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

• Published in: IEEE transactions on ultrasonics, ferroelectrics, and frequency control Vol. 69; no. 7; pp. 2248 - 2256
• Main Authors: Raj, Kiran V., Nabeel, P. M., Joseph, Jayaraj
• Format: Journal Article
• Language: English
• Published: United States IEEE 01.07.2022; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: A-mode; Accuracy; Arteries; Blood; Carotid arteries; Correlation coefficients; Feasibility; Frame design; image-free; Imaging; In vivo methods and tests; local pulse wave velocity (PWV); PWV; Radio frequency; radio frequency (RF); Real time; Real-time systems; Reproducibility; Stiffness; Transducers; transit time; Ultrasonic imaging; vascular aging; Wave velocity
• ISSN: 0885-3010; 1525-8955; 1525-8955
• DOI: 10.1109/TUFFC.2022.3172265

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 <inline-formula> <tex-math notation="LaTeX">=500 </tex-math></inline-formula> Hz, RF sampling rate <inline-formula> <tex-math notation="LaTeX">=125 </tex-math></inline-formula> MHz, LPF cutoff <inline-formula> <tex-math notation="LaTeX">=14 </tex-math></inline-formula> Hz, and order <inline-formula> <tex-math notation="LaTeX">=4 </tex-math></inline-formula>), the system yielded repeatable beat-to-beat measurements (variability <inline-formula> <tex-math notation="LaTeX">=1.9 </tex-math></inline-formula>% and over 15 cycles) and achieved a high accuracy (root-mean-square-error <inline-formula> <tex-math notation="LaTeX">=0.19 </tex-math></inline-formula> m/s and absolute-percentage-error <inline-formula> <tex-math notation="LaTeX">=2.4 </tex-math></inline-formula>%) 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 <inline-formula> <tex-math notation="LaTeX">>0.92 </tex-math></inline-formula>). 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.