Contrast-enhanced Ultrasound in the Assessment of the Transitional Zone of Microwave Ablations in an Ex vivo Perfused Liver Model; is It a Useful Tool?

Background and Aims: Microwave ablation (MWA) under different imaging guidance is a new technique for treating liver malignancies. The ablation creates a transitional zone at the periphery of the ablated region. In this zone, few cancer cells might escape heat causing local recurrence. Therefore, a more defined transitional zone is required to avoid residual cancer.
Study Design: Experimental study with a block design.
Place and Duration of Study: Departments of Hepatobiliary and Pancreatic surgery, department of Radiology and department of Histopathology; University hospitals of Leicester, UK. May-July 2011.
Methodology: MWA with different powers (50 W, 70 W, 90 W) were created in five ex vivo perfused porcine livers. The ablations were evaluated on morphology, grey-scale US, CEUS and histology. Statistical analysis of the data was performed using ANOVA test.
Results: CEUS showed better demarcation of the lesion’s border when compared with the grey-scale US. There was a significant difference in the long axis of the ablation among morphology, grey-scale US and CEUS (P < 0.0001), and a significant difference in the lesion size between powers (P = 0.0064). There was no difference in the short-axis, but a significant difference in the lesion size between powers (P = 0.0306). A significant difference in the width of the transitional zone (TZ) was noticed between powers 50W and 90W (P= 0.015).
Conclusion: CEUS shows better demarcation of the ablated zone when compared with the grey-scale-US, a finding that could provide guidance in the assessment of the ablation zone during treatment. CEUS does not show superiority over morphology or grey-scale US in reflecting the actual size of the lesion. Histology remains the only method to provide exact measurements of the transitional zone width when compared with morphology. Further research is required to confirm these results.