Abstract:
A means for holding a selected cannula such that the cannula is controllably restricted in motion in all but one line, but still able to slide along the line relatively freely. The motion restricting force may be selectively varied, thereby allowing an unrestricted separation of the cannula and the holding/guide device.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to a magnetic system for manipulating the placement of a needle or cannula in a biologic subject. 
       BACKGROUND OF THE INVENTION 
       [0002]    The following applications are incorporated by reference as if fully set forth herein: U.S. application Ser. Nos. 11/258,592 filed Oct. 24, 2005 and 11/874,824 filed Oct. 18, 2007. 
         [0003]    Unsuccessful insertion and/or removal of a cannula, a needle, or other similar devices into vascular tissue may cause vascular wall damage that may lead to serious complications or even death. Image guided placement of a cannula or needle into the vascular tissue reduces the risk of injury and increases the confidence of healthcare providers in using the foregoing devices. Current image guided placement methods generally use a guidance system having a mechanical means for holding specific cannula or needle sizes. The motion and force required to disengage the cannula from the guidance system may, however, contribute to a vessel wall injury, which may result in extravasation. Complications arising from extravasation resulting in morbidity are well documented. Therefore, there is a need for image guided placement of a cannula or needle into vascular tissue while still allowing a health care practitioner to use standard “free” insertion procedures that do not require a guidance system to hold the cannula or needle. 
       SUMMARY OF THE INVENTION 
       [0004]    This invention relates to a magnetic system for manipulating the placement of a needle or cannula for the purposes of positioning via image devices into an artery, vein, or other body cavity and releasing the cannula once the placement is successfully completed. 
         [0005]    The invention provides a means for holding a selected cannula such that the cannula is controllably restricted in motion in all but one line, but still able to slide along that line relatively freely. The motion restricting force may be selectively varied, thereby allowing an unrestricted separation of the cannula and the holding/guide device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Embodiments of the present invention are described in detail below with reference to the following drawings. 
           [0007]      FIG. 1  is a cross-sectional view of a first embodiment; 
           [0008]      FIG. 1B  is an alternate embodiment of the first embodiment; 
           [0009]      FIG. 1C  is a plan view of the first embodiment; 
           [0010]      FIG. 1D  is a plan view of another embodiment; 
           [0011]      FIG. 1E  is a plan view of yet another embodiment; 
           [0012]      FIG. 2A  is a cross-sectional view of a second embodiment; 
           [0013]      FIG. 2B  is a plan view of the second embodiment; 
           [0014]      FIG. 3A  is a cross-sectional view of an alternate embodiment of the second embodiment; 
           [0015]      FIG. 3B  is a plan view of the alternate embodiment of the second embodiment; 
           [0016]      FIG. 4A  is a third embodiment of the invention; 
           [0017]      FIG. 4B  is a plan view of the third embodiment; 
           [0018]      FIG. 5A  is an embodiment of a magnetic strip; 
           [0019]      FIG. 5B  is an alternate embodiment of the magnetic strip; 
           [0020]      FIG. 6A  is an embodiment of a magnetic guide assembly having the embodiments of  FIG. 5A ; 
           [0021]      FIG. 6B  is an alternate embodiment of a magnetic guide assembly having the magnetic strip embodiments of  FIG. 5B ; 
           [0022]      FIG. 7A  schematically depicts removing a strip from the device depicted in  FIG. 6A ; 
           [0023]      FIG. 7B  is a progression of the strip removal of  FIG. 7A ; 
           [0024]      FIG. 7C  is a continuation of strip removal of  FIG. 7B ; 
           [0025]      FIG. 7D  is near complete removal of the strips from the magnetic guidance device; 
           [0026]      FIG. 7E  is an alternate arrangement of the magnetic strips to the magnetic guidance device; 
           [0027]      FIG. 8A  is a cross-section of a fifth embodiment in the form of a magnet-ferrite core assembly; 
           [0028]      FIG. 8B  depicts the assembly of  FIG. 8A  in cross-section holding a cannula in a gap; 
           [0029]      FIG. 8C  depicts the assembly of  FIG. 8A  in cross-section where removal of the magnet causes release of the cannula; 
           [0030]      FIG. 9A  is an alternate embodiment of the magnet-ferrite core assembly of  FIG. 8A ; 
           [0031]      FIG. 9B  depicts the alternate embodiment of  FIG. 9A  magnetically holding a cannula; 
           [0032]      FIG. 9C  schematically shows in cross-section the release of the cannula from the assembly of  FIG. 9A . 
           [0033]      FIG. 9D  shows the complete release of the cannula from the assembly of  FIG. 9A ; 
           [0034]      FIG. 10A  is an isometric view of the magnetic core assembly of  FIG. 8A ; 
           [0035]      FIG. 10B  is a schematic isometric depiction of the operation of the magnet core assembly of  FIG. 8A ; 
           [0036]      FIG. 10C  is a schematic depiction of the operation of the magnet core assembly of  FIG. 8A ; 
           [0037]      FIG. 11A  is an alternate embodiment of an isometric view of the alternate embodiment depicted in  FIG. 9A ; 
           [0038]      FIG. 11B  depicts an operation of the embodiment shown in  FIG. 11A ; 
           [0039]      FIG. 12A  is an alternate embodiment of a pair of magnet core assemblies of  FIG. 8A ; 
           [0040]      FIG. 12B  is an isometric view of a schematic operation of an embodiment of  FIG. 12A ; 
           [0041]      FIG. 13A  is an isometric view schematically depicting an electro magnetic embodiment of  FIG. 12A ; 
           [0042]      FIG. 13B  is an isometric view schematically depicting the electromagnet of  FIG. 13A ; 
           [0043]      FIG. 14  illustrates in a partial isometric and side view of a V-Block configured needle guidance device mounted to an ultrasound transceiver; 
           [0044]      FIG. 15  illustrates in a partial isometric and side view of a magnet-ferrite core configured needle guidance device mounted to an ultrasound transceiver; 
           [0045]      FIG. 16  is an alternate embodiment of  FIG. 8A  for detachably attaching a magnet-ferrite needle guidance to an ultrasound transducer housing; 
           [0046]      FIG. 17  is an alternate embodiment of  FIG. 12A  mounted to a transducer housing; 
           [0047]      FIG. 18A  is a side view of an ultrasound scanner having a magnetic guide assembly; 
           [0048]      FIG. 18B  is an isometric view and exploded view of components of the device of  FIG. 18A ; 
           [0049]      FIG. 19A  is a side view of alternate embodiment of  FIG. 18A  utilizing a rotating magnet; 
           [0050]      FIG. 19B  is an isometric view and exploded view of components of the device of  FIG. 19A ; 
           [0051]      FIG. 20A  is a side view of alternate embodiment of  FIG. 19A  utilizing a pulling magnet; and 
           [0052]      FIG. 20B  is an isometric view and exploded view of components of the device of  FIG. 20A . 
           [0053]      FIGS. 1 and 2  are diagrams showing one embodiment of the present invention; 
           [0054]      FIG. 3  is a diagram showing additional detail for a needle shaft to be used with one embodiment of the invention; 
           [0055]      FIGS. 4A and 4B  are diagrams showing close-up views of surface features of the needle shaft shown in  FIG. 3 ; 
           [0056]      FIG. 5  is a diagram showing imaging components for use with the needle shaft shown in  FIG. 3 ; 
           [0057]      FIG. 6  is a diagram showing a representation of an image produced by the imaging components shown in  FIG. 5 ; 
           [0058]      FIG. 7  is a system diagram of an embodiment of the present invention; 
           [0059]      FIG. 8  is a system diagram of an example embodiment showing additional detail for one of the components shown in  FIG. 2 ; 
           [0060]      FIGS. 9-10  are flowcharts of a method of displaying the trajectory of a cannula in accordance with an embodiment of the present invention; and 
           [0061]      FIG. 11  schematically depicts an alternative embodiment of a needle having a distribution of reflectors located near a bevel of the needle. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0062]    The present invention relates to an apparatus and a method for image guided insertion and removal of a cannula or needle. Many specific details of certain embodiments of the invention are set forth in the following description and in  FIGS. 1 through 20B  to provide a thorough understanding of such embodiments. One skilled in the art, however, will understand that the present invention may have additional embodiments, or that the present invention may be practiced without several of the details described in the following description. 
         [0063]      FIG. 1A  is a schematic cross-section view of a needle/cannula guide device  10  according to an embodiment of the invention. The needle/cannula guide device  10  includes a V-block  12  that supports a needle or cannula  18 . The V-block  12  includes two opposing sections that are coupled to each other at an apex. Magnetic strips  16  are positioned on an exterior portion of the V-block  12  that magnetically retain the cannula  18  within the V-block  12 . Accordingly, the V-block  12  may be fabricated from a suitably non-magnetic material, so that magnetic fields generated by the magnet strips  16  retain the metal needle  18  in the V-block  12 . The non-magnetic material of the V-block  12  may be comprised of a low friction polymeric material such as, for example, Teflon®, Nylon®, or Delrin®. Alternatively, it may be comprised of a ferromagnetic material that may similarly convey the magnetic fields generated by the magnets  16 . The magnets  16  may be fixedly coupled to the V-block  12 . Alternately, the magnets  16  may be removably coupled to the V-block  12 . 
         [0064]      FIG. 1B  is a schematic cross-section view of a needle/cannula guide device  10 A according to another embodiment of the invention. Many of the details of the present embodiment have been described in detail in connection with the embodiment shown in  FIG. 1A , and in the interest of brevity, will not be described further. The guide device  10 A includes a foil wrapper  20  or other suitable wrapper materials that substantially encloses the cannula  18 . The wrapper  20  may be subjected to sterilization procedures so that the assembly  10 A may be sterilized by autoclaving, irradiation, or other known chemical processes. The foil wrapper  20  is generally sealably coupled to the V-block  12  so that the cannula  18  is substantially isolated from contaminants, yet is configured to be easily removed from the V-block  12 . 
         [0065]      FIGS. 1C , D, and E illustrate alternate embodiments of the cannula guide devices  10  and  10 A, as shown in  FIG. 1A  and  FIG. 1B , respectively. 
         [0066]      FIG. 1C  is a plan view of the devices  10  and  10 A where the cannula  18  is positioned in the V-block  12  and is held in position by the magnets  16 , which extend uninterrupted along a length of the V-block  12 .  FIG. 1D  is a plan view of the devices  10  and  10 A that shows a first set of magnets  16 A positioned on first selected portions of the V-block  12 , and a second set of magnets  16 B that are positioned on second selected portions of the V-block  12 . As shown in  FIG. 1D , the second set  16 B may be positioned between the first set  16 A.  FIG. 1E  is a plan view of the devices  10  and  10 A that shows magnets  16 A interruptably positioned on the V-block  12 . Although the magnets  16 ,  16 A and  16 B are generally depicted in  FIG. 1C ,  FIG. 1D  AND  FIG. 1E  as rectangular, it is understood that the magnets  16 ,  16 A and  16 B may have any regular shape. 
         [0067]      FIGS. 2A and 2B  are cross sectional and plan views, respectively, of a cannula guide device  20 A according to another embodiment of the invention. In  FIG. 2A , the V-block  12  includes four magnet strips  24 , positioned on each arm of the V-block  12  that are used to generate a retaining force on the needle  18 . Referring now also to  FIG. 2B , the placement of the magnets  24  on the V-block  12  advantageously permit the V-block  12  to accommodate a variety of needle diameters. 
         [0068]      FIGS. 3A and 3B  are cross sectional and plan views, respectively, of a cannula guide device  20 B according to still another embodiment of the invention. The device  20 B includes magnets  24 B that are operable to generate an attractive force that is different from magnets  24 A. Accordingly, the magnets  24 B may generate a greater attractive force on the needle  18  than the magnets  24 A. Alternately, the magnets  24 A may generate a greater attractive than the magnets  24 B. 
         [0069]      FIGS. 4A and 4B  are cross sectional and plan views, respectively, of a cannula guide device  20 C according to still yet another embodiment of the invention. The device  20 C includes a unitary magnet strips  27  having regions that generate different attractive forces on the needle  18 . Accordingly, the unitary magnetic strips  27  include a first magnetic strip portion  26 A and a second magnetic strip portion  26 B. The attractive force generated by the portion  26 A may be greater than the attractive force generated by the portion  26 B, or the attractive force generated by the portion  26 B may be greater than the attractive force generated by the portion  26 A. 
         [0070]      FIGS. 5A and 5B  are isometric views, respectively, of magnetic strips  30 A and  30 B that may be removably coupled to the V-block  12  ( FIG. 1A ). The magnetic strips  30 A and  30 B include a tab  34  configured to apply a pulling force to the strips  30 A and  30 B. Referring now in particular to  FIG. 5A , a unitary magnetic element  32  is positioned on the strip  30 A that generates a relatively uniform attractive force on the needle  18  (not shown). Magnetic strip  30 B shown in  FIG. 5B  includes a magnetic element  36  that also includes magnetic portions  36 A and  36 B that are configured to generate different attractive forces on the needle  18  (not shown). The magnetic strips  30 A and  30 B may also include an adhesive material that is operable to retain the strips  30 A and  30 B onto external surfaces of the V-block  12 . 
         [0071]      FIGS. 6A and 6B  are respective isometric views of needle guidance devices  40 A and  40 B. In  FIG. 6A , the needle guidance device  40 A includes the magnetic strips  30 A as shown in  FIG. 5A  that are positioned on the exterior of the V-block  12 . The attractive force of the magnetic strips  30 A magnetically holds the needle  18  within an inner portion of the V-block  12 . In  FIG. 6B , the needle guidance device  40 B includes the magnetic strip  30 B of  FIG. 5B  positioned on the V-block  12 . 
         [0072]      FIGS. 7A-7E  are isometric views of the needle guidance device  40 A that will be used to a method of using the needle guidance device  40 A according to another embodiment of the invention.  FIG. 7A  and  FIG. 7B  show a first selected one of the magnetic strips  30 A being progressively removed from the V-block  12 . The first selected one of the strips  30 A may be removed by a user by grasping the tab  34  and applying a pulling force on the tab  34  in the direction shown. Accordingly, the attractive force on the needle  18  is also progressively reduced. A selected length of the strip  30 A may be removed so that a desired attractive force acting on the needle  18  is attained. Referring now to  FIG. 7C , a second selected one of the strips  30 A may be removed by grasping the tab  34  and applying a pulling force on the tab  34  in a suitable direction. As a result, the attractive force on the needle  18  is still further reduced. Although  FIGS. 7A through 7C  show a single magnetic strip applied to external surfaces of the V-block  12 , more than one magnetic strip may be present on an external surface of the V-block  12 . 
         [0073]    Referring now to  FIG. 7D , when the first selected strip and the second selected strip are removed to a desired degree, the needle  18  may be separated from the V-block  12 . 
         [0074]    As shown in  FIG. 7E , the magnetic strips  30 A may be positioned on the V-block  12  so that the strips  30 A are oriented oppositely to those shown in  FIGS. 7A through 7D . 
         [0075]      FIGS. 8A-8C  are respective cross sectional views of a needle guidance device  50  according to yet another embodiment of the invention. The needle guidance device  50  includes a pair of opposing metal cores  54  having a gap  58 A and a gap  58 B between the ferromagnetic cores  54 . The metal cores  54  are generally semi-circularly shaped and may be made of any metal or metal alloy suitable for conveying a magnetic field, such as a ferromagnetic or ferrite material. A magnet  56  is removably positionable within a selected one of the gaps  58 A and  58 B. For purposes of illustration, the magnet  56  is positioned in the gap  56 A. When the magnet  56  is positioned within a selected one of the gaps  58 A and  58 B, a magnetic field is communicated along the cores  54  from the gap  58 A to the gap  58 B. The gap  58 B is configured to accept a needle  18  so that the needle  18  will be retained in the gap  58 B by the magnetic fields communicated from gap  56 A. As shown in  FIG. 8A , the lines of the magnetic force are conveyed across the space  58 B. Referring briefly now to  FIG. 8B , the needle  18  is held within the gap  58 B. Accordingly, the needle  18  will be retained within the gap  58 B while the magnet  56  is positioned within gap  58 A. The gap  58 B progressively narrows to accommodate needles having variable diameters. Turning now to  FIG. 8C , as the magnet  56  is moved outwardly from the gap  58 A of the needle guidance device  50 , the magnetic field spanning the gap  58 B is correspondingly reduced. Accordingly, the needle  18  positioned within the gap  58 B may be gradually released from the needle guidance device  50 . 
         [0076]      FIGS. 9A-9D  are respective cross sectional views of a needle guidance device  60  according to yet still another embodiment of the invention. With reference now to  FIG. 9A , the needle guidance device  60  includes a magnet  66  that is configured to be rotated within the gap  58 A. In  FIG. 9A , the magnet  66  is shown in a first position so that the magnetic lines of force are communicated along the ferromagnetic cores  54 . Accordingly, a magnetic field is established within the gap  58 B, so that the needle  18  is retained within the gap  58 B, as shown in  FIG. 9B . In  FIG. 9C , the magnet  66  is rotated to a second position so that the magnetic lines of force are generally directed away from the ferromagnetic cores  54 . Accordingly, the attractive force that retains the needle  18  within the gap  58 B is reduced so that the needle  18  may be moved away from the gap  58 B. 
         [0077]      FIG. 10A  is an isometric view of the needle guidance device  50  of  FIGS. 8A through 8C . In this schematic view, the needle  18  is held into the gap  58 B by the magnetic field generated by the magnet  56 . The needle  18  is retained from moving through the gap  58 B and into an internal region of the device  50  by providing beveled walls within the gap  58 B that have a minimum distance “d” so that the beveled walls interfere with further movement of the needle  18  through the gap  58 B since the distance “d” is generally selected to be smaller than a diameter of the needle  18 . Referring now to  FIG. 10B , method of disengagement of the needle  18  from the gap  58 B is shown. The disengagement of the needle  18  from the needle guidance device  50  includes moving the magnet  56  upwardly and away from the cores  54 . Correspondingly, a reduction in magnetic holding force occurs within the gap  58 B so that the needle  18  may be removed from the needle guidance device  50 . 
         [0078]      FIG. 10C  shows an alternate method for disengagement of the needle  18  from the needle guidance device  50 . Moving the magnet  56  longitudinally along the gap  58 A so that the magnetic force across the gap  58 B is proportionately reduced effects the disengagement of the needle  18 . Depending upon the relative strength of the magnet  56 , the composition of the cores  54  and the material used to fabricate the needle, a user removing the magnet  56  may find that the magnetic holding force is sufficiently reduced to permit non-injurious disengagement of the needle  18  from the gap  58 B of the needle guidance device  50  when the magnet  56  is only partially disengaged from the gap  58 A. Alternately, the user may be required to completely remove the magnet  56  from the gap  58 A in order to release the needle  18  from the device  50 . 
         [0079]      FIG. 11A  is an isometric view of the needle guidance device  60  that shows the needle  18  held in position by the rotating magnet  66 . In this case, the rotatable magnet  66  is in the vertical position within the gap  58 A, and the magnetic forces hold the needle  18  within the gap  58 B. 
         [0080]      FIG. 11B  shows a completion of the disengagement process from  FIG. 11A . The rotatable magnet  66  is rotated to a horizontal position as indicated by the crosshatched arrow within the gap  58 A. This rotation causes either a reduction of retentive magnetic forces spanning across the gap  58 B or generation of repulsive forces. As indicated by the downward arrow, the needle  18  becomes disengagable from the needle guidance device  60  and eventually separates from the gap  58 B. 
         [0081]      FIG. 12A  is an isometric view of a needle guidance device  70 , according to another embodiment of the invention. The device  70  includes two ferromagnetic core assemblies  54  that are longitudinally spaced apart and share a common movable permanent magnet  56  configured to engage respective gaps  58 A in the core assemblies  54 . The magnet  56  may either be slidably disengaged from each ferromagnetic core assembly  54  either longitudinally or it may be removed from the gap  58 A by moving the magnet  56  in a radial direction and away from the core assemblies  54 . In either event, the progressive removal of permanent magnet  56  from the respective gaps  58 A causes a progressive reduction in magnetic fields across the gaps  58 B. Accordingly, a user may advantageously select a suitable retentive force for the needle  18 . 
         [0082]      FIG. 12B  shows a disengagement of the operation in the orthogonal displacement. Here, the needle guidance device  70  is in a disengagement process where the permanent magnet  56  is removed 90° orthogonal to the spaces  58 A, to each ferrite core assembly  54 . Removal as previously mentioned of a permanent magnet  56  causes a diminution magnetic retentive forces across the gap  58 B resulting in a progressively easier disengagement force to be affected to the needle  18 . 
         [0083]      FIG. 13A  shows a needle guidance  80  being an electromagnetic alternate embodiment to the permanent magnet embodiment  70 . This electromagnetic embodiment  80  includes a DC power assembly that has a power source  82 , a variable resistor  84  connected to the power source  82 , in communication with a coil winding (not shown—see  FIG. 13B  below) electrically connected with the source  82  and resistor  84  via a wire  86 . The wire  86  is connected with the coil winding (not shown) that is wrapped within the groove  158  of the electromagnet  156 . The electromagnet  156  is a non-permanent electromagnet that respectfully occupies the spaces  58 A of metal cores  54 . The dashed arrow  84 A within the variable resistor  84  shows a resistor position when there is sufficient power that is delivered to the core winding occupying the grove  158  to induce a magnetic field of sufficient strength to hold the needle  18  across respective gaps  58 B of each iron or other metal core assembly  54  that is able to convey the magnetic flux fields generated by the electromagnet  156 . Reducing the power indicated by the solid arrow  84 B resistor position progressively causes a reduction of magnetic force due to the diminution of current and/or voltage applied to the windings occupying the grove  158 . Eventually the magnetic power is progressively lessened such that an applied disengagement force by a user permits the removal or non-injurious disengagement of the needle  18 , as indicated by the downward arrow, from the gaps  58 B of the guidance device  80 . 
         [0084]      FIG. 13B  is an isometric view schematically depicting the electromagnet of  FIG. 13A . Within the grooves  158  of the he electromagnet  156  is a coil winding  88 . Application of electrical power by the DC power supply  82  through the variable resistor  84  results in a magnetic force generated by the electromagnet  156  in proportion to the amount of electrical power delivered to the coil winding  88 . North, N and South, S poles are formed along the electromagnet  156 . As the power is gradually lessened between the  84 A and  84 B resistor positions, the retentive magnetic force field generated along the electromagnet  156  is accordingly lessened. 
         [0085]    As previously described for the removal of the magnetic strip embodiments and the permanent magnets and the electromagnet needle guidance devices as previously described provides a means for holding a selected cannula such that the cannula is controllably restricted in motion substantially along one dimension. The user may either manipulate the amount of magnetic strips to vary the magnetic power by the permanent magnets or adjust power to electromagnets so that a user may progressively overcome the retentive forces still applied to the needle  18  and effect the extraction or disengagement of the needle  18  from the respective needle guidance devices in a non-injurious way from a patient or other subject. 
         [0086]      FIGS. 14-20B  are partial isometric views that depict various embodiments of the present invention coupled to an ultrasound transceiver  100 . In the description that follows, it is understood that the various embodiments may be removably coupled to the ultrasound transceiver  100 , or they may be permanently coupled to the transceiver  100 . It is also understood that, although an ultrasound transceiver is described in the following description and shown in the following figures, the various embodiments may also be incorporated into other imaging devices. 
         [0087]      FIG. 14  is a partial isometric side view the V-Block  40 A of  FIG. 6A  and  FIG. 6B  coupled to an ultrasound transceiver  101  to form an assembly  100 . The ultrasound transceiver  101  has the needle guidance device  40 A coupled to a transducer housing  104  of the transceiver  101  using a bridge  108 . The needle guidance device  40 A may be fixedly coupled to the housing  104 , or the device  40 A may be removably coupled to the housing  104 . In either case, the transceiver  100  also includes a trigger  102 , a display  103 , a handle  106 , and a transducer dome  112 . Upon pressing the trigger  102 , an ultrasound scancone  116  emanates from the transducer dome  112  that penetrates a subject or patient. The scancone  116  is comprised of a radial array of scan planes  118 . Within the scanplane  118  are scanlines (not shown) that may be evenly or unevenly spaced. Alternatively, the scancone  116  may be comprised of an array of wedged distributed scancones or an array of 3D-distributed scanlines that are not necessarily confined to a given scan plane  118 . As shown, the scancone  116  is radiates about the transducer axis  11  that bisects the transducer housing  104  and dome  112 . 
         [0088]      FIG. 15  is a partial isometric, side view of the needle guidance device  50  of  FIG. 8A ,  FIG. 8B  and  FIG. 8C  coupled to the ultrasound transceiver  101  to form an assembly  120 . The ultrasound transceiver  101  has the needle guidance device  50  mounted to the transducer housing  104  using the bridge  108  of  FIG. 14 . The device  50  may be fixedly or removably coupled to the housing  104 . A scan cone  116  is similarly projected from the transceiver  101 . Various aiming aids may be placed on the needle guidance device  50  to assist a user in aiming the insertion of a needle that is held by a magnetic force to slide within the gap  58 B. 
         [0089]      FIG. 16  is a partial isometric view of a needle guidance device  90  that may be removably coupled to the housing  104  of an ultrasound transceiver  101 , according to another embodiment of the invention. The needle guidance device  90  is attached to an engagement wedge  92 . The engagement wedge  92  slidably and removably attaches with the slot holder  94  that is positioned on a selected portion of the housing  104 . Various aiming aids may be placed on the needle guidance device  90  to assist a user in aiming the insertion of a needle that is held by a magnetic force to slide within the gap  58 B. 
         [0090]      FIG. 17  is a partial isometric view of a needle guidance device  130  according to another embodiment of the invention. The device  130  is configured to be positioned within a transceiver housing  132 . A pair of magnets  134  and  136  are positioned on a rotational shaft  137  that projects into the housing  132 . The magnets  134  and  136  provide an attractive force on the needle  18  when the magnets  134  and  136  are aligned with the needle  18 . When the magnets  134  and  136  are rotated away from alignment (by manually rotating a wheel  139  coupled to the shaft  138 ) with the needle  18 , the attractive force on the needle  18  is reduced, thus allowing the needle  18  to be moved relative to the housing  132 . 
         [0091]      FIG. 18A  is a side view of an ultrasound scanner having a magnetic guide assembly  144 , according to an embodiment of the invention. The guidance assembly  144  includes the transceiver  101  in which a needle  18  with reservoir  19  is held within a ferrite housing  144 . The ferrite housing  144  is secured to transducer housing  104  by a clip-on clasp  142 . 
         [0092]      FIG. 18B  is an isometric view and exploded view of components of the assembly  144  of  FIG. 18A . In the exploded view, the guidance assembly  144  is seen in greater detail. The ferrite housing  144  receives ferrite cores  146  and  150 . Rotable within the space defined by the ferrite core  146  and gap  58 A of ferrite cores  150  is a rotatable magnet  148 . Located between the clip-on clasp  142  and the ferrite housing  144  is an articulating bridge  143 . The articulating bridge  143  allows the user to alter the entry angle of the needle  18  into the patient relative to the transducer axis  11  as illustrated in  FIG. 14 . Rotating the magnet  148  alters the magnetic holding power to gap  58 B between ferrite cores  150 . 
         [0093]      FIG. 19A  is a side view of alternate embodiment shown in  FIG. 18A  that uses a sliding magnet. A guidance assembly  170  includes the transceiver  101  in which a needle  18  with reservoir  19  is held within a ferrite housing  145 . The ferrite housing  145  is secured to transducer housing  104  by a clip-on clasp  142  and articulating bridge  143 . The ferrite housing  145  is configured to receive three components. 
         [0094]      FIG. 19B  is an isometric view and exploded view of the components of the device  170  of  FIG. 19A . In the exploded view the guidance assembly  170  is seen in greater detail. The ferrite housing  145  receives two ferrite cores  172  and a slidable magnet  176 . The slidable magnet  176  is moveable within the space  56 A defined by the ferrite cores  172 . Opposite the space  56 A is space  56 B that receives the needle  18 . The articulating bridge  143  allows the user to alter the entry angle of the needle  18  into the patient or subject relative to the transducer axis  11  as illustrated in  FIG. 14 . Sliding the magnet  176  alters the magnetic holding power to gap  58 B between ferrite cores  172 . 
         [0095]      FIG. 20A  is a side view of alternate embodiment of the device  170  of  FIG. 19A  utilizing a pulling magnet. A guidance assembly  180  includes the transceiver  101  in which a needle  18  with reservoir  19  is held within a ferrite housing  182 . The ferrite housing  182  is secured to transducer housing  104  by a clip-on clasp  142  and articulating bridge  143 . The ferrite housing  145  is configured to receive three components. 
         [0096]      FIG. 20B  is an isometric view and exploded view of components of the device  180  of  FIG. 20A . In the exploded view the guidance assembly  180  is seen in greater detail. The ferrite housing  182  receives two ferrite cores  188  and a trigger receiver  186 . The trigger receiver  186  receivers the trigger  190  that has a magnet frame  191 . The magnet frame  191  retains the magnet  192 . The magnet  192  is snap-fitted into the magnet frame  191  of the trigger  190 . The magnet-loaded trigger  190  is slidably placed into the trigger receiver  186 . The trigger receiver  186  guides the magnet-loaded trigger  190  within the gap  58 B defined by the two ferrite cores  188 . Pulling the magnet-loaded trigger  190  alters the magnetic holding power to gap  58 B receiving the needle  18  located opposite the gap  58 A between ferrite cores  188 . 
         [0097]    An example embodiment includes a system and method using single or multiple cameras for tracking and displaying the movement of a needle or cannula before and/or during insertion into a blood vessel or other sub-dermal structure and subsequent movements therein. A needle or a cannula-fitted needle may be detachably mounted to an ultrasound transceiver in signal communication with a computer system and display configured to generate ultrasound-acquired images and process images received from the single or multiple cameras. Along the external surfaces of the needle or cannula may be fitted optical reflectors that may be discernable in the camera images. The ultrasound transceiver may be secured against a subject&#39;s dermal area adjacent to a sub-dermal region of interest (ROI). Optical signals may be reflected towards the single or multiple cameras by the needle or cannula embedded reflectors and conveyed to the computer system and display. The trajectories of the needle or cannula movements may be determined by data analysis of the reflector signals detected by the cameras. The trajectories of needle or cannula having one or more reflectors may be overlaid onto the ultrasound images to provide alignment coordinates for insertion of the needle or cannula fitted needle into the ROI along a determined trajectory. 
         [0098]    An example embodiment of the present invention generally includes an ultrasound probe attached to a first camera and a second camera. The example embodiment also generally includes a processing and display generating system that may be in signal communication with the ultrasound probe, the first camera, and/or the second camera. Typically, a user of the system scans tissue containing a target vein using the ultrasound probe and a cross-sectional image of the target vein may be displayed. The first camera captures and/or records a first image of a medical object to be inserted, such as a cannula for example, in a first direction and the second camera captures and/or records a second image of the cannula in a second direction orthogonal to the first direction. The first and/or the second images may be processed by the processing and display generating system along with the relative positions of the ultrasound probe, the first camera, and/or the second camera to determine the trajectory of the cannula. A representation of the determined trajectory of the cannula may be then displayed on the ultrasound image. 
         [0099]      FIG. 1  is a diagram illustrating a side view of one embodiment of the present invention. A two-dimensional (2D) ultrasound probe  10  may be attached to a first camera  14  that takes images in a first direction. The ultrasound probe  10  may be also attached to a second camera  18  via a member  16 . In other embodiments, the member  16  may link the first camera  14  to the second camera  18  or the member  16  may be absent, with the second camera  18  being directly attached to a specially configured ultrasound probe. The second camera  18  may be oriented such that the second camera  18  takes images in a second direction that may be orthogonal to the first direction of the images taken by the first camera  14 . The placement of the cameras  14 ,  18  may be such that they can both take images of a cannula  20  when the cannula  20  may be placed before the cameras  14 ,  18 . A needle may also be used in place of a cannula. The cameras  14 ,  18  and the ultrasound probe  10  may be geometrically interlocked such that the cannula  20  trajectory can be related to an ultrasound image. In  FIG. 1 , the second camera  18  may be behind the cannula  20  when looking into the plane of the page. In an embodiment, the cameras  14 ,  18  take images at a rapid frame rate of approximately 30 frames per second. The ultrasound probe  10  and/or the cameras  14 ,  18  may be in signal communication with a processing and display generating system  61  described in  FIGS. 7 and 8  below. 
         [0100]    In typical operation, a user first employs the ultrasound probe  10  and the processing and display generating system  61  to generate a cross-sectional image of a patient&#39;s arm tissue containing a vein to be cannulated (“target vein”)  19 . This could be done by one of the methods disclosed in the patents, patent publications and/or patent applications which are herein incorporated by reference, such as, for example, U.S. patent application Ser. No. 11/460,182 filed Jul. 26, 2006. The user then identifies the target vein  19  in the image using methods such as simple compression which differentiates between arteries and/or veins by using the fact that veins collapse easily while arteries do not. After the user has identified the target vein  19 , the ultrasound probe  10  may be affixed to the patient&#39;s arm over the previously identified target vein  19  using a magnetic tape material  12 , for example. The ultrasound probe  10  and the processing and display generating system  61  continue to generate a 2D cross-sectional image of the tissue containing the target vein  19 . Images from the cameras  14 ,  18  may be provided to the processing and display generating system  61  as the cannula  20  may be approaching and/or entering the arm of the patient. 
         [0101]    The processing and display generating system  61  locates the cannula  20  in the images provided by the cameras  14 ,  18  and determines the projected location at which the cannula  20  will penetrate the cross-sectional ultrasound image being displayed. The trajectory of the cannula  20  may be determined in some embodiments by using image processing to identify bright spots corresponding to micro reflectors previously machined into the shaft of the cannula  20  or a needle used alone or in combination with the cannula  20 . Image processing uses the bright spots to determine the angles of the cannula  20  relative to the cameras  14 ,  18  and then generates a projected trajectory by using the determined angles and/or the known positions of the cameras  14 ,  18  in relation to the ultrasound probe  10 . In other embodiments, determination of the cannula  20  trajectory may be performed using edge-detection algorithms in combination with the known positions of the cameras  14 ,  18  in relation to the ultrasound probe  10 , for example. 
         [0102]    The projected location may be indicated on the displayed image as a computer-generated cross-hair  66  (shown in  FIG. 7 ), the intersection of which may be where the cannula  20  is projected to penetrate the image. In other embodiments, the projected location may be depicted using a representation other than a cross-hair. When the cannula  20  does penetrate the cross-sectional plane of the scan produced by the ultrasound probe  10 , the ultrasound image confirms that the cannula  20  penetrated at the location of the cross-hair  66 . This gives the user a real-time ultrasound image of the target vein  19  with an overlaid real-time computer-generated image of the position in the ultrasound image that the cannula  20  will penetrate. This allows the user to adjust the location and/or angle of the cannula  20  before and/or during insertion to increase the likelihood they will penetrate the target vein  19 . In other embodiments, the ultrasound image and/or the computer-generated cross-hair may be displayed in near real-time. In an example embodiment, this allows a user to employ normal “free” insertion procedures while having the added knowledge of knowing where the cannula  20  trajectory will lead. 
         [0103]      FIG. 2  is a diagram illustrating a top view of the embodiment shown in  FIG. 1 . It is more easily seen from this view that the second camera  18  may be positioned behind the cannula  20 . The positioning of the cameras  14 ,  18  relative to the cannula  20  allows the cameras  14 ,  18  to capture images of the cannula  20  from two different directions, thus making it easier to determine the trajectory of the cannula  20 . 
         [0104]      FIG. 3  is diagram showing additional detail for a needle shaft  22  to be used with one embodiment of the invention. The needle shaft  22  includes a plurality of micro corner reflectors  24 . The micro corner reflectors  24  may be cut into, or otherwise affixed to or embedded in, the needle shaft  22  at defined intervals Δl in symmetrical patterns about the circumference of the needle shaft  22 . The micro corner reflectors  24  could be cut with a laser, for example. 
         [0105]      FIGS. 4A and 4B  are diagrams showing close-up views of surface features of the needle shaft  22  shown in  FIG. 3 .  FIG. 4A  shows a first input ray with a first incident angle of approximately 90° striking one of the micro corner reflectors  24  on the needle shaft  22 . A first output ray is shown exiting the micro corner reflector  24  in a direction toward the source of the first input ray.  FIG. 4B  shows a second input ray with a second incident angle other than 90° striking a micro corner reflector  25  on the needle shaft  22 . A second output ray is shown exiting the micro corner reflector  25  in a direction toward the source of the second input ray.  FIGS. 4A and 4B  illustrate that the micro corner reflectors  24 ,  25  are useful because they tend to reflect an output ray in the direction from which an input ray originated. 
         [0106]      FIG. 5  is a diagram showing imaging components for use with the needle shaft  22  shown in  FIG. 3  in accordance with an example embodiment of the invention. The imaging components are shown to include a first light source  26 , a second light source  28 , a lens  30 , and a sensor chip  32 . The first and/or second light sources  26 ,  28  may be light emitting diodes (LEDs), for example. In an example embodiment, the light sources  26 ,  28  are infra-red LEDs. Use of an infra-red source is advantageous because it is not visible to the human eye, but when an image of the needle shaft  22  is recorded, the image can show strong bright dots where the micro corner reflectors  24  may be located because silicon sensor chips are sensitive to infra-red light and the micro corner reflectors  24  tend to reflect output rays in the direction from which input rays originate, as discussed with reference to  FIGS. 4A and 4B . In alternative embodiments, a single light source may be used. Although not shown, the sensor chip  32  may be encased in a housing behind the lens  30  and the sensor chip  32  and light sources  26 ,  28  may be in electrical communication with the processing and display generating system  61  shown in  FIG. 7  below. The sensor chip  32  and/or the lens  30  form a part of the first and second cameras  14 ,  18  in some embodiments. In an example embodiment, the light sources  26 ,  28  may be pulsed on at the time the sensor chip  32  captures an image. In other embodiments, the light sources  26 ,  28  may be left on during video image capture. 
         [0107]      FIG. 6  is a diagram showing a representation of an image  34  produced by the imaging components shown in  FIG. 5 . The image  34  may include a needle shaft image  36  that corresponds to a portion of the needle shaft  22  shown in  FIG. 5 . The image  34  also may include a series of bright dots  38  running along the center of the needle shaft image  36  that correspond to the micro corner reflectors  24  shown in  FIG. 5 . A center line  40  is shown in  FIG. 6  that runs through the center of the bright dots  38 . The center line  40  may not appear in the actual image generated by the imaging components, but is shown in the diagram to illustrate how an angle theta (θ) could be obtained by image processing to recognize the bright dots  38  and determine a line through them. The angle theta represents the degree to which the needle shaft  22  may be inclined with respect to a reference line  42  that may be related to the fixed position of the sensor chip  32 . 
         [0108]      FIG. 7  is a system diagram of an embodiment of the present invention and shows additional detail for the processing and display generating system  61  in accordance with an example embodiment of the invention. The ultrasound probe  10  is shown connected to the processing and display generating system via M control lines and N data lines. The M and N variables are for convenience and appear simply to indicate that the connections may be composed of one or more transmission paths. The control lines allow the processing and display generating system  61  to direct the ultrasound probe  10  to properly perform an ultrasound scan and the data lines allow responses from the ultrasound scan to be transmitted to the processing and display generating system  61 . The first and second cameras  14 ,  18  are also each shown to be connected to the processing and display generating system  61  via N lines. Although the same variable N is used, it is simply indicating that one or more lines may be present, not that each device with a label of N lines has the same number of lines. 
         [0109]    The processing and display generating system  61  may be composed of a display  64  and a block  62  containing a computer, a digital signal processor (DSP), and analog to digital (A/D) converters. As discussed for  FIG. 1 , the display  64  can display a cross-sectional ultrasound image. The computer-generated cross hair  66  is shown over a representation of a cross-sectional view of the target vein  19  in  FIG. 7 . The cross hair  66  consists of an x-crosshair  68  and a z-crosshair  70 . The DSP and the computer in the block  62  use images from the first camera  14  to determine the plane in which the cannula  20  will penetrate the ultrasound image and then write the z-crosshair  70  on the ultrasound image provided to the display  64 . Similarly, the DSP and the computer in the block  62  use images from the second camera  18 , which may be orthogonal to the images provided by the first camera  14  as discussed for  FIG. 1 , to write the x-crosshair  68  on the ultrasound image. In other embodiments, the DSP and the computer in the block  62  may use images from both the first camera  14  and the second camera  18  to write each of the x-crosshair  68  and the z-crosshair  70  on the ultrasound image. In still other examples, images from the cameras  14 ,  18  may be used separately or in combination to write the crosshairs  68 ,  70  or other representations of where the cannula  20  is projected to penetrate the ultrasound image. 
         [0110]      FIG. 8  is a system diagram of an example embodiment showing additional detail for the block  62  shown in  FIG. 2 . The block  62  includes a first A/D converter  80 , a second A/D converter  82 , and a third A/D converter  84 . The first A/D converter  80  receives signals from the ultrasound probe  10  and converts them to digital information that may be provided to a DSP  86 . The second and third A/D converters  82 ,  84  receive signals from the first and second cameras  14 ,  18  respectively and convert the signals to digital information that may be provided to the DSP  86 . In alternative embodiments, some or all of the A/D converters are not present. For example, video from the cameras  14 ,  18  may be provided to the DSP  86  directly in digital form rather than being created in analog form before passing through A/D converters  82 ,  84 . The DSP  86  may be in data communication with a computer  88  that includes a central processing unit (CPU)  90  in data communication with a memory component  92 . The computer  88  may be in signal communication with the ultrasound probe  10  and may be able to control the ultrasound probe  10  using this connection. The computer  88  may be also connected to the display  64  and may produce a video signal used to drive the display  64 . In still other examples, other hardware components may be used. A field programmable gate array (FPGA) may be used in place of the DSP, for example. Or, an application specific integrated circuit (ASIC) may replace one or more components. 
         [0111]      FIG. 9  is a flowchart of a process of displaying the trajectory of a cannula in accordance with an embodiment of the present invention. The process is illustrated as a set of operations shown as discrete blocks. The process may be implemented in any suitable hardware, software, firmware, or combination thereof. As such the process may be implemented in computer-executable instructions that can be transferred from one computer to a second computer via a communications medium. The order in which the operations are described is not to be necessarily construed as a limitation. First, at a block  100 , an ultrasound image of a vein cross-section may be produced and/or displayed. Next, at a block  110 , the trajectory of a cannula may be determined. Then, at a block  120 , the determined trajectory of the cannula may be displayed on the ultrasound image. 
         [0112]      FIG. 10  is a flowchart of a process showing additional detail for the block  110  depicted in  FIG. 9 . The process is illustrated as a set of operations shown as discrete blocks. The process may be implemented in any suitable hardware, software, firmware, or combination thereof. As such the process may be implemented in computer-executable instructions that can be transferred from one computer to a second computer via a communications medium. The order in which the operations are described is not to be necessarily construed as a limitation. The block  110  includes a block  112  where a first image of a cannula may be recorded using a first camera. Next, at a block  114 , a second image of the cannula orthogonal to the first image of the cannula may be recorded using a second camera. Then, at a block  116 , the first and second images may be processed to determine the trajectory of the cannula. 
         [0113]      FIG. 11  schematically depicts an alternative embodiment of a needle having a distribution of reflectors located near the bevel of the needle. A needle shaft  52  includes a bevel  54  that may be pointed for penetration into the skin to reach the lumen of a blood vessel. The needle shaft  52  also includes a plurality of micro corner reflectors  24 . The micro corner reflectors  24  may be cut into the needle shaft  52  at defined intervals Δl in symmetrical patterns about the circumference of the needle shaft  52 . In an example, the micro corner reflectors  24  may be cut with a laser and serve to provide light reflective surfaces for monitoring the insertion and/or tracking of the trajectory of the bevel  54  into the blood vessel during the initial penetration stages of the needle  52  into the skin and/or tracking of the bevel  54  motion during guidance procedures. 
         [0114]    While the preferred embodiment of the invention has been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. For example, a three-dimensional ultrasound system could be used rather than a 2D system. In addition, different numbers of cameras could be used along with image processing that determines the cannula  20  trajectory based on the number of cameras used. The two cameras  14 ,  18  could also be placed in a non-orthogonal relationship so long as the image processing was adjusted to properly determine the orientation and/or projected trajectory of the cannula  20 . The radiation emitting from the light sources  26 ,  28  may be of a frequency and intensity that may be sufficiently penetrating in tissue to permit reflection of sub-dermal located reflectors  24  to the detector sensor  32 . The sensor  32  may be suitably filtered to optimize detection of sub-dermal reflected radiation from the reflectors  24  so that sub-dermal trajectory tracking of the needles  22 ,  52  or cannulas  20  having one or more reflectors  24  may be achieved. Also, an embodiment of the invention could be used for needles and/or other devices such as trocars, stylets, or catheters which are to be inserted in the body of a patient. Additionally, an embodiment of the invention could be used in places other than arm veins. Regions of the patient&#39;s body other than an arm could be used and/or biological structures other than veins may be the focus of interest. 
         [0115]    While various embodiments of the invention have been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. For example, electromagnetic strips may be removably attached to V-blocks and the magnetic power controlled by an electric circuit applied to the electromagnetic strips. Permanent magnets used in the various embodiments may be of any metal able to generate and communicate a magnetic force, for example, Iron, Iron alloys, and Neodymnium based magnets. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.