Figure 2

Image post-processing pathway. Examples of: raw PS-OCT B-scans for (a) structural (showing the layers of the skin beneath the surface) and (b) retardance images (birefringence manifests itself as observable skin heterogeneity and tissue organisation, heterogeneity here is due to the presence of structures such as sebaceous glands and hair follicles). Images (a) and (b) were generated in ThorImage 4.3; (c,d) Scans are registered to align slices and provide a horizontal skin surface. Registration is performed by smoothing each A-scan in the structural image and selecting the first peak as the skin-air boundary. The vertical alignment of each A-scan in the structural and birefringence images are then adjusted so the skin-air boundary lies in a horizontal line across the image (using bespoke software (written by the authors) in MATLAB (version R2020a, Mathworks Inc, Mass, USA)). This makes birefringence (retardance) analysis easier as rows of pixels in the registered images correspond to tissue of consistent depth beneath the skin. (e) A-scan [single pixel width depth profile] and (f) averaged A-scan taken across the B-mode image [i.e. averaging all the A-scans over the width of the image to give an averaged measure of where peaks reflected from layers with in the skin occur]. Epidermal thickness was defined as the distance between the depth at which the intensity of the first peak had reached half its maximum value (skin surface) and the depth at which the intensity of the second peak had reached half its maximum value (dermal–epidermal junction); marked as a red horizontal arrow. (g) Shows the cumulative retardance (phase change [radians]) plotted for skin depth (pixels) from skin surface to 100 pixels (shown without errors). The epidermal and dermal peak locations are shown as grey vertical lines. The gradient at the first 30 pixels from the dermal line (used to measure the differences between the groups) is indicated by the red line.