Patent Publication Number: US-2013245640-A1

Title: Device and system for narrow gauge medical instrument navigation

Description:
BACKGROUND OF THE INVENTION 
     The present invention is directed generally to three dimensional navigation systems for medical instruments. 
     It is desirable in many medical procedures to accurately determine the three dimensional spatial position of the distal tip of a medical device or instrument within a patient. Presently, percutaneous image guided procedures are best accomplished when the target lesion is clearly visible in the three dimensional volume image data and the distal tip of the instrument can be tracked while the stylet of the instrument (e.g., a needle) is advanced to the target. Various technologies have been developed to assist with this approach such as image fusion and electromagnetic tracking with an electromagnetic sensor in the tip of the instrument. Placement of the sensor in the tip is essential in many cases because the tip is often difficult to image and the instruments used in percutaneous procedures tend to be relatively thin and flexible. If the instruments were not (i.e. if the stylet of the instrument was reliably straight and rigid and thus in a fixed relation to the handle), a simpler technological solution with an electromagnetic or optical sensor located on the exterior end of the device can be more cheaply and easily applied. 
     In some image guided procedures such as in the lung, brain, and thyroid, very thin (small gauge) stylets of instruments are required to keep tissue damage and risk of complications low. In these cases, the physical limits on the size of the electromagnetic sensors disqualifies electromagnetic tracking technology as a solution for tip tracking. Flexibility of the stylet of the instrument makes tracking on the exterior handle end essentially useless. Also, in some larger diameter but still flexible stylets of instruments such as those used for tissue ablation, the entire space within the needle may be taken up by the energy source components such that there remains insufficient space for electromagnetics. A different device and method must be applied to enable instrument tip tracking in these circumstances. 
     All references cited herein are incorporated herein by reference in their entireties. 
     BRIEF SUMMARY OF THE INVENTION 
     In the present invention, fiber optic technology that measures the relative tip deflection and direction of a stylet portion of an instrument (e.g., a needle) is applied in combination with electromagnetic volume navigation sensors or optical tracking technology during image guided procedures. This added fiber optic technology answers the need for tip tracking in instruments where electromagnetic tracking technology or line of sight optical tracking alone cannot be employed to achieve the desired accuracy. 
     The present invention uses a very thin (for example, as small as approximately 150 microns in diameter) optic cable having a pair of thin fibers inserted along the full length of the stylet portion of an instrument that is then used to precisely track the amount, location along the stylet, and direction of tip deflection relative to the handle end of the instrument. This information is then combined with the handle that is registered to an electromagnetic sensor capable of registering six degree positional information. The electromagnetic sensor is accurately affixed to the instrument for the purpose of precisely tracking the handle within an electromagnetic field, and thus accurately guiding very delicate and flexible instruments during an image guided procedure. 
     Presently, similar diameter optical fibers are being used experimentally in a three fiber spaced array typically around the periphery of instruments/needles in combination with other optics to guide instruments during procedures performed in magnetic resonance imaging devices. This application is because electromagnetics cannot be used in magnetic resonance imaging devices. The present invention takes advantage of optical Fiber Bragg Grating technology to bring that same functionality into a pair of fibers which can be placed centrally or peripherally in a linear instrument, and adds utilization with electromagnetic tracking technology to achieve broad application in image guided medical procedures. 
     In practice, an exemplary system would function as follows: 
     1) an optic cable having a pair of thin fibers are embedded in the wall or placed in the hollow center of a stylet (e.g., a needle) of an instrument. Alternatively, the optic cable could actually be placed freely in the center or function as the filler of a hollow stylet; 
     2) beyond the exterior/handle end of the instrument/needle, a coupling connects a reusable Fiber Bragg Grating interrogator to the individual thin fibers of the optic cable. 
     3) an electromagnetic sensor capable of registering six degrees of positional information is affixed to the handle end of the (preferably disposable) instrument; 
     4) a sterile cover may protect the reusable fiber optic interrogator, the optic cable may be sterile, and the electromagnetic sensor and a power/communication cable connecting it to the processor or computer that reports the tracking data to the user may be sterile or covered with a sterile sleeve; and 
     5) the electromagnetic sensor reports the position and orientation of the handle end of the instrument and the distance to the tip inside the patient while the fiber optics reports the amount, location along the stylet and direction of the tip deflection in relation to the electromagnetic sensor. 
     In this manner, highly-accurate tip tracking can be displayed in real time relative to patient images for virtually any linear instrument in common use for image guided medical procedures. 
     One preferred embodiment for image guided procedures may be that the optic cable is permanently embedded in the instrument at manufacture and then the assembly is presented to the user in a sterile package for single use. Another preferred embodiment may be that the optic cable is a sterile single cable that is introduced into any appropriate hollow stylet or needle at the time of a procedure. The optic cable may then be removed once the instrument tip is in the desired position to complete a procedure. The electromagnetic sensor may also be pre-attached to the instrument or optic cable at the handle end, or independently, removably clipped on to the handle end of the instrument, as desired. The configuration at the handle end of the instrument may allow sterile coupling to a reusable optic cable that is connected to the interrogator, or the optic cable may be continuous from inside the instrument to the interrogator. Alternatively, a pre-sterilized length of fiber optic cable may be plugged into the handle that already includes the electromagnetic sensor. The optic cable may be inserted into any standard hollow needle assembly and secured via a Luer lock connection. The fiber will be inserted along a sufficient length to accurately track the stylet of the instrument&#39;s tip. For procedures where the additional costs can be justified, factory assembly and sterilization of all components may be done for single use. 
     In accordance with the present invention, a device for narrow gauge medical instrument navigation is provided. The device includes a handle and a stylet (such as a needle) that may have a closed or open end. The stylet has a distal end, a proximal end and an axially disposed aperture extending from the distal end to the proximal end. The proximal end is affixed to the handle. A navigation sensor is disposed adjacent to and in fixed relation to the handle wherein the navigation sensor is capable of registering six degree positional information for tracking the location of the handle in space. The distal end of the stylet is at a known location relative to the navigation sensor when the stylet is in an unflexed condition. A pair of thin fibers forming an optic cable is disposed in the aperture of the stylet and is disposed in fixed relation to the navigation sensor. The pair of thin fibers (preferably with Fiber Bragg Grating) form the optic cable that is disposed substantially entirely from the distal end to the proximal end. The optic cable is adapted to measure deflection and the location and direction of deflection of the stylet relative to the electromagnetic sensor. 
     The navigation sensor may be an electromagnetic sensor, an optical tracking sensor, or any other type of sensor capable of establishing its position in three dimensional space. The optic cable containing the pair of thin fibers may be substantially any suitable shape having a maximum diameter of about 300 microns or less. A very thin fiber optic cable of approximately 150 microns to 300 microns in diameter is preferable. The fiber optic sensor preferably utilizes Fiber Bragg Grating technology. 
     In one exemplary embodiment, the stylet may be a needle. The optic cable may be placed in the aperture or otherwise disposed in the aperture such that it is in a fixed position, or embedded at manufacture in the wall of the stylet. A sterile cover may be provided to protect the navigation sensor or any re-usable cables, as required, to develop and maintain a sterile field. The optic cable may be removable by a user during an image guided procedure. The navigation sensor may be removably disposed on the handle. 
     A system for medical instrument navigation is also provided. The system includes the device above, an interrogator coupled to the optic cable in the instrument, and a processor to analyze data from the interrogator and the navigation sensor to determine the precise location of the distal end of the stylet in a defined three dimensional space. The navigation sensor is for reporting its position and orientation in three dimensional space while the interrogator is for reporting the amount, location and direction of the deflection of the distal end of the stylet in relation to the navigation sensor that is in a known and fixed relation to the handle of the instrument. A display for displaying the orientation of the instrument, and/or a position of the distal end of the stylet in a body of a being may also be provided. The interrogator and the processor may be an integral unit. 
    
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
       The invention will be described in conjunction with the following drawings in which like reference numerals designate like elements and wherein: 
         FIG. 1  is a schematic view of a device for narrow gauge medical instrument navigation in accordance with an exemplary embodiment of the present invention; 
         FIG. 2  is an isometric view of an exemplary device for narrow gauge medical instrument navigation of  FIG. 1 ; 
         FIG. 3  is a s cross sectional view of the device for narrow gauge medical instrument navigation of  FIG. 2 , taken substantially along lines III-III of  FIG. 2 ; 
         FIG. 4  is a cross sectional view of a stylet of the device for narrow gauge medical instrument navigation of  FIG. 2 , shown at detail  4  of  FIG. 3 ; 
         FIG. 4A  is a cross sectional view of the stylet of  FIG. 4 , taken substantially along lines IVa-IVa of  FIG. 4 ; 
         FIG. 5  is a simplified schematic diagram of a system for determining the three dimensional position of the distal end of a stylet in the device for narrow gauge instrument navigation of  FIG. 1 ; and 
         FIG. 6  is side, cross-sectional view of the device of  FIG. 2 , shown in sterile packaging. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention will be illustrated in more detail with reference to the following embodiments, but it should be understood that the present invention is not deemed to be limited thereto. Referring now to the drawing figures, wherein like part numbers refer to like elements throughout the several views, there is shown in  FIGS. 1 and 2  a device for narrow gauge medical instrument navigation  10  in accordance with an exemplary embodiment of the present invention. The device includes a handle  12 , a stylet  14  (such as a needle, as shown) having a distal end  16 , a proximal end  18  and an axially disposed aperture  20  extending from the distal end  16  to the proximal end  20 . The proximal end  20  of the stylet  14  is affixed to the handle  12 . 
     A navigation sensor  22  (such as an electromagnetic sensor, an optical tracking sensor, or similar) is disposed adjacent to the handle  12 . The navigation sensor  22  is preferably capable of registering six degree positional information for tracking the location of the handle in space. The distal end  16  of the stylet  14  is at a known location from the navigation sensor  22  when the stylet is in an unflexed condition. The navigation sensor  22  may be connected by a cable  25  that provides power from a power supply  27  and also serves as a data cable. See  FIG. 5 . A pair of thin fibers  23  form an optic cable  24  that is disposed in the axially disposed aperture  20  of the stylet  14  and is disposed in fixed relation to the navigation sensor  22  (for example, located in the aperture  20  or embedded in the aperture). The optic cable is preferably disposed substantially entirely from the distal  16  end to the proximal end  18  of the stylet  14 . The optic cable  24  is adapted to measure deflection and the location and direction of the distal end  16  of the stylet  14  relative to the navigation sensor  22 . 
     An interrogator  26  (such as a Fiber Bragg Grating interrogator) is coupled to the optic cable  24 . The thin fibers  23  that form the optic cable have light attenuation characteristics which vary in accordance with the direction and flex of the stylet  14 , for example, Fiber Bragg Grating, in the portion of the optic cable  24  located in the stylet. See, for example, U.S. Pat. No. 7,903,907 (Park et al.). The interrogator  26  analyzes this data to provide precise positional data in space. The navigation sensor  22  reports its position and orientation in three dimensional space while the interrogator  26  reports the amount and direction of the deflection of the distal end  16  of the stylet  14  in relation to the navigation sensor  22 . A processor  28  analyzes data from the interrogator  26  and the navigation sensor  22  to determine the precise location of the distal end  16  of the stylet  14  in three dimensional space. The processor is preferably connected to a display  32  to display to the physician or other user of the system the precise location of the needle within a patient. 
     It is typically desirable that the fiber optic cable be as thin as possible, for example, approximately 150 microns to 300 microns in diameter. A sterile cover  30  may be provided to protect any element or elements of the device  10 , including the navigation sensor  22 . 
     While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.