Morpho-molecular characterization of a tattooed skin biopsy using co-localized line-field confocal optical coherence tomography (LC-OCT) and confocal Raman microspectroscopy

Abstract

Line-field confocal optical coherence tomography (LC-OCT) is an optical technique generating three-dimensional (3D) images of the skin at cellular resolution. Confocal Raman microspectroscopy (CRM) is an optical modality that provides a point-wise molecular fingerprint of samples. We have developed a method to co-localize data acquired by separate LC-OCT and CRM systems. LC-OCT allows for recording 3D morphological overview images in which points of interest (POIs) can be localized for molecular analysis using CRM. A biopsy of skin with a red-colored tattoo with unknown ink composition was analyzed using co-localized LC-OCT and CRM. After acquisition of a 3D LC-OCT image, specific POIs were targeted inside the biopsy, based on their morphological features: POIs located in the epidermis where no ink was expected to be found as well as POIs located in bright areas of the dermis, down to 275 μm in depth, likely indicating the presence of tattoo ink. Analysis of the spectra at these specific POIs confirmed the absence of tattoo ink in the epidermis and its presence in the bright areas in the dermis. A stronger molecular signal of ink in the brightest areas of the dermis identified with LC-OCT was also revealed, suggesting a higher amount of ink. The combination and co-localization of LC-OCT and CRM brings a new level of characterization of the skin, enabling molecular analysis of POIs based on their morphological aspect at cellular-resolution within a volume, which could be of great interest in dermatology and dermo-cosmetics.