Evaluation of the thermal sensitivity of porcine liver in CT-guided cryoablation: an initial study

Purpose To evaluate computed tomography (CT)-based thermometry in cryoablation, the thermal sensitivity of anex-vivoporcine liver was determined in an initial study design. Methods The CT-guided cryoablation was performed in three porcine liver samples over a period of 10 min. Fiber optic temperature probes were positioned parallel to the shaft of the cryoprobe in an axial slice orientation. During ablation, temperature measurements were performed simultaneously with CT imaging at 5 s intervals. On the CT images, the average CT number was calculated for a region of interest of 3 x 3 pixels just below the tip of each temperature probe. A linear regression analysis was performed using eleven data sets to determine the dependence of the CT number on the temperature. Results With decreasing temperature, an increasing hypodense area around the tip of the cryoprobe was observed on the CT images and decreasing values of the CT number were determined. Starting at a temperature of - 40 degrees C a linear relation between the CT number and the temperature was determined and a thermal sensitivity of 0.95 HU/degrees C (R-2 = 0.73) was obtained. The thermal sensitivity was used to calculate color-coded temperature maps. The calculated temperature distribution corresponds quantitatively to the increasing hypodense area. Conclusions A noninvasive CT-based temperature determination during cryoablation in a normalex vivoporcine liver is feasible. A thermal sensitivity of 0.95 HU/degrees C was determined by linear regression analysis. A color-coded map of the temperature distribution was presented.