Regional Upstroke Tracking for Transit Time Detection to Improve the Ultrasound-Based Local PWV Estimation in Carotid Arteries

Pulse wave velocity (PWV) is the most important index for quantifying the elasticity of an artery. The accurate estimation of the local PWV is of great relevance to the early diagnosis and effective prevention of arterial stiffness. In ultrasonic transit time-based local PWV estimation, the locations of time fiduciary point (TFP) in the upstrokes of the propagating pulse waves (PWs) are inconsistent because of the reflected waves and ultrasonic noise. In this study, a regional upstroke tracking (RUT) approach that involved identifying the most similar TFP-centered region in the upstrokes is proposed to detect the time delay for improving the local PWV estimation. Five RUT algorithms with different tracking points are assessed via simulation and clinical experiments. To quantitatively evaluate the RUT algorithms, the normalized root-mean-squared errors and standard deviations of the estimated PWVs are calculated using an ultrasound simulation model. The reproducibility of the five RUT algorithms based on 30 human subjects is also evaluated using the Bland-Altman analysis and coefficient of variation (CV). The obtained results show that the RUT algorithms with only three tracking points provide greater accuracy, precision, and reproducibility for the local PWV estimation than the TFP methods. Compared with the TFP methods, the RUT algorithms reduce the mean errors from 12.23% ± 3.10% to 7.13% ± 2.31%, as well as the CVs from 21.76% to 13.39%. In conclusion, the proposed RUT algorithms are superior to the TFP methods for local carotid PWV estimation.