fig1 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 . the surgical instrument 16 may assume a wide variety of forms . one preferred embodiment of a surgical apparatus 30 useful in an rf ablation procedure is shown in fig2 . the apparatus 30 includes an outer thin walled tube 32 , an inner thinner walled tube 34 , and may , if desired , include an inner stylet or probe 36 . tubes 32 and 34 and stylet 36 are substantially coaxially mounted relative to each other and are movable in the proximal - distal direction relative to each other . the outer tube 32 preferably includes a collar 38 with a control knob 40 attached at a proximal end thereof . the outer tube 32 further preferably includes at least one slot or aperture 42 located at a distal end thereof . if desired , multiple apertures 42 may be disposed in any desired manner about the circumference of the distal end of the outer tube 32 . the aperture 42 may take on multiple configurations . in the embodiment shown in fig2 the aperture 42 has an elongated oval or elliptical configuration . in one preferred embodiment , the inner tube 34 is configured as a needle electrode . the inner tube 34 , which is slidably received within the outer tube 32 , preferably includes a shutter index element 44 attached adjacent a proximal end thereof . the shutter index element 44 will be discussed in further detail below . attached to a proximal end of the inner tube 34 is a hemostasis valve 46 having a port 48 through which rf ablating fluid , such as but not limited to saline and other conductive solutions , may be supplied from the fluid source 14 ( fig1 ) as indicated by arrow 50 . a distal end of the inner tube 34 includes a plurality of orifices or apertures 52 of varying sizes and shapes as desired . as shown in fig2 there are preferably four sets of the apertures 52 equally spaced about a circumference of the distal end of the inner tube 34 . in one preferred embodiment , each set includes five apertures increasing in size toward a center of the individual set . thus , during use , as fluid flows through the apertures 52 , more of the fluid will flow through the center aperture than will flow through the other apertures . as a result , the bolus of the fluid forming at a particular target site may take on a roughly elliptical shape , making allowances for the tissue at the target site and the vasculature that may be implicated by any particular placement . the inner tube 34 includes at its most distal end an exposed electrode 54 through which rf current can be applied to the tissue . thus , the inner tube 34 may be metallic or otherwise conductive and insulated along its length except for the exposed electrode 54 . the electrode 54 is preferably electrically connected to the current source 12 ( fig1 ). fig3 illustrates a plan view of the distal end of the inner tube or needle electrode 34 . it will be understood that the needle electrode 34 will be insulated except at the distal end to prevent electrical current from flowing into the tissue ( not shown ) at any location except from the distal end thereof . returning to fig2 the probe 36 may take the form of an inner stylet , preferably having a thermocouple ( not shown ) disposed at the distal end thereof . because the probe 36 is movable relative to the electrode 54 , the thermocouple may be placed at a desired location away from the electrode to monitor tissue temperature . fig4 a - 4c illustrate in greater detail the connections between the control knob 40 and the outer tube 32 on the one hand , and the shutter index element 44 and the inner tube 34 on the other . the control knob 40 is preferably connected to the collar 38 of the outer tube 32 by a support 56 . the outer tube 32 and the control knob 40 are rotatable and axially movable relative to the inner tube 34 and the shutter index element 44 . thus , the control knob 40 can be selectively moved into and out of engagement with a portion of the shutter index element 44 . for example , the control knob 40 may be rotated from a first engagement position ( fig4 a ), and then moved axially to a second engagement position ( fig4 b ). the outer tube 32 is maneuvered in conjunction with the control knob 40 , and thus moves relative to the inner tube 34 with movement of the control knob 40 . for example , as best shown in fig4 c , the shutter index element 44 is preferably configured to form axial slots 58 a - 58 d sized to receive the support 56 . each of the axial slots 58 a - 58 d is connected to at least one circumferential slot , similarly sized to receive and selectively maintain the support 56 . for example , the axial slot 58 a is shown as being connected to three circumferential slots 60 , whereas the axial slot 58 b is connected to one circumferential slot 62 . any other number of circumferential slots is equally acceptable and dictates a desired position ( s ) of the outer tube 32 relative to the inner tube 34 , as described in greater detail below . translation of the control knob 40 / outer tube 32 relative to the shutter index element 44 / inner tube 34 and the effect on fluid flow is shown in greater detail in fig5 - 8 . in each of fig5 - 8 , the control knob 40 ( fig4 a ) has not been shown for purposes of clarity . instead , only the support 56 , which extends from the control knob 40 to the collar 38 ( fig4 a ), has been depicted . further , the shutter index element 44 is shown as including the axial slot 58 a connected to four circumferential slots 64 a - 64 d . as previously described , the support 56 can be maneuvered along the axial slot 58 a into selective engagement with each of the circumferential slots 64 a - 64 d , thereby locating the support 56 within any one of the circumferential slots 64 a - 64 d and resulting in a defined relationship of the outer tube 32 relative to the inner tube 34 . to assist a user in positioning the support 56 , the shutter index element 44 may further include indicia 66 a - 66 d associated with the circumferential slots 64 a - 64 d , respectively . the indicia 66 a - 66 d may assume a wide variety of forms for providing a user with an indication of outer tube 32 / inner tube 34 positioning . for example , the indicia 66 a may be a filled circle (“”) representing that all of the orifices 52 of the inner tube 34 are open ; the indicia 66 b may be a half filled circle (“”) representing the orifices 52 being partially open ; the indicia 66 c may be an open circle (“∘”) representing all of the orifices 52 being closed ; and the indicia 66 d may be a dash (“—”) representing the slot 42 of the outer tube 32 being open or aligned with the orifices 52 . fig5 illustrates the situation where the control knob 40 ( fig4 a ) has been moved to a position where the orifices 52 are fully opened and allow rf fluid to flow freely therefrom . that is to say , the support 56 is positioned within the circumferential slot 64 a . at this location , a distal end of the outer tube 32 is proximal the orifices 52 and the electrode 54 . fluid from the fluid source 14 ( fig1 ) is thereby allowed to flow from the orifices 52 . fig6 illustrates the partial blocking of the orifices 52 . in this instance , relative to fig5 the control knob 40 ( fig4 a ) has been rotated relative to the shutter index element 42 and moved distally along the axial slot 58 a so as to move the outer tube 32 distally relative to the inner tube 34 . the control knob 40 has then been rotated radially to lodge the support 56 in the circumferential slot 64 b . movement of the outer tube 32 in this manner ( e . g ., distally ) causes the outer tube 32 to partially block at least some of the orifices 52 and thus restrict or stop rf fluid flow therefrom , as identified by the indicia 66 b . fig7 illustrates the complete blocking of rf fluid flow from all of the apertures 52 . more particularly , the support 56 has been moved into the circumferential slot 66 c , resulting in a distal end of the outer tube 32 being distal the orifices 52 . in fig8 the slot 42 at the distal end of outer tube 32 has been moved such that fluid flows only from the orifices 52 and then through the slot 42 , thus providing in essence a single aperture along a longitudinal length of the outer tube 32 rather than discrete multiple apertures . the indicia 66 d provides visual notice of this relationship to the user . the present invention allows an operator to block the distribution of the rf fluid from the apparatus 30 in a selective manner . this allows the operator to control the volume of the fluid flow and the shape of the bolus or virtual electrode produced in the tissue with some degree of latitude as allowed by the tissue structure in which the apparatus is placed . although the present invention has been described with reference to preferred embodiments , workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention .
a method and apparatus for creating a virtual electrode to ablate bodily tissue . the surgical apparatus includes an inner tube and an outer tube . the inner tube defines a proximal portion and a distal portion . the distal portion forms an orifice for distributing a conductive solution from the inner tube and further forms an electrode . the outer tube coaxially receives the inner tube such that the outer tube is slidable relative to the inner tube . with this configuration , the outer tube selectively blocks flow of conductive solution from the orifice . during use , conductive solution distributed from the orifice is subjected to a current from the electrode , thereby creating a virtual electrode .