M.Sc Thesis

M.Sc StudentWeiss Noam
SubjectThermal Monitoring of HIFU Treatment with X-Ray CT of
Fat Tissue
DepartmentDepartment of Biomedical Engineering
Supervisor PROF. Haim Azhari
Full Thesis textFull thesis text - English Version


In recent years High Intensity Focused Ultrasound (HIFU) treatments for tumor therapy and other clinical applications have gradually became more and more prevalent. Thermal monitoring during HIFU treatment is crucial and is mainly performed today with MRI. However, MRI is a very expensive modality and performs poorly in monitoring of fatty tissues. Alternative imaging modalities for this purpose could be beneficial.

The goal of this study was to examine the feasibility of using X-ray CT for thermal treatment monitoring in general, and particularly in fatty tissues. Our hypothesis was that thermal expansion associated with tissue heating will alter the Hounsfield Units (HU) thus enabling non-invasive monitoring by CT.

The first stage of this research included experiments on several simple materials, such as water, oil and a protein mixture. In the second stage experiments were conducted on ex-vivo fatty tissues.  During the experiments the tested material or tissue was heated by ultrasonic waves or HIFU, simultaneously with CT scanning. 

The simple material testing showed that it is possible to detect the change in temperature from the obtained CT images. In these cases the curves of temperature-HU followed a monotonic behavior, which is attributed to the thermal expansion coefficient. The protein mixture and the fatty tissue results depicted hysteresis phenomenon between the heating and the cooling stage. This presumably stems from denaturation and coagulation processes that occur when the temperature exceeds 43oC.

For fatty tissues, a characteristic temperature-HU curve was found. Using the features of this curve a new non-invasive method for thermal monitoring is suggested.

Furthermore, a few methods for assessing the level of tissue damage, based on quantitative indices of the hysteresis are suggested.

This research has demonstrated feasibility for future clinical application based on the presented technique, which can provide the physician a non-invasive tool for thermal monitoring during HIFU treatments with X-ray CT.