Hepatic radiofrequency ablation with internally cooled probes: effect of coolant temperature on lesion size

Abstract

Radiofrequency (RF) ablation is a minimally invasive method for treatment of primary and metastatic liver tumors. One of the currently commercially available devices employs an internally cooled 17-gauge needle probe. Within the probe, cool water is circulated during ablation, which cools tissue close to the probe resulting in larger lesions. We evaluated the effect of different cooling water temperatures on lesion size. We created a finite-element method model, simulated 12 min impedance-controlled ablation and determined temperature distribution for three water temperatures. Lesion diameters in the model were 33.8, 33.4, and 32.8 mm for water temperatures of 5 degrees C, 15 degrees C, and 25 degrees C, respectively. We solved a simplified model geometry analytically and present dependence of lesion diameter on cooling temperature. We further performed ex vivo experiments in fresh bovine liver. We created four lesions for each water temperature, with the same water temperatures as used in the finite-element method (FEM) model. Average lesion diameters were 28.3, 30, and 29.5 mm for water temperatures of 5 degrees C, 15 degrees C, and 25 degrees C, respectively. Water temperature did not have a significant effect on lesion size in the ex vivo experiments (p = 0.76), the FEM model, and the analytical solution.

Review of the mathematical functions used to model the temperature dependence of electrical and thermal conductivities of biological tissue in radiofrequency ablation

“…At the present time there are two ways of introducing the parameters  and k in RFA theoretical models: 1) using constant values taken from the scientific literature [11,12], and 2) in a more realistic way, using mathematical functions which reflect the dependence of these parameters on temperature, specially for high temperatures [13,14]. We are interested in the second case, consisting of functions which consider temperatures above 100ºC.…”

“…5 At temperatures above 100ºC vaporization occurs and desiccation implies a rapid drop of . There are also discrepancies about the rate of this drop: Byeongman and Aksan [13] considered that  decreases by approximately 2 orders of magnitude between 105ºC and 110ºC, Haemmerich et al [14] assumed a rapid drop by a factor of 10.000 between 100ºC and 102ºC, and Pätz et al [19] considered a discontinuous drop to a value close to zero.…”

“…Most RFA theoretical models have used a constant value for k [14,15,17,[20][21][22], probably due to the fact that changes in k with temperature are not so marked as in  [10,23].…”

É possível diminuir o sangramento em hepatectomias sem a realização de exclusão vascular total ou parcial?: Resultados do uso de radiofrequência bipolar com agulhas resfriadas

“…The procedure described here is grounded in the physical and physiological studies obtained with the use of RF associated with the cooling of the needle 8 . As a fundamental difference highlights the use of a handle with two separate needles, transmitting energy between them, so bipolar, provided linearly controlled area of necrosis, without the risk of dissipation of current to tissue distance, thus preventing heat injuries.…”

“…However, despite the appropriate use of RF ablation, local recurrence at the site of ablation varies around 40% 3 . This high recurrence rate is due to the difficulty to obtain necrosis of tumor cells in regions close to large vessels, as well as larger lesions 3,8 . Lower rates of recurrence, around 5% 14 , have been obtained when the Pringle maneuver is associated with the ablation procedure, which in turn is poorly tolerated in the postoperative period of patients with chronic liver disease with low functional reserve.…”