Microbubbles improve the ablation efficiency of extracorporeal high intensity focused ultrasound against kidney tissues.

Objective: The necrosis rate is low when ablating kidney tissues with extracorporeal high intensity focused ultrasound (HIFU), and this drawback has been limiting the application of ultrasonic therapy. The aim of the present study was to determine whether microbubbles increased the ablation efficiency in vivo.
Methods: Goat kidneys were exposed to HIFU (control group) or microbubble-assisted HIFU (experimental group). Microbubbles were intravenously injected before focused ultrasound exposure. The linear scan was employed and tissue ablation was performed in manner of a clinical regime. The necrosis rate was determined 24 h after HIFU. Pathological examinations were performed to confirm tissue necrosis and to determine whether there were unaffected tissues within the exposed volume.
Results: The necrosis rate was increased in experimental group (4.17 +/- 1.33 vs. 9.32 +/- 2.27 mm(3)/s, P = 0.0007). Ablated tissues formed a hemorrhagic volume on gross examinations, and the boundary between treated and untreated areas was sharp. There was no intact tissue within the exposed volume. Hemorrhage frequently occurred in insonated parenchymas. Destructed ghost cells just inside the demarcation were full of vacuoles, when introducing microbubbles. In control group, the volumes of ablated tissues varied drastically between animals despite a same treatment template.
Conclusion: Microbubbles increased the ablation efficiency of HIFU against kidney tissues. A preoperative regime might poorly predict the therapeutic outcome.