OBJECTIVETo assess the application of gray-scale contrast-enhanced ultrasound (CEUS) and contrast-enhanced spiral computed tomography (CECT) in detection of residual tumor after high intensity focused ultrasound (HIFU) ablation with microbubbles on rabbit hepatic VX2 tumors.

METHODSForty rabbits with hepatic VX2 tumors were randomly divided into three groups before ablation. Group I (n=10) served as sham ablation controls, rabbits in group II (n=15) and group III (n=15) were ablated using HIFU under the manipulation of computer. A bolus of 0.2 ml SonoVue solution was injected via ear marginal vein of rabbits in group III before ablation. Tumors were examined with CEUS and CECT before and within 3h after HIFU ablation. Necropsy and histopathological assessment were performed immediately after the completion of images evaluation.

RESULTSBefore ablation, intense arterial feeding vessels was detected in the tumors (77.5%,31/40 Compared with 52.5%,21/40) or the periphery of the tumors (22.5%,9/40 Compared with 47.5%,19/40) by CEUS and CECT, respectively. The tumors were characterized by quick wash-in and wash-out (high and rapid peak of enhancement in the arterial phase,followed by a fast decrease in enhancement level). The dose parameters used to achieve therapeutic effect in group III were significantly lower than those in group II(P<0.01). There were local residual viable tumor tissues due to incomplete ablation in 60.0% (9/15) of group II and 13.3% (2/15) of group III revealed by histopathology(P<0.05). The concordance rate of CECT and CEUS with histopathology on residual tumor detection was 27.3% and 81.8% (P<0.05), respectively.

CONCLUSIONThe administration of microbubble agent enhances the efficacy of HIFU on rabbit hepatic VX2 tumors. CEUS is more sensitive than CECT in detection of residual viable rabbit VX2 tumor after HIFU.