Performance assessment and optimization of Pulse Wave Imaging (PWI) in ex vivo canine aortas and in vivo normal human arteries

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