Apparatus and method for image guided insertion and removal of a cannula or needle

[0001] This application is claims priority to U.S. provisional patent application Ser. No. 60/621,349 filed Oct. 22, 2004.

[0002] This application is a continuation-in-part of and claims priority to U.S. patent application filed Aug. 26, 2005 under U.S. Express Mail No. EV509173452US.

[0003] This application claims priority to and is a continuation-in-part of U.S. patent application Ser. No. 11/119,355 filed Apr. 29, 2005, which claims priority to U.S. provisional patent application Ser. No. 60/566,127 filed Apr. 30, 2004. This application also claims priority to and is a continuation-in-part of U.S. patent application Ser. No. 10/701,955 filed Nov. 5, 2003, which in turn claims priority to and is a continuation-in-part of U.S. patent application Ser. No. 10/443,126 filed May 20, 2003.

[0004] This application claims priority to and is a continuation-in-part of U.S. patent application Ser. No. 11/061,867 filed Feb. 17, 2005, which claims priority to U.S. provisional patent application Ser. No. 60/545,576 filed Feb. 17, 2004 and U.S. provisional patent application Ser. No. 60/566,818 filed Apr. 30, 2004.

[0005] This application is also a continuation-in-part of and claims priority to U.S. patent application Ser. No. 10/704,966 filed Nov. 10, 2004.

[0006] This application is a continuation-in-part of and claims priority to PCT application serial number PCT/US03/24368 filed Aug. 1, 2003, which claims priority to U.S. provisional patent application Ser. No. 60/423,881 filed Nov. 5, 2002 and U.S. provisional patent application Ser. No. 60/400,624 filed Aug. 2, 2002.

[0007] This application is also a continuation-in-part of and claims priority to PCT Application Serial No. PCT/US03/14785 filed May 9, 2003, which is a continuation of U.S. patent application Ser. No. 10/165,556 filed Jun. 7, 2002.

[0008] This application is also a continuation-in-part of and claims priority to U.S. patent application Ser. No. 10/888,735 filed Jul. 9, 2004.

[0009] This application is also a continuation-in-part of and claims priority to U.S. patent application Ser. No. 10/633,186 filed Jul. 31, 2003 which claims priority to U.S. provisional patent application Ser. No. 60/423,881 filed Nov. 5, 2002 and to U.S. patent application Ser. No. 10/443,126 filed May 20, 2003 which claims priority to U.S. provisional patent application Ser. No. 60/423,881 filed Nov. 5, 2002 and to U.S. provisional application 60/400,624 filed Aug. 2, 2002. This application also claims priority to U.S. provisional patent application Ser. No. 60/470,525 filed May 12, 2003, and to U.S. patent application Ser. No. 10/165,556 filed Jun. 7, 2002. All of the above applications are herein incorporated by reference in their entirety as if fully set forth herein.

[0010] This invention relates to a magnetic system for manipulating the placement of a needle or cannula in a biologic subject.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] Embodiments of the present invention are described in detail below with reference to the following drawings.

[0015] FIG. 1 is a cross-sectional view of a first embodiment;

[0016] FIG. 1B is an alternate embodiment of the first embodiment;

[0017] FIG. 1C is a plan view of the first embodiment;

[0018] FIG. 1D is a plan view of another embodiment;

[0019] FIG. 1E is a plan view of yet another embodiment;

[0020] FIG. 2A is a cross-sectional view of a second embodiment;

[0021] FIG. 2B is a plan view of the second embodiment;

[0022] FIG. 3A is a cross-sectional view of an alternate embodiment of the second embodiment;

[0023] FIG. 3B is a plan view of the alternate embodiment of the second embodiment;

[0024] FIG. 4A is a third embodiment of the invention;

[0025] FIG. 4B is a plan view of the third embodiment;

[0026] FIG. 5A is an embodiment of a magnetic strip;

[0027] FIG. 5B is an alternate embodiment of the magnetic strip;

[0028] FIG. 6A is an embodiment of a magnetic guide assembly having the embodiments of FIG. 5A;

[0029] FIG. 6B is an alternate embodiment of a magnetic guide assembly having the magnetic strip embodiments of FIG. 5B;

[0030] FIG. 7A schematically depicts removing a strip from the device depicted in FIG. 6A;

[0031] FIG. 7B is a progression of the strip removal of FIG. 7A;

[0032] FIG. 7C is a continuation of strip removal of FIG. 7B;

[0033] FIG. 7D is near complete removal of the strips from the magnetic guidance device;

[0034] FIG. 7E is an alternate arrangement of the magnetic strips to the magnetic guidance device;

[0035] FIG. 8A is a cross-section of a fifth embodiment in the form of a magnet-ferrite core assembly;

[0036] FIG. 8B depicts the assembly of FIG. 8A in cross-section holding a cannula in a gap;

[0037] FIG. 8C depicts the assembly of FIG. 8A in cross-section where removal of the magnet causes release of the cannula;

[0038] FIG. 9A is an alternate embodiment of the magnet-ferrite core assembly of FIG. 8A;

[0039] FIG. 9B depicts the alternate embodiment of FIG. 9A magnetically holding a cannula;

[0040] FIG. 9C schematically shows in cross-section the release of the cannula from the assembly of FIG. 9A.

[0041] FIG. D shows the complete release of the cannula from the assembly of FIG. 9A;

[0042] FIG. 10A is an isometric view of the magnetic core assembly of FIG. 8A;

[0043] FIG. 10B is a schematic isometric depiction of the operation of the magnet core assembly of FIG. 8A;

[0044] FIG. 10C is a schematic depiction of the operation of the magnet core assembly of FIG. 8A;

[0045] FIG. 11A is an alternate embodiment of an isometric view of the alternate embodiment depicted in FIG. 9A;

[0046] FIG. 11B depicts an operation of the embodiment shown in FIG. 11A;

[0047] FIG. 12A is an alternate embodiment of a pair of magnet core assemblies of FIG. 8A;

[0048] FIG. 12B is an isometric view of a schematic operation of an embodiment of FIG. 12A;

[0049] FIG. 13A is an isometric view schematically depicting an electro magnetic embodiment of FIG. 12A;

[0050] FIG. 13B is an isometric view schematically depicting the electromagnet of FIG. 13A;

[0051] FIG. 14 illustrates in a partial isometric and side view of a V-Block configured needle guidance device mounted to an ultrasound transceiver;

[0052] FIG. 15 illustrates in a partial isometric and side view of a magnet-ferrite core configured needle guidance device mounted to an ultrasound transceiver;

[0053] FIG. 16 is an alternate embodiment of FIG. 8A for detachably attaching a magnet-ferrite needle guidance to an ultrasound transducer housing;

[0054] FIG. 17 is an alternate embodiment of FIG. 12A mounted to a tranducer housing;

[0055] FIG. 18A is a side view of an ultrasound scanner having a magnetic guide assembly;

[0056] FIG. 18B is an isometric view and exploded view of components of the device of FIG. 18A;

[0057] FIG. 19A is a side view of alternate embodiment of FIG. 18A utilizing a rotating magnet;

[0058] FIG. 19B is an isometric view and exploded view of components of the device of FIG. 19A;

[0059] FIG. 20A is a side view of alternate embodiment of FIG. 19A utilizing a pulling magnet; and

[0060] FIG. 20B is an isometric view and exploded view of components of the device of FIG. 20A.

[0061] 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.

[0062] 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.

[0063] FIG. 1B is a schematic cross-section view of a needle/cannula guide device 10A 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 10A 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 10A 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.

[0064] FIGS. 1C, D, and E illustrate alternate embodiments of the cannula guide devices 10 and 10A, as shown in FIG. 1A and FIG. 1B, respectively. FIG. 1C is a plan view of the devices 10 and 10A 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 10A that shows a first set of magnets 16A positioned on first selected portions of the V-block 12, and a second set of magnets 16B that are positioned on second selected portions of the V-block 12. As shown in FIG. 1D, the second set 16B may be positioned between the first set 16A. FIG. 1E is a plan view of the devices 10 and 10A that shows magnets 16A interruptably positioned on the V-block 12. Although the magnets 16, 16A and 16B are generally depicted in FIG. 1C, FIG. 1D AND FIG. 1E as rectangular, it is understood that the magnets 16, 16A and 16B may have any regular shape.

[0065] FIGS. 2A and 2B are cross sectional and plan views, respectively, of a cannula guide device 20A 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.

[0066] FIGS. 3A and 3B are cross sectional and plan views, respectively, of a cannula guide device 20B according to still another embodiment of the invention. The device 20B includes magnets 24B that are operable to generate an attractive force that is different from magnets 24A. Accordingly, the magnets 24B may generate a greater attractive force on the needle 18 than the magnets 24A. Alternately, the magnets 24A may generate a greater attractive than the magnets 24B.

[0067] FIGS. 4A and 4B are cross sectional and plan views, respectively, of a cannula guide device 20C according to still yet another embodiment of the invention. The device 20C 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 26A and a second magnetic strip portion 26B. The attractive force generated by the portion 26A may be greater than the attractive force generated by the portion 26B, or the attractive force generated by the portion 26B may be greater than the attractive force generated by the portion 26A.

[0068] FIGS. 5A and 5B are isometric views, respectively, of magnetic strips 30A and 30B that may be removably coupled to the V-block 12 (FIG. 1A). The magnetic strips 30A and 30B include a tab 34 configured to apply a pulling force to the strips 30A and 30B. Referring now in particular to FIG. 5A, a unitary magnetic element 32 is positioned on the strip 30A that generates a relatively uniform attractive force on the needle 18 (not shown). Magnetic strip 30B shown in FIG. 5B includes a magnetic element 36 that also includes magnetic portions 36A and 36B that are configured to generate different attractive forces on the needle 18 (not shown). The magnetic strips 30A and 30B may also include an adhesive material that is operable to retain the strips 30A and 30B onto external surfaces of the V-block 12.

[0069] FIGS. 6A and 6B are respective isometric views of needle guidance devices 40A and 40B. In FIG. 6A, the needle guidance device 40A includes the magnetic strips 30A as shown in FIG. 5A that are positioned on the exterior of the V-block 12. The attractive force of the magnetic strips 30A magnetically holds the needle 18 within an inner portion of the V-block 12. In FIG. 6B, the needle guidance device 40B includes the magnetic strip 30B of FIG. 5B positioned on the V-block 12.

[0070] FIGS. 7A-7E are isometric views of the needle guidance device 40A that will be used to a method of using the needle guidance device 40A according to another embodiment of the invention. FIG. 7A and FIG. 7B show a first selected one of the magnetic strips 30A being progressively removed from the V-block 12. The first selected one of the strips 30A 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 30A 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 30A 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.

[0071] 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.

[0072] As shown in FIG. 7E, the magnetic strips 30A may be positioned on the V-block 12 so that the strips 30A are oriented oppositely to those shown in FIGS. 7A through 7D.

[0073] 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 58A and a gap 58B 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 58A and 58B. For purposes of illustration, the magnet 56 is positioned in the gap 56A. When the magnet 56 is positioned within a selected one of the gaps 58A and 58B, a magnetic field is communicated along the cores 54 from the gap 58A to the gap 58B. The gap 58B is configured to accept a needle 18 so that the needle 18 will be retained in the gap 58B by the magnetic fields communicated from gap 56A. As shown in FIG. 8A, the lines of the magnetic force are conveyed across the space 58B. Referring briefly now to FIG. 8B, the needle 18 is held within the gap 58B. Accordingly, the needle 18 will be retained within the gap 58B while the magnet 56 is positioned within gap 58A. The gap 58B progressively narrows to accommodate needles having variable diameters. Turning now to FIG. 8C, as the magnet 56 is moved outwardly from the gap 58A of the needle guidance device 50, the magnetic field spanning the gap 58B is correspondingly reduced. Accordingly, the needle 18 positioned within the gap 58B may be gradually released from the needle guidance device 50.

[0074] 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 58A. 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 58B, so that the needle 18 is retained within the gap 58B, 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 58B is reduced so that the needle 18 may be moved away from the gap 58B.

[0075] 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 58B by the magnetic field generated by the magnet 56. The needle 18 is retained from moving through the gap 58B and into an internal region of the device 50 by providing beveled walls within the gap 58B that have a minimum distance “d” so that the beveled walls interfere with further movement of the needle 18 through the gap 58B 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 58B 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 58B so that the needle 18 may be removed from the needle guidance device 50.

[0076] 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 58A so that the magnetic force across the gap 58B 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 58B of the needle guidance device 50 when the magnet 56 is only partially disengaged from the gap 58A. Alternately, the user may be required to completely remove the magnet 56 from the gap 58A in order to release the needle 18 from the device 50.

[0077] 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 58A, and the magnetic forces hold the needle 18 within the gap 58B.

[0078] 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 58A. This rotation causes either a reduction of retentive magnetic forces spanning across the gap 58B 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 58B.

[0079] 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 58A 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 58A 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 58A causes a progressive reduction in magnetic fields across the gaps 58B. Accordingly, a user may advantageously select a suitable retentive force for the needle 18.

[0080] 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 58A, to each ferrite core assembly 54. Removal as previously mentioned of a permanent magnet 56 causes a diminution magnetic retentive forces across the gap 58B resulting in a progressively easier disengagement force to be affected to the needle 18.

[0081] 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 58A of metal cores 54. The dashed arrow 84A 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 58B 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 84B 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 58B of the guidance device 80.

[0082] 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 84A and 84B resistor positions, the retentive magnetic force field generated along the electromagnet 156 is accordingly lessened.

[0083] 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.

[0084] 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.

[0085] FIG. 14 is a partial isometric side view the V-Block 40A 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 40A coupled to a transducer housing 104 of the transceiver 101 using a bridge 108. The needle guidance device 40A may be fixedly coupled to the housing 104, or the device 40A 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.

[0086] 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 58B.

[0087] 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 58B.

[0088] 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.

[0089] 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.

[0090] 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 58A 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 58B between ferrite cores 150.

[0091] 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.

[0092] 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 56A defined by the ferrite cores 172. Opposite the space 56A is space 56B 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 58B between ferrite cores 172.

[0093] 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.

[0094] 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 58B defined by the two ferrite cores 188. Pulling the magnet-loaded trigger 190 alters the magnetic holding power to gap 58B receiving the needle 18 located opposite the gap 58A between ferrite cores 188.

[0095] While various embodiments 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, 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.