Abstracts
2000 Digestive Disease Week

# 2270 Intraoperative Ultrasound Assessment of Hepatic Radiofrequency Ablation.
D.J. Scott, W.N. Young, L.M. Watumill, G.M. Lindberg, J.B. Fleming, J.F. Huth, R.V.D.R. Jeyarajah, D. B. Jones, Dallas, TX

Ultrasound may be used to monitor the extent of tissue destruction during radiofrequency ablation (RFA). The outline of ablated tissue may not always be easy to delineate on sonographic imaging. Accurate assessment of ablation size is critical to achieving tumor-free margins. The purpose of this study was to determine the accuracy of intraoperative ultrasound assessment during hepatic RFA. Using an agarose tissue-mimic model, 1 cm simulated hepatic tumors (n=26) were created in 9 pigs. Each animal was randomized to open (n=4) or laparoscopic (n=5) RFA. In both groups a 15 GA probe with 4 deployable electrodes was placed into the center of the target under ultrasound guidance and an 8-minute ablation was performed. A radiologist supervised the determination of ablation size immediately post ablation using ultrasound. A 7.5 MHz linear-array transducer was used for open cases; a 7.5 MHz curvilinear-array transducer was used for laparoscopic cases (B&K Medical). A pathologist examined all specimens grossly and microscopically to determine ablation size. Ablation diameter was defined as the average of longitudindal transverse, and anterior-posterior measurements. Analysis was by Mann-Whitney and Fisher Exact tests; values are mean ± s.d., *P <0.05 compared to pathology diameter, **P <0.05 compared to open group. (See Table) Laparoscopic ultrasound underestimated ablation size. The curvilinear-array transducer used for laparoscopic ultrasound may have biased measurements towards underestimation. Mean ultrasound diameter for open cases was not different from pathology, but ultrasound overestimated ablation size by 3.9 mm in 5 of 11 (45%) open cases. Overestimation of ablation size may result in inaccurate margin assessment and incomplete tumor destruction. Ablation size may be difficult to accurately determine using laparoscopic or open ultrasound.