Loading...

An Investigation of Nonlinear Ultrasound Propagation in Soft-tissues and Transferred Energy

Omidvar Pashesar, Amir Hossein | 2018

2585 Viewed
  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 50996 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Ahmadian, Mohammad Taghi
  7. Abstract:
  8. In clinical applications of high intensity focused ultrasound, high amplitude acoustic waves are used to heat and ablate tumors and kidney stones. The high amplitude of ultrasonic waves leads to nonlinear effects within the acoustic filed. Heating stems from the acoustic power absorbed by tissues. The more the acoustic power is absorbed, the more the tissue temperature increases. On the other hand, more absorption means less penetration. Since the wave frequency is one of the important factors in power absorption, a compromise should be reached between the transferred energy and desired penetration depth. In this thesis, first, a problem with common HIFU-therapy conditions is simulated; then, using its outputs, the effects of frequency—at different geometrical focal distances between 8 to 16 cm—on different parameters like the actual focal spot, the maximum peak pressure, the acoustic intensity, the absorbed power, and temperature distribution are investigated. By defining nine optimization functions, the most appropriate frequency value or range is reached to satisfy therapy conditions. For example, at the geometrical focus distance of 8 cm, the mentioned frequency related to the functions of peak pressure, total acoustic power, and thermal dose is derived 3.5, 0.5, and 2.25 MHz. By normalizing these frequency-dependent functions and transferring the curves into one single figure an optimized range can be reached. Using this method, by applying three assumed therapy conditions related to peak pressure, accuracy, and non-target damage the range of 2-2.5 MHz is reached for lithotripsy frequency
  9. Keywords:
  10. Optimization ; Acoustics ; High Intensity Focused Ultrasound (HIFU)Method ; High Amplitude Ultrasound ; Nonlinear Acoustic Waves ; Frequency Effect

 Digital Object List

 Bookmark

...see more