Colourimetric analysis of thermally altered human bone samples

Abstract

At this moment, no method is available to objectively estimate the temperature to which skeletal remains have been exposed during a fire. Estimating this temperature can provide crucial information in a legal investigation. Exposure of bone to heat results in observable and measurable changes, including a change in colour. To determine the exposure temperature of experimental bone samples, heat related changes in colour were systemically studied by means of image analysis. In total 1138 samples of fresh human long bone diaphysis and epiphysis, varying in size, were subjected to heat ranging from room temperature to 900 °C for various durations and in different media. The samples were scanned with a calibrated flatbed scanner and photographed with a Digital Single Lens Reflex camera. Red, Green, Blue values and Lightness, A-, and B-coordinates were collected for statistical analysis. Cluster analysis showed that discriminating thresholds for Lightness and B-coordinate could be defined and used to construct a model of decision rules. This model enables the user to differentiate between seven different temperature clusters with relatively high precision and accuracy. The proposed decision model provides an objective, robust and non-destructive method for estimating the exposure temperature of heated bone samples.

Phosphorescence of thermally altered human bone

“…Next to the retrieval of human skeletal remains, the photoluminescent characteristics can also be helpful when interpreting the degree of thermal destruction and thereby indicating the temperature that bone has been subjected to [1,3]. The estimated temperature that bone reached during a fire can be used to reconstruct the peri-and postmortem events and to substantiate the decision on whether samples are still eligible for molecular analysis, i.e., DNA-or isotope analysis [2,[6][7][8].…”

“…Being able to visually differentiate between the two emission pathways, namely, fluorescence with short-decay phosphorescence and long-decay phosphorescence, can be important for the interpretation of the photoluminescent properties of heated bone in case this feature is temperature dependent and might then even be useful for estimating the exposure temperature [3,6]. Due to the fact that it is currently unknown which emission pathway contributes to the observable heterogenous photoluminescence of thermally altered human bones and whether this is related to the exposure temperature, the long-decay phosphorescence of experimentally heated human bone sections was investigated.…”

Spectrophotometric Color Measurement to Assess Temperature of Exposure in Cortical and Medullar Heated Human Bones: A Preliminary Study

“…Spectrophotometric techniques avoid the subjectivity of color shade comparisons and utilize a white standard as reference with the same measurement conditions, and reproducibility of results has been successfully tested [ 23 , 24 ]. The main advantage of our study is that color measurement is performed directly on the bones, with no intermediate steps between sample and color measurements [ 22 ]. In addition, a major practical advantage of the contact spectrophotometric system used in this study is its portability, facilitating its routine use in practical forensic and anthropological cases.…”

“…High temperatures alter the chemical properties and structural integrity of bones through four stages: dehydration, decomposition, inversion, and fusion. Due to these changes, heat can produce fractures and bone will experiment measurable changes in dimensions, weight, porosity, crystallinity, and color [ 6 , 22 ]. Color bone changes due to heat are related to changes in the chemical composition of the organic components.…”

“…Krap et al [ 19 ] demonstrated that caution should be taken in visual temperature estimation of thermally induced color changes in bone and recommended further research to develop objective methods in order to achieve standard of scientific community. Other recent studies have proposed a range of methods to quantify color changes in heated bone samples, such as colorimetric, spectrophotometric, or spectrographic techniques [ 2 , 20 , 21 , 22 ].…”