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

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.