Radio-frequency-induced Coagulation Necrosis in Rabbits: Immediate Detection at US with a Synthetic Microsphere Contrast Agent

PURPOSE: To determine whether a synthetic ultrasonographic (US) contrast agent can be used to differentiate coagulation necrosis from untreated tumor immediately after radio-frequency ablative therapy. MATERIALS AND METHODS: VX2 (adenocarcinoma) tumors (0.8–1.5-cm diameter) were implanted into 12 rabbits. Gray-scale and color Doppler US were performed with or without intravenous injection of a US contrast agent composed of poly-lactide-co-glycolic acid polymeric (PLGA) microspheres (2-μm diameter) filled with perfluorocarbon gas. Radio frequency was applied to each nodule for 6 minutes at 127 mA ± 33 (mean ± SD) (tip temperature, 92°C ± 2). Repeat US with a second dose of the contrast agent was performed immediately after ablation. In four animals, a third dose was administered 30–120 minutes after ablation. Radiologic-histopathologic correlation was performed and included in vivo staining and studies of mitochondrial function. RESULTS: Intense contrast agent enhancement was seen throughout the tumor prio...