Enhanced ablation of high intensity focused ultrasound with microbubbles: an experimental study on rabbit hepatic VX2 tumors.

Purpose: This study was designed to assess the enhanced effect of high intensity focused ultrasound (HIFU) ablation with microbubbles on rabbit hepatic VX2 tumors and to compare the detection sensitivity of CEUS and CECT to determine the residual viable tissue after ablation of HIFU.

Methods: Forty rabbits with hepatic VX2 tumors were randomly separated into two groups (20 animals per group) before HIFU ablation. A bolus of 0.2 mL of saline or a microbubble-based ultrasound (US) contrast agent was injected intravenously to group I rabbits and group II rabbits, respectively. The HIFU ablation procedure was started 15 s after the injection. Tumors were examined with grayscale contrast-enhanced ultrasound (CEUS) and contrast-enhanced computed tomography (CECT) immediately before and after HIFU ablation. Histopathologic assessment was performed immediately after treatment imaging.

Results: Before ablation, intense contrast enhancement during arterial phase was observed at the whole tumors or the periphery of the tumors by CEUS and CECT. Lower HIFU energy was used in group II than in group I (P < 0.001). Histopathologic assessment revealed local residual viable tumor tissues due to incomplete ablation in 47.4% (9/19) of tumors in group I and 10% (2/20) of tumors in group II (P < 0.05). The concordance rate of CEUS (90.9%) with histopathology on residual tumor detection was higher than that of CECT (27.3%, P < 0.05).

Conclusions: Introduction of the microbubble agent enhances HIFU therapeutic efficacy. CEUS proves to have high sensitivity in assessment of residual viable rabbit VX2 tumor after HIFU.