Coloring the invisible – leveraging short wave infrared wavelengths to equitably visualize skin inflammation in real-time across the full spectrum of human pigmentation

Summary: Abstract Body: Visual and photographic assessment of disease in skin of color (SoC) is prone to misdiagnosis and underestimation of severity, as melanin’s strong absorption at visible (VIS) wavelengths (λs) masks cues like erythema. Shifting from conventional VIS and near-infrared (NIR) imaging λs to short-wave infrared (SWIR, λ=1–1.7 µm) may be more equitable for those with SoC, because melanin absorbs weakly in SWIR. Unlike VIS and NIR, SWIR penetrates deeper into skin and detects chromophores like lipid and water, which are relevant to inflammatory skin disease. However, while SWIR-sensitive cameras are available, they capture grayscale images that are no more useful than black-and-white VIS photos. To fully harness SWIR imaging’s potential, we need VIS-like color photography, where chromophore-specific absorption creates pathognomonic color differences. We developed multispectral imaging systems (MSI-SWIR) that map reflected light intensities at SWIR λs to RGB color channels, leveraging λ-related differences in chromophore absorption to make SWIR λs visible to the eye. Our first system used bulky halogen lamps and a motorized filter wheel to separate reflected light into specific SWIR λs, requiring subjects to stay still for several seconds to generate pseudocolor images. To overcome this limitation, our 2nd-gen system uses compact high-power SWIR LEDs with rapid electronic switching synchronized to camera frames, enabling real-time pseudocolor SWIR imaging. In lightly pigmented and SoC subjects, imperceptible wheals (23 subjects) formed by intradermal saline injection and subtle inflammatory acne lesions (9 subjects) were easily visualized by MSI-SWIR (with high contrast in SWIR pseudocolor regardless of pigmentation and poor contrast in VIS for SoC subjects). SWIR is a novel window into skin physiology that is insensitive to melanin, and thus SWIR-MSI may transform practice by providing an equitable tool for assessing skin inflammation. Ahmad Shafiullah¹, Anmol Jarang¹, Favour Akinjiyan¹, Leonid Shmuylovich¹ 1. Division of Dermatology, Department of Medicine, Washington University in St Louis, St. Louis, MO, United States. Bioinformatics, Computational Biology, and Imaging