Hemodynamics in traumatic bruises assessed by diffuse reflectance spectroscopy and photothermal radiometry

Assessment of bruise age in forensic investigations is based on skin discoloration due to dynamic processes involving extravasated hemoglobin and products of its biochemical decomposition. However, the current protocol relies exclusively on visual inspection and subjective assessment by a medical expert. We are aiming at development of an objective and more accurate approach to aging of bruises by utilizing two optical techniques: Diffuse reflectance spectroscopy (DRS) and pulsed photothermal radiometry (PPTR). This report involves two human volunteers with bruises acquired incidentally at a known time point. DRS spectra in visible spectral range are obtained from laterally uniform lesion sites using an integrating sphere. PPTR measurements involve irradiation with a millisecond laser pulse at 532 nm and recording the resulting transient change of mid-infrared emission with a fast infrared camera. Data from both measurements are analyzed simultaneously by fitting with predictions from a dedicated numerical simulation of light and heat transport in a multi-layer model of human skin. The results show a prominent increase of the dermal hemoglobin content and reduction of its oxygenation level relative to a nearby intact site (resulting from blood extravasation), followed by a rise of the bilirubin content. The parameters of a simple dynamical model of a self-healing bruise are then assessed by fitting together a set of experimental data acquired at different times post injury. The results indicate a rise and subsequent decrease of the hemoglobin decomposition rate, as the inflammatory response first kicks in and then gradually subsides.