Method and apparatus for creating a virtual electrode used for the ablation of tissue

#The present invention relates generally to an apparatus for creating a virtual electrode. More particularly, the present invention relates to an apparatus for the creation of a virtual electrode that is useful for the ablation of soft tissue and neoplasms.

#The utilization of an electric current to produce an ameliorative effect on a bodily tissue has a long history, reportedly extending back to the ancient Greeks. The effects on bodily tissue from an applied electric current, and thus the dividing line between harmful and curative effects, will vary depending upon the voltage levels, current levels, the length of time the current is applied, and the tissue involved. One such effect resulting from the passage of an electric current through tissue is heat generation.

#Body tissue, like all non-superconducting materials, conducts current with some degree of resistance. This resistance creates localized heating of the tissue through which the current is being conducted. The amount of heat generated will vary with the power P deposited in the tissue, which is a function of the product of the square of the current I and the resistance R of the tissue to the passage of the current through it (P=I2R.).

#FIG. 1 is a block diagram of a virtual electrode ablation system in accordance with the present invention;

#FIG. 2 is a perspective view of a surgical apparatus, with portions cut away, in accordance with the present invention;

#FIG. 3 is an enlarged, side view of a distal portion of the surgical apparatus of FIG. 2;

#FIG. 1 illustrates in block form a system 10 for RF ablation useful with the present invention. The system 10 includes a source of radiofrequency alternating electric current 12, a source of RF ablating fluid 14, including but not limited to saline and other conductive solutions, and a surgical instrument 16 for delivering RF current and ablation fluid to a tissue site (not shown) for ablation purposes. In one preferred embodiment, the surgical instrument 16 is connected to the current source 12 and the fluid source 14. It will be understood that the current source 12 and the fluid source 14 may be combined into a single operational structure controlled by an appropriate microprocessor for a controlled delivery of ablating fluid and a controlled application of RF current, both based upon measured parameters such as but not limited to, flow rate, tissue temperature at the ablation site and at areas surrounding the ablation site, impedance, the rate of change of the impedance, the detection of arcing between the surgical instrument and the tissue, the time period during which the ablation procedure has been operating, and additional factors as desired.

#While the surgical instrument 16 is shown as being connected to both the current source 12 and the fluid source 14, the present system is not so limited but could include separate needles or other instruments useful in RF liquid ablation procedures, that is, for example, a single straight or coiled needle having an exposed end and a fluid flow path there through could be used to deliver both fluid and current to the target tissue for ablation purposes. Alternatively, a separate needle could be used to deliver the current and a separate needle or needles could be used to deliver fluid to the target tissue. In addition, the application of the present system is not limited to the use of straight needles or helical needles as surgical instruments but could find use with any type of instrument wherein a conductive solution is delivered to a tissue and an RF current is applied to the tissue through the conductive fluid. Such instruments thus would include straight needles, helical needles, forceps, roller balls, instruments for the treatment of vascular disorders, and any other instrument.

#In one preferred embodiment, the system 10 further includes a second fluid source 18 for delivery of tissue protecting fluid via a delivery instrument 20, to a tissue whose ablation is not desired.