Parametric evaluation of impedance curve in radiofrequency ablation: A quantitative description of the asymmetry and dynamic variation of impedance in bovine ex vivo model

Radiofrequency ablation (RFA) is a treatment for liver tumors with advantages over the traditional treatment of surgical resection. This procedure has the shortest recovery time in early stage tumors. The objective of this study is to parameterize the impedance curve of the RFA procedure in an ex vivo model by defining seven parameters (t1/2, tminimum, tend, Zinitial, Z1/2, Zminimum and Zend). Based on these parameters, three performance indices are defined: one to identify the magnitude of impedance curve asymmetry (δ), one Drop ratio (DR) describing the percentage of impedance decrease until the minimum impedance point is reached, and Ascent Ratio (AR) describing the magnitude of increase in impedance from the minimum impedance point to its maximum point. Fifty ablations were performed in a bovine ex vivo model to measure and evaluate the proposed parameters and performance index. The results show that the groups had an average δ of 29.02%, DR of 22.41%, and AR of 545.33% for RFA without the use of saline or deionized solutions. The saline solution and deionized water-cooled groups indicated the correlation of performance indices δ, DR, and AR with the obtained final ablation volume. Therefore, by controlling these parameters and indices, lower recurrence is achieved.

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Radiofrequency ablation for hepatocellular carcinoma - analysis of the clinical outcome

Srpski arhiv za celokupno lekarstvo ◽

10.2298/sarh160617096m ◽

2017 ◽

Vol 145 (9-10) ◽

pp. 475-480

Author(s):

Dragan Masulovic ◽

Danijel Galun ◽

Ruza Stevic ◽

Aleksandar Filipovic ◽

Aleksandar Bogdanovic ◽

...

Keyword(s):

Hepatocellular Carcinoma ◽

Radiofrequency Ablation ◽

Clinical Outcome ◽

Liver Tumors ◽

Early Stage ◽

Post Treatment ◽

Liver Imaging ◽

Invasive Treatment ◽

Liver Transaminase ◽

Liver Specific Contrast Agent

Introduction/Objective. Radiofrequency ablation (RFA) is a minimally invasive treatment modality for primary and metastatic liver tumors. It can be performed percutaneously or as a laparoscopic or open surgical procedure under ultrasound or computerized tomography guidance. The objective of the study was to evaluate the clinical outcome of the initial 16 patients with hepatocellular carcinoma (HCC) managed by percutaneous RFA at a tertiary institution and to assess the efficacy of this procedure in the management of selected patients with HCC. Method. From June 2011 until December 2013, 16 patients with early-stage HCC were managed by percutaneous radiofrequency ablation at the Clinic for Digestive Surgery, Clinical Center of Serbia, Belgrade. All the patients were treated by the same team composed of an interventional radiologist and a liver surgeon. We analyzed the clinical outcome and the biologic effect of this treatment by comparing the pre- and post-treatment levels of alpha-fetoprotein (AFP). Results. Post-treatment values of liver transaminase levels returned to the pre-treatment values from Day 3. Post-treatment hospital stay was two days. Post-procedural complications included mild pain in all patients, skin necrosis at the site of the electrode puncture in five patients, and transient hepatic decompensation in one patient. In all the patients the AFP level correlated with the findings of liver imaging (ultrasound and/or magnetic resonance imaging with liver-specific contrast agent) indicating viability of the treated tumor. Conclusion. RFA is a feasible and effective procedure providing favorable clinical outcome in patients with early-stage HCC.

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Quantification of Thermal Injury to the Healthy Tissue Due to Imperfect Electrode Placements During Radiofrequency Ablation of Breast Tumor

Journal of Engineering and Science in Medical Diagnostics and Therapy ◽

10.1115/1.4038237 ◽

2017 ◽

Vol 1 (1) ◽

Cited By ~ 1

Author(s):

Sundeep Singh ◽

Ramjee Repaka

Keyword(s):

Radiofrequency Ablation ◽

Breast Tumor ◽

Treatment Time ◽

Numerical Study ◽

Early Stage ◽

Healthy Tissue ◽

Bioheat Transfer ◽

Electrode Placement ◽

Heterogeneous Model ◽

Ablation Volume

Radiofrequency ablation (RFA) has emerged as an alternative treatment modality for treating various tumors with minimum intervention. The application of RFA in treating breast tumor is still in its infancy stage. Nevertheless, promising results have been obtained while treating early stage localized breast cancer with RFA procedure. The outcome of RFA is tremendously dependent on the precise insertion of the electrode into the geometric center of the tumor. However, there remains plausible chances of inaccuracies in the electrode placement that can result in slight displacement of the electrode tip from the actual desired location during temperature-controlled RFA application. The present numerical study aims at capturing the influence of inaccuracies in electrode placement on the input energy, treatment time and damage to the surrounding healthy tissue during RFA of breast tumor. A thermo-electric analysis has been performed on three-dimensional heterogeneous model of multilayer breast with an embedded early stage spherical tumor of 1.5 cm. The temperature distribution during the RFA has been obtained by solving the coupled electric field equation and Pennes bioheat transfer equation, while the ablation volume has been computed using the Arrhenius cell death model. It has been found that significant variation in the energy consumption, time required for complete tumor necrosis, and the shape of ablation volume among different positions of the electrode considered in this study are prevalent.

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Finding Optimal Ablation Parameters for Multipolar Radiofrequency Ablation

Surgical Innovation ◽

10.1177/1553350617692492 ◽

2017 ◽

Vol 24 (3) ◽

pp. 205-213 ◽

Cited By ~ 3

Author(s):

Franz G. M. Poch ◽

Christian Rieder ◽

Hanne Ballhausen ◽

Verena Knappe ◽

Jörg Peter Ritz ◽

...

Keyword(s):

Radiofrequency Ablation ◽

Energy Input ◽

Liver Tumors ◽

Ex Vivo ◽

Test Series ◽

Cross Sectional ◽

Primary Liver Tumors ◽

Ablation Area ◽

Energy Inputs ◽

Internally Cooled

Purpose. Radiofrequency ablation (RFA) for primary liver tumors and liver metastases is restricted by a limited ablation size. Multipolar RFA is a technical advancement of RFA, which is able to achieve larger ablations. The aim of this ex vivo study was to determine optimal ablation parameters for multipolar RFA depending on applicator distance and energy input. Methods. RFA was carried out ex vivo in porcine livers with three internally cooled, bipolar applicators in multipolar ablation mode. Three different applicator distances were used and five different energy inputs were examined. Ablation zones were sliced along the cross-sectional area at the largest ablation diameter, orthogonally to the applicators. These slices were digitally measured and analyzed. Results. Sixty RFA were carried out. A limited growth of ablation area was seen in all test series. This increase was dependent on ablation time, but not on applicator distance. A steady state between energy input and energy loss was not observed. A saturation of the minimum radius of the ablation zone was reached. Differences in ablation radius between the three test series were seen for lowest and highest energy input ( P < .05). No differences were seen for medium amounts of energy ( P > .05). Conclusions. The ablation parameters applicator distance and energy input can be chosen in such a way, that minor deviations of the preplanned ablation parameters have no influence on the size of the ablation area.

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Design of a Novel Electrode of Radiofrequency Ablation for Large Tumors: A Finite Element Study

Journal of Engineering and Science in Medical Diagnostics and Therapy ◽

10.1115/1.4038129 ◽

2017 ◽

Vol 1 (1) ◽

Cited By ~ 5

Author(s):

Zheng Fang ◽

Bing Zhang ◽

Michael Moser ◽

Edwin Zhang ◽

Wenjun Zhang

Keyword(s):

Finite Element ◽

Radiofrequency Ablation ◽

Liver Tumor ◽

Liver Tumors ◽

Safety Margin ◽

Ablation Volume ◽

Sphericity Index ◽

Tissue Interface ◽

Temperature Controlled ◽

Complete Tumor

The aim of the study was to design a novel radiofrequency (RF) electrode for larger and rounder ablation volumes and its ability to achieve the complete ablation of liver tumors larger than 3 cm in diameter using finite element method. A new RF expandable electrode comprising three parts (i.e., insulated shaft, changing shaft, and hooks) was designed. Two modes of this new electrode, such as monopolar expandable electrode (MEE) and hybrid expandable electrode (HEE), and a commercial expandable electrode (CEE) were investigated using liver tissue with (scenario I) and without (scenario II) a liver tumor. A temperature-controlled radiofrequency ablation (RFA) protocol with a target temperature of 95 °C and an ablation time of 15 min was used in the study. Both the volume and shape of the ablation zone were examined for all RF electrodes in scenario I. Then, the RF electrode with the best performance in scenario I and CEE were used to ablate a large liver tumor with the diameter of 3.5 cm (scenario II) to evaluate the effectiveness of complete tumor ablation of the designed RF electrode. In scenario I, the ablation volumes of CEE, HEE, and MEE were 12.11 cm3, 33.29 cm3, and 48.75 cm3, respectively. The values of sphericity index (SI) of CEE, HEE, and MEE were 0.457, 0.957, and 0.976, respectively. The best performance was achieved by using MEE. In scenario II, the ablation volumes of MEE and CEE were 71.59 cm3 and 19.53 cm3, respectively. Also, a rounder ablation volume was achieved by using MEE compared to CEE (SI: 0.978 versus 0.596). The study concluded that: (1) compared with CEE, both MEE and HEE get larger and rounder ablation volumes due to the larger electrode–tissue interface and rounder shape of hook deployment; (2) MEE has the best performance in getting a larger and rounder ablation volume; and (3) computer simulation result shows that MEE is also able to ablate a large liver tumor (i.e., 3.5 cm in diameter) completely, which has at least 0.785 cm safety margin.

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Early Assessment of Response to Radiofrequency Ablation With CT Perfusion Imaging in Rabbit VX2 Liver Tumor Model

Frontiers in Oncology ◽

10.3389/fonc.2021.728781 ◽

2021 ◽

Vol 11 ◽

Author(s):

Xiaofei Yue ◽

Xiangjun Dong ◽

Mengting Huang ◽

Hongli Yang ◽

Kun Qian ◽

...

Keyword(s):

Radiofrequency Ablation ◽

High Efficiency ◽

Liver Tumors ◽

Ct Perfusion ◽

Early Stage ◽

Liver Perfusion ◽

Tumor Model ◽

Diagnostic Value ◽

Early Assessment ◽

Speed Up

ObjectivesTo discriminate viable tumors from benign periablational enhancement (BPE) in early stage after radiofrequency ablation (RFA) is a major confounding problem. The goal of this study is to evaluate quantitative assessment and diagnostic value of CT perfusion between viable tumors and BPE after RFA in the rabbit liver VX2 tumor model, with pathological results as the standard.MethodsTwenty-eight VX2 liver tumors were treated with RFA, on days 1, 3, 7, and 14, seven rabbits were randomly chosen for CT perfusion and performed pathology examinations immediately. The perfusion parameters along with the profile of time-density curves (TDCs) and pseudo-color images of the parameters were observed in both BPE and viable tumors, then compared with the pathology results. The perfusion parameters included blood flow (BF), blood volume (BV), time to peak (TTP), permeability (P), arterial liver perfusion (ALP), portal venous perfusion (PVP) and hepatic perfusion index (HPI).ResultsA total of 26/28 rabbits successfully underwent CT perfusion, while 6/26 lesions were confirmed to be viable tumors. The TDCs of BPE were mainly speed-up platform curves (15/26), while the viable tumors showed mainly speed-up speed-down (3/6) and speed-up platform (2/6) curves. The PVP values were significantly higher, and the HPI values were significantly lower for BPE at all time points than viable tumors (P < 0.05). Both of PVP value and HPI value have high efficiency for the differential diagnosis of the viable tumors and BPE at each time point. These characteristics of CT perfusion parameters were consistent with pathological changes.ConclusionsThe TDCs, PVP and HPI have the potential to indicate BPE and viable tumors effectively early after RFA treatment, the results were highly consistent with pathology. CT perfusion has advantages with great efficacy in monitoring the therapeutic effect early after RFA treatment.

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Design of a Novel Electrode of Radiofrequency Ablation for Large Tumors: A Finite Element Study

Volume 3: Biomedical and Biotechnology Engineering ◽

10.1115/imece2017-70841 ◽

2017 ◽

Author(s):

Zheng Fang ◽

Bing Zhang ◽

Michael Moser ◽

Edwin Zhang ◽

Wenjun Zhang

Keyword(s):

Finite Element ◽

Radiofrequency Ablation ◽

Liver Tumor ◽

Liver Tumors ◽

Ablation Volume ◽

Round Shape ◽

Complete Ablation ◽

Sphericity Index ◽

Tissue Interface ◽

Temperature Controlled

Objective: The aim of this study was to design a novel radiofrequency (RF) electrode for larger and more round ablation volumes and its ability to achieve the complete ablation of liver tumors (> 3 cm in diameter) using finite element method. Methods: A new RF expandable electrode comprising three parts (i.e., insulated shaft, changing shaft, and hooks) was designed. Two modes of this new electrode (i.e., monopolar expandable electrode (MEE) and hybrid expandable electrode (HEE)) and a commercial expandable electrode (CEE) were investigated using liver tissue with and without liver tumor. A temperature-controlled radiofrequency ablation (RFA) protocol with a target temperature of 95 °C and an ablation time of 15 minutes was used in this study. Both the volume and shape of the ablation zone were studied for all RF electrodes. A large liver tumor with the diameter of 3.5 cm was used to evaluate the effectiveness on the complete ablation of the new designed electrode. Results: In the first scenario (without liver tumor), the ablation volumes of CEE, HEE, and MEE were 9.96 cm3, 41.0 cm3, and 46.14 cm3, respectively. The values of sphericity index (SI) of CEE, HEE, and MEE were 0.36, 0.94, and 0.98, respectively. The best performance was achieved by the MEE electrode. In the second scenario (with liver tumor), the ablation volumes of MEE and CEE were 67.56 cm3 and 20.62 cm3, respectively. Also, a rounder ablation volume was generated by MEE compared to CEE (SI: 0.98 vs 0.55). Conclusion: This study concludes that compared with CEE, both MEE and HEE are able to get larger and more round ablation volumes due to the larger electrode-tissue interface and more round shape of hooks; compared with HEE, MEE is better to get a larger and rounder ablation volume; MEE is able to ablate a large liver tumor (i.e., 3.5 cm in diameter) completely.

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Ex vivo quantification of the cooling effect of liver vessels on radiofrequency ablation volume

Deutsche Gesellschaft für Chirurgie - Chirurgisches Forum und DGAV Forum 2009 ◽

10.1007/978-3-642-00625-8_36 ◽

2009 ◽

pp. 93-94

Author(s):

K. S. Lehmann ◽

B. B. Frericks ◽

S. Valdeig ◽

P. Hoffmann ◽

A. Schenk ◽

...

Keyword(s):

Radiofrequency Ablation ◽

Ex Vivo ◽

Cooling Effect ◽

Ablation Volume

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Annular Fiber Probe for Interstitial Illumination in Photoacoustic Guidance of Radiofrequency Ablation

Sensors ◽

10.3390/s21134458 ◽

2021 ◽

Vol 21 (13) ◽

pp. 4458

Author(s):

Hindrik Kruit ◽

Kalloor Joseph Francis ◽

Elina Rascevska ◽

Srirang Manohar

Keyword(s):

Radiofrequency Ablation ◽

Real Time ◽

Optical Fibers ◽

Liver Tumors ◽

Ex Vivo ◽

Bovine Liver ◽

Needle Guidance ◽

Recurrence Rates ◽

Fiber Probe ◽

Device Guidance

Unresectable liver tumors are commonly treated with percutaneous radiofrequency ablation (RFA). However, this technique is associated with high recurrence rates due to incomplete tumor ablation. Accurate image guidance of the RFA procedure contributes to successful ablation, but currently used imaging modalities have shortcomings in device guidance and treatment monitoring. We explore the potential of using photoacoustic (PA) imaging combined with conventional ultrasound (US) imaging for real-time RFA guidance. To overcome the low penetration depth of light in tissue, we have developed an annular fiber probe (AFP), which can be inserted into tissue enabling interstitial illumination of tissue. The AFP is a cannula with 72 optical fibers that allows an RFA device to slide through its lumen, thereby enabling PA imaging for RFA device guidance and ablation monitoring. We show that the PA signal from interstitial illumination is not affected by absorber-to-surface depth compared to extracorporeal illumination. We also demonstrate successful imaging of the RFA electrodes, a blood vessel mimic, a tumor-mimicking phantom, and ablated liver tissue boundaries in ex vivo chicken and bovine liver samples. PA-assisted needle guidance revealed clear needle tip visualization, a notable improvement to current US needle guidance. Our probe shows potential for RFA device guidance and ablation detection, which potentially aids in real-time monitoring.

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