Multispectral Image Analysis of Bruise Age
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The detection and aging of bruises is important within clinical and forensic environments. Traditionally, visual and photographic assessment of bruise color is used to determine age, but this qualitative technique has been shown to be inaccurate and unreliable. Spectroscopy and multi-spectral imaging have demonstrated objectivity in identifying age-dependent features. However these devices are not well suited for clinical environments. The purpose of this study was to develop a technique to spectrally-age bruises that minimizes the filtering and hardware requirements while achieving acceptable accuracy. This approach will then be incorporated into a handheld, point-of-care technology that is clinically-viable and affordable. Sixteen bruises from elder residents of a long term care facility were imaged over time. A multi-spectral system collected images at 11 wavelengths ranging between 370-970 nm that corresponded to skin and blood chromophores. Normalized bruise reflectance (NBR)- defined as the ratio of optical reflectance coefficient of bruised skin over that of normal skin- was calculated for all bruises at all wavelengths. The smallest mean NBR, regardless of bruise age, was found at wavelength between 555 & 577nm suggesting that contrast in bruises are from the hemoglobin chromophores, and that they linger for a long duration. A contrast metric, based on the NBR at 460nm and 650nm, was found to be sensitive to age and requires further investigation. Overall, the study identified four key wavelengths that have promise to characterize bruise age. However, the high variability across bruises complicates the development of a handheld detection system until additional data is available.