Applications and Future Directions for Optical Coherence Tomography in Dermatology

B. Wan; C. Ganier; X. Du-Harpur; N. Harun; F.M. Watt; R. Patalay; M.D. Lynch

Disclosures

The British Journal of Dermatology. 2021;184(6):1014-1022. 

In This Article

Abstract and Introduction

Abstract

Optical coherence tomography (OCT) is a noninvasive optical imaging method that can generate high-resolution en face and cross-sectional images of the skin in vivo to a maximum depth of 2 mm. While OCT holds considerable potential for noninvasive diagnosis and disease monitoring, it is poorly understood by many dermatologists. Here we aim to equip the practising dermatologist with an understanding of the principles of skin OCT and the potential clinical indications. We begin with an introduction to the technology and discuss the different modalities of OCT including angiographic (dynamic) OCT, which can image cutaneous blood vessels at high resolution. Next we review clinical applications. OCT has been most extensively investigated in the diagnosis of keratinocyte carcinomas, particularly basal cell carcinoma. To date, OCT has not proven sufficiently accurate for the robust diagnosis of malignant melanoma; however, the evaluation of abnormal vasculature with angiographic OCT is an area of active investigation. OCT, and in particular angiographic OCT, also shows promise in monitoring the response to therapy of inflammatory dermatoses, such as psoriasis and connective tissues disease. We additionally discuss a potential role for artificial intelligence in improving the accuracy of interpretation of OCT imaging data.

Introduction

Optical coherence tomography (OCT) is a noninvasive optical imaging method that can generate high-resolution en face and cross-sectional images of the skin and cutaneous vasculature in vivo to a maximum depth of 2 mm (Figure 1A, D). While OCT holds considerable promise for noninvasive diagnosis and disease monitoring, it is poorly understood by many dermatologists. Here, our goal is to equip the practising dermatologist with an understanding of the principles of skin OCT and the potential clinical indications.

Figure 1.

Optical coherence tomography (OCT): illustrations, principle and OCT images from different skin anatomical areas. (A) Illustration of an optical coherence tomography device (a), scanning a healthy donor's skin (b) using a probe detector (c). (B) OCT imaging systems operate according to the physical principle of low-coherence interferometry in two dimensions (a). Interferometry refers to the process of projecting coherent light waves onto the tissue specimen and measuring the delay (τ) and the intensity [I(τ)] of its echo (b). (C) An analogy can be made to the complex patterns of constructive and destructive interference that are observed in waves of water. Two waves are said to be coherent when the phase of the wave is synchronous. (D) Two-dimensional OCT images representing skin structure of different skin anatomical areas: abdomen (a), back (b), forearm (c), palm (d), lip (e), nose (f), ear (g) and forehead (h) from a 37-year-old healthy donor. Scale bar = 500 μm.

As skin is an accessible organ, noninvasive diagnosis has long been a goal of dermatologists. For centuries, visual inspection was the main guide to diagnosis, and more recently dermoscopy has assumed a prominent role. In recent decades, a number of additional approaches have emerged permitting noninvasive evaluation of the skin. These can broadly be divided into point probe devices and those that generate images. Apart from high-frequency ultrasound, most imaging techniques have been optically based. These include OCT,[1] reflectance confocal microscopy (RCM),[2] hyperspectral imaging,[3] optoacoustic imaging,[4] coherent anti-Stokes Raman scattering imaging,[5] terahertz imaging[6] and multiphoton microscopy imaging.[7] The most pervasive imaging technologies currently used in clinical practice are RCM and OCT.

The ideal noninvasive imaging device would have unlimited imaging depth and subcellular resolution equivalent to histological images. However, current techniques must balance between depth and resolution (Table 1). For example, high-frequency ultrasound (HFUS) has the greatest imaging depth but the lowest image resolution of the modalities currently applied to skin imaging. Similarly, RCM can achieve 'cellular resolution', but the depth of imaging is restricted to the epidermis and superficial (papillary) dermis.[8] Although a number of OCT variants exist, they lie between HFUS and RCM. The unique advantage of OCT is that it is noncontact. It achieves high axial resolutions of 3–15 μm with penetration depth of 0·4–2 mm,[9] which renders it useful for defining structural boundaries but not at a cellular resolution.

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