Quantitative assessment of acoustic Intensity in HIFU
Nie, Jian Cheng
Date of Issue2016
School of Mechanical and Aerospace Engineering
Background and Objectives High Intensity Focused Ultrasound(HIFU) has became more and more popular and important in tumor therapy. It is so sharp that can easily remove tumors with rapid speed beyond your imagination. Actually HIFU is not a real knife but a ultrasound which is focused by transducer in vitro, converged and formed a sound field with high energy density around the tumor. It can kill the tumor on sight easily by its transient heat effect. There is not enough time to allow heat conduction to take place in surrounding normal tissue that makes HIFU win the fame of noninvasive technique. For safety's sake during the treatment, it is necessary to know exactly the parameters of acoustic field in HIFU, such as power, pressure and intensity. Due to the complexity of HIFU acoustic field, scholars have been unable thus far to give a comprehensive way to accurately detect it. Methodology An evaluation of acoustic intensity in HIFU named infrared imagining method is employed in this thesis. And the method is to use an infrared camera which can get the data of temperature elevation and temperature distribution. With the temperature elevation, the corresponding acoustic intensity can be derived base on Shaw's theoretical model. But in this thesis, the temperature data is gained by HIFU simulator which was developed by Joshua Soneson(2008). The first step is to explore the relationship between the maximum pressure of each harmonic and harmonic order numbers. Next, based on this relationship and infrared imaging method, a absolute value of the intensity of the free field can be derived. The intensity determined from infrared imaging method is then compared with those derived from HIFU simulator. Outcome and results Using three different thickness of rubber, intensity derived by infrared imaging method was 13.1% lower than that calculated by HIFU simulator. And making use of three different materials, intensity derived by infrared imaging method was 22.8% lower than that calculated by HIFU simulator. And making use of Bessel function of the first kind can describe intensity of distribution approximately. Selection of the range and starting point of absorber thickness have effects on simulated results. What the thesis sum up can help people to select the absorber for their experiments.