Comparison of Features in Laser Doppler Vibrometry Spectra That Best Relate to the Degree of Stenosis

Stroke is a major cause of morbidity and mortality worldwide with carotid stenosis established as one of its leading culprits. Clinical practice relies primarily on duplex ultrasound (DUS) for the diagnosis of carotid stenosis due to its several advantages over existing modalities. Nevertheless, population-wide screening could benefit from a portable, and user-friendly device. In the context of assessing the potential of Laser Doppler vibrometer (LDV) for stenosis screening, this study aims at exploring and evaluating the performance of several spectral features that best relate to severe stenosis. An in-vitro setup has been employed for the current investigation with stenosis degree determined using a clamp. Progressive clamping and broadening observed in DUS spectra were considered as references indicating the occurrence and increase in flow instability due to the (increasing) stenosis. We recorded 3 cm downstream of the stenosis, inside-tube DUS spectra as well as direct wall vibration spectra by LDV for several graded constrictions. We investigated 10 distinct spectral features to capture spectral broadening. Present findings showed overall broader spectra for stenosis compared to control measurements, with broadening being proportional to stenosis degree. Spectral entropy - reflecting the spectral irregularity and the shift in the frequency content of LDV signal toward higher frequencies - exhibited superior performance over the other spectral features for indicating the presence of severe stenosis.