Estimation of viscoelasticity of a carotid artery from ultrasound cine images and brachial pressure waveforms: Viscous parameters as a new index of detecting low plaque burden.

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Viscoelasticity may be an important physical index for diagnosing vascular diseases, but wall viscosity has received less attention than elasticity due to difficulties in measurement in clinical scenarios. In this study, viscoelastic parameters were estimated from the pressure diameter relationship using carotid artery ultrasound images and brachial artery pressure waveforms of the patients. Carotid artery diameter waveforms were obtained by analyzing wall motion in ultrasound cine images, and carotid pressure waveforms were estimated from brachial waveforms using a transfer function. The estimated viscoelastic parameters quantitatively agreed with the published data, and three viscous parameters (viscous index, energy dissipation ratio, and phase lag between pressure and diameter waveforms) showed good positive correlations with each other. No significant difference in wall elasticity was found between the no plaque (NP) and low plaque (LP) groups, whereas viscous parameters were lower in the NP group than the LP group. This result suggests that the viscous parameters may be a new mechanical index for detecting early atherosclerosis.