Multiphoton Laser Scanning Microscopy—A Novel Diagnostic Method for Superficial Skin Cancers

DeepDOF-SE: affordable deep-learning microscopy platform for slide-free histology

Histopathology plays a critical role in the diagnosis and surgical management of cancer. However, access to histopathology services, especially frozen section pathology during surgery, is limited in resource-constrained settings because preparing slides from resected tissue is time-consuming, labor-intensive, and requires expensive infrastructure. Here, we report a deep-learning-enabled microscope, named DeepDOF-SE, to rapidly scan intact tissue at cellular resolution without the need for physical sectioning. Three key features jointly make DeepDOF-SE practical. First, tissue specimens are stained directly with inexpensive vital fluorescent dyes and optically sectioned with ultra-violet excitation that localizes fluorescent emission to a thin surface layer. Second, a deep-learning algorithm extends the depth-of-field, allowing rapid acquisition of in-focus images from large areas of tissue even when the tissue surface is highly irregular. Finally, a semi-supervised generative adversarial network virtually stains DeepDOF-SE fluorescence images with hematoxylin-and-eosin appearance, facilitating image interpretation by pathologists without significant additional training. We developed the DeepDOF-SE platform using a data-driven approach and validated its performance by imaging surgical resections of suspected oral tumors. Our results show that DeepDOF-SE provides histological information of diagnostic importance, offering a rapid and affordable slide-free histology platform for intraoperative tumor margin assessment and in low-resource settings.

Non-Invasive Skin Imaging Assessment of Human Stress During Head-Down Bed Rest Using a Portable Handheld Two-Photon Microscope

Spaceflight presents a series of physiological and pathological challenges to astronauts resulting from ionizing radiation, microgravity, isolation, and other spaceflight hazards. These risks cause a series of aging-related diseases associated with increased oxidative stress and mitochondria dysfunction. The skin contains many autofluorescent substances, such as nicotinamide adenine dinucleotide phosphate (NAD(P)H), keratin, melanin, elastin, and collagen, which reflect physiological and pathological changes in vivo. In this study, we used a portable handheld two-photon microscope to conduct high-resolution in vivo skin imaging on volunteers during 15 days of head-down bed rest. The two-photon microscope, equipped with a flexible handheld scanning head, was used to measure two-photon excited fluorescence (TPEF) and second harmonic generation (SHG) images of the left forearm, left front chest, and forehead of volunteers. Changes in TPEF, SHG, and the extended SHG-to-AF(TPEF) aging index of the dermis (SAAID) were measured. It was found that TPEF intensity increased during bed rest and was restored to normal levels after recovery. Meanwhile, SHG increased slightly during bed rest, and the skin aging index increased. Moreover, we found the skin TPEF signals of the left forearm were significantly negatively associated with the oxidative stress marker malondialdehyde (MDA) and DNA damage marker 8-hydroxy-2′-desoxyguanosine (8-OHdG) values of subjects during head-down bed rest. Meanwhile, the SHG signals were also significantly negatively correlated with MDA and 8-OHDG. A significant negative correlation between the extended SAAID of the left chest and serum antioxidant superoxide dismutase (SOD) levels was also found. These results demonstrate that skin autofluorescence signals can reflect changes in human oxidant status. This study provides evidence for in-orbit monitoring of changes in human stress using a portable handheld two-photon microscope for skin imaging.

Two-Photon Absorption: An Open Door to the NIR-II Biological Window?

The way in which photons travel through biological tissues and subsequently become scattered or absorbed is a key limitation for traditional optical medical imaging techniques using visible light. In contrast, near-infrared wavelengths, in particular those above 1000 nm, penetrate deeper in tissues and undergo less scattering and cause less photo-damage, which describes the so-called "second biological transparency window". Unfortunately, current dyes and imaging probes have severely limited absorption profiles at such long wavelengths, and molecular engineering of novel NIR-II dyes can be a tedious and unpredictable process, which limits access to this optical window and impedes further developments. Two-photon (2P) absorption not only provides convenient access to this window by doubling the absorption wavelength of dyes, but also increases the possible resolution. This review aims to provide an update on the available 2P instrumentation and 2P luminescent materials available for optical imaging in the NIR-II window.

Macroscopic and microscopic imaging modalities for diagnosis and monitoring of urogenital schistosomiasis

Urogenital schistosomiasis remains a major global challenge. Optimal management of this infection depends upon imaging-based assessment of sequelae. Although established imaging modalities such as ultrasonography, plain radiography, magnetic resonance imaging (MRI), narrow band imaging, and computerized tomography (CT) have been used to determine tissue involvement by urogenital schistosomiasis, newer refinements in associated technologies may lead to improvements in patient care. Moreover, application of investigational imaging methods such as confocal laser endomicroscopy and two-photon microscopy in animal models of urogenital schistosomiasis are likely to contribute to our understanding of this infection's pathogenesis. This review discusses prior use of imaging in patients with urogenital schistosomiasis and experimentally infected animals, the advantages and limitations of these modalities, the latest radiologic developments relevant to this infection, and a proposed future diagnostic standard of care for management of afflicted patients.

Polarization-resolved SHG imaging as a fast screening method for collagen alterations during aging: Comparison with light and electron microscopy

Our previous study on rat skin showed that cumulative oxidative pressure induces profound structural and ultrastructural alterations in both rat skin epidermis and dermis during aging. Here, we aimed to investigate the biophotonic properties of collagen as a main dermal component in the function of chronological aging. We used second harmonic generation (SHG) and two-photon excited fluorescence (TPEF) on 5 μm thick skin paraffin sections from 15-day-, 1-month- and 21-month-old rats, respectively, to analyze collagen alterations, in comparison to conventional light and electron microscopy methods. Obtained results show that polarization-resolved SHG (PSHG) images can detect collagen fiber alterations in line with chronological aging and that this method is consistent with light and electron microscopy. Moreover, the β coefficient calculated from PSHG images points out that delicate alterations lead to a more ordered structure of collagen molecules due to oxidative damage. The results of this study also open the possibility of successfully applying this fast and label-free method to previously fixed samples.

In vivo multiphoton imaging for non-invasive time course assessment of retinoids effects on human skin

Background

In vivo multiphoton imaging and automatic 3D image processing tools provide quantitative information on human skin constituents. These multiphoton‐based tools allowed evidencing retinoids epidermal effects in the occlusive patch test protocol developed for antiaging products screening. This study aimed at investigating their relevance for non‐invasive, time course assessment of retinoids cutaneous effects under real‐life conditions for one year.

Materials and Methods

Thirty women, 55‐65 y, applied either retinol (RO 0.3%) or retinoic acid (RA 0.025%) on one forearm dorsal side versus a control product on the other forearm once a day for 1 year. In vivo multiphoton imaging was performed every three months, and biopsies were taken after 1 year. Epidermal thickness and dermal‐epidermal junction undulation were estimated in 3D with multiphoton and in 2D with histology, whereas global melanin density and its z‐epidermal distribution were estimated using 3D multiphoton image processing tools.

Results

Main results after one year were as follows: a) epidermal thickening with RO (+30%); b) slight increase in dermal‐epidermal junction undulation with RO; c) slight decrease in 3D melanin density with RA; d) limitation of the melanin ascent observed with seasonality and time within supra‐basal layers with both retinoids, using multiphoton 3D‐melanin z‐epidermal profile.

Conclusions

With a novel 3D descriptor of melanin z‐epidermal distribution, in vivo multiphoton imaging allows demonstrating that daily usage of retinoids counteracts aging by acting not only on epidermal morphology, but also on melanin that is shown to accumulate in the supra‐basal layers with time.

Multiphoton microscopy of the dermoepidermal junction and automated identification of dysplastic tissues with deep learning

Histopathological image analysis performed by a trained expert is currently regarded as the gold-standard for the diagnostics of many pathologies, including cancers. However, such approaches are laborious, time consuming and contain a risk for bias or human error. There is thus a clear need for faster, less intrusive and more accurate diagnostic solutions, requiring also minimal human intervention. Multiphoton microscopy (MPM) can alleviate some of the drawbacks specific to traditional histopathology by exploiting various endogenous optical signals to provide virtual biopsies that reflect the architecture and composition of tissues, both in-vivo or ex-vivo. Here we show that MPM imaging of the dermoepidermal junction (DEJ) in unstained fixed tissues provides useful cues for a histopathologist to identify the onset of non-melanoma skin cancers. Furthermore, we show that MPM images collected on the DEJ, besides being easy to interpret by a trained specialist, can be automatically classified into healthy and dysplastic classes with high precision using a Deep Learning method and existing pre-trained convolutional neural networks. Our results suggest that deep learning enhanced MPM for in-vivo skin cancer screening could facilitate timely diagnosis and intervention, enabling thus more optimal therapeutic approaches.

Imaging and quantifying drug delivery in skin - Part 2: Fluorescence andvibrational spectroscopic imaging methods

Understanding the delivery and diffusion of topically-applied drugs on human skin is of paramount importance in both pharmaceutical and cosmetics research. This information is critical in early stages of drug development and allows the identification of the most promising ingredients delivered at optimal concentrations to their target skin compartments. Different skin imaging methods, invasive and non-invasive, are available to characterize and quantify the spatiotemporal distribution of a drug within ex vivo and in vivo human skin. The first part of this review detailed invasive imaging methods (autoradiography, MALDI and SIMS). This second part reviews non-invasive imaging methods that can be applied in vivo: i) fluorescence (conventional, confocal, and multiphoton) and second harmonic generation microscopies and ii) vibrational spectroscopic imaging methods (infrared, confocal Raman, and coherent Raman scattering microscopies). Finally, a flow chart for the selection of imaging methods is presented to guide human skin ex vivo and in vivo drug delivery studies.

Multiphoton Microscopy for Noninvasive and Label-Free Imaging of Human Skin and Oral Mucosa Equivalents

Multiphoton microscopy has emerged as a powerful modality for noninvasive, spatial, and temporal imaging of biological tissues without the use of labels and/or dyes. It provides complimentary imaging modalities, which include two-photon excited fluorescence (2PEF) and second harmonic generation (SHG). 2PEF from endogenous chromophores such as nicotinamide adenine dinucleotides (NADH), flavins and keratin enable visualization of cellular and subcellular structures. SHG provides visualization of asymmetric macromolecular structures such as collagen. These modalities enable the visualization of biochemical and biological alterations within live tissues in their native state.Organotypic cultures of the skin and oral mucosa equivalents have been increasingly used across basic and translational research. However, assessment of the skin and oral mucosa equivalents is predominantly based on histological techniques which are not suited for real-time imaging and longitudinal studies of the tissues in their native state. 2PEF from endogenous chromophores and SHG from collagen can be effectively used as an imaging tool for noninvasive and label-free acquisition of cellular and matrix structures of live skin and oral mucosa cultures.In this chapter, the methods for noninvasive and label-free imaging of monolayer and organotypic cultures of the skin and oral mucosa using multiphoton microscopy are described.

Skin cancer detection using non-invasive techniques

Skin cancer is the most common form of cancer and is globally rising. Historically, the diagnosis of skin cancers has depended on various conventional techniques which are of an invasive manner. A variety of commercial diagnostic tools and auxiliary techniques are available to detect skin cancer. This article explains in detail the principles and approaches involved for non-invasive skin cancer diagnostic methods such as photography, dermoscopy, sonography, confocal microscopy, Raman spectroscopy, fluorescence spectroscopy, terahertz spectroscopy, optical coherence tomography, the multispectral imaging technique, thermography, electrical bio-impedance, tape stripping and computer-aided analysis. The characteristics of an ideal screening test are outlined, and the authors pose several points for clinicians and scientists to consider in the evaluation of current and future studies of skin cancer detection and diagnosis. This comprehensive review critically analyses the literature associated with the field and summarises the recent updates along with their merits and demerits.

Specific Systems for Imaging

Microscopy allows for the characterization of small objects invisible to the naked eye, a technique that, since its conception, has played a key role in the development across nearly every field of science and technology. Given the nanometer size of the materials explored in the field of nanotechnology, the contributions of modern microscopes that can visualize these materials are indispensable, and the ever-improving technology is paramount to the future success of the field. This chapter will focus on four fundamental areas of microscopy used in the field of nanotechnology including fluorescence microscopy (Sect. 3.1), particle tracking and photoactivated localization microscopy (Sect. 3.2), quantum dots and fluorescence resonance energy transfer (Sect. 3.3), and cellular MRI and PET labeling (Sect. 3.4). The functionality, as well as the current and recommended usage of each given imaging system, will be discussed.

Two-photon microscopy for intracutaneous imaging of stem cell activity in mice

The adult skin is a typical example of a highly regenerative tissue. Terminally differentiated keratinocytes are shed from the external layers of the epidermis or extruded from the skin as part of the growing hair shaft on a daily basis. These are effectively replenished through the activity of skin-resident stem cells. Precise regulation of stem cell activity is critical for normal skin homoeostasis or wound healing and irregular stem cell proliferation or differentiation can lead to skin disease. The scarcity and dynamic nature of stem cells presents a major challenge for elucidating their mechanism of action. To address this, we have recently established a system for visualizing stem cell activity, in real time or long term, in the intact skin of live mice using two-photon microscopy. The purpose of this review was to provide essential information to researchers who wish to incorporate two-photon microscopy and live imaging into their experimental toolbox for studying aspects of skin and stem biology in the mouse model. We discuss fundamental principles of the method, instrumentation and basic experimental approaches to interrogate stem cell activity in the interfollicular epidermis and hair follicle.

The skin-depigmenting potential of Paeonia lactiflora root extract and paeoniflorin: in vitro evaluation using reconstructed pigmented human epidermis

OBJECTIVE

The roots of the herb Paeonia lactiflora ('White Peony') are used in association with other herbs in traditional clinical cosmetic practice in China as oral treatment for skin pigmentary disorders, such as brown or dark pigmentary spots. However, the skin-depigmenting potential of Paeonia lactiflora root extract and its main ingredient paeoniflorin has been scarcely investigated by topical application. The purpose of this study was to evaluate the efficacy of Paeonia lactiflora root extract and paeoniflorin as skin whitening agent in cosmetic application.

METHODS

Paeonia lactiflora root extract (containing 53.25% of paeoniflorin) and paeoniflorin (97% purity) were applied topically on reconstructed pigmented human epidermis model, a three-dimensional (3D) human skin equivalent, showing morphological and functional characteristics similar to those of in vivo human skin. Two specific methods were used for quantifying melanin inside the reconstructed pigmented epidermis: Fontana-Masson staining (2D quantification) and multiphoton microscopy (3D quantification).

RESULTS

Compared to vehicle (dimethyl sulfoxide DMSO), a significant decrease in 2D and 3D melanin content was observed after topical application on reconstructed pigmented epidermis of Paeonia lactiflora extract at 300 μg mL(-1) (-28% and -27%, respectively) and paeoniflorin at 120 μg mL(-1) /250 μM (-30% and -23%, respectively), which is in the same order of magnitude as the positive reference 4-n-butylresorcinol at 83 μg mL(-1) /500 μM (-26% and -40%, respectively).

CONCLUSION

These results demonstrate, for the first time, the depigmenting potential of paeoniflorin and thus the potential interest of using Paeonia lactiflora root extracts containing paeoniflorin in cosmetic or dermatological applications for reducing the severity of some hyperpigmented skin disorders.

Combined reflectance confocal microscopy-optical coherence tomography for delineation of basal cell carcinoma margins: an ex vivo study

We present a combined reflectance confocal microscopy (RCM) and optical coherence tomography (OCT) approach, integrated within a single optical layout, for diagnosis of basal cell carcinomas (BCCs) and delineation of margins. While RCM imaging detects BCC presence (diagnoses) and its lateral spreading (margins) with measured resolution of ∼1  μm, OCT imaging delineates BCC depth spreading (margins) with resolution of ∼7  μm. When delineating margins in 20 specimens of superficial and nodular BCCs, depth could be reliably determined down to ∼600  μm, and agreement with histology was within about ±50  μm.

In vivo visualization of uterine mast cells by two-photon microscopy

Transgenic mice expressing fluorescent proteins in specific cell populations are widely used for the study ofin vivobehavior of these cells. We have recently reported that uterine mast cells (uMCs) are important for implantation and placentation. However, theirin vivolocalization in uterus before and during pregnancy is unknown. Herein, we report the direct observation of uMCsin vivousing double-transgenic C57BL/6JMcpt5-Cre ROSA26-EYFPmice with high expression of enhanced yellow fluorescent protein in MC protease 5 (Cma1(Mcpt5))-expressing cells by intravital two-photon microscopy. We were able to monitor MCs livein uteroduring the murine estrous cycle and at different days of pregnancy. We demonstrated that uMCs accumulated during the receptive phase of the female (estrus) and persisted in large numbers at early pregnancy stages and around mid-gestation and declined in number in non-pregnant animals at diestrus. This intravital microscopy technique, including a custom-made microscope stage and the adaption of the surgical procedure, allowed the access of the uterus and implantations for imaging. The introduced application of intravital microscopy to C57BL/6J-Mcpt5-Cre ROSA26-EYFPmice offers a novel and powerfulin vivoapproach to further address the evident relevance of uMCs to reproductive processes with obvious clinical implications.

A quantitative approach to histopathological dissection of elastin-related disorders using multiphoton microscopy

BACKGROUND

Multiphoton microscopy (MPM) is a novel imaging technology that has recently become applicable for diagnostic purposes. The use of (near) infrared light in MPM allows for deep tissue imaging. In addition, this modality exploits the autofluorescent nature of extracellular matrix fibres within the skin.

OBJECTIVES

To quantitate the structure and abundance of elastic fibres in human dermis in three dimensions utilizing autofluorescent signals generated by MPM for the objective examination of elastin-related skin disorders.

METHODS

Cross-sections of skin samples from elastin-related disorders were analysed by MPM and correlated to histopathology. In situ visualization of elastic fibres by MPM was conducted by en face imaging of ex vivo skin samples through the intact epidermis. Image analysis software was used to quantify elastic fibres in three dimensions.

RESULTS

Based on the MPM-detected elastin-specific autofluorescence, we developed the Dermal Elastin Morphology Index (DEMI), calculated as the ratio of elastic fibre surface area and volume. This enabled objective three-dimensional quantification of elastic fibres. Quantitative scoring of sun-damaged skin using DEMI correlated with qualitative histopathological grading of the severity of solar elastosis. Furthermore, this approach was applied to changes in elastic fibre architecture in other disorders, such as pseudoxanthoma elasticum (PXE), PXE-like syndrome, elastofibroma, focal dermal elastosis, anetoderma, mid-dermal elastolysis and striae distensae. We imaged elastic fibres in intact ex vivo skin imaged en face through the epidermis, indicating that this approach could be used in vivo.

CONCLUSIONS

MPM has the potential for noninvasive in vivo visualization of elastic fibres in the dermis with near histological resolution. DEMI allows objective assessment of elastic fibres to support diagnosis and monitoring of disease progress or therapy of elastin-related skin disorders.

Nonlinear optical microscopy signal processing strategies in cancer

This work reviews the most relevant present-day processing methods used to improve the accuracy of multimodal nonlinear images in the detection of epithelial cancer and the supporting stroma. Special emphasis has been placed on methods of non linear optical (NLO) microscopy image processing such as: second harmonic to autofluorescence ageing index of dermis (SAAID), tumor-associated collagen signatures (TACS), fast Fourier transform (FFT) analysis, and gray level co-occurrence matrix (GLCM)-based methods. These strategies are presented as a set of potential valuable diagnostic tools for early cancer detection. It may be proposed that the combination of NLO microscopy and informatics based image analysis approaches described in this review (all carried out on free software) may represent a powerful tool to investigate collagen organization and remodeling of extracellular matrix in carcinogenesis processes.

Detection and Discrimination of Non-Melanoma Skin Cancer by Multimodal Imaging

Non-melanoma skin cancer (NMSC) belongs to the most frequent human neoplasms. Its exposed location facilitates a fast ambulant treatment. However, in the clinical practice far more lesions are removed than necessary, due to the lack of an efficient pre-operational examination procedure: Standard imaging methods often do not provide a sufficient spatial resolution. The demand for an efficient in vivo imaging technique might be met in the near future by non-linear microscopy. As a first step towards this goal, the appearance of NMSC in various microspectroscopic modalities has to be defined and approaches have to be derived to distinguish healthy skin from NMSC using non-linear optical microscopy. Therefore, in this contribution the appearance of ex vivo NMSC in a combination of coherent anti-Stokes Raman scattering (CARS), second harmonic generation (SHG) and two photon excited fluorescence (TPEF) imaging—referred as multimodal imaging—is described. Analogous to H&E staining, an overview of the distinct appearances and features of basal cell and squamous cell carcinoma in the complementary modalities is derived, and is expected to boost in vivo studies of this promising technological approach.

Three-dimensional multiphoton/optical coherence tomography for diagnostic applications in dermatology

A preliminary clinical trial using state-of-the-art multiphoton tomography (MPT) and optical coherence tomography (OCT) for three-dimensional (3D) multimodal in vivo imaging of normal skin, nevi, scars and pathologic skin lesions has been conducted. MPT enabled visualization of sub-cellular details with axial and transverse resolutions of <2 μm and <0.5 μm, respectively, from a volume of 0.35 × 0.35 × 0.2 mm(3) at a frame rate of 0.14 Hz (512 × 512 pixels). State-of-the-art OCT, operating at a center wavelength of 1300 nm, was capable of acquiring 3D images depicting the layered architecture of skin with axial and transverse resolutions ~8 μm and ~20 μm, respectively, from a volume of 7 × 3.5 × 1.5 mm(3) at a frame rate of 46 Hz (1024 × 1024 pixels). This study demonstrates the clinical diagnostic potential of MPT/OCT for pre-screening relatively large areas of skin using 3D OCT to identify suspicious regions at microscopic level and subsequently using high resolution MPT to obtain zoomed in, sub-cellular level information of the respective regions.

Laser scanning microscopy approach for semiquantitation of in vitro dermal particle penetration

Skin penetration of nanoparticles is a recent research area in focus for the aim of development of topical nanoparticulate delivery systems as well as for health risk analysis. So far, monitoring skin penetration of nanoparticles is mostly based on qualitative microscopical examination. Here, we describe an experimental approach for extracting semiquantitative data from multiphoton images of skin specimens treated with gold nanoparticles. This will aid in depicting the factors responsible for enhancing or limiting nanoparticle penetration through the skin barrier.

High-resolution imaging of basal cell carcinoma: a comparison between multiphoton microscopy with fluorescence lifetime imaging and reflectance confocal microscopy

AIMS

The aim of this study was to compare morphological aspects of basal cell carcinoma (BCC) as assessed by two different imaging methods: in vivo reflectance confocal microscopy (RCM) and multiphoton tomography with fluorescence lifetime imaging implementation (MPT-FLIM).

METHODS

The study comprised 16 BCCs for which a complete set of RCM and MPT-FLIM images were available. The presence of seven MPT-FLIM descriptors was evaluated. The presence of seven RCM equivalent parameters was scored in accordance to their extension. Chi-squared test with Fisher's exact test and Spearman's rank correlation coefficient were determined between MPT-FLIM scores and adjusted-RCM scores.

RESULTS

MPT-FLIM and RCM descriptors of BCC were coupled to match the descriptors that define the same pathological structures. The comparison included: Streaming and Aligned elongated cells, Streaming with multiple directions and Double alignment, Palisading (RCM) and Palisading (MPT-FLIM), Typical tumor islands, and Cell islands surrounded by fibers, Dark silhouettes and Phantom islands, Plump bright cells and Melanophages, Vessels (RCM), and Vessels (MPT-FLIM). The parameters that were significantly correlated were Melanophages/Plump Bright Cells, Aligned elongated cells/Streaming, Double alignment/Streaming with multiple directions, and Palisading (MPT-FLIM)/Palisading (RCM).

CONCLUSION

According to our data, both methods are suitable to image BCC's features. The concordance between MPT-FLIM and RCM is high, with some limitations due to the technical differences between the two devices. The hardest difficulty when comparing the images generated by the two imaging modalities is represented by their different field of view.

Multiphoton tomographic imaging: a potential optical biopsy tool for detecting gastrointestinal inflammation and neoplasia

Endoscopy is widely used to detect and remove premalignant lesions with the goal of preventing gastrointestinal (GI) cancers. Because current endoscopes do not provide cellular resolution, all suspicious lesions are biopsied and subjected to histologic evaluation. Technologies that facilitate directed biopsies should decrease both procedure-related morbidity and cost. Here we explore the use of multiphoton microscopy (MPM), an optical biopsy tool that relies on intrinsic tissue emissions, to evaluate pathology in both experimental and human GI specimens, using hematoxylin and eosin (H&E)-stained sections from these tissues for comparison. After evaluating the entire normal mouse GI tract, MPM was used to investigate disease progression in mouse models of colitis and colorectal carcinogenesis. MPM provided sufficient histologic detail to identify all relevant substructures in ex vivo normal GI tissue, visualize both acute and resolving stages of colitis, and show the progression of colorectal carcinogenesis. Next, ex vivo specimens from human subjects with celiac sprue, inflammatory bowel disease, and colorectal neoplasia were imaged by MPM. Finally, colonic mucosa in live anesthetized rats was imaged in vivo using a flexible endoscope prototype. In both animal models and human specimens, MPM images showed a striking similarity to the results of H&E staining, as shown by the 100% concordance achieved by the study pathologists' diagnoses. In summary, MPM is a promising technique that accurately visualizes histology in fresh, unstained tissues. Our findings support the continued development of MPM as a technology to enhance the early detection of GI pathologies including premalignant lesions.

Quantitative analysis of multiphoton excitation autofluorescence and second harmonic generation imaging for medical diagnosis

In recent years, two-photon excitation fluorescence and second harmonic generation microscopy has become an important tool in biomedical research. The ability of two-photon microscopy to achieve optical sectioning with minimal invasiveness is particularly advantageous for biomedical diagnosis. Advances in the miniaturization of the imaging system have increased its clinical potential, together with the development of quantitative technique for the analysis of data acquired using these imaging modalities. We present a review of the quantitative analysis techniques that have been used successfully with two-photon excitation fluorescence and SHG imaging. Specifically, quantification techniques using ratiometric, morphological, and structural differences to analyze two-photon images will be discussed, and their effectiveness at evaluating dermal and corneal pathologies and cancerous tumor growth will be described.

Imaging-guided two-photon excitation-emission-matrix measurements of human skin tissues

There are increased interests on using multiphoton imaging and spectroscopy for skin tissue characterization and diagnosis. However, most studies have been done with just a few excitation wavelengths. Our objective is to perform a systematic study of the two-photon fluorescence (TPF) properties of skin fluorophores, normal skin, and diseased skin tissues. A nonlinear excitation-emission-matrix (EEM) spectroscopy system with multiphoton imaging guidance was constructed. A tunable femtosecond laser was used to vary excitation wavelengths from 730 to 920 nm for EEM data acquisition. EEM measurements were performed on excised fresh normal skin tissues, seborrheic keratosis tissue samples, and skin fluorophores including: NADH, FAD, keratin, melanin, collagen, and elastin. We found that in the stratum corneum and upper epidermis of normal skin, the cells have large sizes and the TPF originates from keratin. In the lower epidermis, cells are smaller and TPF is dominated by NADH contributions. In the dermis, TPF is dominated by elastin components. The depth resolved EEM measurements also demonstrated that keratin structure has intruded into the middle sublayers of the epidermal part of the seborrheic keratosis lesion. These results suggest that the imaging guided TPF EEM spectroscopy provides useful information for the development of multiphoton clinical devices for skin disease diagnosis.

In vivo multiphoton imaging of human skin: assessment of topical corticosteroid-induced epidermis atrophy and depigmentation

Multiphoton microscopy has emerged in the past decade as a promising tool for noninvasive skin imaging. Our aim was to evaluate the potential of multiphoton microscopy to detect topical corticosteroids side effects within the epidermis and to provide new insights into their dynamics. Healthy volunteers were topically treated with clobetasol propionate on a small region of their forearms under overnight occlusion for three weeks. The treated region of each patient was investigated at D0, D7, D15, D22 (end of the treatment), and D60. Our study shows that multiphoton microscopy allows for the detection of corticoid-induced epidermis modifications: thinning of stratum corneum compactum and epidermis, decrease of keratinocytes size, and changes in their morphology from D7 to D22. We also show that multiphoton microscopy enables in vivo three-dimensional (3-D) quantitative assessment of melanin content. We observe that melanin density decreases during treatment and almost completely disappears at D22. Moreover, these alterations are reversible as they are no longer present at D60. Our study demonstrates that multiphoton microscopy is a convenient and powerful tool for noninvasive 3-D dynamical studies of skin integrity and pigmentation.

Two-photon and second harmonic microscopy in clinical and translational cancer research

Application of two-photon microscopy (TPM) to translational and clinical cancer research has burgeoned over the last several years, as several avenues of pre-clinical research have come to fruition. In this review, we focus on two forms of TPM-two-photon excitation fluorescence microscopy, and second harmonic generation microscopy-as they have been used for investigating cancer pathology in ex vivo and in vivo human tissue. We begin with discussion of two-photon theory and instrumentation particularly as applicable to cancer research, followed by an overview of some of the relevant cancer research literature in areas that include two-photon imaging of human tissue biopsies, human skin in vivo, and the rapidly developing technology of two-photon microendoscopy. We believe these and other evolving two-photon methodologies will continue to help translate cancer research from the bench to the bedside, and ultimately bring minimally invasive methods for cancer diagnosis and treatment to therapeutic reality.

Multiphoton laser microscopy and fluorescence lifetime imaging for the evaluation of the skin

Multiphoton laser microscopy is a new, non-invasive technique providing access to the skin at a cellular and subcellular level, which is based both on autofluorescence and fluorescence lifetime imaging. Whereas the former considers fluorescence intensity emitted by epidermal and dermal fluorophores and by the extra-cellular matrix, fluorescence lifetime imaging (FLIM), is generated by the fluorescence decay rate. This innovative technique can be applied to the study of living skin, cell cultures and ex vivo samples. Although still limited to the clinical research field, the development of multiphoton laser microscopy is thought to become suitable for a practical application in the next few years: in this paper, we performed an accurate review of the studies published so far, considering the possible fields of application of this imaging method and providing high quality images acquired in the Department of Dermatology of the University of Modena.

In vivo fluorescence confocal microscopy: indocyanine green enhances the contrast of epidermal and dermal structures

In recent years, in vivo skin imaging devices have been successfully implemented in skin research as well as in clinical routine. Of particular importance is the use of reflectance confocal microscopy (RCM) and fluorescence confocal microscopy (FCM) that enable visualization of the tissue with a resolution comparable to histology. A newly developed commercially available multi-laser device in which both technologies are integrated now offers the possibility to directly compare RCM with FCM. The fluorophore indocyanine green (ICG) was intradermally injected into healthy forearm skin of 10 volunteers followed by in vivo imaging at various time points. In the epidermis, accurate assessment of cell morphology with FCM was supplemented by identification of pigmented cells and structures with RCM. In dermal layers, only with FCM connective tissue fibers were clearly contoured down to a depth of more than 100 μm. The fluorescent signal still provided a favorable image contrast 24 and 48 hours after injection. Subsequently, ICG was applied to different types of skin diseases (basal cell carcinoma, actinic keratosis, seborrhoeic keratosis, and psoriasis) in order to demonstrate the diagnostic benefit of FCM when directly compared with RCM. Our data suggest a great impact of FCM in combination with ICG on clinical and experimental dermatology in the future.

Quantitative evaluation of healthy epidermis by means of multiphoton microscopy and fluorescence lifetime imaging microscopy

BACKGROUND/PURPOSE

Multiphoton microscopy (MPM) enables the assessment of unstained living biological tissue with submicron resolution, whereas fluorescence lifetime imaging microscopy (FLIM) generates image contrast between different states of tissue characterized by various fluorescence decay rates. The aim of this study was to compare the healthy skin of young individuals with that of older subjects, as well as to assess the skin at different body sites, by means of MPM and FLIM.

METHODS

Nineteen elderly patients were examined on the outer side of the forearm, whereas 30 young individuals were assessed on the dorsal and volar sides of the forearm and on the thigh.

RESULTS

Cell and nucleus diameters, cell density and FLIM vary according to the epidermal cell depth and the skin site. In elderly subjects, epidermal cells show morphologic alterations in shape and size, with smaller cell and nucleus diameters; the number of basal cells is decreased, whereas the mean fluorescence lifetimes at both the upper and the lower layers increase.

CONCLUSION

This study provides quantitative and qualitative data on normal epidermis at different skin sites at different ages and represents a reference for the clinician attempting to understand the effectiveness of MPM and FLIM in discriminating diseased states of the skin from normal ones.

Optical delineation of human malignant melanoma using second harmonic imaging of collagen

Skin cancer incidence has increased exponentially over the last three decades. In 2008 skin cancer caused 2280 deaths in the UK, with 2067 due to malignant melanoma. Early diagnosis can prevent mortality, however, conventional treatment requires multiple procedures and increasing treatment times. Second harmonic generation (SHG) imaging could offer diagnosis and demarcation of melanoma borders non-invasively at presentation thereby short-cutting the excision biopsy stage. To test the efficacy and accuracy of SHG imaging of collagen in skin and to delineate the borders of skin cancers, unstained human melanoma biopsy sections were imaged using SHG microscopy. Comparisons with sister sections, stained with H&E or Melan-A were made for correlation of invasion borders. Fresh ex vivo normal human and rat skin was imaged through its whole thickness using SHG to demonstrate this technique is transferable to in vivo tissues. SHG imaging demonstrated detailed collagen distribution in normal skin, with total absence of SHG signal (fibrillar collagen) within the melanoma-invaded tissue. The presence or absence of signal changes dramatically at the borders of the melanoma, accurately demarcating the edges that strongly correlated with H&E and Melan-A defined borders (p<0.002). SHG imaging of ex vivo human and rat skin demonstrated collagen architecture could be imaged through the full thickness of the skin. We propose that SHG imaging could be used for diagnosis and accurate demarcation of melanoma borders on presentation and therefore potentially reduce mortality rates.

Gold nanorods for intravital vascular imaging of preneoplastic oral mucosa

We explore the feasibility of using gold nanorods with efficient two-photon luminescence properties as contrast agents for intravital imaging of neoplasia. This investigation spanned ex vivo characterization in cells/tissue to in vivo implementation in an oral carcinogenesis model. GNRs were >40 times brighter than surrounding tissue. Intravital imaging revealed 3D microvasculature, and in dysplasia, abnormal vessels (dense and tortuous) compared to normal. GNRs were diffusely distributed in lesions after 24 hours. No known previous study has revealed abnormal vessel structure in dysplasia by imaging. Results suggest GNRs can function as high-contrast agents for in vivo visualization of carcinogenesis features.

Analysis of the metabolic deterioration of ex vivo skin from ischemic necrosis through the imaging of intracellular NAD(P)H by multiphoton tomography and fluorescence lifetime imaging microscopy

Ex vivo human skin has been used extensively for cosmeceutical and drug delivery studies, transplantable skin allografts, or skin flaps. However, it has a half-life of a few days due to ischemic necrosis. Traditional methods of assessing viability can be time-consuming and provide limited metabolic information. Using multiphoton tomography and fluorescence lifetime imaging (MPT-FLIM) we assess ischemic necrosis of ex vivo skin by NAD(P)H autofluorescence intensity and fluorescence lifetime. Ex vivo skin is stored in the presence and absence of nutrient media (Dulbecco Modified Eagle Medium) at -20, 4, and 37 degrees C and room temperature over a 7-day time course to establish different rates of metabolic deterioration. At higher temperatures we observe a decrease in NAD(P)H autofluorescence, higher image noise, and a significant increase in the average fluorescence lifetime (tau(m)) from approximately 1000 to 2000 ps. Additionally, significant distortions in NAD(P)H fluorescence lifetime histograms correspond to the reduction in autofluorescence. Skin kept at 4 degrees C, with or without media, showed the least change. Our findings suggest that MPT-FLIM enables useful noninvasive optical biopsies to monitor the metabolic state and deterioration of human skin for research and clinical purposes.

Recent advances in diagnosing cutaneous melanomas

Early detection of lesions while minimising the unnecessary removal of benign lesions is the clinical aim in melanoma diagnosis. In this context, several non-invasive diagnostic modalities, such as dermoscopy, total body photography, and reflectance confocal microscopy have emerged in recent years aiming at increasing diagnostic accuracy. The main developments in this field are the integration of dermoscopy and digital photography into clinical practice.