electrodes used for spinal cord stimulation are typically implanted in the epidural space 23 between the vertebra 24 and the dura 22 , shown in fig1 . this is done for various reasons , including reduced complexity of the surgery , reduced potential complications , an increased stability of the implant . however , implantation in the epidural space requires a significant amount of additional stimulation power since the signal must be transmitted through the dura 22 and epidural space 23 and cerebrospinal fluid in order to reach its desired neural targets in the spinal cord 20 . anterior roots 25 and posterior roots 26 of the spinal cord 20 and rami communicantes 27 are also shown . there were early stimulator leads 28 which were utilized in the intrathecal space 21 between the spinal cord 20 and the dura 22 without success . typically , these leads resulted in inconsistent stimulation , overstimulation and , generally , ineffective therapy . however , they utilized technology approximately thirty years old . due to development and implementation of better epidural leads , as well as the lack of a concern for energy requirements ( since they were using an external battery pack ), this methodology was quickly abandoned . more recently , intrathecal catheters have been utilized extensively for administration of drugs including morphine and baclofen via implantable drug pumps . catheter complications were so prevalent thirty years ago ( csf leakage , migration , etc .) are no longer a significant problem . of course , administration of a drug does not require a precise electrode placement . this new intrathecal neurostimulation electrode would uses for example four millimeter electrode contacts ( more forgiving when it comes to precise electrode placement ) and yet would require dramatically less power ( less than 20 % of the power required for current epidural electrodes ) because the electrodes would be in direct contact with the csf and much closer to the desired neural targets . the primary insulating factor resulting in higher power requirements for epidural leads is the lack of conductivity of the dura 22 . the shunting effect of electrical current within the csf is a much less significant factor . therefore , an electrode designed with a stabilization means or fixing elements for use in the intrathecal space 21 utilizing materials generally accepted in the art for intrathecal drug administration would provide a unique , novel and advantageous method of stimulation of the spinal cord . fixation methods could include one or more of the following : inflatable balloons , tines which are either retractable with a stilet or simply pliable enough to fit through a specially designed introducer or a novel shape ( d shape ) or the use of nitinol . any of these fixation methods , singly or in combination , can be used to provide stable electrode placement on a long term basis . the advantages of an intrathecal electrode are dramatically reduced size and / or increased life of a neurostimulator implant . in addition , implantation in the intrathecal space allows the use of a larger diameter electrode catheter and , therefore , more electrodes can be placed , providing a wider selection of stimulation sites and stimulation paradigms . these stimulation paradigms could include sophisticated programs that switch stimulation between a number of electrodes slowly ( over seconds or minutes , hours or days ) to avoid accommodation of the stimulation or could be fast ( approximately the same speed of the electrical activity of neurons in the spinal cord ) artificially generating neural signals along the spinal cord 20 which could be perceived as any other sensory function with signals that travel through the spinal cord . for instance , a signal could be generated that would correspond to heat being applied to a patient &# 39 ; s big toe , or pressure being applied to a patient &# 39 ; s foot , or the sensation of a limb in a different orientation than it actually is . theoretically , tastes , smells , sights or even thoughts could be created in this manner allowing various artificial prosthesis ( visual , auditory , etc .) to interface with the human body . a first embodiment is illustrated in fig2 . a catheter lead 30 includes a sheath 32 having a plurality of electrodes 34 at a distal end 36 of the catheter 30 . a proximal end 38 of the catheter 30 have contacts 39 to be connected to a stimulator , not shown . there is one contact 39 for each electrode 34 . the length of the electrodes l 1 are generally two to four millimeters . the distance d 1 between the electrodes is typically six millimeters , for example . the electrodes are shown to extend 270 degrees about the circumference of the catheter . in order to achieve further increases in battery life , the surface area of the active electrode contact can be reduced . an electrode with a specific orientation adjacent to the spinal cord would allow a 30 °- 270 ° electrode as opposed to the 360 ° electrodes used in all current catheter electrodes . this would also enable the electrodes to remain at the preferred three or four millimeters in length making it easier for physicians to hit the desired target and requiring fewer electrode contacts in the lead ( also allowing a smaller lead ). different means could be used to stabilize the electrode in place , including ( 1 ) inflatable balloons , ( 2 ) nitinol , ( 3 ) novel shape electrodes , ( 4 ) mechanical system whereby tines are deployed upon removal of the stilet , ( 5 ) mechanical system of flexible tines . a 270 ° electrode is illustrated in fig2 a 90 ° electrode is illustrated in fig3 a and a 60 ° electrode is illustrated in fig4 a . the small radius electrode , for example , 90 ° or less , allows a focused electrical stimulation field along the physiological midline pm l of the spinal cord 20 and reduces the effective stimulation field in the area of the bending fibers . as illustrated in fig3 the electrode 34 may also be placed at the nerve root midline nrm l it is well known that bending fibers are preferentially stimulated when compared to longitudinal fibers . thus , by positioning the lead adjacent to the desired longitudinal fibers , a focused stimulation of the longitudinal fibers will take place . the small electrodes in the range of 30 °- 60 ° also allows selective activation of the fibers . this is particularly useful where the nerve enters the cord . such placement is illustrated in fig4 where the 60 ° electrode 34 is adjacent to the nerve roots 25 , 26 . for any of the above lead designs , an additional method of decreasing power requirements is to use monopolar stimulation . a large surface area common anode electrode is used in conjunction with a single electrode in the desired stimulation area on the electrode contact array . monopolar stimulation is not new , but does provide the opportunity to decrease the power requirements for effective stimulation . the incorporation of a large surface area anode electrode some distance away from the other active electrodes on the same catheter or along the length of an intrathecal catheter has never been performed or attempted . in the prior systems , the casing of the stimulator acted as the anode in a monopolar mode . its distance from the distal electrodes created a long current path . this new and novel approach reduces the current path , creates a different field and also allows a unitary electrode system so that the stimulator device itself does not have to be made in two different configurations ( one with an active case anode and one without ). therefore , a choice between bipolar and monopolar stimulation can be made after implantation using a stimulator ( pulse generator ) which could normally only provide bipolar stimulation . as illustrated in fig5 an additional electrode 35 is provided at the distal end 36 displaced from the other electrodes 34 . the electrodes 34 are shown as 360 ° electrodes . as illustrated in fig6 catheter electrode 40 includes a sheath 42 with having a plurality of inline electrodes 44 and an additional electrode 45 on the wire or sheath extension 47 extending from the distal end or paddle 46 . the proximal end 48 has contacts 49 connected to each electrode and to a stimulator . the electrodes 34 , 44 all have a length l 1 and the additional electrode 35 , 45 has a length l 2 . length l 2 is greater than l 1 , at least twice its length . thus , for example , if length l 1 is two millimeters , the length l 2 is four millimeters . the length l 2 may be anywhere between 2 - 4 times that of the length l 1 . also , it should be noted that the additional electrode 35 , 45 is spaced by a distance d 2 from the nearest electrode 34 , 44 . where d 1 is approximately six millimeters , the distance d 2 is at least 10 millimeters and can be as much as 20 millimeters . with this distance , the electrode acts as a point source when used in conjunction with a second electrode . the electrodes 34 , 44 act as a point source when used in conjunction with the additional electrode 35 , 45 of the increased area . alternatively , a common anode or additional electrode 35 may be the same length as the other electrodes 34 , but have a greater circumferential dimension than that of the electrode 34 . this would increase the surface area of the additional electrode 35 relative to the other electrodes 34 . therefore , the electrodes 34 may be in the 30 ° to 270 ° configuration previously described . the separation difference between the electrodes 34 and that of 35 will allow operation as described with respect to fig5 and 6 . such an electrode is illustrated in fig1 to be discussed below . a catheter lead capable of stimulation electrically as well as dispensing drugs is illustrated in fig7 - 11 . the catheter lead 50 has a sheath 52 with inline electrodes 54 spaced along the distal end 56 . at the proximal end 58 , terminal contacts 59 are connected internally to each of the electrodes shown . a passage 60 is provided in the sheath 50 . in fig7 an outlet 62 is provided in the tip of the distal end 56 and a balloon fixation device 63 is shown . provision is also made for an optional stilet which is removable and may be used to assist in placement of the catheter . various stilets 61 of different shapes and characteristics may be used with these leads . in fig8 the outlet 64 is shown in the space between the electrodes 54 and a nitinol fixation device 65 is shown in the deployed condition . in fig8 a , nitinol fixation device 65 is shown prior to the deployment through opening 53 in sheath 52 . in fig9 the outlet 64 is shown in or on the electrode 54 and a tine fixation device 67 is shown . although one fixation is illustrated on a specific figure , any fixation device may be used with any of the catheters . fixation methods may also include devices that are actively deployed and / or retracted ( for instance by a stilet ) in addition to the methods shown herein . also , the fixation device may be located at any or more than one location or position along the catheter . a fixation device should be used where the catheter electrode is installed in the intrathecal space . while fig7 - 9 show the passage 60 internal to the sheath 52 , an external delivery 68 may be used as shown in fig1 . the electrode catheter 50 may also include a single or pair of optical channels 70 and 72 having outlets or ports in the distal end . the fiberoptic channels and light energy delivered through a clear translucent area in the catheter is illustrated in fig1 . one of the channels can provide a source of light to be used as a further source of stimulation . the other channel will form a lens for a camera or other monitoring devices . the camera can be used in positioning the electrode or distal end . channel 60 with outlet 64 is also shown for a drug delivery . it should be noted that only a single optical path can be used to provide a source of light for a photon stimulation without the passage 60 or the outlet 64 . it should also be noted that the passage 60 or external passage 68 for drug delivery may be used in combination with the light channel 70 without the electrodes 54 . although two channels 70 , 72 are shown , any number of channels could be used and could include a combination of different types of channels — working channels for instruments , optical channels for light or camera , stilets etc . the catheter of fig7 - 11 may be used in a percutaneous drug treatment method . the drug is administered to the patient and the stimulation cathode is positioned adjacent the tissue to be treated by the drug . the tissue is then stimulated using the catheter . this allows selective and localized drug treatment . certain compounds change chemically when stimulated . compounds can also be delivered via electropheretic means . the intrathecal location of this catheter places it past the blood / brain barrier and therefore offers numerous unique opportunities for combination stimulation / drug treatment regimes . in addition , application of various forms of energy ( heat , cold , etc .) independently or with stimulation allow indirect alteration of brain chemistry . also the production of heat in a tissue may make the tissue more susceptible to absorption of a drug . the drug may be administered through the passage 60 or 68 . the source of stimulation and / or the drugs may be external to the body or totally implantable . the implantable system could include a microprocessor , pump , port and an external port for refilling the pump or selection of a different drug or fluid . the drug may be stimulated by electrical energy using the electrodes 54 or by photonic energy using the optic channel 70 . heat may be produced by either the electrodes 54 or the optical channel 70 . cold may be produced by a peltier effect chip or other means , for example gas or liquids . if the drug is responsive to light energy of a specific wavelength , the stimulation uses light energy of that specific wavelength . finally , intrathecal stimulation by light energy may be administered via the catheter — with or without drugs or electrical stimulation — to activate certain tissues . these tissues may , in some cases , be treated in some manner to increase their sensitivity to this method of activation and maybe used in combination with electrical stimulation . the lead 50 as illustrated in fig1 is curved at its distal end 56 which includes the electrodes 54 . sheath 52 includes a wire extension 57 which includes the additional anode electrode 55 and the electrical contact 59 . the curved distal end 56 wraps around the spinal cord or the nerves . this is another form of a fixing device . the stilet 61 can be inserted through passage 60 to maintain the distal end 56 linear until it is adjacent to the nerve or the spinal cord . the passage 60 may then be used for fluid delivery . different shape stilets may be used ( bent tips for example ) to improve steerability during positioning of the catheter , as illustrated in fig1 . additional electrode 55 has the same length l 1 along the sheath 52 or wire 57 as does the electrodes 54 . the difference is that electrodes 54 are illustrated as 270 ° electrodes , whereas additional electrode 55 is a 180 ° electrode . this difference in circumferential dimension provides the difference in surface area . this provides the minimum 2 to 1 surface area as previously discussed . obviously , the distance d 1 between electrodes 54 is substantially less than the distance d 2 between electrodes 54 and 55 . a modified 90 ° electrode is illustrated in cross - section in fig1 . electrode 54 has a smaller radius or diameter a than sheath &# 39 ; s 52 radius or diameter b . for example , the diameter a may be 0 . 0045 inches and diameter b may be 0 . 065 inches . the shape of the sheath and electrode allows introduction through a standard introducer needle . it still offers a reduced area electrode 54 and a stabilizing shape which may be used with or without tines or other fixation means . although the invention has been described for use with an implanted stimulator system ( externally or internally powered ), it should be noted that the same type of regime can be delivered by a non - implantable device . applications for such non - implantable systems could include intra - operative testing of a stimulator system prior to implantation . an external stimulator system is connected to an implantable electrode for a period of trial stimulation prior to determining whether an implantation should be performed . although the present invention has been described and illustrated in detail , it is to be clearly understood that the same is by way of illustration and example only , and is not to be taken by way of limitation . the spirit and scope of the present invention are to be limited only by the terms of the appended claims .
various stimulation catheters are disclosed to lie along and stimulate tissue in the intrathecal space . the electrodes on the leads are various sizes to conserve the battery as well as allowing a more defined area of stimulation . it may also include multiple channels or passages for delivery of drugs , thermal or photonic energy . the sheath includes a fixing element configured to fix the electrode in place along the tissue .