Tissue shrinkage in microwave ablation of liver: an ex vivo predictive model

Purpose: Developing a predictive model of the shrinkage of liver tissues in microwave ablation. Methods: Thirty-seven cuboid specimens of ex-vivo bovine liver of size ranging from 2 cm to 8 cm were heated exploiting different techniques: 1) using a microwave oven (2.45GHz ) operated at 420 W, 500 W and 700 W for 8 to 20 minutes, achieving complete carbonization of the specimens; 2) using a radiofrequency ablation apparatus (450 kHz ) operated at 70 W for a time ranging from 6 to 7.5 minutes obtaining white coagulation of the specimens and 3) using a microwave (2.45 GHz ) ablation apparatus operated at 60 W for 10 minutes. Measurements of specimens dimensions, carbonized and coagulated regions were performed using a ruler with an accuracy of 1 mm. Based on the results of the first two experiments, an analytical model for the contraction of liver tissue from microwave ablation was constructed and compared to the result of the third experiment. Results: For carbonized tissue, a linear contraction of 31% ± 6% was obtained, independently of the heating source, power and operation time. RF experiments determined that the average percentage linear contraction of white coagulated tissue was 12% ± 5%. The average accuracy of our model was determined to be 3 mm (5%). Conclusions: The proposed model allows predicting the shrinkage of liver tissues upon microwave ablation given the extension of the carbonized and coagulated zones. This may be useful in helping to predict whether sufficient tissue volume is ablated in clinical practice.