Image-Free Fast Ultrasound for Measurement of Local Pulse Wave Velocity: In Vitro Validation and In Vivo Feasibility

Local pulse wave velocity (PWV), a metric of the target artery’s stiffness, has been emerging in its clinical value and adoption. State-of-the-art ultrasound technologies used to evaluate local PWV based on pulse waves’ features are sophisticated, non-real-time, and are not amenable for field and resource-constrained settings. In this work, we present an image-free ultrasound system to measure local PWV in real-time by employing a pair of ultrasound transducer elements. An
in vitro
study was performed on the arterial phantom to: 1) characterize the design aspects of the system and 2) validate its accuracy against beat-by-beat (invasive) local PWV measured by a reference dual-element catheter. Furthermore, a repeatability and reproducibility study on 33 subjects (21–52 years) investigated the in vivo measurement feasibility from the carotid artery. With the experimentally deduced optimal design (frame-rate
$=500$
Hz, RF sampling rate
$=125$
MHz, LPF cutoff
$=14$
Hz, and order
$=4$
), the system yielded repeatable beat-to-beat measurements (variability
$=1.9$
% and over 15 cycles) and achieved a high accuracy (root-mean-square-error
$=0.19$
m/s and absolute-percentage-error
$=2.4$
%) over a wide range of PWVs (2.7–11.4 m/s) from the phantom. Subsequently, on human subjects, the intra- and inter-operator PWV measurements were highly repeatable (intraclass correlation coefficient
$>0.92$
). The system does not impose a demand for special processors with high-computational power while offering real-time feedback on acquisition and measurement quality and provides local PWV online. Future large population and animal studies are required to establish the device’s clinical usability.