Abstract:
A flexible catheter includes two electrical contacts in a distal region of the catheter and a distal aperture of a hose line. The electrical contacts are connected to a high frequency pulse generator for applying pulsed radio frequency energy for nerve stimulation. A temperature sensor is located in the distal region of the catheter. The flexible catheter is inserted into a region in the spinal canal and the pulsed radio frequency generator is operated, thereby applying pulsed radio frequency energy to a localized region to be treated. The temperature at the distal region of the catheter can also be monitored, and the pulsed radio frequency energy is applied in dependance on the monitored temperature. Further, a position of the catheter is probed by applying a test stimulation signal via the electrical contacts.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to nerve stimulation by electrically applying high frequency (radio frequency) energy to a localized region of a body. In particular, this invention relates to a flexible catheter or lead for treatment of a nervous system. More particularly this invention relates to a flexible epidural catheter and a method for applying pulsed radio frequency electrical energy to a region in the spinal canal. A fully implantable embodiment of the catheter further comprises a transducer being adapted to be subcutaneously implanted. 
     2. Description of Related Art 
     Catheters are known technical medical products which are manufactured for various intended purposes of usage in diagnostics or therapy. For instance, epidural catheters are known which can be inserted by a physician into the epidural space in the region of the spinal canal so as to be able to inject pain-killing drugs, for example. Such a method is particularly applied in treatment of chronic pain. The catheter can remain in the body for a time period of 1 to 30 days, for example, and the injection of the drugs can be effected through external or implanted pumps. 
     Instead of catheters also electrodes are used in therapy of chronic pain. Thus, electrodes for implantation are known, which are connected to a pulse generator for permanent stimulation of the spinal cord or the nerves. There are also known electrodes for stimulation which are connected to a transducer that is to be subcutaneously implanted. In this case the pulses of the generator are transmitted inductively to the transducer through the skin of the patient. 
     Moreover, special needles are known which are connected to a generator of pulsed high frequency. Such special needles and high frequency generators are used to trigger the release of pain-inhibiting substances in the spinal cord by selectively stimulating nerves, thereby effecting a pain treatment. 
     However, usage of these rigid special needles is frequently limited due to anatomical reasons or is avoided because of the risk of injury at introducing the special needles. 
     From European patent application EP 1 181 947 A2 an epidural catheter is known having at least three electrodes arranged in line. The electrodes serve to electrically stimulate nerves or the spinal cord. A channel for administration of drugs can be provided to allow for injecting pain-killing drugs in addition to the electrical stimulation of the spinal cord. 
     With the previously mentioned apparatuses operating with electrical stimulation by means of pulses or, in the case of the special needles, by means of pulsed high frequency, control of the effect of the stimulation is solely by feedback from the patient. The mode and intensity of the stimulation is determined on an empirical basis. However, an upper limit of the intensity of the stimulation is given by possible damage or destruction of the tissue and varies depending on the location and the design of the catheter or special needles and on the structure of the surrounding tissue. Hence, there is no definite correlation between the parameters of the applied pulses and the limit where damage occurs, so that a margin of safety has to be observed. The mentioned deficiencies also pertain to the documents acknowledged below. 
     U.S. Pat. No. 4,379,462 to Borkan et al. shows a catheter electrode assembly for spinal cord stimulation which, unlike the present invention, does not include a channel for drug delivery. Frequencies ranging from 10 to 1400 Hz are applied in the stimulation. 
     International application WO 92/07605 shows an epidural catheter intended to be implanted either temporarily or permanently. In a permanently implantable embodiment, the catheter includes an implantable pulse generator and, at a separate branch of the catheter, an implantable drug reservoir. 
     U.S. Pat. No. 5,423,877 to Mackey shows a catheter for use in acute pain management intended for electrical stimulation of the epidural space of the spinal cord. The catheter comprises a conduit for delivery of drugs. The catheter produces a longitudinally elongated electrical field, as leads of the catheter will electrically stimulate a longitudinal distance of from 10 to 15 cm. However, this is not suitable for selective stimulation of nerves. 
     U.S. Pat. No. 5,374,285 to Vaiani et al. discloses a spinal electrode catheter which can be connected to a stimulator. 
     U.S. Pat. No. 5,081,990 to Deletis shows a catheter for spinal epidural injection of drugs and measurement of evoked potentials. Measuring electrodes located on the tip of the catheter are connected to a voltage detector. The electrodes are, however, not adapted for electrical stimulation. 
     German patent application DE 36 02 219 A1 shows a flexible epidural neuroelectrode comprising a channel with lateral apertures. The electrode or catheter allows to administer pharmacological solutions epidurally and to measure the evoked spinal potentials at the same time (spinal cord monitoring). The electrode is, however, not adapted for electrical stimulation. 
     European patent application 1 145 731 A2 shows a multi-lumen, multi-functional catheter system. The catheter system is intended for use for a therapy of the parenchymal tissues of the brain. Amongst the generally mentioned uses is sampling of fluids within the extracellular and interstitial spaces of the brain, spinal cord, or other body tissues, concurrently with drug delivery or electrical recording/stimulating. Information gathered by a sensing element or measuring device is received by a host computer to evaluate a treatment procedure or patient conditions around the locality of treatment. A treatment procedure would be evaluated either by an operator or by artificial intelligence. Possible sensing systems include thermometric sensing systems. However, unlike the present invention, the application EP 1 145 731 A2 does not provide for a flexible epidural catheter having electrical contacts for stimulation. 
     Unlike the present invention, none of the documents described above does provide for the usage of high frequency (radio frequency) energy for electrical nerve stimulation. Also none of these documents describes a flexible catheter comprising a temperature sensor disposed in the distal region of the catheter. Actually, only the European application EP 1 145 731 A2 mentions thermometry at all. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a flexible catheter for treatment of a nervous system, which is suitable for a larger range of application than conventional catheters, electrodes or special needles, and a method for treatment of a nervous system using said catheter. 
     A further object of the invention is to provide a catheter which is adapted for stimulation with pulsed high frequency. 
     A further object of the invention is to provide a catheter and a method for applying pulsed radio frequency energy to a region in the spinal canal. 
     A further object of the invention is to provide a flexible lead for treatment of a nervous system, which is suitable for a larger range of application than conventional catheters, electrodes or special needles, and a method for treatment of a nervous system using said lead. 
     The objects of the present invention are achieved by providing a flexible catheter, particularly a flexible epidural catheter, according to the present invention, which comprises at least two electrical contacts in a distal region of the catheter; leads of the electrical contacts are located inside the catheter; two of the leads have a connection for a high frequency pulse generator for nerve stimulation. 
     In one embodiment, the stimulation catheter for insertion in a body is part of a stimulation system, the system further comprising an external contact; said external contact being adapted to be exposed to an external part of said body. With this system, for example, pulsed high frequency can be applied between said contact in a distal region of the catheter and said external contact. Moreover, nerve conduction can be measured beginning at the nerve root. 
     When said flexible catheter forms a part of a flexible probe having at least a second lead and at least a second electrical contact, said radio frequency energy can be applied between said first and second contacts. Pulsed high frequency can be applied between said two contacts using a bipolar signal generator, for example. 
     A catheter having at least one electrical contact at a distal region is suited for usage with a unipolar pulse generator like, for example, one of the device N50 of the company Stryker Howmedica, the device RFG-3C+ of the company Radionics, and the device Neurotherm of the company RDG Medical. 
     Preferably, the catheter of the invention is adapted to be inserted into one of an epidural space, a spinal space, a paravertebral space, an intracerebral region, and regions of ganglia of the head or neck. 
     Preferably, the catheter is an epidural catheter. When such a catheter is inserted into the region of the spinal canal, it is possible to apply a pulsed high frequency current via two electrical contacts to the spinal cord or the spinal nerves instead of or additionally to the injection of pain-killing drugs, according to requirements. Thus, by stimulating the nerves inside the spinal canal, in many cases a treatment or stimulation of nerve tissue with special needles outside the spinal column or in dangerous regions can be avoided, and also those nerves can be treated with high frequency pulses which otherwise would not have been accessible for this treatment. Thus, the catheter according to the invention opens up a distinctly enlarged range of application as compared to a conventional catheter or conventional needles. 
     The catheter enables the stimulation of spinal dorsal nerve roots proximal to the spinal nerve ganglia with radio frequency and allows to apply pulsed radio frequency (PRF) in the spinal canal and other targets. New treatments are thus possible. With the catheter and the PRF it is possible to reach vulnerable structures and to treat them with PRF without fear of damaging them. 
     The invention includes providing a method for applying pulsed radio frequency energy to a region of the spinal canal, this method comprising the steps of:
         inserting a flexible epidural catheter into said region, said catheter having at least two electrical contacts in a distal region of the catheter;   operating a pulsed radio frequency generator; the pulsed radio frequency generator being coupled to the electrical contacts; thereby applying pulsed radio frequency energy via said electrical contacts to at least one of the spinal cord or spinal nerves;       

     whereby in said region at least one of the spinal cord or spinal nerves is treated. 
     In one embodiment, the method further comprises the step of probing a position of the catheter by applying a test stimulation signal via said electrical contacts and thereby probing a sensual response to the test stimulation signal; thereby gaining information about the position of the catheter relative to the at least one of spinal nerves and a part of a spinal cord which is to be treated. Preferably, the test stimulation signal is applied between two electrical contacts in the distal region of the catheter, even if the pulsed high frequency energy is applied between one of these contacts and an external contact. 
     A method for applying pulsed radio frequency energy to at least one of a nerve, a nerve root, a nerve ganglion, and a part of a spinal cord in a space of a spinal canal can be carried out following the steps of:
         inserting a flexible catheter percutaneously into said space, the catheter having at least one electrical contact at its distal region;   then pushing the catheter forward, thereby positioning said at least one contact in the spinal canal;   adjusting the catheter such that said at least one electrical contact is in a region of the at least one of a nerve, a nerve root, a nerve ganglion, and a part of the spinal cord; and   operating a pulsed radio frequency generator, thereby applying pulsed radio frequency energy via the at least one electrical contact to the region of the at least one of a nerve, a nerve root, a nerve ganglion, and a part of a spinal cord. Thereby, the at least one of a nerve, a nerve root, a nerve ganglion, and a part of a spinal cord is treated.       

     In one embodiment of this method, the method further comprises a step of repeatedly adjusting the catheter to different positions. Thereby, several of nerve roots and parts of the spinal cord can be treated, for example, one after another, without having to insert the catheter twice. 
     The invention includes providing a flexible endoscopic probe. The endoscopic probe comprises at least one electrical contact in a distal region of the probe, a connection for a high frequency pulse generator for nerve stimulation; and at least one electrical conductor running inside the probe; the conductor connecting said at least one contact to said connection. The endoscopic probe allows to position the contact under endoscopic control and to apply pulsed high frequency endoscopically. Preferably, the endoscopic probe is compatible to standard light cables. The endoscopic probe can also be combined with the catheter to one combined catheter/endoscopic probe for stimulation with pulsed high frequency. In one embodiment, the endoscopic probe is at least a double lumen probe. One lumen contains an optical conductor, and another lumen contains a lead or the electrical conductor, thereby constituting a lead. 
     The same methods as described above can be applied using a lead without a lumen for transport of liquid instead of the catheter. By inserting a flexible lead into one of an epidural space, spinal space, paravertebral space, intercerebral region and ganglia of the head and neck, it is possible to treat at least one of a nerve, a nerve root, a nerve ganglion, a part of the spinal cord and a part of the brain, for example. 
     The lead can also pass through an endoscopic probe. This allows to position the lead under endoscopic control and to apply pulsed high frequency endoscopically. 
     In one embodiment of the method, the lead further comprises a temperature sensor at the distal region of the lead, leads of the temperature sensor being located inside the lead, and the method further comprises the step of:
         monitoring a temperature using the temperature sensor at the distal region of the lead;   wherein in the step of operating the pulsed radio frequency generator, the pulsed radio frequency energy is applied depending in a predetermined way on the monitored temperature.       

     In another embodiment, the method comprises the steps of:
         displacing the lead to a second localized region; and then   repeating the step of operating the pulsed radio frequency generator;   whereby in said second localized region at least one of a nerve, a nerve root, a nerve ganglion, a part of the spinal cord and a part of the brain is treated.       

     Indications and targets for application of pulsed radio frequency with the invented catheter, lead and method are: pain treatment, diagnostic and therapeutic stimulation, injection of medicaments. All locations in the spinal canal from the medulla oblongata to the hiatus sacralis can be treated. In particular, indications and targets are: treatment of sympathetic and parasympathetic nerves and fibers in vascular diseases, treatment of spasticity, treatment of spastic and motor disorders and pain in: the brain, midbrain, thalamus, hypothalamus, gasserian ganglion, cerebellum, medulla oblongata, spinal cord, nerve roots and nerves in the spinal canal, retrograde and direct stimulation of the dorsal root ganglia, dorsal root entry zone (DREZ), stimulation of the dorsal column. For some of these uses, little modifications of the catheter are needed, as will be apparent to those skilled in the art. 
     Generally the indication is presently estimated to be at least similar to all indications of the PRF and temperature denervations. In addition following treatments are possible: radicular diseases as the post herpetic neuropathy, mono- or polyneuropathies, complex regional pain syndrome (CRPS), neuralgia, ischaemic disease, pain, spasticity and motor disorders. 
     Preferably, the catheter of the invention further comprises a distal aperture of at least one hose line being located between two of the contacts. Such an arrangement allows to treat the same area with drugs as well as with high frequency stimulation without having to alter the location of the catheter. Moreover, due to the proximity of the contacts to the distal aperture of the catheter, the advantage results that during insertion of the catheter, the location of the catheter can be probed via a test stimulation with reduced voltage and frequency. Thus, stimulation can serve to localize the pain or the pain conducting nerves, and in this manner, a preferably well suited position for the catheter can be found. Another advantage is that the x-ray contrast of the contacts is sufficiently high to allow positioning of the catheter with x-ray monitoring without application of a contrast agent. 
     Preferably, the contacts of the catheter are disposed in a row along the longitudinal direction of the catheter. Preferably, the catheter ends at its distal end with a contact the outer surface of which has the shape of a cap. At least one of the contacts preferably has an outer surface having the shape of an annular strip encircling the catheter. 
     Preferably, the catheter is also connectable to pulse generators being applicable for permanent stimulation of nerves. 
     Several possible and advantageous configurations of the catheter are conceivable. For example, the leads of the contacts can be disposed within a hollow space of the catheter which is separated from the inner space of each hose line. The leads of the contacts can also run within the wall of the catheter. The catheter can also comprise a hose line in the form of a tube disposed within the catheter and, for example, filling a hollow space of the catheter. 
     Preferably, the outer diameter of the catheter is less or equal 1.67 mm, more preferably 1.33 mm, and the catheter preferably has a length of at least about 60 cm. Preferably, the contacts are disposed one after another at a distance of a few millimeters along the longitudinal direction of the catheter. Preferably, said distance is 4 mm. 
     In an embodiment of the invention, the catheter further comprises a temperature sensor in the distal region of the catheter: leads of the temperature sensor are located inside the catheter. 
     Thus, with the catheter further comprising a temperature sensor at the distal region of the catheter, leads of the temperature sensor being located inside the catheter, a method as described above can be carried out, the method further comprising the step of monitoring a temperature using the temperature sensor at the distal region of the catheter, wherein in the step of operating the pulsed radio frequency generator, the pulsed radio frequency energy is applied depending in a predetermined way on the monitored temperature. For example, at least one parameter of the pulse generation is automatically changed when a specific temperature has been reached. 
     When the epidural catheter comprising the temperature sensor is inserted into the area of the spinal canal, and a pulsed high frequency current is applied to the spinal cord or the spinal nerves via two contacts, an increase of temperature caused by the stimulation or effected by the applied electrical energy can be monitored by means of the temperature sensor. For example, a temperature monitoring circuit or device can be provided which automatically switches off or temporarily suppresses the stimulation when an upper temperature limit of 42° C. is reached so as to avoid thermal damaging of the tissue. 
     By monitoring the tissue&#39;s temperature using a temperature sensor, nerves or the spinal cord can be treated with pulses or pulsed high frequency the parameters of which can be varied within larger boundaries without having to worry about thermally damaging the tissue. Thus it is possible to optimally adapt the intensity of the stimulation to the needs of the patient, especially when using pulsed high frequency which is high in energy. Such frequency can also be used with frequently repeated stimulation or permanent stimulation over a longer time, because an accumulated rise of temperature can reliably be monitored. Even if the electrical parameters of the tissue change due to adsorption of tissue or modification of the local tissue structure, and more energy is introduced due to a higher conductive loss, damaging can be avoided because of the temperature monitoring. Thus, the invented catheter opens up a still larger range of application compared to a conventional stimulation catheter. 
     Preferably, the temperature sensor is a thermocouple, for instance of the type nickel-chromium/nickel. The advantage of a thermocouple is that its thermal voltage is independent of the geometry of the point of contact of the two leads. Moreover, the thermocouple can be manufactured with very thin wires having an accordingly low thermal inertia, resulting in immediate detection of an increase of temperature. Since a thermocouple is an active sensor, conducting resistance is unproblematic. The leads of the temperature sensor can be the wires of the thermocouple. 
     Preferably, the temperature sensor is thermally connected to one of the electrical contacts. In this way, the temperature can be measured directly at the heated spot, and a good thermal contact is achieved. 
     One of the connecting leads of the temperature sensor can also serve as a lead of one of the electrical contacts. Thereby, one lead is saved. 
     The leads of the contacts and/or the connecting leads of the temperature sensor can be disposed within a hollow space of the catheter which is separated from the inner space of each hose line. The leads of the contacts and/or the connecting leads of the temperature sensor can also run within the wall of the catheter. 
     In another embodiment the catheter comprises a transducer; the electrical contacts are connected via the leads to the transducer, and the transducer is adapted to be subcutaneously implanted and is adapted to transmit high frequency pulses for nerve stimulation onto the leads; the catheter further comprises a port in a proximal area of the catheter; the port is adapted to be subcutaneously implanted. Preferably, the catheter is an epidural catheter. 
     After insertion of the catheter, the catheter can be completely implanted, including the transducer and the port, beneath the skin near to the point of entrance into the body. When later using the catheter for stimulation of the spinal cord or of nerves, for example, the risk of infection is reduced due to the closed skin and the risk of complications is reduced. Moreover, the catheter being concealed below the skin is easier to handle for the patient. 
     When such a catheter is inserted as an epidural catheter into the area of the spinal canal, for example, in addition to stimulation of the spinal cord or the spinal nerves by means of a pulsed high frequency current, injection of a pain-killing drug via the port can take place, according to requirements. The implanted port can, for example, be configured in form of a septum, which can be reached from external and pierced with a injection needle. 
     Thus, this embodiment of the catheter has further distinct advantages of usage over a conventional catheter and thereby opens up an even further range of application. 
     Optionally, between the port and the catheter, a drug pump can be provided being likewise implantable. Thereby, an evenly distributed dispensing of drugs is achievable over a longer time period. 
     Optionally, the transducer comprises a device for storing energy. This device can effect the energy supply of a drug pump, for example. 
     The high frequency pulses can be transmitted inductively from an external device to the transducer, for example. Alternatively, energy can be supplied inductively to the transducer, and the transducer itself generates the pulses for nerve stimulation. 
     The transducer can also comprise a pulse generator for stimulation or permanent stimulation of nerves. 
     Preferably, the transducer comprises a coil. In particular, the coil can be a coil for sending and receiving. Thus the coil being utilized for sending, the catheter is adapted to send signals to a device outside the body. 
     Preferably, the catheter further comprises a temperature sensor in the distal region of the catheter, and leads of the temperature sensor are located inside the catheter. The feature of the temperature sensor and advantageous applications have been described above in detail. Preferably, the transducer is adapted to receive a signal effected by the temperature sensor. 
     For monitoring the temperature the transducer can send signals to an external device, and a monitoring circuit can be provided externally or disposed within the transducer, said monitoring circuit automatically switching off or temporarily suppressing the stimulation when an upper temperature limit of 42° C., for example, has been reached, so that thermal damaging of the tissue can be avoided. 
     Preferably, the transducer is adapted to receive an electrical signal from the electrical contacts. Thereby, a measurement of an excitation potential of a nerve can take place, for example. 
     In a preferred embodiment the catheter further comprises an injection chamber for the catheter being located at the port. Thereby, the injection of drugs via the port is facilitated and the injection chamber can also serve as a reservoir chamber for an implantable drug pump. 
     In a preferred embodiment, the transducer and the port are disposed in a flat casing being subcutaneously implantable. The combination of the port and the transducer in one casing facilitates locating them in case a drug is to be injected into the catheter, for example. Furthermore, the casing can accommodate the coil of the transducer, for example, and can serve as a supporting surface for the injection chamber or for the port, thus facilitating the handling when introducing an injection needle into the port. 
     All embodiments of the catheter or lead mentioned above can be implanted to remain in the body for a period of, for example, up to several days or weeks. In this way, high frequency pulses can be applied at several times. 
     Further scope of the applicability of the present invention will become apparent from the detailed description of preferred embodiments of the invention given hereinafter. However, it is to be understood that the detailed description and the specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only and thus are not limiting of the present invention and wherein 
         FIG. 1  is a schematic view of an epidural catheter having two contacts, a thermocouple, and a hose line; 
         FIG. 2  is a schematic longitudinal sectional view of a tip of a first embodiment of an epidural catheter; 
         FIG. 3  is a transverse sectional view of the catheter of  FIG. 2 ; 
         FIGS. 4 and 5  show a second embodiment of a catheter in views corresponding to  FIGS. 2 and 3 ; 
         FIGS. 6 and 7  show a third embodiment of a catheter in views corresponding to  FIGS. 2 and 3 ; 
         FIG. 8  is a schematic view of an embodiment of an epidural catheter having a transducer with a coil within a flat casing being subcutaneously implantable, as well as an external device having an antenna; 
         FIG. 9  is another view of the casing and the transducer with the coil; 
         FIG. 10  is a schematic view of a stimulation lead passing through an endoscopic probe; the lead having one electrical contact and a thermocouple; 
         FIG. 11  is a cross-sectional anatomical view of a spinal cord in a spinal column; and 
         FIG. 12  is a sectional view of a spine taken along the length of the spine; 
     
    
    
     For reasons of clarity, the drawings are not drawn to scale. 
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  shows an epidural catheter  10  comprising in its distal region a distal contact  12  and a proximal contact  14  between which a lateral aperture  16  of a hose line  18  is disposed. Contacts  12  and  14  are drawn with hatching. The distal contact  12  forms a cap encasing the end of the catheter  10 . The proximal contact  14  forms an annular strip encircling the catheter  10 . The edges of the contacts  12  and  14  are flush with a mantle  20  of the catheter  10  made of silicone rubber. 
     The outer diameter of the mantle  20  is 1.33 mm, corresponding to a specification of 4 French. In longitudinal direction of the catheter  10  the contacts  12  and  14  extend to a length approximately corresponding to the outer diameter of the mantle  20 . The contacts  12  and  14  are offset to each other by approximately 4 mm in longitudinal direction of the catheter  10 . The overall length of the shown epidural catheter  10  is 60 cm, however, other lengths are also conceivable. 
     Within the catheter  10 , a thermocouple  21  ( FIG. 2 ) is thermally connected to the distal contact  12 . Electrical leads  22  for the electrical contacts  12 ,  14  as well as connecting wires  23  and  24  of the thermocouple  21  run within the mantle  20  parallel to hose line  18  and are, like hose line  18 , indicated with dashed lines in  FIG. 1 . Thermocouple  21  is of the type nickel-chromium/nickel, wire  23  being of nickel-chromium and wire  24  being of nickel. The internal configuration of catheter  10  will be further explained below with  FIGS. 2 and 3 . 
     Catheter  10  comprises a fixation device  25  which can serve to fasten the catheter to a point where the catheter enters a body, the element  25  being configured like in a conventional implantable catheter. Furthermore, in a known manner an aseptic guide wire (not shown) is disposed within the hose line that serves to push the catheter  10  to the desired position in the spinal canal and is then retreated. The guide wire is slightly bendable in the region of its leading end. 
     At a connecting member  26 , the electrical leads  22  are led out of the mantle  20  of catheter  10  in form of electrically isolated wires  28 , and wires  23  and  24  are led out of the mantle  20  into an isolated cord  29 . The hose line  18  continues within a mantle  30 , which is a continuation of mantle  20 , to a connector  32 . Said connector serves for connecting a syringe or a drug pump and is configured in a conventional manner. Between the connector  32  and connecting member  26  is disposed a clip  34  that allows to clamp hose line  18  and re-open it by releasing clip  34 . The clip  34  is configured in a conventional manner, as well, and can also be disposed at the connection  32 . 
     Wires  28  are provided with electrical connectors  36  and  38 . Connector  36  is connected to the distal contact  12 , and a connector  38  is connected to the proximal contact  14  of the catheter. Connectors  36  and  38  are merely schematically shown in the drawing, and can be encoded in terms of color and/or in terms of the shape of contacts of the connectors. Said connectors are adapted to be directly or via an adapter (not shown) connected to a pulse generator  39  generating a pulsed high frequency current. The pulse generator  39  can, for example, be the device N50 of the company Stryker Howmedica, the device RFG-3C+ of the company Radionics, or the device Neurotherm of the company RDG Medical. 
     The connectors  36 ,  38 , wires  28 , leads  22 , and the contacts  12  and  14  are adapted both for application of pulses for a test stimulation of nerves or of a spinal cord having, for example, a voltage in the range of 0 to 12 V, a frequency in the range of 50 to 150 Hz, and a pulse width in the range of 150 to 400 microseconds, as well as for applying pulsed high frequency, for example, within a voltage ranging from 20 to 30 V and a pulsed frequency of 500 kHz and a pulse width of 20 ms. The numerical values given are only examples to illustrate the range of application of the catheter. 
     A bipolar connector  40  of cord  29 , being secured against connecting with the wrong polarity, is connected to the wires  23  and  24  of the thermocouple  21 . Connector  40  is adapted for connecting to a measuring device  41 , which measures the temperature in the region of the distal contact  12  of the catheter using the thermocouple  21 . 
     The measuring device  41  can be integrated into the pulse generator  39  in form of an appropriate circuit, for example, or can be connected to the pulse generator, so as to automatically effect a switching off or a change of parameters of pulse generation when a specific temperature is reached; said specific temperature being adjustable. For example, an adaptive or stepwise control of pulse generation can be provided that reduces the power and/or frequency of the pulses when an intended upper temperature limit is approached. Alternatively or, if the temperature is too high, additionally the pulse generation can be temporarily stopped until a sufficiently low temperature is reached again. 
       FIG. 2  shows the tip of the catheter  10  of  FIG. 1  as a longitudinal sectional view, though the catheter  10  as well as the leads  22  and wires  23 ,  24  disposed in front of and behind the plane of the drawing are shown in a sectional view. 
     The electrical leads  22  and wires  23 ,  24  each comprise an isolation  42 . Leads  22  are internally soldered to the distal contact  12  and the proximal contact  14  respectively. The thermocouple  21  is formed by a contact point of the nickel-chromium wire  23  and the nickel wire  24  and is connected to the contact  12  via the wire  23  in immediate proximity. Thus, a good heat conduction between the contact  12  and the thermocouple  21  is accomplished. 
     The mantle  20  of the catheter  10  comprises an internal partition wall  44  dividing the inside of the catheter  10  into a first hollow space forming the hose line  18  and a second hollow space  46 . The leads  22  and wires  23 ,  24  run within this second hollow space  46 . The electrical contacts  12  and  14  are separated from the hose line  18  by the mantle  20 . The lateral aperture  16  of the mantle  20  opens the hose line  18  to the outside. 
       FIG. 3  shows a cross-sectional view of the catheter  10  along the line III-III of  FIG. 2 . The arrangement of leads  22  and wires  23 ,  24  within the second hollow space  46  of the mantle  20  is shown. 
       FIGS. 4 and 5  show a second embodiment, wherein the mantle  20  has no internal partition wall  44  forming a second hollow space  46 . Instead the electrical leads  22  and the wires  23 ,  24  with their respective isolations  42  run within a thickened area of the wall of the mantle  20  of the catheter  10 . The hose line  18  is formed inside the mantle  20  in a way similar to the first embodiment. 
       FIGS. 6 and 7  show a third embodiment which differs from the second embodiment in that inside the mantle  20 , there is an additional internal tubular layer  48  forming the hose line  18 . The mantle  20  encloses the tube formed by the internal layer  48  as well as the isolations  42  of the electrical leads  22  and wires  23 ,  24 . At least at the aperture  16 , which penetrates the layer  48  and the mantle  20 , the internal layer  48  is tightly connected to the mantle  20 . However, the internal layer  48  can also be a part of a mantle of the catheter constituted of two or more layers. 
     The tube formed by the inner layer  48  ends on the other side of the aperture  16 . It can, however, also extend into the cap formed by the distal contact  12  as indicated by chain dotted lines. The internal layer  48  is isolated by the mantle  20  from the contacts  12  and  14 . 
     The shown embodiments are meant to demonstrate a possible arrangement and contacting of the electrical leads  22  and of the thermocouple  21  and its wires  23 ,  24  and to present possible constructions of the hose line  18 . It is to be understood that the catheter of the invention can also have a configuration that differs from these embodiments, for example a combination of the inner layer  48  of  FIG. 7  with the two hollow spaces of the mantle  20  of  FIG. 3 , or a different location of the thermocouple  21 . 
     Alternatively, the electrical contact  12  can also be configured having the shape of an annular strip. It goes without saying that more than the two shown contacts can be provided. 
       FIGS. 8 and 9  show another embodiment of the catheter  10  the distal part of which is constituted similar to the catheter of the third embodiment shown in  FIGS. 6 and 7 . 
     As the proximal end of the catheter  10 , the catheter is seamlessly connected to a flat casing  52 . The upper region of the casing  52  contains an injection chamber  54  which is connected to the hose line  18 . The upper wall of the injection chamber  24  comprises a bulge forming a port  56  in form of an injection septum. Via the port  26 , the injection chamber of the implanted catheter is accessible from external by way of an injection needle, for example. The injection septum is made in a known manner such that its wall is sufficiently dense and elastic so as to provide a reliable sealing after an injection needle previously inserted through the septum is retracted. 
     In the lower region of the casing  52  a coil  58  is arranged spirally, as can be seen more clearly in  FIG. 9 . The coil  58  is a sending and receiving coil and is connected to a transducer  60 . The transducer  60  has several functions which will be explained hereinafter. 
     At the casing, an aperture for introducing the guide wire is closed before implanting the casing. 
     The electrical leads  22  and the wires  23 ,  24  are connected to the transducer  60 . The transducer is adapted to measure currents and/or voltages. For example, the transducer  60  can measure a thermovoltage on the wires  23  and  24  of the thermocouple, thereby monitoring the temperature at the distal end of the catheter  10 . The transducer  60  can also measure potentials between the electrical contacts  12  and  14 , for example. Such potentials can provide information about the excitation condition of nerve roots or the spinal cord, for example. 
     The transducer  60  is addressed by an external device  70  comprising an antenna  72  cooperating with the sending and receiving coil  58  of the transducer  60 . The pulse generator  39  and indication devices  76  are connectable to the external device  70 . 
     The pulse generator  39  produces a pulsed high frequency current. The high frequency pulses are inductively transmitted by the antenna  72  to the coil  58  and are relayed by the transducer  60  to the leads  22  of the electrical contacts  12  and  14 . The contacts  12  and  14 , the leads  22 , and the transducer  60  and the coil  58  are adapted both for application of pulses for a test stimulation of nerves or of a spinal cord having, for example, a voltage in the range of 0 to 12 V, a frequency in the range of 50 to 150 Hz, and a pulse width in the range of 150 to 400 microseconds, as well as for applying pulsed high frequency, for example, within a voltage ranging from 20 to 30 V and a pulsed frequency of 500 kHz and a pulse width of 20 ms. The numerical values given are only examples to illustrate the range of application of the catheter. 
     During pauses in-between the pulses and at times where no stimulation takes place, the transducer  60  can send signals via the coil  58  to the external device  70 , which receives the signals by means of its antenna  72 . Information can be transmitted concerning the temperature measured by the temperature sensor as well as information concerning electrical signals the transducer  60  receives from the electrical contacts  12  and  14 . Furthermore, further signals can be transmitted from the transducer  60  to the external device  70  or in the opposite direction for control purposes, for example. The indication devices  76  can display measured voltages, currents or temperatures. 
     In case the transducer  60  detects that an allowable maximum temperature of the temperature sensor  21  is exceeded, the transducer  60  can effect an automatic switching off or changing of parameters of pulse generation of the pulse generator  39  by means of control signals, for example. Thus, an adaptive or stepwise control of pulse generation can be provided that reduces the power and/or frequency of the pulses when an intended upper temperature limit is approached. Alternatively or, if the temperature is too high, additionally the pulse generation can be temporarily stopped until a sufficiently low temperature is reached again. 
       FIG. 9  shows the casing  52  of the catheter  10  of  FIG. 8  as viewed from the bottom of  FIG. 8 . The spiral configuration of the coil  58  is visible. 
       FIG. 10  shows an endoscopic probe  80  with a light conductor  82  that contains optical fibers for light delivery and visualization, as is known in the art. However, the endoscopic probe  80  also comprises a stimulation lead  84  having a distal electrical contact  12  in the distal region of the probe  80 . The light conductor  82  ends at the distal end of the probe  80 . 
     The endoscopic probe  80  and the stimulation lead  84  are configured similar to the catheter  10  of  FIG. 1 , the major difference being that the hose line  18  is replaced by the light conductor  82 . Therefore, similar parts are numbered with the same numbers as in  FIG. 1 , and the respective parts of the description of the catheter of  FIG. 1  are included herein by reference. Another difference to the catheter  10  of  FIG. 1  is that the stimulation lead  84  has only one contact  12  in its distal region. This contact  12  is connected to the connector  36 . A second, external contact  86  is connected via a wire  88  to the connector  38 . 
     Contact  12  forms an annular strip encircling the probe  80 . A thermocouple is thermally connected to the contact  12 . At the connecting member  26 , the light conductor  82  continues within a light cable  90  that is compatible to standard light cables for endoscopy and ends at a connector  92 . 
       FIG. 11  shows a sectional view of a spinal cord  100  and a spinal column at a level of a vertebra  102 . Dorsal roots  104  and ventral roots  106  as well as spinal ganglia  108  of spinal nerves  110  are indicated. Within the spinal canal, an epidural space  112  is shown into which the catheter  10  is to be inserted. 
       FIG. 12  schematically shows insertion of the partially shown catheter  10  into the spine. For example, the catheter  10  can be placed at the medullary conus  114  and cauda equina  116 . The 12th thoracic vertebra  118 , the 5th lumbar vertebra  120  and the 1st sacral vertebra  122  are indicated. 
     The catheter  10  can be inserted in a similar manner as conventional spinal cord stimulation (SCS) electrodes. A guide wire (mandrel) is used to steer the catheter in place and can be bent. The procedure is as easy as the placement of an SCS. 
     The inventor found out that it is plausible to place the catheter at the conus  114  and cauda equina  116 . Here the nerve roots converge and can be treated by the passing catheter  10  one by one. Thus, the catheter is, for example, inserted at the contralateral or ipsilateral side into the mid-line of epidural space  112  or laterally and pushed obliquely upwards, passing the dorsal roots  104  of the spinal nerves  110 . The catheter  10  is usually inserted under local or general anesthesia percutaneously through a Tuhoy needle by the loss of resistance technique into the epidural space  112 . The catheter  10  is then pushed forward in an oblique way to lie at the dorso-lateral wall of the spinal canal. 
     The point of insertion of course depends on the nerves intended to treat. If, for example, it is intended to treat the lumbar nerves the catheter is introduced at the L 2 / 3  space, as indicated in  FIG. 12 , pushing it up to the Th.  12  level, thus enabling to stimulate the nerves Th 12  up to L  5 . Or if it is intended to stimulate the sacral nerves the catheter has to be inserted at a deeper level L 3 / 4 , as indicated with a dashed line, pushing it up to the level L 1 . Then it is possible to treat the entire lumbar roots in addition to all sacral roots. 
     To be sure which nerves are affected they can be identified by stimulation with a frequency of 80 Hz, for example. The response of the patient is an accurate indication for the distances of the tip to the desired nerve. 
     After inserting and pushing upwards the catheter  10 , at first the most cranial nerve root is stimulated and there, the PRF application is performed. Then, while stimulating, the catheter  10  is slowly retrieved. The sensations diminish and then when reaching the next nerve root rise again. There, the next PRF application is started. This procedure is repeated until all nerve roots positioned in the course of the catheter have been treated. The temperature sensor at the tip allows to be continuously informed about the temperatures at the tip. 
     The catheter  10  can be left in place up to 30 days. The procedures can be repeated at the same or any other level. It is also possible to add the catheter to an implantable device to repeat the PRF application at any time, as described herein before. 
     The catheter  10  is cannulated and allows to inject fluids, like steroids and other substances used in adhesiolysis, if desired. Medicaments can be injected as in any other catheter. Thus, it is possible to stimulate the dorsal nerve roots and ganglia proximal to the spinal ganglia and to apply PRF. 
     Especially when dealing with several segments and in difficult anatomical structures this flexible catheter is easier and safer to use. There are at least one ore more contacts at the tip of the catheter. The distal contact applies PRF and stimulation with all possible frequencies. This enables a very accurate positioning of the tip. Adapters can be provided for to connect the catheter to any radio frequency generator. 
     If intended for research, nerve conduction can be measured. 
     The catheter allows direct application of pulsed radio frequency to neural structures in the skull, the epidural space and in the spinal canal. This was until today impossible. It largely extends the use of radio frequency which was limited by using thermo-lesion needles outside of the epidural space, the spinal cord or canal. It is safer than heat and can be applied directly to the spinal cord. A permanent temperature control at the top of the catheter makes the procedure safe. 
     Adhesiolysis and the injection of steroids are possible. Exact placement by stimulation is another benefit of the catheter. The new oblique application technique could be of great therapeutic value. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Furthermore, all the disclosed elements and features of each disclosed embodiment of the catheter, stimulation system, lead, endoscopic probe or method can be combined with, or substituted for, the disclosed elements and features of every other disclosed embodiment of the catheter or method, respectively, except where such elements or features are mutually exclusive. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to-be included within the scope of the following claims.