Time-frequency analysis to detect bone fracture in impact biomechanics. Application to the thorax

François Gabrielli (1) , Damien Subit (1) , Erick Ogam (2) , Philippe Guillemain (2) , Richard Kent (3) , Catherine Masson (1)

1 LBA UMR T24 - Laboratoire de Biomécanique Appliquée
2 LMA - Laboratoire de Mécanique et d'Acoustique [Marseille]
3 Center for applied biomechanics

Experimental testing is a major source of data to quantify the tolerance of the human body to impact and to develop protection strategies. Correlating the time of rib fractures with the kinematics of the occupant and the action of safety systems would provide valuable data for assessing safety systems and developing injury risk functions. However, methods for determining rib fractures timing are not yet fully developed. Time history analysis of data from multiple strain gauges mounted directly to ribs is commonly used for this purpose, but this method is not very sensitive and the time and cost required to instrument the ribcage with more than 100 strain gauges is prohibitive for many applications. In this study a new approach based on time-scale analysis of signals obtained from piezoelectric transducers (PZT) is reported. A post-mortem human subject was instrumented with four PZT on ribs 3 and 7 bilaterally and exposed to lateral blunt impacts to the shoulder and the chest. The fractures were documented after each test, and a criterion was developed to process the PZT signals. The criterion consists in detecting in the PZT signal the onset of a high frequency transient generated by the fracture of a rib using the continuous wavelet transform. Two thresholds were successfully determined to detect fractures that occurred (1) on an instrumented rib, and (2) on the adjacent rib. Further development of this method should allow the detection of all rib fractures using only a few PZT.

Mots clés: Thorax; Impact; Wavelet analysis; Fracture detection; Piezoelectric transducer

Domaines: Ingénierie biomédicale

François Gabrielli, Damien Subit, Erick Ogam, Philippe Guillemain, Richard Kent, et al.. Time-frequency analysis to detect bone fracture in impact biomechanics. Application to the thorax. Medical Engineering & Physics, 2009, 31 (8), pp.952-958. ⟨10.1016/j.medengphy.2009.05.007⟩. ⟨hal-00849434⟩