Patent Publication Number: US-2017348511-A1

Title: Medical Devices, Systems And Methods Utilizing Permanent Magnet And Magnetizable Feature

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application No. 62/344,162, filed Jun. 1, 2016, the disclosures of which are incorporated herein by reference in their entirety. 
    
    
     FIELD 
     Principles and embodiments of the present disclosure relate generally to devices, systems and methods including a permanent magnet and a magnetizable feature. 
     BACKGROUND 
     Traditionally, penetration of a needle, guidewire, stylet or other medical device through skin tissue to reach the vein during catheter insertion is invisible to clinicians. For this reason, they must rely on their first-hand experience with device insertion in combination with tactile sense to successfully identify the location of the vein or other location with the body. This may be a difficult task when attempting to access a small vein in a deep location under the skin, or a remote location within a patient&#39;s body such as the pleural cavity, increasing risk of excess pain and/or injury to the patient. 
     Emerging procedural guidance systems utilize a combination of ultrasound and magnetic technologies to provide visualization of subdermal anatomy and device position in the in-plane and out-of-plane orientations. This combination of ultrasound and magnetic methods also allows for the projection or anticipation of the insertion device position relative to the patient&#39;s anatomy, and thereby improves the likelihood of successfully accessing the vasculature or other part of the body and completing the invasive procedure. 
     For needles, one leading technology targets the cannula as the portion of the invasive device for magnetization, while another leading technology uses a permanent magnet located on the needle hub of the device. Although a permanent magnet offers a more reliable magnetic field as it is not subject to the variation of the clinician magnetizing the needle at the point of use, it does rely more on a calculated projection of the needle tip location. The system that relies on magnetizing the cannula prior to insertion can more reliably measure the actual tip location, but this method is subject to variability on consistently magnetizing the cannula as it relies on the clinician to place the needle into a magnetic device to magnetize the needle. Both of these systems utilize a magnetic field generated by a portion of the cannula subassembly, and therefore, it is not able to measure or predict relative motion between the needle hub and catheter adapter subassemblies. Understanding the relative position and motion of these two subassemblies can be used to inform a clinician of procedurally important states of the insertion process, such as when the needle tip reaches the vein, when the catheter tip reaches the vein, when the catheter is advanced to cover the needle tip (“hooding the catheter”) and thereby safe for further advancement. Similar considerations apply with respect to insertion of medical wires such as stylets and guidewires, which can be used in combination with a needle subassembly or catheter subassembly, as it would be desirable to understand the relative position of a wire and a medical device subassembly. It would be desirable to provide medical devices, system and methods that could be used with devices, systems and methods to provide improved visualization during penetration of a wire through a patient&#39;s skin tissue. 
     SUMMARY 
     Various embodiments are listed below. It will be understood that the embodiments listed below may be combined not only as listed below, but in other suitable combinations in accordance with the scope of the disclosure. In one embodiment, a medical device comprises a catheter adapter subassembly and a wire subassembly including a wire, wherein one of the catheter adapter subassembly and the wire subassembly includes a permanent magnet element, and the other of the catheter adapter subassembly and the wire subassembly includes a magnetizable feature to permit measurement of relative motion of the wire subassembly and the catheter adapter subassembly. Another embodiment pertains to a medical device comprising a needle subassembly and a wire subassembly including a wire, wherein one of the needle subassembly and the wire subassembly includes a permanent magnet element, and the other of the needle subassembly and the wire subassembly includes a magnetizable feature to permit measurement of relative motion of the wire subassembly and the needle subassembly. 
     In another embodiment, a guidewire introducer assembly comprises a guidewire introducer subassembly having at least one end and a guidewire extending from the at least one end of the guidewire introducer, wherein one of the guidewire introducer subassembly and the guidewire includes a permanent magnet element, and the other of the guidewire introducer subassembly and the guidewire includes a magnetizable feature. 
     Another embodiment pertains to a system for determining relative position of a catheter adapter subassembly and wire subassembly comprising a catheter having a catheter distal tip and a wire having a wire distal tip; a permanent magnet element associated with one of the catheter adapter subassembly and wire subassembly; a magnetizable feature associated with the other of the catheter adapter subassembly and the wire subassembly; and magnetometers positioned with respect to the catheter adapter subassembly and the wire subassembly, the magnetometers configured to determine relative movement of the catheter adapter subassembly and wire subassembly. Another embodiment pertains to a system for determining relative position of a needle subassembly and wire subassembly comprising a needle having a needle distal tip and a wire having a wire distal tip; a permanent magnet element associated with one of the needle subassembly and wire subassembly; a magnetizable feature associated with the other of the needle subassembly and the wire subassembly; and magnetometers positioned with respect to the needle subassembly and the wire subassembly, the magnetometers configured to determine relative movement of the needle subassembly and wire subassembly. 
     Another embodiment pertains to a method for determining a relative position of a catheter tip and a wire tip, the method comprising providing a catheter adapter subassembly including catheter and a wire subassembly including a wire, the catheter having a catheter distal tip and the wire having a wire distal tip; associating a permanent magnet element with one of the catheter and the wire; associating a magnetizable feature with the other of the catheter and the wire; obtaining a measured position of the permanent magnet; obtaining a measured position of the magnetizable feature to obtain a calculated position of the catheter distal tip and a calculated position of the wire distal tip; and comparing the calculated position of the catheter distal tip with the calculated position of the wire distal tip to determine the relative position of the catheter distal tip and the wire distal tip. Another embodiment pertains to a method for determining a relative position of a wire tip and a needle cannula tip, the method comprising providing a needle subassembly including needle and a wire subassembly including a wire, the needle having a needle distal tip and the wire having a wire distal tip; associating a permanent magnet element with one of the needle and the wire; associating a magnetizable feature with the other of the needle and the wire; obtaining a measured position of the permanent magnet; obtaining a measured position of the magnetizable feature to obtain a calculated position of the needle distal tip and a calculated position of the wire distal tip; and comparing the calculated position of the needle distal tip with the calculated position of the wire distal tip to determine the relative position of the needle distal tip and the wire distal tip. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a catheter assembly that can be utilized according to an embodiment; 
         FIG. 2  is an exploded perspective view of the catheter assembly shown in  FIG. 1 ; 
         FIG. 3  is a top plan view of the catheter assembly shown in  FIG. 1 ; 
         FIG. 4  is a top plan view of a catheter assembly according to an embodiment; 
         FIG. 5  shows the catheter assembly of  FIG. 4  with the needle subassembly and catheter adapter subassembly separated; 
         FIG. 6A  is a top plan view showing a portion of a needle subassembly with the needle disconnected from the needle chamber and a magnetic feature; 
         FIG. 6B  is a top plan view showing a portion of an alternative embodiment of a needle subassembly with the needle disconnected from the needle chamber and a magnetic feature; 
         FIG. 6C  is a top plan view showing a portion of an alternative embodiment of a needle subassembly with the needle disconnected from the needle chamber and a magnetic feature; 
         FIG. 6D  is a top plan view showing a portion of an alternative embodiment of a needle subassembly with the needle disconnected from the needle chamber and a magnetic feature; 
         FIG. 6E  is a top plan view showing a portion of an alternative embodiment of a needle subassembly with the needle disconnected from the needle chamber and a magnetic feature; 
         FIG. 7  is a top plan view of an embodiment of a catheter assembly according to an embodiment; 
         FIG. 8  is a top plan view of an embodiment of a catheter assembly according to an embodiment; 
         FIG. 9  shows the catheter assembly of  FIG. 8  with the needle subassembly and catheter adapter subassembly separated; 
         FIG. 10A  is a top plan view of a catheter adapter subassembly according to an embodiment; 
         FIG. 10B  is a top plan view of a catheter adapter subassembly according to an embodiment; 
         FIG. 10C  is a top plan view of a catheter adapter subassembly according to an embodiment; 
         FIG. 10D  is a top plan view of a catheter adapter subassembly according to an embodiment; 
         FIG. 11  is a perspective view of a catheter assembly showing optional features; 
         FIG. 12A  is a top plan view of an embodiment of a catheter assembly; 
         FIG. 12B  shows the catheter assembly of  FIG. 12A  in a first position; 
         FIG. 12C  shows the catheter assembly of  FIG. 12A  with the needle subassembly and catheter adapter subassembly moved with respect to each other; 
         FIG. 12D  shows the catheter assembly of  FIG. 12A  with the needle subassembly and catheter adapter subassembly moved further apart with respect to each other; 
         FIG. 13  shows an embodiment of a system; 
         FIG. 14  shows an embodiment of a wire and a catheter; 
         FIG. 15  shows an embodiment of a medical device including a catheter adapter subassembly and a wire subassembly; 
         FIG. 16  shows an embodiment of a medical device including a needle subassembly and a wire subassembly; 
         FIG. 17  shows a wire inserted through a needle lumen; and 
         FIG. 18  shows an embodiment of a guidewire introducer assembly. 
     
    
    
     DETAILED DESCRIPTION 
     Before describing several exemplary embodiments, it is to be understood that the disclosure is not limited to the details of construction or process steps set forth in the following description. The disclosure is capable of other embodiments and of being practiced or being carried out in various ways. 
     Reference throughout this specification to “one embodiment,” “certain embodiments,” “various embodiments,” “one or more embodiments” or “an embodiment” means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases such as “in one or more embodiments,” “in certain embodiments,” “in various embodiments,” “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments. 
     Reference will now be made to figures wherein like structures will be provided with like reference designations. It is understood that the drawings are diagrammatic and schematic representations of exemplary embodiments, and are neither limiting nor necessarily drawn to scale. 
     The present disclosure relates to medical devices, systems and methods for enhancing visualization of an invasive procedure requiring procedural guidance, such as providing enhanced visualization of a vascular access device or wire device during an invasive insertion procedure. In one or more embodiments, a catheter assembly is provided which includes a catheter adapter subassembly and a wire subassembly. The catheter adapter subassembly includes either a permanent magnet element or magnetizable feature and the wire subassembly includes a permanent magnet element or a magnetizable feature. Thus, in one embodiment, the catheter adapter subassembly includes a permanent magnet and the wire subassembly includes a magnetizable feature. In another embodiment, the catheter adapter subassembly includes a magnetizable feature and the wire subassembly includes a permanent magnet. In other embodiments, a needle subassembly and a wire subassembly are provided. The needle subassembly includes either a permanent magnet element or magnetizable feature and the wire subassembly includes a permanent magnet element or a magnetizable feature. Thus, in one embodiment, the needle subassembly includes a permanent magnet and the wire subassembly includes a magnetizable feature. In another embodiment, the needle subassembly includes a magnetizable feature and the wire subassembly includes a permanent magnet. In another embodiment, the catheter adapter subassembly includes a magnetizable feature and the wire subassembly includes a permanent magnet. In other embodiments, a guidewire introducer subassembly and a wire are provided. The guidewire introducer subassembly includes either a permanent magnet element or magnetizable feature and the guidewire includes a permanent magnet element or a magnetizable feature. Thus, in one embodiment, The guidewire introducer subassembly includes a permanent magnet and the guidewire includes a magnetizable feature. In another embodiment, the guidewire introducer subassembly includes a magnetizable feature and the guidewire includes a permanent magnet. 
     For clarity it is to be understood that the word “proximal” refers to a direction relatively closer to a clinician using the device to be described herein, while the word “distal” refers to a direction relatively further from the clinician. For example, the end of a needle or wire placed within the body of a patient is considered a distal end of the needle or wire, while the needle or wire end remaining outside the body is a proximal end of the needle. “Magnetic feature” refers to a feature that includes a permanent magnet and/or a magnetizable material that has been magnetized by an externally applied magnetic field such that the magnetic feature can be detected by an ultrasound system. A “magnetizable feature” refers to an element that can become magnetized and is detectable by an ultrasound system as described further herein. 
     Referring now to  FIGS. 1-3 , an exemplary embodiment of a catheter assembly  10  is shown, including a catheter adapter subassembly  12  and a needle subassembly  14 . The catheter adapter subassembly  12  comprises a catheter adapter  16 , catheter tubing  18  and a securement element  22 , and the needle subassembly  14  further includes a needle  20 , connected to a needle hub, at a hub distal end  23  and a vent plug  26 . In other embodiments not shown, the needle  20  can be retracted into the needle hub after the needle  20  has been used to prevent accidental needle sticks of a patient or a clinician. 
     Referring now to  FIGS. 4 and 5 , an embodiment of a medical device  100  comprising a catheter assembly  110  is shown. The catheter assembly  110  includes a catheter adapter subassembly  112  and a needle subassembly  114 . The catheter adapter subassembly  112  further includes a catheter adapter  116 , catheter hub (not shown) and catheter tubing  118 . The needle subassembly  114  further includes a needle  120 , connected to a needle hub (not shown), disposed within a needle hub  124  and a vent plug  126 . In the embodiment shown in  FIGS. 4 and 5 , the catheter adapter subassembly  112  includes a permanent magnet element  132  and the needle subassembly  114  includes a magnetizable feature  130 , in particular on the needle  120 . According to an alternative embodiment (not shown), this configuration is reversed wherein the permanent magnet element  132  is on the needle subassembly  114 , in particular on the needle  120 , and the magnetizable feature  130  is on the catheter adapter subassembly  112 . 
     The use of a permanent magnet element on the catheter adapter subassembly  112  and a magnetizable feature on the needle subassembly  114  provides the ability to calculate the catheter tip position and the needle tip position based on known geometry relative to the position of permanent magnet element  132  on the catheter adapter subassembly  112  from which a calculated catheter tip position and a calculated needle tip position can be determined. The permanent magnet element  132  provides a static magnetic field, while the magnetizable feature  130  on the needle  120  can be magnetized with an externally applied magnetic field prior to insertion of the needle  120  into the patient. 
     In the embodiment shown in  FIGS. 4 and 5 , the magnetizable feature  130  is on the needle  120 , and the catheter adapter subassembly  112  includes the permanent magnet element  132 . The magnetizable feature  130  on the needle  120  can be provided in a variety of ways. In one embodiment, the needle  120  is made from a magnetizable material, for example, a steel material that has a magnetic permeability that permits the needle  120  to be magnetized by application of an external magnetic field. Stainless steel that is typically used to manufacture hypodermic needles for medical use, for example, type 304 stainless steel, may not have the magnetic permeability to be magnetized and used in a device according one or more embodiments. Type 304 stainless steel is an austenitic steel comprising at least 18% chromium, 8% nickel, and a maximum of 0.08% carbon. Type 316 stainless steel is also used in the manufacture of hypodermic needles, and type 316 stainless steel is also austenitic and non-magnetic. The nickel content of type 316 stainless steel is typically higher than type 304 stainless steel, and type 316 stainless steel also includes the addition of molybdenum. According to one or more embodiments, the needle  120  is made from martensitic or ferritic stainless steels, for example, type 420 or type 430 stainless steel. 
     In one or more embodiments, the magnetizable feature  130  on the needle comprises a separate feature on the needle  120 . Referring now to  FIG. 6A , in one embodiment, needle adhesive  140  is placed on a proximal end  121  of the needle  120 , which can be used to secure the needle  120  to the hub within the needle chamber  24 . The needle adhesive  140  can be any suitable adhesive such as a curable glue containing magnetizable nanoparticles such as magnetizable metal nanoparticles or magnetizable metal oxide nanoparticles. The magnetizable metal can include iron, cobalt, nickel and alloys of iron, cobalt, and nickel. According to one or more embodiments, the size of the magnetic nanoparticles is in the range of about 1 nanometer (nm) to about 100 nm. In one embodiment, adhesive is a light-curable glue, and in another embodiment, the adhesive is a heat-curable glue. 
     Referring now to  FIG. 6B , an embodiment is shown in which the magnetizable feature is a needle ferrule  142  adjacent the distal tip  123  of the needle  120 . The needle ferrule  142  is made from a magnetizable metal such as martensitic or ferritic stainless steels, for example, type 420 or type 430 stainless steel. The needle ferrule  142  provides at least a localized area of increased outer diameter. As used herein, the term “ferrule” refers to a separate member attached to the shank portion the needle  120 , providing at least a localized area of increased outer diameter. The term “ferrule” includes a construction wherein the ferrule comprises an integral part of the needle, defining a one-piece monolithic construction composed of both the needle  120  and the needle ferrule  142 , as well as a construction in which the needle ferrule  142  is a piece added to the needle by crimping the needle ferrule  142  onto the shank of the needle  120 . 
     Referring now to  FIG. 6C , an embodiment is shown in which the magnetizable feature is a spot weld  144  adjacent the distal tip  123  of the needle  120 . The spot weld  144  can be made from a magnetizable metal such as martensitic or ferritic stainless steels, for example, type 420 or type 430 stainless steel. 
     Referring now to  FIG. 6D , an embodiment is shown in which the magnetizable feature is a needle safety element, for example, a metal clip  146 , specifically, a metal cannula safety clip adjacent the distal tip  123  of the needle  120 . The metal clip  146  can be made from a magnetizable metal such as martensitic or ferritic stainless steels, for example, type 420 or type 430 stainless steel. In other embodiments, the needle safety element can be embodied in other forms, for example, a spring, a plastic housing including a magnetizable feature, or other suitable safety elements. According to one or more embodiments, the safety element can be made from a materials that are not magnetic or magnetizable and include a magnetizable or magnetic material. 
     Referring now to  FIG. 6E , an embodiment is shown in which the magnetizable feature is a notch  148  in the needle  120 , adjacent the distal tip  123  of the needle  120 . The notch  148  can include an insert made from a magnetizable metal such as martensitic or ferritic stainless steels, for example, type 420 or type 430 stainless steel. The insert fits inside the notch  148  to completely or partially fill the notch  148 . According to one or more embodiments, the insert can be a permanent magnet, magnetic adhesive or other magnetic material. The notch can be partially filled to occupy one-half the length of the notch  148 . 
     Referring now to  FIG. 7 , an embodiment of a medical device  200  comprising a catheter assembly  210  is shown. The catheter assembly  210  includes a catheter adapter subassembly  212  and a needle subassembly  214 . The catheter adapter subassembly  212  includes a catheter adapter  216 , catheter hub (not shown) and catheter tubing  218 , and the needle subassembly  214  further includes a needle  220  connected to the needle hub  224 , disposed within a needle hub  224  and a vent plug  226 . In the embodiment shown in  FIG. 7 , the catheter adapter subassembly  212  includes a permanent magnet element  232  and the needle subassembly  214  includes a magnetizable feature  230 , in particular on the needle  220 . In the specific embodiment shown, the catheter adapter subassembly  212  includes the catheter tubing  218  and a catheter adapter  216 , and a magnetic adhesive  240  attaches the catheter tubing  218  to the catheter adapter  216 . The magnetic adhesive  240  can be any suitable adhesive such as a curable glue containing magnetizable nanoparticles such as magnetizable metal nanoparticles or magnetizable metal oxide nanoparticles. The magnetizable metal can include iron, cobalt, nickel and alloys of iron, cobalt, and nickel. According to one or more embodiments, the size of the magnetic nanoparticles is in the range of about 1 nanometer (nm) to about 100 nm. In one embodiment, adhesive is a light-curable glue, and in another embodiment, the adhesive is a heat-curable glue. 
     Referring now to  FIGS. 8 and 9 , an embodiment of a medical device  300  comprising a catheter assembly  310  is shown. The catheter assembly  310  includes a catheter adapter subassembly  312  and a needle subassembly  314 . The catheter adapter subassembly  312  includes a catheter adapter  316 , catheter hub (not shown) and catheter tubing  318 , and the needle subassembly  314  further includes a needle  320  connected to the needle chamber  324 , disposed within a needle chamber  324  and a vent plug  326 . In the embodiment shown in  FIGS. 8 and 9 , the catheter adapter subassembly  312  includes a magnetizable feature  330  and the needle subassembly  314  includes a permanent magnet element  332 . 
       FIGS. 10A-10D  show various configurations for providing the magnetizable feature  330  on the catheter adapter subassembly  312 . In  FIG. 10A , a securement element in the form of a mandrel  342 , which can be a conical mandrel for connecting the catheter tubing  318  to the catheter adapter  316 , can be the magnetizable feature. According to one or more embodiments, the mandrel  342  is includes or is manufactured from martensitic or ferritic stainless steels, for example, type 420 or type 430 stainless steel. It will be understood that in  FIG. 10A , the mandrel  342  is protruding from the catheter adapter  316 . In other embodiments (not shown), the mandrel  342  can be recessed within the catheter adapter  316 . 
     In  FIG. 10B , the securement element is shown in the form of a catheter tubing adhesive  340  is shown on the catheter tubing  318 , which can be used to provide the magnetizable feature. The catheter tubing adhesive  340  can be any suitable adhesive such as a curable glue containing magnetizable nanoparticles such as magnetizable metal nanoparticles or magnetizable metal oxide nanoparticles. The magnetizable metal can include iron, cobalt, nickel and alloys of iron, cobalt, and nickel. According to one or more embodiments, the size of the magnetic nanoparticles is in the range of about 1 nanometer (nm) to about 100 nm. In one embodiment, adhesive is a light-curable glue, and in another embodiment, the adhesive is a heat-curable glue. 
       FIG. 10C  shows an embodiment in which a blood control component  346  shown exploded from the catheter adapter subassembly  312  to provide the magnetizable feature. In the embodiment shown, the blood control component is a spring that includes a magnetic element or magnetizable material. According to one or more embodiments, the blood control component  346  includes martensitic or ferritic stainless steels, for example, type 420 or type 430 stainless steel. The blood control component (metal spring for instance) moves with the catheter adapter until fully advanced. It will be appreciated that in use the blood control component  346  in the form of a spring would be located within the catheter adapter  316 , and may not be visible, unless the catheter adapter was made from transparent material. 
       FIG. 10D  shows an embodiment in which a magnetic element  348  on the catheter adapter  316  provides the magnetizable feature. According to one or more embodiments, the magnetic element  348  is includes or is made from martensitic or ferritic stainless steels, for example, type 420 or type 430 stainless steel. A magnetic wedge can provide a controlled position on the catheter adapter subassembly  312  to provide a fixed measurement datum in a fixed location relative to the catheter distal tip and a wedge having a highly oriented grain structure due to the cold forming used during is fabrication is also beneficial in providing a measurement datum. In one or more embodiments, the various alternatives discussed with respect to  FIGS. 10A-10D  may not have a position that is as precisely controlled. In one or more embodiments, the wedge, spring, and safety clip, would rely on catheter tip calculated projection rather than positional measurement. 
     In specific embodiments that include a magnetic adhesive, the adhesive can include an additive selected from a paramagnetic additive, a ferromagnetic additive and combinations thereof. The additive, according to one or more embodiments, includes a component selected from powdered iron, magnetic iron oxide, magnetic titanium oxide, magnetic powdered steel, and a magnetic iron alloy, and mixtures thereof. In specific embodiments, the magnetic iron alloy includes one or more of nickel, zinc, and copper. In specific embodiments, the additive further comprises a component selected from chromium, magnesium, molybdenum and combinations thereof. 
     In one or more embodiments, the needle subassembly includes the permanent magnet element, and the catheter adapter subassembly includes the magnetizable feature, wherein the magnetizable feature includes magnetizable catheter tubing. In one or more embodiments, at least a portion of the polyurethane tubing comprises a magnetizable composition which is magnetizable by an externally applied magnetic field, the magnetizable composition comprising a magnetic material dispersed in the polyurethane. In certain embodiments, the magnetic composition is dispersed in the polymeric material, for example, polyurethane, which forms the tubing. In a specific embodiment, the magnetizable composition comprises an inner layer surrounding the lumen of the catheter with an outer layer of non-magnetizable polymeric material, for example, polyurethane. In an alternative specific embodiment, the layer of magnetizable composition is an outer layer surrounding an inner layer of non-magnetizable polyurethane. In one or more embodiments, the magnetizable composition forms longitudinal segments of the catheter separated by longitudinal segments of non-magnetizable polymeric material, for example, polyurethane. 
     In any of the foregoing embodiments of the catheter, the magnetizable composition may further comprise a radiopaque component. Alternatively, in any of the foregoing embodiments, a non-magnetizable portion of catheter may comprise a radiopaque component 
     It will be understood that the permanent magnet element or a magnetized magnetizable feature for the embodiments described above, the orientation of the magnetic field can vary. The permanent magnet element can have north and south poles on axis with the catheter tubing and with the needle. Alternatively, permanent magnet element or magnetized magnetizable feature can have north and south poles off axis with the catheter tubing and with the needle, for example, the north and south poles can be oriented perpendicular to the longitudinal axis of the catheter tubing and the needle. For example, in  FIG. 5 , the magnetizable feature  130  is shown as being magnetized with the north pole  130 N and south pole  130 S of the magnetizable feature  130  oriented parallel of the longitudinal axis of the needle  120 . The permanent magnet element  132  associated with the catheter adapter subassembly  112  is shown with the north pole  132 N and south pole  132 S oriented perpendicular to the longitudinal axis of the catheter tubing  118 . In the configuration shown in  FIG. 9 , the permanent magnet element  332  and the magnetizable feature  330 , which has been magnetized, are shown with the poles  330 N,  330 S,  332 N and  332 S oriented parallel to the longitudinal axis of the needle  320  and the catheter tubing  318 . Other variants are possible such as the permanent magnet element and the magnetizable feature which has been magnetized having their north and south poles both oriented perpendicular or orthogonal to the longitudinal axis of the needle and the catheter tubing. 
     An example of a vascular access device including a catheter according to any of the foregoing embodiments described above is illustrated in  FIG. 11 . The vascular access device  500  shown in  FIG. 11  comprises a catheter adapter subassembly  512  including a catheter adapter body  516  and a catheter tubing  518  and a permanent magnet element  532 . A needle (not shown) within the catheter tubing includes magnetizable feature  530 , which has been magnetized by application of an external magnetic field and can be any of the magnetizable features described herein. Magnetizing the magnetizable feature  530  with an externally applied magnetic field creates a magnetic field  515  in the region of magnetizable feature  530 . 
     The vascular access device  500  may include a lateral access port  556  and may be connected to a section of an extension tube  560  for establishing fluid communication between an IV fluid source and the catheter tubing  518 . In one or more embodiments, the extension tube  560  is built-in to reduce contamination and mechanical phlebitis by eliminating manipulation at the insertion site. In one or more embodiments, the extension tube  560  is compatible with high pressure injection. In one or more embodiments, the extension tube  560  provides continuous confirmation of vessel access during advancement of the catheter into the patient vein. 
     In one or more embodiments, a needle  511  of a needle subassembly  514  is inserted into the lumen (not show) of the catheter tubing  518 . The needle subassembly  514  is shown as including finger grips  584  positioned at the sides of the needle subassembly  514  to facilitate various insertion techniques. In one or more embodiments, bumps may be present on the finger grip to indicate where to the user may grip the device for needle removal. In one or more embodiments, a thumb pad  585 , having a gently convex surface, is provided at the proximal end of the needle subassembly  514 . A flange  586 , having a gently convex surface, is provided at the proximal end of the needle subassembly  514  to provide a finger pad. A wing member  570 , thumb pad  585  and flange  586  may be utilized by the user during insertion, permitting the user to elect which insertion technique to employ. 
     In one or more embodiments, the needle subassembly  514  includes a needle shield  580 . The needle shield  580  may be a design adapted to secure the tip of the needle within the shield after use. In one or more embodiments, the needle shield  580  may be activated passively. The needle tip is completely covered by the needle shield  580  in a fixed position. In one or more embodiments, a ferrule, crimp or other structure may be included near the tip for engagement with a needle shield in certain applications. 
     A push tab  581  may be provided to facilitate catheter advancement during insertion. The push tab  581  also allows for one-handed or two-handed advancement. In one or more embodiments, the push tab  581  is removed with the needle shield  580 . A clamp  582  may also be included on the extension tubing to prevent blood flow when replacing the access port. 
     In one or more embodiments, the vascular access device  500  further includes a first luer access  572  and a second luer access  573  in fluid communication with the extension tube  560 , a blood control split septum  574  associated with the first luer access  572 , and an air vent  576  associated with the second luer access  573 . Split septum  574  allows for a reduction in catheter-related bloodstream infection (CRBSI) while providing unrestricted flow and a straight fluid path and functions as a blood control septum. In one or more embodiments, the split septum  574  may be located in an internal cavity of the catheter adapter or on the distal end of the catheter adapter. In yet another embodiment, the split septum  574  may be located on a distal end of the extension tube  560 . The air vent  576  allows air to escape from the system during insertion, providing continuous confirmation of vascular access while preventing leakage of blood from the system during insertion. In one or more embodiments, the air vent  576  may be at the distal end of extension tube  560 . 
     Another aspect of the disclosure pertains to a system for determining catheter tip location when the catheter tubing is inserted in a patient. According to one or more embodiments, a system provides a way to independently measure the cannula tubing tip location by measuring the location and vector of the permanent magnet, and calculating and predicting the catheter tip location relative to the position of the magnetic sensor(s) on an ultrasound probe and the ultrasound information transmitted from the sensors on the ultrasound probe. A permanent magnet on a device with north and south poles on axis with the catheter and needle and a known geometrical relationship to one or more features fixed on the catheter assembly provides a measurement datum that is measurable by the ultrasound probe magnetic sensors. From the measurement datum based on the one or more features on the catheter assembly, the direction vector and position of the catheter tip, needle tip or other features can be calculated. A magnetized magnetizable needle or feature on the needle can then be used to independently measure the position feature and calculate the position of the needle tip. The calculated position of the needle tip or feature on the needle can then be compared relative to the calculated position of the catheter tip to provide more specific information related to the catheter placement process, such as needle and catheter tip position relative to the patient&#39;s anatomy. This information can be used to determine (a) if the catheter is properly seated and ready for insertion (i.e., no over the bevel condition), (b) when the needle tip is in the “hooded” position (needle tip just inside of the catheter tip), and (c) and (d) when the catheter is advanced to specific distances and at angles suggesting successful placement in the vein. 
     Referring now to  FIGS. 12A-D , an embodiment of a medical device  600  comprising a catheter assembly  610  is shown. The catheter assembly  610  includes a catheter adapter subassembly  612  and a needle subassembly  614 . The catheter adapter subassembly  612  includes a catheter adapter  616 , catheter hub (not shown) and catheter tubing  618  having a distal catheter tip, and the needle subassembly  614  further includes a needle  620  having a needle distal tip  623  connected to a needle hub  624 , and a vent plug  626 . In the embodiment shown in  FIGS. 12A-D , the catheter adapter subassembly  612  includes a permanent magnet element  632  and the needle subassembly  614  includes a magnetizable feature  630 .  FIG. 12B  shows the catheter assembly  610  in  12 A in when the needle distal tip  623  is in the “hooded” position where the needle distal tip  623  is just inside of the catheter distal tip  619 . Since the dimensions of the components of the needle subassembly  614  are fixed and known, placement of the permanent magnet element  632  provides a known geometrical relationship, for example, distance and angular position, with respect to one or more features fixed on the catheter assembly, which provides a measurement datum  633 . 
     Referring now to  FIG. 12C , the catheter adapter subassembly  612  has been advanced in distal direction (toward the patient and away from the clinician), and the measurement datum  633  can be used to determine the distance and angular movement of the needle  620  with respect to the measurement datum  633 . Similarly, if the catheter tubing  618  or other part of the catheter adapter subassembly  612  includes a magnetizable feature, and the needle subassembly  614  includes a permanent magnet, the distance and the angular movement of the catheter tubing  618  can be determined with respect to the measurement datum.  FIG. 12C  shows that the needle  620  has moved a distance D 1 , and the magnetizable feature  630  has moved a distance D 1  from the catheter distal tip  619 . In  FIG. 12D , the needle subassembly  614  has moved in a proximal direction (towards the clinician) for a distance D 2 , and the magnetizable feature  630  is now at a distance D 2  from the catheter distal tip  619 . Each sequential movement of either a permanent magnet element or magnetized magnetizable feature on a needle and/or the cannula can be measured and tracked using an ultrasound system. 
     The location of the magnetized magnetic feature or permanent magnet on a needle or cannula tubing can be accomplished by using a magnetometer to determine the strength of the magnetic field and its direction. As used herein, “magnetometer” refers to a device that detects a magnetic field. In specific embodiments, magnetometers may measure the strength of a magnetic field. When invasive needle or catheter is magnetic and produces a known magnetic field B at a given distance x through tissue of permeability μ r , a mathematical correlation between the two i.e. x=f(B, μ r ) can be derived. In an embodiment, three different magnetometers are arranged in a three-dimensional grid array, orthogonal to each other, are used, and a three-dimensional (3D) correlation can be derived where I=f(B i  μ r ), where i=x or y or z along three axes. Such correlation can be extended to an array of 3-dimensional (3-D) magnetometers to obtain the precise distance to the magnetized catheter or vascular access device from the array of 3D magnetometers. If the location of the array of 3D magnetometers is known in reference to the ultrasound sensor, then the precise location of the magnetized device with respect to the ultrasound sensor can be calculated. An inferred image of the device can then be created and superimposed over the ultrasound image and displayed. An exemplary magnetic sensing method using magnetometers and a lookup table instead of a mathematical function to determine the location of a magnetized invasive device from the magnetic field strength measured outside the body using magnetometers is shown and described in United States Patent Application Publication Number US20140257080 A1. The method described in US20140257080 A1 can be adapted as described herein, for example, a three-dimensional (3D) correlation is from a mathematical function, and the correlation is extended to an array of 3-dimensional (3-D) magnetometers, one of the magnetometers outside the patient&#39;s body, to obtain the precise distance to the magnetized catheter or vascular access device from the array of 3D magnetometers. Another exemplary method of referencing the magnetometers with respect to an ultrasound probe is described in PCT Patent Application Publication Number WO2013034175 A1, which can be adapted as described herein. For example, as shown in  FIG. 13 , an ultrasound system  700  is shown including a catheter adapter subassembly  712  comprising a magnetizable feature  732  that has been magnetized as described herein is shown inside of a patient&#39;s body  800 . It will be appreciated that the sizes shown are not to proportion and the sizes of the catheter adapter subassembly  712  and the magnetizable feature  732  are exaggerated in size to illustrate these elements more clearly. A magnetometric detector  711  comprising an array of magnetometers  720  (which can be housed in a probe of a ultrasound system, not shown) arranged in a 3-D array can be used to sense the magnetic field  714  together with the terrestrial magnetic field and any other background magnetic field. The magnetometric detector  711  is in communication with an ultrasound processor  730  adapted to determine from the detected field the position and orientation of the magnetizable feature  732  relative to the magnetometric detector  711 . This magnetically detected position is then displayed on a display  750  together with the ultrasound image. 
     The ultrasound system  700  can be a standard two dimensional B-mode ultrasound system with a standard ultrasound probe modified by the provision of the magnetometric detector  711 . The ultrasound processor  730 , which can be connected to the ultrasound probe via a cable  735 , sends electrical signals to the magnetometric detector  711  to cause it to generate ultrasound pulses and interpreting the raw data received from the transducer probe housing the magnetometric detector  711 , which represents echoes from the patient&#39;s body, to assemble it into an image of the patient&#39;s tissue. 
     The magnetometric detector  711  can be attached to the ultrasound probe and can be battery powered or powered from the ultrasound system. In specific embodiments, positioning elements are provided on the magnetometric detector  711  to ensure that it is always attached in the same well-defined position and orientation. The magnetometric detector  711  can connected by a wireless connection to a base unit  740  which is in wireless or wired (e.g. USB) communication with the ultrasound processor  730  and the display  750 . The base unit  740  can be integrated with, or some of its functions performed by, the ultrasound processor  730  or the magnetometric detector  711 . 
     The base unit  740  receives normalized measurements from magnetometric detector  711  and calculates the position, or optionally the position and orientation, of magnetizable feature  732 . The base unit  740  can also receive additional information such as the state of charge of the magnetometric detector&#39;s battery and information can be sent from the base unit  740  to the magnetometric detector  711 , such as configuration information. The base unit  740  forwards the results of its calculations, i.e. the position and, optionally, orientation, to the ultrasound processor  730  for inclusion in the displayed ultrasound image of an image of the catheter. 
     In one or more embodiments, the base unit  740  can be integrated into the ultrasound system  700  with the ultrasound processor  730  and the magnetometric detector  711  being in direct communication with the ultrasound system  700  either via wireless link or using the same physical cable  735 . 
     Thus, in one or more embodiments, the magnetizable feature is magnetized using any suitable device that can produce an magnetic field to magnetize a needle or medical device to produce a magnetic field B at a distance x through tissue of permeability μ r , and the correlation is calculated as x=f(B, μ r ). In one or more embodiments, three magnetometers  720  are placed orthogonally to each other are used to derive a 3-dimensional correlation I=f(B i , μ r ), wherein i=x or y or z along three axes. In a specific embodiment, the distance from the magnetizable feature to the 3-dimensional array of magnetometers is calculated. In a further specific embodiment, location of the array of magnetometers in reference to an ultrasound sensor of an ultrasound imaging system is used to calculate a location of the magnetizable feature with respect to the ultrasound sensor. In another specific embodiment, the method comprises displaying an image of the magnetizable feature. 
     As described above with respect to  FIGS. 12A-D , providing a permanent magnet on the needle subassembly and a magnetizable feature on the catheter adapter subassembly (or a reverse configuration in which the magnetizable feature is on the needle subassembly (e.g., the needle or needle hub) and the permanent magnet is on the catheter adapter subassembly) relative positions of a catheter tip and a needle cannula tip can be determined by utilizing an ultrasound system including a three dimensional array of magnetometers. Relative positional changes of the catheter adapter subassembly and needle subassembly can be determined in three axes, x, y and z, as well relative changes in angular motion w of the catheter adapter subassembly and the needle subassembly based on based on a known geometrical relationship to one or more features fixed on the catheter adapter assembly or needle subassembly, which provides a measurement datum that is measurable by the ultrasound probe magnetic sensors. From the measurement datum based on the one or more features, the direction vector and position of the catheter tip or other features can be calculated based on a 3-dimensional correlation I=f(B i , μ r ), wherein i=x or y or z along three axes or predict relative motion between the needle hub and catheter adapter sub-assemblies. Understanding the relative position and motion of these two sub-assemblies can be used to inform a clinician of procedurally important states of the insertion process, such as when the needle tip reaches the vein, when the catheter tip reaches the vein, when the catheter is advanced to cover the needle tip (“hooding the catheter”) and thereby safe for further advancement. 
     Another aspect of the disclosure comprises methods that can be practiced according to any of the previously described systems. A method for determining a relative position of a catheter tip and a needle cannula tip, the method includes providing a catheter having a catheter distal tip and a needle having a needle distal tip, associating a permanent magnet element with one of the catheter and the needle, associating a magnetizable feature with the other of the catheter and the needle, obtaining a measured position of the permanent magnet, obtaining a measured position of the magnetizable feature to obtain a calculated position of the catheter distal tip, and comparing the calculated position of the catheter distal tip with the calculated position of the needle distal tip to determine the relative position of the catheter distal tip and the needle distal tip. In one embodiment, the needle includes the magnetizable feature and the catheter includes the permanent magnet and the relative position of the catheter distal tip and the needle distal tip indicates that the catheter is properly seated on the needle. In another embodiment, the relative position of the catheter distal tip and the needle distal tip indicates that the catheter is in a hooded position on the needle. In another embodiment, the relative position of the catheter distal tip and the needle distal tip indicates that the catheter distal tip is advanced a specific distance or angle. 
     In one embodiment of the method, the catheter adapter subassembly includes the magnetizable feature and the needle subassembly includes the permanent magnet, and relative movement of the catheter adapter subassembly and needle subassembly is determined by a three-dimensional array of magnetometers positioned in proximity to at least one of the permanent magnet the magnetizable feature. In one embodiment of the method, the method includes magnetizing the magnetizable feature by applying an external magnetic field to the magnetizable feature. In one embodiment, the three-dimensional array of magnetometers is part of an ultrasound system, and the ultrasound system derives a three-dimensional correlation to obtain a distance from the grid array to the magnetizable feature or permanent magnet. In another embodiment, the three-dimensional correlation is determined by the function I=f(B i  μ r ), where i=x or y or z along three axes, x, y and z are distances in three planes, B is a known magnetic field produced by the permanent magnet or magnetizable feature, and μ r  is magnetic permeability. 
     In another embodiment of the method, the catheter adapter subassembly includes the permanent magnet and the needle subassembly includes the magnetizable feature, and relative movement of the catheter adapter subassembly and needle subassembly is determined by a three-dimensional array of magnetometers positioned in proximity to at least one of the permanent magnet the magnetizable feature. In one embodiment, the method includes magnetizing the magnetizable feature by applying an external magnetic field to the magnetizable feature. According to another embodiment, the three-dimensional array of magnetometers is part of an ultrasound system, and the ultrasound system derives a three-dimensional correlation to obtain a distance from the grid array to the magnetizable feature or permanent magnet. In one embodiment, the three-dimensional correlation is determined by the function I=f(B i  μ r ), where i=x or y or z along three axes, x, y and z are distances in three planes, B is a known magnetic field produced by the permanent magnet or magnetizable feature, and μ r  is magnetic permeability. 
     Another aspect of the disclosure pertains to a catheter adapter subassembly comprising a magnetic feature selected from the group consisting of a metal mandrel for connecting catheter tubing to the hub, a catheter tubing adhesive, a blood control component of the catheter adapter subassembly, and a magnetic wedge on the catheter adapter body. The catheter adapter subassembly may further comprise magnetic catheter tubing. According to an embodiment, the metal mandrel comprises austentitic stainless steel. 
     While the embodiments of invasive medical devices described in this disclosure primarily are directed to needles, it will be understood that the invasive medical device can also be in the form of a wire, which may be in the form of a guidewire, a catheter introducer or a stylet. Thus, as used herein, “wire” refers to a medical wire that is configured and adapted to be used in a medical procedure by insertion into the body of a patient, for example, a patient&#39;s vasculature, or other part of the body such as a patient&#39;s pleural cavity or vertebral space. As used herein, “stylet” refers to a wire run through a catheter or cannula to render it stiff or to remove debris from its lumen. A “catheter introducer” refers to wire used to facilitate insertion of an intravenous catheter. A “guidewire” is a wire that can be used to guide a catheter into place during venous catheter and other bodily catheter insertions. In venous insertions, the purpose of a guidewire is to gain access to the blood vessels using a minimally invasive technique.  FIG. 14  depicts a wire  1050 , which may be in the form of a catheter introducer, stylet or guidewire, which is sized and shaped to be inserted into an intravenous catheter  1068 . The guidewire, stylet or catheter introducer has an elongate shaft  1052  and a distal tip  1054  that can be inserted into the intravenous catheter  1068  or directly into a patient, such as in pleural placement technique to place a pleural catheter. 
     Other embodiments pertain to medical devices, systems and methods including a wire or wire subassembly in combination with a catheter adapter subassembly and/or needle subassembly. The wire or wire subassembly can include a permanent magnet, and the catheter adapter subassembly and/or needle subassembly can include the magnetizable feature. Alternatively, the wire or wire subassembly can include a magnetizable feature to provide a magnetizable wire, and the catheter adapter subassembly and/or needle subassembly can include the permanent magnet. In other embodiments, a guidewire introducer assembly includes a guidewire introducer subassembly and a guidewire, wherein one of the guidewire introducer subassembly includes a permanent magnet and the guidewire includes a magnetizable feature. In an alternative embodiment, the association of the permanent magnet and magnetizable feature with the guidewire and guidewire introducer subassembly can be reversed. 
     Referring now to  FIG. 15 , an embodiment of a medical device comprising a catheter assembly  1010  is shown. The catheter assembly  1010  includes a catheter adapter subassembly  1012  and a wire assembly in the form of guidewire subassembly  1014 . The wire assembly could also be in the form of a stylet or other medical wire. The catheter adapter subassembly  1012  further includes a catheter adapter  1016 , catheter hub (not shown) and catheter tubing  1018 . The guidewire subassembly  1014  further includes a guidewire  1020 , which may be connected to an introducer body (not shown). In the embodiment shown in  FIG. 15 , the catheter adapter subassembly  1012  includes a permanent magnet element  1032  and the guidewire subassembly  1014  includes a magnetizable feature  1030 , in particular on the guidewire  1020  to provide a magnetizable guidewire. According to an alternative embodiment (not shown), this configuration is reversed wherein the permanent magnet element  1032  is on the guidewire subassembly  1014 , in particular on the guidewire  1020 , and the magnetizable feature  1030  is on the catheter adapter subassembly  1012 . 
     The use of a permanent magnet element on the catheter adapter subassembly  1012  and a magnetizable feature on the guidewire subassembly  1014  provides the ability to calculate the catheter tip position and the guidewire tip position based on known geometry relative to the position of permanent magnet element  1032  on the catheter adapter subassembly  1012  from which a calculated catheter tip position and a calculated guidewire tip position can be determined. The permanent magnet element  1032  provides a static magnetic field, while the magnetizable feature  1030  on the guidewire  1020  can be magnetized with an externally applied magnetic field prior to insertion of the guidewire  1020  into the patient. 
     In the embodiment shown in  FIG. 15 , the magnetizable feature  1030  is on the guidewire  1020 , and the catheter adapter subassembly  1012  includes the permanent magnet element  1032 . The magnetizable feature  1030  on the guidewire  1020  can be provided in a variety of ways. In one embodiment, the guidewire  1020  is made from a magnetizable material, for example, a steel material that has a magnetic permeability that permits the guidewire  1020  to be magnetized by application of an external magnetic field. Type 304 stainless steel may not have the magnetic permeability to be magnetized and used in a device according one or more embodiments. Type 304 stainless steel is an austenitic steel comprising at least 18% chromium, 8% nickel, and a maximum of 0.08% carbon. Type 316 stainless steel is also austenitic and non-magnetic. The nickel content of type 316 stainless steel is typically higher than type 304 stainless steel, and type 316 stainless steel also includes the addition of molybdenum. According to one or more embodiments, the guidewire  1020  is made from martensitic or ferritic stainless steels, for example, type 420 or type 430 stainless steel. Similar to the embodiments shown above with respect to  FIGS. 6A-6E , the magnetizable feature of the wire subassembly can be one or more of an adhesive, the wire, a notch in the wire, a ferrule on the wire, and a spot weld on the wire. In embodiments in which the wire subassembly includes the magnetizable feature, and the catheter adapter subassembly includes a catheter adapter body, catheter tubing and the permanent magnet element, the permanent magnet element can be selected from the group consisting of a metal mandrel for connecting catheter tubing to the catheter adapter body, a catheter tubing adhesive, a blood control component of the catheter adapter subassembly, and a magnetic wedge on the catheter adapter body. In embodiments in which the wire subassembly includes the permanent magnet element, and the catheter adapter subassembly includes the magnetizable feature, the magnetizable feature can includes magnetizable catheter tubing. 
     Referring now to  FIGS. 16 and 17 , an embodiment of a medical device  1110  including a needle subassembly  1112  and a guidewire subassembly  1114 . The needle subassembly  1112  further includes needle hub  1117 , a vent plug  1124  and a needle  1126 . The guidewire subassembly  1114  further includes a guidewire  1120 , which may be connected to an introducer body (not shown). In the embodiment shown in  FIG. 15 , the needle subassembly  1112  includes a permanent magnet element  1132  and the guidewire subassembly  1114  includes a magnetizable feature  1130 A and a second magnetizable feature  1130 B, in particular on the guidewire  1120 . According to an alternative embodiment (not shown), this configuration is reversed wherein the permanent magnet element  1132  is on the guidewire subassembly  1114 , in particular on the guidewire  1120 , and the magnetizable feature  1130  is on the needle subassembly  1112 . 
     The use of a permanent magnet element on the needle subassembly  1112  and a magnetizable feature on the guidewire subassembly  1114  provides the ability to calculate the needle tip position and the guidewire tip position based on known geometry relative to the position of permanent magnet element  1132  on needle subassembly  1112  from which a calculated needle tip position and a calculated guidewire tip position can be determined. The permanent magnet element  1132  provides a static magnetic field, while the magnetizable feature  1130  on the guidewire  1120  can be magnetized with an externally applied magnetic field prior to insertion of the guidewire  1120  into the patient. In embodiments in which the wire subassembly includes the magnetizable feature and the needle subassembly includes the permanent magnet element, and the magnetizable feature of the wire subassembly can be an adhesive, the needle, a ferrule on the wire, and a spot weld on the wire. In embodiments in which the needle subassembly includes the magnetizable feature and the wire subassembly includes the permanent magnet element, and the magnetizable feature of the needle subassembly can be a needle adhesive, the needle, a needle safety element, a notch, a needle ferrule, and a spot weld. As shown in  FIG. 17 , the needle subassembly further comprises a needle cannula having a hollow lumen  1127  and the guidewire  1120  is inserted through the lumen  1127 , wherein the guidewire includes one of a permanent magnet element and a magnetizable feature. 
     Referring now to  FIG. 18 , an embodiment of a medical device in the form a guidewire introducer assembly  1210  including a guidewire introducer subassembly  1216  having at least one end  1212  (a proximal end) and a main body  1224 , a distal end  1226 , and a guidewire  1214  including a distal end  1218  extending from one end of the guidewire introducer subassembly  1216 . One of the guidewire introducer subassembly  1216  and the guidewire  1214  includes a permanent magnet element, and the other of the guidewire introducer subassembly and the guidewire includes a magnetizable feature. In the embodiment shown the guidewire  1214  include a permanent magnet element  1230  and the guidewire introducer subassembly includes the magnetizable element. In other embodiments, this configuration could be reversed where the magnetizable feature is on the guidewire, and the permanent magnet could be on the guidewire introducer subassembly. 
     The use of a permanent magnet element on the guidewire  1214  and a magnetizable feature on the guidewire introducer subassembly  1216  provides the ability to calculate the guidewire distal end  1218  or tip position based on known geometry relative to the position of magnetizable feature  1232  on guidewire introducer subassembly  1216  from which a calculated guidewire distal end  1218  or tip position can be determined. The permanent magnet element  1230  provides a static magnetic field, while the magnetizable feature  1232  on the guidewire introducer subassembly  1216  can be magnetized with an externally applied magnetic field prior to insertion of the guidewire  1214  into the patient. 
     The devices described with respect to  FIGS. 15-18  can be utilized in methods and systems, similar to the system and method described with respect to  FIG. 13 . Thus, in an embodiment, a system for determining relative position of a catheter adapter subassembly and wire subassembly comprises a catheter having a catheter distal tip and a wire having a wire distal tip; a permanent magnet element associated with one of the catheter adapter subassembly and wire subassembly; a magnetizable feature associated with the other of the catheter adapter subassembly and the wire subassembly; and magnetometers positioned with respect to the catheter adapter subassembly and the wire subassembly, the magnetometers configured to determine relative movement of the catheter adapter subassembly and wire subassembly. In an embodiment, the permanent magnet or the magnetizable feature on a fixed location on the catheter adapter subassembly or wire subassembly provides a measurement datum to determine movement of the magnetizable feature and permanent magnet. In an embodiment, the permanent magnet is on the wire subassembly and the magnetizable feature is on the catheter adapter subassembly. In an embodiment, the permanent magnet is on the catheter adapter subassembly and the magnetizable feature is on the wire subassembly. In an embodiment, the magnetometers include three different magnetometers arranged in a three-dimensional grid array as part of an ultrasound system which can derive a three-dimensional correlation to obtain a distance from the grid array to the magnetizable feature or permanent magnet. In an embodiment, the three-dimensional correlation is determined by a function I=f(B i  μ r ), where i=x or y or z along three axes, x, y and z are distances in three planes, B is a known magnetic field produced by the permanent magnet or magnetizable feature, and μ r  is magnetic permeability. In an embodiment, the correlation provides a distance in three planes to determine location of the catheter distal tip. In an embodiment, the correlation provides a distance in three planes to determine location of the wire distal tip. 
     Another embodiment pertains to a system for determining relative position of a needle subassembly and wire subassembly comprising a needle having a needle distal tip and a wire having a wire distal tip; a permanent magnet element associated with one of the needle subassembly and wire subassembly; a magnetizable feature associated with the other of the needle subassembly and the wire subassembly; and magnetometers positioned with respect to the needle subassembly and the wire subassembly, the magnetometers configured to determine relative movement of the needle subassembly and wire subassembly. In an embodiment, the permanent magnet or the magnetizable feature on a fixed location on the needle subassembly or wire subassembly provides a measurement datum to determine movement of the magnetizable feature and permanent magnet. In an embodiment, the permanent magnet is on the wire subassembly and the magnetizable feature is on the needle subassembly. In an embodiment, the permanent magnet is on the needle subassembly and the magnetizable feature is on the wire subassembly. In an embodiment, the magnetometers include three different magnetometers arranged in a three-dimensional grid array as part of an ultrasound system which can derive a three-dimensional correlation to obtain a distance from the grid array to the magnetizable feature or permanent magnet. In an embodiment, the three-dimensional correlation is determined by a function I=f(B i  μ r ), where i=x or y or z along three axes, x, y and z are distances in three planes, B is a known magnetic field produced by the permanent magnet or magnetizable feature, and μ r  is magnetic permeability. In an embodiment, the correlation provides a distance in three planes to determine location of the needle distal tip. In an embodiment, the correlation provides a distance in three planes to determine location of the wire distal tip. 
     Another aspect pertains to a method for determining a relative position of a catheter tip and a wire tip, the method comprising providing a catheter adapter subassembly including catheter and a wire subassembly including a wire, the catheter having a catheter distal tip and the wire having a wire distal tip; associating a permanent magnet element with one of the catheter and the wire; associating a magnetizable feature with the other of the catheter and the wire; obtaining a measured position of the permanent magnet; obtaining a measured position of the magnetizable feature to obtain a calculated position of the catheter distal tip and a calculated position of the wire distal tip; and comparing the calculated position of the catheter distal tip with the calculated position of the wire distal tip to determine the relative position of the catheter distal tip and the wire distal tip. 
     In an embodiment, the wire includes the magnetizable feature and the catheter includes the permanent magnet and the relative position of the catheter distal tip and the wire distal tip indicates that the catheter is properly seated on the wire. In an embodiment, the catheter adapter subassembly includes the magnetizable feature and the wire subassembly includes the permanent magnet, and relative movement of the catheter adapter subassembly and wire subassembly is determined by a three-dimensional array of magnetometers positioned in proximity to at least one of the permanent magnet the magnetizable feature. In an embodiment, the method further comprises magnetizing the magnetizable feature by applying an external magnetic field to the magnetizable feature. In an embodiment, the three-dimensional array of magnetometers is part of an ultrasound system, and the ultrasound system derives a three-dimensional correlation to obtain a distance from the array of magnetometers to the magnetizable feature or permanent magnet. In an embodiment, the three-dimensional correlation is determined by the function I=f(B i  μ r ), where i=x or y or z along three axes, x, y and z are distances in three planes, B is a known magnetic field produced by the permanent magnet or magnetizable feature, and μ r  is magnetic permeability. In an embodiment, the catheter adapter subassembly includes the permanent magnet and the wire subassembly includes the magnetizable feature, and relative movement of the catheter adapter subassembly and wire subassembly is determined by a three-dimensional array of magnetometers positioned in proximity to at least one of the permanent magnet the magnetizable feature. 
     In an embodiment, the method further comprises magnetizing the magnetizable feature by applying an external magnetic field to the magnetizable feature. In an embodiment, the three-dimensional array of magnetometers is part of an ultrasound system, and the ultrasound system derives a three-dimensional correlation to obtain a distance from the array of magnetometers to the magnetizable feature or permanent magnet. In an embodiment, the three-dimensional correlation is determined by the function I=f(B i  μ r ), where i=x or y or z along three axes, x, y and z are distances in three planes, B is a known magnetic field produced by the permanent magnet or magnetizable feature, and μ r  is magnetic permeability. 
     Another aspect pertains to a method for determining a relative position of a wire tip and a needle cannula tip, the method comprising providing a needle subassembly including needle and a wire subassembly including a wire, the needle having a needle distal tip and the wire having a wire distal tip; associating a permanent magnet element with one of the needle and the wire; associating a magnetizable feature with the other of the needle and the wire; obtaining a measured position of the permanent magnet; obtaining a measured position of the magnetizable feature to obtain a calculated position of the needle distal tip and a calculated position of the wire distal tip; and comparing the calculated position of the needle distal tip with the calculated position of the wire distal tip to determine the relative position of the needle distal tip and the wire distal tip. In an embodiment, the wire includes the magnetizable feature and the needle includes the permanent magnet and the relative position of the needle distal tip and the wire distal tip indicates that the needle is properly seated on the wire. In an embodiment, the needle subassembly includes the magnetizable feature and the wire subassembly includes the permanent magnet, and relative movement of the needle subassembly and wire subassembly is determined by a three-dimensional array of magnetometers positioned in proximity to at least one of the permanent magnet the magnetizable feature. In an embodiment, the method further comprises magnetizing the magnetizable feature by applying an external magnetic field to the magnetizable feature. In an embodiment, the three-dimensional array of magnetometers is part of an ultrasound system, and the ultrasound system derives a three-dimensional correlation to obtain a distance from the array of magnetometers to the magnetizable feature or permanent magnet. In an embodiment, the three-dimensional correlation is determined by the function I=f(B i  μ r ), where i=x or y or z along three axes, x, y and z are distances in three planes, B is a known magnetic field produced by the permanent magnet or magnetizable feature, and μ r  is magnetic permeability. In an embodiment, the catheter adapter subassembly includes the permanent magnet and the wire subassembly includes the magnetizable feature, and relative movement of the needle subassembly and wire subassembly is determined by a three-dimensional array of magnetometers positioned in proximity to at least one of the permanent magnet the magnetizable feature. In an embodiment, the method further comprises magnetizing the magnetizable feature by applying an external magnetic field to the magnetizable feature. In an embodiment, the three-dimensional array of magnetometers is part of an ultrasound system, and the ultrasound system derives a three-dimensional correlation to obtain a distance from the array of magnetometers to the magnetizable feature or permanent magnet. In an embodiment, the three-dimensional correlation is determined by the function I=f(B i  μ r ), where i=x or y or z along three axes, x, y and z are distances in three planes, B is a known magnetic field produced by the permanent magnet or magnetizable feature, and μ r  is magnetic permeability. 
     Although the disclosure herein provided a description with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the disclosure. It will be apparent to those skilled in the art that various modifications and variations can be made to the devices, methods and systems described in the of the present disclosure without departing from the spirit and scope thereof. Thus, it is intended that the present disclosure include modifications and variations that are within the scope of the appended claims and their equivalents.