Intratumoral Doppler Ultrasound Blood Flow Signals In The Artery Next To Computer Simulation Study

The aneurysm refers to the arterial expansion caused by the partial vascular degradation and it is a high-risk disease. The continued expansion of the aneurysm can rupture its wall and eventually lead to the death of the patient. With the development of the bio-materials technology, the endovascular stent has an increasingly important application in the treatment of aneurysms. Numerical studies about fluid mechanics can provide theoretical references for the blood flow field around aneurysms and the effects to the blood flow after the implantation of stents on aneurysms. However, the clinical limitations of stents still exist.The Doppler ultrasound technique has been widely used for the clinical diagnosis of a variety of vascular diseases as a noninvasive and reliable technique. In this dissertation, Doppler ultrasound blood flow signals are simulated and signal spectrums are analyzed. The flow field varieties and blood flow movements around sidewall aneurysms after the stent implantation are studied from the perspective of the Doppler ultrasound non-destructive diagnosis.In this dissertation, Doppler ultrasound blood flow signals are simulated by the computer based on the Finite Element Analysis (FEA) principle and the Computational Fluid Dynamics (CFD) model. First, the sidewall aneurysm finite element model is constructed. Then the blood flow velocity distribution is calculated by the numerical fluid dynamics theory using the finite element analysis software ANSYS.Finally Doppler ultrasound blood flow signals from the sidewall aneurysm are generated according to simulation algorithms using the MATLAB and spectrums of simulated signals are then analyzed.This dissertation studies spectral characteristics of simulated Doppler ultrasound flow signals from the sidewall aneurysm in both the steady and pulsatile flow. In the steady flow model, different velocities and sizes of the sidewall aneurysm are taken into account. In the pulsatile flow model, different sizes of the sidewall aneurysm are considered under a complete cardiac cycle. Results show that in the steady flow condition, with the increment of the blood velocity, mean frequencies of simulated signals near the tumor back-end vary more significantly. At the same time, with the increment of the size of the sidewall aneurysm, mean frequencies of simulated signals near the tumor back-end also change more rapidly. In the pulsatile flow condition, mean frequencies of simulated signals vary periodically during a cardiac cycle. These variations are consistent with results of hemodynamic studies. With the increment of the sidewall aneurysm, mean frequencies of simulated signals change more significantly at each corresponding moment.Based on the simulation of the sidewall aneurysm, this dissertation also studies spectral characteristics of simulated Doppler ultrasound flow signals of the stented sidewall aneurysm in both the steady and pulsatile flow. In the steady flow model, different flow velocities, tumor sizes and stent mesh spacing are all taken into account. In the pulsatile flow model, different sizes of stented sidewall aneurysms are considered under a complete cardiac cycle. Results show that in the steady flow condition, when the blood flow velocity is normal, mean frequencies of simulated signals from the stented sidewall aneurysm with different sizes all become stable after the stent implementation.In the pulsatile flow condition, mean frequencies of simulated signals vary periodically during a cardiac cycle and variations are relatively stable after the stent implantation compared to the non-stented sidewall aneurysm's. This shows that the stent implantation can give an improvement for the blood flow condition in the sidewall aneurysm and achieve the satisfying therapeutic effect. It is also found from studies that when the endovascular stent mesh spacing is too large, mean frequencies of simulated signals will still change still obviously. This shows that in this condition, the stent implantation cannot give an improvement for the blood flow condition in the sidewall aneurysm and cannot achieve the satisfying therapeutic effect. Therefore the stent mesh spacing is an important parameter that may influence the treatment effect.In summary, mean frequency characteristics of simulated signals can correctly reflect blood flow field varieties and blood flow movements around the non-stented and stented sidewall aneurysms. This illustrates the effectiveness of the simulation method. This dissertation may contribute to the clinical study of blood flow movements around sidewall aneurysms from the perspective of the Doppler ultrasound non-destructive diagnosis.