Elsevier

Clinics in Dermatology

Volume 39, Issue 4, July–August 2021, Pages 624-634
Clinics in Dermatology

Optical coherence tomography

https://doi.org/10.1016/j.clindermatol.2021.03.008Get rights and content

Abstract

During the past decade, noninvasive imaging has emerged as a valuable tool in clinical dermatology and dermatologic research. Optical coherence tomography (OCT) is one such type of noninvasive imaging. OCT uses the principle of interferometry to produce real-time images. A low-power diode laser shines infrared light onto tissues, which reflects back to an optical fiber interferometer. Using time delay and the backscattered light intensity, a two-dimensional image akin to an ultrasound is rendered. We review the history, types, and modalities of OCT, plus the many applications of frequency domain, high definition, and dynamic OCT in practice, including its utility in diagnosis, monitoring, and grading disease severity in a variety of cutaneous conditions.

Introduction

During the past decade, noninvasive imaging has emerged as a valuable tool in clinical dermatology and dermatologic research. Optical coherence tomography (OCT) is one such type of noninvasive imaging. OCT first emerged around 1990, and its utility was initially described in a publication2 from the Massachusetts Institute of Technology at Cambridge, Massachusetts, USA.1, 2, 3 A low-power diode laser was used to shine infrared light of approximately 870 nm onto biologic tissues. Light was then reflected back to an optical fiber interferometer, which uses time delay and the backscattered light intensity to render a two-dimensional image akin to an ultrasound.2

Although OCT was initially applied to the field of ophthalmology, where it continues to be used in both research and clinical settings, its utility has been demonstrated across multiple fields. For example, OCT angiography is used to evaluate diabetic retinopathy, glaucoma, age-related macular degeneration, and retinal vascular disease.4,5 In cardiology, OCT enables in vivo visualization of coronary arteries with applications in assessing stenosis, gaining insight into the mechanism of stenosis and thrombosis, and as an adjunctive tool in percutaneous coronary interventions.6, 7, 8, 9 In neurology, it can be used to evaluate degenerative conditions such as multiple sclerosis by quantifying axonal loss, as well as other optic neuropathies, and as a potential tool to visualize the epidural space.10, 11, 12, 13, 14 It is also being investigated for its application in dentistry, renal disease, rheumatology, gynecology, and as an adjunct to histopathology both in vivo and ex vivo, among others.15, 16, 17, 18, 19, 20

The application of OCT in dermatology was first demonstrated in 1997,21 when it was used on the skin of healthy volunteers to obtain images from various body sites and to compare those images with corresponding tissue histopathology. OCT was able to identify the following21:

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    The layers of the skin, as well as their variable thickness by anatomic location

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    The nail structure distinguishing between plate, cuticle, proximal nail fold

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    The matrix, features of bullous disease by inducing blisters in volunteer subjects

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    The description of lentigo maligna

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    The isolation of the burrow caused by a scabies mite

Since the original description of OCT imaging in human skin, the technology has been used predominantly not only to aid in the diagnosis of nonmelanoma skin cancer, but also to evaluate a wide range of skin disorders, to provide a diagnosis in lieu of tissue biopsies, to suggest the mechanism of action of treatment modalities, and to monitor therapeutic responses. OCT can offer many advantages to patients and clinicians by obtaining diagnostic information in a painless, noninvasive manner in real time.

Section snippets

Types of OCT

Conventional swept-source multi-beam VivoSight frequency domain OCT (FD-OCT) scans (Michelson Diagnostics, Maidstone, Kent, UK) create cross-sectional (ie, b-scans, similar to histology), as well as en face images (akin to dermatoscopy) of target skin. Depth of penetration is up to 2 mm, allowing for visualization of the epidermis, dermis, skin appendages, and vessels.19 OCT resolution is 7.5 μm in the lateral direction and 5 μm in the axial direction, and the scan provides a 6 × 6-mm field of

Normal skin architecture

On conventional OCT, the stratum corneum often appears as a thin hyperreflective band on the skin's surface. If the skin of the palms or soles is being imaged, the band is thicker. HD-OCT has higher resolution and can provide improved en face images of the stratum corneum. The epidermis appears darker and more homogenous with a well-defined border toward the upper portion of the dermis. The layers of the epidermis are easier to appreciate on HD-OCT.28 The dermoepidermal junction (DEJ) appears

Skin neoplasms

Histopathology has long been the gold standard for diagnosing melanocytic lesions and nonmelanoma skin cancer. Currently, RCM has Category I Procedural Terminology codes for reimbursement comparable to a skin biopsy and is more suitable as a diagnostic tool30; however, given some limitations including a narrow field of view, shallow depth of penetration, and difficulty placing the larger probe of the RCM in anatomically challenging areas (eg, areas around the nose, eyes, and ears), OCT has

FD-OCT

A published review of studies using conventional OCT to diagnose basal cell carcinoma (BCC) summarized the characteristics of BCC in OCT images.28 The most commonly described features include dark ovoid tumor islands often surrounded by a dark, hyporeflective halo, alteration of the DEJ, well-circumscribed signal-poor areas, and dilated vessels (Figure 1).28,32,33

In addition to characterizing lesions, several studies have evaluated the ability of the VivoSight OCT scanner (Michelson

Melanoma

A recent Cochrane Review indicated that there is insufficient evidence to support using OCT in the diagnosis of melanoma51; however, there are preliminary studies that attempt to describe features of melanoma on OCT and determine its diagnostic accuracy for melanoma.

Detecting the vascular progression from dysplastic nevi to invasive melanomas may be aided by dynamic OCT, leading to earlier intervention.27 There are larger dermal vessels with characteristic curves in dysplastic nevi, scattered

FD-OCT

AKs appear as hyperechoic white streaks and dots superficially on the epidermis, corresponding with the hyperkeratotic scale (Figure 3). There is also epidermal thickening, disruption of normal skin architecture, and ill-defined borders at the DEJ.54 Squamous cell carcinoma (SCC) tends to feature a greater degree of epidermal thickening compared with AKs.35 AKs tend to be more hyperkeratotic than Bowen disease and SCC, and the degree of hyperkeratosis may hinder the ability of OCT to provide

Nail disease

Commonly used imaging for nail diseases include ultrasound, high-resolution MRI, and OCT. Although MRI can visualize the bone and soft tissue around the nail, the nail itself is difficult to visualize.57 OCT allows for a higher resolution and more detailed image of the nail when compared with ultrasound and MRI. It has become one of the preferred noninvasive imaging modalities for nail disease. Although RCM has a high resolution, given its limited depth at 200 μm and the normal nail thickness

Inflammatory dermatoses

One of the first studies using OCT to characterize inflammatory skin conditions was conducted in 2003 to investigate patients with psoriasis and irritant dermatitis and to evaluate the thickness of the epidermis and the signal attenuation coefficient in the upper portion of the dermis.67 A thicker epidermis in both psoriasis and irritant dermatitis was shown by OCT when compared with healthy control participants. A decreased signal attenuation was also observed and corresponded to inflammation

Bullous disease

One of the first studies investigating the application of OCT in dermatology provided evidence, in a small sample of patients, that OCT can visualize blisters and could differentiate the level at which the blisters were occurring within the skin.21 Studies have since emerged aiming to determine the value that OCT has in the diagnosis and management of specific bullous disease states.

One observational, retrospective study imaged patients with clinically evident bullous pemphigoid (BP) or

Vascular lesions

Newer OCT devices have the ability to analyze cutaneous vasculature with regard to depth, diameter, and density, allowing for the application to vascular lesions including port-wine stains (PWSs) and hemangiomas.75 The vessels can be viewed en face to provide information regarding the structure of the plexus in the superficial dermis and can produce measurements of diameter and depth of individual vessels. One of the first reports of the use of OCT for PWSs was published in 2001, where OCT was

Fibrosis

One of the applications of OCT in dermatology is its ability to visualize skin collagen, and increased skin collagen is indicative of fibrosis. With conventional OCT, as well as HD-OCT, D-OCT, and polarization-sensitive OCT, it is possible to leverage this principle and use the technology to detect fibrosis in skin diseases such as systemic sclerosis, lichen sclerosus et atrophicus, and various forms of scarring.19,79 Polarization-sensitive OCT measures and displays changes in the polarization

Acne and rosacea

Studies have also been conducted using OCT in the diagnosis and management of acne vulgaris.86, 87, 88, 89 Some of the variables measured included morphology, dermal blood flow, size and orientation of infundibulum, and presence of inflammatory infiltrate. One such study characterized 114 acne lesions.89 The study described closed comedo lesions as having two hypoechogenic structures with an enlarged infundibulum at the top of the lesion, creating a “reverse V-shaped morphology.” Open comedos

Limitations

OCT technology itself has some limitations and it is also limited by the experience of its operators. As with any emerging technology, certain applications of OCT are limited by the paucity of studies and small sample sizes investigated. In addition, most of the studies are conducted by investigators who are expert dermatoscopists and/or reflectance confocal microscopists, and therefore one must consider that the performance of OCT should not be interpreted as an isolated technology, but

Conclusions

In the past 2 decades, OCT has demonstrated promise as a noninvasive imaging device that adds value both to the patient and physician experience. In dermatology, nonmelanoma skin cancer has been the predominant application of this technology to date, and much of the research on OCT has assessed its diagnostic accuracy, ability to monitor response to treatment, and its utility as an adjunct perioperative tool. As interest in the device increases, additional applications are being explored, and

Acknowledgments

Dr. Guiseppina Abignano contributed the OCT images of psoriatic nails and systemic sclerosis.

Conflict of interest

The authors declare no conflict of interest.

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