Background: Microwave ablation is a promising treatment for unresectable liver tumors. Unlike radiofrequency ablation, microwave ablation may be performed with multiple simultaneously active antennae. Methods: Microwave ablation was performed in an in vivo porcine liver model by using a single antenna (n = 11) or three antennae in a triangular array, activated either sequentially (n = 11) or simultaneously (n = 13). Lesions were measured and assigned a qualitative shape score. Results: Single-antenna microwave lesions had a mean volume of 7.4 +mn; 3.9 cm 3, compared with 14.6 +mn; 5.2 cm 3 and 43.1 +mn; 4.3 cm 3 for sequential and simultaneous multiple-probe ablations, respectively (P < .001; analysis of variance). Simultaneous lesions were rounder than sequential ablations and were more effective near blood vessels. Simultaneous lesions created with probe separation of 1.7 cm were round and confluent, whereas clefts were present with distances >1.7 cm (P < .001). Conclusions: Microwave ablation has several theoretical advantages over currently available radiofrequency devices. Simultaneous three-probe microwave ablation lesions were three times larger than sequential lesions and nearly six times greater in volume than single-probe lesions. Additionally, simultaneous multiple-probe ablation results in qualitatively better lesions, with more uniform coagulation and better performance near blood vessels. Simultaneous multiple-probe ablation may decrease inadequate treatment of large tumors and decrease recurrence rates after tumor ablation.
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