Patent Publication Number: US-11045182-B2

Title: Surgical introducer with guidance system receptacle

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. application Ser. No. 15/372,890 filed on Dec. 8, 2016, which claims the benefit of U.S. Provisional Application No. 62/418,507 filed Nov. 7, 2016, both of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to delicate tissue surgical retractor systems for use in the brain or other tissue susceptible to retraction injury. 
     BACKGROUND 
     A variety of different devices have been used to retract delicate tissue during surgical procedures. One such device is illustrated in United States Patent Publication Number 2010/0010315, which is incorporated herein by reference. FIG. 1 of this publication illustrates a soft tissue retractor system having a hollow retractor 100, and an introducer 102 that is selectively inserted into the retractor 100. The retractor 100 and/or introducer 102 may include a handle 104 to facilitate manipulation and placement of the retractor system, and a lock to hold the introducer and retractor together. The handle 104 is configured to connect to a clamp 106, such as the standard surgical clamp 106 shown in FIG. 1. The device in FIG. 1 (with some modifications) is commercially sold as the “VBAS” device by Vycor Medical, Inc. of Boca Raton, Fla. 
     A retractor system such as shown in FIG. 1 is often used by inserting the introducer 102 into the retractor 100 and locking it in place, so the two can be moved and manipulated as a unit. The combined retractor system is inserted into the patient&#39;s body and moved to the surgery site, and then the introducer 102 is unlocked and removed to permit access to the site through the retractor 100. When the unit is in place (either before or after the introducer 102 is removed), the handle 104 may be locked to a clamp 106 to hold the retractor 100 in place. Surgeons using this retractor sometimes do not use a clamp to hold the retractor at the surgery site, and often manually manipulate the retractor to access different parts of the surgery site during the surgical procedure. The retractor system and the retractor may be manipulated by holding the proximal ends of the introducer or retractor or by holding the handle. 
     The device shown in FIG. 1 may have a transparent introducer 102 and/or retractor 100, and surgeons using such devices advantageously use the transparent introducer and retractor to observe the underlying tissue and to visually guide the unit to the surgery site. While it has been found that visual guidance by looking through the introducer 102 is very beneficial, it also has been found that some form of additional guidance or navigation may be desired in some cases. For example, in some cases, surgeons have used a probe or guide wire (a narrow elongated rod) to guide the movement of the retractor system. In such cases, the probe is advanced to the surgery site, and then the interlocked retractor system is slid over the probe until it reaches the surgery site. This is facilitated by the inclusion of a hole at the tip of the introducer that fits around the probe. If the hole through the tip of the introducer is absent, this method cannot be used. This type of system is described in United States Patent Publication Numbers 2008/0109026 and 2009/0048622, which are incorporated herein by reference. These references also show an alternative construction, in which the retractor is not locked to the introducer. 
     It has been found that some surgeons using the above procedure may use a probe that is integrated into a computer navigation system. For example, the probe may include a so-called “starburst” or the like, on the probe&#39;s proximal end (i.e., the end opposite the distal end that is inserted to the surgical site). This and other navigation systems are known in the art. For example, frameless navigation systems and other computerized guidance systems and methods are described in U.S. Publication No. 2001/0027271 (which is incorporated herein by reference in its entirety) and others, and are commercially available from companies such as Medtronic, Inc., Stryker, BrainLab, AG, and GE Healthcare. As used herein, “computerized guidance” encompasses any method of guiding a device to or at a surgical site that relies on computer visualization and/or control. 
     United States Patent Publication Number 2010/0010315 briefly notes the possibility of using stereotactic guidance or navigation in conjunction with a surgical retractor, but does not illustrate or describe this procedure or any apparatus for accomplishing this objective. Nevertheless, surgeons have been known to use a navigation probe “freehand” with a VBAS device such as shown in FIG. 1. In such cases, the surgeon holds the navigation probe in place within the introducer while advancing the unit towards the surgery site. The tip of the probe may be placed in or near an opening through the tip of the introducer, but the opening through the introducer may be somewhat larger than the probe tip and is oval, and does not hold the probe tip in any particular orientation. Such techniques can suffer from inaccuracy and displacement of the probe from the introducer tip, and it can be difficult to hold the probe in place. Also, in some cases the probe tip may extend partially through the introducer tip opening, which can risk damaging underlying tissue. However, freehand use can be helpful to allow occasional removal of the probe to provide an unobstructed view through the introducer of the underlying tissue. 
     While computerized surgical guidance systems are well-known, a number of limitations exist with respect to their use with retractor systems, and particularly with systems like those shown in FIG. 1. For example, while some surgeons use computerized guidance to direct a probe to the surgery site, and then slide the retractor system over the probe to the site, the movement of the retractor may be somewhat imprecise and the process can be unduly cumbersome. This method also is not available if the retractor system does not have a through-hole that fits over the probe (due either to the absence of a hole or a hole that is too small). In addition, the probe does not provide a view of the tissue through which it is advanced, so there is no visual means to perceive and avoid critical tissue (e.g., major blood vessels or nerves) when inserting a probe before inserting a retractor/introducer system. Also, the small-diameter probe may sever delicate tissue cells, such as grey or white brain matter, rather than moving the cells aside and passing between them as would be expected to happen when advancing the retractor system. 
     United States Patent Publication Number 2013/0066154, which is incorporated herein by reference, shows examples of systems for integrating a navigation probe into a surgical introducer. For example, FIGS. 1-6 of this publication show a navigation probe that is secured to the inside of a pre-existing introducer by resilient means, such as rubber plugs or O-rings. Another embodiment uses a slip fit (e.g., FIGS. 7-8), and still another embodiment uses an arm to hold the probe down inside the introducer (FIG. 9). Still other versions mount the navigation device outside the introducer, to an arm that is connected to the retractor assembly (FIGS. 10-11). While these systems may provide suitable performance, they also have certain potential shortcomings. For example, resilient plugs may slip in the presence of fluids and may be difficulty to disengaged to remove the navigation device during surgery, a slip fit requires careful monitoring to ensure proper positioning, an arm as shown in FIG. 9 to hold the probe in place requires the probe to be modified to include a surface against which the arm pushes, and locating the navigation device outside the introducer complicates the correlation between the navigation device and the tip of the introducer or retractor. 
     United States Patent Publication Number 2012/0071748, which is incorporated herein by reference, shows another example of a system for integrating a navigation probe into a surgical introducer. In this case, the probe is retained in a narrow channel through the introducer, and held in place with a threaded locking screw. The locking screw adds an additional potentially-removable part to the operating theater, and therefore this reference adds a separate retaining device (see FIG. 7B) to prevent the locking screw from being removed. The locking screw also can be relatively difficult to manipulate, particularly when wearing surgical gloves. 
     United States Patent Publication Number 2016/0015374, which is incorporated herein by reference, shows yet another example of a system for integrating a navigation probe into a surgical introducer. The device shown in this publication holds the probe in a tube-like sheath that extends distally into the introducer from the proximal open end of the introducer, and has a convenient single-throw clamp to lock the probe in place. This device also optionally includes a mechanism to indicate when the navigation probe is fully seated in the introducer. While this device is useful to ensure greater accuracy and registration between the introducer and the navigation probe, it may obstruct the surgeon&#39;s view to some degree, and may make frequent removal and reinstallation of the navigation probe somewhat cumbersome as compared to freehand use of the probe. 
     It has been found that there still remains a need to provide alternative apparatus and methods for coordinating the use of guidance systems with surgical introducers. 
     SUMMARY OF THE INVENTION 
     In one exemplary aspect, there is provided an introducer system for use with a navigation probe having a navigation element and a navigation probe shaft having a diameter and terminating at a distal probe tip. The introducer system has an introducer having a sidewall and a probe receptacle. The sidewall extends along a longitudinal axis and forms an introducer passage extending from a proximal introducer end to a distal introducer end. The sidewall is larger, in a lateral direction that is orthogonal to the longitudinal axis, than the navigation probe shaft diameter. The probe receptacle is located at the distal introducer end and extends along the longitudinal axis within the introducer passage. The probe receptacle begins at a proximal receptacle end and terminates at a distal receptacle end with the proximal receptacle end being between the proximal introducer end and the distal receptacle end. The probe receptacle has an inner surface that tapers continuously from the proximal receptacle to the distal receptacle end, and the inner surface has a first lateral size in the lateral direction at the proximal receptacle end and a second lateral size in the lateral direction at the distal receptacle end, the first lateral size being greater than the second lateral size. The inner surface is configured and dimensioned to receive the distal probe tip and restrict movement of the distal probe tip in the lateral direction, and the sidewall is configured and dimensioned to allow the navigation probe shaft to move in the lateral direction within the passage when the distal probe tip is positioned in the probe receptacle. 
     In some aspects, a first portion of the inner surface may be located at the proximal receptacle end have a conical shape. 
     In some aspects, a second portion of the inner surface may be located at the distal receptacle end have a hemispherical shape. 
     In some aspects, the sidewall may have a sidewall profile in the lateral direction, and the probe receptacle may be located at a geometric center of the sidewall profile. 
     In some aspects, the introducer system may have an introducer tip opening forming a second fluid communication path through the sidewall at the distal introducer end. 
     In some aspects, the proximal receptacle end may have an outer surface that is spaced from the sidewall in the lateral direction by a gap. The probe receptacle may include at least one opening extending from the outer surface to the inner surface and forming a first fluid communication path between the inner surface and the gap. The introducer may have an introducer tip opening forming a second fluid communication path through the sidewall at the distal introducer end. The second fluid communication path may be connected to the first fluid communication path. The second fluid communication path may extend between the introducer tip opening and the gap, and at least partially bypass the probe receptacle. The at least one opening may include a plurality of slots extending from the inner surface to the outer surface, each of the plurality of slots extending along the longitudinal axis from the proximal receptacle end to a portion of the sidewall located adjacent the distal receptacle end. The introducer tip opening may include one or more annular passages. One or more supports may extend between the sidewall and the probe receptacle to suspend the probe receptacle adjacent the introducer tip opening. The distal receptacle end may be located within the introducer tip opening. The one or more supports may include a plurality of ribs extending along the longitudinal axis. At least part of the one or more supports may be located within the introducer tip opening. 
     In some aspects, the probe receptacle may have a receptacle size in the lateral direction, and the introducer tip opening has an opening size in the lateral direction, and the receptacle size is less than the opening size. 
     In some aspects, at least a portion of the sidewall at the distal introducer end may be transparent and visible from the proximal introducer end when the navigation probe is installed within the introducer. 
     In some aspects, the introducer system may include a probe retainer configured to selectively connect to the proximal introducer end, the probe retainer comprising a receiver configured to receive the navigation probe shaft when the probe retainer is attached to the proximal introducer end and thereby limit movement of the navigation probe shaft in the lateral direction. 
     The foregoing summary of the invention provides a variety of exemplary embodiments that may be used in any suitable combination, and is not intended to impose any limitations upon the invention recited in the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A better understanding of the exemplary embodiments may be understood by reference to the attached drawings, in which like reference numbers designate like parts. The drawings are exemplary, and not intended to limit the claims in any way. 
         FIG. 1  is an example of a prior art delicate tissue retractor system. 
         FIG. 2A  is a cutaway side view of a first embodiment of an introducer having a guidance probe receptacle. 
         FIG. 2B  is a cutaway side view of the distal tip of the embodiment of  FIG. 2A , shown at a slight oblique angle. 
         FIG. 3A  illustrates a distal tip of another embodiment of an introducer having a guidance probe receptacle, as viewed from inside the introducer. 
         FIG. 3B  is a cutaway side view of the distal tip of the embodiment of  FIG. 3A . 
         FIG. 4A  illustrates a distal tip of another embodiment of an introducer having a guidance probe receptacle, as viewed from inside the introducer. 
         FIG. 4B  is a cutaway side view of the distal tip of the embodiment of  FIG. 4A . 
         FIG. 5A  illustrates a distal tip of another embodiment of an introducer having a guidance probe receptacle, as viewed from inside the introducer. 
         FIG. 5B  illustrates the embodiment of  FIG. 5A , as viewed from outside the introducer. 
         FIG. 5C  is a cutaway side view of the distal tip of the embodiment of  FIG. 5A , as shown along line  5 C- 5 C. 
         FIG. 5D  is a cutaway side view of the distal tip of the embodiment of  FIG. 5A , as shown along line  5 D- 5 D. 
         FIGS. 6A-6D  are cross-sectional side views of the distal tips of four different navigation probes. 
         FIGS. 7A-7B  illustrate an embodiment of a centering device that may be used with embodiments of introducers. 
         FIGS. 8A-8B  illustrate the embodiment of  FIGS. 7A-7B  in use. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Embodiments of the invention may provide various features to supplement or advance the state of the art of surgical introducers and retractor systems. As used herein, the term “guidance system” is intended to include any system for assisting a surgeon with advancing the retractor system to the surgery site, and can include passive systems like guide wires, or active systems like navigation probes that are detected and tracked using a computerized telemetry system. The term “surgeon” includes anyone in the operation theater who might use or manipulate the introducer system. Active probes can be tracked by various techniques, including: optically tracking a “starburst” or other marker mounted on a portion of the probe that remains visible during the procedure; directly monitoring the probe&#39;s position using radiation imaging (e.g., X-ray) or magnetic imaging; physically connecting the probe to a frame of reference system to mechanically track the position of the probe; or other means or combinations of means, as known in the art. The terms “navigation” and “guidance” are used interchangeably herein. Embodiments also may be used with manual systems in which the surgeon moves the retractor system entirely by hand, or semi-automated or automated systems that operate under the surgeon&#39;s control or automatically advance the retractor system to the surgery site without the surgeon&#39;s intervention. 
     Embodiments may be used with dedicated systems that are designed anew, or with preexisting systems. For example, embodiments may be used with systems like the one shown in  FIG. 1 , such as by supplementing, modifying or replacing the introducer  102 , or with other introducer assemblies, as will be appreciated by persons or ordinary skill in the art. The embodiments described herein may be used with a retractor  100  as shown in  FIG. 1 , or in other retractors. It will be readily appreciated that the shape of the introducer can be modified to fit into any conventional retractor, and the introducer also may be modified to connect to the retractor (if necessary or desired) using any suitable clamp or other engagement mechanism. For example, embodiments may be used with small-scale versions of introducers like the one shown in  FIG. 1 , in which the embodiment optionally may be scaled down to allow visibility into the retractor, but providing such visibility is not required in all embodiments. 
     The exemplary embodiments described herein are directed towards introducers for use in neurosurgery or other operations in and around the brain or skull. However, uses in other parts of the body are also possible. 
       FIG. 2A  shows an exemplary embodiment of an introducer  200  that is configured to be releasably retained inside a retractor  202  such as retractor  100  of  FIG. 1 . The introducer  200  comprises a sidewall  204  that extends from a proximal introducer end  206  to a distal introducer end  208 . As used herein, “proximal” refers to the end that generally faces the surgeon in use, and “distal” refers to the end that is located towards or inserted into the patient. When connected together, the proximal introducer end  206  may be located at or near a proximal retractor end, and the distal introducer end  208  extends beyond a distal retractor end. The retractor  202  preferably comprises a hollow tubular retractor passage extending along a longitudinal axis from a proximal retractor end to a distal retractor end, and is dimensioned to allow surgical procedures to be undertaken therethrough. 
     The introducer sidewall  204  forms an introducer passage  210  that extends along a longitudinal axis  212  extending from the proximal introducer end  206  to the distal introducer end  208 . When assembled with the retractor  202 , a distal tip portion  214  of the introducer  200  extends beyond the distal end of the retractor  202 . Together, the distal tip portion  214  and the retractor  202  form a generally smooth and continuous surface for gently displacing brain tissue or the like as the assembly is advanced into the body. The distal tip portion  214  preferably is tapered with a rounded (such as shown) or conical shape. A tip opening  216  may be provided at or near the distal introducer end  208 , as discussed in more detail below. A lock (see, e.g.,  FIG. 1 .) may be provided to selectively hold the introducer  200  to the retractor  202 . 
     The sidewall  204  preferably comprises a continuous wall surface such that the passage  210  has a closed outer perimeter, such as shown in  FIG. 1 . This can help prevent unwanted entry of body fluids and provide a smooth continuous surface for viewing through the sidewall  204  (if it is transparent) and for guiding instruments down the length of the passage  210  without risk of displacement. However, one or more openings  218  may be provided in the sidewall  204  in alternative embodiments. 
     The introducer sidewall  204  may have any suitable cross-sectional profile (i.e., profile in a plane orthogonal to the longitudinal axis  212 ). For example, the sidewall  204  may be circular, elliptical, oval or otherwise generally curved (i.e., comprised entirely of curved surfaces and/or very short straight surfaces that effectively simulate a smoothly-curved shape). If desired, the cross-section may include one or more rectilinear segments (e.g., a D-shape), or may be entirely rectilinear (e.g., a square or triangular shape). The sidewall profile also may taper to be larger at the proximal end than at the distal end, and preferably reduces at least slightly in size as it approaches the distal introducer end  208 . The outer surface of the sidewall  204  may be shaped to match the shape of a corresponding inner wall of the retractor  202 , but this is not strictly required. The introducer sidewall  204  also preferably has a generally consistent wall thickness along its length, which can facilitate manufacturing and provide a more suitable optical path for viewing through the sidewall  204 . It will be understood that cross-sectional shape of the passage  210  will be defined by the shape of the sidewall  204 , and therefore the foregoing discussion about the shapes of the sidewall  204  applies also the shape of the passage  210 . 
     The introducer  200  preferably is transparent at least at the distal end  206 , and more preferably at the distal tip portion  214 , and more preferably along most or the full length of the sidewall  202 . The transparent portion allows the surgeon to visualize underlying tissue while advancing the introducer  200  through brain tissue or the like, which can provide significant benefits during surgery. However, in alternative embodiments, the introducer  200  may be opaque. Suitable materials for the introducer  200  include polycarbonate and other kinds of plastic, metals such as aluminum, stainless steel or titanium, glass or ceramic, or other materials that are biocompatible or that can be treated via coatings or the like to be biocompatible. 
     The passage  210  is sized to accommodate a navigation probe  220 . The probe  220  comprises a shaft  222  that extends from a distal probe tip  224  to a proximal probe end  226 . The probe  220  includes a navigation element  228  that is operatively associated with a navigation system to track the position of the probe  220  and convey this information to the surgeon during the course of surgery. 
     The navigation element  228  may comprise, for example, an optical array (e.g. three or more lights or reflectors in a predetermined physical pattern) that provides a three-dimensional registration of the position of the probe tip  224  when viewed by a corresponding navigation camera system. Such an array may be mounted to the proximal probe end  226  or elsewhere where it can be viewed by the navigation cameras. The need for a line-of-sight between the optical array and the cameras is likely to require the navigation element  228  to be positioned outside the introducer  200 . Alternatively, the navigation element  228  may comprise a magnetic element that can be tracked by a corresponding magnetic tracking system. In this case, it may not be necessary to position the navigation element  228  outside the introducer  200 . Other alternatives of navigation elements  228  will be apparent to persons of ordinary skill in the art in view of the present disclosure. Examples of navigation probes  220  and corresponding tracking systems are provided by Stryker Navigation of Kalamazoo, Mich., U.S.A.; Brainlab AG of Feldkirchen, Germany; Synaptive Medical of Toronto, Ontario; and Medtronic of Minneapolis, Minn., U.S.A. 
     The introducer passage  210  is significantly larger in the lateral direction (i.e., perpendicular to the longitudinal axis  212 ) than the probe shaft  222 . This may allow the surgeon to visualize down the length of the passage  210  without her vision being unduly obstructed by the probe  220 . This also may allow the surgeon to insert other instruments such as an endoscope or aspiration tube into the passage  210  while the probe  220  remains in place, and so on. As a consequence of their disparate relative sizes, the sidewall  204  does not hold the navigation probe shaft  222  against lateral movement within the passage  210 . It expected that some lateral movement of the probe shaft  222  within the passage  210  will not critically affect proper navigation, but it is believed to be more important to assure continuous proper registration between the distal probe tip  224  and a fixed location at the distal introducer end  208 . For example, maintaining the probe tip  224  with little or no deviation from the geometric center of the introducer profile at the distal introducer end  208  is expected to provide sufficient registration for accurate navigation, even if the proximal end of the shaft  222  might move laterally within the passage  210 . 
     In the embodiment of  FIGS. 2A and 2B , the probe tip  224  is maintained in registration with the distal introducer end  208  by a probe receptacle  230 . The probe receptacle  230  preferably is located at the geometric center of the introducer profile at the distal introducer end  208  (e.g., the geometric center of the ellipse if the distal introducer end  208  is elliptical), but this is not strictly required in all embodiments. For example, the receptacle  230  may be offset from the introducer&#39;s central axis. 
     The probe receptacle  230 , in this embodiment, comprises a generally circular receptacle wall  232  having an inner surface  236  that extends within the passage  210  from a distal receptacle end  240  to a proximal receptacle end  234 . The inner surface  236  tapers from a relatively large diameter at the proximal receptacle end  234  to a relatively small diameter at a distal receptacle end  240 . The distal receptacle end may be located at or near the distal introducer tip  208 . The receptacle wall  232  is sized to restrict the distal probe tip  224  from moving laterally beyond a predefined range of movement. For example, the receptacle wall  232  may restrict movement of the probe tip  224  to a range of less than 1 millimeter (“mm”) in the lateral direction, or more preferably it may be sized to restrict any movement in the lateral direction. 
     The diameter of the proximal receptacle end  234  may have any size, but preferably is not so large as to significantly obstruct vision through the introducer  200 , and not so small that it is overly difficult to position the probe tip  224  within the receptacle  230  during surgery. The receptacle wall&#39;s tapered surface  236  helps guide the probe tip  224  to the proper location within the receptacle  230 , and the surface  236  may have a conical or curved profile as viewed from the lateral direction. The surface  236  also may have a region with a shape specifically selected to match the shape of the probe tip  224 . For example, if the probe tip  224  is hemispherical, all or a portion of the surface  236  may have a matching shape. As another example, if the probe tip  224  is cylindrical (or has a hemispherical tip with a cylindrical body immediately adjacent the tip), a distal portion of the surface  236  may have a matching cylindrical shape. Other alternatives will be apparent to persons of ordinary skill in the art in view of the present disclosure. 
     The receptacle wall  232  also may be shaped and sized to hold the probe tip  224  in close proximity to the distal introducer end  208 . For example the distance from the distal introducer end  208  to the probe tip, as measured along the longitudinal axis  212 , preferably is less than 5.0 mm, and more preferably less than 1.0 mm, and most preferably 0.5 mm or less. Where the probe tip  224  is at 1.0 mm or less from the distal introducer end  208  it may not be necessary to attempt to correct for this amount of displacement for purposes of navigating into the brain tissue, as this is expected to be within the normal amount of deviation of brain tissue movement within the skull. It is preferred, but not strictly required, that the probe tip  224  does not protrude beyond the distal introducer end  208 . 
     The introducer tip opening  216  (if one is provided) may be located within the probe receptacle  230  at the end of the receptacle wall  232 , such as shown in  FIG. 2B . Alternatively, the introducer tip opening  216  may be located elsewhere in the distal introducer end  208  at a location outside the receptacle  230 . The probe receptacle  230  also may include one or more openings forming flow passages  238  to allow fluid to bypass the receptacle wall  232 ; this feature can help ensure proper drainage of fluids that might otherwise accumulate at the distal end of the passage  210  at locations between the proximal receptacle end  234  and the sidewall  204 . More specifically, a gap  242  may be provided between an outer wall  244  of the probe receptacle  230  and the introducer sidewall  204 , and fluid may accumulate in this gap  242  under some circumstances. The flow passages  238  are provided to allow fluid to exit the gap  242 . 
     In use, the surgeon assembles the introducer  200  and retractor  202  together, places the probe tip  224  into the receptacle  230 , and uses computer-aided navigation provided by the probe  220  to guide the assembly to the surgery site. During navigation, the probe  220  indicates the position of the distal introducer end  208  relative to the underlying tissue via a computer screen overlay of a representation of the probe and a representation of the tissue. Throughout the process, the surgeon preferably can inspect the tissue through transparent walls of the introducer  200  and retractor  202 , and can periodically remove the probe  220  as necessary to obtain a better visual image or to perform intermediate procedures such as suctioning fluid and the like. 
       FIGS. 3A and 3B  illustrate another embodiment of an introducer  300 . For simplicity, only the portion of the introducer  300  located near the distal introducer end  302  is shown in these illustrations, and it will be understood that other features of the introducer  300  such as the remainder of the internal passage and other features described previously herein will be connected to the illustrated portion. In this embodiment, introducer  300  has a probe receptacle  304  that is suspended within the introducer  300  by a number of supports  306 . 
     The probe receptacle  304  may be located on the introducer&#39;s centerline, which is parallel to the introducer&#39;s longitudinal axis  308 , but other locations are possible. The probe receptacle  304  preferably comprises a receptacle wall  310  (which is circular, but can have other shapes) that extends from a proximal receptacle end  312  to a distal receptacle end  314 . The receptacle wall  310  has an inner surface  316  that tapers from a relatively large size at the proximal receptacle end  312  to a relatively small size at the distal receptacle end  314 . The inner surface  316  is sized and shaped to retain the distal probe tip  224  to prevent the probe tip  224  from moving laterally. For example,  FIG. 3B  shows the probe tip  224  at a position shortly before it fully seats in the probe receptacle  304 , to more clearly show that the tapered inner surface  316  transitions from a linearly tapering proximal surface portion  318  to a distal surface portion  320  that is shaped to match the hemispherical shape of the probe tip  224 . When fully seated, the probe tip  224  abuts the distal surface portion  320  in something like a ball-and-socket arrangement, with the semi-hemispherical surface of the distal surface portion  320  cupping and closely conforming to the hemispherical probe tip  224 . In other embodiments, the inner surface  316  may have other shapes to accommodate different shapes and sizes of probe tip  224 . For example, a simple conical shape can accommodate different probes having various tip diameters. 
     The supports  306  are formed as planar ribs that radiate outward from the introducer&#39;s centerline, and extend in parallel with the longitudinal axis  308 . In alternative embodiments, the supports  306  may be replaced by other shapes, such as blocks, pillars, and so on. 
     The probe receptacle  304  may be positioned adjacent to an introducer tip opening  322  that passes through the distal introducer end  302 . The introducer tip opening  322  and probe receptacle  304  are positioned such that fluid located in a gap  328  between the probe receptacle&#39;s outer wall  330  and the sidewall  204  can pass through the introducer tip opening  322  without passing through the probe receptacle  304 . Thus, fluid can flow through the introducer tip opening  322  even when the probe tip  224  is installed within the probe receptacle  304 . The probe receptacle  304  also may include a distal receptacle opening  324  passing thorough the distal receptacle end  314 , which provides an additional flow path when the probe is not installed in the probe receptacle  304  and prevents fluid from pooling in the probe receptacle  304 . 
     In the illustrated embodiment, the distal receptacle end  314  extends into the introducer tip opening  322 , such that it lies at or near the plane of the distal introducer end  302 . Thus, the introducer tip opening  322  is formed as an annular passage that surrounds the probe receptacle  304 , and the supports  306  bridge the gap between the distal introducer end  302  and the probe receptacle  304 . The supports  306  may include arched voids  326  to help reduce any disruption in the flow through the introducer tip opening  322  that the supports  306  might otherwise cause. 
     The placement of the distal receptacle end  314  within the introducer tip opening  322  can place the probe tip  224  as close as possible to the distal introducer end  302 . This simplifies the registration between the probe  220  and the introducer  300  because there is very little offset between their distal ends. However, this arrangement is not required in all embodiments. For example, the probe receptacle  304  may be moved further in the proximal direction (i.e., back into the introducer passage) to allow more fluid flow capacity through the introducer tip opening  322 , to make the introducer tip opening  322  smaller, and for other reasons. If the offset between the probe tip  224  and the distal introducer end  302  is significant, the computer system associated with the probe  220  can be programmed to account for this offset when indicating the position of the introducer  300  to the surgeon, as known in the art. 
     The receptacle  304  is preferably positioned and sized such that at least a portion of the introducer sidewall  204  at the distal introducer end  302  is visible to the surgeon while the probe tip  224  is installed in the receptacle  304 . For example, a pair of transparent faces  332  of the sidewall  204  (which may be flat as shown or curved) may be visible around the receptacle  304  and probe  220 . The surgeon can visually inspect the underlying tissue even while the probe  220  is in place, and can move the probe shaft  222  around within the passage  210  to alter her view without displacing the probe tip  224  from the receptacle  304 . 
       FIGS. 4A and 4B  illustrate another embodiment of an introducer  400 . As with  FIGS. 3A and 3B , only the region of the introducer  400  adjacent the distal introducer end  402  is shown. It will be understood that other features of the introducer  400  such as the remainder of the internal passage and other features described previously herein will be connected to the illustrated portion. In this embodiment, the introducer  400  has a probe receptacle  404  that includes a portion that is suspended within the introducer  400  by a number of supports  406 . The probe receptacle  404  may be located on the introducer&#39;s centerline, which is parallel to the introducer&#39;s longitudinal axis  408 , but other locations are possible. 
     The probe receptacle  404  preferably comprises a receptacle wall  410  (which is circular, but can have other shapes) that extends from a proximal receptacle end  412  to a distal receptacle end  414 . The receptacle wall  410  has an inner surface  416  that tapers from a relatively large size at the proximal receptacle end  412  to a relatively small size at a the distal receptacle end  414 . The inner surface  416  is sized and shaped to retain the distal probe tip  224  to prevent the probe tip  224  from moving laterally when the probe tip  224  is fully seated in the probe receptacle  404 . The inner surface  416  may be similar in construction to the probe receptacle  304  described in relation to  FIGS. 3A and 38 , or have other shapes configured to retain the probe tip  224 . For example, the inner surface  416  may comprise a proximal portion adjacent the proximal receptacle end  412  having a first angle θ 1  relative to the longitudinal axis  408  in the range of 20°-30° (e.g., 25°), an intermediate portion located distally from the upper portion having a second angle θ 2  relative to the longitudinal axis  408  in the range of 5°-15° degrees (e.g., 10°), and a distal portion located distally from the intermediate portion having a hemispherical or semi-hemispherical shape having a radius r in the range of 0.3-0.8 mm. This arrangement is expected to provide simple and repeatable installation of the probe tip  224  into the receptacle  404 , and provide a distinct feel to indicate when the probe tip  224  is fully seated. 
     The probe receptacle  404  is positioned adjacent to an introducer tip opening  418  that passes through the distal introducer end  402 . The introducer tip opening  418  and probe receptacle  404  are positioned such that fluid can pass through the introducer tip opening  418  without passing through the proximal receptacle end  412 . This allows fluid located in a gap  426  between the probe receptacle&#39;s outer wall  428  and the introducer sidewall  204  to flow through the introducer tip opening  418  when the probe tip  224  is installed within the probe receptacle  404 . In the shown embodiment, the outer wall  428  is shown being spaced from the sidewall  204  around its entire perimeter, but it will be appreciated that the outer wall  428  may merge with the sidewall  204  at some locations (such as when the introducer profile is a narrow ellipse or oval, and the receptacle  404  has a circular profile). 
     The probe receptacle  404  also may include a distal receptacle opening  420  passing thorough the distal receptacle end  414 , to provide an additional flow path when the probe is not installed in the probe receptacle  404 , and prevent fluid from pooling in the probe receptacle  404 . The distal receptacle end  414  may extend into the introducer tip opening  418 , such that it lies at or near the plane of the distal introducer end  402 . In this case, the introducer tip opening  418  may be formed as an annular passage that surrounds the probe receptacle  404  with the supports  406  bridging the gap between the distal introducer end  402  and the probe receptacle  404 . The supports  406  may include arched voids to help reduce any disruption in the flow through the introducer tip opening  418  that the supports  406  might otherwise cause. As with the embodiment of  FIGS. 3A and 3B , locating the distal receptacle end  414  within the introducer tip opening  418  can place the probe tip  224  as close as possible to the distal introducer end  402 . However, this arrangement is not required in all embodiments. 
     In this embodiment, the proximal receptacle end  412  is larger in the lateral direction (i.e., perpendicular to the longitudinal axis  408 ) than the introducer tip opening  418 . This provides a relatively large probe receptacle  404  to help guide the probe  220  into place, while keeping the size of the introducer tip opening  418  relatively small to help prevent the possibility of brain tissue or other delicate tissue being damaged by being forced into or cut by the edges of the introducer tip opening  418 .  FIG. 4B  shows how this configuration helps guide the probe tip  224  into the probe receptacle  404 , even when it starts at a location that is significantly offset from the probe receptacle&#39;s centerline (which, in this example, is collinear with the geometric center of the introducer  400 ). 
     Where the proximal receptacle end  412  is larger than the introducer tip opening  418 , it may be particularly favorable to provide additional provisions for assuring suitable flow through the introducer tip opening  418 . To this end, the probe receptacle  404  may include one or more (preferably three) openings at a location between the proximal receptacle end  412  and the distal receptacle end  414  to allow fluid to flow to the introducer tip opening  418  without passing through the proximal receptacle end  412 . Such openings may be, for example, slots  422  extending inward from the outer surface of the probe receptacle  404  to the introducer tip opening  418 . These slots  422  allow fluid to drain from the most distal parts of the introducer passage to prevent pooling around the outer perimeter of the probe receptacle  404  at the distal end of the introducer. The slots  422  in the shown embodiment extend in the longitudinal direction from the proximal receptacle end  412  to a portion of the sidewall  204  located adjacent the distal receptacle end  414 , but other embodiments may have slots having different lengths in the longitudinal direction. 
     Each slot  422  may terminate at its inner end at an annular passage  424  that overlies the introducer tip opening  418 . The annular passage  424  passes through the inner surface  416  of the receptacle  424  and extends to the introducer tip opening  418 , and is expected to help redistribute fluids passing through the introducer tip opening  418  into a more uniform and less restricted flow. The supports  406  bridge and interrupt the annular passage  424  to join the proximal receptacle end  412  to the distal receptacle end  414  and to suspend the distal receptacle end  414  at the introducer tip opening  418 . The slots  422  and annular passage  424  are sized to prevent the probe tip  224  from entering them (e.g., by having a 0.5 mm maximum width if the smallest probe tip  224  to be used is 0.8 mm or larger). 
     As with the other embodiments, the receptacle  404  is preferably positioned and sized such that a transparent portion of the introducer sidewall  204  at the distal introducer end  402  is visible to the surgeon while the probe tip  224  is installed in the receptacle  404 , to allow visualization of the underlying tissue while the probe  220  is in place. 
       FIGS. 5A through 5D  illustrate another embodiment of an introducer  500 , of which only the region of the introducer  500  adjacent the distal introducer end  502  is shown. As with the previous embodiments, it will be understood that other features of the introducer  500  will be connected to the illustrated portion. In this embodiment, the introducer  500  has a probe receptacle  504  having primary supports  506  joining a proximal receptacle end  508  to a distal receptacle end  510 . The distal receptacle end  510  is adjacent (and preferably within) an introducer tip opening  512 . The proximal receptacle end  508  is larger, in a direction perpendicular to the longitudinal axis  514  of the introducer  500 , than the introducer tip opening  512 . The structure of this probe receptacle  504  is similar to the one illustrated in  FIGS. 4A and 4B , and can include the same variations and features (e.g., a distal receptacle opening, etc.). The description of  FIGS. 4A and 4B  applies equally to the embodiment of  FIGS. 5A-5D . 
     The embodiment of  FIGS. 5A-5D  differs from  FIGS. 4A and 4B  in that secondary supports  516  joining the proximal receptacle end  508  to the distal receptacle end  510  are provided on either side of each slot  518 . The secondary supports  516  preferably have larger voids at their distal ends to provide a more continuous flow passage adjacent the introducer tip opening  512 . For example, the primary supports  506  may be connected to the distal receptacle end  510  by ribs  520  having a lower end located within or near the introducer tip opening  512 , while the secondary supports  516  are connected to the distal receptacle end  510  by ribs  522  that are spaced above the introducer tip opening  512 , such as best shown in  FIG. 5C . This arrangement provides additional structures to support the distal receptacle end  510  and to prevent a surgeon from lodging the probe tip  224  in the slots  518  or the gaps between the proximal receptacle end  508  and the distal receptacle end  510 , while still providing an annular passage  524  ( FIG. 5B ) (which may be interrupted at some locations by the primary support ribs  520 ) at the introducer tip opening  512  to allow relatively free flow therethrough. Openings  526 , located between the secondary supports  516  and primary supports  506 , provide flow passages that pass through the inner surface of the probe receptacle  504  and extend along the longitudinal axis  514  to the introducer tip opening  512 , to allow vertical fluid flow at various locations. As with the previous embodiments, fluid located in a gap  528  between the probe receptacle&#39;s outer wall  530  and the introducer sidewall  204  can flow through the introduced tip opening  512  without having to pass through the proximal introducer end  508 , which helps reduce any flow restriction that might be caused by the probe tip  224 . 
     It is also contemplated that the primary supports  506  may be constructed like the shown secondary supports  516  (i.e., with high arched ribs  522  joining to the distal receptacle end  510 ). However, the lower ribs of the primary supports  506  such as shown in  FIGS. 5A-5D  may be helpful to add strength and to prevent tissue from entering the introducer tip opening  512 . Alternatively, the secondary supports  516  can be structurally identical to the primary supports  506 , if it is found that the added support is desirable and the restriction to flow through the introducer tip opening  512  is not unduly compromised. Other alternatives will be apparent to persons of ordinary skill in the art in view of the present disclosure. 
     The probe receptacle of any given embodiment may have any suitable shape to fit any desired navigation probe. The probe receptacle may be configured to fit one particular kind of probe, or it may be configured to retain a number of different navigation probes. For example, a probe receptacle as described above with reference to  FIGS. 2A-5D  may be configured to interchangeably receive any one of four or more different probes such illustrated in  FIGS. 6A to 6D . A first probe  600  has a tip diameter D of 1.0 mm and a taper angle θ of approximately 6.0°. A second probe  602  has a tip diameter D of 0.8 mm and a taper angle θ of approximately 7.5°. A third probe  604  has a tip diameter D of 1.0 mm and a taper angle θ of approximately 18.0°. A fourth probe  606  has a tip diameter D of 1.0 mm and a 1.0 mm diameter cylindrical shaft  608  extending proximally from the tip. Each of these probes can be inserted with the probe tip seated at the distal end of the receptacle, within 1.0 mm and more preferably within 0.5 mm of the distal introducer end, to hold probe tip against lateral movement. 
     The receptacle may be formed such that it is not likely for the surgeon to “wedge” the probe tip in place, as this may cause difficulty with removing the probe. To this end, it is preferred for the taper angle of the receptacle&#39;s inner wall to not exactly match the taper angle of any particular probe tip in such a way to lock the two parts together. It is also preferred for the material of the receptacle to be relatively hard to prevent it from deforming to allow the probe tip to become lodged therein. Polycarbonate plastic is expected to be suitable for this purpose, but other materials may be used. Of course, a surgeon applying a very large force on the probe might lodge it in the receptacle regardless of how the receptacle is designed, so it will be understood that these preferences are predicated on normal use of the instrument and are not intended to set strict requirements for all embodiments under all circumstances. 
     Alternatively, the receptacle may be deliberately formed to tend to capture the probe tip in place. For example, the probe tip may include an enlarged end that snaps into a corresponding shape within the receptacle such that a force is required to remove the probe, or the receptacle may include thin deformable ribs that tend to grip the tip of the probe. This may require more care when removing the probe, but add the benefit of not requiring the surgeon to handhold the probe at all times. 
     The foregoing embodiments are expected to help surgeons use introducer and retractor systems with navigation systems. It is expected that surgeons will use the device by assembling the introducer with a retractor, placing the navigation probe in the introducer until the tip of the probe reaches the end of the probe receptacle, and then advancing the three parts forward into the tissue as a unit. During the process, the surgeon can remove the probe to get a better view into the introducer or to insert other instruments or devices into the introducer. If desired, a clamp or other device may be provided to hold the probe in place to free up the surgeon&#39;s hands for other tasks. Examples of clamps are disclosed in the incorporated references, but other mechanisms may be used. Other uses and methods will be apparent to those of ordinary skill in the art in view of this disclosure. 
     The introducer tip opening may add significant benefits to the system, such as by allowing fluids to ventilate to prevent an excessive accumulation of pressure around the introducer, allowing removal of fluids, and if the opening is large enough allowing resection or manual movement of tissue adjacent the opening. The tip opening also may allow air to vent towards the tissue as the introducer is withdrawn from the retractor after the assembly is placed at the surgery site, which can help prevent the introducer from generating suction that pulls on the tissue as the introducer is withdrawn. Other benefits will be apparent in view of the this disclosure and with further use of the system. 
     While it is expected that the foregoing embodiments can be used “freehand” by simply placing the probe tip  224  into the probe receptacle, in some cases a surgeon may wish to lock the probe  220  in place within the introducer  200 . This may be accomplished by using a retaining mechanism, such as the exemplary probe retainer  700  shown in  FIGS. 7A-8B . 
     The probe retainer  700  comprises a receiver  702  that is affixed to the introducer  200  by a pair of clamps  704 . The receiver  702  includes a channel  706  sized to receive a probe  220 . The channel  706  preferably is a closed passage having a diameter suitable to accommodate a probe  220 , but it may include a longitudinal slot or have a “C” or “U” shaped profile, or the like, in other embodiments. The channel  706  has a proximal channel end  708  facing towards the surgeon, and a distal channel end  710  that extends into the introducer  200 . When the probe shaft  222  is located in the channel  706 , the channel  706  limits and may completely restrict movement of the probe shaft  222  in the lateral direction. 
     The receiver  702  may be configured to selectively lock the probe  220  in place within the channel  706 . For example, the proximal channel end  708  may have a threaded outer surface  712  that is configured to engage a corresponding lock nut  714 , and one or more cutout sections  716  passing through the proximal channel end  708 . The threaded outer surface  712  and lock nut  714  are configured such that the lock nut  714  compresses the threaded outer surface  712  as it is tightened onto the threaded outer surface  712 , such as by providing one or both with a slight taper or making the lock nut&#39;s threads slightly smaller in diameter than the threads on the outer threaded surface  712 . The cutout sections  716  provide reliefs to allow the threaded surface  712  to move inwards as the lock nut  714  is tightened. Thus, as the lock nut  714  is tightened on the threaded outer surface  712 , the threaded outer surface  712  moves radially inwards, and an inner surface  718  of the proximal channel end  708  clamps against and secures the probe  220  in place. The receiver  702  also may include one or more retaining lips  720  to prevent the lock nut  714  from being fully removed from the receiver  702 . 
     Other locking mechanisms may be used in other embodiments. For example, the lock nut  714  may be replaced by a band clamp, a set screw, or other devices. Examples of alternative locks are provided in the incorporated references, and other options will be apparent to the person of ordinary skill in the art in view of this disclosure. 
     In the shown embodiment, the receiver  702  may include a number of slots  722  (e.g., three slots) that extend proximally from the distal channel end  710 . The exemplary slots  722  extend longitudinally along the longitudinal axis  212  of the assembly, but other orientations may be used (e.g. helical). The inner surface of the channel  706  is also may be gently tapered such that the diameter of the channel  706  decreases as it approaches the distal channel end  710 . The final diameter of the channel  706  at the distal channel end  710  may be slightly less than the largest diameter probe  220  expected to be used with the device, such that the probe  220  is slightly compressed by the receiver  702  at the distal channel end  710 . The slots  722  allow the channel  706  to flex outwards at the distal channel end  710  to accommodate probes  220  of different sizes. This feature is expected to provide a useful slight retaining force, and may help center the probe  220  within the channel  706 . 
     The receiver also may be configured to direct the distal probe tip  224  towards a receptacle (e.g., receptacle  230 ,  304 ,  404  or  504 ) as the probe  220  is installed into the introducer  200 . The foregoing tapered and slotted arrangement is expected to accomplish this by orienting the channel  706  towards a corresponding receptacle at the distal introducer tip, but other embodiments may use other configurations to do the same thing. Preferably, the channel  706  extends in the longitudinal direction, so that it prevents significant angulation of the probe  220  within the channel  706  (i.e., it prevents angulation that could prevent the distal probe tip  224  from entering the receptacle). For example, the channel  706  may have an inner diameter that is no more than 110% of the largest probe diameter, and a length that is at least 300% and more preferably at least 1000% of the largest probe diameter. 
     Despite the foregoing, in other embodiments the channel  706  may comprise a simple ring or passage that is not tapered and does not include slots, or the taper and slots may be replaced by a flexible diaphragm or cantilevered arms that help center the probe  220  within the channel  706 . Other alternatives will be apparent to persons of ordinary skill in the art in view of the present disclosure. 
     The clamps  704  are attached to the receiver  702 , and configured to hold the receiver  702  at a fixed location relative to the introducer  200 . The receiver  702  may be centered on the introducer  200 , such as shown, or it may be offset from the introducer&#39;s centerline. In this embodiment, the clamps  704  are connected to the receiver  702  by clamp arms  724  that are shaped to generally match the shape of the introducer sidewall  204  at the proximal introducer end  206 . Thus, each clamp arm  724  has an opening  726  through which the surgeon can view into the introducer passage  210 . 
     Each clamp  704  comprises a tab  728  that is shaped to receive a user&#39;s finger, and a hook  730  that is shaped to wrap around a corresponding lip  800  ( FIGS. 8A-B ) on the introducer. The clamp arms  724  are located between the tab  728  and the hook  730 . The clamp arms  724  and hooks  730  are movable between a latched position in which the hooks  730  are relatively close to one another, and an unlatched position in which the hooks  730  are relatively far from one another. In their latched position, the hooks  730  are spaced by a first distance at which they wrap around the corresponding lips  800  to secure the probe retainer  700  to the introducer  200 . The hook spacing in the latched position may be slightly greater than their natural resting position when not attached to an introducer  200 . Thus, when attached to the introducer  200 , the clamp arms  724  may be under a slight bending force caused by flexing the hooks  730  from their resting position to their latched position. This can help provide a stronger locking connection, and may reduce the likelihood of shifting or moving when connected. 
     When the surgeon pinches the tabs  728  together, the clamp arms  724  flex and provide a fulcrum about which the hooks  730  rotate until they are located at a second distance from one another. In this position, the hooks  730  release the lips  800  and the probe retainer  70  can be removed from the introducer. The clamps  704  may be reinstalled onto the introducer  200  by reversing this operation, and the hooks  730  may include ramped surfaces to allow them to be snapped onto the lips  800  simply by pressing the probe retainer  700  against the proximal introducer end  206 . 
     In the exemplary embodiment, there are two clamp arms  724 , each of which has two spaced portions that surround an opening  726  to allow visualization into the introducer  200 . Each clamp arm  724  is connected to the receiver  702  at two locations on opposite sides of the receiver  702 . The attachments between the receiver  702  and the clamp arms  724  may have buttresses  732  to increase the rigidity of the connection. This is expected to help the clamp arms  724  flex in a more predictable manner during the detachment and installation process. 
     The foregoing clamp  704  arrangement is expected to provide simple and reliable engagement to selectively connect the probe retainer  700  to the introducer  200 . However, other embodiments may use different structures to hold the probe in place. For example, the flexible clamp arms  724  may be replaced by more rigid members having a mechanical pivot such as a pivot pin or the like and a return spring to bias the hooks  730  to the clamped position. As another example, each clamp arm  724  may have a single portion located on one side of the introducer  200 , rather than two spaced portions, and the clamps  704  may be turned 90° relative to the shown position such that the grip the introducer  200  from the side rather than from the top. Other alternatives will be apparent to persons of ordinary skill in the art in view of the present disclosure. 
       FIGS. 8A and 8B  show the embodiment of  FIGS. 7A-B  as it appears when installed on an exemplary introducer  200 . The introducer  200  is shown assembled with a corresponding retractor  202 . The introducer  200  preferably includes a probe tip receptacle such as those described previously herein, but it is also envisioned that the probe retainer  700  may be used with introducers that do not have a probe tip receptacle, such as those discussed with reference to  FIG. 1 . The assembly of the probe retainer  700  and navigation probe  220  preferably can be removed from or installed into the introducer  200  without separating the introducer  200  from the retractor  202 . This provides rapid access to the introducer interior, if necessary. 
     It will be appreciated that the foregoing embodiments may be modified in various ways. As one example, features disclosed in one embodiment may be used with any of the other embodiments. As another example, the probe receptacles described herein can be formed integrally with the introducer by additive manufacturing or molding (the illustrated embodiments show various configurations in which conventional two-part injection molding processes may be used to make the introducer and probe receptacle as a single integrally molded part), or formed separately and attached to the introducer. As another example, the probe receptacle may have any sidewall profile shape, rather than the generally circular shapes shown in the embodiments. The probe receptacles also may have any combination of conical, cylindrical, hemispherical, or other shapes. It is also envisioned that the probe receptacle may have openings such as the flow passages of  FIG. 26  and slots of the later embodiments, even when the introducer does not have an introducer tip opening, which can be beneficial to displace fluid from the receptacle to allow free entry of the probe tip. Other alternatives will be apparent to persons of ordinary skill in the art in view of the present disclosure. 
     The present disclosure describes a number of new, useful and nonobvious features and/or combinations of features that may be used alone or together. The embodiments described herein are all exemplary, and are not intended to limit the scope of the inventions. It will be appreciated that the inventions described herein can be modified and adapted in various and equivalent ways, and all such modifications and adaptations are intended to be included in the scope of this disclosure and the appended claims.