Abstract:
An OCT probe for imaging patient tissue may include an actuation system arranged to displace an optical fiber within a cannula. The actuation system may include a driver actuatable to displace a portion of the optical fiber, with the driver acting in an angled direction relative to the axis of the cannula. The actuation system also may include a pivot feature operably engaged with the optical fiber in a manner permitting the optical fiber to pivot on the pivot feature when the driver actuates to displace the portion of the optical fiber.

Description:
CROSS-REFERENCED TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/878,311, filed Sep. 16, 2013, the entire contents of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to apparatuses and methods for scanning tissue with an OCT probe, and more particularly, to apparatus and methods that have a pivoting optical fiber. 
     BACKGROUND 
     Optical Coherence Tomography (OCT) systems are used to capture and generate three-dimensional images of patient tissue layers. These systems include OCT probes that often invasively penetrate tissue to obtain visualization of tissue within a patient. In ophthalmology, OCT probes are used to obtain detailed images of tissue about the eye or even forming a part of the eye, such as the retina. 
     In use, an optical light beam is directed through the probe at the tissue. A small portion of this light reflects from sub-surface features of the tissue and is collected through the same probe. Most light is not reflected but, rather, diffusely scatters at large angles. In conventional imaging, this diffusely scattered light contributes to background that obscures an image. However, in OCT, a technique called interferometry records the optical path length of received photons, and provides data that rejects most photons that scatter multiple times before detection. This results in images that are more clear and that extend in the depth of the tissue. 
     SUMMARY 
     In an exemplary aspect, the present disclosure is directed to an OCT probe for imaging patient tissue. The OCT probe may include a cannula having a cannula axis. It may also have a selectively displaceable light-carrying optical fiber disposed within the cannula and having a distal end. The optical fiber may be arranged to emit light from the distal end. An actuation system may be arranged to displace the optical fiber within the cannula. The actuation system may include a driver actuatable to displace a portion of the optical fiber, the driver acting in an angled direction relative to the axis of the cannula. The actuation system also may include a pivot feature operably engaged with the optical fiber. The optical fiber may be pivotable about the pivot feature in response to a displacement of the portion of the optical fiber by the driver. 
     In an aspect, a stiffening tube may be disposed about the optical fiber and separating the optical fiber and the pivot feature. The stiffening tube may directly engage the pivot feature in a pivot relationship. In an aspect, the stiffening tube extends from at least the pivot feature to the driver. In an aspect, the OCT probe may include a constraining feature disposed in the cannula. The constraining feature may be shaped to constrain displacement of the optical fiber to a particular range of motion. In an aspect, the particular range of motion is a plane. In an aspect, the constraining feature is a localized constriction permitting a higher amount of cross-lateral displacement and a relatively lower amount of lateral displacement. 
     In an aspect, the pivot feature is a crimp in the cannula. In an aspect, the pivot feature is an insert disposed in the cannula. In an aspect, the pivot feature is disposed at a location proximal of the cannula. In an aspect, the driver is disposed at a side of the optical fiber and arranged to displace the portion of the optical fiber in a direction orthogonal to the axis of the cannula. 
     In an aspect, the OCT probe may include a probe housing, the cannula extending from the probe housing and the driver being disposed in the probe housing. In an aspect, wherein the driver is spaced from the pivot feature along the optical fiber by a first distance, and wherein the distal end of the optical fiber is spaced from the pivot feature by a second distance greater than the first distance. 
     In another exemplary aspect, the present disclosure is directed to an OCT probe for imaging patient tissue. The OCT probe may include a cannula adapted to penetrate patient tissue and having a cannula axis, and may include a selectively displaceable light-carrying optical fiber disposed within the cannula and having a distal end. The optical fiber may be adapted to emit light from the distal end and out of the cannula. An actuation system may include a driver adapted to displace a portion of the optical fiber a first distance and to displace the distal end of the optical fiber a second distance greater than the first distance. 
     In an aspect, the actuation system includes a pivot feature that forms a fulcrum for the optical fiber. In an aspect, the driver is spaced from the pivot feature a first distance, and wherein the distal end of the optical fiber is spaced from the pivot feature a second distance, the second distance being greater than the first distance. In an aspect, the pivot feature is disposed between the driver and the distal end of the optical fiber. 
     In another exemplary aspect, the present disclosure is directed to a method of scanning with an OCT probe that includes emitting light from a distal end of an optical fiber in a cannula of the OCT probe, and actuating a driver to pivot the optical fiber about a pivot feature. The pivot feature may be disposed relative to the driver and relative to the distal end of the optical fiber to create a positive mechanical advantage that displaces the distal end of the optical fiber a distance greater than the actuation distance of the driver. 
     In an aspect, actuating a driver to pivot the optical fiber about a pivot feature includes actuating the driver in a direction orthogonal to an axis of the cannula. In an aspect, the pivot feature is one of a crimp in the cannula and an insert in the cannula. In an aspect, the pivot feature is disposed proximal of the cannula. In an aspect, the method also includes restricting lateral movement of the optical fiber with a constraining feature while actuating the driver to pivot the optical fiber about the pivot feature. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory in nature and are intended to provide an understanding of the present disclosure without limiting the scope of the present disclosure. In that regard, additional aspects, features, and advantages of the present disclosure will be apparent to one skilled in the art from the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings illustrate embodiments of the devices and methods disclosed herein and together with the description, serve to explain the principles of the present disclosure. 
         FIG. 1  is a block diagram of an exemplary OCT imaging system. 
         FIG. 2  is a cross-sectional view of an example OCT probe. 
         FIG. 3  is another cross-sectional view of the example OCT probe shown in  FIG. 2 . 
         FIG. 4  is a detail cross-sectional view of a portion of the example OCT probe shown in  FIG. 2  illustrating a pivot feature thereof. 
         FIG. 5  is a cross-sectional view of a portion of another example OCT probe illustrating a pivot feature thereof. 
         FIG. 6  is a cross-sectional view of a portion of another example OCT probe showing a pivot feature thereof. 
         FIG. 7  is a cross-sectional view of a of another example OCT probe. 
         FIG. 8  is a cross-sectional view of an example pivot feature taken along  8 - 8  in  FIG. 4 . 
         FIG. 9  is a cross-sectional view of an example constraining feature. 
         FIG. 10  is a cross-sectional view of an example pivot feature taken along  10 - 10  in  FIG. 5 . 
         FIG. 11  is a cross-sectional view of another example constraining feature. 
     
    
    
     DETAILED DESCRIPTION 
     For the purposes of promoting an understanding of the principles of the present disclosure, reference will now be made to the exemplary embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is intended. Any alterations and further modifications to the described devices, instruments, methods, and any further application of the principles of the present disclosure are fully contemplated as would normally occur to one skilled in the art to which the disclosure relates. In particular, it is fully contemplated that the features, components, and/or steps described with respect to one embodiment may be combined with the features, components, and/or steps described with respect to other embodiments of the present disclosure. For the sake of brevity, however, the numerous iterations of these combinations will not be described separately. For simplicity, in some instances the same reference numbers are used throughout the drawings to refer to the same or like parts. 
     The present disclosure relates generally to OCT probes, OCT systems, and methods that scan tissue to obtain an OCT image. The probe includes a light system including a lens and an optical fiber that directs light through the lens and captures reflected light that passes back through the lens. To obtain a scan of an area or a line, rather than merely a point, at least a portion of the light system moves relative to the tissue. 
     In an aspect described herein, the OCT probes, OCT systems, and methods disclosed herein utilize a pivoting technique to move an optical fiber within a long and narrow cannula to deflect light by laterally offsetting the light input to a lens, thereby causing the output beam to deflect angularly. The pivoting technique includes using the optical fiber as an extending lever arm to obtain a mechanical advantage. The movement of the light source relative to the tissue provides the scan, increasing the distance or area of the scanned tissue in order to create an image. 
       FIG. 1  shows an exemplary example of an OCT imaging system  100 . The system  100  includes a console  102 , a user interface  104 , and an OCT probe  106 . The console  102  includes an OCT engine including, among other elements, a light source  108  and a controller  110 . In some instances, the light source  108  is configured to provide near-infrared light. In other implementations, radiation having other frequencies may be used. Any defined bandwidth of light frequencies may be used with OCT. For many ophthalmic applications, near-infrared may be used. For example, radiation bandwidth frequencies of 700 to 900 nm with a center wavelength of 800 nm may be used in some ophthalmic applications. In other instances, a radiation wavelength band of 1250-1450 with a center wavelength of 1350 nm may be used. Still further, a radiation wavelength band of 1400-1600 with a center wavelength of 1500 nm may be used. Further, while examples provided herein may be described in the context of ophthalmic procedures, the scope of the application is not so limited. Rather, the concepts presented herein may also be used in other applications. For example, the concepts may be used in other medical procedures. Still further, the concepts described herein may be used in any other suitable area. Particularly, the concepts described may be used in areas outside of the medical arts. 
     The light may be directed toward and reflected and captured from the target biological tissue through the OCT probe  106 . In some embodiments, the light source  108  may include super-luminescent diodes, ultra-short pulsed lasers, or supercontinuum lasers that provide relative long wavelength light. The controller  110  may include a processor and memory that may include an executable program for operating the light source  108 , the user interface  104 , and the OCT probe  106 , and for executing and performing functions and processes to carry out an OCT imaging procedure. 
     In some embodiments, the user interface  104  is carried on or forms a part of the console  102 . The user interface  104  may be a display configured to present images to a user or a patient, and display tissue scanned by the probe  106  during an OCT imaging procedure. The user interface  104  also may include input devices or systems including, by way of non-limiting example, a keyboard, a mouse, a joystick, dials, and/or buttons, among other input devices. 
     The OCT probe  106  is sized and shaped to be handled by a user, such as a surgeon or other medical professional, and to protrude into a body of the patient. In the embodiment shown, the OCT probe  106  is in electrical and optical communication with the console  102  and configured to present light from the light source  108  onto patient tissue for the purpose of imaging the tissue. 
       FIGS. 2 and 3  show cross-sectional views of an exemplary OCT probe  106 . As will be described in greater detail below, the OCT probe  106  includes a mechanism for actuation of an optical fiber carrying light from the light source  108  in a manner that moves the optical fiber relative to a lens. Light from the optical fiber transmits through the lens. An angular scan is produced by moving the position of the light beam laterally with respect to the lens. 
     Referring to both  FIGS. 2 and 3 , the OCT probe  106  includes a probe housing  200 , a cannula  202 , a lighting system  204 , and an actuation system  206 . In some implementations, the cannula may be formed form a metal, a polymer, a composite material, or any other suitable or desired material. The probe housing  200  is configured to be grasped and manipulated by a user, such as during an OCT procedure. A portion of the housing  200  may form a handle or grip and may house components of the OCT probe  106 . The cannula  202  projects from a distal end  207  of the probe housing  200  and is configured and arranged to penetrate patient tissue in order to obtain an OCT image. The cannula  202  includes a distal end  208  and a proximal end  209 . The proximal end  209  of the cannula  202  is disposed within and supported by the probe housing  200 . In some embodiments, a lumen  216  of the cannula  202  receives a portion of the actuation system  206  and the lighting system  204  in the manner described below. In some instances, the cannula  202  may be sized to penetrate and be used within an eye and may be used to scan tissue of a patient. For example, in some instances, the cannula  202  may be utilized to scan eye tissue of a patient, such as retina tissue. The cannula  202  defines a central axis  203 . 
     The lighting system  204  includes a lens  210  and an optical fiber  214 . The lighting system  204  receives and transmits light from the light source  108 . In some implementations, the lens  210  may be a gradient index (GRIN) lens having flat surfaces through which light from the optical fiber  214  may pass. In some implementations, the gradient index may be spherical, axial, or radial. In other instances, the lens  210  may be a spherical lens. In still other instances, other lens shapes may be used. 
     The optical fiber  214  is configured to transmit light from the light source  108  to the lens  210 , and ultimately to the tissue under observation. In some instances, the optical fiber  214  may be a single optical fiber. In other instances, the optical fiber  214  may be a bundle of optical fibers. In some instances, the optical fiber  214  may be a continuous optical fiber extending from the light source  108  to distal end  218  of the optical fiber  214 . In other instances, the optical fiber  214  may be formed from two or more optical fibers extending from the light source  108 . Further, in still other implementations, the optical fiber  214  may receive light from the light source  108  from an optical fiber extending from the console  102  to the OTC probe  106 . 
     In some instances, a proximal end (not shown) of the optical fiber  214  may be disposed adjacent the light source  108 , while a distal end  218  may be disposed adjacent the lens  210  in a manner directing light through the lens  210 . As shown in  FIGS. 2 and 3 , the optical fiber  214  is not directly connected to the lens  210 , and the lens  210  is fixed in place relative to the cannula  202 . Accordingly, the optical fiber  214  may move relative to the cannula  202  and the lens  210 . The distal end  218  of the optical fiber  214  may be positioned a pre-determined distance from a proximal face  211  of the lens  210  to achieve prescribed optical working distance and focus spot size. 
     The actuation system  206  may be disposed primarily within the probe housing  200 . In this example, the actuation system  206  includes a driver  220 , a pivot feature  222 , and a stiffening tube  224 . The actuation system  206  is operable to move the optical fiber  214  of the lighting system  204  relative to the cannula  202  in order to provide either one or two dimensional directional scanning to create 2D or 3D images with the OCT imaging system  100 . 
     The driver  220  may be a microelectrical mechanical systems (MEMS) micrometer, a linear motor, a piezoelectric motor, an electro-magnetic motor, a pneumatic piston, diaphragms, electrical solenoid, or other such element. The driver  220  is configured to impart a force on the optical fiber  214  to physically displace the optical fiber  214  in as the directions indicated by the arrows  213 ,  215  associated with the driver  220  in  FIG. 2 . Because of the arrangement described below and providing a positive mechanical advantage, the driver  220  may be selected to have a stroke distance that is less than a desired displacement distance of the distal end  218  of the optical fiber  214 . In some embodiments, the driver  220  is electrically powered and is electrically connected to the console  102  by a power cable (not shown) extending from the OCT probe  106 . In other embodiments, the driver  220  is disposed in the probe housing  200  and is configured to be self-contained on the driver  220 . Accordingly, such embodiments may include a power source carried on the probe housing  200  that provides power to the driver  220  to physically displace the optical fiber  214  within the cannula  202 . For example, the power source may be in the form of a one or more batteries or other power sources. In some embodiments, the driver  220  is configured to displace the portion the optical fiber  214  in a back and forth direction by applying force or loading on opposing sides of the optical fiber  214 , to create a rocking effect about the pivot feature  222 . In other embodiments, the driver  220  is configured to displace the portion the optical fiber  214  in only a single direction by applying force of loading on one side of the optical fiber  214  or in one direction. A biasing member (not shown), such as a spring, may act on the opposing side to create a rocking effect about the pivot feature  222 . 
     In some instances, the pivot feature  222  may be a local constriction arranged to permit at least a portion of the lighting system  204  to pivot so that a portion of the lighting system  204  moves relative to the cannula  202 . The pivot feature  222  may be formed of any structure providing a pivot point that enables a portion of the lighting system  204  to move so as to provide one or two dimensional directional scanning. In the exemplary embodiment shown, the pivot feature  222  is one or more fulcrums cooperating to allow the optical fiber  214  to pivot as a lever. The pivot feature  222  may be a first and second fulcrum. As shown in  FIGS. 2 and 3 , the pivot feature  22  may be formed as a result of a crimp in the cannula  202  on at least one side of the optical fiber  214 . In other embodiments, the pivot feature  222  may be a component or element separate from the cannula  202 , or that may be inserted into the cannula  202  in order to function as the fulcrum. In some embodiments, the pivot feature  222  is a protruding body disposed about the optical fiber  214 , such as an O-ring or other body. In other embodiments, the pivot feature  222  is formed of a component disposed at the proximal end  209  of the cannula  202 , and the optical fiber  214  extends therethrough. In yet other embodiments, the pivot feature  222  may be in the form of an opening through one or more components of the OTC probe  106 . For example, the pivot feature  222  may be formed as an opening in the probe housing  200 . Yet other pivot features  222  are contemplated. 
     The stiffening tube  224  includes a hollow channel through which the optical fiber  214  extends. The stiffening tube  224  may be formed from metal, a polymer, a composite material, or any other suitable or desired material. The stiffening tube  224  may be formed of a rigid material in order to provide rigidity to the optical fiber  214  and, at the same time, provide a rigid interface that cooperates with the pivot feature  222 . Because of the rigid interface, the stiffening tube  224  may pivot about the fulcrum formed by the pivot feature  222  with minimal resistance, and therefore in response to a minimal force. This may help the driver  220  pivot the optical fiber  214  in an efficient manner with a minimal level of loading. In the embodiment shown, the stiffening tube  224  extends from a location just proximal of the driver  220  to a location just distal of the pivot feature  222 . However, in other embodiments, the stiffening tube  224  extends the length of the optical fiber  214  from adjacent the distal end  218  to a location adjacent or just proximal the driver  220 . The stiffening tube  224  may be disposed along or may extend along other lengths of the optical fiber  214 . 
     The actuation system  206  is configured to pivot the optical fiber  214  in a manner that causes the distal end  218  of the optical fiber to displace relative to the cannula  202 , and thereby move the optical fiber  214  in at least a single plane to perform a scan. Scanning allows light to be taken over an area of the tissue being evaluated, rather than a specific spot or point on the tissue. The scan is then converted into a 2D or 3D image by the OCT system  100  that may be evaluated by the health care provider. 
     The embodiment shown in  FIGS. 2 and 3  is arranged so that the actuation system  206  can produce movement of the optical fiber  214  for the scan with a low amount of input energy and with a minimal amount of driver displacement or driver stroke, enabling smaller cost-efficient drivers to be utilized. This is possible due to the actuation system  206  being disposed and arranged on the optical fiber  214  to provide a positive mechanical advantage. Here, the pivot feature  222  is disposed between the driver  220  and the distal end  218  of optical fiber  214 , dividing the optical fiber  214  into a length L 1  referenced herein as an actuation arm length, and a length L 2  referenced herein as a fiber arm length, as shown in  FIG. 3 . For a simple lever, the mechanical advantage MA may be determined using the equation:
 
MA=fiber arm length L2/actuation arm length L1
 
     In the example shown, since the fiber arm length L 2  is greater than the actuation arm length L 1 , the actuation system  206  is configured to provide a positive mechanical advantage, in that mechanical advantage MA is greater than the value 1. The practical effect is that a small displacement of the optical fiber  214  at the location of the driver  220  results in a larger displacement at the distal end  218  of the optical fiber  214 . By using an arrangement that provides a positive mechanical advantage MA, a minimal input may be used to provide a suitable displacement to carry out a scan procedure. In some embodiments, the actuation arm length L1 is within a range of about 2 mm to 12 mm, and the fiber arm length L 2  is a range of about 4 mm to 35 mm. Thus, in some instances, a mechanical advantage in the range of 2 to 12.5 may be provided. In some embodiments, the actuation arm length L 1  is about 8 mm, and the fiber arm length L 2  is about 25 mm. This provides a mechanical advantage MA in the range of about 3:1. However, in some embodiments, the actuation system  206  may be arranged to provide any positive mechanical advantage. Because of the mechanical advantage MA, displacement of the distal end  218  of the optical fiber  214  may be greater than the stroke at the driver  220 , enabling relatively small drivers to be employed to move the optical fiber. 
     For the example OCT probe  106  shown in  FIGS. 2 and 3 , the pivot feature  222  is disposed between the lens  210  and the driver  220 , with the driver  220  proximal of the pivot feature  222 . However, other arrangements are contemplated that provide a mechanical advantage. In some implementations, the driver  220  is disposed distal of the pivot feature  222 , between the pivot feature  222  and the distal end  218 . In such instances, the pivot feature  222  may still be arranged to provide a positive mechanical advantage. Other arrangements are also contemplated. 
       FIG. 3  shows the OCT probe  106  with the optical fiber  214  deflected from the central axis  203  of the cannula  202 . The optical fiber  214  is deflected about the fulcrum formed by the pivot feature  222 . As can be seen, a small deflection d 1  from the central axis at the driver  220  results in a larger deflection d 2  at the distal end  218  of the optical fiber  214 . Because a small deflection or stroke at the driver  220  may result in a larger scan or displacement of the distal end  118  of the optical fiber  214 , the driver  220  may be selected with a relatively small stroke or to displace the optical fiber  214  only a short distance, while still effecting the larger desired displacement of the distal end  218  of the optical fiber  214 . 
       FIG. 4  shows a portion of the OCT probe  106  with an enlarged pivot feature  222 , shown in cooperation with the optical fiber  214  and the stiffening tube  224 . In this example the pivot feature  222  is shown as a crimp  350  formed in a cannula  202  of the probe  106 . Here, the crimp  350  on opposing sides of the cannula allows the optical fiber  214  and the stiffening tube  224  to be maintained along a central axis through the cannula, providing a high range of pivot capability. A cross-sectional view of the crimp  350  as the pivot feature  222  is shown in  FIG. 8 , taken along  8 - 8  in  FIG. 4 . As can be seen, the crimp  350  is a local constriction in the cannula  202  that restricts or limits lateral displacement of the optical fiber  214  at the fulcrum, allowing the optical fiber  214  to pivot about the crimp  350 . 
       FIG. 5  shows a portion of the OCT probe  206  with an alternative pivot feature  222 , shown as an insert  360  in the cannula  202 . The insert  360  is arranged to fit into the cannula  202  and may be bonded or otherwise secured in place. The insert  360  includes a peak  362  that acts as a fulcrum in the manner described above. Here, the insert  360  is shown in cross-section and has a circular exterior cross-sectional shape configured to match or otherwise conform to an inner cross-sectional shape a lumen  364  of the cannula  202 , and includes tapered inner walls  366 ,  368  that converge to form the peak  362 . The peak  362  defines a pivot location for the optical fiber  214  and the stiffening tube  224 . A cross-sectional view of the insert  360  as the pivot feature  222  is shown in  FIG. 10 , taking along  10 - 10  in  FIG. 5 . As can be seen, the insert  360  in the cannula  202  forms a constriction that restricts or limits movement at the fulcrum in at least one direction, allowing the optical fiber  214  to pivot about the insert  360 . 
       FIG. 6  shows a detail view of an alternative example OCT probe  400 . The OCT probe  400  includes a probe housing  402 , a cannula  404 , an optical fiber  406  forming a part of a light source, such as in a manner similar to that described above. The OCT probe  400  may also include an actuation system  408  and may otherwise be similar to the OCT probe  106  describe above except where otherwise described. 
     The actuation system  408  may include a driver  420 , a pivot feature  422 , and a stiffening tube  424 . Here, the pivot feature  422  is separate and independent of the cannula  404 . The pivot feature  422  includes pivot protrusions  430  that project from a portion of the probe housing  402 . These pivot protrusions  430  forms a narrow passage through which the optical fiber  406  passes and operates in the manner similar to that described above. Thus, these pivot protrusions also act as local constrictions or fulcrums about which the optical fiber  406  can pivot. As can be seen in  FIG. 6 , the pivot protrusions  430  extend to maintain the optical fiber  406  in a central position aligned with a central axis  412  of the cannula  202 . The driver  420  operates from a location proximal of the pivot feature  422  and is arranged to provide a positive mechanical advantage. 
       FIG. 7  shows another example OCT probe  450 . The OCT probe  450  includes the lighting system  204  and the actuation system  206  described above. Here, however, the stiffening tube  224  is shown as extending along a longer portion of the optical fiber  214  than the stiffening tube  224  shown in  FIGS. 2 and 3 . The OCT probe  450  also includes a constraining feature  452  that cooperates with the pivot feature  222  to constrain the motion of the optical fiber  214  and stiffening tube  224  within a plane. 
       FIGS. 8 and 9  respectively show the pivot feature  222  and the constraining feature  452  that cooperate to constrain the motion of the optical fiber  214  to a particular range of motion, such as motion within a plane.  FIG. 8  shows the pivot feature  222  as a crimp  350  in the cannula  202 . Examples of crimps forming pivot features are shown in  FIGS. 4 and 7 . As can be seen in  FIG. 8 , the optical fiber  214 , with or without the stiffening tube  224 , passes through the opening at the crimp  350  in a manner that allows the sides of the crimp  350  to act as fulcrums. 
       FIG. 9  is a cross-sectional view of the constraining feature  452  shown in  FIG. 7 . In some instances, the constraining feature  452  may be formed as a crimp  410  in the cannula  202 . In some instances, the crimp  410  may be formed to be orthogonal to the crimp  350  so that the constraining feature  452  constrains the motion of the optical fiber  214  through a single plane while the fiber pivots at the crimp  350 . The orthogonal relationship between crimp  410  and crimp  350  is shown in  FIGS. 8 and 9 , as these two cross-sections represent the orientation of these features relative to each other along the cannula  202 . 
     A constriction  413  formed by the crimp  410  through which the optical fiber  214  and, in some instances, stiffening tube  224  may be sized to constrain the motion of the optical fiber  214  and the stiffening tube  224  in lateral directions such as those indicated by arrows  414 ,  416 . While constraining movement of the optical fiber  214  in lateral directions  414 ,  416 , the configuration of the constriction  413  may also allow motion in a cross-lateral, or orthogonal, direction indicated by arrows  418 ,  420 . Accordingly spurious motions outside the desired envelope of motion may be reduced, minimized, and/or eliminated. In some implementations, the constraining feature  452  may be situated at a location distal of the pivot feature  222 , as shown in  FIG. 7 . 
       FIGS. 10 and 11  respectively show the pivot feature  222  and the constraining feature  452  that cooperate to constrain the motion of the optical fiber  214  a particular range of motion, such as constraining motion to a plane. As described above, the pivot feature  222  in  FIG. 10  is the insert  360  insertable in the cannula  202 , as shown in  FIG. 5 . As can be seen, the optical fiber  214 , with or without the stiffening tube  224 , passes through the opening at the pivot feature  222  in a manner that allows the peaks  362  of the insert  360  to act as fulcrums. 
     In this embodiment, the constraining feature  452  is also an insert  460  that may be disposed in the cannula  202  at a location distal of the pivot feature  222  and may provide a constriction orthogonal to the constriction of the pivot feature  222 . The size of opening in the constraining feature  452  may be sufficiently sized to constrain the motion of the optical fiber  214  and the stiffening tube  224  in a lateral direction, while allowing motion in a cross-lateral, or orthogonal, direction. Here, the opening of the constraining feature  462  is oriented orthogonal to the opening of the insert  360  forming the pivot feature  222 . The constraining feature  462  serves to constrain the motion of the optical fiber  214  within a plane defined by the narrow opening  462  formed by the constraining feature  360 . The size of the opening  462  in the constraining feature  360  may be selected to be long enough to sufficiently constrain the motion of the optical fiber  214  in unwanted directions. In some embodiments, both the pivot feature  222  and the constraining feature  452  are formed of the same insert. That is, in some implementations, two identical inserts may be used for both insert  360  and insert  460 , one being rotated 90° relative to the other. In still other implementations, the pivot feature  222  and the constraining feature  452  may be formed in a single insert disposed within the cannula  202 . 
     While the examples above are shown as having the lens  210  fixed in place relative to the cannula  202 , other embodiments have the lens  210  in a fixed spatial relationship with the distal end  218  of the optical fiber  214  (e.g., the optical fiber  214  and lens  210  are coupled together). This optical arrangement forms the basis of an A-scan OCT in which the information is gathered at the single focal point. If the optical fiber  214  and lens  210  are then physically moved, a scan can be produced. Yet other embodiments are contemplated. 
     In operation, a user controls the OCT probe  106  at the console  102  and then orients the OCT probe  106  at a location adjacent tissue to be evaluated. With the OCT probe  106  at its desired location, the OCT probe  106  is activated to begin a scanning procedure. To do this, the actuation system  206  operates to physically displace the optical fiber  214  relative to the cannula  202  (and in some embodiments the lens) in a back and forth motion. The driver  220  operates to displace the optical fiber  214  in a direction substantially orthogonal to the axial direction of the optical fiber  214 , causing the optical fiber  214  to pivot about the pivot feature  222 , which may be formed of local constrictions in the manner described herein. The OCT probe  400  may be operated in a similar manner. 
     The OCT probe  106  is arranged so that a physical displacement by the driver  220  of a first amount results in a physical displacement of the distal end  218  of the optical fiber  214  by a second amount greater than the first amount. Accordingly, the OCT probe  106  is arranged to provide a positive mechanical advantage. 
     Embodiments having both a pivot feature and a constraining feature may be arranged so that the fiber displacement occurs substantially within a plane defined by the constraining features. In some embodiments, the constraining feature is oriented orthogonally to the pivot feature. 
     In some aspects, by creating a fulcrum by means of several possible embodiments described, and taking advantage of the multiplication of stroke from an actuator, present disclosure solves a problem of the limitation of availability of inexpensive actuators with sufficient stroke to provide adequate actuation. 
     Although the disclosure provides numerous examples, the scope of the present disclosure is not so limited. Rather, a wide range of modification, change, and substitution is contemplated in the foregoing disclosure. It is understood that such variations may be made to the foregoing without departing from the scope of the present disclosure. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the present disclosure.