An in silico assessment on the potential of using saline infusion to overcome non-confluent coagulation zone during two-probe, no-touch bipolar radiofrequency ablation of liver cancer
- Authors: Yip, Wai , Kho, Antony , Ooi, Ean , Ooi, Ean Tat
- Date: 2023
- Type: Text , Journal article
- Relation: Medical Engineering and Physics Vol. 112, no. (2023), p.
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- Description: No-touch bipolar radiofrequency ablation (bRFA) is known to produce incomplete tumour ablation with a ‘butterfly-shaped’ coagulation zone when the interelectrode distance exceeds a certain threshold. Although non-confluent coagulation zone can be avoided by not implementing the no-touch mode, doing so exposes the patient to the risk of tumour track seeding. The present study investigates if prior infusion of saline into the tissue can overcome the issues of non-confluent or butterfly-shaped coagulation. A computational modelling approach based on the finite element method was carried out. A two-compartment model comprising the tumour that is surrounded by healthy liver tissue was developed. Three cases were considered; i) saline infusion into the tumour centre; ii) one-sided saline infusion outside the tumour; and iii) two-sided saline infusion outside the tumour. For each case, three different saline volumes were considered, i.e. 6, 14 and 22 ml. Saline concentration was set to 15% w/v. Numerical results showed that saline infusion into the tumour centre can overcome the butterfly-shaped coagulation only if the infusion volume is sufficient. On the other hand, one-sided infusion outside the tumour did not overcome this. Two-sided infusion outside the tumour produced confluent coagulation zone with the largest volume. Results obtained from the present study suggest that saline infusion, when carried out correctly, can be used to effectively eradicate liver cancer. This presents a practical solution to address non-confluent coagulation zone typical of that during two-probe bRFA treatment. © 2023 IPEM
An in silico derived dosage and administration guide for effective thermochemical ablation of biological tissues with simultaneous injection of acid and base
- Authors: Mak, Nguoy , Ooi, Ean , Lau, Ee , Ooi, Ean Tat , Pamidi, Narendra , Foo, Ji , Mohd Ali, Ahmad
- Date: 2022
- Type: Text , Journal article
- Relation: Computer Methods and Programs in Biomedicine Vol. 227, no. (2022), p.
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- Description: Background and objectives: Thermochemical ablation (TCA) is a thermal ablation technique involving the injection of acid and base, either sequentially or simultaneously, into the target tissue. TCA remains at the conceptual stage with existing studies unable to provide recommendations on the optimum injection rate, and reagent concentration and volume. Limitations in current experimental methodology have prevented proper elucidation of the thermochemical processes inside the tissue during TCA. Nevertheless, the computational TCA framework developed recently by Mak et al. [Mak et al., Computers in Biology and Medicine, 2022, 145:105494] has opened new avenues in the development of TCA. Specifically, a recommended safe dosage is imperative in driving TCA research beyond the conceptual stage. Methods: The aforesaid computational TCA framework for sequential injection was applied and adapted to simulate TCA with simultaneous injection of acid and base at equimolar and equivolume. The developed framework, which describes the flow of acid and base, their neutralisation, the rise in tissue temperature and the formation of thermal damage, was solved numerically using the finite element method. The framework will be used to investigate the effects of injection rate, reagent concentration, volume and type (weak/strong acid-base combination) on temperature rise and thermal coagulation formation. Results: A higher injection rate resulted in higher temperature rise and larger thermal coagulation. Reagent concentration of 7500 mol/m3 was found to be optimum in producing considerable thermal coagulation without the risk of tissue overheating. Thermal coagulation volume was found to be consistently larger than the total volume of acid and base injected into the tissue, which is beneficial as it reduces the risk of chemical burn injury. Three multivariate second-order polynomials that express the targeted coagulation volume as functions of injection rate and reagent volume, for the weak-weak, weak-strong and strong-strong acid-base combinations were also derived based on the simulated data. Conclusions: A guideline for a safe and effective implementation of TCA with simultaneous injection of acid and base was recommended based on the numerical results of the computational model developed. The guideline correlates the coagulation volume with the reagent volume and injection rate, and may be used by clinicians in determining the safe dosage of reagents and optimum injection rate to achieve a desired thermal coagulation volume during TCA. © 2022 Elsevier B.V.
Bipolar radiofrequency ablation treatment of liver cancer employing monopolar needles : a comprehensive investigation on the efficacy of time-based switching
- Authors: Yap, Shelley , Ooi, Ean , Foo, Ji , Ooi, Ean Tat
- Date: 2021
- Type: Text , Journal article
- Relation: Computers in Biology and Medicine Vol. 131, no. (2021), p.
- Full Text: false
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- Description: Radiofrequency ablation (RFA) is a thermal ablative treatment method that is commonly used to treat liver cancer. However, the thermal coagulation zone generated using the conventional RFA system can only successfully treat tumours up to 3 cm in diameter. Switching bipolar RFA has been proposed as a way to increase the thermal coagulation zone. Presently, the understanding of the underlying thermal processes that takes place during switching bipolar RFA remains limited. Hence, the objective of this study is to provide a comprehensive understanding on the thermal ablative effects of time-based switching bipolar RFA on liver tissue. Five switch intervals, namely 50, 100, 150, 200 and 300 s were investigated using a two-compartment 3D finite element model. The study was performed using two pairs of RF electrodes in a four-probe configuration, where the electrodes were alternated based on their respective switch interval. The physics employed in the present study were verified against experimental data from the literature. Results obtained show that using a shorter switch interval can improve the homogeneity of temperature distribution within the tissue and increase the rate of temperature rise by delaying the occurrence of roll-off. The coagulation volume obtained was the largest using switch interval of 50 s, followed by 100, 150, 200 and 300 s. The present study demonstrated that the transient thermal response of switching bipolar RFA can be improved by using shorter switch intervals. © 2021 Elsevier Ltd
Comparisons between impedance-based and time-based switching bipolar radiofrequency ablation for the treatment of liver cancer
- Authors: Yap, Shelley , Ooi, Ean , Foo, Ji , Ooi, Ean Tat
- Date: 2021
- Type: Text , Journal article
- Relation: Computers in Biology and Medicine Vol. 134, no. (2021), p.
- Full Text: false
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- Description: Switching bipolar radiofrequency ablation (bRFA) is a cancer treatment technique that activates multiple pairs of electrodes alternately based on a predefined criterion. Various criteria can be used to trigger the switch, such as time (ablation duration) and tissue impedance. In a recent study on time-based switching bRFA, it was determined that a shorter switch interval could produce better treatment outcome than when a longer switch interval was used, which reduces tissue charring and roll-off induced cooling. In this study, it was hypothesized that a more efficacious bRFA treatment can be attained by employing impedance-based switching. This is because ablation per pair can be maximized since there will be no interruption to RF energy delivery until roll-off occurs. This was investigated using a two-compartment 3D computational model. Results showed that impedance-based switching bRFA outperformed time-based switching when the switch interval of the latter is 100 s or higher. When compared to the time-based switching with switch interval of 50 s, the impedance-based model is inferior. It remains to be investigated whether the impedance-based protocol is better than the time-based protocol for a switch interval of 50 s due to the inverse relationship between ablation and treatment efficacies. It was suggested that the choice of impedance-based or time-based switching could ultimately be patient-dependent. © 2021 Elsevier Ltd
Extension of the scaled boundary finite element method to treat implicitly defined interfaces without enrichment
- Authors: Natarajan, Sundararajan , Dharmadhikari, Prasad , Annabattula, Ratna , Zhang, Junqi , Ooi, Ean , Song, Chongmin
- Date: 2020
- Type: Text , Journal article
- Relation: Computers and Structures Vol. 229, no. (2020), p.
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- Description: In this paper, the scaled boundary finite element method (SBFEM) is extended to solve the second order elliptic equation with discontinuous coefficients and to treat weak discontinuities. The salient feature of the proposed technique is that: (a) it requires only the boundary to be discretized and (b) does not require the interface to be discretized. The internal boundaries are represented implicitly by the level set method and the zero level sets are used to identify the different regions. In the regions containing the interface, edges along the boundary are assigned different material properties based on their location with respect to the zero level set. A detailed discussion is provided on the implementation aspects, followed by a few example problems in both two and three dimensions to show the robustness, accuracy and effectiveness of the proposed approach in modelling materials with interfaces. The proposed technique can easily be integrated to any existing finite element code. © 2019 Elsevier Ltd
Modelling strong and weak discontinuities with the scaled boundary finite element method through enrichment
- Authors: Jiang, Shou-yan , Du, Chengbin , Ooi, Ean
- Date: 2019
- Type: Text , Journal article
- Relation: Engineering Fracture Mechanics Vol. 222, no. (Dec 2019), p. 25
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- Description: In this paper, a technique to model strong and weak discontinuities with the scaled boundary finite element method through enrichment is proposed. The main advantage of the method is that the enriched elements, in the spirit of the extended finite element method (XFEM), do not need to physically conform to the geometry of features, e.g. internal interfaces and cracks, and remeshing is unnecessary as the interfaces evolve. All the advantages of the SBFEM and the XFEM are retained. The stress singularity at the crack tip can be captured accurately and the stress intensity factors (SIFs) can be directly computed based on the singular displacement or stress at the crack tip within the framework of the SBFEM. The numerical properties and performance for the proposed method are assessed using several numerical examples. In particular, problems with discontinuities, e.g. voids, inclusions, and cracks are analysed. The results show that the accuracy and convergence rate of the new approach for solving void or inclusion problems are identical to those of the XFEM, but requires less number of degrees-of-freedom than the XFEM. For crack problems, compared with the XFEM with topological enrichment, the developed method is superior.
The effects of vaporisation, condensation and diffusion of water inside the tissue during saline-infused radiofrequency ablation of the liver: A computational study
- Authors: Kho, Antony , Ooi, Ean , Foo, Ji , Ooi, Ean Tat
- Date: 2022
- Type: Text , Journal article
- Relation: International journal of heat and mass transfer Vol. 194, no. (2022), p. 123062
- Full Text: false
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- Description: •Effect of vaporisation, condensation & diffusion on saline-infused RFA was studied.•Condensation significantly affects the prediction of the RFA treatment outcome.•Water diffusion is insignificant when compared to condensation.•The model serves as benchmark for the accurate modelling of saline-infused RFA. [Display omitted] 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.