Investigation of a noninvasive method for monitoring intracranial pressure using sheep skulls

Abstract

It has been previously demonstrated that resonance frequencies of fluid-filled shells of simple geometry are shifted in proportion to fluid pressure [J.Acoust. Soc. Am. 131, EL506 (2012)]. We investigate the applicability of this approach for measuring changes of intracranial pressure in ovine skulls. A catheter inserted through the foramen magnum of a complete sheep’s head enables the control of hydrostatic pressure, which is measured independently using a pressure transducer inserted into the parenchyma through a drilled hole in the skull. The vibrational response is measured using a small modal impact hammer to gently tap the skull with small accelerometers mounted at different locations on skull. Acceleration normalized by impact force is computed in the frequency domain, averaged over multiple taps. Significant peaks in the response spectrum are identified and associated with vibrational modes observed using a laser Doppler vibrometer. The consistency with which peaks shift in frequency in proportion to ICP is reported. The effect of tap location and accelerometer placement is also explored.