Label-free multi-photon imaging of dysplasia in Barrett's esophagus

Characterization of lamina propria remodeling in pediatric eosinophilic esophagitis using second harmonic generation microscopy

Eosinophilic esophagitis (EoE) is a chronic inflammatory condition characterized by an intense infiltration of eosinophils into the esophageal epithelium. When not adequately controlled, eosinophilic inflammation can lead to changes in components of the extracellular matrix (ECM) of the lamina propria. Particularly, alterations to the collagen fiber matrix can lead to lamina propria fibrosis (LPF), which plays an important role in the fibrostenotic complications of EoE. Current approaches to assess LPF in EoE are prone to inter-observer inconsistencies and provide limited insight into the structural remodeling of the ECM. An objective approach to quantify LPF can eliminate inter-observer inconsistencies and provide novel insights into the fibrotic transformation of the lamina propria in EoE. Second harmonic generation (SHG) microscopy is a powerful modality for objectively quantifying disease associated alterations in ECM collagen structure that is finding increasing use for clinical research. We used SHG with morphometric analysis (SHG-MA) to characterize lamina propria collagen fibers and ECM porosity in esophageal biopsies collected from children with active EoE (n = 11), inactive EoE (n = 11), and non-EoE (n = 11). The collagen fiber width quantified by SHG-MA correlated positively with peak eosinophil count (r = 0.65, p < 0.005) and histopathologist scoring of LPF (r = 0.52, p < 0.005) in the esophageal biopsies. Patients with active EoE had a significant enlargement of ECM pores compared to inactive EoE and non-EoE (p < 0.005), with the mean pore area correlating positively with EoE activity (r = 0.76, p < 0.005) and LPF severity (r = 0.65, p < 0.005). These results indicate that SHG-MA can be utilized to objectively characterize and provide novel insights into lamina propria ECM structural remodeling in children with EoE, which could aid in monitoring disease progression.

Label-free multimodal imaging with simultaneous two-photon and three-photon microscopy and kernel-based nonlinear scaling denoising

We report on a compact multimodal imaging system that can acquire two-photon microscopy (2PM) and three-photon microscopy (3PM) images simultaneously. With dual excitation wavelengths, multiple contrasts including two-photon-excitation-fluorescence (2PEF), second harmonic generation (SHG), and third harmonic generation (THG) are acquired simultaneously from cells, collagen fibers, and interfaces, all label-free. Challenges related to the excitation by two wavelengths and the effective separation of 2PM and 3PM signals are discussed and addressed. The data processing challenge where multiple contrasts can have significantly varying signal levels is also addressed. A kernel-based nonlinear scaling (KNS) denoising method is introduced to reduce noise from ultra-low signal images and generate high-quality multimodal images. Simultaneous 2PM and 3PM imaging is demonstrated on various tissue samples. The simultaneous acquisition speeds up the imaging process and minimizes the commonly encountered problem of motion artifacts and mechanical drift in sequential acquisition. Multimodal imaging with simultaneous 2PM and 3PM will have great potential for label-free in-vivo imaging of biological tissues.

Toward next-generation endoscopes integrating biomimetic video systems, nonlinear optical microscopy, and deep learning

According to the World Health Organization, the proportion of the world's population over 60 years will approximately double by 2050. This progressive increase in the elderly population will lead to a dramatic growth of age-related diseases, resulting in tremendous pressure on the sustainability of healthcare systems globally. In this context, finding more efficient ways to address cancers, a set of diseases whose incidence is correlated with age, is of utmost importance. Prevention of cancers to decrease morbidity relies on the identification of precursor lesions before the onset of the disease, or at least diagnosis at an early stage. In this article, after briefly discussing some of the most prominent endoscopic approaches for gastric cancer diagnostics, we review relevant progress in three emerging technologies that have significant potential to play pivotal roles in next-generation endoscopy systems: biomimetic vision (with special focus on compound eye cameras), non-linear optical microscopies, and Deep Learning. Such systems are urgently needed to enhance the three major steps required for the successful diagnostics of gastrointestinal cancers: detection, characterization, and confirmation of suspicious lesions. In the final part, we discuss challenges that lie en route to translating these technologies to next-generation endoscopes that could enhance gastrointestinal imaging, and depict a possible configuration of a system capable of (i) biomimetic endoscopic vision enabling easier detection of lesions, (ii) label-free in vivo tissue characterization, and (iii) intelligently automated gastrointestinal cancer diagnostic.

Label-free highly multimodal nonlinear endoscope

We demonstrate a 2 mm diameter highly multimodal nonlinear micro-endoscope allowing label-free imaging of biological tissues. The endoscope performs multiphoton fluorescence (3-photon, 2-photon), harmonic generation (second-SHG and third-THG) and coherent anti-Stokes Raman scattering (CARS) imaging over a field of view of 200 µm. The micro-endoscope is based on a double-clad antiresonant hollow core fiber featuring a high transmission window (850 nm to 1800 nm) that is functionalized with a short piece of graded-index (GRIN) fiber. When combined with a GRIN micro-objective, the micro-endoscope achieves a 1.1 µm point spread function (PSF). We demonstrate 3-photon, 2-photon, THG, SHG, and CARS high resolution images of unlabelled biological tissues.

Dual-wavelength multimodal multiphoton microscope with SMA-based depth scanning

We report on a multimodal multiphoton microscopy (MPM) system with depth scanning. The multimodal capability is realized by an Er-doped femtosecond fiber laser with dual output wavelengths of 1580 nm and 790 nm that are responsible for three-photon and two-photon excitation, respectively. A shape-memory-alloy (SMA) actuated miniaturized objective enables the depth scanning capability. Image stacks combined with two-photon excitation fluorescence (TPEF), second harmonic generation (SHG), and third harmonic generation (THG) signals have been acquired from animal, fungus, and plant tissue samples with a maximum depth range over 200 µm.

Tumor extracellular matrix: lessons from the second-harmonic generation microscopy

Extracellular matrix (ECM) represents more than a mere intercellular cement. It is physiologically active in cell communication, adhesion and proliferation. Collagen is the most abundant protein, making up to 90% of ECM, and 30% of total protein weight in humans. Second-harmonic generation (SHG) microscopy represents an important tool to study collagen organization of ECM in freshly unfixed tissues and paraffin-embedded tissue samples. This manuscript aims to review some of the applications of SHG microscopy in Oncologic Pathology, mainly in the study of ECM of epithelial tumors. It is shown how collagen parameters measured by this technique can aid in the differential diagnosis and in prognostic stratification. There is a tendency to associate higher amount, lower organization and higher linearity of collagen fibers with tumor progression and metastasizing. These represent complex processes, in which matrix remodeling plays a central role, together with cancer cell genetic modifications. Integration of studies on cancer cell biology and ECM are highly advantageous to give us a more complete picture of these processes. As microscopic techniques provide topographic information allied with biologic characteristics of tissue components, they represent important tools for a more complete understanding of cancer progression. In this context, SHG has provided significant insights in human tumor specimens, readily available for Pathologists.

Optical biopsy of laryngeal lesions using femtosecond multiphoton microscopy

Laryngeal squamous cell carcinoma (LSCC) is one of the most prevalent malignancy of the upper aerodigestive tract. Detection of early lesions in vivo could improve the survival rate significantly. In this study, we demonstrated that femtosecond multiphoton microscopy (MPM) is an effective tool to visualize the microscopic features within fixed laryngeal tissues, without sectioning, staining, or labeling. Accurate detection of lesions and determination of the tumor grading can be achieved, with excellent consistency with conventional histological examination. These results suggest that MPM may represent a powerful tool for in-vivo or fast ex-vivo diagnosis of laryngeal lesions at the point of care.

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.

Characterization of multiphoton microscopes by the nonlinear knife-edge technique

Imaging submicron fluorescent microspheres are the standard method for measuring resolution in multiphoton microscopy. However, when using high-energy pulsed lasers, photobleaching and heating of the solution medium may deteriorate the images, resulting in an inaccurate resolution measurement. Moreover, due to the weak higher-order response of fluorescent microspheres, measuring three-photon resolution using three-photon fluorescence (3PEF) and third-harmonic generation (THG) signals is more difficult. In this report, we demonstrate a methodology for complete characterization of multiphoton microscopes based on second- and third-harmonic generation signals from the sharp edge of GaAs wafers. This simple methodology, which we call the nonlinear knife-edge technique, provides fast and consistent lateral and axial resolution measurement with negligible photobleaching effect on semiconductor wafers. In addition, this technique provides information on the field curvature of the imaging system, and perhaps other distortions of the imaging system, adding greater capability compared to existing techniques.

Feasibility of multimodal multiphoton microscopy to facilitate surgical margin assessment in pancreatic cancer

Pancreatic cancer is a common cancer with poor odds of survival for the patient, with surgical resection offering the only hope of cure. Current surgical practice is time-consuming and, due to time constraints, does not sample the whole cut surface sufficiently to check for remaining cancer. Although microscopy with hematoxylin and eosin (H&E) stain is the gold standard for microscopic evaluation, multiphoton microscopy (MPM) has emerged as an alternative tool for imaging tissue architecture and cellular morphology without labels. We explored the use of multimodal MPM for the label-free identification of normal and cancerous tissue of the pancreas in a mouse model by comparing the images to H&E microscopy. Our early studies indicate that MPM using second-harmonic generation, third-harmonic generation, and multiphoton excitation of endogenous fluorescent proteins can each contribute to the label-free analysis of the pancreatic surgical margin.

Circular pyramidal kirigami microscanner with millimeter-range low-power lens drive

This paper proposes an electrothermally-actuated circular pyramidal kirigami microscanner with a millimeter-range low-power lens drive for endoscopic biomedical applications. A variation of Japanese origami art, kirigami involves creation of out-of-plane structures by paper cutting and folding. The proposed microscanner is composed of freestanding kirigami film on which the spiral-curved thermal bimorphs are strategically placed. The kirigami microscanner is electrothermally transformed into an out-of-plane circular multistep pyramid by Joule heating. The circular pyramidal kirigami microscanner on a small footprint of 4.5 mm × 4.5 mm was fabricated by microelectromechanical system processes. A large four-step pyramidal actuation was successfully demonstrated, and a large 1.1-mm lens travel range at only 128 mW was achieved.

Second and third harmonic generation microscopy visualizes key structural components in fresh unprocessed healthy human breast tissue

Real-time assessment of excised tissue may help to improve surgical results in breast tumor surgeries. Here, as a step towards this purpose, the potential of second and third harmonic generation (SHG, THG) microscopy is explored. SHG and THG are nonlinear optical microscopic techniques that do not require labeling of tissue to generate 3D images with intrinsic depth-sectioning at sub-cellular resolution. Until now, this technique had been applied on fixated breast tissue or to visualize the stroma only, whereas most tumors start in the lobules and ducts. Here, SHG/THG images of freshly excised unprocessed healthy human tissue are shown to reveal key breast components-lobules, ducts, fat tissue, connective tissue and blood vessels, in good agreement with hematoxylin and eosin histology. DNA staining of fresh unprocessed mouse breast tissue was performed to aid in the identification of cell nuclei in label-free THG images. Furthermore, 2- and 3-photon excited auto-fluorescence images of mouse and human tissue are collected for comparison. The SHG/THG imaging modalities generate high quality images of freshly excised tissue in less than a minute with an information content comparable to that of the gold standard, histopathology. Therefore, SHG/THG microscopy is a promising tool for real-time assessment of excised tissue during surgery.

Compact fiber-based multi-photon endoscope working at 1700 nm

We present the design, implementation and performance analysis of a compact multi-photon endoscope based on a piezo electric scanning tube. A miniature objective lens with a long working distance and a high numerical aperture (≈ 0.5) is designed to provide a diffraction limited spot size. Furthermore, a 1700 nm wavelength femtosecond fiber laser is used as an excitation source to overcome the scattering of biological tissues and reduce water absorption. Therefore, the novel optical system along with the unique wavelength allows us to increase the imaging depth. We demonstrate that the endoscope is capable of performing third and second harmonic generation (THG/SHG) and three-photon excitation fluorescence (3PEF) imaging over a large field of view (> 400 μm) with high lateral resolution (2.2 μm). The compact and lightweight probe design makes it suitable for minimally-invasive in-vivo imaging as a potential alternative to surgical biopsies.

Pancreatic cancer cell detection by targeted lipid microbubbles and multiphoton imaging

Surgical resection of pancreatic cancer represents the only chance of cure and long-term survival in this common disease. Unfortunately, determination of a cancer-free margin at surgery is based on one or two tiny frozen section biopsies, which is far from ideal. Not surprisingly, cancer is usually left behind and is responsible for metastatic disease. We demonstrate a method of receptor-targeted imaging using peptide ligands, lipid microbubbles, and multiphoton microscopy that could lead to a fast and accurate way of examining the entire cut surface during surgery. Using a plectin-targeted microbubble, we performed a blinded in-vitro study to demonstrate avid binding of targeted microbubbles to pancreatic cancer cells but not noncancerous cell lines. Further work should lead to a much-needed point-of-care diagnostic test for determining clean margins in oncologic surgery.

All-reflective multiphoton microscope

We present the design, construction, and characterization of a multiphoton microscope that uses reflective elements for beam shaping and steering. This compact all reflective design removes the adverse effects of dispersion on laser pulse broadening as well as chromatic aberration in the focusing of broadband and multicolored laser sources. The design of this system is discussed in detail, including aberrations analysis via ray-tracing simulation and opto-mechanical design. The resolution of this mirror based all-reflective microscope is characterized using fluorescent microbeads. The performance of the system at multiple wavelengths is investigated along with some potential multiphoton imaging and writing applications.

Imaging of targeted lipid microbubbles to detect cancer cells using third harmonic generation microscopy

The use of receptor-targeted lipid microbubbles imaged by ultrasound is an innovative method of detecting and localizing disease. However, since ultrasound requires a medium between the transducer and the object being imaged, it is impractical to apply to an exposed surface in a surgical setting where sterile fields need be maintained and ultrasound gel may cause the bubbles to collapse. Multiphoton microscopy (MPM) is an emerging tool for accurate, label-free imaging of tissues and cells with high resolution and contrast. We have recently determined a novel application of MPM to be used for detecting targeted microbubble adherence to the upregulated plectin-receptor on pancreatic tumor cells. Specifically, the third-harmonic generation response can be used to detect bound microbubbles to various cell types presenting MPM as an alternative and useful imaging method. This is an interesting technique that can potentially be translated as a diagnostic tool for the early detection of cancer and inflammatory disorders.