Multiple-Electrode Radiofrequency Ablation Creates Confluent Areas of Necrosis: In Vivo Porcine Liver Results1
ABSTRACT To prospectively evaluate, in vivo in pigs, an impedance-based multiple-electrode radiofrequency (RF) ablation system for creation of confluent areas of hepatic coagulation.
The study was preapproved by the institutional research animal care and use committee. A prototype multiple-electrode RF system that enables switching between three electrically independent electrodes at impedance spikes was created. Forty-two coagulation zones (18 with single, 12 with cluster, and 12 with multiple [three single electrodes spaced 2 cm apart] electrodes) were created at laparotomy in 15 female pigs. Half the ablations were performed for 12 minutes, and half were performed for 16 minutes. The coagulation zones were excised and sliced into approximately 3-mm sections for measurement. Analysis of variance and two-sample t tests (with Bonferroni correction, alpha = .0033) were used to assess for differences between groups.
At 12 minutes, the mean multiple-electrode coagulation was significantly larger than the mean single-electrode coagulation (minimum diameter, 2.8 vs 1.6 cm; maximum diameter, 4.2 vs 2.0 cm; volume, 22.1 vs 6.7 cm(3); P < .0033 for all comparisons). The mean maximum diameter achieved at 12 minutes with multiple electrodes was significantly larger than that achieved with the cluster electrode (4.2 vs 2.9 cm, P = .02). At 16 minutes, the mean multiple-electrode coagulation (minimum diameter, 3.2 cm; maximum diameter, 4.2 cm; volume, 29.1 cm(3)) was significantly larger than the mean single-electrode (minimum diameter, 1.7 cm; maximum diameter, 2.2 cm; volume, 7.1 cm(3); P < .0033 for all comparisons) and cluster-electrode (minimum diameter: 2.3 cm, P = .007; maximum diameter: 3.2 cm, P = .005; volume: 13.1 cm(3), P = .001) coagulations.
Compared with the single and cluster systems used as controls, the multiple-electrode RF ablation system enabled the creation of significantly larger coagulation zones.
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ABSTRACT: Radiofrequency ablation (RFA) is a minimally invasive technique that is useful in treating soft tissue tumour. Although RFA has been widely used in treating patients, more studies on its biophysical principles are needed to improve the RFA techniques. The purpose of this study was to characterize the ablation size in the bovine liver in terms of the RFA duration, the temperature of the cooling system to the RFA electrode and the RF generator’s ablation mode. RFA were performed on ex vivo bovine livers using Cooltip ™ single electrode kits and Cool-tip™ RF Ablation System. A 12-channel thermometer was used to record the temperature distribution in the ablation volume. The thermometer probes were placed at 10, 20 and 30 mm radially away from the RFA electrode. A Perspex jig with custom drilled holes was used for placing the RFA electrode and temperature probes at the precise location. Fifty monopolar RFAs were performed in 16 different modes of parameters. The duration of RFA was set at 5, 7, 10 and 12 minutes. Distilled water was used as the cooling system to the RFA electrode at 5°±1°C and 25°±1°C. The Cool-tip™ RF Ablation System has two modes of ablation, which are the impedance control and manual control, where the power output was always set at maximum during the ablation. The ablation size increased as the duration of RFA increased. Larger ablation size was created when the Cool-tip™ RF Ablation System was switched to impedance control, as compared to the manual control. Smaller ablation size and charring was observed in manual-controlled RFAs.
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Conference Paper: A 1.8 GHz CMOS voltage-controlled oscillator[Show abstract] [Hide abstract]
ABSTRACT: This paper describes the factors that limit the tuning range of monolithic LC voltage-controlled oscillators (VCOs), especially at low supply voltages, and introduces circuit techniques that alleviate this problem. Incorporating such techniques, a 1.8 GHz CMOS oscillator achieves a tuning range of 120 MHz with a relatively constant gain while exhibiting a phase noise of -100 dBc/Hz at 500 kHz offset. The actual implementation is a quadrature generator consisting of two coupled oscillators. Since the two oscillators are identical, only one is considered hereSolid-State Circuits Conference, 1997. Digest of Technical Papers. 43rd ISSCC., 1997 IEEE International; 03/1997