure interactions in constricted flow

Constricted flow in a thin cylindrical shell with an idealized blunt constriction is modeled using ADINA. Highly disturbed recirculation region is observed at the constriction exit where pressure fluctuations and consequential vessel wall vibrations display broadband spectral content over a range of several hundred Hz. Maximum dynamic pressure and vibration amplitudes are observed around the reattachment point and they gradually decrease along downstream of flow. Results obtained by numerical simulations are compared with relevant studies in the literature and are in good agreement in terms of general spectral behavior. However, the amplitudes were significantly lower as compared to experimental results

Kan Damarlarındaki Daralma Seviyesi ve Şekillerinin Tanısal Amaçlı Olarak Kullanımının Sayısal Benzetimlerle İncelenmesi

Stenoz probleminin akışkanlar mekaniği kısmına odaklanılacak ve problem sayısal tekniklerle çözülecektir. Özellikle damardaki daralma sonrasında oluşan yüksek frekanslı basınç dalgalanmaları incelenecek ve daralma mertebesi ve şeklinin bu dalgalanmalara olan etkisi araştırılacaktır