A 1600 nm optical coherence tomography platform for the assessment of skin inflammation caused by atopic dermatitis

Atopic dermatitis, or eczema, is a widespread chronic skin condition mainly treated with steroid creams, which can cause side effects such as skin thinning. Optical coherence tomography (OCT) allows for rapid non-invasive skin examination in the clinic. However, imaging depth at the popular 1300 nm wavelength is limited to similar to 1 mm due to scattering, making it difficult to assess severely inflamed skin. Skin optical properties, specifically scattering and absorption, vary with wavelength. Longer wavelengths centered at 1600 nm offer potential for deeper penetration due to lower scattering and minimal water absorption. Here we demonstrate a fiber-based, spectral-domain 1600 nm OCT system to study improvements in penetration depth in human skin. We use a supercontinuum laser source optimized for long-wavelength emission ranging from 1446 nm to 1694 nm to achieve high skin penetration depth, while maintaining an axial resolution of similar to 8-10 mu m in the tissue (for the refractive index ranging n = 1.35 to 1.55 for different skin layers). Our system sensitivity is -90 dB at an A-scan rate of 76 kHz and approximately 8 mW of optical power on the skin. Simultaneous B-scans from a semi-transparent tape and human skin were obtained at 1600 nm and 1300 nm wavelengths, demonstrating and quantifying improvements in the imaging depth.