Structured light imaging mesoscopy: application to skin changes in scleroderma

Scleroderma is a chronic, autoimmune disorder, characterized by the fibrosis of skin and internal organs. The extent of skin fibrosis is a good predictor of disease severity and mortality. Structured light imaging mesoscopy (SLIM) is a noncontact and label-free imaging technique that requires minimal postprocessing and no inverse model. SLIM may provide improved disease diagnosis and monitoring of scleroderma.

We aim to evaluate SLIM as a new optical method to assess skin involvement in scleroderma.

SLIM measurements were collected from 25 scleroderma patients and 18 healthy controls across a range of spatial frequencies and wavelengths to find the optimal imaging parameters across skin tones. Monte Carlo simulations were conducted on a multilayer skin model that mimicked known biological changes in scleroderma.

Clinical data and simulations show that optimal spatial frequency ( $f_x$ ) and spectral ( $\lambda$ ) imaging parameters for scleroderma monitoring lie in the range of $f_x=0.15$ to $0.2{\mathrm{mm}}^{-1}$ and $\lambda =811$ to 851 nm, irrespective of subject skin tone. SLIM measurements taken with these parameters provided discrimination of scleroderma from healthy skin with an area under the curve of $\ge 0.87$ . We hypothesize that these changes correspond to changes in dermal collagen.

SLIM can be used as a quantitative and objective method to assess skin involvement in scleroderma. The optimal imaging parameters target the relevant depths of the skin, making it sensitive to biological changes in scleroderma.