Using Wavelet Analysis to Distinguish Cavitation Acoustic Emissions From Blunt Impact Noise

Abstract

Cavitation has been shown to have implications for head injury, but currently there is no solution for detecting the formation of cavitation through the skull during blunt impact. The goal of this communication is to confirm the wideband acoustic wavelet signature of cavitation collapse, and determine that this signature can be differentiated from the noise of a blunt impact. A controlled, laser induced cavitation study was conducted in an isolated water tank to confirm the wide band acoustic signature of cavitation collapse in the absence of a blunt impact. A clear acrylic surrogate head was impacted to induce blunt impact cavitation. The bubble formation was imaged using a high speed camera, and the collapse was synched up with the wavelet transform of the acoustic emission. Wideband acoustic response is seen in wavelet transform of positive laser induced cavitation tests, but absent in laser induced negative controls. Clear acrylic surrogate tests showed the wideband acoustic wavelet signature of collapse can be differentiated from acoustic noise generated by a blunt impact. Broadband acoustic signal can be used as a biomarker to detect the incidence of cavitation through the skull as it consists of frequencies that are low enough to potentially pass through the skull but high enough to differentiate from blunt impact noise. This lays the foundation for a vital tool to conduct CSF cavitation research in-vivo.

Cavitation in blunt impact traumatic brain injury

“…The US Navy sponsored important early work on cavitation because it can occur on the trailing faces of propellors, damaging them (Plesset & Ellis 1955 ) and making them audible to the enemy (Mellen 1954 ). While cavitation noise may be problematic in combat, it is useful in the laboratory because it allows hydrophones to detect cavitation (Eckersley et al 2020 , 2021 ). In all circumstances, a decline in pressure relative to ambient conditions causes cavitation.…”

“…The pig skull is very thick so creating a port in it through which the cranial vault could be observed would be difficult. Cavitation due to impact has been detected acoustically in an intact cadaveric pig head (Eckersley et al 2021 ; Eckersley et al 2020 ). This measurement has not thus far been reported in a living pig, but it is feasible in theory.…”