Multi-wavelength imaging photoplethysmography for non-invasive and non-contact assessment of burn severity

We report a non-contact burn severity assessment system using the image-based photoplethysmography (IPPG) technique by fabricating a multi-wavelength imaging system. In this burn assessment system, four wavelengths (visible light wavelengths of 405 nm, 520 nm, 660 nm, and near-infrared wavelength of 940 nm) were used, and burn severity was identified based on the fact that each wavelength has different penetration depths. Each wavelength was set to irradiate with the same optical power (1 mW/cm²), and IPPG was acquired using images captured at 35 frames per second for wavelengths with different penetration depths. To measure burn severity, we created burn lesion models using hairless mice. For each degree of burn, we acquired images of the burn area at four different wavelengths, measured IPPG from the acquired images, and observed the signal change at each wavelength to evaluate burn severity. In addition, while monitoring the healing process, we observed that IPPG recovered as the blood flow in the tissue normalized. Through the results of this study, we expect that IPPG technology will be used not only as a non-contact technology to evaluate burn severity, but also as a new method to monitor the burn recovery process in real time.