M.Sc Thesis

M.Sc StudentWinkler Itai
SubjectReal Time Monitoring of Thermal Ablation with Ultrasound
DepartmentDepartment of Biomedical Engineering
Full Thesis textFull thesis text - English Version


  Primary and secondary malignant hepatic tumors are some of the most common malignant tumors worldwide. Chemotherapy and Radiation therapy are ineffective against primary and secondary hepatic tumors so only resection surgery can be a solution. Yet only a small percentage of the patients are candidates for this surgery. In recent years minimal invasive approaches have been suggested and introduced into clinics. Radio Frequency Ablation (RFA) is one of these methods.

  RFA Procedure was approved by FDA for various targets within the body and is intensively used for liver tumors. However, this method suffers from lack of sufficient monitoring, guiding and control. As a result, a very high recurrence rate of 30-50% is typically reported from different health centers around the world.

  Previous reports have shown that during tissue heating, micro-bubbles are formed. Under ultrasound these bubbles may be driven to nonlinear motion that produces acoustic emission such as sub-harmonics. These low frequency emissions may be used to monitor ablation surgery.

  The research objectives were to study the behavior of these low emissions during the ablation treatment and to try to develop a monitoring algorithm based on these results.

  In this study, a modified commercial ultrasound system was used for transmitting ultrasound beams and for recording raw RF-lines from a scan plane in porcine (ex-vivo) and rabbit (in-vivo) livers, during RFA.

  Results show that mean energies at the low-frequency band (LFB energy), as well as at the transmission frequency band (TFB energy) increase substantially in areas adjacent to the RFA needle. These energies also changes abruptly for higher temperatures, thus producing great variance of the received energy. Mean energies in areas distant from RFA needle showed little change and variation during treatment. It is also shown that a significant 3dB increase in low frequencies energy is typically obtained at regions elevated to temperatures above 54.3±5.5 ºC.

 An algorithm based on sum of absolute difference (SAD) of LFB energy is used to image treatment progress ex-vivo. A comparison between lesion diameter measured from the algorithm to the diameter measured manually produced a correlation coefficient of r=0.8. The in-vivo algorithm was based on LFB energy calculations measured on a much lower band width. The algorithm was a moving average of the LFB calculations. A comparison between a manual measurement of the lesion to the lesion diameter measured from the algorithm, produced a correlation coefficient of r=0.73. Thus proving the method feasibility in-vivo