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Numerical Simulation of the Effect of Ultrasound and Bubble Dynamic for the Application of Gas Embolotherapy Technique

Salajeghe, Roozbeh | 2018

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 50725 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Saeedi, Mohammad Saeed
  7. Abstract:
  8. Gas embolotherapy is a therapeutic method which is a suitable replacement for traditional embolotherapy techniques. This method is especially applicable for vascularized tumors which cannot be treated using other tumor treatments. In Gas embolotherapy technique, droplets made of Perfluorocarbon, whose evaporation temperature is below body temperature are injected into blood stream. The size of this droplets is chosen so that they can freely circulate in human vasculature and finally reach the specified target. At the target point, an ultrasound transducer is focused which causes the droplets to evaporate and turn into bubbles. During the evaporation process, bubbles expand volumetrically to 125-fold of initial droplet. As a results of this volumetric expansion, the bubbles can lodge in tumor vasculature and cause its necrosis.In this study, acoustic simulation and bubble dynamic simulation have been investigated numerically in two separate parts. In bubble dynamics simulation part, the bubble movement has been modeled both in channel with contraction and bifurcation. This modeling has been done using finite volume method in open source openFOAM software. Two phase flow has been simulated by volume of fluid method. The influence of static and dynamic contact angles, gravity and bubble length has been studied in this simulation. It was observed that while bubble lodging was not occurred in the pressures and velocities typical of arteries, it may happen in lower pressures and velocities which are related to the arterioles. It was also observed that activation of gravitational acceleration will increase the pressure threshold of bubble lodging. Other results include the fact that dynamic contact angle gives rise to higher pressure loss compared to static contact angle. In the second part, the effects of acoustic wave on the droplet evaporation has been modeled using finite element method in COMSOL MULTIPHYSICS software. In this part, the impact of the main frequency and the first harmonic on the peak negative pressure within the droplet has been investigated. The results showed more influence from first harmonic in comparison with the main frequency for larger droplets. Considering the first harmonic other than the main frequency is a consequence of nonlinear wave propagation. For smaller droplets, the contribution of main frequency to the pressure field inside the droplet was more than the first harmonic. At the end, an array transducer for focusing acoustic wave was modeled and some of its parameters were optimized. These parameters include elemental pitch, for which a value near and a bit higher than half of wavelength yields the best results
  9. Keywords:
  10. Dynamic Contact ; Contact Angle ; Acoustic Droplet Vaporization ; Gas Embolotherapy ; Bubble Dynamics in a Bifurcation ; Array Transducer

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