M.Sc Thesis

M.Sc StudentMargolin Raisa
SubjectThe Study of Transient Changes of Echogenicity in
Ultrasound Images of Heated Tissue
DepartmentDepartment of Biomedical Engineering


Thermal therapy of tumors has received considerable attention in recent years because of its potential to lower morbidity, its potential utilization in an outpatient setting, and its decreased cost. The aim of this minimally invasive technique is to treat malignant lesions while causing minimal damage to the normal surrounding tissue. The success of the clinical implementation of this technique depends mostly on the ability to monitor in real-time the tissue damage. Very high temperatures (500C to 1000C or more) are produced locally in the target tissue, and destruction can spread rapidly into surrounding healthy tissue. Thus, the extent of thermal damage must be closely controlled. The goal of this study was to investigate and bring to practical implementation a method of controlling the thermal damage. Cavitation (formation of air/vapor bubbles), caused by tissue heating, was used to detect changes in the tissue during laser heating. In vivo and in vitro experiments were performed in our laboratory to monitor these changes during therapeutic procedures. Real-time monitoring by a modified commercial Ultrasound Imaging system and RF processing of ultrasound echoes were used in conjunction with temperature measurements and post treatment visualization of the heated area. Based on nonlinear behavior of microbubbles, the data analysis was mainly of the sub-harmonic frequencies within the ultrasound response. The amplitudes of the sub-harmonic increase during the treatment, significantly in close distance to the laser, an less so at distant locations. The later decrease of the amplitudes signifies termination of treatment. The results obtained show the feasibility of non-invasive control of thermal therapy at the lesion area.