Applying visible hyperspectral (chemical) imaging to estimate the age of bruises

Hyperspectral (chemical) imaging collects spectroscopic data in a two-dimensional spatial format. The potential application for the determination of the age of bruises is demonstrated and compared to reflectance probe spectrophotometry as well as photography. Blood was deposited on white cotton cloth or injected subcutaneously into pig skin to simulate a 'fresh bruise'. A mixture of blood and bile was used to simulate 'old' bruises. On the cloth background all the photographic methods clearly separated the two groups of samples (i.e. 'blood only' from 'blood plus bile'). However, on the pig skin the two groups could be separated by one of the photographic methods only. Separation of blood from blood and bile mixtures was obtained on the cloth and skin backgrounds using spectrophotometry and hyperspectral imaging. In a test using serial dilutions of blood and bile mixtures, the hyperspectral system performed slightly better than the spectrophotometer. The former also had the advantage of imaging a wider area and providing spatial data. Hyperspectral (chemical) imaging and spectrophotometry are superior to photography for the detection of bilirubin on a background of skin (due to the presence of yellow chromophores); this technology combined with mathematical analysis of the spectral data warrants further investigation.