Patent Publication Number: US-2020289209-A1

Title: Navigation guidance method for complex catheters

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a Divisional of U.S. patent application Ser. No. 15/259,683 filed Sep. 8, 2016 VARIABLE GEOMETRY COOLING CHAMBER, the entirety of which is incorporated herein by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     n/a 
     TECHNICAL FIELD 
     The present invention relates to a method and system for determining a target location for a medical device having complex geometry relative to an anatomical feature, and for navigating and positioning the medical device at the target location. 
     BACKGROUND 
     In many non-invasive or minimally invasive surgical and treatment procedures, navigating a medical device within a patient&#39;s body can be very challenging. Navigation systems are frequently used to help the user identify the location of the medical device and to steer the medical device to the target treatment location. For example, navigation is an important tool in many electrophysiological (EP) procedures because it helps the user understand the placement of the medical device within the cardiac space. Additionally, navigation is often used to place medical devices at areas targeted for thermal treatment and/or ablation. 
     When the medical device is a focal catheter, for instance, the ablating surface may be directly imaged on the navigation system and there is a close coupling between the navigation and the delivered therapy. However, other medical devices, such as balloon catheters, may have more complex geometry, and navigation electrodes on the device may not exactly correlate with the ablating surface (e.g., the surface of the balloon). Additionally, placement of these complex-geometry devices may be difficult to infer from fluoroscopic imaging or navigation systems relative to the targeted tissue regions. 
     SUMMARY 
     The present invention advantageously provides a method and system for determining a target location for a medical device having complex geometry relative to an anatomical feature, and for navigating and positioning the medical device at the target location. A system for determining a target location for a medical device relative to an anatomical feature may include a medical device including and treatment element, such as an expandable treatment element, having a centroid, one or more navigation electrodes, and a longitudinal axis and a navigation system in communication with the one or more navigation electrodes, the navigation system including a processing unit having processing circuitry. The processing circuitry may be configured to define a plane that approximates a surface of the anatomical feature, define a centroid of the anatomical feature, define a vector that is normal to the plane and extends away from the centroid of the anatomical feature, and determine a target location for the treatment element of the medical device based on the vector. The medical device may include a first navigation electrode and a second navigation electrode. Further, the first navigation electrode may be distal to the treatment element and the second navigation electrode may be proximal to the treatment element. The processing circuitry may be further configured to determine a target location for each of the first and second navigation electrodes. The navigation system may further include a display, and the processing circuitry may be further configured to display a first graphical indicator for the target location for the first navigation electrode and display a second graphical indicator for the target location for the second navigation electrode. The first and second graphical indicators may be superimposed on a three-dimensional image of the anatomical feature. The anatomical feature may be a pulmonary vein, and the display may show the first graphical indicator superimposed on the three-dimensional image at a location within the pulmonary vein and may show the second graphical indicator superimposed on the three-dimensional image at a location within a left atrium. The processing circuitry may be further configured to determine the target location for the first navigation electrode according to the equation: 
     
       
         
           
             
               e 
               d 
             
             = 
             
               
                 [ 
                 
                   
                     
                       
                         x 
                         d 
                       
                     
                   
                   
                     
                       
                         y 
                         d 
                       
                     
                   
                   
                     
                       
                         z 
                         d 
                       
                     
                   
                 
                 ] 
               
               = 
               
                 
                   [ 
                   
                     
                       
                         
                           x 
                           b 
                         
                       
                     
                     
                       
                         
                           y 
                           b 
                         
                       
                     
                     
                       
                         
                           z 
                           b 
                         
                       
                     
                   
                   ] 
                 
                 - 
                 
                   
                     l 
                     d 
                   
                    
                   
                     [ 
                     
                       
                         
                           a 
                         
                       
                       
                         
                           b 
                         
                       
                       
                         
                           c 
                         
                       
                     
                     ] 
                   
                 
               
             
           
         
       
     
     where l d  is a distance between the centroid of the treatment element and the first navigation electrode. The processing circuitry may be further configured to determine the target location for the second navigation electrode according to the equation: 
     
       
         
           
             
               e 
               p 
             
             = 
             
               
                 [ 
                 
                   
                     
                       
                         x 
                         p 
                       
                     
                   
                   
                     
                       
                         y 
                         p 
                       
                     
                   
                   
                     
                       
                         z 
                         p 
                       
                     
                   
                 
                 ] 
               
               = 
               
                 
                   [ 
                   
                     
                       
                         
                           x 
                           b 
                         
                       
                     
                     
                       
                         
                           y 
                           b 
                         
                       
                     
                     
                       
                         
                           z 
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                   ] 
                 
                 + 
                 
                   
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                     p 
                   
                    
                   
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                           a 
                         
                       
                       
                         
                           b 
                         
                       
                       
                         
                           c 
                         
                       
                     
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     where l p  is a distance between the centroid of the treatment element and the second navigation electrode. The processing circuitry may be further configured to display a line corresponding to the vector. The processing circuitry may further be configured to determine the target location such that the longitudinal axis of the device lies along the vector. 
     A system for determining a target location for a medical device relative to a target anatomical feature, such as a pulmonary vein, may include: a medical device including and treatment element having complex geometry and a centroid, a first navigation electrode distal to the treatment element, a second navigation electrode proximal to the treatment element, and a longitudinal axis; a navigation system in communication with the one or more navigation electrodes, the navigation system including a display and a processing circuitry configured to: define a plane that approximates a surface of the target anatomical feature; define a centroid of the target anatomical feature and a boundary of the target anatomical feature; define a vector that is normal to the plane and extends away from the centroid of the target anatomical feature; determine a first target location for the treatment element; determine a second target location for the first navigation electrode and a third target location for the second navigation electrode; and show on the display a first graphical indicator for the target location for the first navigation electrode, a second graphical indicator for the target location for the second navigation electrode, and a line corresponding to the vector, the processing circuitry being configured to determine the first target location in three dimensions according to a first equation: 
     
       
         
           
             
               [ 
               
                 
                   
                     
                       x 
                       b 
                     
                   
                 
                 
                   
                     
                       y 
                       b 
                     
                   
                 
                 
                   
                     
                       z 
                       b 
                     
                   
                 
               
               ] 
             
             = 
             
               
                 [ 
                 
                   
                     
                       
                         x 
                         0 
                       
                     
                   
                   
                     
                       
                         y 
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                         z 
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                  
                 
                   [ 
                   
                     
                       
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                         b 
                       
                     
                     
                       
                         c 
                       
                     
                   
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     where d is a distance between the centroid of the treatment element and the centroid of the target anatomical feature calculated according to a second equation: 
     
       
         
           
             d 
             = 
             
               
                 r 
                 b 
               
                
               
                 cos 
                  
                 
                   ( 
                   
                     
                       sin 
                       
                         - 
                         1 
                       
                     
                      
                     
                       ( 
                       
                         
                           r 
                           
                             os 
                             , 
                             max 
                           
                         
                         
                           r 
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                       ) 
                     
                   
                   ) 
                 
               
             
           
         
       
     
     where r 0s,max  is a distance between the centroid and the boundary of the anatomical feature and r b  is a distance between the centroid of the treatment element and the boundary of the target anatomical feature, the processing circuitry being configured to determine the second target location in three dimensions according to a third equation: 
     
       
         
           
             
               e 
               d 
             
             = 
             
               
                 [ 
                 
                   
                     
                       
                         x 
                         d 
                       
                     
                   
                   
                     
                       
                         y 
                         d 
                       
                     
                   
                   
                     
                       
                         z 
                         d 
                       
                     
                   
                 
                 ] 
               
               = 
               
                 
                   [ 
                   
                     
                       
                         
                           x 
                           b 
                         
                       
                     
                     
                       
                         
                           y 
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                           z 
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                 - 
                 
                   
                     l 
                     d 
                   
                    
                   
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                           a 
                         
                       
                       
                         
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                           c 
                         
                       
                     
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     and determining the third target location in three dimensions according to a fourth equation: 
     
       
         
           
             
               e 
               p 
             
             = 
             
               
                 [ 
                 
                   
                     
                       
                         x 
                         p 
                       
                     
                   
                   
                     
                       
                         y 
                         p 
                       
                     
                   
                   
                     
                       
                         z 
                         p 
                       
                     
                   
                 
                 ] 
               
               = 
               
                 
                   [ 
                   
                     
                       
                         
                           x 
                           b 
                         
                       
                     
                     
                       
                         
                           y 
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                   ] 
                 
                 + 
                 
                   
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                     p 
                   
                    
                   
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                           a 
                         
                       
                       
                         
                           b 
                         
                       
                       
                         
                           c 
                         
                       
                     
                     ] 
                   
                 
               
             
           
         
       
     
     where l d  is a distance between the centroid of the treatment element and the first navigation electrode and l p  is a distance between the centroid of the treatment element and the second navigation electrode. 
     A method for navigating a medical device to a target location relative to an anatomical feature may include: obtaining an image of the anatomical feature; defining a plane that approximates a surface of the anatomical feature; defining a centroid of the target anatomical feature and a boundary of the target anatomical feature that each lies in the plane; defining a vector that is normal to the plane and extends away from the centroid of the anatomical feature; determining a target location for a treatment element of the medical device such that a longitudinal axis of the medical device lies along the vector; and displaying the target location on a display of a navigation system. The method may further include displaying the medical device on the display of the navigation system and displaying a line on the display of the navigation system, the display corresponding to the vector. The medical device may have at least one navigation electrode and the treatment element has a centroid, and the method may further comprise providing a navigation system having processing circuitry, the navigation system being in communication with the medical device and determining a recommended distance between the centroid of the treatment element and the centroid of the target anatomical feature. The processing circuitry may be configured to determine the recommended distance between the centroid of the treatment element and the centroid of the target anatomical feature according to the equation: 
     
       
         
           
             d 
             = 
             
               
                 r 
                 b 
               
                
               
                 cos 
                  
                 
                   ( 
                   
                     
                       sin 
                       
                         - 
                         1 
                       
                     
                      
                     
                       ( 
                       
                         
                           r 
                           
                             os 
                             , 
                             max 
                           
                         
                         
                           r 
                           b 
                         
                       
                       ) 
                     
                   
                   ) 
                 
               
             
           
         
       
     
     where r 0s,max  is a distance between the centroid of the target anatomical feature and the boundary of the anatomical feature, and r b  is a distance between the centroid of the treatment element and the boundary of the target anatomical feature. The medical device may have a first navigation electrode located distal to the treatment element and a second navigation electrode location proximal to the treatment element, and the method may further comprise determining a recommended location for the first navigation electrode determining a recommended location for the second navigation electrode. The processing circuitry may be configured to determine the recommended location for the first navigation electrode according to the equation: 
     
       
         
           
             
               e 
               d 
             
             = 
             
               
                 [ 
                 
                   
                     
                       
                         x 
                         d 
                       
                     
                   
                   
                     
                       
                         y 
                         d 
                       
                     
                   
                   
                     
                       
                         z 
                         d 
                       
                     
                   
                 
                 ] 
               
               = 
               
                 
                   [ 
                   
                     
                       
                         
                           x 
                           b 
                         
                       
                     
                     
                       
                         
                           y 
                           b 
                         
                       
                     
                     
                       
                         
                           z 
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                   ] 
                 
                 - 
                 
                   
                     l 
                     d 
                   
                    
                   
                     [ 
                     
                       
                         
                           a 
                         
                       
                       
                         
                           b 
                         
                       
                       
                         
                           c 
                         
                       
                     
                     ] 
                   
                 
               
             
           
         
       
     
     where l d  is a distance between the centroid of the treatment element and the first navigation electrode. The method may further include displaying on the display of the navigation system a first graphical indicator at a location corresponding to the recommended location for the first navigation electrode, the first graphical indicator being superimposed on a three-dimensional image of the target anatomical feature. The processing circuitry may be configured to determine the recommended location for the second navigation electrode according to the equation: 
     
       
         
           
             
               e 
               p 
             
             = 
             
               
                 [ 
                 
                   
                     
                       
                         x 
                         p 
                       
                     
                   
                   
                     
                       
                         y 
                         p 
                       
                     
                   
                   
                     
                       
                         z 
                         p 
                       
                     
                   
                 
                 ] 
               
               = 
               
                 
                   [ 
                   
                     
                       
                         
                           x 
                           b 
                         
                       
                     
                     
                       
                         
                           y 
                           b 
                         
                       
                     
                     
                       
                         
                           z 
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                   ] 
                 
                 + 
                 
                   
                     l 
                     p 
                   
                    
                   
                     [ 
                     
                       
                         
                           a 
                         
                       
                       
                         
                           b 
                         
                       
                       
                         
                           c 
                         
                       
                     
                     ] 
                   
                 
               
             
           
         
       
     
     where l p  is a distance between the centroid of the treatment element and the second navigation electrode. The method may further include displaying on the display of the navigation system a second graphical indicator at a location corresponding to the recommended location for the second navigation electrode, the second graphical indicator being superimposed on a three-dimensional image of the target anatomical feature. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present invention, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: 
         FIG. 1  shows an exemplary medical system that includes a first medical device having complex geometry; 
         FIG. 2  shows an exemplary medical system that includes a second medical device having complex geometry; 
         FIG. 3  shows a geometric representation of a calculation of optimal placement of a treatment element of a medical device; 
         FIG. 4  shows an exemplary simplified representation of recommended device placement indicators; and 
         FIGS. 5-7  together show an exemplary simplified representation of placement of a treatment element of a medical device at recommended landing zones. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawing figures in which like reference designations refer to like elements, an embodiment of a medical system constructed in accordance with the principles of the present invention is shown in  FIGS. 1 and 2 , generally designated as “ 10 .” The system  10  generally includes a medical device  12  that may be coupled to a control unit  14  or operating console and a navigation system  16  in communication with the device  12  and the control unit  14 . The medical device  12  may generally include one or more diagnostic or treatment elements for energetic, therapeutic, and/or investigatory interaction between the medical device  12  and a treatment site or region. The diagnostic or treatment region(s) may deliver, for example, cryogenic therapy, radiofrequency energy, ultrasound energy, laser energy, or other energetic transfer with a tissue area in proximity to the treatment region(s), including cardiac tissue. 
     The medical device  12  may be a treatment and/or mapping device. The medical device  12  may include an elongate body  18  passable through a patient&#39;s vasculature and/or proximate to a tissue region for diagnosis or treatment. For example, the device  12  may be a catheter that is deliverable to the tissue region via a sheath or intravascular introducer (not shown). The elongate body  18  may define a proximal portion  20 , a distal portion  22 , and a longitudinal axis  24 , and may further include one or more lumens disposed within the elongate body  18  thereby providing mechanical, electrical, and/or fluid communication between the elongate body proximal portion  20  and the elongate body distal portion  28 . 
     The medical device  12  may further include one or more treatment elements  30  at, coupled to, or on the elongate body distal portion  22  that have or are capable of achieving complex geometry during use in the patient. In the non-limiting embodiment shown in  FIG. 1 , the device may include a treatment element  30  that is expandable, such as one or more balloons. Alternatively, in the non-limiting embodiment shown in  FIG. 2 , the device may include one or more treatment elements  30  that are not expandable. For example, the device  12  may be a focal catheter that includes one or more electrodes  32  on the distal portion  22 , and each electrode may be considered to be a treatment element  30 . A focal catheter is shown in  FIG. 2 . The focal catheter may have a linear configuration, but may also be manipulatable into a curvilinear, looped, spiral, or other configuration, as shown. The expandable treatment element  30  of the system shown in  FIG. 1  may be coupled to a portion of the elongate body distal portion  22 . The device may optionally include a shaft that is slidably disposed within the elongate body  18  and at least a portion of the shaft may be located within the expandable treatment element  30 . The shaft may further include or define a distal tip  34  that may protrude beyond the distal end of the expandable treatment element  30 . The expandable treatment element  30  may further include one or more material layers providing for puncture resistance, radiopacity, or the like. If the device  12  is used to delivery cryotherapy (or if used with another energy modality that requires fluid to be delivered to the inner chamber of the treatment element  30 ), the device may also include one or more fluid injection elements. A device having a non-expandable treatment element may also include one or more fluid injection elements within the elongate body  18  proximate the one or more treatment elements  30  (for example, treatment electrode(s)  32 ). Further, if the device  12  is used or mapping in addition to or instead of for the delivery of treatment, the device  12  may include one or more mapping electrodes. Although the term “treatment element” is used herein, it will be understood that a mapping element or mapping electrodes could be used instead. 
     As is discussed in more detail below, the device  12  may also include one or more navigation electrodes  38  that are used by the navigation system  16  to visualize the device  12  on a control unit display and/or a navigation system display. For example, the device  12  shown in  FIG. 1  may include a first navigation electrode  38   a  distal to the expandable portion of the treatment element  30  and a second navigation electrode  38   b  proximal to the expandable portion of the treatment element  30 . Although the navigation electrodes  38   a ,  38   b  are shown as being coupled to the portion of the treatment element  30  that is coupled to the elongate body and/or shaft of the device, the navigation electrodes  38   a ,  38   b  could alternatively be located distal and proximal to all portions of the treatment element. Likewise, the device  12  shown in  FIG. 2  may include a first navigation electrode  38   a  near the distal tip  40  of the device and a second navigation electrode  38   b  at a location proximal to the first navigation electrode  38   a . 
     Each treatment electrode  32  and navigation electrode  38  may be electrically conductive segments for conveying an electrical signal, current, or voltage to a designated tissue region and/or for measuring, recording, receiving, receiving, assessing, or otherwise using one or more electrical properties or characteristics of surrounding tissue or other electrodes. The electrodes  32  may be configured in a myriad of different geometric configurations or controllably deployable shapes, and may also vary in number to suit a particular application, targeted tissue structure or physiological feature. 
     Each treatment electrode  32  may be electrically coupled to an output portion of a power source  42 , such as a radiofrequency energy generator or other type of energy generator, and may be in electrical communication with the control unit  14 . Each navigation electrode  38  may also be in communication with the navigation system  16  and the control unit  14 , and may be configured to receive magnetic or electric signals from the navigation system and transmit signals to the control unit  14  and/or navigation system  16  in a wired and/or wireless connection. 
     The system  10  may include one or more sensors to monitor the operating parameters throughout the system, including for example, pressure, temperature, flow rates, volume, power delivery, impedance, or the like in the control unit  14  and/or the medical device  12 , in addition to monitoring, recording or otherwise conveying measurements or conditions within the medical device  12  or the ambient environment at the distal portion of the medical device  12 . The sensor(s) may be in communication with the control unit  14  for initiating or triggering one or more alerts or therapeutic delivery modifications during operation of the medical device  12 . One or more valves, controllers, or the like may be in communication with the sensor(s) to provide for the controlled dispersion or circulation of fluid through the lumens/fluid paths of the medical device  12 . Such valves, controllers, or the like may be located in a portion of the medical device  12  and/or in the control unit  14 . 
     The medical device  12  may include a handle  44  coupled to the elongate body proximal portion  20 . The handle  44  may include circuitry for identification and/or use in controlling of the medical device  12  or another component of the system. Additionally, the handle  44  may also include connectors  46  that are mateable to the control unit  14  to establish communication between the medical device  12  and one or more components or portions of the control unit  14 . The handle  44  may also include one or more actuation or control features that allow a user to control, deflect, steer, or otherwise manipulate a distal portion of the medical device  12  from the proximal portion of the medical device  12 . For example, the handle  44  may include one or more components such as a lever or knob  46  for manipulating the elongate body  18  and/or additional components of the medical device  12 . 
     As used herein, the term “control unit  14 ” for simplicity may include any system components that are not part of the medical device  12  itself, other than components of the navigation system, regardless of whether the component is physically located within or external to the control unit  14 . Further, the navigation system  16  may be a standalone system in communication with the control unit  14  or may be contained within or integrated with the control unit  14 , even though it is shown as being physically separated from the control unit in  FIGS. 1 and 2 . The control unit  14  may include one or more components for the delivery of one or more energy modalities for which the system is used. For example, if the system  10  is used to deliver cryotherapy, the control unit  14  may include a supply  48  of a fluid such as a coolant, cryogenic refrigerant, or the like, an exhaust or scavenging system for recovering or venting expended fluid for re-use or disposal, as well as various control mechanisms. In addition to providing an exhaust function for the fluid or coolant supply  48 , the control unit  14  may also include pumps, valves, controllers or the like to recover and/or re-circulate fluid delivered to the handle  44 , the elongate body  18 , and/or the fluid pathways of the medical device  12 . Further, a vacuum pump  50  in the control unit  14  may create a low-pressure environment in one or more conduits within the medical device  12  so that fluid is drawn into the conduit(s)/lumen(s) of the elongate body  18 , away from the distal portion  22  and towards the proximal portion  20  of the elongate body  18 . Additionally or alternatively, the control  14  unit may include a radiofrequency generator or power source  42  as a treatment or diagnostic mechanism in communication with the treatment electrode(s)  32  of the medical device  12 . The radiofrequency generator  42  may have a plurality of output channels, with each channel coupled to an individual treatment electrode  32 . The radiofrequency generator  42  may be operable in one or more modes of operation. 
     The control unit  14  may include one or more controllers, processors, and/or software modules  52  containing circuitry configured to execute instructions or algorithms to provide for the automated operation and performance of the features, sequences, calculations, or procedures described herein. For example, the processor(s)  52  may be configured, programmed, or programmable to perform the calculations and make the determinations discussed in greater detail below to identify a target location for a medical device relative to an anatomical feature, even if that device has complex geometry that has traditionally made the process challenging. Further, the control unit  14  may include one or more user input devices, controllers, and displays  54  for collecting and conveying information from and to the user. 
     The navigation system  16  may be any commercially available navigation system suitable for use with the control unit  14 , device  12 , and type of procedure. As a non-limiting example, the navigation system  16  may include a plurality of surface electrodes  56 , a reference electrode (not shown), and a processing unit  58  that collects and processes signals from the navigation electrodes  38 , and a display that displays to the user the location of the device  12  within the patient&#39;s body  57  and/or relative to the target anatomical feature (for example, a pulmonary vein ostium), and recommended landing zones for the device  12 . The processing unit  58  may include processing circuitry including a memory and a processor, the memory in communication with the processor and having instructions that, when executed by the processor, configure the processor to perform the calculations and determinations discussed herein. Additionally or alternatively, this information may be displayed on the display  64  of the control unit  14 . The navigation system  16  may also include an energy generator (not shown) for delivering energy to the plurality of surface electrodes  56 . Alternatively, the navigation system may be in communication with the control unit power source  42 . It will be understood that the calculations discussed herein may additionally or alternatively be performed by one or more processors  64  within the control unit  14 . 
     As shown in  FIGS. 1 and 2 , the surface electrodes  56  may be applied to the patient&#39;s skin and may deliver relatively low-frequency radiofrequency energy through the patient toward the procedure site, current device location, or the target anatomical feature. The navigation electrode(s)  38  on the device  12  may each record a voltage and impedance from this energy and transmit data to the processing unit  58 , which may then determine a position of the electrode(s)  38 , and therefore the device  12 , within the patient. The processing unit  58  may perform this calculation many times during a procedure, frequently updating the registered location and displaying such to the user so the user can visualize the location of the device relative to the target anatomical feature in real time. However, it will be understood that the navigation electrode(s)  38  may be configured to be used with navigation systems other than impedance-based systems, such as navigation systems that are magnetic field based, hybrid impedance/magnetic field based, ultrasound field based, and/or radiation based, and/or navigation systems that may be developed in the future. 
     Now referring to  FIG. 3 , a geometric representation of the calculation performed by the system  10  is shown. It will be understood that the elements of  FIG. 3  are not drawn to scale and are meant only to show the geometric relationship between components used to calculate an optimal device position relative to a target anatomical feature  70 . The system  10  may identify one or more target anatomical features, such as pulmonary vein(s), prior to or during the procedure. A target pulmonary vein ostium, for example, may be manually defined by the user or automatically or semi-automatically defined by the control unit  14  or navigation system  16  using an algorithm executed by the processor(s)  64  or processing unit  58 . When executed, the algorithm may be used to trace the centroid  72  of each pulmonary vein as the pulmonary vein enters the left atrium, and it may then be used identify the various planes and contours of each pulmonary vein. Subsequently, the algorithm may be used to derive the axis and location of at least one target position (which may be referred to herein as a “landing zone”) based on design information for the device  12  being used. This information may include measurements such as r b , l d , and l p , defined and discussed below. 
     The process performed by the processing unit  58  of the navigation system  16  is now discussed in more detail. However, if the algorithm for the initial identification of the target anatomical feature is executed by the processor(s)  64  of the control unit  14 , this information will be transmitted from the control unit  14  to the navigation system  16 , which may then perform the calculations/execute further algorithm(s) for determining the optimal device position for the procedure. 
     First, the processing unit  58  of the navigation system  16  may define or determine a plane P 1  that approximates a surface of the target anatomical feature  70 . For example, the plane may approximate the pulmonary vein ostium, which may not naturally be perfectly planar. The plane may be expressed by the following equation: 
         ax+by+cz+d= 0   (1)
 
     The plane described by equation (1) is described by a normalized vector perpendicular to the surface of the plane expressed as [a b c] T . 
     The processing unit  58  may then determine a border C 1  of the target anatomical feature  70 , such as a pulmonary vein ostium, and calculate the location of the centroid  72  of the border C 1 . As the border C 1  may not be perfectly circular or symmetric, the centroid may be calculated as the arithmetic mean (average) of all the points in the shape. The centroid of a pulmonary vein ostium (x 0 , y 0 , z 0 ) may be calculated as the point lying in the centroid of the surface on plane P 1  bounded by C 1  (as shown in  FIG. 3 ). 
     The processing unit  58  may then define or determine a vector {right arrow over (n)} that is normal to the plane P 1  and extends away from the target anatomical feature  70 . For example, although  FIG. 3  shows the vector {right arrow over (n)} as extending from a point in the plane that is not the centroid of the target anatomical feature, the vector {right arrow over (n)} may have a starting point within plane P 1  that is the centroid  72  location, and may extend away from the pulmonary vein ostium and into the left atrium. The vector {right arrow over (n)} may be expressed by the following equation: 
     
       
         
           
             
               
                 
                   
                     n 
                     → 
                   
                   = 
                   
                     
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                               x 
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                       ] 
                     
                     + 
                     
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                        
                       
                         [ 
                         
                           
                             
                               a 
                             
                           
                           
                             
                               b 
                             
                           
                           
                             
                               c 
                             
                           
                         
                         ] 
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     where parameters a, b, and c are defined by the plane P 1 , δ is a scaling factor to create a line in the direction of the vector. [x 0 , y 0 , z 0 ] T  of equation (2) represents the centroid  72  shown in  FIG. 3 . 
     Further, the treatment element  30  shown in  FIG. 3  is an expandable treatment element, such as a balloon. Even though the treatment element  30  is shown as being circular (or spherical), it will be understood that this is for simplicity and that that treatment element may have other shapes, sizes, and configurations. The treatment element  30  may have a center  74  if it is a circular treatment element (or centroid of a non-circular treatment element) (x b , y b , z b ) and a radius r b  between the center/centroid  74  of the treatment element and the border C 1  of the pulmonary vein ostium. As shown in  FIG. 3 , the distance d between the centroid  72  of, for example, the pulmonary vein ostium (x 0 , y 0 , z 0 ) and the center/centroid  74  of the treatment element (x b , y b , z b ) the and the distance r os,max  between the centroid  72  of the pulmonary vein ostium and the outermost reach of the border C 1  of the pulmonary vein ostium may be calculated. The optimal distance d between the center/centroid  74  of the treatment element  30  and the centroid  72  of the pulmonary vein ostium may be calculated using the following equation: 
     
       
         
           
             
               
                 
                   d 
                   = 
                   
                     
                       r 
                       b 
                     
                      
                     
                       cos 
                        
                       
                         ( 
                         
                           
                             sin 
                             
                               - 
                               1 
                             
                           
                            
                           
                             ( 
                             
                               
                                 r 
                                 
                                   os 
                                   , 
                                   max 
                                 
                               
                               
                                 r 
                                 b 
                               
                             
                             ) 
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     Although r os,max  is shown as the distance between the center/centroid  72  of the pulmonary vein ostium and the border C 1 , in  FIG. 3 , r os,max  may alternatively be calculated as a distance between a point along the longitudinal axis  24  of the device (that passes through the center/centroid  72  of the pulmonary vein ostium and the navigation electrode(s)  38 ), and the border C 1 . 
     The processing unit  58  may use these calculations to recommend at least one target position or “landing zone” for the device  12 . For example, the processing unit  58  may recommend that the device may be positioned such that its longitudinal axis  24  lies along the vector {right arrow over (n)} that extends away from the centroid  72  of the target anatomical feature, such as a pulmonary vein ostium, and into the left atrium. In other words, the center/centroid  74  of the treatment element  30  (x b , y b , z b ) may be calculated to be normal to the surface of the plane P 1 , passing through the centroid  72  of the pulmonary vein ostium (x 0 , y 0 , z 0 ). Thus, the location of the center/centroid  74  of the treatment element  30  (x b , y b , z b ) may be calculated using the following equation (where d is calculated as in equation (3)): 
     
       
         
           
             
               
                 
                   
                     [ 
                     
                       
                         
                           
                             x 
                             b 
                           
                         
                       
                       
                         
                           
                             y 
                             b 
                           
                         
                       
                       
                         
                           
                             z 
                             b 
                           
                         
                       
                     
                     ] 
                   
                   = 
                   
                     
                       [ 
                       
                         
                           
                             
                               x 
                               0 
                             
                           
                         
                         
                           
                             
                               y 
                               0 
                             
                           
                         
                         
                           
                             
                               z 
                               0 
                             
                           
                         
                       
                       ] 
                     
                     + 
                     
                       d 
                        
                       
                         [ 
                         
                           
                             
                               a 
                             
                           
                           
                             
                               b 
                             
                           
                           
                             
                               c 
                             
                           
                         
                         ] 
                       
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     The one or more navigation electrodes  38  may be used to visualize the location of the device  12  using the navigation system  16  and/or a mapping system (not shown). Further, using the exact location(s) of the navigation electrode(s)  38  on the device  12 , the processing unit  58  may calculate an optimal location for the each electrode  38 . For example, the optimal location of a navigation electrode  38  may be calculated relative to the center/centroid  74  of the treatment element  30  (x b , y b , z b ) along the direction of the vector {right arrow over (n)}. Additionally, if the device  12  includes a distal first navigation electrode  38   a  (e d ) and a proximal second navigation electrode  38   b  (e p ), an optimal location for each of these electrodes may also be calculated. If the distance between the center/centroid  74  of the treatment element  30  and the distal navigation electrode  38   a  (e d ) is l d  and the distance between the center/centroid  74  of the treatment element  30  and the proximal navigation electrode  38   b  (e p ) is l p , the optimal location of e d  and e p  may be calculated using the following equations: 
     
       
         
           
             
               
                 
                   
                     e 
                     d 
                   
                   = 
                   
                     
                       [ 
                       
                         
                           
                             
                               x 
                               d 
                             
                           
                         
                         
                           
                             
                               y 
                               d 
                             
                           
                         
                         
                           
                             
                               z 
                               d 
                             
                           
                         
                       
                       ] 
                     
                     = 
                     
                       
                         [ 
                         
                           
                             
                               
                                 x 
                                 b 
                               
                             
                           
                           
                             
                               
                                 y 
                                 b 
                               
                             
                           
                           
                             
                               
                                 z 
                                 b 
                               
                             
                           
                         
                         ] 
                       
                       - 
                       
                         
                           l 
                           d 
                         
                          
                         
                           [ 
                           
                             
                               
                                 a 
                               
                             
                             
                               
                                 b 
                               
                             
                             
                               
                                 c 
                               
                             
                           
                           ] 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
             
               
                 
                   
                     e 
                     p 
                   
                   = 
                   
                     
                       [ 
                       
                         
                           
                             
                               x 
                               p 
                             
                           
                         
                         
                           
                             
                               y 
                               p 
                             
                           
                         
                         
                           
                             
                               z 
                               p 
                             
                           
                         
                       
                       ] 
                     
                     = 
                     
                       
                         [ 
                         
                           
                             
                               
                                 x 
                                 b 
                               
                             
                           
                           
                             
                               
                                 y 
                                 b 
                               
                             
                           
                           
                             
                               
                                 z 
                                 b 
                               
                             
                           
                         
                         ] 
                       
                       + 
                       
                         
                           l 
                           p 
                         
                          
                         
                           [ 
                           
                             
                               
                                 a 
                               
                             
                             
                               
                                 b 
                               
                             
                             
                               
                                 c 
                               
                             
                           
                           ] 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
     In equation (5), the placement of e d  would be distal (as the term is used for the device  12 ) to the center/centroid  74  of the treatment element  30 , in the direction of the target anatomical feature  70 , while e p  would be proximal of both the centroid  72  of the anatomical feature  70  and the center/centroid  74  of the treatment element  30 . Parameters r b , l d , and l p  may be known for the particular device being used. 
     The navigation system display  60  and/or the control unit display  54  may show device placement graphical indicators  78  for both the optimal location of each of the one or more navigation electrodes  58  and may show the real-time coordinates of the navigation electrode(s)  58 . Thus, the user could see the recommended “landing zones” for each of the electrode(s) and could then navigate the device to achieve the recommended device location before beginning the treatment and/or mapping procedure at the target site. Positioning the device at the recommended location may help ensure proper placement of the treatment element  30  with respect to depth as well as orientation, which may create an optimal treatment profile in the target anatomical feature  70 . 
     The navigation system display  60  and/or the control unit display  54  may show an image of an area proximate the target anatomical feature  70 , such as the cardiac space surrounding one or more pulmonary veins, and the graphical indicators may be superimposed on this image. The image may be obtained from an imaging system such as a computed tomography (CT) system, a magnetic resonance imaging (MRI) system, or other system suitable for creating images of locations within a patient&#39;s body. For example, the imaging system may create images in Digital Imaging and Communications in Medicine (DICOM) format. The imaging system may be in communication with and digitally transmit images to the navigation system  16  and/or the control unit  14  for further processing. Alternatively, images recorded by the imaging system may be recorded and transferred to the navigation system  16  and/or the control unit  14  by a user. The device  12  may also be shown, as well as the navigation electrodes  38 . Optionally, the graphical indicators or “landing zones”  78  for each of the navigation electrodes  38  may be differentiated in some way for enhanced visualization. For example, the graphical indicator  78  for each electrode may have a different color, fill pattern, numerical reference number, or the like. 
     Referring now to  FIG. 4 , an exemplary simplified representation of recommended treatment device placement locations is shown. The target anatomical feature  70  in  FIG. 4  may be any or all of four pulmonary veins located on the left atrial wall  80  having border C: the right superior pulmonary vein (RSPV)  70   a  with border C RSPV ; the left superior pulmonary vein (LSPV)  70   b  with border C LSPV ; the right inferior pulmonary vein (RIPV)  70   c  with border C RIPV ; and/or the left inferior pulmonary vein (LIPV)  70   d  with border C LIPV . The device  12  may have a distal first navigation electrode  38   a  (e d ) and a proximal second navigation electrode  38   b  (e p ). The display may show a vector line  84 , a graphical indicator  78   a  for the distal navigation electrode  38   a , and a graphical indicator  78   b  for the proximal navigation electrode  38   b  for each pulmonary vein. Although a simplified view is shown in  FIG. 4 , it will be understood that the actual displayed image may be three dimensional and may show additional tissue characteristics, anatomical features, or the like. Further, as the image is rotated in space, the pulmonary vein ostia, vector lines, and graphical indicators rotate accordingly. 
     Now referring to  FIGS. 5-7 , an exemplary placement of a treatment element of a device at recommended target positions or “landing zones” is shown. The images shown in  FIGS. 5-7 , like that shown in  FIG. 4 , are simplified representations of what may be shown on a system display in more detail. The display  54  and/or  60  may show an area of tissue surrounding the target anatomical feature(s)  70 , such as a left atrial wall  80 , the target anatomical feature(s)  70 , the device treatment element  30 , a vector line  84 , and at least one graphical indicator  78  for the recommended landing zone(s). In the images shown in  FIGS. 5-7 , the device  12  may include two navigation electrodes  38   a ,  38   b  proximal and distal to the treatment element  30 , labeled as e d  and e p  in the figures. Consequently, the display may show two graphical indicators  78   a ,  78   b , corresponding to the two navigation electrodes  38   a ,  38   b , respectively. 
     In  FIG. 5 , the display may allow the user to visualize the device  12  within the treatment space, for example, the left atrium. The user may then use this image to align the longitudinal axis  24  of the device with the vector line  84 . In other words, the user may use the image to approach the target anatomical feature, here a right superior pulmonary vein ostium  70   a , at the recommended location. In  FIG. 6 , the display may allow the user to visualize the device  12  moving closer to the pulmonary vein ostium  70   a  and recommended alignment. The objective may be to align the navigation electrodes  38   a ,  38   b  (e d  and e p ) with the graphical indicators  78   a ,  78   b , respectively. Finally, in  FIG. 7 , the display may allow the user to visualize the device  12  positioned at the optimal treatment location, wherein the navigation electrodes  38   a ,  38   b  are properly aligned with the graphical indicators  78   a ,  78   b , respectively. As a non-limiting example, the first graphical indicator  78   a  may be a small distance inside the pulmonary vein whereas the second graphical indicator  78   b  may be a distance away from the pulmonary vein, within the left atrium. This may ensure that a portion of the treatment element  30  having the widest diameter is positioned at the pulmonary vein ostium, occluding the pulmonary vein. If the device is used to deliver cryotreatment, this alignment may help ensure that a circular ablation lesion is created at the pulmonary vein ostium. Further, the user may monitor alignment of the device during the procedure in real time. 
     Once the treatment element  30  of the device  12  is properly aligned, the treatment procedure may begin. If the device is a cryotreatment device, a known or estimated cooling profile of the treatment element  30  and placement of the treatment element  30  relative to the target anatomical feature may be used to provide additional feedback on the cooling profile across the contacted tissue. 
     It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope and spirit of the invention, which is limited only by the following claims.