Patent Publication Number: US-8971994-B2

Title: Systems and methods for positioning a catheter

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 12/369,625, filed Feb. 11, 2009, now U.S. Pat. No. 8,478,382 which claims the benefit of U.S. Provisional Application No. 61/027,710, filed Feb. 11, 2008, each of which is incorporated herein by reference in its entirety. 
    
    
     BRIEF SUMMARY 
     Briefly summarized, embodiments of the present invention are directed to a method for displaying a position of a medical device, such as a catheter, during insertion thereof into a patient. 
     In one example embodiment, the method includes obtaining a first set of detected position data relating to a location marker, then determining a possible first position of the location marker. A first confidence level relating to a match between the first set of detected position data and a first set of predicted position data is assigned. A determination is made whether the first confidence level meets or exceeds a first threshold. If the first confidence level meets or exceeds the first threshold, a determination is then made whether the first position of the location marker is within a first detection zone. If the first position of the location marker is within the first detection zone, the first position of the location marker is displayed. 
     These and other features of embodiments of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of embodiments of the invention as set forth hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more particular description of the present disclosure will be rendered by reference to specific embodiments thereof that are illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. Example embodiments of the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
         FIG. 1  illustrates an embodiment of a catheter being advanced through the vasculature of a patient to a destination; 
         FIG. 2A  illustrates an embodiment of a stylet including a magnetic location marker; 
         FIG. 2B  illustrates an embodiment of a guidewire including a magnetic location marker; 
         FIG. 2C  illustrates an embodiment of a stylet including an electromagnetic field-producing location marker; 
         FIG. 3  illustrates an embodiment of a tip location detector positioned proximate to the chest of a patient; 
         FIG. 4  illustrates the detector of  FIG. 3  with a portion of an embodiment of a first detection zone and a portion of an embodiment of a second detection zone superimposed thereon; 
         FIG. 5  illustrates another embodiment of a detector with a portion of an embodiment of a first detection zone and a portion of an embodiment of a second detection zone superimposed thereon; 
         FIG. 6  illustrates an embodiment of a catheter tip within the first detection zone of the detector of  FIG. 3 ; 
         FIG. 7  illustrates an embodiment of a display depicting the detector of  FIG. 3 ; 
         FIG. 8  illustrates the display of  FIG. 6  showing an embodiment of a marker symbol representing a location of a catheter tip relative to the detector of  FIG. 3 ; 
         FIG. 9  illustrates an embodiment of a system configured to locate a marker and display a graphical representation of the marker; 
         FIG. 10  illustrates in simplified block format a tip location system that serves as one example environment in which embodiments of the present invention can be practiced; 
         FIG. 11  depicts various stages of a method for displaying a location marker associated with a medical device, according to one embodiment; and 
         FIG. 12  depicts various stages of a method for displaying the location marker associated with the medical device, according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION OF SELECTED 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 of the present invention, and are neither limiting nor necessarily drawn to scale. 
       FIGS. 1-12  depict various features of embodiments of the present invention, which is generally directed to methods and systems for detecting a location of a catheter, or of a catheter placement device, within a patient. Certain of such methods and systems relate more particularly to the detection and graphical representation of a location of a catheter or catheter placement device. In some embodiments, the systems and methods can represent the location relatively accurately and/or can reduce the number of erroneous identifications of the location, as further described below. 
     With reference to  FIG. 1 , in certain embodiments, a catheter  10  can be inserted in a vasculature  20  of a patient  25 . The catheter  10  can be advanced in a distal direction from an entry point  28  to a destination  30 , such as a target site or a desired or predetermined location within the patient  25 . The catheter  10  can thus be advanced along a path  35  through the patient. In some embodiments, the catheter  10  can comprise a peripherally inserted central catheter (“PICC”), a central venous catheter (“CVC”), or another suitable catheter or medical device. In some embodiments, the destination  30  for a distal end  50  of the catheter  10  is within the superior vena cava (“SVC”). In other embodiments, the catheter  10  can be advanced to other suitable destinations  30  within the patient  25 . 
     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 catheter placed within the body of a patient is considered a distal end of the catheter, while the catheter end remaining outside the body is a proximal end of the catheter. Further, the words “including,” “has,” and “having,” as used herein, including the claims, shall have the same meaning as the word “comprising.” 
     In certain embodiments, the catheter  10  is operably associated with a location marker  40 . The location marker  40  can be at the distal end  50  of the catheter  10 , and in some embodiments, may be integrally formed therewith. The location marker  40  can comprise an energy emitter or field producer of any suitable variety, and can include one or more permanent magnets (e.g., rare earth magnets), electromagnetic coils, or other magnetized materials or structures. In yet other embodiments, the location marker can comprise ultrasonic emitters, electromagnetic field emitters, visible/infrared photon emitters, ionizing radiation emitters, etc. 
     In one embodiment, the location marker can be tracked using the teachings of one or more of the following U.S. Pat. Nos.: 5,775,322; 5,879,297; 6,129,668; 6,216,028; and 6,263,230. The contents of the afore-mentioned U.S. patents are incorporated herein by reference in their entireties. 
     As mentioned, the location marker  40 , when associated with the catheter  10  as described above, enables the distal end  50  of the catheter to be tracked during its advancement through the vasculature. The direction in which the catheter tip is pointing can also be ascertained, thus further assisting accurate catheter placement. The location marker  40  further assists the clinician in determining when a malposition of the catheter distal end  50  has occurred, such as in the case where the distal end has deviated from a desired venous path into another vein. 
     With reference to  FIG. 2A , in some embodiments, the location marker  40  is included on a stylet  60 . The stylet  60  can be preloaded into a lumen of the catheter  10  prior to advancing the catheter  10  through the vasculature  20  of the patient  25 , and may extend substantially to the distal end  50  of the catheter  10  such that the location marker  40  is substantially co-terminal with the catheter distal end. In some embodiments, only a distal portion of the stylet  60  includes the location marker  40 . For example, a discrete section of a distal portion of the stylet may include permanent magnetic materials. In other embodiments, a larger portion of the stylet can comprise permanent magnetic materials. In some embodiments, the stylet  60  is removed from the lumen of the catheter  10  once the distal end  50  of the catheter has been positioned at the destination  30 . 
     In greater detail, the stylet  60  includes a proximal end  62  and a distal end  70 . A handle  64  is included at the stylet proximal end  62 , with a core wire  66  extending distally therefrom. A magnetic assembly of magnetic elements that form the location marker  40  in the present embodiment is disposed distally of the core wire  66 . The magnetic assembly includes the one or more magnetic materials disposed adjacent one another proximate the stylet distal end  70  and encapsulated by tubing  68 . In the present embodiment, a plurality of permanent magnetic elements is included, each element including a solid, cylindrically shaped ferromagnetic stacked end-to-end with the other magnetic elements. An adhesive tip  69  can fill the distal tip of the tubing  68  adjacent the magnetic elements of the location marker  40 . This configuration is exemplary; other location marker configurations are also contemplated. 
     Note that in other embodiments, the magnetic elements described above may vary from the design in not only shape, but also composition, number, size, magnetic type, and position in the stylet, guidewire, etc. For example, in one embodiment, the plurality of ferromagnetic magnetic elements is replaced with an electromagnetic assembly, such as an electromagnetic coil, which produces an electromagnetic field for detection by the sensor. Another example of an assembly usable here can be found in U.S. Pat. No. 5,099,845 entitled “Medical Instrument Location Means,” which is incorporated herein by reference in its entirety. Yet other examples of stylets including magnetic elements that can be employed with the catheter tip location modality described herein can be found in U.S. Pat. No. 8,784,336, entitled “Stylet Apparatuses And Methods Of Manufacture,” which is incorporated herein by reference in its entirety. These and other variations are therefore contemplated by embodiments of the present invention. It should be appreciated herein that “stylet” as used herein can include any one of a variety of devices configured for removable placement within a lumen of the catheter to assist in placing a distal end of the catheter in a desired location within the patient&#39;s vasculature. 
     With reference to  FIG. 2B , in another embodiment, the location marker  40  including a plurality of magnetic elements or other suitable structure is included on a distal portion of the guidewire  80  proximate a distal end  90  thereof. In this embodiment, the distal tip  90  of the guidewire  80  is advanced to the destination  30  within the patient  25 . The catheter  10  can then be advanced over the guidewire  80  until the distal end  50  of the catheter  10  is at the destination  30 . The guidewire  80  can then be removed from the patient  25 . 
       FIG. 2C  gives various details regarding a distal portion of a stylet  92  including the location marker  40  configured in accordance with one possible embodiment. A coil assembly  96  is included proximate a stylet distal end  94  and is operably connected to leads  96 A. The leads  96 A are in turn operably connected to corresponding circuitry in a tip location system ( FIG. 10 ) configured to produce an electric pulse signal so as to enable the coil assembly  96  to be electrically pulsed during operation and produce an electromagnetic field having a predetermined frequency or pattern that is detectable by one or more sensors included in a detector placed proximate to the patient  25  ( FIG. 3 ) during transit of the catheter through the vasculature when the coil assembly is within the detectable range of the sensor. Note that the coil assembly described herein is but one example of a field-producing element, or a component capable of producing an electromagnetic field for detection by the sensor. Indeed, other devices and assembly designs can be utilized here to produce the same or similar functionality. 
     The coil assembly  96  and leads  96 A are disposed within tubing  98  that extends the length of the stylet  92 . The coil assembly and leads can be protected in other ways as well. A core wire  99  can be included within the tubing  98  in one embodiment to offer stiffness and/or directional torqueability to the stylet  92 . The core wire  99  in one embodiment includes nitinol and can extend to the distal end  94  of the stylet  92  or terminate proximal thereto. 
     With reference to  FIG. 3 , in certain embodiments, a tip location detector  100  is positioned adjacent or proximate to the patient  25  as the catheter  10  is advanced to the destination  30  within the patient vasculature. For example, in the illustrated embodiment, the detector  100  can be positioned on the chest of the patient  25 . 
     The detector  100  includes in the present embodiment one or more sensors  110 . Two sensors  110  are shown schematically in the illustrated embodiment. In some embodiments, the location detector  100  can include one or more, two or more, etc. sensors  110 . For instance, in one embodiment, the detector  100  includes ten sensors  110  placed in a spaced-apart configuration within the detector body. The sensors  110  are configured to detect the location marker  40 . For example, each sensor  110  can be configured to detect the strength of a magnetic field produced by the location marker  40  at the position of the sensor  110  and by so doing enable the system to calculate an approximate location and orientation of the location marker. 
     In some embodiments, the detector  100  defines one or more branches  120 . In some embodiments, two branches  120   a ,  120   b  of the detector  100  extend upward and outward from a lower branch  120   c  such that the detector  100  is substantially “Y”-shaped. Terms such as “upper” and “lower” are used herein by way of convenience, and not limitation, to describe the embodiments depicted in the figures. Accordingly, the upper branches  120   a ,  120   b  are closer to the head of the patient  25  than is the lower branch  120   c.    
       FIG. 3  illustrates an axis convention that will be used throughout the remainder of this disclosure by way of convenience and not limitation. In the illustrated embodiment, three dimensional Cartesian coordinate system is centered on the lower branch  120   c  of the detector  100 . The positive portion of the X-axis runs toward the right of the page (i.e., toward the left side of the patient  25 ), the positive portion of the Y-axis runs toward the top of the page (i.e., toward the head of the patient  25 ), and the positive portion of the Z-axis extends directly out of the page (i.e., away from the chest of the patient  25 ). Accordingly, the portion of the Z-axis extends through the patient  25  such that a more negative Z-value is deeper within the patient relative to the detector  100 . 
     In some embodiments, a portion of the detector  100  can be expected to be more sensitive to the initial detection of the location marker  40  than other portions of the detector  100 . For example, in some embodiments, the location marker  40  may be expected to pass beneath (i.e., below, relative to the Z-axis) the branch  120   a  of the detector  100  before passing beneath other portions of the detector  100  as the catheter  10  is advanced toward the superior vena cava of the patient  25 . In some embodiments, data processing algorithms based on such an expectation can be used to reduce or eliminate misidentification of a position of the location marker  40  or “false positive” identifications that represent something other than the marker  40 . 
     With reference to  FIG. 4 , in some embodiments, the detector  100  is in communication with a processor  130 . The processor  130  can comprise any suitable storage and/or computing device, such as, for example, a computer configured to run one or more programs, or a microprocessor. The processor  130  can be configured to receive data obtained by the detector  100  (e.g., via the sensors  110 ) and to process the data to determine a position of the location marker  40 , as further described below. In some embodiments, the processor  130  utilizes detection zones in processing the data received from the detector  100  and/or in delivering a representation of the position of the location marker  40  for display. One possible environment in which the processor  130  is included is seen in  FIG. 10 , as described further below. 
     In some embodiments, the processor  130  utilizes a first detection zone  140  and a second detection zone  150 . In some embodiments, the first detection zone  140  encompasses a relatively large portion of the upper branches  120   a ,  120   b  of the detector  100 . For example, in some embodiments, the first detection zone  140  extends from a base portion of each branch  120   a ,  120   b  to a position above the detector  100  in the positive Y direction, beyond the detector  100  in both the positive and negative X directions, and below the detector  100  in the negative Z direction. As such, the first detection zone  140  and second detection zone  150  define imaginary rectangular volumes of space proximate the detector  100  that extend into the body of the patient  25 . In one embodiment, for example, the size of the first detection zone  140  is about 28 centimeters (cm) in the X direction, about 10.5 cm in the Y direction, and about 8 cm in the Z direction. The size of the second detection zone  150  is about 23 cm in the X direction, about 15 cm in the Y direction, and about 11 cm in the Z direction. Other detection zone dimensions are also possible. 
     In other embodiments, the first detection zone  140  does not include the detector  100 . For example, in some embodiments, the first detection zone  140  can be substantially as shown in  FIG. 4 , but begins at a position below the detector  100  (i.e., at a position in the negative Z direction), and extends toward more negative Z-values. 
     One or more of the first and second detection zones  140 ,  150  can include a portion of the path  35  along which the catheter  10  is advanced. In some embodiments, the first detection zone  140  includes a portion of the path  35  that is proximal of a portion of the path  35  that runs through the second detection zone  150 . In other embodiments, only the first detection zone  140  may include a portion of the path  35 . 
     In some embodiments, the first and second detection zones  140 ,  150  can overlap each other. For example, in the illustrated embodiment, the second detection zone  150  includes a portion of the upper branches  120   a ,  120   b  that is also included in the first detection zone  140 . The first and second detection zones  140 ,  150  can define the same or different areas in any of the XY-, YZ-, or ZX-planes and can define the same or different volumes. 
     More or fewer detection zones are possible. Additionally, detection zones can define a variety of shapes, such as, for example, boxes, spheres, ellipsoids, and paraboloids. Detection zones may be suitably described in a variety of coordinate systems, such as, for example, Cartesian or polar coordinates. 
       FIG. 5  illustrates another embodiment of a detector  100  having an upper detection zone  160  and a lower detection zone  170  superimposed thereon.  FIG. 5  provides approximate dimensions and approximate relative positions of the upper and lower detection zones  160 ,  170 . In the illustrated embodiment, the detection zones  160 ,  170  begin at a position of about −1 centimeter from the origin of the Z-axis and terminate at a position of about −6 cm from the origin of the Z-axis. 
     Other dimensions than those illustrated in the instant embodiment are also possible. For example, one or more of the upper and lower detection zones  160 ,  170  can extend from about −1 centimeter to about −25 centimeters, from about −1 centimeter to about −15 centimeters, from about −1 centimeter to about −12 centimeters, or from about −1 centimeter to about −9 centimeters from the Z-origin. In some embodiments, the upper limit of the depth of one or more of the upper and lower detection zones  160 ,  170  can be within a range of between about 0 centimeters and −5 centimeters, and the lower limit of the depth of one or more of the first and second detection zones  160 ,  170  can be within a range of between about −5 centimeters and about −30 centimeters. Other ranges for the upper and lower detection zones  160 ,  170  are possible. The first and second detection zones  140 ,  150  can be defined in one embodiment by the same or different dimensions as the upper and lower detection zones  160 ,  170 . 
       FIG. 6  depicts a catheter  10  having the location marker  40  positioned beneath the detector  100  of  FIG. 4 . A magnetic field produced by the location marker  40  is schematically illustrated by concentric circles. In the illustrated embodiment, the location marker  40  is within the first detection zone  140 . 
     With reference to  FIG. 7 , in certain embodiments, the processor  130  can be in communication with a display device  200 , such as, for example a graphical user interface on a screen (see also  FIG. 10 ). In some embodiments, the display  200  includes a detector representation  210 , which can depict a projection of the detector  100  in the XY-plane. A depth indicator  220  can depict a Z-coordinate of the location marker  40 . 
     As shown in  FIG. 8 , in some embodiments, the display  200  can include a marker symbol  230  that represents a position of the location marker  40  relative to the detector  100  (compare  FIG. 6 ), such as within a portion of the vasculature of the patient when the detector is positioned on the patient&#39;s chest. The marker symbol  230  can also indicate a direction in which the location marker  40  is moving or the direction that the location marker  40  is facing. For instance, in the view shown in  FIG. 8 , the location marker  40  indicates that the catheter  10  is generally advancing from the left side of the page toward the right side thereof. As further discussed below, in some embodiments, whether or not the marker symbol  230  is displayed and/or the position on the display  200  at which the marker symbol  230  is displayed is based on information received from the processor  130 . 
     In some embodiments, the display  200  can include button icons  240  that correspond to buttons or controls located on a button control interface included in a console ( FIG. 10 ) in which the display  200  is housed. Further informational or control icons  250  can be included on the display  200 . In further embodiments, the display  200  comprises a touch screen such that a user can deliver instructions to the processor  130  and/or the tip location detector  100  via the buttons or controls appearing on the screen. Other systems and methods for providing instructions to the processor  130  and/or the tip location detector  100  are also possible. 
     With reference to  FIG. 9 , in certain embodiments, a tip location system  300  can include the detector  100 , the processor  130 , and/or the display  200 . The system  300  can be configured to detect the location marker  40  and to display the marker symbol  230 , as described above. In some embodiments, the detector  100  is positioned relative to the patient  25 . The system  300  is then zeroed to calibrate to (or account for) local magnetic fields. In some embodiments, after the system  300  has been zeroed, the system  300  actively measures magnetic fields. For example, in an implementation where the location marker  40  includes a plurality of magnetic elements positioned at the distal end  70  of a stylet  60  pre-loaded in the catheter  10  (see the stylet  60  shown in  FIG. 2A ), the detector  100  can monitor or measure magnetic fields via the sensors  110  during transit of the catheter through the vasculature of the patient. The measurements can be obtained continuously, for example, or iteratively at regular or irregular intervals as determined by the processor  130  or other suitable control component of the system  300 . 
     In some embodiments, a model  310  of the location marker  40  is stored in the system  300 . For example, in some embodiments, the model  310  is stored in a memory portion of the processor  130  for access when needed. The model  310  can comprise magnetic strength patterns that are each representative of a magnetic field produced by the location marker  40  at one of a multitude of possible marker locations. In some embodiments, the processor  300  compares data received from the detector  100 , which data relate to the position of the location marker  40  with respect to one or more of the detector sensors  110 , with the model  310  to ultimately determine whether the location marker  40  is within one or more of the detection zones  140 ,  150 . 
     In some embodiments, the processor  130  can execute a program or set of executable instructions that implements one or more algorithms for determining how well a data set of a possible location marker position gathered by the detector  100  corresponds with the model  310 . The program can provide a confidence level regarding the data set. In some embodiments, the confidence level indicates how well such a data set and the model  310  match. In further embodiments, the confidence level indicates the degree of certainty that the location marker  40  is at a specific position. In still further embodiments, the confidence level represents how well a gathered data set and the model  310  match as well as the degree of certainty that the location marker  40  is at a specific position. The confidence level can be expressed as an absolute or a scalar value, in some embodiments. An example of a program that is suitable for use with certain embodiments described herein is software marketed under the trademark ZAP™, which is distributed by Lucent Medical Systems. 
     In certain embodiments, the processor  130  provides instructions to depict the marker symbol  230  ( FIG. 8 ) corresponding to the detected position of the location marker  40  on the display  200  when certain conditions are met. For example, in some embodiments, after the system  300  has been zeroed or calibrated, in order for the display to initially depict the marker symbol  230 , the center of the location marker  40  must be identified as being within the first detection zone  140  with a confidence level above a first threshold value (or with a confidence level within a first range). For example, in certain embodiments that use ZAP™ software, the center of the location marker  40  must be identified as being within the first detection zone  140  (which can, for example, be at a depth of between about 1 centimeter and about 8 centimeters below the detector  100 ), with a COST of less than or equal to  500 . COST is a term associated with ZAP™ software that represents in one embodiment an absolute value of a comparative match between measured magnetic field data as detected by the detector  100  and predicted magnetic field data as computed by the processor  130 . The COST value is on a reverse scale such that a lower value represents a relatively higher threshold value or level of confidence. 
     In some embodiments, multiple identification and validation sequences, or solution sequences, regarding a position of a possible location marker  40  are performed before the marker symbol  230  is initially displayed. For example, in some embodiments, the conditions relating to resolution of the possible location marker position with respect to the first and/or second detection zones  140 ,  150  and determination of a confidence level described in the preceding paragraph must be satisfied in eight consecutive sequences before the marker symbol  230  will initially be displayed. In other embodiments, the conditions must be met in five consecutive sequences before an initial display of the marker symbol  230 . In certain of such embodiments, subsequent cycles may aid in pinpointing or converging on a more accurate location of the marker symbol  230 , such that the marker symbol  230  may drift slightly after it is initially displayed. Other series of solution sequences are also possible. 
     After the initial display of the marker symbol  230 , separate conditions may be implemented in order to continue displaying the maker symbol  230  after it has met the conditions to be displayed initially. For example in some embodiments, the marker symbol  230  will continue to be displayed if the center of the location marker  40  is within either the first detection zone  140  or the second detection zone  150  and if the confidence level is above a second threshold value (or within a second confidence range). In some embodiments, the second threshold value is lower then the first threshold value (i.e., the second threshold value can represent a lesser degree of confidence than does the first threshold value). For example, in certain embodiments that use ZAP™ software, the center of the location marker  40  must be identified as being within the first or second detection zones  140 ,  150  with a COST of less than or equal to 1000 in order for the marker symbol  230  to continue to be displayed. 
     In further embodiments, the first and second detection zones  140 ,  150  can be expanded in size after the initial identification of the location marker  40  and initial display of the marker symbol  230 . For example, in some embodiments, the first and second detection zones  140 ,  150  extend between a depth of about 1 centimeter and about 8 centimeters below the detector  100  before the initial display of the marker symbol  230 , and can extend between a depth of about 1 centimeter and about 12 centimeters below the detector after the initial display of the marker symbol  230 . Of course, modification of the detection zone sizes in amounts different from those outlined above is also possible. 
     An initial display of the marker symbol  230  can occur after events other than or in addition to zeroing the system  300 . For example, in some embodiments, the system  300  may be turned off after having displayed the marker symbol  230 . Upon being turned on again, a subsequent showing of the marker symbol  230  can be referred to as an initial display of the marker symbol  230 . In other embodiments, the system  300  can be reset without powering down such that a first display of the marker symbol  230  after the resetting event would be an initial display of the marker symbol  230 . 
     In some embodiments, the system  300  can employ separate criteria for displaying the marker symbol  230  after the system  300  has tracked the position of the location marker  40 , e.g., after initially displaying and continuing to display the marker symbol  230 . For example, in some embodiments, if the location marker  40  is moved out of the sensing range of the detector  100 , e.g., outside of the first and second detection zones  140 ,  150  and subsequently moved back into the sensing range, the tracking can start again if the detector  100  senses that the location marker  40  is within the first detection zone  140  or the second detection zone  150  and is above the first threshold value, e.g., COST is less than or equal to 500. Similarly, in some embodiments, if the system  300  loses the tracking of the location marker  40 , e.g., fails to identify the position of the location marker  40  during a solution sequence, the tracking can commence again if the detector  100  senses that the location marker  40  is within the first detection zone  140  or the second detection zone  150  and is above the first threshold value. 
     In some embodiments, the system  300  may be preset such that the threshold values are fixed. In other embodiments, the system  300  can be altered by a user to vary one or more threshold values, as desired. 
       FIG. 10  depicts in simplified form an example implementation of a tip location system, i.e., the system  300  partially depicted in  FIG. 9 , in which embodiments of the present invention can be practiced. As shown, the system  300  generally includes a console  420 , display  200 , probe  440 , and detector  100 , each of which is described in further detail below. As mentioned above, the system  300  is employed to ultimately position a distal end  50  of the catheter  10  in a desired position within the patient vasculature. In one embodiment, the desired position for the catheter distal end  50  is proximate the patient&#39;s heart, such as in the lower one-third (⅓ rd ) portion of the SVC ( FIG. 1 ). Of course, the system  300  can be employed to place the catheter distal end in other locations. 
     A processor  422 , including non-volatile memory such as EEPROM for instance, is included in the console  420  for controlling system function during operation of the system  300 , thus acting as a control processor. A digital controller/analog interface  424  is also included with the console  420  and is in communication with both the processor  422  and other system components to govern interfacing between the probe  440 , detector  100 , and other system components. 
     The system  300  further includes ports  452  for connection with the detector  100  and optional components  454  including a printer, storage media, keyboard, etc. The ports in one embodiment are USB ports, though other port types or a combination of port types can be used for this and the other interfaces connections described herein. A power connection  456  is included with the console  420  to enable operable connection to an external power supply  458 . An internal battery  460  can also be employed, either with or exclusive of an external power supply. Power management circuitry  459  is included with the digital controller/analog interface  424  of the console to regulate power use and distribution. 
     The display  200  in the present embodiment is an LCD-based device, is integrated into the console  420 , and is used to display information to the clinician during the catheter placement procedure. In another embodiment, the display may be separate from the console. In one embodiment, the console button interface  432  ( FIGS. 1 ,  8 C) and buttons included on the probe  440  can be used to control the display  200  and thus assist the clinician during the placement procedure. 
     In one embodiment the system  300  optionally includes the probe  440 , which is employed in connection with ultrasound (“US”)-based visualization of a vessel, such as a vein, in preparation for insertion of the catheter  10  into the vasculature. Such visualization gives real time ultrasound guidance for initially introducing the catheter into the vasculature of the patient and assists in reducing complications typically associated with such introduction, including inadvertent arterial puncture, hematoma, pneumothorax, etc. After the catheter has been initially placed in the patient vasculature, the system  300  can be used to locate the distal end  50  of the catheter  10  via detection of a corresponding location marker, as has been described above. In one embodiment, another modality can be added to the system  300 , wherein an ECG-based confirmation of correct catheter distal tip placement with respect to a node of the patient&#39;s heart is employed. Further details regarding the US, tip location, and ECG-based modalities of the system  300  can be found in U.S. Pat. No. 8,388,541, entitled “INTEGRATED SYSTEM FOR INTRAVASCULAR PLACEMENT OF A CATHETER,” which is incorporated herein by reference in its entirety. 
       FIG. 10  shows that the probe  440  further includes button and memory controller  442  for governing button and probe operation. The button and memory controller  442  can include non-volatile memory, such as EEPROM, in one embodiment. The button and memory controller  442  is in operable communication with a probe interface  444  of the console  420 , which includes a piezo input/output component  444 A for interfacing with a piezoelectric array included in the probe, and a button and memory input/output component  444 B for interfacing with the button and memory controller  442 . 
     Embodiments of the present invention may comprise a special purpose or general-purpose computer including computer hardware. Embodiments within the scope of the present invention also include computer-readable media for carrying or having computer-executable instructions or data structures stored thereon. Such computer-readable media can be any available media that can be accessed by a general purpose or special purpose computer. By way of example, and not limitation, computer-readable media can include physical (or recordable-type) computer-readable storage media, such as, RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, non-volatile and flash memory, or any other medium which can be used to store desired program code means in the form of computer-executable instructions or data structures and which can be accessed by a general purpose or special purpose computer. 
     In this description and in the following claims, a “network” is defined as one or more data links that enable the transport of electronic data between computer systems and/or modules. When information is transferred or provided over a network or another communications connection (either hardwired, wireless, or a combination of hardwired or wireless) to a computer, the computer properly views the connection as a computer-readable medium. Thus, by way of example, and not limitation, computer-readable media can also include a network or data links which can be used to carry or store desired program code means in the form of computer-executable instructions or data structures and which can be accessed by a general purpose or special purpose computer. 
     Computer-executable instructions comprise, for example, instructions and data which cause a general purpose computer, special purpose computer, or special purpose processing device to perform a certain function or group of functions. The computer executable instructions may be, for example, binaries, intermediate format instructions such as assembly language, or even source code. Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the described features or acts described above. Rather, the described features and acts are disclosed as example forms of implementing the claims. 
     Those skilled in the art will appreciate that the embodiments of the present invention may be practiced in computing environments with one or more types of computer system configurations, including, personal computers, desktop computers, laptop computers, message processors, hand-held devices, multi-processor systems, microprocessor-based or programmable consumer electronics, network PCs, minicomputers, mainframe computers, mobile telephones, PDAs, pagers, and the like. Embodiments may also be practiced in distributed system environments where local and remote computer systems, which are linked (either by hardwired data links, wireless data links, or by a combination of hardwired and wireless data links) through a network, both perform tasks. In a distributed system environment, program modules may be located in both local and remote memory storage devices. 
     Thus, in one embodiment, and as depicted in  FIG. 11 , a method  500  for displaying a position of a medical device includes calibrating the system  300  at stage  510 . At stage  520 , a first set of detected position data relating to a possible first position of a location marker is obtained. As has been described, the position data can relate to an X-Y-Z-coordinate on a Cartesian coordinate axis grid centered on or proximate to the detector  100 , as shown in  FIG. 4 . In the present embodiment, the position data includes data from the magnetic field produced by the magnetic assembly of the location marker of the stylet as sensed by each of the sensors  110  of the detector  100 . These data are forwarded to the processor  130  of the system  300 . 
     At stage  525 , the possible first position of the location marker is determined. In one embodiment, the possible first position relates to the initial detection of the location marker by the system and is estimated by a neural net functionality provided by the processor  130  or other suitable component of the system. In brief, the neural net functionality continually monitors detected position data and provides a best guess of the position of the location marker. In the present embodiment, the neural net functionality is pre-programmed, or “trained,” with sample location marker position data, i.e., magnetic field data, for a variety of possible location marker positions and orientations with respect to the detector  100 . This training enables the neural net to make a best fit determination between its pre-programmed sample position data and the detected position data obtained in stage  520  to determine a possible first position of the location marker. Determination of the possible first position of the location marker in this stage is made in the present embodiment by the processor  130  or other suitable component via execution of the ZAP™ Software. 
     At stage  530 , a first confidence level relating to a match between the first set of detected position data and a first set of predicted position data relating to the possible first position of the location marker is assigned. The predicted position data in the present embodiment is provided by the processor  130  or other suitable component via execution of the ZAP™ Software, which calculates the predicted data based on physics-based characteristics of the location marker (in the present embodiment, a stack of magnetic elements as seen in  FIG. 2A ) assumed to be positioned at the possible first position. The resulting first set of predicted position data includes data for each sensor of the detector on the chest of the patient and is compared to the corresponding first set of detected position data for each sensor. This comparison yields the first confidence level, which is a quantitative, absolute value indicating the degree of matching between the detected data obtained at stage  520  and the predicted data. As has been discussed above, the COST value produced by the ZAP™ Software is one example of a confidence level that can be employed in the present method  500 . Again, further details regarding the ZAP™ Software and the COST value are given in one or more of U.S. Pat. No. 5,775,322, 5,879,297, 6,129,668, 6,216,028, and 6,263,230, each of which is incorporated herein by reference in its entirety. Of course, other algorithms utilizing other confidence level configurations can also be used. 
     In one embodiment, stages  525  and  530  above are iteratively executed in order to better pinpoint the possible first position of the location marker. With each iteration, the possible first position is modified, which in turn modifies the set of predicted position data, in the interest of better matching the predicted data with the detected position data obtained at stage  520 . This in turn increases the first confidence level, i.e., reduces the COST value in the present embodiment where the ZAP™ Software is employed. Such an iterative method is also referred to as a convergence algorithm. Once a minimum COST value is obtained via the convergence algorithm, the method can proceed. In other embodiments, a predefined number of iterations can be performed; in still other embodiments no additional iterations are performed. 
     At stage  540 , it is determined whether the first confidence level meets or exceeds a first threshold, such as a predetermined COST value in the present embodiment, as described further above. As described above, the present stage, as well as stages  525  and  530 , is executed in the present embodiment by the ZAP™ Software, or other suitable algorithm. If the first confidence level fails to meet or exceed the first threshold, such as a COST value of  500  in one embodiment, the possible location marker is not displayed and the method cycles back to stage  520  to continue monitoring for the presence of a possible location marker. 
     If the first confidence level meets or exceeds the first threshold, however, stage  550  is executed, wherein it is determined whether the first position of the possible location marker is within a first detection zone, such as the first detection zone  140  shown in  FIG. 4 . This stage is executed in one embodiment by the processor  130  of the system  300 , as shown in  FIG. 10 . If the first position is not within the first detection zone, the possible location marker is not displayed and the method cycles back to stage  520  to continue monitoring for the presence of a possible location marker. If the first position is within the first detection zone, however, stage  560  is executed, wherein the first position of the location marker is displayed, such as on the display  200  shown in  FIGS. 8 and 10 , for instance. 
     In one embodiment, stages  520  through  550  are repeated in sequence a predetermined number of times before stage  560  is executed and the location marker is displayed. In one embodiment, stages  520  through  550  are successfully executed eight times, after which the location marker is displayed. Of course, the number of iterations can vary. 
     Reference is now made to  FIG. 12 . In one embodiment, the method for displaying the position of a medical device can continue after display of the first position of the location marker at stage  560  such that further advancement of the location marker  40  associated with the medical device, such as the catheter  10  progressing through a vasculature, can be progressively displayed. At stage  570 , a second set of detected position data relating to a possible second position of the location marker is obtained. 
     At stage  575 , the possible second position of the location marker is determined. In the present embodiment, the possible second position relates to the first position of the location marker, and as such no best fit guessing by a neural net component of the ZAP™ Software or other suitable algorithm need be performed. 
     At stage  580 , a second confidence level relating to a match between the second set of detected position data and a second set of predicted position data, is assigned. As was the case with stages  525  and  530  of  FIG. 11 , stages  575  and  580  can be iteratively performed in the present embodiment in order to find a minimum COST value. In other embodiments, a predetermined number of iterations, or no iterations, can be performed. 
     At stage  590 , it is determined whether the second confidence level meets or exceeds a second threshold, such as a predetermined COST value in the present embodiment, as described further above. As has been described, the second threshold in one embodiment is relatively lower, i.e., the COST value is higher, than the first threshold. In the present embodiment, the COST value is 1000, for instance. If the second confidence level fails to meet or exceed the second threshold, the possible location marker is not displayed and the method can cycle back to stage  570  to continue monitoring for further location marker position data. 
     If the second confidence level meets or exceeds the second threshold, however, stage  600  is executed, wherein it is determined whether the second position of the location marker is within at least one of the first and second detection zones, such as the first detection zone  140  and second detection zone  150  shown in  FIG. 4 . If not, the possible location marker is not displayed and the method can cycle back to stage  570  to continue monitoring for further location marker position data. If the second position is within the first detection zone and/or the second detection zone, however, stage  610  is executed, wherein the second position of the location marker is displayed. 
     In one embodiment, stages  570  through  600  are repeated in sequence a predetermined number of times before stage  610  is executed and the location marker is displayed. In another embodiment, no repetitions of the sequence are performed before display at stage  610  is executed. 
     In one embodiment, stage  580  includes ensuring that the second position of the location marker is within a predetermined distance range from the first position of the location marker within a predetermined amount of time so as to prevent maverick detection of non-location marker targets from being validated as location markers. It is noted that one or more of stages  570 - 610  of the method  500  can be successively repeated to find and display additional positions of the location marker during advancement of the catheter  10  through the patient&#39;s vasculature. 
     Embodiments of the invention may be embodied in other specific forms without departing from the spirit of the present disclosure. The described embodiments are to be considered in all respects only as illustrative, not restrictive. The scope of the embodiments is, therefore, indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.