In-vivo Pulse Wave Imaging for arterial stiffness measurement under normal and pathological conditions

Numerous studies have identified arterial stiffening as a strong indicator of cardiovascular pathologies such as hypertension and abdominal aortic aneurysm (AAA). Pulse Wave Imaging (PWI) is a novel, noninvasive ultrasound-based method to quantify regional arterial stiffness by measuring the velocity of the pulse wave that propagates along arterial walls after each left ventricular contraction. The PWI method employs 1D cross-correlation speckle tracking to compute axial incremental displacements, then tracks the position of the displacement wave in the anterior wall of the vessel to estimate pulse wave velocity (PWV). PWI has been validated on straight tube aortic phantoms and aortas of healthy humans as well as normal and AAA murine models. This paper presents and compares preliminary PWI results from normal, hypertensive, and AAA human subjects. PWV was computed in select cases from each subject category. The measured PWV values in hypertensive (N = 5) and AAA (N = 2) subjects were found to be significantly higher than in normal subjects (N = 8). In all subjects, the spatio-temporal profile and waveform morphologies of the pulse wave were generated from the displacement data for visualization and qualitative evaluation of the pulse wave propagation. While the waveforms were found to maintain roughly the same shape in normal subjects, those in the AAA and most hypertensive cases changed drastically along the imaged aortic segment, suggesting non-uniform wall mechanical properties.