In vivo optical coherence tomography imaging of human skin: norm and pathology

Background/aims: Since the majority of skin diseases are known to be accompanied by structural alterations, research efforts are focused on the development of various novel diagnostic techniques capable of providing in vivo information on the skin structure. An essential parameter here is spatial resolution. In this paper we demonstrate the capabilities of optical coherence tomography (OCT) in detecting in vivo specific features of thin and thick skin. A particular focus is made on the identification of OCT patterns typical of certain pathological processes in skin, by performing parallel histological and tomographical studies. Methods: To obtain images of the skin, we used a compact fiber OCT system developed at the Institute of Applied Physics of the Russian Academy of Sciences. A low coherence source (superluminescent diode) operated at a wavelength of 1280 nm; the output power was 0.5–2 mW. This power is low enough to conform to the ANSI safety standards for light exposure. The in‐depth resolution limited by the spectral bandwidth (40–50 nm) of the probing light was ～20 μm. The lateral resolution determined by the probe light focusing ranged from 15 to 30 μm. In this series of experiments the maximum depth of imaging did not extend beyond 1.5 mm. Obtaining images of skin regions 2–6 mm long took 2–4 s. OCT capabilities for imaging normal skin of different localization and some skin diseases were studied in 12 healthy volunteers and 24 patients. Results: OCT imaging of the skin can detect in vivo such general pathological reactions of the human body as active inflammation and necrosis. OCT is useful for in vivo diagnosis of some specific processes in the skin, including hyperkeratosis, parakeratosis and formation of intradermal cavities. OCT imaging is noninvasive and therefore allows frequent multifocal examination of skin without any adverse effects. OCT can perform monitoring of disease progress and recovery in the course of therapy. Morphometric studies, measurements of the depth and extension of skin pathology within the human body can be easily performed by OCT. Conclusions: OCT allows imaging of subsurface soft tissues with the spatial resolution of 15–20 μm, a resolution one order of magnitude higher than that provided by other clinically available noninvasive diagnostic techniques. An imaging depth of up to 1.5–2 mm, given by current OCT technology, is sufficient to examine the skin. Real time OCT imaging can provide information not only on the structure, but also on some specific features in the functional state, of tissues. OCT imaging is a noninvasive technique, i.e., OCT does not cause trauma and has no side effects since it utilizes radiation in the near infrared wavelength range at a power as low as 1 mW.     

In vivo determination of skin surface topography using an optical 3D device

BACKGROUND/PURPOSE: Topography of the skin surface is a mirror of the functional skin status. Therefore, its evaluation is of great interest for dermatological research. In the present study, a new optical measuring system was applied to evaluate human skin surface topography in vivo and non-invasively, in order to determine elastotic and mimic wrinkles dependent on age, body site and therapy. METHODS: The measurements were performed on the back (n=5), the flexor forearm (n=14) of volunteers in different age groups and on the face of women (n=4) participating in an anti-wrinkle study. The evaluation of the three-dimensional-profiles was performed determining skin surface parameters (mean roughness (R(a)), mean depth of roughness (R(z)), maximum roughness (R(m)) and waviness (W(t))) and applying Fourier analysis. RESULTS: Significant increases in all surface parameters were obtained on the forearms with increasing age. Differences between the surface topographies of forearm and back were only expressed by the waviness and the Fourier analysis. The treatment with botulinum Toxin A led to a diminution of mimic wrinkles as reflected by the furrow profiles. CONCLUSIONS: The results show a significant dependence of the skin surface topography on the age of the volunteer and the body site measured. Particularly the waviness, the Fourier analysis and the furrow profiles reflect such dependencies. The system used also fulfils the requirements for the testing of therapies, as was demonstrated by the reduction of mimic wrinkles after treatment with botulinum Toxin A.     

A novel image processing workflow for the in vivo quantification of skin microvasculature using dynamic optical coherence tomography

Background

Currently, imaging technologies that can accurately assess or provide surrogate markers of the human cutaneous microvessel network are limited. Dynamic optical coherence tomography (D‐OCT) allows the detection of blood flow in vivo and visualization of the skin microvasculature. However, image processing is necessary to correct images, filter artifacts, and exclude irrelevant signals. The objective of this study was to develop a novel image processing workflow to enhance the technical capabilities of D‐OCT.

Materials and methods

Single‐center, vehicle‐controlled study including healthy volunteers aged 18‐50 years. A capsaicin solution was applied topically on the subject's forearm to induce local inflammation. Measurements of capsaicin‐induced increase in dermal blood flow, within the region of interest, were performed by laser Doppler imaging (LDI) (reference method) and D‐OCT.

Results

Sixteen subjects were enrolled. A good correlation was shown between D‐OCT and LDI, using the image processing workflow. Therefore, D‐OCT offers an easy‐to‐use alternative to LDI, with good repeatability, new robust morphological features (dermal‐epidermal junction localization), and quantification of the distribution of vessel size and changes in this distribution induced by capsaicin. The visualization of the vessel network was improved through bloc filtering and artifact removal. Moreover, the assessment of vessel size distribution allows a fine analysis of the vascular patterns.

Conclusion

The newly developed image processing workflow enhances the technical capabilities of D‐OCT for the accurate detection and characterization of microcirculation in the skin. A direct clinical application of this image processing workflow is the quantification of the effect of topical treatment on skin vascularization.

     

High-resolution optical coherence tomography as a non-destructive monitoring tool for the engineering of skin equivalents

BACKGROUND: Three dimensional skin equivalents are widely used in dermatopharmacological and toxicological studies and as autologous transplants in wound healing. In pharmacology, there is tremendous need for monitoring the response of engineered skin equivalents to external treatment. Transplantation of skin equivalents for wound healing requires careful verification of their quality prior to transplantation. Optical coherence tomography (OCT) is a non-contact, non-destructive imaging technique for living tissues offering the potential to fulfill these needs. This work presents an analysis of OCT for high-resolution monitoring of skin equivalents at different stages during the culture process. METHODS: We developed a high-resolution OCT imaging setup based on a commercially available OCT system. A broadband femtosecond laser light source replaces the original superluminescence diode. Tomograms of living skin equivalents were recorded with an axial resolution of 3 mum and correlated with histology and immunofluorescence images. Comparison with standard low-resolution OCT is presented to emphasize the advantages of high-resolution OCT for this application. RESULTS: OCT is particularly able to distinguish between different layers of skin equivalents including stratum corneum, epidermal and dermal layer as well as the basement membrane zone. The high-resolution OCT scans correlate closely with two key benchmarks, histology and immunofluorescence imaging. CONCLUSIONS: This study clearly demonstrates the benefits of high-resolution OCT for identifying living tissue structure and morphology. Compared with the current gold standard histology, OCT offers non-destructive tissue imaging, enabling high-resolution evaluation of living tissue morphology and structure as it evolves.     

In vivo reflectance confocal microscopy: automated diagnostic image analysis of melanocytic skin tumours

Background In vivo reflectance confocal microscopy (RCM) has been shown to be a valuable imaging tool in the diagnosis of melanocytic skin tumours. However, diagnostic image analysis performed by automated systems is to date quite rare. Objectives In this study, we investigated the applicability of an automated image analysis system using a machine learning algorithm on diagnostic discrimination of benign and malignant melanocytic skin tumours in RCM. Methods Overall, 16 269 RCM tumour images were evaluated. Image analysis was based on features of the wavelet transform. A learning set of 6147 images was used to establish a classification tree algorithm and an independent test set of 10 122 images was applied to validate the tree model (grouping method 1). Additionally, randomly generated ‘new’ learning and test sets, tumour images only and different skin layers were evaluated (grouping method 2, 3 and 4). Results The classification tree analysis correctly classified 93.60% of the melanoma and 90.40% of the nevi images of the learning set. When the classification tree was applied to the independent test set 46.71 ± 19.97% (range 7.81–83.87%) of the tumour images in benign melanocytic skin lesions were classified as ‘malignant’, in contrast to 55.68 ± 14.58% (range 30.65–83.59%; t‐test: P < 0.036) in malignant melanocytic skin lesions (grouping method 1). Further investigations could not improve the results significantly (grouping method 2, 3 and 4). Conclusions The automated RCM image analysis procedure holds promise for further investigations. However, to date our system cannot be applied to routine skin tumour screening.     

In vivo morphological characterisation of skin by MRI micro-imaging methods

BACKGROUND/PURPOSE: Quantitative assessments in skin layers using images obtained with standard magnetic resonance imaging (MRI) sequences are limited, since the stratum corneum and dermis, the layers of most clinical interest, have low signal due to their short spin-spin relaxation, T2. METHODS: In the present work, different methods of MRI contrast, such as magnetisation transfer contrast (MTC), T1-weighting (where T1 is spin-lattice relaxation time), T2*-weighting (where T2* is the combination of T2 and magnetic field in-homogeneity effect) and chemical shift, were used. These techniques were combined with high-resolution MRI. RESULTS: We found that skin is a very MT active tissue, and MTC provides data enabling the evaluation of how the tissue in skin layers interacts with the interstitial fluids. Details obtained from high-resolution high-quality in vivo skin images with different contrast allowed for differentiation of skin layers, sub-layers and excellent correlation of MR data with known histological features and water constituent of skin layers. CONCLUSION: Combining MT and other MRI data employing other contrast mechanisms provides a superior non-invasive in vivo technique for visualisation and also quantitative assessment of the constituents of the stratum corneum, epidermis, papillary dermis, reticular dermis and hypodermis as major structural layers of the skin. This type of study can be extended to cutaneous disease states or skin ageing, where defects in water mobility, concentration and/or macromolecular structural changes are expected.     

In vivo study of skin mechanical properties in Raynaud''s phenomenon

BACKGROUND/AIM: Raynaud's phenomenon (RP) is usually the first symptom in patients with systemic sclerosis (SS) and may precede skin changes by several months or years. Non-invasive measurements of skin elasticity are very sensitive and appropriate for objective and quantitative evaluation of sclerodermatous skin. The aim of this study was to investigate and compare the mechanical properties of the skin in patients with primary, secondary, and suspected secondary RP. MATERIALS/METHODS: A total of 63 patients were studied. They were classified as having scleroderma-type nailfold capillary abnormalities--17 with indurative phase of scleroderma (group 1), nine with edematous phase of scleroderma (group 2), 18 with suspected secondary RP (group 3) and as having RP-type nailfold capillary abnormalities, 19 with primary RP (group 4). Thirty-nine sex- and age-matched healthy individuals with normal nailfold capillaroscopy pattern were also studied as controls. Mechanical properties of the skin were evaluated using a non-invasive suction device (Cutometer) equipped with a 2 mm probe. Measurements were performed over five anatomic regions: cheeks, volar forearms, wrists, hands, and proximal phalanx of the fingers. The skin mechanical parameters analyzed were distensibility (Uf), elasticity (Ua/Uf) and viscoelasticity (Uv/Ue). RESULTS: Most demonstrative changes were observed over volar forearms. Patients included in groups 1-3 were characterized by significantly lower Uf and higher Uv/Ue compared with patient group 4 and controls. Patient groups 1 and 2 showed significantly lower Ua/Uf, as well. There were no significant differences in skin mechanical parameters between patient group 4 and control group. CONCLUSION: Mechanical properties of the skin in patients with suspected secondary RP significantly differ from these in patients with primary RP and resemble those in patients with edematous phase of scleroderma. Our findings suggest that the non-invasive measurements of skin elasticity could be helpful in identifying patients with RP at risk of developing SS.     

In vivo characterization of minipig skin as a model for dermatological research using multiphoton microscopy

Minipig skin is one of the most widely used non-rodent animal skin models for dermatological research. A thorough characterization of minipig skin is essential for gaining deeper understanding of its structural and functional similarities with human skin. In this study, three-dimensional (3-D) in vivo images of minipig skin was obtained non-invasively using a multimodal optical imaging system capable of acquiring two-photon excited fluorescence (TPEF) and fluorescence lifetime imaging microscopy (FLIM) images simultaneously. The images of the structural features of different layers of the minipig skin were qualitatively and quantitatively compared with those of human skin. Label-free imaging of skin was possible due to the endogenous fluorescence and optical properties of various components in the skin such as keratin, nicotinamide adenine dinucleotide phosphate (NAD(P)H), melanin, elastin and collagen. This study demonstrates the capability of optical biopsy techniques, such as TPEF and FLIM, for in vivo non-invasive characterization of cellular and functional features of minipig skin, and the optical image-based similarities of this commonly utilized model of human skin. These optical imaging techniques have the potential to become promising tools in dermatological research for developing a better understanding of animal skin models, and for aiding in translational pre-clinical to clinical studies.     

Application of optical coherence tomography in non-invasive characterization of skin vascular lesions

Background: Optical coherence tomography (OCT) is a new non-invasive approach for real-time in vivo tissue characterization. A promising use of OCT can be the assessment of the architecture of lesions with some degree of inhomogeneities, such as vascular lesions. Knowledge of the size and depth of the vascular structures can be useful for the diagnosis and for choosing the best treatment.
Objective: The purpose of this study was to investigate a series of vascular lesions by means of OCT in order to obtain new insights into the non-invasive, pre-operative analysis of these lesions.
Methods: Seven vascular lesions were included in the study. Histopathological diagnosis showed two haemangiomas and one haemolymphangioma; the remaining four cases were classified as haemangiomas on the basis of their clinical appearance.
Results: In all lesions, OCT analysis was able to visualize different areas of the lesion from the horny layer to the dermis showing a clear image of the vascular proliferation. Specifically, oval to roundish signal-poor areas sharply demarcated by a surrounding signal-rich layer were observed in good correlation with histopathology.
Conclusion: The analysis of vascular lesions by OCT provides a new insight into non-invasive diagnosis and can be helpful in the selection of the most appropriate treatment.