Multispectral SWIR imaging for equitable pigmentation-insensitive assessment of inflammatory acne in darkly pigmented skin

Acne occurs in nearly 10% of the world’s population. While acne in lightly pigmented skin (LPS) appears as striking red pustules, in darkly pigmented skin (DPS) acne appears subtly as dark spots that visually overlap with background skin, resolved acne, and noninflammatory pigmented lesions. This visual ambiguity leads to systemic underestimation of severity and undertreatment of acne in DPS. To overcome these challenges, an equitable approach that assesses acne equally well in LPS and DPS is needed. Acne lesions have increased sebum and tissue water secondary to local inflammation. Unlike the visible spectrum, in the short-wave infrared (SWIR, 1000 to 1700nm) sebum and water have high optical absorption while melanin has low optical absorption. Thus SWIR imaging may enable equitable acne assessment. We developed a SWIR multispectral system (SWIR-MSI) that acquires images at 6 wavelengths (540, 650, 850, 1200, 1300, 1600nm) and generates pseudocolor visualizations by mapping SWIR wavelengths into RGB channels. Ex-vivo SWIR-pseudocolor images of sebum and water demonstrated that these constituents were distinguishable with different colors. We next enrolled DPS subjects with acne (n=8), 3 of which had dermatosis papulosa nigra (DPN, a noninflammatory pigmented lesion) (n=3), and hypothesized that SWIR-MSI would 1) provide higher contrast acne assessment than visible photography, and 2) differentiate acne from DPN. SWIR-MSI demonstrated significant qualitative and quantitative contrast enhancement over visible photography between acne and background skin. Furthermore in SWIR-MSI, low absorbing DPN was easily distinguishable from highly absorbing acne. These results suggest that SWIR-MSI may transform practice by enhancing diagnostic accuracy and severity assessment of inflammatory acne in diverse populations.