Ultrasonic investigation of bones with different post-mortem intervals

In the interest of constantly improving their diagnoses, the experts in forensic anthropology of the french Gendarmerie Nationale are interested in new evaluation methods to estimate post- mortem interval (PMI) of human bone. Indeed, currently used physico-chemical methods based on Nile Blue colorimetry allow to estimate PMI up to 30 years. However, the prescription period is 20 years and the desired estimation must be less than this delay. The development of non-destructive methods would allow coupling PMI estimations of different methods without alteration of the sample and thus improving accuracy. There are several studies validating the use of ultrasonic waves for the structural characterization of bones in medical applications. The objective of this work is therefore the implementation of non-destructive ultrasonic evaluation techniques to determine whether wave parameters allowing the estimation of PMI emerge from structural variations between individuals. Firstly, this paper studies the wave propagation along the main axis of the bone. In collaboration with the Institut de Recherche Criminelle de la Gendarmerie Nationale (IRCGN), the experiments were performed on bone samples with different PMI using (1) contact transducers (1 MHz center frequency) for the measurement of acoustic signature in transmission mode and (2) a laser vibrometer for monitoring the propagation of the generated waves. Preliminary results show that the acoustic signatures make possible to monitor the structural changes of bone. Secondly, the problem of extracting relevant characteristic parameters of bones arises when taking into account the composition and the internal architecture that change from one individual to another and for which storage conditions and ageing are variable. Statistical study on a large number of individuals should make it possible to define the robustness of the parameters selected for the estimation of the PMI.