Spark discharges for surgical applications

We have investigated the potential of spark discharges as a minimally invasive surgical tool. The spark was generated between the tips of two 0.4-mm acupuncture needles, which were inserted into the tissue. The needle tips were facing each other at a distance of 7 mm. Using a Blumlein pulse forming network, high voltage pulses with a nominal duration of 380 ns were applied to these electrodes. The tissue-load was matched to the 100-Ohm impedance of the pulse generator by an equivalent resistor. Depending on tissue type (muscle, liver, fat) and pulse amplitude, several tissue-conditioning pulses had to be applied before breakdown could be achieved. During the application of these pre-breakdown pulses, tissue impedances dropped noticeably. The breakdown voltage for this electrode geometry and these pulse parameters was higher than for air (at atmospheric pressure) but much lower than expected for liquids or solids. The energy that was stored in the system and dissipated in the spark at the highest charging voltage was on the order of 1 J. A visual inspection of the tissue damage showed a highly localized incision, running between the tips of the needle electrodes. Tissue was ablated in a nearly straight and narrow channel of 1-2 mm in diameter. No significant damage to the adjacent tissue was observed. The preliminary histological analysis suggests that the damage is mostly caused by the Shockwave associated with the spark. As such, we believe that the method can be used as a surgical tool, in particular, where a high degree of accuracy is required.