Saline-infused Radiofrequency Ablation Research Articles

The effects of vaporisation, condensation and diffusion of water inside the tissue during saline-infused radiofrequency ablation of the liver: A computational study

Saline-infused radiofrequency ablation (RFA) is a thermal ablation technique that combines saline infusion and Joule heating to destroy cancer tissues. During treatment, the intense heat generated can cause water from the infused saline and inside the tissue to vaporise. Conventionally, the effects of vaporisation have been modelled by adopting the apparent heat capacity method. However, this approach does not account for the loss of water content during vaporisation, which raises questions on its accuracy, primarily because of the large water content present during saline-infused RFA. To address this, the present study proposes an alternative approach to model vaporisation effects during saline-infused RFA. The approach adopts and modifies the water fraction method to account for the effects of vaporisation, condensation and diffusion of water inside the tissue during saline-infused RFA. The framework was compared against the commonly used apparent heat capacity method through numerical simulations carried out on 3D finite element models of the liver. Results indicated that unlike condensation, the role of diffusion of water during saline-infused RFA was not as significant as condensation, where the latter was found to affect the ablation process. With the water fraction method, there was a trend of exponential decrease in tissue electrical conductivity with time, which ultimately led to the prediction of smaller coagulation volume than that of the apparent heat capacity method.

The Effects of Vaporisation, Condensation and Diffusion of Water Inside the Tissue During Saline-Infused Radiofrequency Ablation of the Liver: A Computational Study

The Effects of Vaporisation, Condensation and Diffusion of Water Inside the Tissue During Saline-Infused Radiofrequency Ablation of the Liver: A Computational Study

How does saline backflow affect the treatment of saline-infused radiofrequency ablation?

Background and objective: Saline infusion is applied together with radiofrequency ablation (RFA) to enlarge the ablation zone. However, one of the issues with saline-infused RFA is backflow, which spreads saline along the insertion track. This raises the concern of not only thermally ablating the tissue within the backflow region, but also the loss of saline from the targeted tissue, which may affect the treatment efficacy. Methods: In the present study, 2D axisymmetric models were developed to investigate how saline backflow influence saline-infused RFA and whether the aforementioned concerns are warranted. Saline-infused RFA was described using the dual porosity-Joule heating model. The hydrodynamics of backflow was described using Poiseuille law by assuming the flow to be similar to that in a thin annulus. Backflow lengths of 3, 4.5, 6 and 9 cm were considered. Results: Results showed that there is no concern of thermally ablating the tissue in the backflow region. This is due to the Joule heating being inversely proportional to distance from the electrode to the fourth power. Results also indicated that larger backflow lengths led to larger growth of thermal damage along the backflow region and greater decrease in coagulation volume. Hence, backflow needs to be controlled to ensure an effective treatment of saline-infused RFA. Conclusions: There is no risk of ablating tissues around the needle insertion track due to backflow. Instead, the risk of underablation as a result of the loss of saline due to backflow was found to be of greater concern.

Role of saline concentration during saline-infused radiofrequency ablation: Observation of secondary Joule heating along the saline-tissue interface

Infusion of saline prior to radiofrequency ablation (RFA) is known to enlarge the thermal coagulation zone. The abundance of ions in saline elevate the electrical conductivity of the saline-saturated region. This promotes greater electric current flow inside the tissue, which increases the amount of RF energy deposition and subsequently enlarges the coagulation zone. In theory, infusion of higher concentration of saline should lead to larger coagulation zone due to the greater number of ions. Nevertheless, existing studies on the effects of concentration on saline-infused RFA have been conflicting, with the exact role of saline concentration yet to be fully elucidated. In this paper, computational models of saline-infused RFA were developed to investigate the role of saline concentration on the outcome of saline-infused RFA. The elevation in tissue electrical conductivity was modelled using the microscopic mixture model, while RFA was modelled using the coupled dual porosity-Joule heating model. Results obtained indicated that the presence of a concentration threshold to which no further elevation in tissue electrical conductivity and enlargement in thermal coagulation can occur. This threshold was determined to be at 15% NaCl. Analysis of the Joule heating distribution revealed the presence of a secondary Joule heating site located along the interface between wet and dry tissue. This secondary Joule heating was responsible for the enlargement in coagulation volume and its rapid growth phase during ablation.

Shape-shifting thermal coagulation zone during saline-infused radiofrequency ablation: A computational study on the effects of different infusion location

Background and objective: The majority of the studies on radiofrequency ablation (RFA) have focused on enlarging the size of the coagulation zone. An aspect that is crucial but often overlooked is the shape of the coagulation zone. The shape is crucial because the majority of tumours are irregularly-shaped. In this paper, the ability to manipulate the shape of the coagulation zone following saline-infused RFA by altering the location of saline infusion is explored.Methods: A 3D model of the liver tissue was developed. Saline infusion was described using the dual porosity model, while RFA was described using the electrostatic and bioheat transfer equations. Three infusion locations were investigated, namely at the proximal end, the middle and the distal end of the electrode. Investigations were carried out numerically using the finite element method.Results: Results indicated that greater thermal coagulation was found in the region of tissue occupied by the saline bolus. Infusion at the middle of the electrode led to the largest coagulation volume followed by infusion at the proximal and distal ends. It was also found that the ability to delay roll-off, as commonly associated with saline-infused RFA, was true only for the case when infusion is carried out at the middle. When infused at the proximal and distal ends, the occurrence of roll-off was advanced. This may be due to the rapid and more intense heating experienced by the tissue when infusion is carried out at the electrode ends where Joule heating is dominant.Conclusion: Altering the location of saline infusion can influence the shape of the coagulation zone following saline-infused RFA. The ability to ‘shift’ the coagulation zone to a desired location opens up great opportunities for the development of more precise saline-infused RFA treatment that targets specific regions within the tissue.

In Vitro Bovine Liver Experiment of Cisplatin-Infused and Normal Saline-Infused Radiofrequency Ablation with an Internally Cooled Perfusion Electrode

To evaluate the efficacy of cisplatin-infused and normal saline-infused radiofrequency ablation (RFA) with internally cooled perfusion (ICP) electrode. Using a 200W generator, thirty ablation zones were created and divided into three groups of 10 each as follows: group A, RFA alone with 16 gauge monopolar internally cooled (IC) electrode; group B, cisplatin-infused RFA with 16 gauge ICP electrode; and group C, normal saline-infused RFA with 16 gauge ICP electrode. Radiofrequency was applied to the explanted bovine liver for 12min. During RFA, cisplatin and normal saline were injected into tissue at a rate of 0.5mL/min through the ICP electrode by injection pump. Dimensions of the ablation zone and technical parameters were compared between the three groups. In the cisplatin-infused RFA group, the ablation zone size was significantly larger than that of the RFA-alone group but significantly smaller than normal saline-infused RFA group. The width of longitudinal section and volume were 3.39 ± 0.22cm2 and 26.55 ± 4.62cm3 in RFA-alone group, 3.88 ± 0.32cm2 and 36.45 ± 5.46cm3 in cisplatin-infused RFA group, and 4.52 ± 0.50cm2 and 49.44 ± 7.55cm3 in normal saline-infused RFA group, respectively (p < 0.05 between any two groups). The mean impedance in group A, B, and C were 60.0 ± 7.2, 50.3 ± 2.5, and 40.3 ± 4.0 Ω, respectively (p < 0.05 between any two groups). Cisplatin-infused RFA with ICP electrode created the larger size of ablation zone than that of monopolar RFA with an IC electrode, but created the smaller size of ablation zone than that of normal saline-infused RFA.

Abstract No. 685 In vitro bovine liver experiment of cisplatin-infused and normal saline-infused radiofrequency ablation with an internally cooled perfusion electrode

Cisplatin is an effective agent for the treatment of many malignant tumors and is mainly administered through intraarterial or intravenous route. Internally cooled perfusion electrode allows interstitial solution infusion during radiofrequency ablation (RFA). Purpose of this study was to evaluate the influence of cisplatin-infused and normal saline-infused radiofrequency ablation with internally cooled perfusion electrode on the size of ablated lesions. Using a 200W generator, thirty ablation zones were divided into three groups of 10 each and created as follows: group A, RFA alone with 16 gauge monopolar internally cooled electrode; group B, cisplatin-infused RFA with 16 gauge internally cooled perfusion electrode; and group C, normal saline-infused RFA with 16 gauge internally cooled perfusion electrode. RF was applied to the explanted bovine liver for 12 minutes. During RFA, cisplatin and normal saline were injected into tissue at a rate of 0.5 mL/min through the internally cooled perfusion electrode by injection pump. Dimensions of the ablation zone and technical parameters were compared between the three groups. In the cisplatin-infused RFA group, the ablation zone size was significantly larger than that of the RFA alone group but significantly smaller than normal saline-infused RFA group. The width of longitudinal section and volume were 3.39 ± 0.22 cm2 and 26.55 ± 4.62 cm3 in RFA alone group, 3.88 ± 0.32 cm2 and 36.45 ± 5.46 cm3 in cisplatin-infused RFA group, and 4.52 ± 0.50 cm2 and 49.44 ± 7.55 cm3 in normal saline-infused RFA group, respectively (p<0.05 between any two groups). The mean impedance in group A, B, and C were 60.0 ± 7.2, 50.3 ± 2.5, and 40.3 ± 4.0 Ω, respectively (p<0.05 between any two groups). Cisplatin-infused RFA with internally cooled perfusion electrode created the larger size of ablation zone than that of monopolar RFA with an internally cooled electrode, but created the smaller size of ablation zone than that of normal saline-infused RFA.

Comparison between single- and dual-porosity models for fluid transport in predicting lesion volume following saline-infused radiofrequency ablation

A recent study by Ooi and Ooi (EH Ooi, ET Ooi, Mass transport in biological tissues: Comparisons between single- and dual-porosity models in the context of saline-infused radiofrequency ablation, Applied Mathematical Modelling, 2017, 41, 271-284) has shown that single-porosity (SP) models for describing fluid transport in biological tissues significantly underestimate the fluid penetration depth when compared to dual-porosity (DP) models. This has raised some concerns on whether the SP model, when coupled with models of radiofrequency ablation (RFA) to simulate saline-infused RFA, could lead to an underestimation of the coagulation size. This paper compares the coagulation volumes obtained following saline-infused RFA predicted based on the SP and DP models for fluid transport. Results showed that the SP model predicted coagulation zones that are consistently 0.5 to 0.9 times smaller than that of DP model. This may be explained by the low permeability value of the tissue interstitial space, which causes the majority of the saline to flow through the vasculature. The absence of fluid flow tracking in the vasculature in the SP model meant that any flow of saline into the vasculature is treated as losses and do not contribute to the saline penetration depth of the tissue. Comparisons with experimental results from the literature revealed that the DP models predicted coagulation zone sizes that are closer to the experimental values than the SP models. This supports the hypothesis that the SP model is a poor choice for simulating the outcome of saline-infused RFA.

Effects of saline volume on lesion formation during saline-infused radiofrequency ablation

Radiofrequency ablation (RFA) is hindered when tissue temperature reaches 100 °C. At this temperature, tissue vaporization occurs, which prevents electrical currents from flowing into the tissue. Smaller lesions are created as a result. One way to overcome this is to infuse saline into the tissue prior to RFA. Saline can increase the electrical conductivity of the surrounding tissue due to the abundance of ions inside the solution. This permits a greater distribution of electrical currents that can lead to larger lesion sizes. Although this procedure has been shown to produce larger lesions, the technique is risky due to the potential for the saline to extravasate into healthy regions of the tissue; hence, leading to unnecessary ablation. A computational model is developed in this paper to predict the formation of lesion following saline-infused RFA. The model incorporates the transport of saline inside the tissue, the resistive heating during ablation and the formation of lesion through cell death modeling. Results show that there is an optimal infusion volume that leads to the largest increase in the lesion size. With further developments, the model may be used for the planning of saline-infused RFA treatment.

Mass transport in biological tissues: Comparisons between single- and dual-porosity models in the context of saline-infused Radiofrequency Ablation

Conventional method for modelling mass transport in biological tissues is based on the single-porosity (SP) model, which assumes a homogeneous pressure and concentration in the vasculature. Over the years, the dual-porosity (DP) model, which was originally derived for describing water flow in fractured rocks, has seen an increase in its application to describe flow in biological tissues. In DP models, two porous continua (the interstitium and the vasculature) co-exist within the same space. Flows in both continua are modelled explicitly, which allows for a more accurate representation of the hydraulic interaction between the interstitium and the vasculature. This raises the question on the validity and accuracy of the SP model for describing saline transport in biological tissues. This paper seeks to answer this question by performing a comparative study on the numerical predictions obtained using the SP and DP models in the context of saline-infused radiofrequency ablation (RFA). The results suggest that the SP model has a tendency to underestimate the saline penetration depth inside the tissue. Results from the present study are applicable only in the context of saline-infused radiofrequency ablation. They should not be generalized to other medical and biological applications, as comparison between the SP and DP models for these applications may yield observations that are different from those in the present study.

Ex Vivo Liver Experiment of Hydrochloric Acid-Infused and Saline-Infused Monopolar Radiofrequency Ablation: Better Outcomes in Temperature, Energy, and Coagulation.

To compare temperature, energy, and coagulation between hydrochloric acid-infused radiofrequency ablation (HAIRFA) and normal saline-infused radiofrequency ablation (NSIRFA) in ex vivo porcine liver model. 30 fresh porcine livers were excised in 60 lesions, 30 with HAIRFA and the other 30 with NSIRFA. Both modalities used monopolar perfusion electrode connected to a RF generator set at 103 °C and 30 W. In each group, ablation time was set at 10, 20, or 30 min (10 lesions from each group at each time). We compared tissue temperatures (at 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 cm away from the electrode tip), average power, deposited energy, deposited energy per coagulation volume (DEV), coagulation diameters, coagulative volume, and spherical ratio between the two groups. Temperature-time curves showed that HAIRFA provided progressively greater heating than that of NSIRFA. At 30 min, mean average power, deposited energy, coagulation volumes (113.67 vs. 12.28 cm(3)) and diameters, and increasing in tissue temperature were much greater with HAIRFA (P < 0.001 for all), except DEV was lower (456 vs. 1396 J/cm(3), P < 0.001). The spherical ratio was closer to 1 with HAIRFA (1.23 vs. 1.46). Coagulation diameters, volume, and average power of HAIRFA increased significantly with longer ablation times. While with NSIRFA, these characteristics were stable till later 20 min, except the power decreased with longer ablation times. HAIRFA creates much larger and more spherical lesions by increasing overall energy deposition, modulating thermal conductivity, and transferring heat during ablation.

Estimation of saline-mixed tissue conductivity and ablation lesion size

In radiofrequency ablation (RFA), saline infusion is beneficial for enhancing electrical conductivity, which allows more energy dissipation into target tissue, resulting in increased lesion size. Computational simulation has been a popular method to estimate lesion size from RFA treatment, but it has not been used effectively for saline-infused RFA, for lack of methods to address the conductivity properties of saline–tissue mixtures. To fill this gap, we propose a microscopic mixture model to derive the effective temperature-dependent conductivities of a saline–tissue mixture. We modeled a small block of 6% hypertonic saline-infused liver tissue as a 1×1×1cm cube, which was divided into 64–1000 elements, with each element representing either liver tissue or saline. A 1:1 mixing of saline and liver tissue was assumed to calculate the effective conductivities at 30, 50, 70, and 90°C. Different mixing conditions (2:1 and 1:2 of saline to liver tissue) were also tested to observe the effect of mixing ratio on the resulting data. Then, the derived conductivities were applied for 3D hypertonic saline-infused RFA simulation. The results matched our previous experimental measurements within 13%. The proposed model is customizable in constructing mixtures of multiple components, and can thus be expanded to include the effects of various anatomical microstructures and materials.

COMPARISON OF LAPAROSCOPIC SALINE INFUSED TO DRY RADIO FREQUENCY ABLATION OF RENAL TISSUE: EVOLUTION OF HISTOLOGICAL INFARCT IN THE PORCINE MODEL

We investigated and compared the gross and histopathological features of radio frequency (RF) ablated renal tissue using saline infused RF ablation (RFA) vs dry RFA in a porcine model. Ten porcine kidneys underwent laparoscopic RFA. The lower and upper poles of each right kidney were treated with 1 and 2 cycles of saline augmented (wet) RFA, respectively. The upper pole of each left kidney was RF ablated without saline infusion (dry RFA) and a control lesion was created in the lower pole. The animals were sacrificed immediately after ', 2 and 9 days after (subacute), and 14 and 21 days after (chronic) treatment, respectively. Gross pathological and histological changes caused by the different RF treatments were compared. Mean time to attain target temperature was shorter with wet than with dry RFA. Grossly the lesion sizes achieved were larger using wet RFA but independent of the number of wet RFA treatment cycles. Gross lesion sizes decreased with time for each treatment modality. No histopathological differences were seen between the 2 RFA treatment modalities as well as between 1 vs 2 cycles of wet RFA. In the acute phase hematoxylin and eosin staining of ablated tissue revealed focal areas of alterations in renal tubular histology. However, nicotinamide adenine dinucleotide staining of corresponding areas confirmed the lack of cellular viability except for glomeruli. In the subacute phase there were focal coagulation necrosis and thrombosed blood vessels. Within the necrotic areas the glomeruli were the last structures to lose viability. In the chronic phase fibrosis with decreased lesion size was seen. Nicotinamide adenine dinucleotide staining demonstrated that the cellular kill was permanent during the entire study period. The effects of RFA of renal tissue has 2 phases, namely initial direct thermal ablation causing acute cell death and a later subacute phase causing subsequent infarction of the distal arterial vascular supply to the ablated region, resulting in more cell death and coagulative necrosis. Glomeruli are the last structures to lose viability in necrotic areas. Most importantly cellular death caused by RFA is permanent.