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Finding bones by projection

Two Norwegian scientists have developed an NIR spectroscopy-based technique for identifying tiny bone fragments on complex surfaces such as forest floors.

Most dramatically, such bone fragments are located at crime scenes, but identifying bone fragments is also required in archaeology, medicine and food science, where the bones are not human. At the moment, locating bone fragments on complex surfaces involves manual inspection, which is obviously very time-consuming and means that fragments are often missed.

To produce a more convenient and accurate method, Bjørn Alsberg at the Norwegian University of Science and Technology in Trondheim turned to an analytical instrument he had developed a few years earlier. Known as the PryJector, this instrument combines hyperspectral imaging, a form of NIR spectroscopy that produces images in which every pixel contains spectral data, with chemometric modelling and back-projection.

The idea is to develop an NIR model for identifying a specific material based on its spectral signature and then use that model to locate the material in an image of a surface produced by the NIR hyperspectral camera. This image is then projected back onto the surface, with the regions of the image identified as containing the material of interest shown in a different colour, allowing the material to be physically located and extracted from the surface.

Locating bone fragments is clearly an ideal application for this instrument. So, together with his colleague Jørgen Rosveld, Alsberg first built an NIR model for identifying bone fragments on a forest floor, using fragments of chicken bone dispersed in a mixture of soil, sand, stones, leaves, moss and bark. When used with the PryJector, this model proved highly accurate at identifying the location of chicken bone fragments on this kind of complex surface. As they report in the Journal of Forensic Sciences, it was also flexible enough to identify bones of various ages, up to 60 years old, from various other animals, including a fox, bear, goose and seal.

Still, Alsberg thinks this method could be made even more flexible and useful by constructing the model from bones that have been chemically or physically altered in some way, such as by burning or being submerged in water. The method would also benefit from a portable version of the PryJector; at the moment, samples of the surface, such as the forest floor in a crime scene, would have to be brought into the laboratory for analysis.

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