In vivo imaging of unstained tissues using a compact and flexible multiphoton microendoscope

Improved Liver Intravital Microscopic Imaging Using a Film-Assisted Stabilization Method

Intravital microscopy (IVM) is a valuable method for biomedical characterization of dynamic processes, which has been applied to many fields such as neuroscience, oncology, and immunology. During IVM, vibration suppression is a major challenge due to the inevitable respiration and heartbeat from live animals. In this study, taking liver IVM as an example, we have unraveled the vibration inhibition effect of liquid bridges by studying the friction characteristics of a moist surface on the mouse liver. We confirmed the presence of liquid bridges on the liver through fluorescence imaging, which can provide microscale and nondestructive liquid connections between adjacent surfaces. Liquid bridges were constructed to sufficiently stabilize the liver after abdominal dissection by covering it with a polymer film, taking advantage of the high adhesion properties of liquid bridges. We further prototyped a microscope-integrated vibration-damping device with adjustable film tension to simplify the sample preparation procedure, which remarkably decreased the liver vibration. In practical application scenarios, we observed the process of liposome phagocytosis by liver Kupffer cells with significantly improved image and video quality. Collectively, our method not only provided a feasible solution to vibration suppression in the field of IVM, but also has the potential to be applied to vibration damping of precision instruments or other fields that require nondestructive ″soft″ vibration damping.

In vivo methods for imaging blood-brain barrier function and dysfunction

The blood-brain barrier (BBB) is the interface between the central nervous system and systemic circulation. It tightly regulates what enters and is removed from the brain parenchyma and is fundamental in maintaining brain homeostasis. Increasingly, the BBB is recognised as having a significant role in numerous neurological disorders, ranging from acute disorders (traumatic brain injury, stroke, seizures) to chronic neurodegeneration (Alzheimer's disease, vascular dementia, small vessel disease). Numerous approaches have been developed to study the BBB in vitro, in vivo, and ex vivo. The complex multicellular structure and effects of disease are difficult to recreate accurately in vitro, and functional aspects of the BBB cannot be easily studied ex vivo. As such, the value of in vivo methods to study the intact BBB cannot be overstated. This review discusses the structure and function of the BBB and how these are affected in diseases. It then discusses in depth several established and novel methods for imaging the BBB in vivo, with a focus on MRI, nuclear imaging, and high-resolution intravital fluorescence microscopy.

Two-Photon Endoscopy: State of the Art and Perspectives

In recent years, the demand for non-destructive deep-tissue imaging modalities has led to interest in multiphoton endoscopy. In contrast to bench top systems, multiphoton endoscopy enables subcellular resolution imaging in areas not reachable before. Several groups have recently presented their development towards the goal of producing user friendly plug and play system, which could be used in biological research and, potentially, clinical applications. We first present the technological challenges, prerequisites, and solutions in two-photon endoscopic systems. Secondly, we focus on the applications already found in literature. These applications mostly serve as a quality check of the built system, but do not answer a specific biomedical research question. Therefore, in the last part, we will describe our vision on the enormous potential applicability of adult two-photon endoscopic systems in biological and clinical research. We will thus bring forward the concept that two-photon endoscopy is a sine qua non in bringing this technique to the forefront in clinical applications.

Label-free second harmonic generation imaging of cerebral vascular wall in local ischemia mouse model in vivo

Second harmonic generation (SHG) imaging is label-free and non-invasive, and it has been extensively applied in multiple biological and medical studies, but not in the brain in vivo. In this study, we modified classical two photon excited fluorescence (TPEF) system to perform in vivo simultaneous TPEF and SHG imaging in the local ischemia mouse model. In cerebral vascular walls, we found strong SHG signal, which co-localized with collagen. In the continuous 2 days' in vivo imaging, this SHG signal remained stable in the local ischemic blood vessel in the initial 4 hours, then its signal abruptly increased and got spatially thickened 5 hours after thrombosis, and this tendency continued in the following 48 hours. This study provides direct and precise timeline of rapid collagen change in cerebral vascular walls in vivo, and reveals the subtle but significant temporal-spatial dynamics of this structural signal during local ischemia. Thus, this cerebral in vivo SHG imaging provides a powerful tool to identify the early and subtle pathological change of collagen around clinical key therapeutic time window.

Comparative Study Between a Customized Bimodal Endoscope and a Benchtop Microscope for Quantitative Tissue Diagnosis

Nowadays, surgical removal remains the standard method to treat brain tumors. During surgery, the neurosurgeon may encounter difficulties to delimitate tumor boundaries and the infiltrating areas as they have a similar visual appearance to adjacent healthy zones. These infiltrating residuals increase the tumor recurrence risk, which decreases the patient’s post-operation survival time. To help neurosurgeons improve the surgical act by accurately delimitating healthy from cancerous areas, our team is developing an intraoperative multimodal imaging tool. It consists of a two-photon fluorescence fibered endomicroscope that is intended to provide a fast, real-time, and reliable diagnosis information. In parallel to the instrumental development, a large optical database is currently under construction in order to characterize healthy and tumor brain tissues with their specific optical signature using multimodal analysis of the endogenous fluorescence. Our previous works show that this multimodal analysis could provide a reliable discrimination response between different tissue types based on several optical indicators. Here, our goal is to show that the two-photon fibered endomicroscope is able to provide, based on the same approved indicators in the tissue database, the same reliable response that could be used intraoperatively. We compared the spectrally resolved and time-resolved fluorescence signal, generated by our two-photon bimodal endoscope from 46 fresh brain tissue samples, with a similar signal provided by a standard reference benchtop multiphoton microscope that has been validated for tissue diagnosis. The higher excitation efficiency and collection ability of an endogenous fluorescence signal were shown for the endoscope setup. Similar molecular ratios and fluorescence lifetime distributions were extracted from the two compared setups. Spectral discrimination ability of the bimodal endoscope was validated. As a preliminary step before tackling multimodality, the ability of the developed bimodal fibered endoscope to excite and to collect efficiently as well as to provide a fast exploitable high-quality signal that is reliable to discriminate different types of human brain tissues was validated.

Assessment of Ultra-Early-Stage Liver Fibrosis in Human Non-Alcoholic Fatty Liver Disease by Second-Harmonic Generation Microscopy

Non-alcoholic fatty liver disease (NAFLD) is associated with the chronic progression of fibrosis. In general, the progression of liver fibrosis is determined by a histopathological assessment with a collagen-stained section; however, the ultra-early stage of liver fibrosis is challenging to identify because of the low sensitivity in the collagen-selective staining method. In the present study, we demonstrate the feasibility of second-harmonic generation (SHG) microscopy in the histopathological diagnosis of the liver of NAFLD patients for the quantitative assessment of the ultra-early stage of fibrosis. We investigated four representative NAFLD patients with early stages of fibrosis. SHG microscopy visualised well-matured fibrotic structures and early fibrosis diffusely involving liver tissues, whereas early fibrosis is challenging to be identified by conventional histopathological methods. Furthermore, the SHG emission directionality analysis revealed the maturation of each collagen fibre of each patient. As a result, SHG microscopy is feasible for assessing liver fibrosis on NAFLD patients, including the ultra-early stage of liver fibrosis that is difficult to diagnose by the conventional histopathological method. The assessment method of the ultra-early fibrosis by using SHG microscopy may serve as a crucial means for pathological, clinical, and prognostic diagnosis of NAFLD patients.

Clinically Available Optical Imaging Technologies in Endoscopic Lesion Detection: Current Status and Future Perspective

Endoscopic optical imaging technologies for the detection and evaluation of dysplasia and early cancer have made great strides in recent decades. With the capacity of in vivo early detection of subtle lesions, they allow modern endoscopists to provide accurate and effective optical diagnosis in real time. This review mainly analyzes the current status of clinically available endoscopic optical imaging techniques, with emphasis on the latest updates of existing techniques. We summarize current coverage of these technologies in major hospital departments such as gastroenterology, urology, gynecology, otolaryngology, pneumology, and laparoscopic surgery. In order to promote a broader understanding, we further cover the underlying principles of these technologies and analyze their performance. Moreover, we provide a brief overview of future perspectives in related technologies, such as computer-assisted diagnosis (CAD) algorithms dealing with exploring endoscopic video data. We believe all these efforts will benefit the healthcare of the community, help endoscopists improve the accuracy of diagnosis, and relieve patients' suffering.

Novel endoscopic optical diagnostic technologies in medical trial research: recent advancements and future prospects

Novel endoscopic biophotonic diagnostic technologies have the potential to non-invasively detect the interior of a hollow organ or cavity of the human body with subcellular resolution or to obtain biochemical information about tissue in real time. With the capability to visualize or analyze the diagnostic target in vivo, these techniques gradually developed as potential candidates to challenge histopathology which remains the gold standard for diagnosis. Consequently, many innovative endoscopic diagnostic techniques have succeeded in detection, characterization, and confirmation: the three critical steps for routine endoscopic diagnosis. In this review, we mainly summarize researches on emerging endoscopic optical diagnostic techniques, with emphasis on recent advances. We also introduce the fundamental principles and the development of those techniques and compare their characteristics. Especially, we shed light on the merit of novel endoscopic imaging technologies in medical research. For example, hyperspectral imaging and Raman spectroscopy provide direct molecular information, while optical coherence tomography and multi-photo endomicroscopy offer a more extensive detection range and excellent spatial-temporal resolution. Furthermore, we summarize the unexplored application fields of these endoscopic optical techniques in major hospital departments for biomedical researchers. Finally, we provide a brief overview of the future perspectives, as well as bottlenecks of those endoscopic optical diagnostic technologies. We believe all these efforts will enrich the diagnostic toolbox for endoscopists, enhance diagnostic efficiency, and reduce the rate of missed diagnosis and misdiagnosis.

Throughput-Speed Product Augmentation for Scanning Fiber-Optic Two-Photon Endomicroscopy

Compactness, among several others, is one unique and very attractive feature of a scanning fiber-optic two-photon endomicroscope. To increase the scanning area and the total number of resolvable pixels (i.e., the imaging throughput), it typically requires a longer cantilever which, however, leads to a much undesired, reduced scanning speed (and thus imaging frame rate). Herein we introduce a new design strategy for a fiber-optic scanning endomicroscope, where the overall numerical aperture (NA) or beam focusing power is distributed over two stages: 1) a mode-field focuser engineered at the tip of a double-clad fiber (DCF) cantilever to pre-amplify the single-mode core NA, and 2) a micro objective of a lower magnification (i.e.,  ∼ 2× in this design) to achieve final tight beam focusing. This new design enables either an ~9-fold increase in imaging area (throughput) or an ~3-fold improvement in imaging frame rate when compared to traditional fiber-optic endomicroscope designs. The performance of an as-designed endomicroscope of an enhanced throughput-speed product was demonstrated by two representative applications: (1) high-resolution imaging of an internal organ (i.e., mouse kidney) in vivo over a large field of view without using any fluorescent contrast agents, and (2) real-time neural imaging by visualizing dendritic calcium dynamics in vivo with sub-second temporal resolution in GCaMP6m-expressing mouse brain. This cascaded NA amplification strategy is universal and can be readily adapted to other types of fiber-optic scanners in compact linear or nonlinear endomicroscopes.

Prognostic value of tumor stromal collagen features in patients with hepatocellular carcinoma revealed by second-harmonic generation microscopy

INTRODUCTION

Hepatocellular carcinoma (HCC) is the sixth most common cancer worldwide. The search for new biomarkers that predict the outcome of HCC patients is ongoing. We propose the second harmonic generation-based quantitative assessment approach to evaluate the prognostic value of tumor stromal collagen in HCC.

MATERIALS AND METHODS

We evaluated tumor stromal collagen in paraffin-embedded specimens from 109 HCC patients by second-harmonic generation imaging. The parameters and quantitative assessment of collagen were obtained using a fiber network extraction algorithm. The relationships between collagen features and clinical pathological features and overall survival were statistically analyzed.

RESULT

Among the collagen features, some parameters of aggregated collagen correlated well with clinical pathological features, especially the aggregated collagen cross-linked density. Cross-linked collagen fibers form a fiber network in moderately and poor differentiated HCCs. Kaplan-Meier analyses and the multivariate Cox proportional hazard model showed that high aggregated collagen cross-linked density was associated with poor overall survival. The chi-squared test showed that aggregated cross-link density was significantly associated with histological grade and tumor recurrence.

CONCLUSION

Our results indicate the prognostic value of the quantitative evaluation of tumor stromal collagen using second harmonic generation imaging of patients with HCC.

Multiphoton microscopy for pre-clinical evaluation of flow-diverter stents for treating aneurysms

BACKGROUND

Conventional histological analyses are the gold standard for the study of aneurysms and vascular pathologies in pre-clinical research. Over the past decade, in vivo and ex vivo imaging using multiphoton microscopy have emerged as powerful pre-clinical tools for detailed tissue analyses that can assess morphology, the extracellular matrix (ECM), cell density and vascularisation. Multiphoton microscopy allows for deeper tissue penetration with minor phototoxicity.

OBJECTIVE

The present study aimed to demonstrate the current status of multimodality imaging, including multiphoton microscopy, for detailed analyses of neo-endothelialisation and ECM evolution after flow-diverter stent (FDS) treatment in an experimental rabbit model of aneurysms.

METHODS

Multiphoton microscopy tools for assessing autofluorescence and second harmonic generation (SHG) signals from biological tissues were used to evaluate the endovascular treatment of intracranial aneurysms in an animal model of aneurysms (pig, rabbit). Results from multiphoton microscopy were compared to those from standard histology, electronic and bright field microscopy.

CONCLUSIONS

The present study describes novel evaluation modes based on multiphoton microscopy for visualising tissue morphology (e.g., collagen, elastin, and cells) to qualify and quantify the extent of neo-intimal formation of covered arteries and device integration into the arterial wall using a rabbit model of intracranial aneurysms treated with FDS.

Label-free multiphoton microscopic imaging as a novel real-time approach for discriminating colorectal lesions: A preliminary study

BACKGROUND AND AIM

Although various endoscopic technologies have been developed to increase the visual diagnostic accuracy of colorectal precancerosis and early carcinoma, the biopsy-dependent pathology still remains the golden standard. During routine endoscopy, real-time optical histological diagnosis is desired. Without fluorescent label, multiphoton microscopy (MPM) imaging directly reveals live cellular morphology and tissue microenvironment based on intrinsic two-photon excited fluorescence and second harmonic generation signals. Its high-imaging resolution and performance are comparable with the histopathology. We thus aimed to initially investigate the original features of colorectal diseases under MPM and evaluate its potential for real-time diagnosis.

METHODS

Experimental and diagnostic cohorts were designed. Multiphoton images of 40 ex vivo fresh tissues confirmed pathologically of colorectal normal tissues, hyperplastic polyps, adenomas, and adenocarcinomas were collected. Features were recorded to establish diagnostic standards with MPM. For the second cohort with 92 fresh tissues, we distinguished the various colorectal diseases with conclusive MPM features.

RESULTS

Through the investigation, the colorectal diseases were presented differences in the crypt opening, gland structure, epithelial cells, and collagen fibers. With the typical features, we preliminarily tested the diagnostic efficiency and found that its sensitivity for distinguishing normal, hyperplastic polyps, adenoma and adenocarcinoma was 88.89%, 76.47%, 83.33%, and 97.92%, while the specificity was 99.32%, 94.00%, 94.92%, and 94.12%, respectively.

CONCLUSION

The real-time multiphoton microscopic imaging can be effective to identify the colorectal lesions with high resolution. Via integrating with the endoscopes in the future, it could promote precise optical diagnosis in clinics.

Characterization of a multicore fiber image guide for nonlinear endoscopic imaging using two-photon fluorescence and second-harmonic generation

Multiphoton microscopy (MPM) has the capacity to record second-harmonic generation (SHG) and endogenous two-photon excitation fluorescence (2PEF) signals emitted from biological tissues. The development of fiber-based miniaturized endomicroscopes delivering pulses in the femtosecond range will allow the transfer of MPM to clinical endoscopy. We present real-time SHG and 2PEF ex vivo images using an endomicroscope, which totally complies with clinical endoscopy regulations. This system is based on the proximal scanning of a commercial multicore image guide (IG). For understanding the inhomogeneities of the recorded images, we quantitatively characterize the IG at the single-core level during nonlinear excitation. The obtained results suggest that these inhomogeneities originate from the variable core geometries that, therefore, exhibit variable nonlinear and dispersive properties. Finally, we propose a method based on modulation of dispersion precompensation to address the image inhomogeneity issue and, as a proof of concept, we demonstrate its capability to improve the nonlinear image quality.

Optical Molecular Imaging of Inflammatory Cells in Interventional Medicine-An Emerging Strategy

The optical molecular imaging of inflammation is an emerging strategy for interventional medicine and diagnostics. The host's inflammatory response and adaptation to acute and chronic diseases provides unique signatures that have the potential to guide interventions. Thus, there are emerging a suite of molecular imaging and sensing approaches for a variety of targets in this area. This review will focus on two key cellular orchestrators that dominate this area, neutrophils and macrophages, with recent developments in molecular probes and approaches discussed.

Two-photon images reveal unique texture features for label-free identification of ovarian cancer peritoneal metastases

For cancer patients, treatment selection fundamentally relies on staging, with "under-staging" considered a common problem. Imaging modalities that can complement conventional white-light laparoscopy are needed to detect more accurately small metastatic lesions in patients undergoing operative cancer care. Biopsies from healthy parietal peritoneum and ovarian peritoneal metastases obtained from 8 patients were imaged employing a two-photon laser scanning microscope to generate collagen-second harmonic generation (SHG) and fluorescence images at 755 nm and 900 nm excitation and 460 ± 20 nm and 525 ± 25 nm emission. Forty-one images were analyzed by automated image processing algorithms and statistical textural analysis techniques, namely gray level co-occurrence matrices. Two textural features (contrast and correlation) were employed to describe the spatial intensity variations within the captured images and outcomes were used for discriminant analysis. We found that healthy tissues displayed large variations in contrast and correlation features as a function of distance, corresponding to repetitive, increased local intensity fluctuations. Metastatic tissue images exhibited decreased contrast and correlation related values, representing more uniform intensity patterns and smaller fibers, indicating the destruction of the healthy stroma by the cancerous infiltration. The textural outcomes resulted in high classification accuracy as evaluated quantitatively by discriminant analysis.

A Review of New and Emerging Techniques For Optical Diagnosis of Colonic Polyps

BACKGROUND AND AIMS

Endoscopic imaging is a rapidly progressing field and benefits from miniaturization of advanced imaging technologies, which may allow accurate real-time characterization of lesions. The concept of the "optical biopsy" to predict polyp histology has gained prominence in recent years and may become clinically applicable with the advent of new imaging technology. This review aims to discuss current evidence and examine the emerging technologies as applied to the optical diagnosis of colorectal polyps.

METHODS

A structured literature search and review has been carried out of the evidence for diagnostic accuracy of image-enhanced endoscopy and emerging endoscopic imaging technologies. The image-enhanced endoscopy techniques are reviewed, including their basic scientific principles and current evidence for effectiveness. These include the established image-enhancement technologies such as narrow-band imaging, i-scan, and Fuji intelligent chromoendoscopy. More recent technologies including optical enhancement, blue laser imaging, and linked color imaging are discussed. Adjunctive imaging techniques in current clinical use are discussed, such as autofluorescence imaging and endocytoscopy. The emerging advanced imaging techniques are reviewed, including confocal laser endomicroscopy, optical coherence tomography, and Raman spectroscopy.

CONCLUSIONS

Large studies of the established image-enhancement techniques show some role for the optical diagnosis of polyp histology, although results have been mixed, and at present only the technique of narrow-band imaging is appropriate for the diagnosis of low-risk polyps when used by an expert operator. Other image-enhancement techniques will require further study to validate their accuracy but show potential to support the use of a "resect-and-discard" approach to low-risk polyps. New technologies show exciting potential for real-time diagnosis, but further clinical studies in humans have yet to be performed.

Association of the Collagen Signature in the Tumor Microenvironment With Lymph Node Metastasis in Early Gastric Cancer

Importance

Lymph node status is the primary determinant in treatment decision making in early gastric cancer (EGC). Current evaluation methods are not adequate for estimating lymph node metastasis (LNM) in EGC.

Objective

To develop and validate a prediction model based on a fully quantitative collagen signature in the tumor microenvironment to estimate the individual risk of LNM in EGC.

Design, Setting, and Participants

This retrospective study was conducted from August 1, 2016, to May 10, 2018, at 2 medical centers in China (Nanfang Hospital and Fujian Provincial Hospital). Participants included a primary cohort (n = 232) of consecutive patients with histologically confirmed gastric cancer who underwent radical gastrectomy and received a T1 gastric cancer diagnosis from January 1, 2008, to December 31, 2012. Patients with neoadjuvant radiotherapy, chemotherapy, or chemoradiotherapy were excluded. An additional consecutive cohort (n = 143) who received the same diagnosis from January 1, 2011, to December 31, 2013, was enrolled to provide validation. Baseline clinicopathologic data of each patient were collected. Collagen features were extracted in specimens using multiphoton imaging, and the collagen signature was constructed. An LNM prediction model based on the collagen signature was developed and was internally and externally validated.

Main Outcomes and Measures

The area under the receiver operating characteristic curve (AUROC) of the prediction model and decision curve were analyzed for estimating LNM.

Results

In total, 375 patients were included. The primary cohort comprised 232 consecutive patients, in whom the LNM rate was 16.4% (n = 38; 25 men [65.8%] with a mean [SD] age of 57.82 [10.17] years). The validation cohort consisted of 143 consecutive patients, in whom the LNM rate was 20.9% (n = 30; 20 men [66.7%] with a mean [SD] age of 54.10 [13.19] years). The collagen signature was statistically significantly associated with LNM (odds ratio, 5.470; 95% CI, 3.315-9.026; P < .001). Multivariate analysis revealed that the depth of tumor invasion, tumor differentiation, and the collagen signature were independent predictors of LNM. These 3 predictors were incorporated into the new prediction model, and a nomogram was established. The model showed good discrimination in the primary cohort (AUROC, 0.955; 95% CI, 0.919-0.991) and validation cohort (AUROC, 0.938; 95% CI, 0.897-0.981). An optimal cutoff value was selected in the primary cohort, which had a sensitivity of 86.8%, a specificity of 93.3%, an accuracy of 92.2%, a positive predictive value of 71.7%, and a negative predictive value of 97.3%. The validation cohort had a sensitivity of 90.0%, a specificity of 90.3%, an accuracy of 90.2%, a positive predictive value of 71.1%, and a negative predictive value of 97.1%. Among the 375 patients, a sensitivity of 87.3%, a specificity of 92.1%, an accuracy of 91.2%, a positive predictive value of 72.1%, and a negative predictive value of 96.9% were found.

Conclusions and Relevance

This study's findings suggest that the collagen signature in the tumor microenvironment is an independent indicator of LNM in EGC, and the prediction model based on this collagen signature may be useful in treatment decision making for patients with EGC.

A biopsy-needle compatible varifocal multiphoton rigid probe for depth-resolved optical biopsy

In this work, we report a biopsy-needle compatible rigid probe, capable of performing three-dimensional (3D) two-photon optical biopsy. The probe has a small outer diameter of 1.75 mm and fits inside a gauge-14 biopsy needle to reach internal organs. A carefully designed focus scanning mechanism has been implemented in the rigid probe, which, along with a rapid two-dimensional MEMS scanner, enables 3D imaging. Fast image acquisition up to 10 frames per second is possible, dramatically reducing motion artifacts during in vivo imaging. Equipped with a high-numerical aperture micro-objective, the miniature rigid probe offers a high two-photon resolution (0.833 × 6.11 μm, lateral × axial), a lateral field of view of 120 μm, and an axial focus tuning range of 200 μm. In addition to imaging of mouse internal organs and subcutaneous tumor in vivo, first-of-its-kind depth-resolved two-photon optical biopsy of an internal organ has been successfully demonstrated on mouse kidney in vivo and in situ.

Integrative microendoscopic system combined with conventional microscope for live animal tissue imaging

Intravital optical imaging technology is essential for minimally invasive optical diagnosis and treatment in small animal disease models. High-resolution imaging requires high-resolution optical probes, and high-resolution optical imaging systems based on highly precise and advanced technologies and therefore, associated with high-system costs. Besides, in order to acquire small animal live images, special types of animal imaging setups are indispensable. In this paper, a microendoscopic system is designed as an add-on to existing conventional imaging microscopes, reducing the price of complete confocal endomicroscopic systems. The proposed attachable system can be configured for confocal microscopes from common manufacturers and this enables users to acquire live animal cellular images from a conventional system. It features a 4f optical plane relay system, a rotary stage for side-view endoscopic probes, and an endoscopic probe mount which swings between the horizontal and the vertical. The system could be widely useful for biological studies of animal physiology and disease models.

Identifying Two Common Types of Breast Benign Diseases Based on Multiphoton Microscopy

Multiphoton microscopy has attracted increasing attention and investigations in the field of breast cancer, based on two-photon excited fluorescence (TPEF) and second-harmonic generation (SHG). However, the incidence of breast benign diseases is about 5 to 10 times higher than breast cancer; up to 30% of women suffer from breast benign diseases and require treatment at some time in their lives. Thus, in this study, MPM was applied to image fibroadenoma and fibrocystic lesion, which are two of the most common breast benign diseases. The results show that MPM has the capability to identify the microstructure of lobule and stroma in normal breast tissue, the interaction of compressed ducts with surrounding collagen fiber in fibroadenoma, and the architecture of cysts filled with cystic fluid in fibrocystic disease. These findings indicate that, with integration of MPM into currently accepted clinical imaging system, it has the potential to make a real-time diagnosis of breast benign diseases in vivo, as well as breast cancer.

Second-harmonic imaging microscopy for identifying colorectal intraepithelial neoplasia

In this study, second-harmonic imaging microscopy was used to monitor precancerous colorectal lesions at different stages. It was found that the morphology of glands and lamina propria in mucosa changes with the progression of colorectal diseases from normal to low-grade intraepithelial neoplasia to high-grade intraepithelial neoplasia and this microscopy has the ability of direct visualization of these warning symptoms. Furthermore, two morphologic variables were quantified to determine the changes of glands and collagen in lamina propria during the development of colorectal intraepithelial neoplasia. These results suggest that second-harmonic imaging microscopy has the potential in label-freely and effectively distinguishing between normal and precancerous colorectal tissues, and will be helpful for early diagnosis and treatment of colorectal diseases.

In vivo multiphoton microscopy using a handheld scanner with lateral and axial motion compensation

This paper reports a handheld multiphoton fluorescence microscope designed for clinical imaging that incorporates axial motion compensation and lateral image stabilization. Spectral domain optical coherence tomography is employed to track the axial position of the skin surface, and lateral motion compensation is realised by imaging the speckle pattern arising from the optical coherence tomography beam illuminating the sample. Our system is able to correct lateral sample velocities of up to approximately 65 μm s^-1 . Combined with the use of negative curvature microstructured optical fibre to deliver tunable ultrafast radiation to the handheld multiphoton scanner without the need of a dispersion compensation unit, this instrument has potential for a range of clinical applications. The system is used to compensate for both lateral and axial motion of the sample when imaging human skin in vivo.

Towards two-photon excited endogenous fluorescence lifetime imaging microendoscopy

In situ fluorescence lifetime imaging microscopy (FLIM) in an endoscopic configuration of the endogenous biomarker nicotinamide adenine dinucleotide (NADH) has a great potential for malignant tissue diagnosis. Moreover, two-photon nonlinear excitation provides intrinsic optical sectioning along with enhanced imaging depth. We demonstrate, for the first time to our knowledge, nonlinear endogenous FLIM in a fibered microscope with proximal detection, applied to NADH in cultured cells, as a first step to a nonlinear endomicroscope, using a double-clad microstructured fiber with convenient fiber length (> 3 m) and excitation pulse duration (≈50 fs). Fluorescence photons are collected by the fiber inner cladding and we show that its contribution to the impulse response function (IRF), which originates from its intermodal and chromatic dispersions, is small (< 600 ps) and stable for lengths up to 8 m and allows for short lifetime measurements. We use the phasor representation as a quick visualization tool adapted to the endoscopy speed requirements.

Label-free imaging of atherosclerotic plaques using third-harmonic generation microscopy

Multiphoton microscopy using laser sources in the mid-infrared range (MIR, 1,300 nm and 1,700 nm) was used to image atherosclerotic plaques from murine and human samples. Third harmonic generation (THG) from atherosclerotic plaques revealed morphological details of cellular and extracellular lipid deposits. Simultaneous nonlinear optical signals from the same laser source, including second harmonic generation and endogenous fluorescence, resulted in label-free images of various layers within the diseased vessel wall. The THG signal adds an endogenous contrast mechanism with a practical degree of specificity for atherosclerotic plaques that complements current nonlinear optical methods for the investigation of cardiovascular disease. Our use of whole-mount tissue and backward scattered epi-detection suggests THG could potentially be used in the future as a clinical tool.

Monitoring neoadjuvant therapy responses in rectal cancer using multimodal nonlinear optical microscopy

Most patients with rectal cancer have a better prognosis after receiving neoadjuvant therapy because of its remarkable curative effect. However, no device delivers real-time histopathologic information on treatment response to help clinicians tailor individual therapeutic strategies. We assessed the potential of multimodal nonlinear optical microscopy to monitor therapeutic responses, including tumoral and stromal responses. We found that two-photon excited fluorescence imaging can, without labeling, identify colloid response, inflammatory cell infiltration, vascular proliferation, and tumor regression. It can also directly detect rare residual tumor cells, which may be helpful for distinguishing tumor shrinkage from tumor fragmentation. In addition, second harmonic generation imaging shows the ability to monitor three types of fibrotic responses: mature, intermediate, and immature. We also determined nonlinear spectra, collagen density, and collagen orientation indexes to quantitatively analyze the histopathologic changes induced by neoadjuvant therapy in rectal cancer. Our work demonstrates that nonlinear optical microscopy has the potential to become a label-free, real-time, in vivo medical imaging technique and provides the groundwork for further exploration into the application of nonlinear optical microscopy in a clinical setting.

Identifying the neck margin status of ductal adenocarcinoma in the pancreatic head by multiphoton microscopy

Complete surgical resection is the only option for improving the survival of patients with ductal adenocarcinoma in the pancreatic head. After resection, determining the status of resection margins (RMs) is crucial for deciding on the nature of the follow-up treatment. The purpose of this study was to evaluate whether multiphoton microscopy (MPM) could be considered a reliable tool for determining the status of pancreatic neck margins by identifying tumour cells of ductal adenocarcinoma in these margins in the pancreatic head, and our results were affirmative. In particular, MPM could identify tumour cells in the nerves. It was also found that the quantification of the difference between normal duct cells and tumour cells was possible. In addition, the content of collagen could be quantified and used as a marker for differentiating ductal adenocarcinoma in the pancreatic head from normal pancreatic tissues, eventually leading to the identification of R0 and R1 resections of the pancreatic neck margin. With the development of the clinical applications of the multiphoton endoscope, MPM has the potential to provide in vivo real-time identification of RM status during surgery.

Nonlinear optical endomicroscopy for label-free functional histology in vivo

This manuscript reports on the first two-photon, label-free, metabolic imaging of biological tissues in vivo at histological resolution on an extremely compact, fiber-optic endomicroscopy platform. This system provides new opportunities for performing non-invasive and functional histological imaging of internal organs in vivo, in situ and in real time. As a routine clinical procedure, traditional histology has made significant impacts on medicine. However, the procedure is invasive and time consuming, suffers random sampling errors, and cannot provide in vivo functional information. The technology reported here features an extremely compact and flexible fiber-optic probe ~2 mm in diameter, enabling direct access to internal organs. Unprecedented two-photon imaging quality comparable to a large bench-top laser scanning microscope was achieved through technological innovations in double-clad fiber optics and miniature objective lenses (among many others). In addition to real-time label-free visualization of biological tissues in situ with subcellular histological detail, we demonstrated for the first time in vivo two-photon endomicroscopic metabolic imaging on a functioning mouse kidney model. Such breakthroughs in nonlinear endoscopic imaging capability present numerous promising opportunities for paradigm-shifting applications in both clinical diagnosis and basic research.

Ultrathin endoscopes based on multicore fibers and adaptive optics: a status review and perspectives

We take stock of the progress that has been made into developing ultrathin endoscopes assisted by wave front shaping. We focus our review on multicore fiber-based lensless endoscopes intended for multiphoton imaging applications. We put the work into perspective by comparing with alternative approaches and by outlining the challenges that lie ahead.

Autofluorescence multiphoton microscopy for visualization of tissue morphology and cellular dynamics in murine and human airways

The basic understanding of inflammatory airway diseases greatly benefits from imaging the cellular dynamics of immune cells. Current imaging approaches focus on labeling specific cells to follow their dynamics but fail to visualize the surrounding tissue. To overcome this problem, we evaluated autofluorescence multiphoton microscopy for following the motion and interaction of cells in the airways in the context of tissue morphology. Freshly isolated murine tracheae from healthy mice and mice with experimental allergic airway inflammation were examined by autofluorescence multiphoton microscopy. In addition, fluorescently labeled ovalbumin and fluorophore-labeled antibodies were applied to visualize antigen uptake and to identify specific cell populations, respectively. The trachea in living mice was imaged to verify that the ex vivo preparation reflects the in vivo situation. Autofluorescence multiphoton microscopy was also tested to examine human tissue from patients in short-term tissue culture. Using autofluorescence, the epithelium, underlying cells, and fibers of the connective tissue, as well as blood vessels, were identified in isolated tracheae. Similar structures were visualized in living mice and in the human airway tissue. In explanted murine airways, mobile cells were localized within the tissue and we could follow their migration, interactions between individual cells, and their phagocytic activity. During allergic airway inflammation, increased number of eosinophil and neutrophil granulocytes were detected that moved within the connective tissue and immediately below the epithelium without damaging the epithelial cells or connective tissues. Contacts between granulocytes were transient lasting 3 min on average. Unexpectedly, prolonged interactions between granulocytes and antigen-uptaking cells were observed lasting for an average of 13 min. Our results indicate that autofluorescence-based imaging can detect previously unknown immune cell interactions in the airways. The method also holds the potential to be used during diagnostic procedures in humans if integrated into a bronchoscope.

Deep insights: intravital imaging with two-photon microscopy

Intravital multiphoton microscopy is widely used to assess the structure and function of organs in live animals. Although different tissues vary in their accessibility for intravital multiphoton imaging, considerable progress has been made in the imaging quality of all tissues due to substantial technical improvements in the relevant imaging components, such as optics, excitation laser, detectors, and signal analysis software. In this review, we provide an overview of the technical background of intravital multiphoton microscopy. Then, we note a few seminal findings that were made through the use of multiphoton microscopy. Finally, we address the technical limitations of the method and provide an outlook for how these limitations may be overcome through future technical developments.

Remodeling of the Epithelial-Connective Tissue Interface in Oral Epithelial Dysplasia as Visualized by Noninvasive 3D Imaging

Early neoplastic features in oral epithelial dysplasia are first evident at the basal epithelium positioned at the epithelial-connective tissue interface (ECTI), separating the basal epithelium from the underlying lamina propria. The ECTI undergoes significant deformation in early neoplasia due to focal epithelial expansion and proteolytic remodeling of the lamina propria, but few studies have examined these changes. In the present study, we quantitated alterations in ECTI topography in dysplasia using in vivo volumetric multiphoton autofluorescence microscopy and second harmonic generation microscopy. The label-free method allows direct noninvasive visualization of the ECTI surface without perturbing the epithelium. An image-based parameter, "ECTI contour," is described that indicates deformation of the ECTI surface. ECTI contour was higher in dysplasia than control or inflamed specimens, indicating transition from flat to a deformed surface. Cellular parameters of nuclear area, nuclear density, coefficient of variation in nuclear area in the basal epithelium and collagen density in areas adjacent to ECTI were measured. ECTI contour differentiated dysplasia from control/benign mucosa with higher sensitivity and specificity than basal nuclear density or basal nuclear area, comparable with coefficient of variation in nuclear area and collagen density. The presented method offers a unique opportunity to study ECTI in intact mucosa with simultaneous assessment of cellular and extracellular matrix features, expanding opportunities for studies of early neoplastic events near this critical interface and potentially leading to development of new approaches for detecting neoplasia in vivo Cancer Res; 76(16); 4637-47. ©2016 AACR.

Third harmonic generation imaging for fast, label-free pathology of human brain tumors

In brain tumor surgery, recognition of tumor boundaries is key. However, intraoperative assessment of tumor boundaries by the neurosurgeon is difficult. Therefore, there is an urgent need for tools that provide the neurosurgeon with pathological information during the operation. We show that third harmonic generation (THG) microscopy provides label-free, real-time images of histopathological quality; increased cellularity, nuclear pleomorphism, and rarefaction of neuropil in fresh, unstained human brain tissue could be clearly recognized. We further demonstrate THG images taken with a GRIN objective, as a step toward in situ THG microendoscopy of tumor boundaries. THG imaging is thus a promising tool for optical biopsies.

Miniature fiber-optic multiphoton microscopy system using frequency-doubled femtosecond Er-doped fiber laser

We report on a miniature fiber-optic multiphoton microscopy (MPM) system based on a frequency-doubled femtosecond Er-doped fiber laser. The femtosecond pulses from the laser source are delivered to the miniature fiber-optic probe at 1.58 µm wavelength, where a standard single mode fiber is used for delivery without the need of free-space dispersion compensation components. The beam is frequency-doubled inside the probe by a periodically poled MgO:LiNbO3 crystal. Frequency-doubled pulses at 786 nm with a maximum power of 80 mW and a pulsewidth of 150 fs are obtained and applied to excite intrinsic signals from tissues. A MEMS scanner, a miniature objective, and a multimode collection fiber are further used to make the probe compact. The miniature fiber-optic MPM system is highly portable and robust. Ex vivo multiphoton imaging of mammalian skins demonstrates the capability of the system in imaging biological tissues. The results show that the miniature fiber-optic MPM system using frequency-doubled femtosecond fiber laser can potentially bring the MPM imaging for clinical applications.

Quantification of liver fibrosis via second harmonic imaging of the Glisson's capsule from liver surface

Liver surface is covered by a collagenous layer called the Glisson's capsule. The structure of the Glisson's capsule is barely seen in the biopsy samples for histology assessment, thus the changes of the collagen network from the Glisson's capsule during the liver disease progression are not well studied. In this report, we investigated whether non-linear optical imaging of the Glisson's capsule at liver surface would yield sufficient information to allow quantitative staging of liver fibrosis. In contrast to conventional tissue sections whereby tissues are cut perpendicular to the liver surface and interior information from the liver biopsy samples were used, we have established a capsule index based on significant parameters extracted from the second harmonic generation (SHG) microscopy images of capsule collagen from anterior surface of rat livers. Thioacetamide (TAA) induced liver fibrosis animal models was used in this study. The capsule index is capable of differentiating different fibrosis stages, with area under receiver operating characteristics curve (AUC) up to 0.91, making it possible to quantitatively stage liver fibrosis via liver surface imaging potentially with endomicroscopy.

Intravital Fluorescence Excitation in Whole-Animal Optical Imaging

Whole-animal fluorescence imaging with recombinant or fluorescently-tagged pathogens or cells enables real-time analysis of disease progression and treatment response in live animals. Tissue absorption limits penetration of fluorescence excitation light, particularly in the visible wavelength range, resulting in reduced sensitivity to deep targets. Here, we demonstrate the use of an optical fiber bundle to deliver light into the mouse lung to excite fluorescent bacteria, circumventing tissue absorption of excitation light in whole-animal imaging. We present the use of this technology to improve detection of recombinant reporter strains of tdTomato-expressing Mycobacterium bovis BCG (Bacillus Calmette Guerin) bacteria in the mouse lung. A microendoscope was integrated into a whole-animal fluorescence imager to enable intravital excitation in the mouse lung with whole-animal detection. Using this technique, the threshold of detection was measured as 10³ colony forming units (CFU) during pulmonary infection. In comparison, the threshold of detection for whole-animal fluorescence imaging using standard epi-illumination was greater than 10⁶ CFU.

Development of a real-time flexible multiphoton microendoscope for label-free imaging in a live animal

We present a two-photon microendoscope capable of in vivo label-free deep-tissue high-resolution fast imaging through a very long optical fiber. First, an advanced light-pulse spectro-temporal shaping device optimally precompensates for linear and nonlinear distortions occurring during propagation within the endoscopic fiber. This enables the delivery of sub-40-fs duration infrared excitation pulses at the output of 5 meters of fiber. Second, the endoscopic fiber is a custom-made double-clad polarization-maintaining photonic crystal fiber specifically designed to optimize the imaging resolution and the intrinsic luminescence backward collection. Third, a miniaturized fiber-scanner of 2.2 mm outer diameter allows simultaneous second harmonic generation (SHG) and two-photon excited autofluorescence (TPEF) imaging at 8 frames per second. This microendoscope’s transverse and axial resolutions amount respectively to 0.8 μm and 12 μm, with a field-of-view as large as 450 μm. This microendoscope’s unprecedented capabilities are validated during label-free imaging, ex vivo on various fixed human tissue samples, and in vivo on an anesthetized mouse kidney demonstrating an imaging penetration depth greater than 300 μm below the surface of the organ. The results reported in this manuscript confirm that nonlinear microendoscopy can become a valuable clinical tool for real-time in situ assessment of pathological states.

Monitoring the progression from intraductal carcinoma to invasive ductal carcinoma based on multiphoton microscopy

Intraductal carcinoma is a precancerous lesion of the breast and the immediate precursor of invasive ductal carcinoma. Multiphoton microscopy (MPM) was used to monitor the progression from intraductal carcinoma to invasive ductal carcinoma, which can improve early detection of precursor lesions and halt progression to invasive neoplastic disease. It was found that MPM has the capability to reveal the qualitative changes in features of cells, structure of basement membranes, and architecture of collagens during the development from intraductal carcinoma to invasive ductal carcinoma, as well as the quantitative alterations in nuclear area, circle length of basement membrane, and collagen density. Combined with intra-fiberoptic ductoscopy or transdermal biopsy needle, MPM has the potential to provide immediate histological diagnosis of tumor progression in the field of breast carcinoma.

In vivo nonlinear optical imaging to monitor early microscopic changes in a murine cutaneous squamous cell carcinoma model

Early detection of cutaneous squamous cell carcinoma (cSCC) can enable timely therapeutic and preventive interventions for patients. In this study, in vivo nonlinear optical imaging (NLOI) based on two-photon excitation fluorescence (TPEF) and second harmonic generation (SHG), was used to non-invasively detect microscopic changes occurring in murine skin treated topically with 7,12-dimethylbenz(a)anthracene (DMBA). The optical microscopic findings and the measured TPEF-SHG index show that NLOI was able to clearly detect early cytostructural changes in DMBA treated skin that appeared clinically normal. This suggests that in vivo NLOI could be a non-invasive tool to monitor early signs of cSCC. In vivo axial NLOI scans of normal murine skin (upper left), murine skin with preclinical hyperplasia (upper right), early clinical murine skin lesion (lower left) and late or advanced murine skin lesion (lower right).

Dynamic multiphoton microscopy: focusing light on acute kidney injury

Acute kidney injury (AKI) is a major global health problem; much research has been conducted on AKI, and numerous agents have shown benefit in animal studies, but none have translated into treatments. There is, therefore, a pressing unmet need to increase knowledge of the pathophysiology of AKI. Multiphoton microscopy (MPM) provides a tool to non-invasively visualize dynamic events in real time and at high resolution in rodent kidneys, and in this article we review its application to study novel mechanisms and treatments in different forms of AKI.

Fiber-coupled high-speed asynchronous optical sampling with sub-50 fs time resolution

We present a fiber-coupled pump-probe system with a sub-50 fs time resolution and a nanosecond time window, based on high-speed asynchronous optical sampling. By use of a transmission grism pulse compressor, we achieve pump pulses with a pulse duration of 42 fs, an average power of 300 mW and a peak power exceeding 5 kW at a pulse repetition rate of 1 GHz after 6 m of optical fiber. With this system we demonstrate thickness mapping of soft X-ray mirrors at a sub-nm thickness resolution on a cm(2) scan area. In addition, terahertz field generation with resolved spectral components of up to 3.5 THz at a GHz frequency resolution is demonstrated.

Experimenting liver fibrosis diagnostic by two photon excitation microscopy and Bag-of-Features image classification

The accurate staging of liver fibrosis is of paramount importance to determine the state of disease progression, therapy responses, and to optimize disease treatment strategies. Non-linear optical microscopy techniques such as two-photon excitation fluorescence (TPEF) and second harmonic generation (SHG) can image the endogenous signals of tissue structures and can be used for fibrosis assessment on non-stained tissue samples. While image analysis of collagen in SHG images was consistently addressed until now, cellular and tissue information included in TPEF images, such as inflammatory and hepatic cell damage, equally important as collagen deposition imaged by SHG, remain poorly exploited to date. We address this situation by experimenting liver fibrosis quantification and scoring using a combined approach based on TPEF liver surface imaging on a Thioacetamide-induced rat model and a gradient based Bag-of-Features (BoF) image classification strategy. We report the assessed performance results and discuss the influence of specific BoF parameters to the performance of the fibrosis scoring framework.

Characterization, comparison, and choice of a commercial double-clad fiber for nonlinear endomicroscopy

Several endomicroscope prototypes for nonlinear optical imaging were developed in the last decade for in situ analysis of tissue with cellular resolution by using short infrared light pulses. Fourier-transform-limited pulses at the tissue site are necessary for optimal excitation of faint endogenous signals. However, obtaining these transform-limited short pulses remains a challenge, and previously proposed devices did not achieve an optimal pulse delivery. We present a study of fibered endomicroscope architecture with an efficient femtosecond pulse delivery and a high excitation level at the output of commercially available double-clad fibers (DCFs). The endomicroscope incorporates a module based on a grism line to compensate for linear and nonlinear effects inside the system. Simulations and experimental results are presented and compared to the literature. Experimentally, we obtained short pulses down to 24 fs at the fiber output, what represents to the best of our knowledge the shortest pulse duration ever obtained at the output of a nonlinear endoscopic system without postcompression. The choice of the optimal DCF among four possible commercial components is discussed and evaluated in regard to multiphoton excitation and fluorescence emission.

Multiphoton microscopy: a potential "optical biopsy" tool for real-time evaluation of lung tumors without the need for exogenous contrast agents

CONTEXT

Multiphoton microscopy (MPM) is an emerging, nonlinear, optical-biopsy technique, which can generate subcellular-resolution images from unprocessed and unstained tissue in real time.

OBJECTIVE

To assess the potential of MPM for lung tumor diagnosis.

DESIGN

Fresh sections from tumor and adjacent nonneoplastic lung were imaged with MPM and then compared with corresponding hematoxylin-eosin slides.

RESULTS

Alveoli, bronchi, blood vessels, pleura, smokers' macrophages, and lymphocytes were readily identified with MPM in nonneoplastic tissue. Atypical adenomatous hyperplasia (a preinvasive lesion) was identified in tissue adjacent to the tumor in one case. Of the 25 tumor specimens used for blinded pathologic diagnosis, 23 were diagnosable with MPM. Of these 23 cases, all but one adenocarcinoma (15 of 16; 94%) was correctly diagnosed on MPM, along with their histologic patterns. For squamous cell carcinoma, 4 of 7 specimens (57%) were correctly diagnosed. For the remaining 3 squamous cell carcinoma specimens, the solid pattern was correctly diagnosed in 2 additional cases (29%), but it was not possible to distinguish the squamous cell carcinoma from adenocarcinoma. The other squamous cell carcinoma specimen (1 of 7; 14%) was misdiagnosed as adenocarcinoma because of pseudogland formation. Invasive adenocarcinomas with acinar and solid pattern showed statistically significant increases in collagen. Interobserver agreement for collagen quantification (among 3 observers) was 80%.

CONCLUSIONS

Our pilot study provides a proof of principle that MPM can differentiate neoplastic from nonneoplastic lung tissue and identify tumor subtypes. If confirmed in a future, larger study, we foresee real-time intraoperative applications of MPM, using miniaturized instruments for directing lung biopsies, assessing their adequacy for subsequent histopathologic analysis or banking, and evaluating surgical margins in limited lung resections.

Characterization and improvement of three-dimensional imaging performance of GRIN-lens-based two-photon fluorescence endomicroscopes with adaptive optics

Inherent aberrations of gradient index (GRIN) lenses used in fluorescence endomicroscopes deteriorate imaging performance. Using adaptive optics, we characterized and corrected the on-axis and off-axis aberrations of a GRIN lens with NA 0.8 at multiple focal planes. We demonstrated a rotational-transformation-based correction procedure, which enlarged the imaging area with diffraction-limited resolution with only two aberration measurements. 204.8 × 204.8 µm² images of fluorescent beads and brain slices before and after AO corrections were obtained, with evident improvements in both image sharpness and brightness after AO correction. These results show great promises of applying adaptive optical two-photon fluorescence endomicroscope to three-dimensional (3D) imaging.

Two-photon lensless endoscope

We report a first demonstration of two-photon endoscopic imaging with a lensless endoscope. The endoscope probe is a double-clad bundle of single-mode fibers; point excitation and scanning is achieved by coherent combining of femtosecond light pulses propagating in the single-mode fibers; and back-scattered two-photon signal is collected through the multi-mode inner cladding. We demonstrate the two-photon endoscope on a test sample of rhodamine 6G crystals.

Miniature varifocal objective lens for endomicroscopy

A miniature catadioptric lens for endoscopic imaging based on the principle of wavelength division multiplexing is presented. We demonstrate change of the magnification and the field of view (FOV) of the lens without any mechanical adjustment of the optical elements. The lens provides magnifications of ~-1.5× at 406-750 nm and ~-0.2× at 800 nm. The lens is used to demonstrate large-FOV (1.3 mm) reflectance imaging and high-resolution (0.57 μm) multiphoton fluorescence imaging of unstained mouse tissues.

Multiphoton morpho-functional imaging of healthy colon mucosa, adenomatous polyp and adenocarcinoma

Two-photon spectral resolved imaging was used to image fresh human biopsies of colon tissue and to characterize healthy colon mucosa, adenomatous polyp and adenocarcinoma by means of a morpho-functional analysis. Morphological examination, performed using endogenous tissue fluorescence, discriminated adenomatous and adenocarcinoma tissues from normal mucosa in terms of cellular asymmetry and nucleus-to-cytoplasm ratio. Good agreement was found between multiphoton images and histological examination performed on the same samples. Further characterization, performed by means of spectral-resolved analysis of NADH and FAD fluorescence, demonstrated an altered metabolic activity in both adenomatous and adenocarcinoma tissues compared to healthy mucosa. This morpho-functional approach may represent a powerful method to be used in combination with endoscopy for in vivo optical diagnosis of colon cancer and may be extended to other tissues.

Multiphoton microscopy to identify and characterize the transition zone in a mouse model of Hirschsprung disease

BACKGROUND

The distribution of ganglion cells in the transition zone of Hirschsprung Disease (HD) colons is extremely variable. Determining the resection margin based on intraoperative biopsies may be imprecise. Multiphoton microscopy (MPM) is a novel imaging technology with the ability to visualize tissues in real time. In this study, we evaluate the potential of MPM to quantify ganglion cells in a murine model of HD.

METHODS

After IACUC approval, formalin-fixed colons from 7 wild type (WT) and 6 Endothelin Receptor B gene (EdnrB) homozygous knockout (KO) mice with distal colonic aganglionosis were assessed by MPM for the presence of myenteric ganglion cells. MPM images were captured starting from the anus progressing proximally at 5mm intervals. Hematoxylin and eosin (H&E) stained biopsies of the imaged were correlated with MPM findings.

RESULTS

WT specimens showed normal myenteric plexus ganglia throughout the examined colon. In contrast, distal colons of EdnrB KO animals were devoid of ganglia up to 10mm from the anus. Ganglion cells were visible starting at 20-30 mm proximal to the anus. The density of ganglion cells seen by MPM and histology correlated well.

CONCLUSIONS

MPM can clearly identify the myenteric plexus ganglia in both WT and KO mouse colons. Comparison with the H&E-stained sections showed reproducible correlation. MPM-based real-time imaging of the myenteric plexus may become a useful intraoperative decision-making tool in the future.