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Propagation Modeling of High Intensity Focused Ultrasound Wave through Multi Layer Tissue along with Experimental Validation

Haddadi, Samaneh | 2017

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 49966 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Ahmadian, Mohammad Taghi
  7. Abstract:
  8. One of the main problems in human health, both in advanced societies and in growing societies, is a variety of cancers, one of which is brain tumor. One of the non-invasive methods of treating tumors is the use of ultrasound.HIFU (High Intensity Focused Ultrasound) therapy method is known as one of the most advanced surgical techniques in tumor ablation therapy. HIFU are produced and concentrated by powerful transducers. The two main mechanisms in HIFU are mechanical and thermal mechanisms, and the effects of these two mechanisms appear as thermal effects and cavitation. The fundamental mechanism in the HIFU is to absorb ultrasonic waves and to convert them into heat.The purpose of this study is to investigate the interaction of ultrasound with soft tissue and to determine the amount of absorption and generated heat due to the concentration of waves at the desired point. Therefore, the wave equation is solved to simulate the interaction of ultrasound with soft tissue and the model’s outputs will be compared with the experimental results. In addition to theoritical modeling, a HIFU system was made by using piezoelectric sensors and ultrasound radiation was tested on the soft tissue. The nonlinear Westervelt and KZK equations were used to simulate ultrasonic waves. Experiments and simulations were carried out for different operating powers and aperture angles. According to the simulation results for the powers of 5/33 W to 134 W, the pressure at the focal point were between 1.1 and 4.3 MPa. In the study of temperature variations at the focal point, the average errors calculated for the experimental data compared to the simulation results obtained from the Westerwalt equation and the KZK equation were 6.6% and 4.6% for the aperture angles of 16°, and 4.3% and 12.8% for the aperture angle of 30°, respectively. Based on experimental data, the maximum temperature at the focal point for aperture angles of 16° and 30° were 67°C and 75.5°C, respectively. The results showed that the experimental data were consistent with the simulation results. Also, different working conditions of the device were investigated due to the distribution of tissue temperature and ablated area
  9. Keywords:
  10. Ultrasonic Waves ; Wave Propagation ; High Intensity Focused Ultrasound (HIFU)Method ; KZK Equation ; Validation ; Westervelt Equation

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