Abstract:
A method and apparatus are disclosed for improving accuracy of placement of needles during delivery of high frequency signals near a neural structure to form lesions. The apparatus includes a needle that can deliver electrical current where a portion of the needle is electrically insulated and a portion of the needle is exposed and electrically active, thereby causing lesions. The needle includes radiopaque marking to differentiate the electrically insulated region from the exposed region, allowing it to be better discerned in the body under fluoroscopy.

Description:
TECHNICAL FIELD  
         [0001]    The invention relates to a needle that delivers electrical current and more particularly to a needle that delivers high frequency electrical current in the vicinity of a neural structure.  
         BACKGROUND OF THE ART  
         [0002]    A minimally invasive technique of delivering high frequency electrical current has shown to relieve localized pain in many patients. The high frequency electrical current is typically delivered from a generator via connected electrodes that are placed in a patient&#39;s body. The needles include an insulated shaft with an exposed electrically conductive tip. Tissue resistance to the high frequency electrical current at the tip causes heating of adjacent tissue. When temperature increases sufficiently tissue coagulates. The temperature that is sufficient to coagulate unmyelinated nerve structures is 45° C., at which point a lesion is formed and pain signals are blocked. This results in relief from pain.  
           [0003]    Needles with varying geometries are used in such applications. For example, the exposed tip of the needle can be pointed, blunt and rounded or open, varying in shape in accordance with the needs of different procedures. Pointed tips are self-penetrating while rounded tips are useful in soft tissue areas such as the brain where it is critical not to damage nerves. However, blunt needles can do more tissue damage than small diameter sharp needles. Open tips can be used to deliver a therapeutic agent during electrical treatment. U.S. Pat. No. 6,146,380 to Racz et al. describes electrical needles with curved tips used in high frequency lesioning.  
           [0004]    This technique of relieving back pain has also been used with needles penetrating the intervertebral disk. U.S. Pat. Nos. 5,433,739 and 5,571,147 to Sluijter et al. and WIPO publication WO 01/45579 to Finch et al. describe needles that are used in the intervertebral disk to relieve back pain caused by herniated disks.  
           [0005]    For treatment, the needle having a hollow shaft and a removable stylet therein is inserted into the patient&#39;s body and positioned. Once the needle is positioned, the stylet is withdrawn and a distal end of a high frequency probe is inserted until the distal end of the probe is at least flush with the distal end of the shaft, (i.e. the exposed tip). The probe is connected to an external signal generator that generates high frequency electrical current.  
           [0006]    These needles are often used to denervate certain portions of a spine of the patient. Accurate placement of the needle in a complicated structure like the spine requires great technical skill by a treating clinician. In these procedures, the needle is viewed via X-ray or a fluoroscope to assist placement and is guided into the body. One limitation of the technique used currently is that the insulated shaft is not distinguishable from the exposed tip of the needle under X-ray or fluoroscopy. Therefore, accurate visualization of the exposed tip is not possible.  
           [0007]    Prior art devices for accurate placement have not been used in conjunction with radio frequency needles. Radiopaque marking has been used to accomplish precise placement of catheters and stents. U.S. Pat. No. 5,429,597 to Demello et al. discloses a balloon catheter having a radiopaque distal tip composed of a polymer mixed with a radiopaque powder such as tungsten. U.S. Pat. No. 6,315,790 to Gerberding et al. describes a catheter constructed with radiopaque polymer hubs where the hubs provided the dual function of stent crimping and marker bands.  
           [0008]    An example of a catheter utilizing an external marker band is described in U.S. Pat. No. 5,759,174 to Fischell et al. The catheter has a single external metal marker band to identify the central portion of the stenosis once the delivery catheter is removed.  
           [0009]    In spite of the improved illumination of the aforementioned devices when marked, there are some limitations to their application. Upon attachment conventional radiopaque markers may project from the surface of the catheter or stent, thereby causing a departure from its ideal profile. Some markers add rigidity to the stent and catheter in areas that had been designated for deformation. A needle for delivering radio frequency that overcomes some or all of the limitations of the prior art is desired.  
         SUMMARY OF THE INVENTION  
         [0010]    The present invention provides for improved placement of a needle delivering high frequency energy by incorporating radiopaque markers to distinguish the exposed tip from the shaft under fluoroscopic visualization.  
           [0011]    To facilitate precise placement of the exposed tip, the tip is distinguishable from the rest of the needle when viewed under X-rays and fluoroscopy. When a needle with radiopaque marking, according to the present invention, is inserted in the patient&#39;s body, the location of a lesion made or to be made by the needle can be easily determined, as the tip of the needle can be distinguished from the electrically insulated shaft.  
           [0012]    The present invention provides a needle for insertion into a patient&#39;s body comprising an electrically insulated shaft having an electrically conductive tip portion and a radiopaque marker associated with at least one of the shaft and the tip portion.  
           [0013]    The tip portion of the needle is the exposed tip and can be of varying dimensions. The radiopaque marker distinguishes the electrically insulated portion of the needle from the tip portion. This effectively identifies the position of the needle when in the body. The marker may be adapted to needles having various geometric shapes. The insulated portion of the needle may include an insulating coating. The coating may cover the radiopaque marker on the needle preventing a departure from the needle&#39;s true profile.  
           [0014]    The radiopaque marker can comprise bands or radiopaque coatings of metals/polymers, or radiopaque materials deposited on the surface of the needle by techniques such as ion implantation or vapor deposition. These features and others will be apparent in the detailed description that follows. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    In order that the invention may be readily understood, embodiments of the invention are illustrated by way of examples in the accompanying drawings, in which:  
         [0016]    [0016]FIG. 1 is a schematic illustration of a needle connected to a high frequency generator, in accordance with the present invention;  
         [0017]    [0017]FIG. 2 is a side elevation view of an embodiment of the needle of the present invention, including a stylet;  
         [0018]    FIGS.  3  to  7  illustrate side elevation views of different embodiments of the needle in accordance with the present invention, with radiopaque marking; and  
         [0019]    [0019]FIG. 8 illustrates a stylet according to the present invention including radiopaque marking. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]    In accordance with an aspect of the invention a medical apparatus is provided for delivering high frequency electrical current to neural structures. As illustrated in FIG. 1, the medical apparatus comprises a generator  100  for producing high frequency electrical current, a needle  102  with an electrical probe  110  connected to the generator  100  that is placed in the needle  102  for delivering the high frequency electrical current and a reference electrode  101  that completes the circuit. The needle  102  with the probe  110  is placed in a portion of a patient&#39;s body indicated generally at  106 .  
         [0021]    As can be seen more clearly in FIG. 2, the hollow shaft of the needle  102  is covered with an insulating coating  103  leaving a portion of the tip  104  uncoated, exposed and electrically conductive. The tip  104  may have a sharpened end that will assist with penetration of the tip  104  into the tissue of the body  106  during percutaneous entry. The exposed tip  104  represents the active electrode area. The reference electrode  101  typically has a much larger area than the exposed tip  104  so that there is no heating at the surface of the body  106  where the reference electrode  101  is attached. The passage of high frequency electrical current through the needle  102  produces a lesion  105  in the region of the exposed tip  104 . The lesion  105  causes coagulation of the neural structures in that region and is responsible for pain relief. It is therefore important to know the position of the exposed tip  104  to gauge the relative position and region that will be affected by the high frequency electrical current.  
         [0022]    As stated above, FIG. 2 depicts the needle  102  having a hollow shaft typically of one or more metals and a hub  201 . Preferably the hub  201  is a Luer lock type molded to the shaft; however, other methods of attachment may be used as will be understood by a person skilled in the art. Insulated in needle  102  through the hollow shaft is an elongate stylet  205  shown in dotted outline. The stylet  205  is adapted to assist in piercing the skin and tissue for entry to a treatment area. The stylet  205  comprises a cap  200  cooperating with Luer lock hub  201 . The hub  201  is also operable to accommodate an electrical probe  110  that is inserted into the shaft of the needle  102  when the stylet  205  is removed. A portion of the shaft is covered with an electrically insulating coating  103  leaving the tip  104  exposed. The end-point of the insulating coating  103  on the needle  102  is indicated at numeral  204 . In use, the needle  102  with the stylet  205  is inserted into the body  106 . Once a correct position has been attained the stylet  205  is removed and the electrical probe  110  that delivers the high frequency electrical current is inserted through the needle  102 .  
         [0023]    The needle  102  with the stylet  205  is inserted into the patient&#39;s body  106  under X-ray/fluoroscopic guidance. One common method for inserting the needle  102  is to locate an X-ray source along one or more desired axes. An image detector on the opposite side of the body portion  106  where the needle  102  is inserted receives the X-rays, thereby permitting verification of the proper location and orientation of the tip  104 . Radiopaque marking on the needle  102  or stylet  205  will enable its better visualization in this process. A radiopaque marker could be applied on selected portions of the needle  102  by, for example, use of masks. Advantageously selected patterns of radiopacity will allow the precise orientation to be discerned by inspection of the fluoroscopic image. FIGS.  3  to  8  illustrate different exemplary embodiments of patterns of radiopacity that can be adopted in this invention. It will be understood by persons skilled in the art that other shapes and patterns may be adopted.  
         [0024]    In the embodiment illustrated in FIG. 3 a radiopaque band  300  is located at the edge  204  of the coating and thereby aids in distinguishing between the coated region  103  and uncoated region  104 . The radiopaque band  300  may be located before the coating end-point  204  or just after the coating end point  204 . It may run 360° around the shaft or be applied through a certain distance of the circumference, for example through 180° or 90°. FIG. 3 illustrates one embodiment that includes a radiopaque band  300  through 180° of the shaft, on the side of the beveled tip, just before the coating end-point  204 . This provides a clear demarcation between the coated  103  and exposed regions  104  of the needle  102 .  
         [0025]    The band  300  can be applied in a number of ways including techniques such as, but not limited to, vapor deposition, ion implantation, dip coating, metal plating and electro plating. Bands of radiopaque materials such as platinum iridium bands can also be fused onto the needle  102 .  
         [0026]    An alternate embodiment of the invention is depicted in FIG. 4. A radiopaque marker  400  may be placed on the needle  102  to distinguish between the coated metal shaft  103  and the exposed metal tip  104  and may be a variety of shapes and sizes. The shape of the marker  400  may also be used to indicate the direction of the beveled tip.  
         [0027]    [0027]FIG. 5 illustrates another embodiment of the invention. The entire exposed part  104  of the needle  102 , is radiopaque indicated at numeral  500  and can be discerned better when viewed under a fluoroscope. The coated region of the needle  103  can be masked and the exposed tip  104  coated with a radiopaque material. Techniques such as vapor deposition and ion bombardment can be used to achieve such coating.  
         [0028]    An alternate embodiment of this invention can be obtained by imparting radiopacity to the insulating coating  600  as illustrated in FIG. 6. The insulating coating on the needle can be made radiopaque in a number of ways such as vapor deposition, ion-bombardment and ion-implantation. This renders the entire insulated portion of the needle radiopaque.  
         [0029]    [0029]FIG. 7 illustrates the needle  102  with two radiopaque bands  700  at the coating end-point  204  and the edge of the exposed tip  104 . This defines the region of the exposed tip  104  where delivery of high frequency electrical current to the tissue  106  occurs.  
         [0030]    [0030]FIG. 8 illustrates the stylet  205  with radiopaque marking  800 , which may include any of the embodiments described in FIGS. 3-7 above. The stylet  205  and needle  102  are inserted into the patient&#39;s body  106  to ensure correct placement. The radiopacity on the stylet  205  will serve to identify the exposed tip  104  on the needle  102 .  
         [0031]    An example of suitable material that may be used to impart the desired radiopacity is radiopaque ink with tungsten that is pad printed. The material is selected based on its radiopacity. Other suitable materials include, but are not limited to, high-density metals such as platinum, iridium, gold, silver, tantalum or their alloys, or radiopaque polymeric compounds. Such materials are highly visible under fluoroscopic illumination and are therefore visible even at minimal thickness.  
         [0032]    The embodiments of the invention described above are intended to be exemplary only. The scope of the invention is therefore intended to be limited solely by the scope of the appended claims.