Radiofrequency coil for the creation of large ablations: ex vivo and in vivo testing.

PURPOSE: Various radiofrequency (RF) ablation electrode designs have been developed to increase ablation volume. Multiple heating cycles and electrode positions are often required, thereby increasing treatment time. The objective of this study was to evaluate the performance of a high-frequency monopolar induction coil designed to produce large thermal lesions (>3 cm) with a single electrode insertion in a treatment time of less than 10 minutes. MATERIALS AND METHODS: A monopolar nitinol interstitial coil operated at 27.12 MHz and 200 W was evaluated. Ex vivo performance was tested in excised bovine liver (n = 22). In vivo testing (n = 10) was conducted in livers of seven Yorkshire pigs. Visual inspection, contrast-enhanced computed tomography (CT), and pathologic evaluation of ablation zones were performed. RESULTS: Average ablation volumes in ex vivo and in vivo tests were 60.5 cm(3) ± 14.1 (5.9 × 4.4 × 4.4 cm) and 57.1cm(3) ± 13.8 (6.1 × 4.5 × 4.1cm), with average treatment times of 9.0 minutes ± 3.0 and 8.4 minutes ± 2.7, respectively. Contrast-enhanced CT ablation volume measurements corresponded with findings of gross inspection. Pathologic analysis showed morphologic and enzymatic changes suggestive of tissue death within the ablation zones. CONCLUSIONS: The RF ablation coil device successfully produced large, uniform ablation volumes in ex vivo and in vivo settings in treatment times of less than 10 minutes. Ex vivo and in vivo lesion sizes were not significantly different (P = .53), suggesting that the heating efficiency of this higher-frequency coil device may help to minimize the heat-sink effect of perfusion.

Improving the gait performance of non-fluid-based swing-phase control mechanisms in transfemoral prostheses.

A prosthetic swing-phase control mechanism simulates the action of leg musculature, aiding gait function by controlling the duration of swing, extent of heel-rise, and by allowing the shank to smoothly decelerate into full knee extension without excessive impact. Non-fluid-based mechanisms have the potential to provide a durable and affordable solution as required in many parts of the world, but the design variables that lead to improved performance of non-fluid-based swing-phase control technologies are not well established. Seven transfemoral amputees were fitted with a prosthetic knee joint and different non-fluid-based swing-phase setups were systematically assessed. Clinical testing included walk tests utilizing a potentiometer (to measure knee flexion angles) and accelerometer (to measure terminal impact decelerations) mounted on the prosthetic limb. As hypothesized, the friction and spring systems improved gait function. This includes an increased walking speed that closely matched high-end hydraulic prosthetic knee joints, decreased and more normal maximum prosthetic knee flexion, decreased flexion duration, and lower terminal impact. Further improvements were obtained using a dual spring system, two springs in series, over the more conventional single spring system. Non-fluid-based swing-phase control mechanisms are simple and significantly improve the performance of prostheses. Their application is ideal where size, weight and cost may be constrained.