Radiofrequency ablation is a well established, minimally invasive approach for the treatment of tumors. However, at present there is a lack of suitable imaging modalities for accurate online monitoring of the coagulation process. The aim of this work is to evaluate the potential of various tissue characterizing ultrasonic parameters from spectral and spatial domain to differentiate between coagulated and noncoagulated tissue. The calculated parameters include first and second order texture parameters, estimates of attenuation coefficients, spectral parameters (slope, intercept and midband value) and coefficients of autoregressive spectral estimates. As a measure of selectivity of each parameter the area under the receiver operating characteristic (ROC) curve was utilized. The best performing parameters can be used to be processed by a classification system.
Radiofrequency (RF) ablation using high-frequency current has become an important treatment method for patients with non-resectable liver tumors. Tumor recurrence is associated with tissue cooling in the proximity of large blood vessels. This study investigated the influence of blood flow rate on tissue temperature and lesion size during monopolar RF ablation at a distance of 10 mm from single 4- and 6-mm vessels using two different approaches: 1) an ex vivo blood perfusion circuit including an artificial vessel inserted into porcine liver tissue was developed; and 2) a finite element method (FEM) model was created using a novel simplified modeling technique for large blood vessels. Blood temperatures at the inflow/outflow of the vessel and tissue temperatures at 10 and 20 mm from the electrode tip were measured in the ex vivo set-up. Tissue temperature, blood temperature and lesion size were analyzed under physiological, increased and reduced blood-flow conditions. The results show that changes in blood flow rate in large vessels do not significantly affect tissue temperature and lesion size far away from the vessel. Monopolar ablation could not produce lesions surrounding the vessel due to the strong heat-sink effect. Simulated tissue temperatures correlated well with ex vivo measurements, supporting the FEM model.
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