Abstract No. 377 - CT findings after irreversible electroporation ablation in a porcine model: Radiologic-pathologic correlation

Abstract

Purpose To characterize computed tomography (CT) findings after irreversible electroporation (IRE) in a porcine model Materials and Methods Twenty two CT-guided IRE lesions were created in livers of 12 pigs. Energy was delivered at 2250-3000 V (pulse length, 90-100 μsec; pulse repetition, 70-90) by using two 18-gauge electrodes with 2-2.5 cm active tip, 1.5-2.0 cm distance between electrodes and a Nanoknife generator (Angiodynamics, Fremont, CA). Triple-phase multi-detector CT imaging was performed prior to IRE application and immediately before euthanasia (2 hours after ablation). Multiple CT imaging features were studied, including: dimensions; coagulation zone attenuation; and presence, as well as characteristics of post ablation enhancement. Zones of ablation were evaluated at gross and histopathologic examination, correlated with CT findings, and subjected to statistical analysis. Results The mean ablation volume measured by CT imaging and gross pathology was 31.8 cm 3 [95% CI: (14.3, 49.4)] and 15.2 cm 3 [95% CI: (12.8,17.6)]. Using a mixed-effects regression model, the two volume means are significantly different (p=0.04) with the size of the ablation zone on the CT appearing larger than the gross size (p=0.0416). Two hours after IRE energy application, the ablation zone appeared as a well demarcated hypoattenuating area. Mean pre, arterial and portal HU for the zone of ablation was 79.6 [95% CI: (73.1, 87.2), 64.3 [95% CI: (57.3, 72.0)], and 73.9 [95% CI: (61.8, 86.1). An incomplete rim of enhancement was observed surrounding the zone of ablation in both the arterial and portal phase with a median thickness of 2.5 mm. Histologic examination revealed a clear demarcation between the ablated liver and adjacent unaffected parenchyma. Coagulation zone was characterized by hepatocellular dissociation often associated with hemorrhage and sinusoidal dilatation. Conclusion CT imaging in the acute period after IRE depicts the ablation zone as a hypoattenuating lesion with a surrounding rim of enhancement. However, it appears to overestimate the dimensions of the ablative injury.