Patent Publication Number: US-10314469-B1

Title: Spectrally encoded probes

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     n/a 
     FIELD OF THE DISCLOSURE 
     The present disclosure generally relates to endoscopes, and in particular the present disclosure relates to a method of aligning distal optics of spectrally encoded endoscopic probes. 
     BACKGROUND INFORMATION 
     Medical endoscopic probes have the ability to provide images from inside a patient&#39;s body. Considering the potential damage to a human or animal body caused by the insertion of a foreign object, it is preferable for the endoscopic probe to be as small as possible. Additionally, for non-medical applications, the ability to image within small conduits such as small ducts, pipes, tubing, and internal inspection through cracks and other tight spaces, etc., requires a probe of small size. 
     One useful medical probe employs spectrally encoded endoscopy (“SEE”), which is a miniature endoscopy technology that can conduct high-definition imaging through a sub-mm diameter probe. In a typical SEE probe, broadband light is diffracted by a grating at the distal end of an optical fiber to produce a dispersed spectrum of different wavelengths (colors) on a sample. Light returned from the sample is detected using a spectrometer; and each resolvable wavelength corresponds to reflectance from a different point on the sample. Thus, a SEE probe encodes light reflected from a given point in the sample by wavelength. The principle of the SEE technique and a SEE probe with a diameter of 0.5 mm (500 μm) have been described by D. Yelin et al., in a publication entitled “Three-dimensional miniature endoscopy”, Nature Vol. 443, 765-765 (2006). Another similar example is described by G. Tearney et al., in “Spectrally encoded miniature endoscopy”, Opt. Lett., 27(6): p. 412-414, 2002. Imaging with SEE can produce high-quality images in two- and three-dimensions. 
     Spectrally-encoded endoscopy utilizes the ability of the diffraction grating that deflects incident light to a diffraction angle according to wavelength. When the deflected light hits an object, light is scattered by the object. Detecting the scattered light intensity at each wavelength is equivalent to detecting the intensity from the corresponding diffraction angle. Thus, a one-dimensional, line image of the object can be obtained. A two-dimensional image is obtained by rotating the SEE probe. A three-dimensional image can be obtained by rotating and translating (moving linearly) the SEE probe. Moreover, when incorporated into a sample arm of an interferometer, the SEE probe can also acquire depth information from a sample (e.g., tissue). 
     Spectrally-encoded endoscopy probes are designed with side-viewing or forward-viewing characteristics. Forward view SEE probes are preferable for many applications. Forward view SEE imaging is particularly advantageous for applications such as orthopedics, ear, nose and throat (ENT), laparoscopy, and pediatric surgery. The forward-viewing (or front-view) probe type consists of multiple components including lenses, spacer elements, prisms and gratings, which makes the probe design complicated. Examples of such designs can be found, for example, in C. Pitris et al., Optical Express Vol. 11 120-124 (2003) and U.S. Pat. No. 8,145,018, both of which disclose a dual prism configuration where a grating is sandwiched between two prisms (a “grism”). The grism directs spectrally dispersed light such that at least one of the wavelengths propagates parallel to the optical axis of the probe. The grism consists of multiple components (grating, prisms) which need proper alignment. The need of a grism to construct a forward-view probe increases the cost, complexity of fabrication and size of the probe. Publication WO2015/116951 discloses another forward view endoscope where an angled reflective side surface makes the light incidence angle on the grating such that at least one of the wavelengths propagates parallel to the optical axis of the lens. However, these known designs of forward view SEE probes have drawbacks. 
     In particular, due to miniature size of the optics, the alignment of the spacer and the lens poses challenges during fabrication. Further, the illumination fiber is generally arranged off-axis to the GRIN lens, which introduces additional difficulties in fabrication as well as optical aberrations. 
     Accordingly, it can be beneficial to address and/or overcome at least some of the deficiencies indicated herein above, and thus to provide a new SEE probe having forward direction view, and an apparatus to use such a probe, e.g., for imaging in a small optics. 
     SUMMARY 
     According to at least one embodiment of the present disclosure, there is provided a method of aligning the distal optics of an endoscopic probe comprising: aligning a light guiding component; a light focusing component; and a light diffusing component (e.g., a grating), such that light which is put into the proximal end of light guiding component can emit from the distal end thereof focused by the focusing component onto the light diffusing component to thereby generate a dispersed light line, and arranging the light guiding component, light focusing component and light diffusing component within a drive cable so that at least one wavelength of the dispersed light line goes to the direction of axis of the drive cable. 
     According to another embodiment, a probe having a proximal end and a distal end arranged inside a drive cable, comprises: a light guiding component; a light focusing component; and a grating component. The probe is configured for guiding light from the light guiding component, through the light focusing component, and to the grating component, and then forwarding a spectrally dispersed light line from the grating component towards a sample, wherein an optical component assembly of the probe is arranged in the drive cable so that at least one wavelength of the spectrally dispersed light line goes to the direction of axis of the drive cable. 
     According to yet another embodiment, there is disclosed a system comprising: light source, a probe having a proximal end and a distal end arranged inside a drive cable, a rotary element connected to the distal end of the probe, one or more detection fibers surrounding the proximal end of the probe, one or more detectors, and one or more processors. The probe is configured for guiding light from the light source through the light guiding component, through the light focusing component, and to the grating component, and then forwarding a spectrally dispersed light line from the grating component towards a sample, wherein an optical component assembly of the probe is arranged in the drive cable so that at least one wavelength of the spectrally dispersed light line goes to the direction of axis of the drive cable. 
     These and other objects, features, and advantages of the present disclosure will become apparent upon reading the following detailed description of exemplary embodiments of the present disclosure, when taken in conjunction with the appended drawings, and provided claims. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Further objects, features and advantages of the present disclosure will become apparent from the following detailed description when taken in conjunction with the accompanying figures showing illustrative embodiments of the present disclosure. 
         FIG. 1  is a diagram of an exemplary SEE probe according to an exemplary embodiment of the present disclosure. 
         FIG. 2A  shows imaging parameters of an exemplary SEE probe having forward view characteristics.  FIG. 2B  shows a spectrally encoded illumination line  110  as seen at the field of view (FOV) of a SEE probe. 
         FIG. 3  illustrates an example of a fabrication process for assembling the SEE probe. 
         FIG. 4  shows an exemplary assembled SEE endoscope. 
         FIG. 5A  shows geometrical parameters in an example of distal optics of the SEE probe, according to an embodiment.  FIG. 5B  shows a Cartesian coordinate system (first coordinate system) x″, y″, z″.  FIG. 5C  shows a Cartesian coordinate system (second coordinate system) x′, y′, z′. 
         FIG. 6  shows grating surface parameters as viewed from the normal to the surface of the grating. 
         FIG. 7  shows the plane of incidence and the plane of diffracted light of the grating  240  as seen in another Cartesian coordinate system (a third coordinate system) x, y, z. 
         FIG. 8A  shows the view angles of the spectrally dispersed illumination line (rainbow curve).  FIG. 8B  shows the angle of rainbow lateral shift θ RLS  as a function of grating pattern tilt α. 
         FIGS. 9A and 9B  illustrate an example of a method of active alignment performed during the probe fabrication process of fixing the distal optics of probe  200  to a drive cable  310 . 
         FIGS. 10A and 10B  show the field of view observed at the imaging plane during an active alignment process using a broadband dispersed light line. 
         FIGS. 11A and 11B  show the field of view observed at the imaging plane during an active alignment process using broadband dispersed light spots. 
         FIGS. 12A and 12B  show the field of view observed at the imaging plane during an active alignment process using a single color dispersed light spots. 
         FIG. 13  is a diagram of an imaging system including the SEE endoscope according to an exemplary embodiment of the present disclosure. 
         FIG. 14  is a block diagram of an exemplary imaging console. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Throughout the figures, the same reference numerals and characters, unless otherwise stated, are used to denote like features, elements, components or portions of the illustrated embodiments. Moreover, while the subject disclosure will now be described in detail with reference to the figures, it is done so in connection with the illustrative exemplary embodiments. It is intended that changes and modifications can be made to the described exemplary embodiments without departing from the true scope and spirit of the subject disclosure as defined by the appended claims. 
     The embodiments disclosed herein describe SEE probes that can have good resolution in both the scanning direction and the spectral direction due to a fuller use of the available field of view. These embodiments also provide images with minimal distortion. 
     &lt;SEE Probe Structure&gt; 
       FIG. 1  shows a diagram of an exemplary embodiment of a forward view SEE probe  100  according to the present disclosure. The exemplary SEE probe  100  includes, from its proximal end to distal end thereof, an optical fiber  10  (light guiding component), a focusing or collimating lens  12  (light focusing component), and a spacer assembly  14  arranged along an axis Ox. The spacer assembly  14  includes a mirror surface  15  and a diffraction grating  16  (grating component). Broadband light or other electro-magnetic radiation (shown as left-to-right arrow) can be coupled or otherwise provided to the fiber  10  from a non-illustrated light source. The light or electro-magnetic radiation is focused by the lens  12  to form a substantially collimated light beam. The light (or other electro-magnetic radiation) travels through the focusing lens  12 , the spacer  14 , is reflected by the mirror surface  15 , and then incident on the grating  16 . At the grating  16 , the light is diffracted according to its wavelength and incidence angle. Each diffracted light (having a wavelength λ or a wavelength band Δλ) is focused on a unique spatial location on a target sample  18  (e.g., tissue). 
     As shown in  FIG. 1 , positions X 1 , X 2 , and X 3  are unique spatial locations on the sample  18  where dispersed light of wavelengths λ 1 , λ 2 , and λ 3 , respectively, imping on the sample to form a spectrally dispersed light line  20 . In other words, grating  16  causes the light (or other electro-magnetic radiation) to be focused into a plane or line  20  formed on the sample. The plane or line  20  shown in  FIG. 1  is referred to as a spectrally-encoded line. The grating  16  is designed to cause one of the wavelengths (e.g., λ 1  in  FIG. 1 ) in the light beam to propagate substantially parallel to the axis (Ox) of the probe  100 . The other wavelengths (e.g., λ 2 ,λ 3 , etc.) are diffracted at different angles with respect to the axis Ox. Light (or other electro-magnetic radiation) scattered by the sample  18  can be coupled or otherwise provided back to the fiber  10  or to a different fiber (not shown), and then the collected light can be delivered to a detector (not shown) that includes a spectrometer (not shown). At the spectrometer, the spectrum of the returning light (or other electro-magnetic radiation) can be read out as an electrical signal, which can then be used to generate a line image of the tissue using a computer or other digital processor (not shown). 
     In order to acquire two-dimensional (2D) images of the target sample (e.g., cavities such as vessels, esophagus and nasal cavity, generally referred to as “bodily lumens”), the exemplary SEE probe  100  can be scanned rotationally around the axis Ox as shown by the rotational arrow  22 , e.g., by rotating or oscillating the probe in ways which should be understood to those having ordinary skill in the art. In addition, the probe  100  can be moved (translated) longitudinally so that images of a target sample are obtained at different depths or different working distances. This longitudinal movement may be performed by pulling the tip (distal end) of the probe back towards the proximal end in a process referred to as a “pullback” operation. 
       FIG. 2A  shows imaging parameters of an exemplary SEE probe  200 . In  FIG. 2A , the diffracted light emitted from the exemplary SEE probe  200  is incident on an imaging plane  150  (illumination plane) to form a spectrally dispersed (encoded) illumination line no at a working distance (Wd). As shown in  FIG. 2A , the probe axis Ox is the z axis; at the imaging plane  150 , the probe axis passes through a center point  120  where the z axis crosses the x and y axes. When any of the optics of SEE probe  200  is misaligned, for example when the grating groove direction is tilted on the probe, or the bonding of the illumination fiber to the lens is defective, the illumination line no is shifted from the center  120  of the imaging plane iso. As a result, at least portion of the light line no does not go in the direction of the probe axis. 
       FIG. 2B  shows the spectrally encoded illumination line no as seen at the field of view (FOV) of SEE probe  200 , when the SEE probe is rotated. By rotating the probe  200  around the axis Ox, the spectrally encoded line no can scan the target sample in a two-dimensional (2D) area  130 . However, when the illumination line  110  is shifted from the center  120 , there will be an area  140  at center of field of view where no illumination light hits. This means that no information can obtained from this area  140  of the target sample in the SEE image reconstruction process. In other words, the non-illuminated area  140  acts as an obscuration area in the center of the field of view. To avoid this obscuration and to be able to obtain information from the area  140 , the distal end of the probe could be moved or tilted in the x and y directions of the imaging plane iso, but such movement may be mechanically restricted or could be detrimental to the subject. In addition, when imaging small-sized tubular target samples (e.g., when imaging narrow lumens such as capillaries), it may not possible to move or tilt the probe in the x and y directions of the imaging plane due to spatial limitations. Therefore, in accordance with at least one embodiment of the present disclosure, appropriate alignment of the distal optics of the probe  200  ensures that no obscuration occurs in the center of the field of view. Expressed in another way, appropriate alignment of the distal optics of the probe  200  ensures that the entire field of view is appropriately illuminated so that better imaging can be achieved. 
     &lt;Probe Fabrication Process&gt; 
       FIG. 3  illustrates an example of a fabrication process for assembling the SEE probe  200 . At STEP  1 , of  FIG. 3 , a fiber  202  and a lens  210  are assembled together by bonding or splicing in a manner known to those skilled in the art. In parallel, at STEP  2 , an spacer assembly  220  is constructed by polishing a glass rod into the desired spacer shape, and then making a mirror surface  230 , and forming a grating  240 . It should be understood that the drawing provided in  FIG. 3  shows exemplary fiber, lens, and spacer elements for illustration only. The shape and dimensions of these elements are not limiting, as these elements make take numerous other shapes or dimensions. For example, for the spacer, several glass (or plastic) rods with different diameters can be used. To form the mirror surface  230  and the grating  240 , the glass rod can be polished at the desired angle. After polishing, the polished surface can be cleaned and polished to form the mirror, and in the same manner the grating  240  may be formed on a different polished surface of spacer  220 . 
     At STEP  3 , the lens  210  is assembled together with the spacer assembly  220 , e.g., by bonding or splicing. As a result, the distal optics of the probe  200  are assembled. Now, at STEP  4 , the distal optics and fiber of the probe  200  are inserted into a drive cable  310  (drive cable or guide cable), and fixed therein to form an integral body. Finally, the drive cable  310  containing the distal optics of probe  200  thereinside is further arranged inside an inner sheath  320  of an endoscope assembly, as further described below. As it will be appreciated by those skilled in the art appropriate alignment of the distal optics in probe  200  is important for high-quality imaging. However, even if care is taken to align the fiber with the distal optics, it is unlikely that perfect alignment can be achieved and more likely that there will be some lateral and rotational misalignment between the fiber and the distal optical elements. 
       FIG. 4  shows an assembled SEE endoscope  300  containing thereinside the SEE probe  200 . In the endoscope  300 , the distal optics of the assembled probe  200  are arranged inside the inner diameter of the drive cable  310 , for example, by bonding. The distal optics of probe  200  along with the drive cable  310  is rotated inside the inner sheath  320  by a non-illustrated torque generating motor located at the proximal end of the probe. At least at the distal end of the endoscope assembly, detection fibers  330  are arranged around the outer surface of the inner sheath  320 . To protect the detection fibers, an outer sheath  340  covers the detection fibers  330 . At the distal tip of the outer sheath  340 , a transparent window cover  350  is provided so as to cover at least the distal optics of the probe  200  and the detection fibers  330 . 
     During the assembly process of steps  1 - 4  in  FIG. 3 , fabrication errors can occur due to an accumulation of misalignments of the distal optics, or misalignment of the SEE probe  200  inside drive cable  310 . Specifically, as it will be appreciated by those skilled in the art appropriate alignment of the distal optics in probe  200  is important for high-quality imaging. However, even if care is taken to align the imaging fiber with the distal optics, it is unlikely that perfect alignment can be achieved and more likely that there will be some lateral and rotational misalignment between the fiber and the distal optical elements. This accumulation of small misalignments causes the spectrally encoded illumination line no to not pass trough the center of the field of view. Such fabrication error includes misalignment of the fiber  202  and lens  210 , misalignment of the mirror surface  230  (e.g., due to errors in polishing), misalignment of the surface of grating  240  (e.g., due to errors in the fabrication of the spacer), misalignment in direction of the grating pattern, and misalignment of bonding the lens  210  and spacer  220 . For example, as described in more detail below, if the grating pattern is tilted by 1 degree, the spectrally encoded illumination line from the illumination optics of the design described above can be shifted from the optical axis by about 1.6 degrees in terms of the viewing angle, when n=1.528, and the mirror and grating surface angles, Θ M  and Θ G  are 41.4 and 42.7 degrees, respectively. The grating  240  has 650 lines/mm groove density. In this case, 416 nm light is diffracted in −6 th  order in direction of the axis Ox of the probe  200  for blue color. In this example, the ratio 1:1.6 between pattern tilt and illumination line shift angles is calculated from equation (13), which is discussed in more detail below, for specific probe parameters. In other words, the ratio between pattern tilt and illumination line shift angles is different at different probe parameters. 
     &lt;SEE Probe Geometrical Parameters&gt; 
       FIG. 5A  shows the geometrical parameters in an example of the distal optics of the SEE probe  200 , according to an embodiment. As shown in  FIG. 5A , the distal optics includes the fiber  202  bonded to the lens  210 , and the lens  210  in turn connected to the spacer  220 . The spacer  220  includes the mirror surface  230  and the grating  240 . In an embodiment, the fiber  202  can be a single mode fiber or multimode fiber. The lens  210  can be a graded-index (GRIN) lens or a ball lens. The spacer  220  can be made of glass or molded plastic. 
     Through the fiber  202  broadband light is delivered from a non-illustrated light source, and the light guided to the GRIN lens  210 . The light is then collimated by the lens  210  and a collimated beam is delivered on to the spacer  220 . The spacer  220  can have a light reflecting surface, such as mirror surface  230 . The mirror surface  230  can be made by polishing a part of the spacer or coating a part of the spacer with a reflective metal layer. The light beam traveling through the spacer  220  is incident on the mirror surface  230  at an angle larger than the critical angle with respect the mirror surface  230 , and therefore the light incident on the surface  230  is completely reflected towards the grating  240 . The grating  240  has a grating pattern formed on another surface of the spacer  220 . The grating pattern can be made of glass or resin in a known manner. The light reflected at the mirror surface  230  is incident on the grating surface of the grating  24   o  and then diffracted towards a target sample (not shown). The diffracted light goes to the target sample as illumination light in spectrally encoded light having different wavelengths (λ 1 , λ 2 , λ 3 ) incident on different points of the target sample. 
     The fiber can be a singlemode fiber or multimode fiber. The lens can be a GRIN lens or a ball lens. The spacer can be made of glass or plastic. Thought the fiber broadband light (or monochromatic light) is delivered from a light source to the lens. In one exemplary embodiment, the spacer material has a refractive index n=1.528, and the mirror and grating surface angles, Θ M  and Θ G  are 41.4 and 42.7 degrees, respectively. The grating  240  has 650 lines/mm groove density. In this case, 416 nm light is diffracted in −6 th  order in direction of the axis Ox of the probe  200  for blue color. For green and red color, 498 nm and 621 nm respectively, light is diffracted in −5 th  and −4 th  order in. 
     In the forward view SEE probe  200  shown in  FIG. 5A , we define a Cartesian coordinate system (first coordinate system) x″, y″, z″ so that the probe optical axis is the z″ axis, and the mirror normal and grating normal are in the x″-z″ plane.  FIG. 5B  shows the Cartesian coordinate system (first coordinate system) x″, y″, z″. We also define another Cartesian coordinate system (second coordinate system) x′, y′, z′, so that the z′ axis is parallel to the grating surface normal, and the y′ axis is parallel to y″ axis.  FIG. 5C  shows the Cartesian coordinate system (second coordinate system) x′, y′, z′. 
     &lt;SEE Probe Inclination Angle Calculation and Simulation&gt; 
       FIG. 6  shows the grating surface viewed from the normal to the surface of the grating  240 . Here, we introduce another Cartesian coordinate system (a third coordinate system) x, y, z, so that the grating lattice vector is parallel to the x axis, and the z axis is parallel to z′ axis. In this third coordinate system, it is assumed the grating pattern (x direction in  FIG. 6 ) is tilted by an angle α with respect to the x′ direction. 
     Now, considering the three different Cartesian coordinate systems defined above,  FIG. 7  shows the plane of incidence and the plane of diffracted light of the grating  240 . In  FIG. 7 , we now define a wave vector of a chief ray of an incident beam in the spacer  220  as k s , and a wave vector of the diffracted beam in air as k d . We then define each component of vectors k s  and k d  in the coordinate system x, y, z, as (k sx , k sy , k sz ), and (k dx , k dy , k dz ), respectively. 
     Based on the foregoing definitions, we can now calculate the magnitude of the wave vectors as follows. The magnitude of the wave vectors are 
     
       
         
           
             
               
                 
                   
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     where λ is the wavelength in vacuum and n s  is the refractive index of the material of spacer  220 . 
     From the geometry defined in  FIGS. 6 and 7 , we obtain Equation (3) 
                     (           k   sx               k   sy               k   sz           )     =         k   s     ⁡     (           sin   ⁢           ⁢     θ   i     ⁢   cos   ⁢           ⁢   α               sin   ⁢           ⁢     θ   i     ⁢   sin   ⁢           ⁢   α               cos   ⁢           ⁢     θ   i             )       ⁢           ⁢   where             (   3   )                 θ   i     =       2   ⁢     Θ   M       +     Θ   G     -       π   2     .               (   4   )               
Each component of k d  is calculated by
 
 k   dx   =k   sx +2π mG   (5)
 
 k   dy   =k   sy   (6)
 
and
 
 k   dz =√{square root over ( k   d   2   −k   dx   2   −k   dy   2 )}.  (7)
 
     The components of k d  in coordinate system x′, y′, z′, are 
                     (           k     dx   ′                 k     dy   ′                 k     dz   ′             )     =       (           cos   ⁢           ⁢   α           sin   ⁢           ⁢   α         0               -   sin     ⁢           ⁢   α           cos   ⁢           ⁢   α         0           0       0       1         )     ⁢     (           k   dx               k   dy               k   dz           )               (   8   )               
and the components of k d  in coordinate system x″, y″, z″ are
 
     
       
         
           
             
               
                 
                   
                     
                       
                         
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                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     
                                       Θ 
                                       G 
                                     
                                     ⁢ 
                                     sin 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     α 
                                   
                                 
                                 
                                   
                                     sin 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     
                                       Θ 
                                       G 
                                     
                                   
                                 
                               
                             
                             ) 
                           
                           ⁢ 
                           
                             
                               ( 
                               
                                 
                                   
                                     
                                       k 
                                       dx 
                                     
                                   
                                 
                                 
                                   
                                     
                                       k 
                                       dy 
                                     
                                   
                                 
                                 
                                   
                                     
                                       k 
                                       dz 
                                     
                                   
                                 
                               
                               ) 
                             
                             . 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
           
         
       
     
     Note that the y″ component of the diffracted light wave vector k dy ″ is given by Equation (10), where k dy ″ is not zero when α is not zero. 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           k 
                           
                             dy 
                             ″ 
                           
                         
                         = 
                           
                         ⁢ 
                         
                           
                             
                               - 
                               
                                 k 
                                 dx 
                               
                             
                             ⁢ 
                             sin 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             α 
                           
                           + 
                           
                             
                               k 
                               dy 
                             
                             ⁢ 
                             cos 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             α 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                         ⁢ 
                         
                           
                             
                               - 
                               
                                 ( 
                                 
                                   
                                     k 
                                     sx 
                                   
                                   + 
                                   
                                     2 
                                     ⁢ 
                                     π 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     m 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     G 
                                   
                                 
                                 ) 
                               
                             
                             ⁢ 
                             sin 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             α 
                           
                           + 
                           
                             
                               k 
                               sy 
                             
                             ⁢ 
                             cos 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             α 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                         ⁢ 
                         
                           
                             - 
                             2 
                           
                           ⁢ 
                           π 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           m 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           G 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           sin 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           α 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   10 
                   ) 
                 
               
             
           
         
       
     
     This means when the grating pattern is tilted, the diffracted light rainbow does not go toward the probe axis direction. In other words, at least part of the SEE light does not reach the center of the field of view due to a lateral shift. 
     Here, we define an angle of illumination rainbow lateral shift, θ RLS , as Equation (11). 
     
       
         
           
             
               
                 
                   
                     θ 
                     RLS 
                   
                   = 
                   
                     
                       arctan 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         
                           k 
                           
                             dy 
                             ″ 
                           
                         
                         
                           k 
                           
                             dz 
                             ″ 
                           
                         
                       
                     
                     ⁢ 
                     
                       | 
                       
                         
                           k 
                           
                             dx 
                             ″ 
                           
                         
                         = 
                         0 
                       
                     
                   
                 
               
               
                 
                   ( 
                   11 
                   ) 
                 
               
             
           
         
       
     
     Now, we introduce λ 0 , which is the wavelength satisfying the grating equation when α=0 and k dx″ =0, 
     
       
         
           
             
               
                 
                   
                     
                       n 
                       s 
                     
                     ⁢ 
                     
                       | 
                       
                         λ 
                         = 
                         
                           λ 
                           0 
                         
                       
                     
                     ⁢ 
                     
                       
                         sin 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         
                           θ 
                           i 
                         
                       
                       + 
                       
                         sin 
                         ⁡ 
                         
                           ( 
                           
                             
                               π 
                               2 
                             
                             - 
                             
                               Θ 
                               G 
                             
                           
                           ) 
                         
                       
                     
                   
                   = 
                   
                     
                       - 
                       m 
                     
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     G 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       
                         λ 
                         0 
                       
                       . 
                     
                   
                 
               
               
                 
                   ( 
                   12 
                   ) 
                 
               
             
           
         
       
     
     When α is small and k dy″ &lt;&lt;k d , θ RLS  can be approximated as 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           
                             
                               θ 
                               RLS 
                             
                             ≅ 
                               
                             ⁢ 
                             
                               
                                 k 
                                 
                                   dy 
                                   ″ 
                                 
                               
                               
                                 k 
                                 d 
                               
                             
                           
                           ⁢ 
                           
                             | 
                             
                               
                                 k 
                                 
                                   dx 
                                   ″ 
                                 
                               
                               = 
                               0 
                             
                           
                         
                         = 
                         
                           
                             ( 
                             
                               
                                 
                                   - 
                                   m 
                                 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 G 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 λ 
                               
                               ⁢ 
                               
                                 | 
                                 
                                   
                                     k 
                                     
                                       dx 
                                       ″ 
                                     
                                   
                                   = 
                                   0 
                                 
                               
                             
                             ) 
                           
                           · 
                           α 
                         
                       
                     
                   
                   
                     
                       
                         ≅ 
                           
                         ⁢ 
                         
                           
                             - 
                             m 
                           
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           G 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             λ 
                             0 
                           
                           ⁢ 
                           α 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   13 
                   ) 
                 
               
             
           
         
       
     
     which means the rainbow lateral shift angle θ RLS  is proportional to the grating pattern inclination angle α. 
     Simulation Results 
     Table 1 shows parameters based on an exemplary design of a prototype color SEE probe fabricated by the applicant of the present application. Here, a simulation was performed to check rainbow curve shift of blue channel light with respect to the center of the field of view on the illumination plane. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Sample Probe parameters 
               
            
           
           
               
               
               
            
               
                   
                 Probe parameter 
                 Value 
               
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Mirror surface angle (deg) Θ M   
                 41.4 
               
               
                   
                 Grating surface angle (deg) Θ G   
                 42.7 
               
               
                   
                 Grating groove density  
                 1000/1.54 = 649.4 
               
               
                   
                 (lines/mm) G 
                   
               
               
                   
                 Spacer material 
                 OHARA S-BSL7 
               
               
                   
                 Diffraction order for blue  
                 −6 
               
               
                   
                 channel m 
                   
               
               
                   
                 Wavelength at FOV center  
                 416.4 
               
               
                   
                 when α = 0 (nm) λ 0   
                   
               
               
                   
               
            
           
         
       
     
     For refractive index of S-BSL7, we use the Sellmeier equation 
                     n   s   2     =     1   +         B   1     ⁢     λ   2           λ   2     -     C   1         +         B   2     ⁢     λ   2           λ   2     -     C   2         +         B   3     ⁢     λ   2           λ   2     -     C   3                   (   14   )               
with the coefficients of the Sellmeier equation shown in Table 2, where each term of the sum represents an absorption resonance of strength B i  at a wavelength √{square root over ( )}C i .
 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Sellmeier coefficients of S-BSL7 
               
            
           
           
               
               
               
            
               
                   
                 Coefficient 
                 Value 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                   
                 B 1   
                 1.1515019 
               
               
                   
                 B 2   
                 0.118583612 
               
               
                   
                 B 3   
                 1.26301359 
               
            
           
           
               
               
               
               
            
               
                   
                 C 1   
                 0.010598413  
                 (μm 2 ) 
               
               
                   
                 C 2   
                 −0.011822519  
                 (μm 2 ) 
               
               
                   
                 C 3   
                 129.617662  
                 (μm 2 ) 
               
               
                   
                   
               
            
           
         
       
     
     Now,  FIG. 8A  shows the view angle of the rainbow curve calculated by Eq. (9). The wavelength range is 400 to 480 nm. The grating pattern tilt α is 0, 0.5, 1.0, and 1.5 degrees. The view angle is measured from the probe axis (z″). The view angle is calculated as arctangent of 
                 k     dy   ″         k     dz   ″         ,     and   ⁢           ⁢       k     dx   ″         k     dz   ″                 
for the y″ and x″ directions, respectively. Note that x″ is the spectrally encoding direction.
 
       FIG. 8B  shows the angle of rainbow lateral shift θ RLS  for grating pattern tilt α calculated by Eq. (11), and its approximation calculated by Eq. (13). In this range of wavelengths and angles, the results plotted in  FIG. 8B  show Eq. (13) is a good approximation to values calculated by Eq. (ii). Here −mGλ 0  is 1.62. The results show that when the grating pattern is tilted by 1 degree but the other probe/sheath parts are assembled as designed in the example described above, there will be a blind area (obscuration area) of 3.2 degrees in diameter at FOV center even if we correct the imaging data in post processing. 
     The results shown in  FIGS. 8A and 8B  indicate that there can be a blind area at the FOV center when the grating pattern is tilted. The same type of error would be expected with any other misalignment, as described above. To avoid this obscuration, one option could be to increase the precision of assembly to make the tolerance for the tilt as close to zero as possible. However, this solution will increase the fabrication time and costs. Another option is to compensate this tilt effect by changing other parts assembly angles. 
     One option can be to attach the fiber/GRIN lens assembly on the spacer in such a way that k dy″ =0 when k dx″ =0. Instead of Eq. (3), change ray angle from GRIN lens to the grating surface to satisfy 
     
       
         
           
             
               
                 
                   
                     
                       k 
                       
                         dy 
                         ″ 
                       
                     
                     ⁢ 
                     
                       
                         
                            
                           
                             
                               k 
                               
                                 dx 
                                 ″ 
                               
                             
                             = 
                             0 
                           
                         
                         ⁢ 
                         
                           = 
                           
                             { 
                             
                               
                                 
                                   - 
                                   
                                     ( 
                                     
                                       
                                         k 
                                         sx 
                                       
                                       + 
                                       
                                         2 
                                         ⁢ 
                                         π 
                                         ⁢ 
                                         
                                             
                                         
                                         ⁢ 
                                         m 
                                         ⁢ 
                                         
                                             
                                         
                                         ⁢ 
                                         G 
                                       
                                     
                                     ) 
                                   
                                 
                                 ⁢ 
                                 sin 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 α 
                               
                               + 
                               
                                 
                                   k 
                                   sy 
                                 
                                 ⁢ 
                                 cos 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 α 
                               
                             
                             } 
                           
                         
                          
                       
                       
                         
                           k 
                           
                             dx 
                             ″ 
                           
                         
                         = 
                         0 
                       
                     
                   
                   = 
                   0. 
                 
               
               
                 
                   ( 
                   15 
                   ) 
                 
               
             
           
         
       
     
     Another option is to tilt the probe optical axis from drive cable rotation axis by an angle of the rainbow lateral shift θ RLS . Therefore, in the fabrication step, it would be advantageous to actively perform an alignment process where, for example, a laser beam can be introduced into the probe to aide in the alignment of the distal optics so as to ensure that the rainbow light from the probe can go through rotation axis direction. In both cases it is important to minimize grating pattern tilt because tilting parts by a large angle is not easy if the size of the endoscope is limited. 
     Therefore, in order to know the effects of active alignment, the applicant has developed a simulation model for tilted grating pattern in forward view SEE imaging. The simulation results for an exemplary SEE color probe confirm that if the pattern is tilted and other parts are assembled as conventionally designed a blind area at the FOV center exists. Therefore, an alignment solution presented herein can avoid or at least minimize the obscuration of the center FOV, and therefore improved imaging results can be attained. Notably, the simulation model can be used to estimate a priori the amount of inclination (an alignment range) to ensure that no obscuration occurs at the center of the illumination FOV. 
     &lt;SEE Probe Method of Alignment&gt; 
       FIGS. 9A and 9B  show an example of an active alignment performed during the probe fabrication process of fixing the distal optics of probe  200  to the drive cable  310 .  FIGS. 10A and 10B  show the field of view observed at the imaging plane during the active alignment process. 
     An example of the active alignment can be performed as shown in  FIGS. 9A and 9B .  FIG. 9A  shows the illumination optics assembly of the probe  200  and the drive cable  310  viewed from the x direction in the x, y, z coordinate system. In this example, the illumination optics of probe  200  and drive cable  310  are aligned such that the drive cable axis  500  is parallel to (an concentric with) the axis Ox of the optical probe. In this case, due to the fabrication errors described above, spectrally encoded illumination line  510  does not pass the axis Ox of the illumination optics of probe  200 . As a result, the illumination light at the field of view does not pass the drive cable axis  500 , and thus it does not irradiate the area  140  around the center  120  of the scanned area  130 , as shown in  FIG. 10A . 
     To ensure that the illumination light irradiates the center  120  of the scanning area  130 , in the fabrication step of fixing the illumination optics of probe  200  and drive cable  310 , an active alignment is performed. In the active alignment, a beam of light (e.g., laser beam) can be transmitted through the probe  200  and a screen or a sensor located in front of the distal end of probe  200 , for example, at the working distance (Wd), can be used to actively check where the drive cable axis  500  is located on the screen or sensor. Then by introducing light from a broadband light source like a supercontinuum laser, LED, or lamp into the fiber  202  of the illumination optics, it is possible to monitor directly or indirectly when the illumination line no passes the axis  500 . When fixing the illumination optics of probe  200  with the drive cable  310 , we can tilt the illumination optics of probe  200  as shown in  FIG. 9B  so that the spectrally encoded illumination line no passes the drive cable axis  500  and the illumination light arrives to the center of the field of view, as shown in  FIG. 10B . Once the alignment process ensures that the spectrally encoded illumination line no passes the drive cable axis  500  and the illumination light arrives to the center of the field of view, it is possible to secure (fix) the optics of the probe  200  to the drive cable  310 , for example, by mechanical retaining elements  960  and  962 , as shown in  FIG. 9B . Mechanical retaining elements  960  and  962  used for aligning and securing (fixing) the optics of the probe  200  to the drive cable  310  can be prefabricated tubular structures or can be deposits of epoxy or resin that serve to hold one or more optical elements of the probe  200  at the desired angle. 
     In this manner, SEE optical probe  200  can be arranged such that the probe axis Ox is at an inclination angle α with respect to the axis  500  of the drive cable  310 . The inclination angle can be obtained from the above-described inclination calculation and simulation. That is, a range of inclination angles and corresponding rainbow lateral shift angles, as those shown in  FIGS. 8A and 8B , can be used to align the distal optics of the SEE probe in a manner to ensure that the illumination light arrives to the center of the field of view and obscuration is avoided. 
     In the alignment above, multiple monochromatic light sources which have different wavelengths can be used instead of using broadband light source. In this case, multiple light spots  610  ( 610   a ,  610   b ,  610   c ) which is light of a specific wavelength diffracted by the grating  240  appear on the screen or sensor as shown in  FIG. 11A . From the spots  610 , it is possible to estimate the location of spectrally encoded illumination line no which is diffracted light from the illumination optics of probe  200 . Therefore, to ensure that no obscuration area remains in the field of view, as shown in  FIG. 11B , we can tilt the illumination optics of probe  200  within the drive cable  310 , as shown in  FIG. 10B , until the spectrally encoded illumination line no passes the drive cable axis  500 . 
     When the probe generates diffracted light in multiple orders, one monochromatic light source can be used in the alignment above. For example, the probe in  FIG. 5A  could generate blue light in −6th order, but at the same time there is light diffracted in other orders, for example, in −5th order and −4th order (shown as lambda1-3, respectively). 
     In this case of having diffracted light in multiple orders, one light spot  710  and two light spots  720  ( 720   a ,  720   b ) which are light diffracted in −6th order and −5th/−4th orders by the grating  240 , respectively, appear on the screen or sensor as shown in  FIG. 12A . From the spots  710  and  720 , it is possible to accurately estimate the location of spectrally encoded illumination line no which is diffracted light from the illumination optics of probe  200  when broadband light is input into the probe. Here too, we can tilt the illumination optics of probe  200  as shown in  FIG. 10B  so that spectrally encoded illumination line no passes the drive cable axis  500  and the entire field of view is accurately illuminated as shown in  FIG. 12B . 
     As discussed above, in the technical simulation, the spectrally encoded illumination line  110  on the target sample can be a slightly curved. Any negative effects cause by this curve on the image can be safely and accurately compensated in post processing. For example, by SEE imaging using calibration chart which can have fixed pattern like grid, we can figure out a relation between wavelength-time coordinates (data from spectrometer) and polar coordinates or Cartesian coordinates (processed image) for the curved illumination line. By applying the relation into post processing we can compensate data in wavelength-time domain from the spectrometer sensor into a corrected image. 
     &lt;Imaging System&gt; 
     A system  1300  to acquire an image using the SEE probe according to an exemplary embodiment of the present disclosure is shown in the diagram of  FIG. 13 . The system  1300  of  FIG. 13  includes, for example, a light source  1370 , a detector/spectrometer  1380 , a fiber optic rotary joint (FORJ)  1330 , an imaging wand  1340 , and an image processing computer  1350 . The light source  1370  can be a supercontinuum laser or lamp that outputs light of broadband spectrum, or laser diode or an LED that outputs light of a single color or a narrow band spectrum, or a source of other electro-magnetic radiation. The range of the wavelength can be within the visible region, which is from about 400 nm thorough 800 nm. However, other wavelengths may also be used. In the exemplary imaging system  1300 , the light can be directly guided or otherwise coupled into a source fiber, which may be referred to as an illumination fiber  1372 . The illumination fiber  1372  can be connected to the FORJ  1330 , and the light further guided to (and/or associated with) the illumination fiber  1302  of the imaging wand or SEE probe  1340 . 
     The SEE probe  1340  is connected at the proximal end thereof to the FORJ  1330 . The SEE probe  1340  includes the illumination fiber  1302  and an assembly of distal optics  1315  arranged within a drive cable  1310 ; and the drive cable  1310  in turn is arranged within an outer sheath  1320 . In this manner, illumination light emitted from light source  1370  is delivered to the distal optics assembly  1315 , and then diffracted by a grating onto a forward-viewing imaging plane. The light scattered back from an object or target sample (e.g., tissue) can be collected by detecting fibers arranged around the distal end of the SEE probe  1340 , and the collected light is guided by one or more detection fibers  1382 , which are arranged outside the FORJ  1330 . The detection fiber  1382  can be connected to the detector/spectrometer  1380  via a collimating or dispersing optical system  1384 . The detector/spectrometer  1380  can detect the intensity of a selected wavelength. This exemplary function of detecting the selected wavelength can be performed by the spectrometer. 
     By mechanically rotating the wand or probe  1340  in a direction  1328  with a mechanical scanning unit contained within the FORJ  1330 , it is possible to obtain a two-dimensional image of the target sample. The mechanical scanning unit (not shown) can be implemented by, e.g., a Galvo scanner or motor to rotate the drive cable  310  together with the illumination fiber  1302  and the distal optics assembly  1315 . Computer  1350  includes one or more microprocessors configured to control and operate the various parts of system  1300 , by executing computer-executable instructions (program code). Computer  1350  can also be programmed to reconstruct images based on signals obtained from detector/spectrometer  1380 . 
       FIG. 14  a schematic block diagram of a control and processing system applicable to the system illustrated in  FIG. 13 . As shown in  FIG. 14 , the computer control system is representative of computer  1350  shown in  FIG. 13 . In  FIG. 14 , the computer  1350  includes central processing unit (CPU)  1401 , a storage memory (RAM)  1402 , a user input/output (I/O) interface  1403 , and a system interface  1404 . The computer  1350  illustrated in  FIG. 14  can issue a command that can be transmitted to the imaging system  1300  via the system interface  1404 . A touch panel screen can be included as part of the user interface unit/imaging processor, in addition a key board, mouse, joy-stick, ball controller, and foot pedal can also be included as part of the user interface. The user can cause a command to be initiated to observe inside a lumen of the human body through the exemplary front-view SEE probe using the user interface unit/imaging processor. For example, when the user inputs a command via the user interface  1403 , the command is transmitted to the central processing unit CPU  1401  for execution thereby causing the CPU to issue a command via the system interface  1404  to one or more of the light source  1370 , the detector/spectrometer  1380 , or the FORJ  1330 . 
     The CPU  1401  is comprised of one or more processors (microprocessors) configured to read and perform computer-executable instructions stored in the storage memory  1402 . The computer-executable instructions may include program code for the performance of the novel processes, methods and/or calculations disclosed herein. 
     The computer  1350  functions as imaging processor that can be programmed to apply exemplary image processing such as noise reduction, coordinate distortion correction, contrast enhancement and so on. After or even during the image processing is performed, the data can be transmitted from the imaging processor to a display (not shown). A liquid crystal display (LCD) can be the display. The display can display, for example, the individual images obtained from a single color or a composite color image according to the various exemplary embodiments of the present disclosure. The display can also display other information than the image, such as the date of observation, what part of the human body is observed, the patient&#39;s name, operator&#39;s name and so on. 
     The CPU  1401  is configured to read and perform computer-executable instructions stored in the Storage/RAM  1402 . The computer-executable instructions may include those for the performance of the methods and/or calculations described herein. For example, CPU  1401  may calculate the angular momentum or speed of rotation of the SEE probe, and can use that information (rotation speed or angular momentum) to operate the FORJ. In this manner, computer  1350  can obtain a new set of images where their angular positions are corrected. Storage/RAM  1402  includes one or more computer readable and/or writable media, and may include, for example, a magnetic disc (e.g., a hard disk), an optical disc (e.g., a DVD, a Blu-ray), a magneto-optical disk, semiconductor memory (e.g., a non-volatile memory card, flash memory, a solid state drive, SRAM, DRAM), an EPROM, an EEPROM, etc. Storage/RAM  1402  may store computer-readable data and/or computer-executable instructions. The components of the processor may communicate via a bus. 
     The system I/O interface  1404  provides communication interfaces to input and output devices, which may include a keyboard, a display, a mouse, a printing device, a touch screen, a light pen, an optical storage device, a scanner, a microphone, a camera, a drive, communication cable and a network (either wired or wireless). 
     The system I/O interface  1404  also provides communication interfaces to input and output devices. The detector may include, for example a photomultiplier tube (PMT), a photodiode, an avalanche photodiode detector (APD), a charge-coupled device (CCD), multi-pixel photon counters (MPPC), or other. Also, the function of detector may be realized by computer executable instructions (e.g., one or more programs) recorded on a Storage/RAM  1402 . 
     In an exemplary operation, the user can place the exemplary SEE probe into a sheath, and then can insert such arrangement/configuration into a predetermined position of a human body. The sheath alone may be inserted into the human body in advance, and it is possible to insert the SEE probe into the sheath after sheath insertion. The exemplary probe can be used to observe inside human body and works as an endoscope such as arthroscopy, bronchoscope, sinuscope, vascular endoscope and so on. 
     &lt;Definitions&gt; 
     In referring to the description, specific details are set forth in order to provide a thorough understanding of the examples disclosed. In other instances, well-known methods, procedures, components and circuits have not been described in detail as not to unnecessarily lengthen the present disclosure. 
     It should be understood that if an element or part is referred herein as being “on”, “against”, “connected to”, or “coupled to” another element or part, then it can be directly on, against, connected or coupled to the other element or part, or intervening elements or parts may be present. In contrast, if an element is referred to as being “directly on”, “directly connected to”, or “directly coupled to” another element or part, then there are no intervening elements or parts present. When used, term “and/or”, includes any and all combinations of one or more of the associated listed items, if so provided. 
     Spatially relative terms, such as “under” “beneath”, “below”, “lower”, “above”, “upper”, “proximal”, “distal”, and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the various figures. It should be understood, however, that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, a relative spatial term such as “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein are to be interpreted accordingly. Similarly, the relative spatial terms “proximal” and “distal” may also be interchangeable, where applicable. 
     The term “about,” as used herein means, for example, within 10%, within 5%, or less. In some embodiments, the term “about” may mean within measurement error. 
     The term “substantially”, as used herein means that, within fabrication parameters and/or measurement error. 
     The terms first, second, third, etc. may be used herein to describe various elements, components, regions, parts and/or sections. It should be understood that these elements, components, regions, parts and/or sections should not be limited by these terms. These terms have been used only to distinguish one element, component, region, part, or section from another region, part, or section. Thus, a first element, component, region, part, or section discussed below could be termed a second element, component, region, part, or section without departing from the teachings herein. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms “a”, “an”, and “the”, are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should be further understood that the terms “includes” and/or “including”, when used in the present specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof not explicitly stated. 
     The foregoing merely illustrates the principles of the disclosure. Various modifications and alterations to the described exemplary embodiments will be apparent to those skilled in the art in view of the teachings herein. Indeed, the arrangements, systems and methods according to the exemplary embodiments of the present disclosure can be used with any SEE system or other imaging systems, and for example with those described in U.S. Pat. Nos. 6,341,036; 7,796,270; 7,843,572; 7,859,679; 8,045,177; 8,145,018; 8,780,176; and 8,812,087; and U.S. Patent Application Nos. 2008/0013960 and 2011/0237892; and PCT publications WO2015/116951 and WO2015116939, the disclosures of which are incorporated by reference herein in their entireties. 
     In describing example embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent application is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner. 
     While the present disclosure has been described with reference to exemplary embodiments, it is to be understood that the present disclosure is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.