Patent Publication Number: US-2021186314-A1

Title: Dual endoscope device and methods of navigation therefor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to U.S. provisional application 62/952,770, filed Dec. 23, 2019, the disclosure of which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND INFORMATION 
     Field of Disclosure 
     The present disclosure relates to medical devices. More particularly, the disclosure exemplifies various embodiments of a dual endoscope system and methods of operation therefor. 
     Description of Related Art 
     Medical imaging probes, such as endoscopes and catheters, can be inserted through natural orifices or small surgical incisions of a patient&#39;s body to provide detailed images from inside the patient&#39;s body while being minimally invasive to the patient&#39;s comfort. An endoscope is a medical device comprising a tubular conduit with one or more longitudinal channels through which a bodily lumen can be imaged, examined, and/or treated. Endoscopes which include a camera mounted on the distal end of the tube can provide visual access to difficult to reach areas while a medical professional navigates the endoscope into a body cavity looking for abnormalities. These difficult to reach areas are, at times, in sensitive areas where navigation errors can cause harm to the patient. The likelihood of navigation error is small when it is a rigid zero-degree endoscope, which looks straight ahead in a forward direction, and the user can observe the image through a video monitor. However, as the orientation of the scope deviates from zero degrees in order to provide lateral views, or when the endoscope is flexible and it travels through tortuous paths, the presentation of images on a video monitor, and the navigation based on such images becomes more and more difficult. 
     Previous attempts to address the above-described issues include image guided navigation, for example, as described in U.S. Pat. Nos. 5,638,819 and 8,000,890. However, image guided navigation generally relies on extensive three-dimensional (3D) computer enhancement and reconstruction of tomogram images taken prior to the actual navigation procedure. However, no amount of computer enhancement and reconstruction of tomogram images taken at a past point in time could accurately represent the patient&#39;s anatomy during real time endoscope navigation. More specifically, although modern computers can perform complex 3D analysis of previously acquired tomogram images in near real time, the actual instrument positioning and navigation could still be hampered by changes in the patient&#39;s anatomy or patient&#39;s movement. That is, image navigation systems which are based on previously acquired tomograms merely track actions already taken by the endoscope user, but fail to adequately inform the user of what actions are necessary to take in order to safely guide an instrument along a specific trajectory without causing damage to a patient. 
     Other attempts to improve endoscope navigation towards difficult to reach areas includes the provision of dual-view endoscopes which include dual viewing ports one for forward viewing and one for lateral viewing, for example, as described in U.S. Pat. No. 4,846,154. U.S. Pat. Nos. 6,554,767 and 8,182,422 disclose an endoscope device and a component attachable-to and detachable-from the endoscope distal end to provide an existing endoscope with an auxiliary imaging device. Multiple endoscopes are occasionally used in combination. By way of example, a so-called mother endoscope may be used with a so-called daughter or baby endoscope. By way of example, the daughter or baby scope may be used to view areas beyond the reach of the mother endoscope. U.S. Pat. No. 4,979,496 and patent application publication US 2010/0228086 disclose a primary (mother) endoscope into which a secondary (daughter) endoscope is inserted through the working channel of the mother endoscope. In these documents, the daughter endoscope could be used to explore and treat areas lateral or tangential to the mother endoscope. However, mother-daughter endoscope systems generally require two operators (one for each endoscope), and the mother endoscope does not provide a direct view of an insertion path for the daughter endoscope. 
     Therefore, while there are a variety of endoscopes with front and side-viewing capabilities, endoscopes with attachable auxiliary cameras, and multi-channel endoscopes which can provide improved navigation, these endoscopes are still limited by certain disadvantages. Some of these disadvantages include, but are not limited to, not visualizing insert tools, not indicating the position of inserted tools, or even not having the capability of inserting bent or bendable tools. 
     Spectrally encoded endoscopy (SEE) probes are submillimeter (miniaturized) imaging probes which employ a few or single optical fibers with a miniature diffraction grating at the distal end of the fiber to image the inside of a bodily lumen. An example of a miniaturized SEE probe is described by Tearney et al., in “Spectrally encoded miniature endoscopy”, published in Opt. Lett. 27: 412-414 (2002). SEE probes can be configured for forward-view imaging or for side-view imaging. In either case, broadband light is delivered by the optical fiber or fibers from a light source to the distal end of the probe and focused by a miniature lens. A diffraction grating, which is positioned after the miniature lens, disperses the broadband light into multiple beams with different wavelengths (colors) to generate a spectrally resolved line of light on the imaging plane. Each line illuminates a sample (e.g., tissue) in a different direction from the end of the probe, and thus encodes light reflected from the sample in a given transverse coordinate by wavelength. A line image of the sample is acquired by digitally analyzing the spectral frequency of light reflected from the tissue and returned by the probe. A two-dimensional (2D) image is formed by slowly scanning the spectrally encoded line on the sample along another transverse coordinate (orthogonal to the first transverse coordinate). The other transverse coordinate, which is typically perpendicular to the spectrally-encoded coordinate, is scanned by rotating the SEE probe with a small motor that is typically located in the endoscope handle outside of the patient. 
     Miniaturized SEE probes have the potential to more easily navigate and reach hard-to-reach imaging areas within a bodily lumen of a patient. For example, SEE probes can be used to obtain images from inside the maxillary sinus by inserting the endoscope through the natural ostium of a patient. To access the maxillary sinus, by inserting a thin endoscope through the natural ostium, the endoscope should be flexible and/or should have a predefined curved shape. In such cases, endoscope users have to rotate and/or bend the endoscope guide to advance from the entry point (the nasal passage) through a tortuous path (the natural ostium) to reach the target location (maxillary sinus) while observing a live image in a video monitor. A similar issue arises when navigating an endoscope or other imaging probe along other tortuous biological paths, such as navigating a patient&#39;s airway going from the trachea through the carina and into the lungs. In this case, to have a more intuitive procedure, endoscope users want the endoscope image orientation to be the same as the patient&#39;s orientation so that the user will not lose track of where the endoscope tip is (position) and where it is looking (orientation) while the endoscope advances through the tortuous path towards the specific target location. 
     However, when the SEE endoscope or other imaging probe is in a tortuous path and needs to access a specific location as the maxillary sinus or lungs described above, and the movement of the endoscope is limited by the geometry of the endoscope and/or the anatomy of the lumen, users cannot intuitively navigate towards the desired specific location. Therefore, there remains a need for an endoscope device which can allow a user to easily navigate through tortuous paths without causing any detriment to the patient&#39;s sensitive areas. 
     SUMMARY OF EXEMPLARY EMBODIMENTS 
     According to at least one embodiment of the present disclosure, there is provided an endoscope system, comprising: a main endoscope having a first tubular shaft which is rigid and substantially straight extending from a proximal end to a distal end; a secondary endoscope having a second tubular shaft which has a straight portion and a bent portion at the distal end thereof; and a display device configured to display an image received from the main endoscope and/or the secondary endoscope, wherein the main endoscope and the secondary endoscope are joined together along a length of the first and second tubular shafts and are configured to be simultaneously inserted into a lumen, wherein the main endoscope is arranged to acquire a first image of a field of view from inside the lumen, and the secondary endoscope is arranged to acquire a second image of an area which is tangential or lateral to the field of view, and wherein the display device displays the first image acquired by main endoscope and a graphic object depicting a position and orientation of the secondary endoscope with respect to the main endoscope. 
     According on an aspect of the present disclosure, it is further provided an endoscope system for performing a medical procedure, comprising: a first endoscope probe having opposite proximal and distal ends, wherein at least a distal portion of the first endoscope probe is rigid and substantially straight and configured to be inserted into a bodily lumen for forward-view imaging; and a second endoscope probe having opposite proximal and distal ends and configured to be inserted into the bodily lumen for side-view imaging, wherein at least the distal end of the second endoscope probe is bent at an angle with respect to a proximal portion thereof. The first endoscope probe and the second endoscope probe are joined together substantially parallel to each other such that the first endoscope probe is arranged to take forward-view images from a field of view that includes the distal end of the second endoscope probe when the second endoscope probe is navigated through the bodily lumen. 
     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 showing a first embodiment of a dual-scope endoscope system  100  which includes a main endoscope  150 , a secondary endoscope  130 , a console  110 , and a display  115 . 
         FIG. 2  illustrates an exemplary block diagram of constituent parts of the console  110 . 
         FIG. 3A  and  FIG. 3B  show detailed schematics of an example of the secondary endoscope  130 . 
         FIG. 4A  illustrates an example of an arrangement where the main endoscope  150  is attached to the secondary endoscope  160  via a mechanical joint  160 .  FIG. 4B  shows an example of a video image  401  obtained from the main endoscope  150  and displayed on a screen of display  115  together with a graphic object  405  which indicates the position and orientation of the tip of the secondary endoscope  130  with respect to field-of-view of the main endoscope  150 . 
         FIG. 5A  shows another example of an arrangement where the main endoscope  150  is attached to the secondary endoscope  160  via a mechanical joint  160 .  FIG. 5B  shows an example of a video image  501  obtained from the main endoscope  150  and displayed on a screen of display  115  together with a graphic object  505  which indicates the position and orientation of the tip of the secondary endoscope  130  with respect to field-of-view of the main endoscope  150 . 
         FIG. 6A  shows an embodiment where the secondary endoscope (SEE scope)  130  can be temporarily attached to the main endoscope  150  via pressure fitting cylindrical clamps  161   a  and  161   b .  FIG. 6B  shows a display  115  with video image  601  together with a graphic object  605  which indicates the position and orientation of the tip of the secondary endoscope  130  with respect to field-of-view of the main endoscope  150 . 
         FIG. 7  shows an embodiment where the secondary endoscope (SEE scope)  130  can be temporarily attached to the main endoscope  150  via a sleeve or cylindrical tube  165 . 
         FIG. 8  shows an embodiment where the secondary endoscope (SEE scope)  130  can be temporarily attached to the main endoscope  150  via a guide rail  162   a  and an engaging member  162   b.    
         FIG. 9  illustrates an exemplary embodiment of the handle  120  configured to operate one or both of the main endoscope  150  and the secondary endoscope  130 . 
         FIG. 10A  illustrates an example of the endoscope system  100  arranged to be used in navigation or insertion mode.  FIG. 10B  shows an example of the endoscope system  100  arranged to be used in a procedure or imaging mode. 
         FIG. 11  illustrates a flowchart of a tracking procedure for monitoring in real time the relative position of the secondary endoscope with respect to the main endoscope. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The exemplary embodiments disclosed herein are based on an objective of providing a first endoscope probe and the second endoscope probe joined together substantially parallel to each other such that the first endoscope probe is arranged to take forward-view images from a field of view that includes the distal end of the second endoscope probe when the second endoscope probe is navigated through a bodily lumen. The second endoscope probe is preferably a fiber-optic-based imaging probe that can be fabricated easily, at low cost, and can maintain the ability to provide high quality images. As used herein, imaging probes and optical elements thereof include miniaturized components having physical dimensions of 1.5 millimeters (mm) or less in diameter. 
     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. In addition, while the subject disclosure is described in detail with reference to the enclosed figures, it is done so in connection with 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. Although the drawings represent some possible configurations and approaches, the drawings are not necessarily to scale and certain features may be exaggerated, removed, or partially sectioned to better illustrate and explain certain aspects of the present disclosure. The descriptions set forth herein are not intended to be exhaustive or otherwise limit or restrict the claims to the precise forms and configurations shown in the drawings and disclosed in the following detailed description. 
     When a feature or element is herein referred to as being “on” another feature or element, it can be directly on the other feature or element or intervening features and/or elements may also be present. In contrast, when a feature or element is referred to as being “directly on” another feature or element, there are no intervening features or elements present. It will also be understood that, when a feature or element is referred to as being “connected”, “attached”, “coupled” or the like to another feature or element, it can be directly connected, attached or coupled to the other feature or element or intervening features or elements may be present. In contrast, when a feature or element is referred to as being “directly connected”, “directly attached” or “directly coupled” to another feature or element, there are no intervening features or elements present. Although described or shown with respect to one embodiment, the features and elements so described or shown in one embodiment can apply to other embodiments. It will also be appreciated by those of skill in the art that references to a structure or feature that is disposed “adjacent” to another feature may have portions that overlap or underlie the adjacent feature. 
     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 are not limited by these terms of designation. These terms of designation 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 merely for purposes of distinction but without limitation and without departing from structural or functional meaning. 
     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”, “comprises” and/or “comprising”, “consists” and/or “consisting” when used in the present specification and claims, 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. Further, in the present disclosure, the transitional phrase “consisting of” excludes any element, step, or component not specified in the claim. It is further noted that some claims or some features of a claim may be drafted to exclude any optional element; such claims may use exclusive terminology as “solely,” “only” and the like in connection with the recitation of claim elements, or it may use of a “negative” limitation. 
     The term “about” or “approximately” as used herein means, for example, within 10%, within 5%, or less. In some embodiments, the term “about” may mean within measurement error. In this regard, where described or claimed, all numbers may be read as if prefaced by the word “about” or “approximately,” even if the term does not expressly appear. The phrase “about” or “approximately” may be used when describing magnitude and/or position to indicate that the value and/or position described is within a reasonable expected range of values and/or positions. For example, a numeric value may have a value that is +/−0.1% of the stated value (or range of values), +/−1% of the stated value (or range of values), +/−2% of the stated value (or range of values), +/−5% of the stated value (or range of values), +/−10% of the stated value (or range of values), etc. Any numerical range, if recited herein, is intended to include all sub-ranges subsumed therein. As used herein, the term “substantially” is meant to allow for deviations from the descriptor that do not negatively affect the intended purpose. For example, deviations that are from limitations in measurements, differences within manufacture tolerance, or variations of less than 5% can be considered within the scope of substantially the same. The specified descriptor can be an absolute value (e.g. substantially spherical, substantially perpendicular, substantially concentric, etc.) or a relative term (e.g. substantially similar, substantially the same, etc.). 
     The present disclosure generally relates to medical devices, and it exemplifies embodiments of an optical probe which may be applicable to a spectroscopic apparatus (e.g., an endoscope), an optical coherence tomographic (OCT) apparatus, or a combination of such apparatuses (e.g., a multi-modality optical probe). The embodiments of the optical probe and portions thereof are described in terms of their state in a three-dimensional space. As used herein, the term “position” refers to the location of an object or a portion of an object in a three-dimensional space (e.g., three degrees of translational freedom along Cartesian X, Y, Z coordinates); the term “orientation” refers to the rotational placement of an object or a portion of an object (three degrees of rotational freedom—e.g., roll, pitch, and yaw); the term “posture” refers to the position of an object or a portion of an object in at least one degree of translational freedom and to the orientation of that object or portion of object in at least one degree of rotational freedom (up to six total degrees of freedom); the term “shape” refers to a set of posture, positions, and/or orientations measured along the elongated body of the object. As it is known in the field of medical devices, the terms “proximal” and “distal” are used with reference to the manipulation of an end of an instrument extending from the user to a surgical or diagnostic site. In this regard, the term “proximal” refers to the portion of the instrument closer to the user, and the term “distal” refers to the portion of the instrument further away from the user and closer to a surgical or diagnostic site. 
     As used herein the term “catheter” generally refers to a flexible and thin tubular instrument made of medical grade material designed to be inserted through a narrow opening into a bodily lumen (e.g., a vessel) to perform a broad range of medical functions. The more specific term “optical catheter” refers to a medical instrument comprising an elongated bundle of one or more flexible light conducting fibers disposed inside a protective sheath made of medical grade material and having an optical imaging function. A particular example of an optical catheter is a fiber optic catheter which comprises a sheath, a coil, a protector and an optical probe. In some applications a catheter may include a “guide catheter” which functions similarly to a sheath. 
     As used herein the term “endoscope” refers to a rigid or flexible medical instrument which uses light guided by an optical probe to look inside a body cavity or organ. A medical procedure, in which an endoscope is inserted through a natural opening, is called an endoscopy. Specialized endoscopes are generally named for how or where the endoscope is intended to be used, such as the bronchoscope (mouth), sigmoidoscope (rectum), cystoscope (bladder), nephroscope (kidney), bronchoscope (bronchi), laryngoscope (larynx), otoscope (ear), arthroscope (joint), laparoscope (abdomen), and gastrointestinal endoscopes. 
     In the present disclosure, the terms “optical fiber”, “fiber optic”, or simply “fiber” refers to an elongated, flexible, light conducting conduit capable of conducting light from one end to another end due to the effect known as total internal reflection. The terms “light guiding component” or “waveguide” may also refer to, or may have the functionality of, an optical fiber. The term “fiber” may refer to one or more light conducting fibers. An optical fiber has a generally transparent, homogenous core, through which the light is guided, and the core is surrounded by a homogenous cladding. The refraction index of the core is larger than the refraction index of the cladding. Depending on design choice some fibers can have multiple claddings surrounding the core. 
     As outlined above, there is a need for an endoscope device which can provide lateral views and still allow a user to easily navigate through tortuous paths without causing any detriment to the patient&#39;s sensitive areas. A solution outlined in this disclosure is to incorporate a main endoscope (mother endoscope) in conjunction with a secondary (daughter) endoscope in order to enable a user to maintain precise tracking and orientation of the daughter endoscope during navigation. 
     &lt;FIG.  1 &gt; 
       FIG. 1  shows a first embodiment of a dual-scope endoscope system  100  including a main endoscope  150  and a secondary endoscope  130 . The main endoscope  150  is not limited to any particular type of endoscope, but the secondary endoscope  130  is preferably a miniaturized endoscope (i.e., smaller than the main endoscope), such as, an SEE endoscope device, for example. 
     The endoscope system  100  includes a console  110 , a display  115 , a handle  120 , a main endoscope  150 , and a secondary endoscope  130 . The console  110  and the handle  120  are operably connected to each other by a cable bundle  125 . The display  115  is an image display device, such as an LCD, LED, OLED monitor, which shows a live view image (video image) acquired by the main endoscope  150 , and a processed endoscopic image acquired by the secondary endoscope  130 . According to one embodiment, the main endoscope  150  and the secondary endoscope  130  are removably attached to each other by a mechanical joint  160 . 
     The main endoscope  150  may be implemented as any suitable device for use in a medical procedure, and which is configured to obtain a live image (i.e., a video image) within a field of view  152  of a site where a medical procedure is to be performed. The main endoscope  150  is not particularly limited to any specific implementation, as long as it is a suitable device for use in a medical procedure, and is configured to obtain a live image (a video image) of a lumen. To that end, the main endoscope  150  is shaped as a substantially tubular shaft extending along a longitudinal axis A 1 . The main endoscope  150  may include at least an imaging device  151 , such as imaging chip (e.g., a CMOS or CCD sensor) disposed at the distal end of the tubular shaft, and may include additional hardware necessary for image acquisition and for navigating the endoscope through a lumen. For example, the main endoscope  150  may include, in addition to the imaging device  151 , a guide wire, a catheter, a biopsy or ablation needle, or other similar devices. The main endoscope  150  may also include, in addition to the imaging device  151 , one or more working channels for the manipulation of tools (e.g., forceps or tweezers) and for delivery or extraction of fluids such as blood or gas. 
     The secondary endoscope  130  is enclosed in an endoscope guide  135  which is independent from (not part of) the main endoscope  150 . The endoscope guide  135  is a tubular shaft having a longitudinal axis A 2  and extending from a proximal end  131  to a distal end  139 . According to at least one embodiment, the endoscope guide  135  may include a distal section  138  and a proximal section  137 . The proximal section  137  is substantially strain and linear, while the distal section  139  is bent, bendable, or steerable. The proximal section  137  is substantially parallel to the shaft of the main endoscope  150 . The distal section can be bent at an angle in a range from about 25 to 90 degrees with respect to shaft of the main endoscope  150 . The endoscope guide  135  contains inside the tubular shaft thereof, among other things, the secondary endoscope  130  which in turn includes endoscope optics also referred to as an optical probe. Endoscope optics includes at least illumination optics and detection optics, as described more in detail with respect to  FIG. 3A  and  FIG. 3B . In at least some embodiments, the secondary endoscope may also include certain end effectors. 
     In an embodiment where the secondary endoscope  130  is an SEE endoscope, the illumination optics emits a illumination light within a field of view  142 , such that a spectrally-encoded illumination light  140  reaches a sample  200  which is tangential to the FOV  152  of the main endoscope  150 . In an SEE endoscope, the detection optics collects light reflected and/or scattered by the sample  200  (e.g., an inner wall of a bodily lumen or an area adjacent or lateral to the lumen). The sample  200  can be a hard-to-reach area in a bodily lumen of a patient. For example, in nasal endoscopy, the secondary endoscope  130  may include an SEE probe inside an endoscope guide  135  used to obtain images from inside the maxillary sinus by inserting the secondary endoscope through the natural ostium of a patient. 
     The endoscope guide  135  can be a rigid and curved tubular shaft with a predetermined angle of orientation which bends towards (or away from) the main endoscope  150 . In some embodiments, the endoscope guide  135  of the secondary endoscope  130  can be at least partially flexible and configured to be actively bent (e.g., by kinematic actuation) with respect to the main endoscope  150 . The handle  120  is configured to enable a user to manually operate the main endoscope  150  and/or the secondary endoscope  130 . The handle  120  may include a controller circuit  121  and an interface unit  122  which are configured to indicate or select which endoscope among the main endoscope  150  and the secondary endoscope  130  should be controlled during a procedure. 
     For an exemplary nasal endoscopy procedure, the main endoscope  150  may be a zero-degree (straight) nasal endoscope which allows for a straight view into the patient&#39;s nose through the nostril to examine the nasal passages. The secondary endoscope  130  may be a flexible or pre-curved endoscope (e.g., pre-shaped at 30, 45, 70 or 90 degrees of angled curvature) to allow for deeper “around-the-corner” views into the patient&#39;s difficult-to-reach areas, such as sinus cavities or the maxillary sinus. The use of the two endoscopes simultaneously can provide maximum visualization of the patient&#39;s sensitive areas to make diagnoses and/or perform procedures with high accuracy and enhanced patient safety. 
     Endoscopic data from the main endoscope  150  may be captured according to one or more of various endoscopic or catheter imaging modalities, including video endoscopy (through a videoscope), spectroscopy, fluoroscopy, optical coherence tomography (OCT), e.g., using an OCT catheter, or other similar endoscopic modalities. In some embodiments, the main endoscope  150  may include a working channel for one or more medical instruments and means for providing a forward view image of the lumen; the forward view of the lumen can be used as a live view for navigation, or can be stored in the system for correlation with the imaging of the secondary endoscope  130 . In some embodiments, the secondary endoscope  130  may be permanently attached to an outer surface of the main endoscope  150 . In other embodiments, the mother or main endoscope  150  may function as a primary modality such as an OCT catheter, while the daughter of secondary endoscope  130  may be temporarily attached to the side of the main endoscope  150  to aid the navigation of the main endoscope. Alternatively, main endoscope  150  aids in the navigation of the secondary endoscope  130 . In either case, image data from the two endoscopes is preferably recorded and processed separately by the console  110 , but the images can be viewed together or separately in the display  115 , as desired by the user. 
     As shown in  FIG. 1 , the secondary endoscope  130  is arranged in close proximity, and substantially parallel, to the main endoscope  150  such that the distal end  139  (the tip) of the secondary endoscope  130  is within the field of view  152  of the main endoscope  150 . In this manner, the user can observe the tip of the secondary endoscope in the field of view shown on the mother endoscope monitor, as further explained with reference to  FIG. 4B  and  FIG. 5B  discussed below. To facilitate assembling, reduce space, and improver procedure accuracy, the first axis A 1  of the main endoscope  150  and the second axis A 2  of the secondary endoscope  130  are parallel to each other at least a portion of their length thereof. 
     &lt;FIG.  2 &gt; 
     As mentioned above, the endoscope system  100  includes a console  110  and a handle  120  which are in operable communication with each other to control the operations of one or both of the main endoscope  150  and the secondary endoscope  130 .  FIG. 2  illustrates an exemplary block diagram of constituent components of the console  110 . Console  110  may be implemented by, for example, a general purpose computer specifically programmed with algorithms to execute endoscope navigation and image orientation control, for example, as described with reference to  FIGS. 4B and 5B . The console  110  includes or is operably attached to the display  115  for displaying the images acquired with endoscope system  100 . To that end, console  110  includes a central processing unit (CPU)  261 , a storage memory (ROM/RAM)  262 , a user input/output (I/O) interface  263 , and a system interface  264  which are all interconnected via a data bus  265 . The console  110  can programmed to issue a command that can be transmitted to the various parts of the imaging system  100  upon receiving a user input via the user interface  263 . An input device, such as key board, a mouse, and/or a touch panel screen in the display  115  can be provided as part of the user interface  263 . 
     The CPU  261  may be configured to read and perform computer-executable instructions stored in the storage memory  262 . The computer-executable instructions may include program code for the performance of the methods, measurements, and/or calculations of the system  100 , as described herein. For example, CPU  261  may receive signals from handle  120  corresponding to a selection or operation of the main endoscope  150  or the secondary endoscope  130  to obtain images from a bodily lumen sample  200 . 
     The system interface  264  provides an electronic interface for the various components connected to or provided in the console  110 . For example, the system interface  264  provides an electronic interface for one or more a light source (not shown) which emits broadband light to the second endoscope  130 , a detector or spectrometer (not shown), the cable bundle  125 , and the display  115 . The system interface  264  includes electronics necessary to receive electrical signals corresponding to images acquired by the main endoscope  150  and the secondary endoscope  130 , and to output a video signal out to the display  115 . 
     The console  110  may contain, in addition to a CPU  261 , for example, one or more of a field-programmable gate array (FPGA), a digital signal processor (DSP), an application specific integrated circuit (ASIC), a graphic processing unit (GPU), a system on chip (SoC) or combinations thereof, which perform some or the entire image processing and signaling of the endoscope system  100 . 
     &lt;FIG.  3 A and FIG.  3 B&gt; 
       FIG. 3A  and  FIG. 3B  show detailed schematics of an example of the secondary endoscope  130 . As shown in  FIG. 3A , the secondary endoscope  130  is enclosed inside the endoscope guide  135 . The secondary endoscope  130  includes an outer sheath  244 , an inner sheath  242 , a drive cable  216 , and a probe  220  arranged enclosed in the inner diameter of drive cable  216 . The drive cable  216  is rotated together with the probe  220  inside of the inner sheath  242 . The inner sheath  242  is surrounded by detection optics  240  which can be a ring of detection waveguides  245  (e.g., a ring of optical fibers or a fiber bundle). The inner sheath  242  supports a transparent window  228  at the distal end of the endoscope  130 . The transparent window  228  protects the illumination optics of probe  220  from the outside environment surrounding the endoscope guide. Concentrically surrounding the detection optics  240  there is provided the outer sheath  244  to protect the ring of optical fibers or fiber bundle which constitutes the detection optics  240 . All of the foregoing components are enclosed inside of the inner diameter of endoscope guide  135 . As described above, the endoscope guide  135  can be rigid or flexible, and it is preferably bent at the distal end thereof to facilitate navigation and side-view imaging of specific anatomical features, such as the maxillary sinus. At the proximal end, the endoscope guide  135  is fixedly connected to the endoscope handle  120 . In an imaging operation, the endoscope guide  135  is not mechanically rotated, but the user operates the endoscope guide  135  to pitch, roll, and change its direction of view, by manipulating the endoscope handle  120 . 
     As shown in  FIG. 3B , the illumination optics probe  220  includes an illumination waveguide  215  which can be a single mode or multi-mode fiber (a light guiding element), a focusing element  221  which can be a graded index (GRIN) lens or a ball lens, a spacer  222 , and a diffractive element  224 . The spacer  222  can be a transparent component having at least two surfaces configured to guide illumination light  209  provided through the illumination waveguide  215  and the focusing element  221 . Specifically, the spacer  222  includes a first surface which is a reflective surface  223  and a second surface which includes a grating surface containing the diffractive element  224 . The spacer  222  can be made of transparent plastic, e.g., by injection molding, or can be made of glass, e.g., by glass compression molding, or it can be a piece of coreless optical fiber. The reflective surface  223  can be made by polishing a part of the spacer to satisfy total internal reflection (TIR) conditions, or it can be a mirror-coated surface. The second surface containing the diffractive element  224  can be made by applying UV-curable resin on the second surface of the spacer  222  and stamping a master grating on the resin, by a nanoimprint technique, e.g., as described in U.S. patent Ser. No. 10/261,223 which is incorporated by reference herein in its entirety. The illumination light  209  from the illumination waveguide  215  is slightly focused by the focusing element  221  and reflected by the reflective surface  223 , and thereafter diffracted by the diffractive element  224  so that a spectrally-encoded illumination line  140  is formed over the sample  200 , at a working distance from the probe&#39;s distal end. 
     &lt;FIG.  4 A- 5 B: Navigation and Tracking&gt; 
     Turning now to  FIG. 4A through 5B  an example of navigation and tracking of the dual endoscope is described.  FIG. 4A  shows an example embodiment where the main endoscope  150  and the secondary endoscope  160  are attached to each other via a mechanical joint  160 . As shown in  FIG. 4A , at least a portion of the main endoscope  150  at the distal end thereof is rigid and substantially straight (i.e., not curved or bent). On the other hand, at least a portion of the secondary endoscope  130  at the distal end thereof is bent at a predetermined angle, or is flexible so as to be bent at an arbitrary angle, with respect to the main endoscope  150 . In the arrangement shown in  FIG. 4A , the distal portion of the secondary endoscope  130  is bent away from the shaft of the main endoscope  150 . This particular arrangement can be advantageous in certain applications, such as for imaging the maxillary sinus by inserting the secondary endoscope via the natural ostium of a patient&#39;s ostiomeatal complex (OMC). OMC is a common channel that links the frontal sinus, anterior ethmoid air cells and the maxillary sinus to the middle meatus, allowing airflow and mucociliary drainage. The distal end of the secondary endoscope  130  can be bent a priori or can be actively controlled to bend, for example, by about 30, 45 or 70 degrees, which are typical inclinations for nasal endoscopes. 
     As it will be understood by persons skilled in the art, endoscope navigation through the OCM channel possesses significant challenges in that the OCM channel represents a highly tortuous path, where it is important that the tip of the endoscope is visible at all times and no pressure whatsoever is exerted on the lateral nasal wall to prevent accidental discomfort or injury to the patient. To that end, according to the present disclosure, it is advantageous to use a highly flexible or pre-angled ultrathin secondary endoscope together with a conventional endoscope. The secondary endoscope  130  can have a pre-set shape, or can be steerable (e.g., by kinematic action) from the handle  120 . In the case where the secondary endoscope  130  is bent away from the main endoscope  150  and the distal end of the secondary endoscope is not within the field of view  152  of the main endoscope (e.g., as illustrated in  FIG. 4A ), the mechanical joint  160  can be used as a reference point to track the orientation of the secondary endoscope  130  with respect to the main endoscope  150  during insertion into a lumen. 
     To track the orientation of the secondary endoscope  130  with respect to the main endoscope  150 , the console  110  receives a video image from the main endoscope  150  and displays the video image on a screen of a display  115 .  FIG. 4B  shows an example of a video image  401  obtained from the main endoscope  150  and displayed on a screen of display  115 . To track the orientation of the secondary endoscope  130 , the display  115  also shows a pointer  405  (a graphic object) which corresponds to the position of mechanical joint  160  with respect to the main endoscope  150 . In this manner, during a procedure, when the endoscope operator uses the main endoscope  150  to advance through a lumen, the pointer  405  will be shown at a fixed position with respect to video image  401 . And, when the operator rotates the main endoscope  150 , the pointer  405  shown on the display  115  will move around the edge of video image  401  to show the direction and amount of rotation. In  FIG. 4B , the pointer  405  is shown as a temporary pointer  405   a  indicating a clockwise rotation of the dual endoscope. This will inform the user of the exact position and orientation of the tip of the secondary endoscope  130  with respect to the lumen being imaged. According to the arrangement of  FIG. 4A , the main endoscope  150  and the secondary endoscope  130  can rotate locked together as unit. In this case, pointer  405  can be advantageously used to show the endoscope operator the direction in which the tip of the secondary endoscope is pointed to. In other embodiments, however, the main endoscope  150  and the secondary endoscope  130  may rotate independently of each other. 
       FIG. 5A  shows another example where the main endoscope  150  and the secondary endoscope  160  are attached to each other via a mechanical joint  160 . As show in  FIG. 5A , the distal portion of the secondary endoscope  130  is bent towards the shaft of the main endoscope  150 . In this arrangement, the main endoscope  150  is arranged to take forward-view images from a field of view  152  that includes the distal end  139  of the secondary endoscope  130 . With this arrangement, the secondary endoscope  130  can be used to obtain side-view images of the bodily lumen or of areas tangential to the lumen, while the main endoscope  150  is used for live view navigation through the lumen. 
     This particular arrangement can be advantageous in certain applications, such as for imaging the maxillary sinus by inserting the endoscope via the natural ostium and constantly monitoring that the distal end  139  of the secondary endoscope  130  exerts no pressure whatsoever on the lateral nasal wall to prevent accidental injury to the patient. 
     Similar to the previous example, the console  110  can show a live image in the display  115  to track in real time the position of the main endoscope  150  and the orientation of the secondary endoscope  130  with respect to the main endoscope. To that end, the console  110  receives a video image from the main endoscope  150  and displays the video image on a screen of display  115 .  FIG. 5B  shows an example of a video image  501  as it would be obtained from the main endoscope  150  and displayed on a screen of display  115 . To track the orientation of the secondary endoscope  130 , the display  115  also shows either a live image of the distal end  139  of secondary endoscope  130  and/or a pointer  505  inside the edge of the image  501 . In this manner, during a procedure, the image of the distal end of the secondary endoscope or the pointer  505  shown on the display  115  will move together with the video image  501  and will track the position/orientation of the secondary endoscope with respect to the main endoscope. In  FIG. 5B , an initial position (12 o&#39;clock) of the pointer  505  is shown as rotating in a counter clockwise direction to a second position (9 o&#39;clock) as pointer  505   a . This will inform the user of the exact position and orientation of the tip of the secondary endoscope  130  with respect to lumen being imaged. 
     In the foregoing illustrations of  FIG. 1 ,  FIG. 4A , and  FIG. 5A  the secondary scope can be considered to be fixedly attached to the main endoscope  150  in a known position relative to each other. In this case, the mechanical joint  160  can be a permanent attachment, such as a mechanical weld, permanent bond by adhesive, or pressure fitting, a keyway and pin engagement, such that the position and orientation of the secondary endoscope  130  is substantially permanently fixed to the main endoscope  150 . In this case, because the position of the secondary endoscope is relatively fixed to the main endoscope  150 , an indicator can be displayed at all times on the endoscope monitor showing the relative position between the two endoscopes. In alternative embodiments, the mechanical joint can be a non-permanent joint such that the position and orientation of the secondary endoscope  130  with respect to the main endoscope  150  can be changed. 
     &lt;FIG.  6 A- 8 : Mechanical Joint&gt; 
       FIG. 6A ,  FIG. 7 , and  FIG. 8  show various alternative embodiments for implementing the mechanical joint  160  to join together the main endoscope  150  to the secondary endoscope  130 .  FIG. 6A  shows an embodiment where the secondary endoscope (e.g., an SEE scope)  130  can be temporarily attached to the main endoscope  150  via pressure-fitted cylindrical clips. In this case, the mechanical joint  160  includes a connection clip assembly comprised of a plurality of pressure fitting cylindrical clamps  161   a  and  161   b  which are sized to engage around the outer surface of the main endoscope  150 . Naturally, the cylindrical clamps  161   a  and  161   b  can be provided on the main endoscope and sized to engage around the outer surface of the secondary endoscope  130 . The two endoscopes can be easily attached to and detached from each other by a simple mechanical action  601  of bringing one endoscope towards the other and pressure fitting the clamps  161   a  and  161   b  over the outer surface of the tubular shaft of the main endoscope. To avoid longitudinal slippage of one endoscope with respect to the other, the main endoscope  150  may be provided with annular lips, rings, or channels to abut against one or more the cylindrical clamps. 
       FIG. 6B  shows an example of a video image  601  obtained from the main endoscope  150  and displayed on a screen of display  115 . In this arrangement, since the distal end  139  of the secondary endoscope  130  is bent towards the field of view of main endoscope  150 , the display  115  can show an actual image of the tip of the secondary endoscope  130 . Alternatively, the display  155  can show a graphic object  605  such as pointer or circle or other making inside the edge of the image  601  (superposed on part of the video image). This graphic object serves to inform the user of the relative position of the secondary endoscope with respect to the main endoscope. In this manner, during a navigating procedure where the secondary endoscope may rotate with respect to the main endoscope, the graphic object  605  corresponding to the distal end of the secondary endoscope will move along the edge of the video image  601  (as shown by the dashed arrow). In  FIG. 6B , an initial position/orientation of the secondary endoscope  130  is shown as the graphic object  605  and a second positon/orientation of the secondary endoscope is shown as a graphic object  605   a . This will inform the user of the exact position, orientation and rotational direction of the tip of the secondary endoscope  130  with respect to field-of-view of the main endoscope  150 . In other words, the graphic object  605  is a probe tip indicator configured to provide information about position and orientation of the secondary endoscope with respect to the main endoscope. 
       FIG. 7  shows an embodiment where the secondary endoscope (e.g., an SEE scope)  130  can be temporarily attached to the main endoscope  150  in a known position via a cylindrical sleeve. In this case, the mechanical joint  160  includes a cylindrical tube  165  which is sized to fit the outer diameter of main endoscope  150 . The cylindrical tube  165  works as a coupling sleeve which defines a cylindrical opening for receiving therein the main endoscope  150 . The two endoscopes can be easily attached and detached from each other by a simple mechanical action  701  of sliding the main endoscope  150  into the cylindrical tube  165 . The cylindrical tube  165  can be permanently welded, or otherwise it can be temporarily secured to the secondary endoscope  130 . In either case, the mechanical joint  160  serves to maintain the main endoscope  150  in a known position with respect to the secondary endoscope  130 . 
       FIG. 8  shows an embodiment where the secondary endoscope (e.g., an SEE scope)  130  can be temporarily attached to the main endoscope  150  via a rail structure. In this case, the mechanical joint  160  includes a track in the form of a guide rail  162   a  provided in a first one of the two endoscopes (provided in the main endoscope  150 ) and an engaging member  162   b  in the form of a flange or a pillar provided on the second one of the two endoscopes. Endoscope mechanical junctions of this type are described, for example, in US patent application publication US 2004/0230096, the disclosure of which is incorporated by reference herein. With this arrangement, the two endoscopes can be easily attached and detached from each other by a simple mechanical action  801  of bringing one endoscope towards the other and sliding the engaging member  162   b  into the guide rail  162   a . Because the position of the secondary endoscope  130  (SEE scope) is relatively fixed to the main endoscope  150 , an indicator (similar to graphic object  605 ) can be displayed in the endoscope monitor showing the position of the secondary endoscope with respect to the main endoscope. 
     Any of the mechanical joints shown in  FIG. 6 ,  FIG. 7 , and  FIG. 8  can be made from medical grade plastic material, such as polyethylene, Teflon®, or polypropylene to provide a low coefficient of friction between the members as they slide relative to one another. Alternatively, these mechanical joints can be made of medial grade metal (e.g., stainless steel or nitinol) covered with biocompatible lubricious polymers having a low friction coefficient. Additionally, while the mechanical joint  160  is shown and described as being formed from two or more separate parts, the mechanical joint  160  can be formed as a unitary piece, in particular when the two endoscopes are permanently joined together. Likewise, the mechanical joint  160  can be custom made to join an already existing conventional rigid zero-degrees endoscope with an ultrathin submillimeter flexible endoscope, such as the SEE endoscope shown in  FIG. 3A - FIG. 3B . In this case, the mechanical joint  160  can be formed as a unitary piece (e.g., as a cylindrical clamp shown in  FIG. 6A ) made by an extrusion process or molding process, and thereafter the unitary piece can be joined to either the main endoscope or the secondary endoscope by any suitable attachment method or material. In some embodiments, at least part of the mechanical joint  160  can be made of, or it can include, a radiopaque material, so that the joint  160  can serve as a radiopaque marker in certain image guided procedures. As a further alternative, at least part of the mechanical joint  160  can be made of magnetic material (e.g., by mixing magnetic particles into extrusion polymer material or adding magnets to stainless steel or nitinol metal) covered with biocompatible lubricious additives. 
     While one mode of operation of the dual endoscope system  100  would be to have the main and secondary scopes move/rotate together as a fixed unit. In some embodiments, as described below, the dual endoscope system  100  can be operated in a manner that the main endoscope and secondary endoscope move/rotate independent from each other even if they are joined prior to insertion into a lumen. 
     &lt;FIG.  9 -FIG.  10 : Exemplary Modes of Operation&gt; 
       FIG. 9  illustrates an embodiment of the handle  120  configured to connect the main endoscope  150  and the secondary endoscope  130  to the console  110  shown in  FIG. 1 . The handle  120  may include a first connector  940  and a second connector  920  respectively configured to connect the main endoscope  150  and the secondary endoscope  130  to the console  110 . The dual endoscope system  100  can operate in a navigation mode and an imaging mode. A navigation mode refers to a mode of operation of the endoscope system  100  to insert the two endoscopes into a bodily lumen, and linearly advance at least one of the main and secondary endoscopes to a specific location inside the lumen. An imaging mode refers, for example, to a mode of obtaining an endoscopic image with the use of the secondary endoscope after navigating the distal end  139  of secondary endoscope  130  to the desired location. To do that, according to  FIG. 9 , for example, the handle  120  may include a rotation mechanism  230  which can be controlled by the controller  121  (located in the handle  120 ) or by the console  110  (as shown in  FIG. 1 ). The rotation mechanism  230  may include a first motor  231 , a second motor  290 , and a tracking mechanism composed of a rotating target  232  and a sensor  233 . 
     During an imaging operation, the rotation mechanism  230  can use a hollow-shaft motor  231  which can be configured to rotate or oscillate the secondary endoscope  130  inside its endoscope guide  135 . A tracking mechanism such as an encoder comprised of the rotating target  232  and sensor  233  can track rotation and orientation of the endoscope  130 . However, during a navigation operation (e.g. during insertion towards a desired lumen location), an additional rotation mechanism (e.g., a second hollow-shaft motor  290  or other rotating mechanism) can be configured to also rotate the endoscope guide  135  together with the secondary endoscope  130  by a predetermined amount of rotation (a rotation action  901 ) which can be less than a single revolution (i.e., less than 360 degrees) to only change the orientation of the distal end  139  of the secondary endoscope  130 . 
     More specifically, when using a secondary endoscope with a rotatable imaging probe, the hollow-shaft motor  231  would normally rotate the probe  220  together with the drive cable  216  in order to scan the sample with the illumination line  140  (refer to  FIGS. 1, 3A , and  3 B). In addition, it would be advantageous to actively control the orientation of the distal end  139  of the secondary endoscope  130  to minimize the likelihood of navigation errors and to improve patient safety. To that end, for example, the additional rotation mechanism or second motor  290  (shown in  FIG. 9 ) can be configured to selectively engage only with the guide  135  and rotate the guide  135  to place the distal end  139  of the secondary endoscope  130  inside or outside of the field of view  152  of the main endoscope, as shown in  FIG. 10A  and  FIG. 10B . 
     As shown in  FIG. 3A , the probe  220  is arranged inside the drive cable  216 , and the hollow-shaft motor  231  normally rotates the drive cable  216  together with the illumination optics of probe  220  in a rotation direction R. A rotation detection unit including, for example, a rotating disc  232  and an encoder module  233  is provided to obtain rotation information of the drive cable  216  with respect to the guide  135 . The rotating disc  232  is fixedly attached to the drive cable  216 , so that the encoder module  233  can obtain the rotation information of the drive cable  216 . The rotation information obtained by encoder module  233  can include the rotation speed, rotation direction (clockwise or counter-clockwise) and/or rotation position (angular position) of the drive cable  216 . The rotation information is sent from the encoder module  233  to console  110 . At the console  110 , the CPU  261  ( FIG. 2 ) uses the rotation information provided by the rotation detection unit and the spectral information obtained from the collected light for the image reconstruction process to form and output a reconstructed image of the arear of interest. The same type of control (i.e., the same rotating disc  232  and encoder module  233 ) can be used to control the orientation of the distal end  139  of the secondary endoscope to place the secondary endoscope  130  at an orientation that the user prefers. That is, according to the embodiment shown in  FIG. 10A  and  FIG. 10B  it is possible to actively place the distal end  139  of the secondary endoscope inside or outside of the field of view  152  of the main endoscope  150 , by rotating the endoscope guide  135  and tracking the rotation thereof with the encoder module  233 . Alternatively, other position sensor, such as a Hall-effect sensor can be used to sense the rotation of the secondary endoscope  130  with respect to the main endoscope  150  or vice versa. 
       FIG. 10A  illustrates an example of the endoscope system  100  used in the navigation mode where the main endoscope  150  is assembled (joined) together with the secondary endoscope  130  via the mechanical joint  160  prior to being inserted into a lumen. In this configuration, the main endoscope  150  and the secondary endoscope  130  are joined together such that the first endoscope probe is arranged to take forward-viewing live images from a field of view  152  that includes the distal end  139  of the second endoscope probe when the second endoscope probe is moved linearly for navigating towards a specific location of interest. As shown in  FIG. 1A , in the navigation mode, the secondary endoscope  130  may be navigated through the lumen without emitting any illumination light  140 . As noted above, this arrangement is advantageous because the distal end  139  of the secondary endoscope can be continuously monitored by a live view image of the main endoscope during insertion into a bodily lumen. This procedure can occur during linear movement of insertion into a bodily lumen prior to using the secondary endoscope to obtain side-view images of tangential areas of the bodily lumen. 
       FIG. 10B  shows an example embodiment of the endoscope system  100  used in the imaging mode where the secondary endoscope  130  (or more precisely, the endoscope guide  135 ) is actively rotated so that the distal end  139  is moved out of the field of view  152  of the main endoscope  150  for obtaining an image of an area tangential or lateral to the field of view  152 . Here, a rotation action  901  of the endoscope guide  135  indicates a pivoting movement of the bent portion of the endoscope  130  while the straight portion of the endoscope  130  remains attached to the main endoscope  150 . This pivoting movement for rotation action  901  can be achieved, for example, when the two endoscopes are joined together by a mechanical joint  161   a  or  161   b  as shown in  FIG. 6A  or a cylindrical sleeve as shown in  FIG. 7 . In this case too, a graphic object such as that shown in any of  FIG. 4B ,  FIG. 5B , or  FIG. 6B  can be used to inform the user of the exact position and orientation of the tip of the secondary endoscope  130  with respect to field-of-view of the main endoscope  150 . 
     In other words, while one mode of operation of the dual endoscope system  100  would be to have the main and secondary scopes move/rotate together as a unit, the dual endoscope system  100  can also be operated in a manner that the main endoscope  150  and the secondary endoscope  130  can move and/or rotate independent from each other as shown in  FIG. 10A  and  FIG. 10B . Once the secondary endoscope  130  is safely navigated together with main endoscope  150  through the bodily lumen to a target area of interest (as shown in  FIG. 10A ), the secondary endoscope  130  can be independently rotated or guided to image areas tangential or lateral to the field of view. 
     &lt;Tracking Procedure&gt; 
       FIG. 11  shows a flowchart of an example tracking procedure (tracking algorithm) for the dual endoscope system  100 . The operation of the tracking procedure is described in connection with the dual endoscope system  100  shown in  FIG. 1  and the various embodiments of the mechanical joint  160 . Referring to  FIG. 11 , the tracking procedure includes a step S 1102  which assumes the main endoscope  150  and secondary endoscope  130  are joined together as unit and inserted into a lumen or cavity of patient. Once inserted into a lumen or cavity, at step S 1102 , the system  100  acquires a live video image from the main endoscope  150 , and it may also obtain an image from the secondary endoscope  130 . At step S 1104 , a determination is made as to whether the distal end of the secondary endoscope  130  is present within the field of view (FOV) of the main endoscope. The determination at step S 1104  can be made by the user observing the acquired live video image in the display device  115 , and providing a manual input for the flow process executed by the system  100 . Alternatively, the determination at step S 1104  can be made by image analysis (software analysis) of the live video image to determine if an image of the distal end of secondary endoscope  130  is detected within one or more frames of the video stream. 
     In the case where a positive determination is made (YES in S 1104 ) asserting that the secondary endoscope is within the FOV of the main endoscope, the process advances to step S 1108  where the system  100  adds a graphic object to the live video image shown in the display device. For example, the display device adds a graphic object  505  as shown in  FIG. 5B . In the case where a negative determination is made (NO in S 1104 ) indicating that the secondary endoscope is not observed within the FOV of the main endoscope, the process advances to step S 1106  where the system  100  actively determines the position and/or orientation of the secondary endoscope with respect to the main endoscope. As previously described, the secondary endoscope  130  can be attached to the main endoscope  150  with an orientation pointing away from the main endoscope (e.g., as shown in  FIG. 4A ). In this case, the distal end of the secondary endoscope  130  will not be seen in the live video image of main endoscope  150 . However, the position of the secondary endoscope  130  with respect to the main endoscope  150  can be known before the two endoscopes are inserted into the lumen. Alternatively, the position and orientation of the secondary endoscope  130  can be sensed or determined, e.g., by image guidance. Therefore, at step S 1106 , the system  100  may receive the known position of the secondary endoscope  130 , and then at step S 1108  the system will add a graphic object to the live video image shown in the display device. For example, at step S 1108 , the display device adds a graphic object  405  as shown in  FIG. 4B . 
     At step S 1110 , while the joined main and secondary endoscopes advance through the lumen, or when the main or secondary endoscopes are maneuvered inside the lumen at a desired target location, the system  100  continues to track the relative position and orientation of the secondary endoscope with respect to the main endoscope. That is, at step S 1112 , the system makes a determination as to whether the position of the secondary endoscope  130  relative to the main endoscope  150  has changed. In the case where the relative position of the main and secondary endoscope has not changed (NO at S 112 ), the system continues to acquire live video images (returns to S 1102 ) and repeats the process of displaying the graphic object together with the live video images. On the other hand, in the case where the relative position of the secondary endoscope relative to the main endoscope has changed (YES at S 112 ), the flow advances to S 114  where the system  100  updates the position of the graphic object with respect to the live image on the display  115 . After the position of the graphic object is updated, the system continues to acquire live video images (returns to S 1102 ) and repeats the process of displaying the graphic object together with the live video images until the tracking process is terminated at the user discretion. In this manner, the system  100  can be configured to change or update the graphic object in real time to track the relative position and orientation of the secondary endoscope  130  with respect to the main endoscope  150 . 
     &lt;Exemplary Application&gt; 
     According to one or more of the embodiments described herein, the dual endoscope system  100  can be implemented as a nasal endoscope. Nasal endoscopy allows a detailed examination of the nasal and sinus cavities of a patient. Nasal endoscopy is typically performed by an Otolaryngologist (Ear Nose Throat doctor) using either a zero degree or an angled nasal endoscope. Nasal endoscopy is a method of evaluating medical problems such as nasal stuffiness and obstruction, sinusitis, nasal polyps, nasal tumors, and epistaxis (nose bleeds). Typically, nasal endoscopy is performed with a zero degree endoscope using the “three pass” technique, visualizing three main areas in the nasal and sinus cavities. The zero degree nasal endoscope allows a straight view from the tip of the instrument into the nose. In the first pass the nasal floor and the back of the nose (nasopharynx) are viewed. The endoscope is then brought out and turned upwards and sideways in order to view the drainage areas of the nasal sinuses (middle and superior meati and the spheno-ethmoidal recess), in a second pass. In the third pass, the endoscope is used to view the roof of the nose and the area of the olfactory cleft (smell region). The “angled” (30/45/70 degree) endoscopes, in which the view is at an angle from the tip of the endoscope, provide an “around the corner” view, deep into the sinus cavities. However, the angled endoscope does not provide direct straight view into the nasal passages, so there is a possibility for navigation errors or patient injury. 
     Therefore, with either modality (i.e., with zero degrees or angled endoscopes), in order to minimize patient discomfort, just before nasal endoscopy the nose will be sprayed with a nasal decongestant and a local anesthetic. The nasal decongestant is used to reduce the swelling in the nasal membranes to permit an easy passage of the endoscope; and the local anesthetic temporarily numbs the nose of a patient, and helps decrease the chances of sneezing from patient&#39;s sensitivity to foreign objects. Nevertheless, some patients may experience discomfort if the nasal cavity is unusually narrow or the nasal lining is swollen. Moreover, potential complications such as mucosal trauma and bleeding may occur, particularly in susceptible patients with increased risk of bleeding. 
     The dual endoscope system  100  disclosed herein improves on the above-described conventional “three pass” technique and avoids (or at least) significantly reduces navigation error and patient injury because the main endoscope and the secondary endoscope are joined together along a length of the first and second tubular shafts and are configured to be simultaneously inserted into a lumen, wherein the main endoscope is arranged to acquire a first image of a field of view from inside the lumen, and the secondary endoscope is arranged to acquire a second image of an area which is tangential or lateral to the field of view, and wherein the display device displays the first image acquired by main endoscope and a graphic object depicting a position and orientation of the secondary endoscope with respect to the main endoscope. Moreover, the graphic object updates in real time to track movement of the secondary endoscope with respect to the main endoscope. 
     The dual endoscopy system  100  described herein offers the following advantages, among others: (a) avoidance of reduction of injury to the patient, in particular to the inner surface of a bodily lumen, due to the possibility of simultaneous optical monitoring via the acquisition of images with both the main endoscope and secondary endoscope; (b) in contrast to the multi-pass technique for nasal endoscopy, the nasal insertion of the endoscope does not require multiple insertions because the main endoscope can image the field of view directly in front of the main endoscope, while the secondary endoscope can image areas of lumen which are tangential or lateral to the field of view; (c) in contrast to conventional dual endoscopy operation, which requires two operators, the dual endoscope system described herein requires a single operator; this naturally reduces operation costs; (d) the graphic object updates in real time to track movement of the secondary endoscope with respect to the main endoscope. 
     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. Unless defined otherwise herein, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The breadth of the present invention is not to be limited by the subject specification, but rather only by the plain meaning of the claim terms employed. 
     In describing example embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification 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.