M.Sc Thesis

M.Sc StudentKalfon Ziv
SubjectThermo-Graphic Imaging using Ultrasonic Tomography
DepartmentDepartment of Biomedical Engineering
Supervisor PROF. Haim Azhari


Worldwide clinical trends point towards precise, minimally invasive procedures as the method of choice for many surgeries. Recently, attention has been drawn to selective heating of defined tissue regions by non-invasive means such as high intensity focused ultrasound, Laser or RF probes. The key for a successful thermal treatment is thermal mapping

   The objective of this study was to explore the feasibility of using ultrasonic computerized tomography (UCT) for thermal mapping.  The suggested method was based on the assumption that the speed of sound has a monotonic dependency on tissue temperature and that this relation can be used for thermal mapping using UCT based on time of flight (TOF) scans.

   A theoretical analysis of the expected performance of such system was done in order to evaluate the accuracies needed in TOF measurements and the expected sensitivity to thermal changes and the expected spatial resolution. A series of in-vitro experiments were preformed on bovine liver. The sensitivity of several TOF estimators was experimentally evaluated. The monotonic relationship between the TOF and temperature was established for the temperatures range of 20 to 55 degrees. Then using a special computerized ultrasonic scanner TOF projections were collected from heated objects The experiments with the TOF projections indicated that there were significant changes in the TOF values in the order of magnitude of microseconds. Finally, using the inverse-Radon transform UCT images depicting TOF changes resulting from heating were reconstructed. The UCT scans have shown differences of 3รท9 nanoseconds for 0.5mm pixels between the hot scans and the reference cold scan. Distinct hot regions were noted in the UCT reconstructions.

The results obtained from this study indicate that UCT thermal mapping based on TOF mapping is feasible.