Fluorescence fibre-optic confocal microscopy of skin in vivo: microscope and fluorophores

Fluorescent fibre-optic confocal characterization of in vivo epidermal changes in atopic eczema

BACKGROUND/AIMS

Fibre-optic confocal imaging (FOCI) allows non-invasive visualization of live skin in vivo. A contrast agent, a fluorophore, is injected into the dermis. FOCI images are horizontal optical sections with cellular resolution. The aim was to study in vivo epidermal changes and the cellular structure of keratinocytes in moderate to severe atopic eczema (AE).

METHODS

Eight patients with AE with active lesions on the forearms were studied and compared to a control group of six healthy individuals, and two cases of AE without activity. Fluorescein sodium was used as fluorophore. A hand-held fibre-optic laser scanner (Stratum^® ) was used. The study included morphometric analyses.

RESULTS

The confocal in vivo images identified characteristic features of epidermis and keratinocytes in active AE vs healthy skin controls. FOCI could non-invasively image acanthosis, spongiosis, and parakeratosis in AE. Epidermal oedema and micro-vesicles were visualized. Morphometry based on FOCI demonstrated 14% increased width of keratinocytes of atopic skin vs healthy controls. The epidermal structures and organization in distinctive cell layers were deviant as a result of the disease.

CONCLUSIONS

Fibre-optic confocal imaging can visualize essential epidermal structures of atopic eczema directly in vivo, in real-time, and with cellular resolution thus without disturbing the natural state of the skin. FOCI is primarily a research tool, but with a potential to become used in the clinic for non-invasive microscopic diagnosis of AE and monitoring of effect of therapies.

The exogenous fluorophore, fluorescein, enables in vivo assessment of the gastrointestinal mucosa via confocal endomicroscopy: optimization of intravenous dosing in the dog model

This study described the pharmacokinetics of the intravenous fluorophore, fluorescein, and aimed to evaluate its utility for use in upper gastrointestinal confocal endomicroscopy (CEM). Six healthy, mature, mixed-breed dogs were anesthetized and then dosed intravenously with fluorescein at 15 mg/kg. Blood samples were collected at predetermined time-points. Dogs were examined by upper gastrointestinal confocal endomicroscopy and monitored for adverse effects. Plasma fluorescein concentrations were measured using high-performance liquid chromatography (HPLC) with UV/Vis detection. Mean plasma concentration at 5 min was 57.6 ± 18.2 mg/L, and plasma concentrations decreased bi-exponentially thereafter with a mean concentration of 2.5 mg/L ± 1.26 at 120 min. Mean terminal plasma elimination half-life (t½β ) was 34.8 ± 8.94 min, and clearance was 9.1 ± 3.0 mL/kg/min. Apparent volume of distribution at steady-state was 0.3 ± 0.06 L/kg. Fluorescein provided optimal fluorescent contrast to enable in vivo histologically equivalent evaluation of topologic mucosal morphology within the first 30 min following intravenous administration. Adverse effects were not observed. Based upon the calculated clearance, a constant rate infusion at a rate of 0.18 mg/kg/min is predicted to be adequate, following an initial loading dose (2 mg/kg), to maintain plasma concentration at 20 mg/L for optimal CEM imaging during the study period.

The use of reflectance confocal microscopy for monitoring response to therapy of skin malignancies

SUMMARY

Reflectance confocal microscopy (RCM) is a new non-invasive imaging technique that enables visualizing cells and structures in living skin in real-time with resolution close to that of histological analysis. RCM has been successfully implemented in the assessment of benign and malignant lesions. Most importantly, it also enables monitoring dynamic changes in the skin over time and in response to different therapies, e.g., imiquimod, photodynamic therapy, and others. Given the often traumatic nature of skin cancer that affects both the physiology and the psychology of the patients, it is crucial to have methods that enable monitoring the response to treatment but that minimize the distress and discomfort associated with such process. This article provides a very brief overview of the fundamentals of RCM and then focuses on its recent employment as a monitoring tool in skin cancer and other pathologies that may require frequent follow-up.

Combining in vivo reflectance with fluorescence confocal microscopy provides additive information on skin morphology

BACKGROUND

Within the last decade, confocal microscopy has become a valuable non-invasive diagnostic tool in imaging human skin in vivo. Of the two different methods that exist, reflectance confocal microscopy (RCM) displays the backscattering signal of naturally occurring skin components, whereas fluorescence confocal microscopy (FCM) provides contrast by using an exogenously applied fluorescent dye.

METHODOLOGY

A newly developed multilaser device, in which both techniques are implemented, has been used to combine both methods and allows to highlight different information in one image. In our study, we applied the fluorophore sodium fluorescein (SFL) intradermally on forearm skin of 10 healthy volunteers followed by fluorescence and reflectance imaging.

RESULTS

In fluorescence mode the intercellular distribution of SFL clearly outlines every single cell in the epidermis, whereas in reflectance mode keratin and melanin-rich cells and structures provide additional information. The combination of both methods enables a clear delineation between the cell border, the cytoplasm and the nucleus. Imaging immediately, 20, 40 and 60 minutes after SFL injection, represents the dynamic distribution pattern of the dye.

CONCLUSION

The synergism of RCM and FCM in one device delivering accurate information on skin architecture and pigmentation will have a great impact on in vivo diagnosis of human skin in the future.

Fluorescent fibre-optic confocal imaging of lesional and non-lesional psoriatic skin compared with normal skin in vivo

BACKGROUND/AIMS

Fibre-optic confocal imaging (FOCI) allows non-invasive visualization of live skin in vivo. A contrast agent, a fluorophore, is injected in the dermis. FOCI images are optical sections from a horizontal (en face) view. The aim was to study epidermis and the cellular structure of keratinocytes of psoriatic plaques and adjacent non-lesional with healthy skin as a reference.

METHODS

Twelve patients with stable plaque psoriasis were studied and compared with a control group of eight healthy individuals. Fluorescein sodium was used as fluorophore. A hand held fibre-optic laser scanner (Stratum(®); Optiscan Pty., Melbourne, Australia) was used. The study included morphometric analyses.

RESULTS

The confocal in vivo images demonstrated characteristic features of epidermis and keratinocytes in lesional and non-lesional skin vs. healthy skin. Morphometry based on FOCI demonstrated an approximately 30% increased width of keratinocytes of psoriatic skin vs. healthy control, and the number of keratinocytes per viewing field was reduced. FOCI allowed non-invasive visualization of cell nuclei and parakeratosis of psoriatic epidermis. The horizontal width of dermal papillae of psoriatic skin was increased by approximately 50% as compared with healthy skin, and the flow of erythrocytes in the papillar vessels could be observed in real-time.

CONCLUSION

FOCI can directly visualize essential epidermal structures of plaque psoriasis in vivo, in real-time and with cellular resolution without the need of taking biopsies and thus without disturbing the natural state of the skin. FOCI is a versatile future tool for non-invasive microscopic diagnosis and therapy follow-up of psoriasis.

Reflectance confocal microscopy for the evaluation of acute epidermal wound healing

The dynamic process of wound healing is routinely evaluated by clinical or histological evaluation. Recently, a number of non-invasive imaging techniques have been evaluated for their clinical applicability in dermatology. Among them, reflectance confocal microscopy (RCM) represents a non-invasive imaging technique that allows the in vivo characterization of the skin at near-histological resolution. The aim of this study was to monitor epidermal wound repair using RCM in a model of tissue damage induced by cryosurgery. For this purpose, contact cryosurgery was performed at -32 °C for 10 seconds on the volar forearm of five healthy volunteers. Clinical and RCM evaluations were performed at nine consecutive time points. RCM allowed the visualization of edema formation and blood vessel dilatation immediately after cryosurgery, as well as morphologic features of wound repair, including the formation of finger-like protusions of keratinocytes into the wound bed, the appearance of hairpin-like vessels, and inflammatory cells. This pilot study illustrates that RCM represents a promising technique for quasi-real-time monitoring the kinetics of wound repair non-invasively and over time, thus offering new insights into in vivo processes of cutaneous wound repair and angiogenesis, as well as potential effects of topically applied drugs on the process of tissue repair.

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.

Intradermal indocyanine green for in vivo fluorescence laser scanning microscopy of human skin: a pilot study

Background

In clinical diagnostics, as well as in routine dermatology, the increased need for non-invasive diagnosis is currently satisfied by reflectance laser scanning microscopy. However, this technique has some limitations as it relies solely on differences in the reflection properties of epidermal and dermal structures. To date, the superior method of fluorescence laser scanning microscopy is not generally applied in dermatology and predominantly restricted to fluorescein as fluorescent tracer, which has a number of limitations. Therefore, we searched for an alternative fluorophore matching a novel skin imaging device to advance this promising diagnostic approach.

Methodology/Principal Findings

Using a Vivascope®-1500 Multilaser microscope, we found that the fluorophore Indocyanine-Green (ICG) is well suited as a fluorescent marker for skin imaging in vivo after intradermal injection. ICG is one of few fluorescent dyes approved for use in humans. Its fluorescence properties are compatible with the application of a near-infrared laser, which penetrates deeper into the tissue than the standard 488 nm laser for fluorescein. ICG-fluorescence turned out to be much more stable than fluorescein in vivo, persisting for more than 48 hours without significant photobleaching whereas fluorescein fades within 2 hours. The well-defined intercellular staining pattern of ICG allows automated cell-recognition algorithms, which we accomplished with the free software CellProfiler, providing the possibility of quantitative high-content imaging. Furthermore, we demonstrate the superiority of ICG-based fluorescence microscopy for selected skin pathologies, including dermal nevi, irritant contact dermatitis and necrotic skin.

Conclusions/Significance

Our results introduce a novel in vivo skin imaging technique using ICG, which delivers a stable intercellular fluorescence signal ideal for morphological assessment down to sub-cellular detail. The application of ICG in combination with the near infrared laser opens new ways for minimal-invasive diagnosis and monitoring of skin disorders.

Robust optimal design of diffusion-weighted magnetic resonance experiments for skin microcirculation

Skin microcirculation plays an important role in several diseases including chronic venous insufficiency and diabetes. Magnetic resonance (MR) has the potential to provide quantitative information and a better penetration depth compared with other non-invasive methods such as laser Doppler flowmetry or optical coherence tomography. The continuous progress in hardware resulting in higher sensitivity must be coupled with advances in data acquisition schemes. In this article, we first introduce a physical model for quantifying skin microcirculation using diffusion-weighted MR (DWMR) based on an effective dispersion model for skin leading to a q-space model of the DWMR complex signal, and then design the corresponding robust optimal experiments. The resulting robust optimal DWMR protocols improve the worst-case quality of parameter estimates using nonlinear least squares optimization by exploiting available a priori knowledge of model parameters. Hence, our approach optimizes the gradient strengths and directions used in DWMR experiments to robustly minimize the size of the parameter estimation error with respect to model parameter uncertainty. Numerical evaluations are presented to demonstrate the effectiveness of our approach as compared to conventional DWMR protocols.

Clinical applicability of in vivo fluorescence confocal microscopy for noninvasive diagnosis and therapeutic monitoring of nonmelanoma skin cancer

Excisional biopsies and routine histology remains the gold standard for the histomorphologic evaluation of normal and diseased skin. However, there is increasing interest in the development of noninvasive optical technologies for evaluation, diagnosis, and monitoring of skin disease in vivo. Fluorescent confocal microscopy is an innovative optical technology that has previously been used for morphologic evaluation of live human tissue. We evaluate the clinical applicability of a fluorescent confocal laser scanning microscope (FLSM) for a systematic evaluation of normal and diseased skin in vivo and in correlation with routine histology. A total of 40 patients were recruited to participate in the study. Skin sites of 10 participants with no prior history of skin disease served as controls and to evaluate topographic variations of normal skin in vivo. Thirty patients with a suspected diagnosis of nonmelanoma skin cancer were evaluated, whereby FLSM features of actinic keratoses (AK) and basal cell carcinoma (BCC) were recorded in an observational analysis. Selected BCCs were monitored for their skin response to topical therapy using Imiquimod as an immune-response modifier. A commercially available fluorescence microscope (OptiScan Ltd., Melbourne, Australia) was used to carry out all FLSM evaluations. Common FLSM features to AK and BCC included nuclear pleomorphism at the level of the granular and spinous layer and increased vascularity in the superficial dermal compartment. Even though the presence of superficial disruption and mere atypia of epidermal keratinocytes was more indicative of AK, the nesting of atypical basal cells, increased blood vessel tortuosity, and nuclear polarization were more typical for BCC. All diagnoses were confirmed by histology. FLSM allowed a monitoring of the local immune response following therapy with Imiquimod and demonstrated a continuous normalization of diseased skin on repeated evaluations over time. This study illustrates potential applications of FLSM in clinical dermatology for the evaluation of dynamic skin conditions and monitoring of cutaneous response to noninvasive therapies. The findings are of preliminary nature and warrant further investigations in the future.

Diagnosis of nonmelanoma skin cancer/keratinocyte carcinoma: a review of diagnostic accuracy of nonmelanoma skin cancer diagnostic tests and technologies

BACKGROUND

Nonmelanoma skin cancer (NMSC) is the most prevalent cancer in the light-skinned population. Noninvasive treatment is increasingly used for NMSC patients with superficial lesions, making the development of noninvasive diagnostic technologies highly relevant.

OBJECTIVE

The scope of this review is to present data on the current state-of-the-art diagnostic methods for keratinocyte carcinoma: basal cell carcinoma, squamous cell carcinoma, and actinic keratosis.

METHODS AND MATERIALS

MEDLINE, BIOSIS, and EMBASE searches on NMSC and physical and clinical examination, biopsy, molecular marker, ultrasonography, Doppler, optical coherence tomography, dermoscopy, spectroscopy, fluorescence imaging, confocal microscopy, positron emission tomography, computed tomography, magnetic resonance imaging, terahertz imaging, electrical impedance and sensitivity, specificity, and diagnostic accuracy.

RESULTS

State-of-the-art diagnostic research has been limited in this field, but encouraging results from the reviewed diagnostic trials have suggested a high diagnostic accuracy for many of the technologies. Most of the studies, however, were pilot or small studies and the results would need to be validated in larger trials.

CONCLUSIONS

Some of these new imaging technologies have the capability of providing new, three-dimensional in vivo, in situ understanding of NMSC development over time. Some of the new technologies described here have the potential to make it from the bench to the clinic.

In vivo confocal scanning laser microscopy: comparison of the reflectance and fluorescence mode by imaging human skin

Optical, noninvasive methods have become efficient in vivo tools in dermatological diagnosis and research. From these promising imaging techniques, only the confocal scanning laser microscopy (CSLM) provides visualization of subsurface skin structures with resolutions similar to those of light microscopy. Skin annexes, as well as cutaneous cells from different epidermal layers, can be distinguished excellently. Currently, two forms of application have been established in dermatological practice: the reflectance mode, predominantly in the clinical field, and the fluorescence mode in dermatological research. Differences in both methods exist in the preparative protocol, in maximum imaging depth and, particularly, in the gain of contrast extraction. The reflectance mode demonstrates naturally occurring tissue components, whereas the fluorescent CSLM achieves contrast by administering fluorescence dye, representing the dynamic distribution pattern of the dye's fluorescent emission. Therefore, the reflectance and fluorescent modes highlight various skin microstructures, providing dissimilar in vivo confocal images of the skin. This permits different predications and information on the state of the tissue. We report the advantages and disadvantages of both optical imaging modes. The comparison was drawn by scanning human skin in vivo. Representative images in varying depths were obtained and analyzed; preparation procedures are shown and discussed.

Spectrally encoded slit confocal microscopy

A simple and cost-effective method for real-time imaging in confocal microscopy is proposed. Spectrally encoded slit confocal microscopy (SESCoM) uses a spectral encoding technique together with a confocal slit aperture to achieve two-dimensional images. Simulation and experimental results of the SESCoM's axial and lateral performances are presented. The measured FWHM of the axial response is 1.15 mum when an objective with a NA of 0.95 is used. FWHMs of the lateral line spread functions are measured to be 236 and 244 nm along the x and y directions, respectively. Both the axial and the lateral experimental results agree well with the simulation results.