Investigation of the influence of blood flow rate on large vessel cooling in hepatic radiofrequency ablation / Untersuchung des Einflusses der Blutflussgeschwindigkeit auf die Gefäßkühlung bei der Radiofrequenzablation von Lebertumoren

Abstract

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.

Ex situ quantification of the cooling effect of liver vessels on radiofrequency ablation

“…Glass has a heat conductivity similar to liver tissue and therefore does not impede heat distribution [16]. Although the glass tube isolates the fluid inside the vessel from the electrical field, it has been shown that electrical heating is negligible compared to heating by thermal conduction [16].…”

Intermittent Pringle maneuver may be beneficial for radiofrequency ablations in situations with tumor-vessel proximity

“…Therefore, the study was performed with a glass tube that simulated a liver vessel to achieve a standardized setup. The isolating properties of the glass tube can be neglected, as it was situated outside of the electrical field of the applicators [9], [11], [12], [26]. Energy transmission took place at the position of the glass tube by direct temperature transfer.…”

“…Energy transmission took place at the position of the glass tube by direct temperature transfer. Glass has thermal properties that are similar to those of liver tissue and does not interfere with heat conduction [11], [26]. The thermal properties of the vascular wall itself were disregarded within this study.…”

Study of flow effects on temperature‐controlled radiofrequency ablation using phantom experiments and forward simulations

“…For example, Poch et al 30 examined flow through a perfused glass tube using an impedance‐controlled RF generator with automatically modulated power and found incomplete ablation at different vessel‐to‐applicator distances as well as changes in shape. Welp et al 31 compared ablation experiments with a perfused glass vessel and constant power input to a finite element model. Blood flow did not affect the lesion diameter for large distances between electrode and vessel, although shape deformations occurred.…”