Fabrication and operation of GRIN probes for in vivo fluorescence cellular imaging of internal organs in small animals

Intravital two-photon microscopy of the native mouse thymus

The thymus, a key organ in the adaptive immune system, is sensitive to a variety of insults including cytotoxic preconditioning, which leads to atrophy, compression of the blood vascular system, and alterations in hemodynamics. Although the thymus has innate regenerative capabilities, the production of T cells relies on the trafficking of lymphoid progenitors from the bone marrow through the altered thymic blood vascular system. Our understanding of thymic blood vascular hemodynamics is limited due to technical challenges associated with accessing the native thymus in live mice. To overcome this challenge, we developed an intravital two-photon imaging method to visualize the native thymus in vivo and investigated functional changes to the vascular system following sublethal irradiation. We quantified blood flow velocity and shear rate in cortical blood vessels and identified a subtle but significant increase in vessel leakage and diameter ~24 hrs post-sublethal irradiation. Ex vivo whole organ imaging of optically cleared thymus lobes confirmed a disruption of the thymus vascular structure, resulting in an increase in blood vessel diameter and vessel area, and concurrent thymic atrophy. This novel two-photon intravital imaging method enables a new paradigm for directly investigating the thymic microenvironment in vivo.

Refractive index measurement deflectometry for measuring gradient refractive index lens

A method based on deflectometry to measure the refractive index distribution of radial gradient refractive index (GRIN) lens is proposed in this paper. The method establishes the relationship between the refractive index distribution and the direction of light ray by deriving the propagation equation of light in a non-uniform medium. By measuring the deflection angle using the principle of deflectometry and the assumption of central refraction, the refractive index distribution of the radial GRIN lens is determined. The specific principle of refractive index measurement deflectometry (RIMD) is described in detail, and the correctness and accuracy of the method are verified through numerical simulations. Furthermore, the effects of calibration error, lens surface shape on the accuracy of the measurement results are analyzed. In the experimental section, the proposed method is applied to measure a radial GRIN lens, and the results are compared with the nominal parameters in terms of shape distribution and numerical values, demonstrating good consistency. The measurement error is controlled within the order of 10-3. This method enables rapid and convenient acquisition of full-field information of GRIN lens and holds promising potential for playing an important role in lens manufacturing and production.

Miniaturized, high numerical aperture confocal fluorescence detection enhanced with pyroelectric droplet accumulation for sub-attomole analyte diagnosis

To meet the growing demand for early fatal disease screening among large populations, current fluorescence detection instruments aiming at point-of-care diagnosis have the tendency to be low cost and high sensitivity, with a high potential for the analysis of low-volume, multiplex analytes with easy operation. In this work, we present the development of a miniaturized, high numerical aperture confocal fluorescence scanner for sub-micro-liter fluid diagnosis. It is enhanced with high-rate analyte accumulation using a pyroelectro-hydrodynamic dispensing system for generating tiny, stable sample droplets. The simplified confocal fluorescence scanner (numerical aperture 0.79, working distance 7.3 mm) uses merely off-the-shelf mass-production optical components. Experimental results show that it can achieve a high-sensitive, cost-efficient detection for sub-micro-liter, low-abundant (0.04 µL, 0.67 attomoles) fluid diagnosis, promising for point-of-care diagnosis.

Enhanced light focusing inside scattering media with shaped ultrasound

Light focusing is the primary enabler of various scientific and industrial processes including laser materials processing and microscopy. However, the scattering of light limits the depth at which current methods can operate inside heterogeneous media such as biological tissue, liquid emulsions, and composite materials. Several approaches have been developed to address this issue, but they typically come at the cost of losing spatial or temporal resolution, or increased invasiveness. Here, we show that ultrasound waves featuring a Bessel-like profile can locally modulate the optical properties of a turbid medium to facilitate light guiding. Supported by wave optics and Monte Carlo simulations, we demonstrate how ultrasound enhances light focusing a factor of 7 compared to conventional methods based on placing optical elements outside the complex medium. Combined with point-by-point scanning, images of samples immersed in turbid media with an optical density up to 15, similar to that of weakly scattering biological tissue, can be reconstructed. The quasi-instantaneous generation of the shaped-ultrasound waves, together with the possibility to use transmission and reflection architectures, can pave the way for the real-time control of light inside living tissue.

Sub-diffraction computational imaging via a flexible multicore-multimode fiber

An ultra-thin multimode fiber is an ideal platform for minimally invasive microscopy with the advantages of a high density of modes, high spatial resolution, and a compact size. In practical applications, the probe needs to be long and flexible, which unfortunately destroys the imaging capabilities of a multimode fiber. In this work, we propose and experimentally demonstrate sub-diffraction imaging through a flexible probe based on a unique multicore-multimode fiber. A multicore part consists of 120 Fermat's spiral distributed single-mode cores. Each of the cores offers stable light delivery to the multimode part, which provides optimal structured light illumination for sub-diffraction imaging. As a result, perturbation-resilient fast sub-diffraction fiber imaging by computational compressive sensing is demonstrated.

Spectral Multiplexing of Fluorescent Endoscopy for Simultaneous Imaging with Multiple Fluorophores and Multiple Fields of View

Complex clinical procedures and small-animal research procedures can benefit from dual-site imaging provided by multiple endoscopic devices. Here, an endoscopic system is proposed which enables multiple fluorescence microendoscopes to be spectrally multiplexed on a single microscope base, enabling light sources and optical relays to be shared between endoscopes. The presented system is characterized for resolution using USAF-1951 resolution test charts and for modulation transfer function using the slanted edge method. Imaging is demonstrated both directly and with microendoscopes attached. Imaging of phantoms was demonstrated by targeting USAF charts and fiber tissues dyed for FITC and Texas Red fluorescence. Afterwards, simultaneous liver and kidney imaging was demonstrated in mice expressing mitochondrial Dendra2 and injected with Texas Red-dextran. The results indicate that the system achieves high channel isolation and submicron and subcellular resolution, with resolution limited by the endoscopic probe and by physiological movement during endoscopic imaging. Multi-channel microendoscopy provides a potentially low-cost means of simultaneous multiple endoscopic imaging during biological experiments, resulting in reduced animal harm and potentially increasing insight into temporal connections between connected biological systems.

Imaging stretching and displacement using gradient-index elements during the lens design process

In this study, we propose an approach to stretch or translate images using gradient-index (GRIN) elements with a rotationally symmetric shape in lens systems. In this method, the GRIN material, instead of optical surfaces, are utilized to enable a breaking of rotational symmetry for the two image translations. GRIN expression with anamorphic and tilting terms is introduced. A pair of GRIN elements in front of the given system alters the magnification in two orthogonal directions using the anamorphic terms in the expression, which realizes image stretching. A pair of GRIN elements with tilting terms is used after the given system tilts the optical path to achieve a transverse displacement of the image. The structure of the given system remains unchanged when these translations are performed. A design method for the GRIN elements is presented. Additionally, a design example is presented whose image is stretched by 1.33 times in one direction and displaced to one side of its axis to demonstrate the feasibility of the proposed approach. The approach in this study may enable novel imaging GRIN lens system designs with flexible image positions or special optical functions.

Learned end-to-end high-resolution lensless fiber imaging towards real-time cancer diagnosis

Recent advances in label-free histology promise a new era for real-time diagnosis in neurosurgery. Deep learning using autofluorescence is promising for tumor classification without histochemical staining process. The high image resolution and minimally invasive diagnostics with negligible tissue damage is of great importance. The state of the art is raster scanning endoscopes, but the distal lens optics limits the size. Lensless fiber bundle endoscopy offers both small diameters of a few 100 microns and the suitability as single-use probes, which is beneficial in sterilization. The problem is the inherent honeycomb artifacts of coherent fiber bundles (CFB). For the first time, we demonstrate an end-to-end lensless fiber imaging with exploiting the near-field. The framework includes resolution enhancement and classification networks that use single-shot CFB images to provide both high-resolution imaging and tumor diagnosis. The well-trained resolution enhancement network not only recovers high-resolution features beyond the physical limitations of CFB, but also helps improving tumor recognition rate. Especially for glioblastoma, the resolution enhancement network helps increasing the classification accuracy from 90.8 to 95.6%. The novel technique enables histological real-time imaging with lensless fiber endoscopy and is promising for a quick and minimally invasive intraoperative treatment and cancer diagnosis in neurosurgery.

Bendable long graded index lens microendoscopy

Graded index (GRIN) lens endoscopy has broadly benefited biomedical microscopic imaging by enabling accessibility to sites not reachable by traditional benchtop microscopes. It is a long-held notion that GRIN lenses can only be used as rigid probes, which may limit their potential for certain applications. Here, we describe bendable and long-range GRIN microimaging probes for a variety of potential micro-endoscopic biomedical applications. Using a two-photon fluorescence imaging system, we have experimentally demonstrated the feasibility of three-dimensional imaging through a 500-µm-diameter and ∼11 cm long GRIN lens subject to a cantilever beam-like deflection with a minimum bend radius of ∼25 cm. Bend-induced perturbation to the field of view and resolution has also been investigated quantitatively. Our development alters the conventional notion of GRIN lenses and enables a range of innovative applications. For example, the demonstrated flexibility is highly desirable for implementation into current and emerging minimally invasive clinical procedures, including a pioneering microdevice for high-throughput cancer drug selection.

Optimization of a flexible fiber-optic probe for epi-mode quantitative phase imaging

Quantitative oblique back-illumination microscopy (qOBM) is an emerging label-free optical imaging technology that enables 3D, tomographic quantitative phase imaging (QPI) with epi-illumination in thick scattering samples. In this work, we present a robust optimization of a flexible, fiber-optic-based qOBM system. Our approach enables in silico optimization of the phase signal-to-noise-ratio over a wide parameter space and obviates the need for tedious experimental optimization which could easily miss optimal conditions. Experimental validations of the simulations are also presented and sensitivity limits for the probe are assessed. The optimized probe is light-weight (∼40g) and compact (8mm in diameter) and achieves a 2µm lateral resolution, 6µm axial resolution, and a 300µm field of view, with near video-rate operation (10Hz, limited by the camera). The phase sensitivity is <20nm for a single qOBM acquisition (at 10Hz) and a lower limit of ∼3 nm via multi-frame averaging. Finally, to demonstrate the utility of the optimized probe, we image (1) thick, fixed rat brain samples from a 9L gliosarcoma tumor model and (2) freshly excised human brain tissues from neurosurgery. Acquired qOBM images using the flexible fiber-optic probe are in excellent agreement with those from a free-space qOBM system (both in-situ), as well as with gold-standard histopathology slices (after tissue processing).

A Two-Photon Microimaging-Microdevice System for Four-Dimensional Imaging of Local Drug Delivery in Tissues

Advances in the intratumor measurement of drug responses have included a pioneering biomedical microdevice for high throughput drug screening in vivo, which was further advanced by integrating a graded-index lens based two-dimensional fluorescence micro-endoscope to monitor tissue responses in situ across time. While the previous system provided a bulk measurement of both drug delivery and tissue response from a given region of the tumor, it was incapable of visualizing drug distribution and tissue responses in a three-dimensional (3D) way, thus missing the critical relationship between drug concentration and effect. Here we demonstrate a next-generation system that couples multiplexed intratumor drug release with continuous 3D spatial imaging of the tumor microenvironment via the integration of a miniaturized two-photon micro-endoscope. This enables optical sectioning within the live tissue microenvironment to effectively profile the entire tumor region adjacent to the microdevice across time. Using this novel microimaging-microdevice (MI-MD) system, we successfully demonstrated the four-dimensional imaging (3 spatial dimensions plus time) of local drug delivery in tissue phantom and tumors. Future studies include the use of the MI-MD system for monitoring of localized intra-tissue drug release and concurrent measurement of tissue responses in live organisms, with applications to study drug resistance due to nonuniform drug distribution in tumors, or immune cell responses to anti-cancer agents.

Optical OAM tweezer based on graded-index multimode fibers

A fiber-optic probe consisting of a section of graded-index multimode fiber (GIMF) fused onto a few-mode fiber (FMF) is proposed in this paper. The orbital angular momentum (OAM) mode guided by the FMF was launched into the GIMF, and a focused OAM beam profile was obtained by tailoring the length of the GIMF. Based on the analysis of the propagation trajectory, the intensity distributions, and the phase distributions of the vortex beam in GIMF, the focusing properties of the OAM mode were investigated. It is found that there exists a maximum working distance at an optimal GIMF length, and a trade-off between the beam size and working distance should be taken into account for optical tweezer applications. These results are expected to be applied to optical fiber tweezers for more flexible and efficient optical manipulation of particles.

Long-GRIN-Lens Microendoscopy Enabled by Wavefront Shaping for a Biomedical Microdevice: An Analytical Investigation

We analytically investigate the feasibility of long graded-index (GRIN)-lens-based microendoscopes through wavefront shaping. Following the very well-defined ray trajectories in a GRIN lens, mode-dependent phase delay is first determined. Then, the phase compensation needed for obtaining diffraction limited resolution is derived. Finally, the diffraction pattern of the lens output is computed using the Rayleigh-Sommerfeld diffraction theory. We show that diffraction-limited resolution is obtained for a 0.5 mm diameter lens with a length over 1 m. It is also demonstrated that different imaging working distances (WDs) can be realized by modifying the phase compensation. When a short design WD is used, a large imaging numerical aperture (NA) higher than 0.4 is achievable even when a low NA lens (NA = 0.1) is used. The long- and thin-GRIN-lens-based microendoscope investigated here, which is attractive for biomedical applications, is being prioritized for use in a clinical stage microdevice that measures three-dimensional drug responses inside the body. The advance described in this work may enable superior imaging capabilities in clinical applications in which long and flexible imaging probes are favored.

Recent advances in intravital microscopy for investigation of dynamic cellular behavior in vivo

Currently, most biological research relies on conventional experimental techniques that allow only static analyses at certain time points in vitro or ex vivo. However, if one could visualize cellular dynamics in living organisms, that would provide a unique opportunity to study key biological phenomena in vivo. Intravital microscopy (IVM) encompasses diverse optical systems for direct viewing of objects, including biological structures and individual cells in live animals. With the current development of devices and techniques, IVM addresses important questions in various fields of biological and biomedical sciences. In this mini-review, we provide a general introduction to IVM and examples of recent applications in the field of immunology, oncology, and vascular biology. We also introduce an advanced type of IVM, dubbed real-time IVM, equipped with video-rate resonant scanning. Since the real-time IVM can render cellular dynamics with high temporal resolution in vivo, it allows visualization and analysis of rapid biological processes.

A Miniaturized Platform for Multiplexed Drug Response Imaging in Live Tumors

Simple Summary

We have developed an implantable microdevice that is placed into a live tumor, and can directly image how effective various chemotherapy drugs are at inducing cell death, without having to remove or process the tumor tissue. Currently drug optimization is performed by assessing tumor shrinkage after treating a patient with systemic doses of a chemotherapy agent; this only evaluates a single treatment at a time and typically takes weeks-months before an optimal treatment strategy is found (if found at all) for a specific patient. In contrast, using the technology presented here, a personalized cancer treatment strategy can potentially be optimized and tailored to a specific patient’s tumor characteristics within several hours, without requiring surgical tissue removal or prolonged trials of potentially ineffective chemotherapies.

Abstract

By observing the activity of anti-cancer agents directly in tumors, there is potential to greatly expand our understanding of drug response and develop more personalized cancer treatments. Implantable microdevices (IMD) have been recently developed to deliver microdoses of chemotherapeutic agents locally into confined regions of live tumors; the tissue can be subsequently removed and analyzed to evaluate drug response. This method has the potential to rapidly screen multiple drugs, but requires surgical tissue removal and only evaluates drug response at a single timepoint when the tissue is excised. Here, we describe a “lab-in-a-tumor” implantable microdevice (LIT-IMD) platform to image cell-death drug response within a live tumor, without requiring surgical resection or tissue processing. The LIT-IMD is inserted into a live tumor and delivers multiple drug microdoses into spatially discrete locations. In parallel, it locally delivers microdose levels of a fluorescent cell-death assay, which diffuses into drug-exposed tissues and accumulates at sites of cell death. An integrated miniaturized fluorescence imaging probe images each region to evaluate drug-induced cell death. We demonstrate ability to evaluate multi-drug response over 8 h using murine tumor models and show correlation with gold-standard conventional fluorescence microscopy and histopathology. This is the first demonstration of a fully integrated platform for evaluating multiple chemotherapy responses in situ. This approach could enable a more complete understanding of drug activity in live tumors, and could expand the utility of drug-response measurements to a wide range of settings where surgery is not feasible.

Micro-endoscopy for Live Small Animal Fluorescent Imaging

Intravital microscopy has emerged as a powerful technique for the fluorescent visualization of cellular- and subcellular-level biological processes in vivo. However, the size of objective lenses used in standard microscopes currently makes it difficult to access internal organs with minimal invasiveness in small animal models, such as mice. Here we describe front- and side-view designs for small-diameter endoscopes based on gradient-index lenses, their construction, their integration into laser scanning confocal microscopy platforms, and their applications for in vivo imaging of fluorescent cells and microvasculature in various organs, including the kidney, bladder, heart, brain, and gastrointestinal tracts, with a focus on the new techniques developed for each imaging application. The combination of novel fluorescence techniques with these powerful imaging methods promises to continue providing novel insights into a variety of diseases.

Extended field-of-view ultrathin microendoscopes for high-resolution two-photon imaging with minimal invasiveness

Imaging neuronal activity with high and homogeneous spatial resolution across the field-of-view (FOV) and limited invasiveness in deep brain regions is fundamental for the progress of neuroscience, yet is a major technical challenge. We achieved this goal by correcting optical aberrations in gradient index lens-based ultrathin (≤500 µm) microendoscopes using aspheric microlenses generated through 3D-microprinting. Corrected microendoscopes had extended FOV (eFOV) with homogeneous spatial resolution for two-photon fluorescence imaging and required no modification of the optical set-up. Synthetic calcium imaging data showed that, compared to uncorrected endoscopes, eFOV-microendoscopes led to improved signal-to-noise ratio and more precise evaluation of correlated neuronal activity. We experimentally validated these predictions in awake head-fixed mice. Moreover, using eFOV-microendoscopes we demonstrated cell-specific encoding of behavioral state-dependent information in distributed functional subnetworks in a primary somatosensory thalamic nucleus. eFOV-microendoscopes are, therefore, small-cross-section ready-to-use tools for deep two-photon functional imaging with unprecedentedly high and homogeneous spatial resolution.

Stereotaxic endoscopy for the ocular imaging of awake, freely moving animal models

Stereotaxic instruments are increasingly used in research animals for the study of disease, but typically require restraints and anesthetic procedures. A stereotaxic head mount that enables imaging of the anterior chamber of the eye in alert and freely mobile mice is presented in this study. The head mount is fitted based on computed tomography scans and manufactured using 3D printing. The system is placed noninvasively using temporal mount bars and a snout mount, without breaking the skin or risking suffocation, while an instrument channel stabilizes the ocular probes. With a flexible micro-endoscopic probe and a confocal scanning laser microscopy system, <20 μm resolution is achieved in vivo with a field of view of nearly 1 mm. Discomfort is minimal, and further adaptations for minimally invasive neuroscience, optogenetics and auditory studies are possible.

Development of large diameter nanostructured GRIN microlenses enhanced with temperature-controlled diffusion

Nanostructured GRIN components are optical elements which can have an arbitrary refractive index profile while retaining flat-parallel entry and exit facets. A method of their fabrication requires assembly of large quantities of glass rods in order to satisfy subwavelength requirement of the effective medium theory. In this paper, we present a development of gradient index microlenses using a combination of methods: nanostructurization of the preform and controlled diffusion process during lens drawing on a fiber drawing tower. Adding a diffusion process allows us to overcome limits of the effective medium theory related to maximum size of nanorods in the lens structure. We show that nanorods are dissolved during the fiber drawing process in high temperature and glass components are locally quasi-uniformly distributed. To demonstrate feasibility of the proposed approach, we have developed and experimentally verified the performance of a nGRIN microlens with a diameter of 115 µm composed of 115 rods on the diagonal, and length of 200 µm devoted to work for the wavelength over 658 nm.

Complex vectorial optics through gradient index lens cascades

Graded index (GRIN) lenses are commonly used for compact imaging systems. It is not widely appreciated that the ion-exchange process that creates the rotationally symmetric GRIN lens index profile also causes a symmetric birefringence variation. This property is usually considered a nuisance, such that manufacturing processes are optimized to keep it to a minimum. Here, rather than avoiding this birefringence, we understand and harness it by using GRIN lenses in cascade with other optical components to enable extra functionality in commonplace GRIN lens systems. We show how birefringence in the GRIN cascades can generate vector vortex beams and foci, and how it can be used advantageously to improve axial resolution. Through using the birefringence for analysis, we show that the GRIN cascades form the basis of a new single-shot Müller matrix polarimeter with potential for endoscopic label-free cancer diagnostics. The versatility of these cascades opens up new technological directions.

The manufacturing process for GRIN lenses causes a symmetric birefringence variation which is considered a deficiency. Here, the authors show how this birefringence can generate vector vortex beams and form the basis of a Müller matrix polarimeter with potential for endoscopic label-free cancer diagnostics.

Endoscopic vitreoretinal surgery: principles, applications and new directions

Purpose

To analyze endoscopic vitreoretinal surgery principles, applications, challenges and potential technological advances.

Background

Microendoscopic imaging permits vitreoretinal surgery for tissues that are not visible using operating microscopy ophthalmoscopy. Evolving instrumentation may overcome some limitations of current endoscopic technology.

Analysis

Transfer of the fine detail in endoscopic vitreoretinal images to extraocular video cameras is constrained currently by the caliber limitations of intraocular probes in ophthalmic surgery. Gradient index and Hopkins rod lenses provide high resolution ophthalmoscopy but restrict surgical manipulation. Fiberoptic coherent image guides offer surgical maneuverability but reduce imaging resolution. Coaxial endoscopic illumination can highlight delicate vitreoretinal structures difficult to image in chandelier or endoilluminator diffuse, side-scattered lighting. Microendoscopy’s ultra-high magnification video monitor images can reveal microscopic tissue details blurred partly by ocular media aberrations in contemporary surgical microscope ophthalmoscopy, thereby providing a lower resolution, invasive alternative to confocal fundus imaging. Endoscopic surgery is particularly useful when ocular media opacities or small pupils restrict or prevent transpupillary ophthalmoscopy. It has a growing spectrum of surgical uses that include the management of proliferative vitreoretinopathy and epiretinal membranes as well as the implantation of posterior chamber intraocular lenses and electrode arrays for intraretinal stimulation in retinitis pigmentosa. Microendoscopy’s range of applications will continue to grow with technological developments that include video microchip sensors, stereoscopic visualization, chromovitrectomy, digital image enhancement and operating room heads-up displays.

Conclusion

Microendoscopy is a robust platform for vitreoretinal surgery. Continuing clinical and technological innovation will help integrate it into the modern ophthalmic operating room of interconnected surgical microscopy, microendoscopy, vitrectomy machine and heads-up display instrumentation.

Miniaturized omnidirectional flexible side-view endoscope for rapid monitoring of thin tubular biostructures

Endoscopic imaging allows longitudinal observation of epithelial pathologies in tubular organs throughout the body. However, the imaging and optical diagnosis of tubular biostructures such as small animal models and small pediatric organs require appropriately miniaturized devices. A miniaturized catadioptric flexible side-view endoscope is proposed with omnidirectional field of view (FOV) in the transverse direction and sub-mm-scale feature resolution. The FOV in the longitudinal direction is 50°. Images are unwrapped and stitched together to form composite images of the target by two different algorithms, revealing a composite FOV of more than 3.5 cm × 360°. The endoscope is well suited for minimally invasive rapid monitoring of thin tubular organs in pediatric patients, as well as for imaging of small animal disease models at near-cellular resolution.

Label-Free Multiphoton Endomicroscopy for Minimally Invasive In Vivo Imaging

Multiphoton microscopy of cellular autofluorescence and second harmonic generation from collagen facilitates imaging of living cells and tissues without the need for additional fluorescent labels. Here, a compact multiphoton endomicroscope for label-free in vivo imaging in small animals via side-viewing needle objectives is presented. Minimal invasive imaging at cellular resolution is performed in colonoscopy of mice without surgical measures and without fluorescent dyes as a contrast agent. The colon mucosa is imaged repeatedly in the same animal in a mouse model of acute intestinal inflammation to study the process of inflammation at the tissue level within a time period of ten days, demonstrating the capabilities of label-free endomicroscopy for longitudinal studies for the first time.

Toolbox for In Vivo Imaging of Host-Parasite Interactions at Multiple Scales

Animal models have for long been pivotal for parasitology research. Over the last few years, techniques such as intravital, optoacoustic and magnetic resonance imaging, optical projection tomography, and selective plane illumination microscopy developed promising potential for gaining insights into host-pathogen interactions by allowing different visualization forms in vivo and ex vivo. Advances including increased resolution, penetration depth, and acquisition speed, together with more complex image analysis methods, facilitate tackling biological problems previously impossible to study and/or quantify. Here we discuss advances and challenges in the in vivo imaging toolbox, which hold promising potential for the field of parasitology.

Longitudinal micro-endoscopic monitoring of high-success intramucosal xenografts for mouse models of colorectal cancer

Colorectal cancer (CRC) is one of the most frequently lethal forms of cancer. Intramucosal injection allows development of better mouse models of CRC, as orthotopic xenografts allow development of adenocarcinoma in the submucosa of the mouse colon wall. In this paper, a method of orthotopic injection is monitored longitudinally using cellular-resolution real-time in vivo fluorescence microendoscopy, following the injection of three different cell lines: 3T3-GFP to confirm immunosuppression and HCT116-RFP cells to model CRC. Adenoma formation is first observable after 7 to 10 days, and by use of 33 G needles a tumor induction rate of greater than 85% is documented. An additional experiment on the injection of rapamycin reveals drug efficacy and localization between 24 and 48 hours, and suggests the promise of real-time cellular-resolution fluorescence micro-endoscopy for developing longitudinal therapy regimes in mural models of CRC.

Micro-endoscopic In Vivo Monitoring in the Blood and Lymphatic Vessels of the Oral Cavity after Radiation Therapy

Radiotherapy, although used worldwide for the treatment of head, neck, and oral cancers, causes acute complications, including effects on vasculature and immune response due to cellular stress. Thus, the ability to diagnose side-effects and monitor vascular response in real-time during radiotherapy would be highly beneficial for clinical and research applications. In this study, recently-developed fluorescence micro-endoscopic technology provides non-invasive, high-resolution, real-time imaging at the cellular level. Moreover, with the application of high-resolution imaging technologies and micro-endoscopy, which enable improved monitoring of adverse effects in GFP-expressing mouse models, changes in the oral vasculature and lymphatic vessels are quantified in real time for 10 days following a mild localized single fractionation, 10 Gy radiotherapy treatments. Fluorescence micro-endoscopy enables quantification of the cardiovascular recovery and immune response, which shows short-term reduction in mean blood flow velocity, in lymph flow, and in transient immune infiltration even after this mild radiation dose, in addition to long-term reduction in blood vessel capacity. The data provided may serve as a reference for the expected cellular-level physiological, cardiovascular, and immune changes in animal disease models after radiotherapy.

Improving collection efficiency in two-photon endoscopy with reflective waveguiding

Two-photon endoscopy based on a gradient-index lens has been widely utilized for studying cellular behaviors in deep-lying tissues with minimal invasiveness in vivo. Although the efficient collection of emitted light is critical to attain high-contrast spatiotemporal information, the intrinsic low numerical aperture of the endoscopic probe poses a physical limitation. We report a simple solution to overcome this limit by incorporating a reflective waveguide ensheathing the endoscopic probe, which improves the collection efficiency by approximately two-fold. We describe its principle, fabrication procedure, optical characterization, and utilities in biological tissues.

Longitudinal intravital imaging of transplanted mesenchymal stem cells elucidates their functional integration and therapeutic potency in an animal model of interstitial cystitis/bladder pain syndrome

Rationale: Mesenchymal stem cell (MSC) therapy may be a novel approach to improve interstitial cystitis/bladder pain syndrome (IC/BPS), an intractable disease characterized by severe pelvic pain and urinary frequency. Unfortunately, the properties of transplanted stem cells have not been directly analyzed in vivo, which hampers elucidation of the therapeutic mechanisms of these cells and optimization of transplantation protocols. Here, we monitored the behaviors of multipotent stem cells (M-MSCs) derived from human embryonic stem cells (hESCs) in real time using a novel combination of in vivo confocal endoscopic and microscopic imaging and demonstrated their improved therapeutic potency in a chronic IC/BPS animal model.

Methods: Ten-week-old female Sprague-Dawley rats were instilled with 10 mg of protamine sulfate followed by 750 μg of lipopolysaccharide weekly for 5 weeks. The sham group was instilled with phosphate-buffered saline (PBS). Thereafter, the indicated dose (0.1, 0.25, 0.5, and 1×10⁶ cells) of M-MSCs or PBS was injected once into the outer layer of the bladder. The distribution, perivascular integration, and therapeutic effects of M-MSCs were monitored by in vivo endoscopic and confocal microscopic imaging, awake cystometry, and histological and gene expression analyses.

Results: A novel combination of longitudinal intravital confocal fluorescence imaging and microcystoscopy in living animals, together with immunofluorescence analysis of bladder tissues, demonstrated that transplanted M-MSCs engrafted following differentiation into multiple cell types and gradually integrated into a perivascular-like structure until 30 days after transplantation. The beneficial effects of transplanted M-MSCs on bladder voiding function and the pathological characteristics of the bladder were efficient and long-lasting due to the stable engraftment of these cells.

Conclusion: This longitudinal bioimaging study of transplanted hESC-derived M-MSCs in living animals reveals their long-term functional integration, which underlies the improved therapeutic effects of these cells on IC/BPS.

In Vivo Fluorescence Microendoscopic Monitoring of Stent-Induced Fibroblast Cell Proliferation in an Esophageal Mouse Model

PURPOSE

To evaluate the feasibility of self-expanding metal stent (SEMS) placement and fluorescence microendoscopic monitoring for determination of fibroblast cell proliferation after stent placement in an esophageal mouse model.

MATERIALS AND METHODS

Twenty fibroblast-specific protein (FSP)-1 green fluorescent protein (GFP) transgenic mice were analyzed. Ten mice (Group A) underwent SEMS placement, and fluoroscopic and fluorescence microendoscopic images were obtained biweekly until 8 weeks thereafter. Ten healthy mice (Group B) were used for control esophageal values.

RESULTS

SEMS placement was technically successful in all mice. The relative average number of fibroblast GFP cells and the intensities of GFP signals in Group A were significantly higher than in Group B after stent placement. The proliferative cellular response, including granulation tissue, epithelial layer, submucosal fibrosis, and connective tissue, was increased in Group A. FSP-1-positive cells were more prominent in Group A than in Group B.

CONCLUSIONS

SEMS placement was feasible and safe in an esophageal mouse model, and proliferative cellular response caused by fibroblast cell proliferation after stent placement was longitudinally monitored using a noninvasive fluorescence microendoscopic technique. The results have implications for the understanding of proliferative cellular response after stent placement in real-life patients and provide initial insights into new clinical therapeutic strategies for restenosis.

Discovering Macrophage Functions Using In Vivo Optical Imaging Techniques

Macrophages are an important component of host defense and inflammation and play a pivotal role in immune regulation, tissue remodeling, and metabolic regulation. Since macrophages are ubiquitous in human bodies and have versatile physiological functions, they are involved in virtually every disease, including cancer, diabetes, multiple sclerosis, and atherosclerosis. Molecular biological and histological methods have provided critical information on macrophage biology. However, many in vivo dynamic behaviors of macrophages are poorly understood and yet to be discovered. A better understanding of macrophage functions and dynamics in pathogenesis will open new opportunities for better diagnosis, prognostic assessment, and therapeutic intervention. In this article, we will review the advances in macrophage tracking and analysis with in vivo optical imaging in the context of different diseases. Moreover, this review will cover the challenges and solutions for optical imaging techniques during macrophage intravital imaging.

Ultrahigh-Resolution Optical Coherence Elastography Images Cellular-Scale Stiffness of Mouse Aorta

Cellular-scale imaging of the mechanical properties of tissue has helped to reveal the origins of disease; however, cellular-scale resolution is not readily achievable in intact tissue volumes. Here, we demonstrate volumetric imaging of Young's modulus using ultrahigh-resolution optical coherence elastography, and apply it to characterizing the stiffness of mouse aortas. We achieve isotropic resolution of better than 15 μm over a 1-mm lateral field of view through the entire depth of an intact aortic wall. We employ a method of quasi-static compression elastography that measures volumetric axial strain and uses a compliant, transparent layer to measure surface axial stress. This combination is used to estimate Young's modulus throughout the volume. We demonstrate differentiation by stiffness of individual elastic lamellae and vascular smooth muscle. We observe stiffening of the aorta in regulator of G protein signaling 5-deficient mice, a model that is linked to vascular remodeling and fibrosis. We observe increased stiffness with proximity to the heart, as well as regions with micro-structural and micro-mechanical signatures characteristic of fibrous and lipid-rich tissue. High-resolution imaging of Young's modulus with optical coherence elastography may become an important tool in vascular biology and in other fields concerned with understanding the role of mechanics within the complex three-dimensional architecture of tissue.

Label-free nanoscale optical metrology on myelinated axons in vivo

In the mammalian nervous system, myelin provides electrical insulation for the neural circuit by forming a highly organized, multilayered thin film around the axon fibers. Here, we investigate the spectral reflectance from this subcellular nanostructure and devise a new label-free technique based on a spectroscopic analysis of reflected light, enabling nanoscale imaging of myelinated axons in their natural living state. Using this technique, we demonstrate three-dimensional mapping of the axon diameter and sensing of dynamic changes in the substructure of myelin at nanoscale. We further reveal the prevalence of axon bulging in the brain cortex in vivo after mild compressive trauma. Our novel tool opens new avenues of investigation by creating unprecedented access to the nanostructural dynamics of live myelinated axons in health and disease.

Compact plasmonic optical biosensors based on nanostructured gradient index lenses integrated into microfluidic cells

We report on a compact and cost-effective integrated label-free biosensor configuration which is based on the refractive index sensitivity of the localized surface plasmon resonance (LSPR) of gold nanostructures. Aiming for compactification and miniaturization of the sensor, arrays of nanodiscs were fabricated on the planar surface of a gradient index (GRIN) lens, which acts as a substrate as well as an imaging objective for the light scattered by the gold structures. Integration of the lens into a microfluidic flow cell enabled the controlled exchange of liquid media at the sensor surface. The light scattered by the nanostructures was investigated spatially and spectrally resolved making use of the imaging properties of the GRIN lens. Dynamic spectral analysis during refractive index changes was conducted, revealing high sensitivities of up to 372 nm per refractive index unit for the shift of the LSPR. Biosensing capabilities were demonstrated by the detection of binding of an analyte by means of a testosterone-immunoassay.

Ultrahigh-resolution optical coherence elastography through a micro-endoscope: towards in vivo imaging of cellular-scale mechanics

In this paper, we describe a technique capable of visualizing mechanical properties at the cellular scale deep in living tissue, by incorporating a gradient-index (GRIN)-lens micro-endoscope into an ultrahigh-resolution optical coherence elastography system. The optical system, after the endoscope, has a lateral resolution of 1.6 µm and an axial resolution of 2.2 µm. Bessel beam illumination and Gaussian mode detection are used to provide an extended depth-of-field of 80 µm, which is a 4-fold improvement over a fully Gaussian beam case with the same lateral resolution. Using this system, we demonstrate quantitative elasticity imaging of a soft silicone phantom containing a stiff inclusion and a freshly excised malignant murine pancreatic tumor. We also demonstrate qualitative strain imaging below the tissue surface on in situ murine muscle. The approach we introduce here can provide high-quality extended-focus images through a micro-endoscope with potential to measure cellular-scale mechanics deep in tissue. We believe this tool is promising for studying biological processes and disease progression in vivo.

Controlled delivery and minimally invasive imaging of stem cells in the lung

Intratracheal delivery of stem cells into injured or diseased lungs can provide a variety of therapeutic and immunomodulatory effects for the treatment of acute lung injury and chronic lung disease. While the efficacy of this approach depends on delivering the proper cell dosage into the target region of the airway, tracking and analysis of the cells have been challenging, largely due to the limited understanding of cell transport and lack of suitable cell monitoring techniques. We report on the transport and deposition of intratracheally delivered stem cells as well as strategies to modulate the number of cells (e.g., dose), topographic distribution, and region-specific delivery in small (rodent) and large (porcine and human) lungs. We also developed minimally invasive imaging techniques for real-time monitoring of intratracheally delivered cells. We propose that this approach can facilitate the implementation of patient-specific cells and lead to enhanced clinical outcomes in the treatment of lung disease with cell-based therapies.

Improved efficacy and in vivo cellular properties of human embryonic stem cell derivative in a preclinical model of bladder pain syndrome

Interstitial cystitis/bladder pain syndrome (IC/BPS) is an intractable disease characterized by severe pelvic pain and urinary frequency. Mesenchymal stem cell (MSC) therapy is a promising approach to treat incurable IC/BPS. Here, we show greater therapeutic efficacy of human embryonic stem cell (hESC)-derived multipotent stem cells (M-MSCs) than adult bone-marrow (BM)-derived counterparts for treating IC/BPS and also monitor long-term safety and in vivo properties of transplanted M-MSCs in living animals. Controlled hESC differentiation and isolation procedures resulted in pure M-MSCs displaying typical MSC behavior. In a hydrochloric-acid instillation-induced IC/BPS animal model, a single local injection of M-MSCs ameliorated bladder symptoms of IC/BPS with superior efficacy compared to BM-derived MSCs in ameliorating bladder voiding function and histological injuries including urothelium denudation, mast-cell infiltration, tissue fibrosis, apoptosis, and visceral hypersensitivity. Little adverse outcomes such as abnormal growth, tumorigenesis, or immune-mediated transplant rejection were observed over 12-months post-injection. Intravital confocal fluorescence imaging tracked the persistence of the transplanted cells over 6-months in living animals. The infused M-MSCs differentiated into multiple cell types and gradually integrated into vascular-like structures. The present study provides the first evidence for improved therapeutic efficacy, long-term safety, and in vivo distribution and cellular properties of hESC derivatives in preclinical models of IC/BPS.

Volume holographic imaging endoscopic design and construction techniques

A reflectance volume holographic imaging (VHI) endoscope has been designed for simultaneous in vivo imaging of surface and subsurface tissue structures. Prior utilization of VHI systems has been limited to ex vivo tissue imaging. The VHI system presented in this work is designed for laparoscopic use. It consists of a probe section that relays light from the tissue sample to a handheld unit that contains the VHI microscope. The probe section is constructed from gradient index (GRIN) lenses that form a 1:1 relay for image collection. The probe has an outer diameter of 3.8 mm and is capable of achieving 228.1 ?? lp / mm resolution with 660-nm Kohler illumination. The handheld optical section operates with a magnification of 13.9 and a field of view of 390 ?? ? m × 244 ?? ? m . System performance is assessed through imaging of 1951 USAF resolution targets and soft tissue samples. The system has also passed sterilization procedures required for surgical use and has been used in two laparoscopic surgical procedures.

Methodological advances in imaging intravital axonal transport

Axonal transport is the active process whereby neurons transport cargoes such as organelles and proteins anterogradely from the cell body to the axon terminal and retrogradely in the opposite direction. Bi-directional transport in axons is absolutely essential for the functioning and survival of neurons and appears to be negatively impacted by both aging and diseases of the nervous system, such as Alzheimer’s disease and amyotrophic lateral sclerosis. The movement of individual cargoes along axons has been studied in vitro in live neurons and tissue explants for a number of years; however, it is currently unclear as to whether these systems faithfully and consistently replicate the in vivo situation. A number of intravital techniques originally developed for studying diverse biological events have recently been adapted to monitor axonal transport in real-time in a range of live organisms and are providing novel insight into this dynamic process. Here, we highlight these methodological advances in intravital imaging of axonal transport, outlining key strengths and limitations while discussing findings, possible improvements, and outstanding questions.

Aberrations of the point spread function of a multimode fiber due to partial mode excitation

We investigate the point spread function of a multimode fiber. The distortion of the focal spot created on the fiber output facet is studied for a variety of the parameters. We develop a theoretical model of wavefront shaping through a multimode fiber and use it to confirm our experimental results and analyze the nature of the focal distortions. We show that aberration-free imaging with a large field of view can be achieved by using an appropriate number of segments on the spatial light modulator during the wavefront-shaping procedure. The results describe aberration limits for imaging with multimode fibers as in, e.g., microendoscopy.

In Vivo Voltage-Sensitive Dye Imaging of Subcortical Brain Function

The whisker system of rodents is an excellent model to study peripherally evoked neural activity in the brain. Discrete neural modules represent each whisker in the somatosensory cortex (“barrels”), thalamus (“barreloids”), and brain stem (“barrelettes”). Stimulation of a single whisker evokes neural activity sequentially in its corresponding barrelette, barreloid, and barrel. Conventional optical imaging of functional activation in the brain is limited to surface structures such as the cerebral cortex. To access subcortical structures and image sensory-evoked neural activity, we designed a needle-based optical system using gradient-index (GRIN) rod lens. We performed voltage-sensitive dye imaging (VSDi) with GRIN rod lens to visualize neural activity evoked in the thalamic barreloids by deflection of whiskers in vivo. We stimulated several whiskers together to determine the sensitivity of our approach in differentiating between different barreloid responses. We also carried out stimulation of different whiskers at different times. Finally, we used muscimol in the barrel cortex to silence the corticothalamic inputs while imaging in the thalamus. Our results show that it is possible to obtain functional maps of the sensory periphery in deep brain structures such as the thalamic barreloids. Our approach can be broadly applicable to functional imaging of other core brain structures.

In vivo longitudinal cellular imaging of small intestine by side-view endomicroscopy

Visualization of cellular dynamics in the gastrointestinal tract of living mouse model to investigate the pathophysiology has been a long-pursuing goal. Especially, for chronic disease such as Crohn's disease, a longitudinal observation of the luminal surface of the small intestine in the single mouse is highly desirable to investigate the complex pathogenesis in sequential time points. In this work, by utilizing a micro-GRIN lens based side-view endomicroscope integrated into a video-rate confocal microscopy system, we successfully performed minimally-invasive in vivo cellular-level visualization of various fluorescent cells and microvasculature in the small intestinal villi. Also, with a transgenic mouse universally expressing photoconvertible protein, Kaede, we demonstrated repetitive cellular-level confocal endoscopic visualization of same area in the small intestinal lumen of a single mouse, which revealed the continuous homeostatic renewal of the small intestinal epithelium.

In vivo fluorescence microscopy: lessons from observing cell behavior in their native environment

Microscopic imaging techniques to visualize cellular behaviors in their natural environment play a pivotal role in biomedical research. Here, we review how recent technical advances in intravital microscopy have enabled unprecedented access to cellular physiology in various organs of mice in normal and diseased states.

Super-resolution endoscopy for real-time wide-field imaging

Resolving subcellular structures in vitro beyond optical diffraction barrier by a light microscope has achieved significant development since the advancement of super-resolution fluorescence microscopes, such as stimulated emission depletion (STED) microscopy, stochastic optical reconstruction microscopy (STORM) and photoactivated localization microscopy (PALM). However, the resolution of observation in deep and dense in vivo tissues is still confined to cellular level presently, and hence, exploring image details at subcellular level or even beyond organelle level in vivo has continued to attract much research attention. Currently, endoscopy provides an effective way to achieve in vivo observations and is compatible with mature optical microscopy technologies, but its resolution is usually confined to ~1 µm. Here we report a new endoscopy method by functionalizing graded-index (GRIN) lens with microspheres for real-time white-light or fluorescent super-resolution imaging. The capability of resolving objects with feature size of ~λ/5, which breaks the diffraction barrier of traditional GRIN lens based endoscopes by a factor of two, has been demonstrated by using this super-resolution endoscopy method. Further development of such a super-resolution endoscopy technique may provide new opportunities for in vivo life sciences studies.

Molecular imaging needles: dual-modality optical coherence tomography and fluorescence imaging of labeled antibodies deep in tissue

Molecular imaging using optical techniques provides insight into disease at the cellular level. In this paper, we report on a novel dual-modality probe capable of performing molecular imaging by combining simultaneous three-dimensional optical coherence tomography (OCT) and two-dimensional fluorescence imaging in a hypodermic needle. The probe, referred to as a molecular imaging (MI) needle, may be inserted tens of millimeters into tissue. The MI needle utilizes double-clad fiber to carry both imaging modalities, and is interfaced to a 1310-nm OCT system and a fluorescence imaging subsystem using an asymmetrical double-clad fiber coupler customized to achieve high fluorescence collection efficiency. We present, to the best of our knowledge, the first dual-modality OCT and fluorescence needle probe with sufficient sensitivity to image fluorescently labeled antibodies. Such probes enable high-resolution molecular imaging deep within tissue.

Longitudinal Tracing of Spontaneous Regression and Anti-angiogenic Response of Individual Microadenomas during Colon Tumorigenesis

Angiogenesis is essential for the progression of cancer, but its involvement in the initial phase of colon tumorigenesis is not well understood. Using intravital endomicroscopy, we visualized the natural history of early pre-tumorous lesions and adenomas in the colon of conditional Apc-knockout and Apc/Kras double mutant mouse models. Early lesions emerged about 4 weeks after the onset of somatic mutations, accompanying vascular dilation when the size of lesions reached about 200 μm, but most lesions regressed spontaneously and cleared within 10 weeks after their emergence. Anti-angiogenic treatments with vascular endothelial growth factor receptor (VEGFR) antagonists reduced the size of the early lesions and the number of polyps. We found surprisingly that anti-angiogenic treatments delayed the natural clearance of transient lesions by up to several weeks in both genetic models. The results represent the previously unexpected role of early angiogenesis on the spontaneous regression of early-stage colon tumors.

Intravital microscopic interrogation of peripheral taste sensation

Intravital microscopy is a powerful tool in neuroscience but has not been adapted to the taste sensory organ due to anatomical constraint. Here we developed an imaging window to facilitate microscopic access to the murine tongue in vivo. Real-time two-photon microscopy allowed the visualization of three-dimensional microanatomy of the intact tongue mucosa and functional activity of taste cells in response to topically administered tastants in live mice. Video microscopy also showed the calcium activity of taste cells elicited by small-sized tastants in the blood circulation. Molecular kinetic analysis suggested that intravascular taste sensation takes place at the microvilli on the apical side of taste cells after diffusion of the molecules through the pericellular capillaries and tight junctions in the taste bud. Our results demonstrate the capabilities and utilities of the new tool for taste research in vivo.

Optimization and characterization of nonlinear excitation and collection through a gradient-index lens for high-resolution nonlinear endomicroscopy

We report a study of gradient index (GRIN) lenses as a miniaturized micro-objective for in vivo imaging in the context of the development of a nonlinear endomicroscope. A numerical study of the parameters influencing the lateral resolution, excitation, and collection efficiency, when GRIN lens is coupled with a double clad fiber (DCF), is exposed. Four commercial DCFs, previously identified from the literature as potential endoscopic fibers, are simulated. Then, an experimental study characterizes two GRIN lenses (one commercial, one homemade) by their dispersion and nonlinear effects, potential intrinsic fluorescence, and use for fluorescence lifetime measurements. Images of neural cells from brain tissues of mice through a GRIN lens are presented.

Polarization-controlled images based on double-exposure polarization holography in an azobenzene liquid-crystalline polymer

Polarization-controlled optical image operations were demonstrated based on the double-exposure polarization holographic method. Two images were stored in the same volume of an azobenzene liquid-crystalline polymer by recording superimposed holograms, a pair of polarization gratings with one spatial frequency, using two orthogonal circularly polarized 532 nm beams and were reconstructed with a 650 nm laser. The recorded polarization holographic gratings were investigated to show distinctive polarization selectivity, high diffraction efficiency, and good stability. The brightness and the polarization of the diffracted images were found to be dependent on the polarization of the readout beam, and two images could be reconstructed individually or simultaneously.

Reflectance confocal endomicroscope with optical axial scanning for in vivo imaging of the oral mucosa

This paper presents the design and evaluation of a reflectance confocal laser endomicroscope using a miniature objective lens within a rigid probe in conjunction with an electrically tunable lens for axial scanning. The miniature lens was characterized alone as well as in the endoscope across a 200 µm axial scan range using the tunable lens. The ability of the confocal endoscope to probe the human oral cavity is demonstrated by imaging of the oral mucosa in vivo. The results indicate that reflectance confocal endomicroscopy has the potential to be used in a clinical setting and guide diagnostic evaluation of biological tissue.

Gradient index lens based combined two-photon microscopy and optical coherence tomography

We report a miniaturized probe-based combined two-photon microscopy (TPM) and optical coherence tomography (OCT) system. This system is to study the colorectal cancer in mouse models by visualizing both cellular and structural information of the colon in 3D with TPM and OCT respectively. The probe consisted of gradient index (GRIN) lenses and a 90° reflecting prism at its distal end for side-viewing, and it was added onto an objective lens-based TPM and OCT system. The probe was 2.2 mm in diameter and 60 mm in length. TPM imaging was performed by raster scanning of the excitation focus at the imaging speed of 15.4 frames/s. OCT imaging was performed by combining the linear sample translation and probe rotation along its axis. This miniaturized probe based dual-modal system was characterized with tissue phantoms containing fluorescent microspheres, and applied to image mouse colonic tissues ex vivo as a demonstration. As OCT and TPM provided structural and cellular information of the tissues respectively, this probe based multi-modal imaging system can be helpful for in vivo studies of preclinical animal models such as mouse colonic tumorigenesis.