WO2024238428A2 - Polarimetric endoscope - Google Patents

Abstract

A polarimetric endoscope includes an insertion tube and a polarization imaging channel. The polarization imaging channel includes (i) an imaging fiber bundle having a plurality of optical fibers and being at least partially in the insertion tube, (ii) an imaging lens at a distal tube-end, of the insertion tube, that forms an image at a distal bundle-end of the imaging fiber bundle, and (iii) a polarizer array having a plurality of polarizers each aligned to a distal end of a respective one of the plurality of optical fibers and transmitting one of a plurality of polarization states. Each of the imaging fiber bundle and the first and second illumination channels is at least partially in the insertion tube.

Description

^PATENT A_{ttorney Docket No: UOAZ.P2142PCT/00608558} P^{OLARIMETRIC ENDOSCOPE} C_{ROSS-REFERENCE TO RELATED APPLICATIONS} [^{0001] This application claims the benefit of U.S. Provisional Application No.} _{63/466,067, filed on 12 May 2023, the disclosure of which is incorporated herein by reference in its entirety. GOVERNMENT RIGHTS} [^{0002] This invention was made with government support under Grant No.} _{W81XWH-22-1-0211 awarded by ARMY/MRDC. The government has certain rights in the invention. BACKGROUND} [^{0003] Esophagogastroduodenoscopy (EGD) offers an unparalleled view of the luminal wall of major gastrointestinal organs afflicted by high incidence and mortality from cancer and is the only tool that allows for simultaneous visualization, biopsy, and mucosal or submucosal resection. Current endoscopes are primarily limited to the use white light imaging (WLI) and narrow-band imaging. White light imaging (WLI) yields contrast via absorption and reflection of broadband illumination aggregated in three red, green, and} _{blue (RGB) imaging filters. Narrow-band imaging yields vasculature contrast via narrow band illumination at hemoglobin absorption peaks of 415 nm and 540 nm. Incidence and mortality, early diagnosis miss rates, biopsy sampling error/quantity, and burdens on histopathology, indicate a significant need for improved imaging tools that can: detect and localize early, otherwise unseen lesions; be incorporated into endoscopy for screening and evaluation of early symptoms; and provide biopsy guidance. SUMMARY OF THE EMBODIMENTS} [^{0004] In a first aspect, a polarimetric endoscope includes an insertion tube and a polarization imaging channel. The polarization imaging channel includes (i) an imaging fiber bundle having a plurality of optical fibers and being at least partially in the insertion} _{tube, (ii) an imaging lens at a distal tube-end, of the insertion tube, that forms an image at a distal bundle-end of the imaging fiber bundle, and (iii) a polarizer array having a plurality} 1 LEGAL\70494295\11 ^{Attorney Docket No: UOAZ.P2142WO/00608558 of polarizers each aligned to a distal end of a respective one of the plurality of optical fibers and transmitting one of a plurality of polarization states. Each of the imaging fiber bundle} _{and the first and second illumination channels is at least partially in the insertion tube. BRIEF DESCRIPTION OF THE FIGURES} [^{0005] FIG. 1 shows preliminary imaging data averaged over a region of interest} _{(ROI) exhibiting a decrease in the degree of linear polarization (DOLP) in cancerous tissue biopsies.} [^{0006] FIG. 2 demonstrates data collected by a hyperspectral imaging system} _{averaged over a region of interest.} [^{0007] FIGs. 3, 4, and 5 are respective schematics of a polarimetric endoscope, in an} _embodiment. [^{0008] FIG. 6 is a schematic of an imaging fiber bundle and micropolarizer array} _{(MPA), which are examples of an imaging fiber bundle and MPA of the polarimetric endoscope of FIGs 3–5.} [^{0009] FIG. 7 is a schematic of a polarimetric endoscope, which is an example of the} _{polarimetric endoscope of FIGs 3–5. DETAILED DESCRIPTION OF THE EMBODIMENTS} [^{0010] In recent years, numerous label-free imaging-based techniques have emerged that are candidates for optical detection of neoplasia. Among these are spectral and polarimetric imaging, which involve different light-tissue interactions. Probing multiple light-tissue interactions, known as multimodal imaging, integrates complimentary sources of biological contrast to the scene due to the quasi-mutual exclusivity of each} _{interaction. Spectral imaging can capture wavelength encoded light-tissue interactions from chromophores, tissue microstructure, higher nuclei density, or collagen matrix transformations. Polarimetric imaging reveals tissue scattering and absorption information and provides insight into directional mechanical properties of tissue to monitor pathological changes in collagen and elastin.} [^{0011] Current approaches to flexible polarimetric endoscopy have significant} _{system design or performance drawbacks. For example, using a single fiber scanning} 2 LEGAL\70494295\11 ^{Attorney Docket No: UOAZ.P2142WO/00608558 approach necessitates real time-feedback of the fiber’s transmission matrix properties, and requires a high brightness source like a laser, which could introduce speckle and ultimately result in insensitivity to tissue depolarization properties. Additional complexities arise in} _{miniaturization of actuation components. Advances in flexible polarimetric endoscopy could significantly improve EGD in identifying neoplastic lesions and guidance of biopsies, and perhaps could eventually serve as an optical biopsy tool.} [^{0012] Polarimetric imaging reveals tissue scattering and absorption information and provides insight into directional mechanical properties of tissue to monitor pathological changes in collagen and elastin. Early tumor development causes collagen reorganization and disruption to the extracellular matrix; thus, polarization imaging} _{provides information about the microstructural changes of early cancer. In parallel, spectral imaging and polarimetric imaging can highlight pathological features ranging from micro- and macro- architecture of vasculature and collagen reorganization providing a multimodal set rich with measures that can distinguish normal from neoplastic lesions.} [^{0013] Embodiments of endoscopes disclosed herein measure spatially resolved partial polarimetric information of light-tissue interactions with a flexible endoscope. A key feature of certain embodiments is a micro-polarizer array (MPA) between the imaging fiber bundle and an imaging lens. This is an important step forward in flexible endoscopy because imaging fiber bundles scramble polarization information. By contrast, the MPA} _{captures the state of polarization prior to entering the imaging fiber bundle. The approach could be widely translatable to other miniaturized polarimetric imaging systems (e.g., laparoscopy, non-GI endoscopy) and has potential to dramatically reduce complexity and cost of polarimetric imaging enabling use in low cost/resource settings. Endoscopes disclosed herein address a significant need for improved imaging tools to localize early neoplastic tissue.} Overview^of^a^multi‐modal^endoscope [^{0014] The imaging requirements of the endoscope may be based on commercial diagnostic endoscopes for EGDs. The polarimetric and spectral imaging channels may be} _{forward viewing, have a field of view of approximately 120 degrees, and a depth of field between 2 mm and 100 mm. To enable polarimetric measurements, a micro-array} 3 LEGAL\70494295\11 ^{Attorney Docket No: UOAZ.P2142WO/00608558 polarizer (MPA) may be bonded to the imaging fiber bundle at the distal tip. Illumination at the peripheral circumference of the distal tip provides six polarization illumination states.} _{To enable spectral imaging, a similar approach to narrow-band imaging may be used to provide narrow band illumination at multiple wavelengths with a 300-W xenon arc lamp source.} [^{0015] In embodiments, the polarization imaging channel includes an MPA bonded onto the fiber bundle face of the distal tip. Multiple illumination fibers (e.g., six) may be} _{delivered to the outer edges of the distal end of the endoscope for a complete achromatic generator of polarized illumination. In embodiments, the ^^# of the imaging optics is matched to that of the etendue of the imaging fiber bundle.} [^{0016] Pursuit of integrating polarimetric imaging into flexible endoscopy is in part motivated by our preliminary data. Benchtop ex-vivo imaging systems in our lab have been used to capture the hyperspectral (470 – 900 nm), autofluorescence (5 excitation, 7} _{emission channels), polarimetric (5 wavelength, reflectance, full Mueller matrix), and optical coherence tomography (1300-nm central wavelength) datasets of 13 matched patient jumbo forceps biopsies from the esophagus of normal adjacent and tissue with adenocarcinoma, squamous cell carcinoma, and/or Barrett’s esophagus.} [^{0017] FIG. 1 shows imaging data averaged over a region of interest (ROI) exhibiting a decrease in the degree of linear polarization (DOLP) in cancerous tissue biopsies across} _{various illumination wavelengths. FIG. 1 shows ROI average DOLP at five wavelengths for two patients with matched esophageal biopsies of adjacent normal tissue and tumor tissue.} [^{0018] DOLP only requires the first three elements of the first column of the 4×4 Mueller matrix. We have also observed diattenuation, calculated from the first row of the 4×4 Mueller matrix, to provide contrast between normal adjacent and tumor tissues across} _{all wavelengths – with a pronounced improvement in the 543-nm and 632-nm wavelengths. The full Mueller matrix is critical for ex-vivo benchtop studies to validate system design decisions, however, in endoscopy it is critical to reduce system complexity.} [^{0019] FIG. 2 demonstrates data collected by the hyperspectral imaging system averaged over an ROI that has been normalized by the maximum at the 770-nm} _{wavelength. In FIG. 2, ROI normalized average hyperspectral signature of matched} 4 LEGAL\70494295\11 ^{Attorney Docket No: UOAZ.P2142WO/00608558 esophageal biopsies of adjacent normal and tumor tissue with the difference squared of the} _{unnormalized data.} [^{0020] Further insight is drawn from the difference square of the unnormalized spectrographs between adjacent normal and tumor tissue. Sub-sampling to several wavelengths that demonstrate a large and negligible difference in the spectrographs are} _{critical to creating abundance maps that heatmap suspected neoplasms. Therefore, the spectral imaging channel may sub-select imaging at 405 nm, 543 nm, and 632 nm, which shares polarimetric illumination wavelengths.} Embodiment^of^a^polarimetric^endoscope^ [^{0021] FIG. 3 is a schematic cross-sectional view of a polarimetric endoscope 300. FIG. 4 is a schematic plan view of a distal end 309 of polarimetric endoscope 300. FIG. 5 is a} _{schematic of polarimetric endoscope 300 illustrating optical components thereof. FIGs. 3–5 are best viewed together in the following description.} [^{0022] Polarimetric endoscope 300 includes an insertion tube 310 and a polarization imaging channel 320. Polarimetric endoscope 300 may also include at least one illumination channel 330, such as illumination channels 330(1) and 330(2) shown in FIG. 3. Insertion tube 310 has a proximal tube-end 311 and a distal tube-end 319. As shown} _{in FIG. 5, polarimetric endoscope 300 may also include a working channel 502 and one or more additional channels 504, such as an air channel and a water channel. Insertion tube 310 may be more flexible at distal tube-end 319 than at proximal tube-end 311} [^{0023] Polarization imaging channel 320 includes (i) an imaging fiber bundle 322 having a plurality of optical fibers 324, (ii) an imaging lens 327 at distal tube-end 319 that} _{forms an image at a distal bundle-end 323 of imaging fiber bundle 322, and (iii) a polarizer array 360. Imaging fiber bundle 322 and imaging fiber bundle 342 have respective distal bundle-ends 325 and 345.} [^{0024] Polarizer array 360 has a plurality of polarizers 364 each aligned to a distal end of a respective one of the plurality of optical fibers 324. At distal bundle-end 323 the} _{optical axis of imaging lens 327 may be coaxial with or parallel to an optical axis of imaging fiber bundle 322. In embodiments, at least one of distal bundle-end 323 and polarizer array} 5 LEGAL\70494295\11 ^{Attorney Docket No: UOAZ.P2142WO/00608558 360 is within a depth of field of imaging lens 327. Polarizer array 360 may be between} _{imaging lens 327 and distal bundle-end 323.} [^{0025] Each polarizer 364 transmits one of a plurality of polarization states of converging light incident thereon propagating from lens 327. Examples of the polarization states include linear polarizations and circular polarizations, as shown in FIG. 5. The} _{polarization states shown in FIG. 5 are examples of the plurality of polarization states transmitted by a polarizer 364. The plurality of polarization states may differ from those shown in FIG. 5 without departing from the scope hereof.} [^{0026] Each of the imaging fiber bundle 322 and illumination channels 330 is at} _{least partially in insertion tube 310. At least part of imaging lens 327 and at least part of polarizer array 360 may be within insertion tube 310.} [^{0027] Illumination channel 330(1) emits, from distal tube-end 319, a first illumination having a first polarization state of the plurality of polarization states. Illumination channel 330(2) emits, from distal tube-end 319, a second illumination having a second polarization state of the plurality of polarization states. The first and the second polarization states may be orthogonal. Polarimetric endoscope 300 may include additional illumination channels 330( ^^), where index ^^ greater than equal to three. The plurality of} _{polarization states may include multiple pairs of orthogonal polarization states. In embodiments, a single illumination channel 330 may emit the first polarization state during a first time period and emit the second polarization state during a second time period that follows the first time period. In embodiments, one or more illumination channels 330 may emit illumination that is either unpolarized, partially polarized, or includes multiple polarizations.} [^{0028] Each illumination channel 330( ^^) may emit a respective one of ^^ polarization states of the plurality of polarization states. Illumination channel 330 has a distal end 339. In embodiments, each illumination channel 330( ^^) has a respective polarizer 336( ^^) at its} _{distal end 339( ^^). For example illumination channels 330(1) and 330(2) may have a respective polarizer 336(1) and 336(2) at their respective distal ends 339. Polarimetric endoscope 300 may include multiple illumination channels 330 that emit the same polarization state.} 6 LEGAL\70494295\11 ^{Attorney Docket No: UOAZ.P2142WO/00608558 [0029] At distal tube-end 319, respective locations of illumination channels 330 may} _{define vertices of a polygon surrounding imaging lens 327. For example, in FIG. 4 the polygon is a hexagon.} [^{0030] In embodiments, each polarizer 364 of polarizer array 360 may transmit one of the plurality of polarization states. In embodiments, at least one of (i) polarizer array 360 is bonded to distal bundle-end 323 and (ii) polarizer array 360 is a pixelated} _{micropolarizer array. For each of the plurality of polarization states, polarizer array 360 may include at least one polarizer 364 that transmits the polarization state. Polarizer array 360 may include, for each of the ^^ polarization states, multiple polarizers 364 that transmit the ^^^୦ polarization state.} [^{0031] Polarimetric endoscope 300 may include a spectral imaging channel 340. Spectral imaging channel 340 includes an imaging fiber bundle 342 at least partly in} _{insertion tube 310. Imaging fiber bundle 342 includes an additional plurality of optical fibers. Imaging channel 340 also includes an imaging lens 347 at distal tube-end 319. At least part of imaging lens 347 may be within insertion tube 310.} [^{0032] Imaging lens 347 forms an image at a distal bundle-end 343 of imaging fiber bundle 342. Respective fields of view of imaging lenses 327 and 347 overlap, such that} _{imaging lenses 327 and 347 capture an image of a scene defined by this overlap, and polarimetric endoscope 300 captures both a polarimetric image and a spectral image of the scene.} [^{0033] In embodiments, MPA 360 is attached to the distal end of imaging fiber} bundle 322. This enables a partial polarization analyzer that samples light after its _{interaction with tissue prior to being scrambled by the imaging fiber bundle.} [^{0034] Polarimetric endoscope 300 may include a plurality of light sources 370 (FIG. 3) each coupled to a respective illumination channel 330. At least one of light sources 370} _{may be a polarized light source, in which case the illumination channel 330 coupled thereto may include one or more polarization-maintaining optical fibers.} [^{0035] Polarimetric endoscope 300 may include one or more sensors 372, which may be high-speed, back-illuminated sensors. For example, distal bundle-end 325 and} _{distal bundle-end 345 of respective imaging fiber bundles 322 and 342 may be directly bonded to respective sensors 372(1) and 372(2).} 7 LEGAL\70494295\11 ^{Attorney Docket No: UOAZ.P2142WO/00608558 [0036] FIG. 6 is a schematic of an imaging fiber bundle 622, with an MPA 660 on its distal end. Fiber bundle 622 and MPA 660 are respective examples of imaging fiber bundle 322 and MPA 360. Imaging fiber bundle 622 may have a square lattice configuration, as} _{shown in FIG. 6, or a hexagonal lattice configuration. The pitch may equal ten micrometers, for example. The distal end of the flexible imaging fiber bundle may be bonded to MPA 660.} [^{0037] MPA 660 includes a plurality of micropolarizers 664. MPA 660 may include an array of super pixels 662, each of which includes an array of micropolarizers 664. In the} _{example of MPA 660, each super pixel 662 is a 2×2 array of micropolarizers 664 that transmit a different polarization state, e.g., different linear and/or circular polarizations. Each micropolarizer 664 is an example of polarizer 364.} [^{0038] The diameter of MPA 360 may be between 3.5 mm and 4 mm. This configuration provides a resolution of approximately 50-line pairs per mm (lp/mm) in} _{image space. In embodiments, MPA 360 is aligned to distal bundle-end 323 of imaging fiber bundle 322 with a microscope and micro positioning stages and bonded with a UV activated adhesive.} [^{0039] FIG. 7 is a schematic of an endoscope 700 coupled to one or more output devices 790. Output devices 790 may include at least one of computer, a mobile device, and an augmented reality headset. Endoscope 700 is an example of endoscope 300. Endoscope 700 includes polarization imaging channel 720, illumination channels 730, spectral} _{imaging channel 740, and a light source 770, which are examples of polarization imaging channel 320, illumination channels 730, spectral imaging channel 340, and light sources 370, respectively. Channels 720 and 740 includes respective imaging fiber bundle 322 and 342. Light source 770 includes multiple LEDs, which in this example emit light at 632 nm, 543 nm, and 405 nm.} Generating^a^stereoscopic^3D^model^from^the^imaging^channels [^{0040] In embodiments, a model generation method includes generating, with an image processing algorithm, a 3D object model of lesion topography from the images captured by polarimetric endoscope 300. A subsequent step includes, using markings along} _{the length of the endoscope tubing, assigning displacement between captured images, which enables an absolute measurement scale to be applied to the 3D model. This} 8 LEGAL\70494295\11 ^{Attorney Docket No: UOAZ.P2142WO/00608558 technique provides height information of the organ traversed by the endoscope, thereby} _{highlighting irregularities in small bumps or divots that would otherwise go unseen by standard imaging.} A^method^for^rendering^a^still^AR^scene^from^stereo^data^from^the^endoscope [^{0041] In embodiments, polarization imaging channel 320 and spectral imaging channel 340 endoscope 300 act as two pupils similar to the vision system of a human. The method includes porting images from spectral channel 340 to one eye and porting images from polarimetric channel 320 to the other eye to form a 3D scene. This method does not require heavy computational processing associated with 3D modeling from stereoscopic} _{images. The method may include adjusting the respective images corresponding to one scene to have similar mean gray values across the different illumination wavelengths. The method may also include loading, into an output device 790, such as an AR display, the images captured by each imaging channel and displaying the images to the left and right eye of the user.} Combinations^of^Features^ [^{0042] Features described above, as well as those claimed below, may be combined} _{in various ways without departing from the scope hereof. The following enumerated examples illustrate some possible, non-limiting combinations.} [^{0043] Embodiment 1. A polarimetric endoscope comprising: an insertion tube having a proximal tube-end and a distal tube-end; a polarization imaging channel including (i) an imaging fiber bundle having a plurality of optical fibers and being at least partially in the} _{insertion tube (ii) an imaging lens at the distal tube-end that forms an image at a distal bundle-end of the imaging fiber bundle, and (iii) a polarizer array having a plurality of polarizers each aligned to a distal end of a respective one of the plurality of optical fibers and transmitting one of a plurality of polarization states.} [^{0044] Embodiment 2. The endoscope of embodiment 1, an optical axis of the imaging} _{lens being coaxial with the imaging fiber bundle at the distal bundle-end.} 9 LEGAL\70494295\11 ^{Attorney Docket No: UOAZ.P2142WO/00608558 [0045] Embodiment 3. The endoscope of either one embodiments 1 or 2, at least one} _{of the distal bundle-end and the polarizer array being within a depth of field of the imaging lens.} [^{0046] Embodiment 4. The endoscope of any one embodiments 1–3, the polarizer} _{array being between the imaging lens and the distal bundle-end.} [^{0047] Embodiment 5. The endoscope of any one embodiments 1–4, further comprising: a spectral imaging channel including (i) an additional imaging fiber bundle at} _{least partly in the insertion tube and including an additional plurality of optical fibers, and (ii) an additional imaging lens at the distal tube-end that forms an additional image at an additional distal bundle-end of the additional imaging fiber bundle.} [^{0048] Embodiment 6. The endoscope of any one embodiments 1–5, the polarizer} _{array being bonded to the distal bundle-end.} [^{0049] Embodiment 7. The endoscope of any one embodiments 1–6, the polarizer} _{array being a pixelated micropolarizer array.} [^{0050] Embodiment 8. The endoscope of any one embodiments 1–7, the plurality of} _{polarization states including multiple pairs of orthogonal polarization states.} [^{0051] Embodiment 9. The endoscope of any one embodiments 1–8, the insertion} _{tube being more flexible at the distal tube-end than at the proximal tube-end.} [^{0052] Embodiment 10. The endoscope of any one embodiments 1–9, further comprising: a first illumination channel, at least partially in the insertion tube, that emits,} _{from the distal tube-end, first illumination having a first polarization state of the plurality of polarization states.} [^{0053] Embodiment 11. The endoscope of embodiment 10, the plurality of polarizers} _{including multiple polarizers that transmit the first polarization.} [^{0054] Embodiment 12. The endoscope of either one of embodiments 10 or 11, the} _{first illumination channel including a polarization-maintaining fiber.} [^{0055] Embodiment 13. The endoscope of any one embodiments 10–12, further} _{comprising a light source coupled to the first illumination channel.} [^{0056] Embodiment 14. The endoscope of any one embodiments 10–13, further} _{comprising: a second illumination channel, at least partially in the insertion tube, that} 10 LEGAL\70494295\11 ^{Attorney Docket No: UOAZ.P2142WO/00608558 emits, from the distal tube-end, second illumination having a second polarization state of} _{the plurality of polarization states.} [^{0057] Embodiment 15. The endoscope of embodiment 14, the second polarization} _{being orthogonal to the first polarization.} [^{0058] Embodiment 16. The endoscope of either one of embodiments 14 or 15, the} _{plurality of polarizers including multiple polarizers that transmit the second polarization.} [^{0059] Embodiment 17. The endoscope of any one embodiments 14–16, further comprising a plurality of illumination channels that each emit, from the distal tube-end,} _{illumination having one of the plurality of polarization states, the first illumination channel and the second illumination channel each being one of plurality of illumination channels.} [^{0060] Embodiment 18. The endoscope of embodiment 17, at the distal tube-end,} _{respective locations the plurality of illumination channels defining vertices of a polygon surrounding the imaging lens.} [^{0061] Embodiment 19. The endoscope of either one of embodiments 17 or 18, each} _{of the plurality of illumination channels including one of a plurality of polarizers at a distal end of the illumination channel.} [^{0062] Embodiment 20. The endoscope of embodiment 19, each of the plurality of} _{polarizers transmitting one of the plurality of polarization states. * * *} [^{0063] Changes may be made in the above methods and systems without departing from the scope of the present embodiments. It should thus be noted that the matter contained in the above description or shown in the accompanying drawings should be} _{interpreted as illustrative and not in a limiting sense. Herein, and unless otherwise indicated the phrase “in embodiments” is equivalent to the phrase “in certain embodiments,” and does not refer to all embodiments.} [^{0064] Regarding instances of the terms “and/or” and “at least one of,” for example, in the cases of “A and/or B” and “at least one of A and B,” such phrasing encompasses the} _{selection of (i) A only, or (ii) B only, or (iii) both A and B. In the cases of “A, B, and/or C” and “at least one of A, B, and C,” such phrasing encompasses the selection of (i) A only, or (ii) B} 11 LEGAL\70494295\11 ^{Attorney Docket No: UOAZ.P2142WO/00608558 only, or (iii) C only, or (iv) A and B only, or (v) A and C only, or (vi) B and C only, or (vii)} _{each of A and B and C. This may be extended for as many items as are listed.} [^{0065] The following claims are intended to cover all generic and specific features} _{described herein, as well as all statements of the scope of the present method and system, which, as a matter of language, might be said to fall therebetween.} 12 LEGAL\70494295\11

Claims

^{Attorney Docket No: UOAZ.P2142WO/00608558 We claim: 1. A polarimetric endoscope comprising: an insertion tube having a proximal tube-end and a distal tube-end; a polarization imaging channel including (i) an imaging fiber bundle having a plurality of optical fibers and being at least partially in the insertion tube, (ii) an imaging lens at the distal tube-end that forms an image at a distal bundle-end of the imaging fiber bundle, and (iii) a polarizer array having a plurality of polarizers each aligned to a distal end of a respective one of the plurality of optical fibers and transmitting one of a plurality of polarization states. 2. The endoscope of claim 1, an optical axis of the imaging lens being coaxial with the imaging fiber bundle at the distal bundle-end. 3. The endoscope of claim 1, at least one of the distal bundle-end and the polarizer array being within a depth of field of the imaging lens.} 4_{. The endoscope of claim 1, the polarizer array being between the imaging lens and the distal bundle-end. 5. The endoscope of claim 1, further comprising: a spectral imaging channel including (i) an additional imaging fiber bundle at least partly in the insertion tube and including an additional plurality of optical fibers, and (ii) an additional imaging lens at the distal tube-end that forms an additional image at an additional distal bundle-end of the additional imaging fiber bundle. 6. The endoscope of claim 1, the polarizer array being bonded to the distal bundle-end. 7. The endoscope of claim 1, the polarizer array being a pixelated micropolarizer array. 8. The endoscope of claim 1, the plurality of polarization states including multiple pairs of orthogonal polarization states.} 13 LEGAL\70494295\11 ^{Attorney Docket No: UOAZ.P2142WO/00608558 9. The endoscope of claim 1, the insertion tube being more flexible at the distal tube-end than at the proximal tube-end. 10. The endoscope of claim 1, further comprising: a first illumination channel, at least partially in the insertion tube, that emits, from the distal tube-end, first illumination having a first polarization state of the plurality of polarization states. 11. The endoscope of claim 10, the plurality of polarizers including multiple polarizers that transmit the first polarization. 12. The endoscope of claim 10, the first illumination channel including a polarization- maintaining fiber. 13. The endoscope of claim 10, further comprising a light source coupled to the first illumination channel.} _{14. The endoscope of claim 10, further comprising: a second illumination channel, at least partially in the insertion tube, that emits, from the distal tube-end, second illumination having a second polarization state of the plurality of polarization states. 15. The endoscope of claim 14, the second polarization being orthogonal to the first polarization. 16. The endoscope of claim 14, the plurality of polarizers including multiple polarizers that transmit the second polarization. 17. The endoscope of claim 14, further comprising a plurality of illumination channels that each emit, from the distal tube-end, illumination having one of the plurality of polarization states, the first illumination channel and the second illumination channel each being one of plurality of illumination channels.} 14 LEGAL\70494295\11 ^{Attorney Docket No: UOAZ.P2142WO/00608558 18. The endoscope of claim 17, at the distal tube-end, respective locations the plurality of illumination channels defining vertices of a polygon surrounding the imaging lens. 19. The endoscope of claim 17, each of the plurality of illumination channels including one} o_{f a plurality of polarizers at a distal end of the illumination channel. 20. The endoscope of claim 19, each of the plurality of polarizers transmitting one of the plurality of polarization states.} 15 LEGAL\70494295\11