Simulation study of the cooling effect of blood vessels and blood coagulation in hepatic radio-frequency ablation

Abstract

Purpose: Computer simulations of hepatic radio-frequency ablation (RFA) were performed to: (i) determine the dependence of the vessel wall heat transfer coefficient on geometrical parameters; (ii) study the conditions required for the occurrence of the directional effect of blood; and (iii) classify blood vessels according to their effect on the thermal lesion while considering blood coagulation. The information thus obtained supports the development of a multi-scale bio-heat model tailored for more accurate prediction of hepatic RFA outcomes in the vicinity of blood vessels. Materials and methods: The simulation geometry consisted of healthy tissue, tumor tissue, a monopolar RF-needle, and a single cylindrical blood vessel. The geometrical parameters of interest were the RF-needle active length and those describing blood vessel configuration. A simple, novel method to incorporate the effects of blood coagulation into the simulation was developed and tested. Results: A closed form expression giving the dependence of the vessel wall heat transfer coefficient on geometrical parameters was obtained. Directional effects on the thermal lesion were found to occur for blood vessel radii between 0.4 mm and 0.5 mm. Below 0.4 mm blood coagulation blocked the flow. Conclusions: The closed form expression for the heat transfer coefficient can be used in models of RFA to speed up computation. The conditions on vessel radii required for the occurrence of directional effects on the thermal lesion were determined. These conditions allow the classification of blood vessels. Different approximations to the thermal equation can thus be used for these vessel classes.

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

“…In the present study, the objective was to study the effect of varying flow rate and radius independently. The smallest channel radius of 0.275 mm was chosen since it is small enough to guarantee directional effects (based on our previous simulation results 22 ). The larger radii of 0.9 and 2.3 mm were arbitrarily chosen within the range of vein radii observed in human livers 35 to investigate the effect of increasing radius.…”

“…Figure 4 shows a schematic of directional effects on the thermal lesion in RFA. The average lesion boundary displacement (%) 22 was used to quantify the directional effect and is given by,where , , and are defined as shown in Figure 4. The displacements and are positive in the direction of flow and negative otherwise.…”

“…This figure is based on a figure from Ref. [22] (Vaidya et al, 2021), licensed under the CreativeCommons Attribution‐NonCommercial license [Color figure can be viewed at wileyonlinelibrary.com]…”

“…Vessel diameters of 1 and 2 mm were studied, and directional effects were only observed for 1 mm. We have, in the past, performed a simulation study on the directional effect of blood vessels in RFA 22 . While assuming a dependence of flow rate on the vessel radius as suggested by Murray's law, 23 directional effects were found to occur below vessel radii of 0.5 mm and, if considering blood coagulation effects, above 0.4 mm for the blood vessel parameters considered.…”

Influences of blood flow parameters on temperature distribution during liver tumor microwave ablation

“…Also, the temperature dependences of these parameters were ignored. Vaidya et al [11] studied the influences of blood coagulation effect of vessels less than 1 mm in diameter on the ablation results during MWA. The direction of blood flow in the 0.4 mm-0.5 mm vessel had the most significant effect on the coagulation zone.…”