The value of ultrahigh resolution OCT in dermatology - delineating the dermo-epidermal junction, capillaries in the dermal papillae and vellus hairs

Abstract

Optical coherence tomography (OCT) imaging of the skin is gaining recognition and is increasingly applied to dermatological research. A key dermatological parameter inferred from an OCT image is the epidermal (Ep) thickness as a thickened Ep can be an indicator of a skin disease. Agreement in the literature on the signal characters of Ep and the subjacent skin layer, the dermis (D), is evident. Ambiguities of the OCT signal interpretation in the literature is however seen for the transition region between the Ep and D, which from histology is known as the dermo-epidermal junction (DEJ); a distinct junction comprised of the lower surface of a single cell layer in epidermis (the stratum basale) connected to an even thinner membrane (the basement membrane). The basement membrane is attached to the underlying dermis. In this work we investigate the impact of an improved axial and lateral resolution on the applicability of OCT for imaging of the skin. To this goal, OCT images are compared produced by a commercial OCT system (Vivosight from Michaelson Diagnostics) and by an in-house built ultrahigh resolution (UHR-) OCT system for dermatology. In 11 healthy volunteers, we investigate the DEJ signal characteristics. We perform a detailed analysis of the dark (low) signal band clearly seen for UHR-OCT in the DEJ region where we, by using a transition function, find the signal transition of axial sub-resolution character, which can be directly attributed to the exact location of DEJ, both in normal (thin/hairy) and glabrous (thick) skin. To our knowledge no detailed delineating of the DEJ in the UHR-OCT image has previously been reported, despite many publications within this field. For selected healthy volunteers, we investigate the dermal papillae and the vellus hairs and identify distinct features that only UHR-OCT can resolve. Differences are seen in tracing hairs of diameter below 20 μm, and in imaging the dermal papillae where, when utilising the UHR-OCT, capillary structures are identified in the hand palm, not previously reported in OCT studies and specifically for skin not reported in any other optical imaging studies.

Amplitude noise and coherence degradation of femtosecond supercontinuum generation in all-normal-dispersion fibers

“…Despite these obstacles, fs-pumped ANDi SC generation has received significant attention because of its ability to generate temporally coherent SC pulses; a feature that is unachievable in the anomalous dispersion regime. This gives such systems potential in a range of fields including optical coherence tomography (OCT), optical metrology, photo-acoustic imaging, and spectroscopy [6][7][8][9][10][11].…”

Noise of supercontinuum sources in spectral domain optical coherence tomography

“…The spectral characteristics of the employed light source are central in designing the OCT system, whose axial resolution is inversely proportional to the optical bandwidth of the employed source and directly proportional to the central wavelength squared, and in addition, the optical properties of the sample depend on the central wavelength too. For these reasons exactly, supercontinuum sources are increasingly applied in OCT due to their octavespanning, high-power spectra covering the visible and near-infrared spectral regions, which allow great freedom in tunability by filtering, both in terms of bandwidth and central wavelength [2][3][4][5]. However, most commercially available supercontinuum sources generate broadband light by non-linear amplification of quantum noise as well as strongly phase and amplitude dependent non-linear interactions between optical solitons.…”

Supercontinuum noise reduction by fiber undertapering

“…Supercontinuum sources have found applications in many fields due to their exceptional spectral bandwidth and brightness, despite their often poor noise properties compared to alternative choices. Recently, a lot of work has been carried out within the field of SC-based Spectral Domain Optical Coherence Tomography (SD-OCT), [3][4][5][6][7][8], with a focus on the visible and near infrared wavelength ranges of 500 − 800 nm and 1150 − 1450 nm. A common trend in the conclusions of this work is that there is a need for SC sources with lower noise, as the noise directly influences the background noise and thus both contrast and image quality.…”