Abstract:
A method for forming a microcoil includes attaching a conducting trace of conductive material to a film of insulating material and affixing an attaching trace of conductive material to the film, wherein the attaching trace is electrically isolated from the conducting trace of conductive material. The method also includes operably coupling the attaching trace to a mandrel prior to rolling of the mandrel and rolling the mandrel with the attaching trace attached thereto to circumferentially wrap the conducting trace of conductive material more than one revolution around a longitudinal axis of rolling. The attaching trace remains electrically isolated from the conducting trace after rolling the mandrel.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 11/735,287 filed Apr. 13, 2007, now U.S. Pat. No. 7,774,043 issued Aug. 10, 2010, which is a continuation of U.S. patent application Ser. No. 09/736,529 filed Dec. 13, 2000, now U.S. Pat. No. 7,210,223 issued May 1, 2007. The entire disclosures of the above applications are incorporated herein by reference. 
    
    
     FIELD OF APPLICATION 
     This invention relates to microcoils and their construction. Specifically, this invention relates to microcoils for use in medical devices used to obtain a magnetic resonance image of a region within a natural organism or patient (such as within a human) or elsewhere. 
     BACKGROUND 
     The use of magnetic resonance medical devices provides enhanced imaging within the region of interest and can be used for various internal procedures including targeted drug delivery. The term microcoil or MR microcoil is used to denote a magnetic resonance device used for imaging internally from a patient. This term is in contrast to MR coils that are conventionally used externally to the body for MR imaging purposes. A microcoil may contain one winding of electrical conductor, or multiple windings that are spaced a distance apart from each other. Typically multiple windings are joined together at a predetermined spacing with the planes of the windings parallel to each other. 
     The MR microcoil may be mounted at the tip of a catheter or other insertion device used to probe the interior of a body. The combination of the microcoil mounted on another device provides quick and direct access to the region where imaging is required. Medical procedures such as image-guided and minimal access surgery, performed within small regions of a patient&#39;s anatomy, demand the ability to visualize the internal terrain and/or the procedure being performed by the surgeon. While alternative methods, including x-ray imaging and fiber optic viewing offer possible alternative means of performing the visualization of terrain and the location of physical secondary devices, magnetic resonance imaging methods are a particularly convenient means of doing this, especially given the highly localized nature of the procedures being performed. 
     As with any manufactured device, new methods of manufacturing components are always being pursued to enhance performance and lower manufacturing costs. Conventionally, microcoils are manufactured by hand winding of an electrical conductor around a mandrel, or alternatively machine winding an electrical conductor around a mandrel. The resulting winding may have to be removed from the mandrel, and the leads for each end of the winding must be isolated. Additionally, where multiple windings are joined together in a device, the ends from multiple windings need to be connected. Handling windings in the manufacturing process can cause damage to the fragile windings resulting in manufacturing yield loss. The trend of smaller devices only increases this problem. With minimally invasive surgical procedures, the electrical conductor diameters used must be increasingly smaller to provide smaller coils. These coils are more easily damaged. 
     In manufacturing microcoils, there are also dimensional control variations within a single winding, and between windings. The diameter of the an electrical conductor used in a single winding may vary and affect the electrical characteristics of the resulting winding. Similarly, the insulating coating around the electrical conductor may vary in thickness and affect the electrical properties of the winding. 
     From one winding to another, variations in electrical conductor diameter and coating thickness are still a manufacturing variable. In addition, the number of turns from one winding to the next must be controlled by measuring the length of electrical conductor used in each winding. Also, the distance between windings in a microcoil containing multiple windings must be controlled by carefully joining the ends of a conventional winding at a measured distance. 
     While these conventional approaches to the manufacture of windings and microcoils result in functioning microcoils, the process is time consuming with several steps. Manufacturing yield is a problem due to the handling necessary in the conventional process, and consistent quality control is difficult. 
     SUMMARY 
     What is needed is a microcoil that can be manufactured more easily and which results in a more uniform microcoil with more consistent quality. What is also needed is a microcoil made by attaching a conductor onto an insulating film and configuring the film to form a winding or multiple windings. The manufacturing process of the microcoil requires minimal processing steps and minimal exposure to handling damage during processing. The process of manufacturing the microcoil is also conducive to tight quality control standards yet it is easily adapted to accommodate product design changes. The novel manufacturing process is capable of producing a novel microcoil that is extremely small and inexpensive, with a high manufacturing yield. 
     Microcoils produced by this process could be round or have other shapes depending on the mandrel or form that the film wraps around. A microcoil can be formed by soldering an end of the film to the mandrel and turning it to wrap the film into a winding. Multiple windings could also be included in one microcoil to make a series of connected windings. 
     In a further embodiment of the invention, the conductor is deposited as a trace onto the film using lithography and sputtering deposition techniques. The shape of the resulting microcoils is easily controlled by changing the mask pattern for the conducting trace deposited on the film. The electrical properties of the trace of conducting material are easily controlled by varying the trace material, and the width/thickness of the trace. 
     The microcoil might be applied with a medical device such as a catheter where the catheter is guided by magnetic resonance imaging using the microcoil. The microcoil might be further combined with other electrical devices nested at least partially inside the coil. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a top view of a trace unit in a flat condition. 
         FIG. 2  is a sectional view along line  2 - 2  of the trace unit in a flat condition in  FIG. 1 . 
         FIG. 3   a  is a perspective view of a trace unit and a mandrel. 
         FIG. 3   b  is a perspective view of a trace unit being rolled onto a mandrel. 
         FIG. 4   a  is a side view of a microcoil. 
         FIG. 4   b  is a front view of a single winding of a microcoil. 
         FIG. 4   c  is a sectional view along line  4   c - 4   c  of a single winding in  FIG. 4   b.    
         FIG. 5  is a perspective view of a microcoil. 
         FIG. 6  is a perspective view of a catheter device. 
         FIG. 7  is a close up view of an end of a catheter device. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     A catheter  100  is shown in  FIG. 6 , is used to probe areas of interest inside a patient. The distal end  101  of the catheter  100  can be inserted by controls at its proximal end  102 . In order to image the area of interest, and potentially steer the distal end  101  of the catheter to the desired location, it is helpful to include an MR microcoil  60  at the distal end  101  of the catheter  100 . The microcoil  60  uses magnetic resonance imaging techniques to characterize the tissue in its immediate vicinity. Signals from the microcoil  60  are sent along a length  104  of the catheter  101  through an electrical channel  103  to the proximal end  102  of the catheter where they can be used by the surgeon to indicate where the distal end  101  of the catheter is, and what types of tissue are near the distal end  101 . 
     A microcoil  60  as shown in  FIG. 5  is manufactured by rolling a trace unit  10  as shown in  FIG. 1  in such a way as to form at least one winding  70 . A preferred embodiment of the microcoil  60  contains both a first winding  70 , and a second winding  75  electrically connected and spaced apart by a joining portion  39 . The microcoil  60  and method for forming the microcoil  60  are described in detail below. 
       FIG. 1  shows a trace unit  10  that is comprised of a flexible film  20 , a conducting trace  30 , and an attaching trace  45 . As shown in  FIG. 2 , the flexible film  20  has a thickness  21  and the conducting trace  30  has a thickness  46 . In a preferred embodiment, the thickness  21  and the thickness  46  are constant across the trace unit  10 , however, the thickness  21  and the thickness  46  may vary in alternate embodiments. The flexible film  20  may have several shapes. It may be continuous, or it may contain openings in the film in areas other than where it supports the conducting trace  30 . 
     Looking again at  FIG. 1 , the conducting trace  30  can be further broken down into a first leg  31  having a first leg length  32  and a second leg  33  having a second leg length  34 . The first leg  31  has a lead end  41  and a joining end  42 , and the second leg  32  also has a lead end  43  and a joining end  44 . The first leg  31  and the second leg  33  have a trace width  49 , which is uniform throughout the legs in a preferred embodiment. 
     The first leg  31  and the second leg  33  are substantially parallel to a trace unit axis  11  of the trace unit  10 . However, as shown in  FIG. 1 , they are not exactly parallel to the trace unit axis  11 . The legs  31  and  33  are shown in a preferred embodiment in  FIG. 1  as having a slight curve, with the curve being more pronounced near a joining portion  39 . The orientation of the legs  31  and  33  as shown in  FIG. 1  is only one preferred embodiment. One skilled in the art would recognize that several configurations of legs would be possible to form other preferred embodiments without departing from the scope of the invention. 
     The conducting trace  30  also includes a first lead  35  and a second lead  37 , having a first lead length  36  and a second lead length  38 , and a first lead width  47 , and a second lead width  48 . The width of trace elements such as the legs and leads can be varied between elements, and within elements to alter the electrical characteristics of the trace. For example, a lead  35  could be wider than a leg  31 , or a leg  31  could have a varying width along its length  32 . 
     The first and second leads  35 ,  37  are attached to the first and second legs  31  and  33  at the first and second leg lead ends  41  and  43  respectively. The leads  35  and  37  may alternatively be attached elsewhere along the conducting trace  30  without departing from the scope of the invention. Supplemental leads (not shown) may also be electrically connected to the conducting trace to give device feedback or insert device instructions. The two legs  31  and  33  are joined at their respective joining ends  42  and  44  by a joining portion  39  of the conducting trace  30 . The joining portion  39  has a length  40 . 
     The trace unit  10  also includes an attaching trace  45  located adjacent to the joining portion  39 . The attaching trace  45  is electrically isolated from the conducting trace  30 . In a preferred embodiment, the attaching trace  45  is parallel with the joining portion  39  of the trace unit  10 . In a preferred embodiment, the attaching portion is also substantially perpendicular to the legs  31  and  33 . 
     The conducting trace  30  is comprised of copper because of its high conductivity and ductility. The ductility allows the copper to be rolled without cracking or breaking or otherwise causing an electrical failure. Any other conducting material that satisfies these conditions would be acceptable. The flexible film is comprised of polyimide because it exhibits good insulating properties and is readily available. It is also flexible, and withstands the deposition process used to attach the conducting trace. Any other flexible insulating material would be acceptable. 
     The conducting trace is attached to the flexible film by using a sheet of conductor, adhesive, and a basic lithography or photolithography technique commonly known in the industry. First a sheet of copper is adhered to the flexible film using a suitable adhesive. A mask layer is then deposited onto the sheet of copper with a positive image of the conducting trace  30  and the attaching trace  45 . The flexible film  20  and the mask layer are then exposed to an etching chemical capable of removing copper, which removes the copper in the unmasked regions of the sheet. Once the excess copper is removed from the flexible film  20 , the mask layer is removed to leave behind only the flexible film  20 , the conducting trace  30 , and the attaching trace  45 . While this method of attaching the conducting trace  20  and the attaching trace  45  is preferred, it should be noted that any of several methods for attaching, including sputtering, physical vapor deposition, chemical vapor deposition, or mechanical attachment could be used to produce the invention. 
     In alternative embodiments, additional layers of flexible insulator and areas of conducting material may be attached and deposited onto the flexible film  20 . Additional layers of flexible insulator may be used to protect the conducting trace  30 , or they may be used to isolate additional areas of conducting material from the conducting trace  30 . Additional areas of conducting material may be used to form electrical devices such as capacitors, integral with the trace unit  10 . 
     The trace unit  10  is next prepared for rolling by attaching the trace unit  10  to a mandrel  50  as shown in  FIG. 3   a . The mandrel  50  may be round or square or any of several variations in cross section. The mandrel  50  may also be solid or hollow. The mandrel  50  may be made from any of a number of materials such as plastic or glass or non-magnetic metal. The mandrel  50  may not include magnetic materials due to interference with the magnetic resonance imaging that the coils are designed for in end use. The mandrel  50  may also be made up of more than one material. In this embodiment, the mandrel  50  is a semi-rigid coaxial line that is comprised of silver-plated copper on its outside diameter. The semi-rigid coaxial line is electrically conductive which allows information from the coil to be transmitted back to the user through the coaxial line. 
     A preferred manufacturing process of the microcoil  60  begins when the trace unit  10  is attached to the mandrel  50  by soldering the attaching trace  45  to the outside diameter of the mandrel  50 . The attaching trace  45  is soldered such that it is parallel with a longitudinal axis  51  of the mandrel  50 . More importantly, the attaching trace  45  and mandrel  50  are oriented such that when rolled, the legs  31  and  33  of the conducting trace  30  form windings  70  and  75  as shown in  FIG. 5 . Although a mandrel  50  is used to roll the trace unit  10  in a preferred embodiment, the trace unit  10  may be rolled without using a mandrel  50  without departing from the scope of the invention. 
     In a preferred manufacturing process, once the trace unit  10  is attached to the mandrel  50 , the mandrel is rolled about the longitudinal axis  51  in direction  52  as shown in  FIG. 3   b . In a preferred embodiment, the rolling of the trace unit  10  about the mandrel  50  forms a microcoil  60  comprised of a first winding  70  and a second winding  75  as shown in  FIG. 5 , one winding formed from each leg  31  and  33 . The joining portion  39  electrically connects the pair of windings  70  and  75 . Alternative embodiments could form only one winding, which would not require a joining portion, or several windings could be formed, which would require multiple joining portions. 
     Design variations of the resulting microcoil  60  are easily accommodated with a preferred manufacturing process. The number of turns in the windings  70  and  75  may be controlled by varying the lengths  32  and  33  of the legs  31  and  33  respectively when forming the conducting trace  30  on the trace unit  10 . Alternatively, the diameter  53  of the mandrel  50  that is chosen can be varied to change the resulting number of turns. Nine turns are used for a preferred embodiment. 
     As shown in  FIG. 5 , a longitudinal winding spacing  61  between windings  70  and  75  in the microcoil  60  is controlled by varying the length  40  of the joining portion or portions  39  when forming the conducting trace  30  on the trace unit  10 . 
       FIG. 4   a  shows a side view of the microcoil  60 . In this side view only the first winding  70  of the microcoil  60  is visible. The first winding  70  is further shown in  FIG. 4   b  and sectional view  4   c  of  FIG. 4   b . As shown in  FIG. 4   c , within a given winding, a radial trace spacing  71  is controlled by selecting or varying the thickness  21  of the flexible insulating film  20 . Also, a longitudinal axis trace spacing  72  is controlled by varying the shape and orientation of the legs  31  and  33  on the trace unit  10 . 
     As shown in  FIG. 3   a , the legs  31  and  33  are substantially perpendicular to the longitudinal axis of rolling  51 . However, the degree of perpendicularity varies along the legs  31  and  33 . In a preferred embodiment, a given portion of a leg near the attaching trace  45  is less perpendicular to the longitudinal axis of rolling  51  than a portion of a leg proximal from the attaching trace  45 . For example, the orientation of a generally linear leg could be varied such that the angle the generally linear leg makes with the longitudinal axis of rolling is more or less than 90 degrees. The shape of a leg could also be varied such that a leg is more linear or more arc shaped. These shape and orientation variations translate into variations of the longitudinal axis trace spacing  72 . 
     Once the rolling of the trace unit  10  is complete, a microcoil  60  has been formed. A temporary retaining band  80  may then be placed around the microcoil  60  to hold its shape during the final placement of the microcoil  60  into its associated medical device. After the leads  35 ,  37  and possibly supplemental leads have been electrically connected to the medical device, the temporary band  80  may be removed. A more permanent protective oversleeve  90  as shown in  FIG. 7  is then used to protect the microcoil and to hold its shape. If needed, other electrical component such as capacitors (not shown) may be embedded or partially embedded inside the structure of the microcoil  60 . 
     As shown in  FIGS. 6 and 7 , a catheter device  100  is used in a preferred embodiment. The catheter device  100  has a distal end  101  and a proximal end  102 . The microcoil  60  is located at the distal end  101  of the catheter. In operation, data from the microcoil travels along the length  104  of the catheter  100  through an electrical channel  103 . A continuing electrical channel such as a coaxial line (not shown) transmits the data from the electrical channel  103  to another device such as a monitor device. This device receives information from the microcoil  60  concerning location of the distal end  101 , or concerning the nature and condition of the tissue near the distal end  101 . 
     Although specific embodiments have been illustrated and described herein, it will be appreciated by those skilled in the art that any arrangement which is calculated to achieve the same purpose may be substituted for the specific embodiment shown. This application is intended to cover any adaptations of variations of the present invention. It is to be understood that the above description is intended to be illustrative, and not restrictive. The scope of the invention includes any other applications in which the above structures and fabrication methods are used. The scope of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.