Objectives: In recent years, high intensity focused ultrasound (HIFU) was shown to have promising effect on ablating tumors. However, the size of each ablation lesion is small and thus the duration for complete tumor destruction is long. In this study, the effect of using ultrasound contrast agent (UCA) to enhance the thermal effect, and thus enlarge the lesion size, was studied both in vivo and in vitro. Methods: Different concentration of UCA was mixed evenly with polyacrylamide gel phantoms containing egg white, or intravenously injected into rabbits before performing HIFU ablations. Results: UCA significantly increased the lesion size and reduced the necessary power to form a lesion of a certain size. 30% reduction of the power level was achieved. However, the shift of the most heating position also increased with the concentration of UCA. With regard to mechanism, tissue boiling and inertial cavitation both played important but different roles in the process of lesion formation and transformation. Animal experiment showed similar enhancement effect. Conclusions: UCA effectively increased the lesion size, but the migration of heating center increased the risk of injuring normal structures. Optimal conditions, which enlarge lesions significantly but produce acceptable shifts, should be determined in advance for safety.
Date:
2006-05
Relation:
Ultrasound in Medicine and Biology. 2006 May;32(5, Suppl):P110.
