Design of a Novel Electrode of Radiofrequency Ablation for Large Tumors: In Vitro Validation and Evaluation.

In a prior study, we proposed a novel monopolar expandable electrode (MEE) for use in radiofrequency ablation (RFA). The purpose of our work was to now validate and evaluate this electrode using on in vitro experimental model and computer simulation. Two commercially available RF electrodes (conventional electrode (CE) and umbrella electrode (UE)) were used to compare the ablation results with the novel MEE using an in vitro egg white model and in vivo liver tumor model to verify the efficacy of MEE in the large tumor ablation, respectively. The sharp increase in impedance during RFA procedures was taken as the termination of RFA protocols. In the in vitro egg white experiment, the ablation volume of MEE, CE, and UE was 75.3 ± 1.6 cm3, 2.7 ± 0.4 cm3, and 12.4±1.8 cm3 (P < 0.001), respectively. Correspondingly, the sphericity was 88.1±0.9%, 12.9±1.3%, and 62.0 ± 3.0% (P < 0.001), respectively. A similar result was obtained in the in vitro egg white computer simulation. In the liver tumor computer simulation, the volume and sphericity of ablation zone generated by MEE, CE, and UE were 36.6 cm3 and 93.6%, 3.82 cm3 and 16.9%, and 13.5 cm3 and 56.7%, respectively. In summary, MEE has the potential to achieve complete ablation in the treatment of large tumors (>3 cm in diameter) compared to CE and UE due to the larger electrode-tissue interface and more round shape of hooks.

A new approach to feedback control of radiofrequency ablation systems for large coagulation zones.

AIM: The aim of this study was to investigate the feasibility of achieving relatively large coagulation zones (i.e. ≥3 cm in diameter) with radiofrequency ablation (RFA) by using a broad control system. MATERIALS AND METHODS: A broad control system consists of information such as (i) the area of the tumour tissue for feedback control, (ii) the set-point temperature and (iii) the control law. The proposed approach has advanced knowledge in (i) and (ii) in particular. RFA is known to be limited by tissue dehydration that occurs around the electrode, which results in impedance such that no further energy can be delivered to the tissues. We proposed the notion of "energy gate", an area on the electrode, which is not covered by the dehydrated tissue and through which energy can still be delivered to the surrounding tissues. Given a specific size of energy gate, both (i) the area of the tissue in which the temperature is monitored and (ii) the set-point temperature were determined. A reliable finite element model or simulator for a commercially available electrode was used and the tissue surrounding the RFA electrode was divided into three areas for a comprehensive study of the issues (i) and (ii). Porcine liver tissue (30 specimens in total) and a custom-made RFA device with a RF power generator (100 W and 460 ± 30 kHz) and a Covidien cool-tip electrode (17 gauge and 30 mm exposure) were used to validate the findings regarding the area of the tissue for feedback control and the set-point temperature. RESULTS: The size of coagulation zone achieved was maximised when the area of tissue surrounding the middle part of the active tip (i.e. Point 7) was used for feedback control and when the set-point temperature was set to 90 ^ C (this temperature is determined based on the energy gate through a trial-and-error procedure). At both 80 and 90 ^ C, the coagulation zones generated using Area II were significantly larger than that generated using Area I (p = 0.0028 and 0.0003, respectively) and Area III (P = 0.0010 and < 0.0001, respectively). A similar finding regarding the control area and set-point temperature was confirmed by the in-vitro experiment. When compared with Point a (p < 0.0001) and Point c (p < 0.0001), the largest coagulation zone (1066.7 ± 36.1 mm2) was achieved by controlling the temperature of the tissue area surrounding the middle part of the active tip (i.e. Point b) at 90 ^ C. CONCLUSION: The judicious selection of the control area within the biological tissue for temperature monitoring and the set-point temperature for feedback control is critical in increasing the size of the coagulation zone in the treatment of RFA.

Numerical analysis of the relationship between the area of target tissue necrosis and the size of target tissue in liver tumours with pulsed radiofrequency ablation.

PURPOSE: Radiofrequency ablation (RFA) is currently restricted to the treatment of target tissues with a small size (<3 cm in diameter). To overcome this problem with RFA, some phenomena need to be understood first. The study presented in this paper investigated the relationship between the area of target tissue necrosis (TTN) and the size of target tissue in pulsed radiofrequency ablation (PRFA). MATERIALS AND METHODS: Liver tumour, one of the common targets of RFA in clinical practice, was used as the target tissue in this study. Two types of pulsed RF power supply methods (half-square and half-sine) and three target tissues with different sizes (25 mm, 30 mm and 35 mm in diameter) were studied using finite element modelling. The finite element model (FEM) was validated by using an in vitro experiment with porcine liver tissue. The first roll-off occurrence or 720 s, whichever occurs first, was chosen as the ablation termination criterion in this study. RESULTS: For each target tissue size, the largest TTN area was obtained using the maximum voltage applied (MVA) without roll-off occurrence. In this study, target tissues with a 25 mm diameter can be ablated cleanly but target tissues with 30-mm and 35-mm failed to be ablated. CONCLUSIONS: The half-square PRFA could achieve a larger TTN area than the half-sine PRFA. The MVA decreases with an increase in the target tissue diameter in both the half-square PRFA and the half-sine PRFA. The findings of this study are in agreement with the clinical results that lesions (≥ 3 cm in diameter) have less favourable results from RFA.

Study of the relationship between the target tissue necrosis volume and the target tissue size in liver tumours using two-compartment finite element RFA modelling.

PURPOSE: The aim of this study was to investigate the relationship between the target tissue necrosis volume and the target tissue size during the radiofrequency ablation (RFA) procedure. MATERIALS AND METHODS: The target tissues with four different sizes (dxy = 20, 25, 30 and 35 mm) were modelled using a two-compartment radiofrequency ablation model. Different voltages were applied to seek the maximum target tissue necrosis volume for each target tissue size. The first roll-off occurrence or the standard ablation time (12 min) was taken as the sign for the termination of the RFA procedure. RESULTS: Four different maximum voltages without the roll-off occurrence were found for the four different sizes of target tissues (dxy = 20, 25, 30 and 35 mm), and they were 36.6, 35.4, 33.9 and 32.5 V, respectively. The target tissues with diameters of 20, 25 mm can be cleanly ablated at their own maximum voltages applied (MVA) but the same finding was not found for the 35-mm target tissue. For the target tissue with diameter of 30 mm, the 50 °C isothermal contour (IT50) result showed that the target tissue can be cleanly ablated, but the same result did not show in the Arrhenius damage model result. Furthermore, two optimal RFA protocols with a minimal thermal damage to the healthy tissues were found for the target tissues with diameters of 20 and 25 mm, respectively. CONCLUSIONS: The study suggests that target tissues of different sizes should be treated with different RFA protocols. The maximum target tissue volume was achieved with the MVA without the roll-off occurrence for each target tissue size when a constant RF power supply was used.

Methicillin-resistant Staphylococcus aureus: implications for the radiology department.

OBJECTIVE: The purpose of this article is to discuss some of the implications of methicillin-resistant Staphylococcus aureus (MRSA) for the radiology department. CONCLUSION: MRSA is an infectious organism that has been increasing in prevalence and has presented a challenge to hospitals worldwide due to its drug resistance and propensity to cause serious infections. The radiology department is a site of high patient traffic and regularly encounters MRSA-positive patients. Guidelines for implementation of MRSA infection control practices are available and should be adapted to the radiology department. A summary of recommendations for MRSA infection control in the radiology department is provided.

Idiopathic infantile arterial calcification in a 12-year-old girl presenting as chronic mesenteric ischemia: imaging findings and angioplasty results.

We report an unusual case of chronic mesenteric ischemia presenting in a 12-year-old girl with idiopathic infantile arterial calcinosis (IIAC). This is the first reported case in the literature of chronic mesenteric ischemia in the setting of IIAC. The girl presented with a classical history of postprandial abdominal pain. Imaging demonstrated significant stenoses of the celiac axis, superior mesenteric artery (SMA) and inferior mesenteric artery (IMA). Angioplasty of the celiac axis and SMA was attempted, with successful dilation of the SMA only. At 3-, 6- and 12-month follow-ups, the child's symptoms had almost resolved. This case report has three important ramifications: chronic mesenteric ischemia is a possible clinical presentation in children with IACC, pre-angioplasty imaging is important in guiding treatment approach, and angioplasty was effective in this case of chronic mesenteric ischemia and offers hope for other similarly affected children.

A Novel Method to Increase Tumor Ablation Zones With RFA by Injecting the Cationic Polymer Solution to Tissues: In Vivo and Computational Studies.

OBJECTIVE: This study aims to examine, for the first time, the introduction of cationic polymer solutions to improve radiofrequency ablation (RFA) in terms of a potentially enlarged ablation zone. METHODS: By using in vivo and computational RFA studies, two cationic polymers, Chitooligosaccharides (COS) and carboxymethyl chitosan (CMC), diluted in deionized water, were injected into tissues separately surrounding the RF bipolar electrode prior to power application. A total of 9 rabbits were used to 1) measure the increase in electrical conductivity of tissues injected with the cationic polymer solutions, and 2) explore the enhancement of the ablation performance in RFA trials. A computer model of RFA comprising a model of the solution diffusion with an RF thermal ablation model was also built, validated by the in vivo experiment, to quantitatively study the effect of cationic polymer solutions on ablation performances. RESULTS: Compared to the control group, the electrical conductivity of rabbit liver tissues was increased by 42.20% (0.282 ± 0.006 vs. 0.401 ± 0.048 S/m, P = 0.001) and 43.97% (0.282 ± 0.006 vs. 0.406 ± 0.042 S/m, P = 0.001) by injecting the COS and CMC solution at the concentration of 100 mg/mL into the tissues, denoted COSDW100 and CMCDW100, respectively. Consequently, the in vivo experiments show that the ablation zone was enlarged by 95% (47.6 ± 6.3 vs. 92.6 ± 11.5 mm2, P < 0.001) and 87% (47.6± 6.3 vs. 88.8 ± 9.6 mm2, P < 0.001) by COSDW100 and CMCDW100, respectively. The computer simulation shows that the ablation zone was enlarged by 71% (51.9 vs. 88.7 mm2) and 63% (51.9 vs. 84.7 mm2) by COSDW100 and CMCDW100, respectively. CONCLUSION: The injection of the cationic solution can greatly improve the performance of RFA treatment in terms of enlarging the ablation zone, which is due to the increase in the electrical conductivity of liver tissues surrounding the RF electrode. SIGNIFICANCE: This study contributes to the improvement of RFA in the treatment of large tumors.

Tumor Ablation Enhancement by Combining Radiofrequency Ablation and Irreversible Electroporation: An In Vitro 3D Tumor Study.

We hypothesized and demonstrated for the first time that significant tumor ablation enhancement can be achieved by combining radiofrequency ablation (RFA) and irreversible electroporation (IRE) using a 3D cervical cancer cell model. Three RFA (43, 50, and 60 °C for 2 min) and IRE protocols (350, 700, and 1050 V/cm) were used to study the combining effect in the 3D tumor cell model. The in vitro experiment showed that both RFA enhanced IRE and IRE enhanced RFA can lead to a significant increase in the size of the ablation zone compared to IRE and RFA alone. It was also noted that the sequence of applying ablation energy (RFA â†’ RE or IRE â†’ RFA) affected the efficacy of tumor ablation enhancement. The electrical conductivity of 3D tumor was found to be increased after preliminary RFA or IRE treatment. This increase in tumor conductivity may explain the enhancement of tumor ablation. Another explanation might be that there is repeat injury to the transitional zone of the first treatment by the second one. The promising results achieved in the study can provide us useful clues about the treatment of large tumors abutting large vessels or bile ducts.

Development of a statistical model for cervical cancer cell death with irreversible electroporation in vitro.

PURPOSE: The aim of this study was to develop a statistical model for cell death by irreversible electroporation (IRE) and to show that the statistic model is more accurate than the electric field threshold model in the literature using cervical cancer cells in vitro. METHODS: HeLa cell line was cultured and treated with different IRE protocols in order to obtain data for modeling the statistical relationship between the cell death and pulse-setting parameters. In total, 340 in vitro experiments were performed with a commercial IRE pulse system, including a pulse generator and an electric cuvette. Trypan blue staining technique was used to evaluate cell death after 4 hours of incubation following IRE treatment. Peleg-Fermi model was used in the study to build the statistical relationship using the cell viability data obtained from the in vitro experiments. A finite element model of IRE for the electric field distribution was also built. Comparison of ablation zones between the statistical model and electric threshold model (drawn from the finite element model) was used to show the accuracy of the proposed statistical model in the description of the ablation zone and its applicability in different pulse-setting parameters. RESULTS: The statistical models describing the relationships between HeLa cell death and pulse length and the number of pulses, respectively, were built. The values of the curve fitting parameters were obtained using the Peleg-Fermi model for the treatment of cervical cancer with IRE. The difference in the ablation zone between the statistical model and the electric threshold model was also illustrated to show the accuracy of the proposed statistical model in the representation of ablation zone in IRE. CONCLUSIONS: This study concluded that: (1) the proposed statistical model accurately described the ablation zone of IRE with cervical cancer cells, and was more accurate compared with the electric field model; (2) the proposed statistical model was able to estimate the value of electric field threshold for the computer simulation of IRE in the treatment of cervical cancer; and (3) the proposed statistical model was able to express the change in ablation zone with the change in pulse-setting parameters.

Steerable catheters for minimally invasive surgery: a review and future directions.

The steerable catheter refers to the catheter that is manipulated by a mechanism which may be driven by operators or by actuators. The steerable catheter for minimally invasive surgery has rapidly become a rich and diverse area of research. Many important achievements in design, application and analysis of the steerable catheter have been made in the past decade. This paper aims to provide an overview of the state of arts of steerable catheters. Steerable catheters are classified into four main groups based on the actuation principle: (1) tendon driven catheters, (2) magnetic navigation catheters, (3) soft material driven catheters (shape memory effect catheters, steerable needles, concentric tubes, conducting polymer driven catheters and hydraulic pressure driven catheters), and (4) hybrid actuation catheters. The advantages and limitations of each of them are commented and discussed in this paper. The future directions of research are summarized.