M.Sc Thesis

M.Sc StudentGabbai Ronen
SubjectAcoustic Parameter Estimation in Biological Tissue, and the
Analysis of Their Changes as a Result of Heating
DepartmentDepartment of Biomedical Engineering


Thermal therapy can be used as a treatment for localized malignancies. One of the essential elements needed for the development of such clinical treatment is, non-invasive temperature monitoring technique. Ultrasound based techniques may serve as a good option for such monitoring. The main reasons are its low price, the lack of harmful effects and the ability to perform in real time. The aim of this research was to study the directions and techniques for the use of ultrasound as a temperature monitoring tool during thermal treatment.

In an attempt to achieve this aim, two major ultrasound beam properties influenced by heating were investigated: (1) Beam refraction - governed by Snell law. The speed-of-sound changes, resulted from the temperature changes, cause the ultrasound beam to refract. (2) Air/vapor bubbles formation - The formation of bubbles a long the US path have major influence on the backscatter and the speed of sound measurements. 

In-vitro experiments were conducted using fresh bovine liver. Refraction effects, caused by the beam path through heated region, were investigated by measuring the passing signal energy changes. The effect of air/vapor bubbles formation, caused by tissue heating, was investigated by measuring backscatter changes. The results show clearly that the changes in the beam path are not to be neglected, and are influenced by both the tissue geometry and heating geometry, with the second having a stronger effect. These results are expected to help future research of monitoring thermal treatment, by pointing to ultrasound limitations and to possible solutions.