Instant Outcome Evaluation of Microwave Ablation With Subtraction CT in an In Vivo Porcine Model

Abstract

Objectives The aim of this study was to investigate whether the accuracy of multislice contrast-enhanced computed tomography (MS-CECT) may be improved by performing additional subtraction CT. Materials and Methods Thirty-five microwave ablations were performed under CT guidance in 12 healthy and anesthetized pigs. Preablation and postablation MS-CECT scans were obtained in arterial and venous contrast phases. These scans were reconstructed and subtracted from each other. Lesion size was measured in a region of interest drawn around the ablation area. Computed tomography measurements were compared with standardized macroscopic images of explanted liver tissue, obtained immediately after ablation. Paired correlation and Bland-Altman analyses were performed for assessing agreement between modalities and ratings. Results The correlation between lesion size measured in CT and histology was very strong for subtracted images (r = 0.91; 95% confidence interval [CI], 0.8–0.96) and strong for standard MS-CECT images (r = 0.85; 95% CI, 0.68–0.93). Interrater agreement for all measurements was excellent (intraclass correlation coefficient, 0.99; 95% CI, 0.98–0.99 for subtraction and intraclass correlation coefficient, 0.99; 95% CI, 0.98–1.00 for MS-CECT). All differences were statistically significant (P < 0.05). Conclusions Subtraction CT was superior to nonsubtracted MS-CECT in measurement of liver lesion size after microwave ablation in a porcine model, achieving a very strong correlation with pathologic measurement and a significantly lower overestimation of lesion size compared with MS-CECT.