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17 Feb 2004
Scientists in Norway develop a low-cost optical technique that determines the age of a bruise.
Forensic science could soon be benefiting from an optical system that can accurately determine the age of a bruise. Unveiled at Photonics West in January, Lise Randeberg and colleagues from the Norwegian University of Science and Technology in Trondheim, say their approach is safe, low-cost, fast and non-invasive.
The trained eye of a forensic expert usually gauges the age of a bruise but this approach has its drawbacks. “All the current methods are subjective and depend on the experience of the forensic expert,” Randeberg told OLE. “Studies show that visual evaluation of the age of bruises is very inaccurate. No objective, quantitative methods exist.”
Bruises are caused by trauma to the skin, which causes red blood cells to leak from vessels into the surrounding tissue. Randeberg explains that as the haemoglobin in the bruise breaks down, it produces several chromophores (such as bilirubin) which can be detected using optical spectroscopy.
The team uses an integrating sphere containing a light bulb to illuminate the skin with diffuse broadband light. A fiber optic spectrometer collects reflection spectra between 400 – 850 nm from the bruise and the normal skin adjacent to it. The set-up allows the researchers to monitor how the concentration of bilirubin, the average blood volume fraction and the average oxygenation in the bruise and the normal skin vary with time.
The researchers believe that, once optimized, their technique will be able to tell the age of the bruise in “days from injury”.
“So far, we have done a pilot project with 25 bruises and the results from these measurements are very promising,” said Randeberg. “We are able to quantify the amount of bilirubin in a bruise and find traces of bilirubin before it is visible to the naked eye. We are now working on an algorithm for aging bruises of unknown origin.”
Randeberg and colleagues are now planning a larger project and hope to examine bruises on extremities and in the thorax [chest] region.
“We are also planning a pilot project on pigs to do controlled experiments with a known impact – such as a baseball bat, hand or cane,” said Randeberg. “We will try to find a correlation between the visible injury and its cause. Forensic experts are often asked about the age and the cause of the injury. We will try to find an answer to both.”
Author
Jacqueline Hewett is news reporter on Optics.org and Opto & Laser Europe magazine.
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