The propagation behavior of the arterial pulse wave may provide valuable diagnostic information for cardiovascular pathology. Pulse Wave Imaging (PWI) is a noninvasive, ultrasound imaging-based technique capable of mapping multiple wall motion waveforms along a short arterial segment over a single cardiac cycle, allowing for the regional pulse wave velocity (PWV) and propagation uniformity to be evaluated. The purpose of this study was to improve the clinical utility of PWI using a conventional ultrasound system. The tradeoff between PWI spatial and temporal resolution was evaluated using an ex vivo canine aorta (n = 2) setup to assess the effects of varying image acquisition and signal processing parameters on the measurement of the PWV and the pulse wave propagation uniformity r2. PWI was also performed on the carotid arteries and abdominal aortas of 10 healthy volunteers (24.8 ± 3.3 y.o.) to determine the waveform tracking feature that would yield the most precise PWV measurements and highest r2 values in vivo. The ex vivo results indicated that the highest precision for measuring PWVs ~ 2.5 – 3.5 m/s was achieved using 24–48 scan lines within a 38 mm image plane width (i.e. 0.63 – 1.26 lines/mm). The in vivo results indicated that tracking the 50% upstroke of the waveform would consistently yield the most precise PWV measurements and minimize the error in the propagation uniformity measurement. Such findings may help establish the optimal image acquisition and signal processing parameters that may improve the reliability of PWI as a clinical measurement tool.

The aortic stiffness has been found to be a useful independent indicator of several cardiovascular diseases such as hypertension and aneurysms. Existing methods to estimate the aortic stiffness are either invasive, e.g. catheterization, or yield average global measurements which could be inaccurate, e.g., tonometry. Alternatively, the aortic pulse wave velocity (PWV) has been shown to be a reliable marker for estimating the wall stiffness based on the Moens–Korteweg (M–K) formulation. Pulse Wave Imaging (PWI) is a relatively new, ultrasound-based imaging method for noninvasive and regional estimation of PWV. The present study aims at showing the application of PWI in obtaining localized wall mechanical properties by making PWV measurements on several adjacent locations along the ascending thoracic to the suprarenal abdominal aortic trunk in its intact vessel form. The PWV estimates were used to calculate the regional wall modulus based on the M-K relationship and were compared against conventional mechanical testing. The findings indicated that for the anisotropic aortic wall, the PWI estimates of the modulus are smaller than the circumferential modulus by an average of −32.22% and larger than the longitudinal modulus by an average of 25.83%. Ongoing work is focused on the in vivo applications of PWI in normal and pathological aortas with future implications in the clinical applications of the technique.

Abstract-The amplitude, velocity, and morphology of the arterial pulse wave may all provide valuable diagnostic information for cardiovascular pathology. Pulse Wave Imaging (PWI) is an ultrasound-based method developed by our group to noninvasively visualize and map the spatio-temporal variations of the pulse wave-induced vessel wall motion. Because PWI is capable of acquiring multiple wall motion waveforms successively along an imaged arterial segment over a single cardiac cycle in vivo, the regional morphological changes, amplitudes, and velocity (i.e. pulse wave velocity, or PWV) of the pulse wave can all be evaluated. In this study, an ex vivo setup was used to assess the effects of varying PWI image acquisition variables (beam density/frame rate and scanning orientation) and signal processing methods (beam sweep compensation scheme and waveform feature tracking) on the PWV estimation in order to validate the optimal parameters. PWI was also performed on the carotid arteries and abdominal aortas of six healthy volunteers for identification of several salient features of the waveforms over the entire cardiac cycle that may aid in assessing the morphological changes of the pulse wave. The ex vivo results suggest that the PWI temporal resolution is more important for PWV estimation than the PWI spatial resolution, and also that the reverse scanning orientation (i.e. beam sweeping direction opposite the direction of fluid flow) is advantageous due to higher precision and less dependence on the frame rate. In the in vivo waveforms, the highest precision PWV measurements were obtained by tracking the 50% upstroke of the waveforms. Finally, the dicrotic notch, reflected wave, and several inflection points were qualitatively identified in the carotid and aortic anterior wall motion waveforms and shown in one representative subject.