Evaluation of Local Carotid Arterial Wall Stiffness Using Ultrasound and Applanation Tonometr
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Arterial wall stiffness is an important diagnostic parameter. The gold-standard method for assessing stiffness is the cfPWV technique. The method measures the time it takes the pressure pulse to travel between the carotid and femoral arteries. The corresponding average Young’s modulus is then obtained from the Moens–Korteweg equation, which requires estimates of mean arterial diameter, and wall thickness along the path between the measurement sites, as well as distance between them. The objective of this study was to determine the equivalent local stiffness of the carotid artery by combining deformation measurements from gated ultrasound with blood pressure recordings obtained using an applanation tonometer. The local Young’s modulus was then estimated using an extended Kalman filter. Three models were analyzed: a linear-elastic analytical model of a thin-walled cylinder under pressure, a corresponding thick-walled cylinder model, and a large-strain numerical formulation. The last two produced results that differed by only 1%, whereas the thin-walled model, underpinning the Moens-Korteweg equation coupled with the Bramwell-Hill equation, yielded nonphysical local values of Young's modulus. All models rely on the same simplifying assumptions: the vessel is modeled as a one-dimensional hollow cylinder, and the wall material is considered isotropic and linearly elastic, with layered structures and anisotropy neglected. Consequently, the resulting Young’s modulus is comparable to that obtained from the Moens–Korteweg equation. In both approaches, an effective value valid over the diastolic-to-systolic pressure range is determined. However, while the standard method provides an average over the two distant measurement sites, the proposed method delivers a local value at the point of interest. The inverse problem solver was first verified on synthetic data and then applied to 8 healthy volunteers. Based on these findings, the thick-walled cylinder model is recommended to assess local arterial stiffness.
