Pulse wave imaging of human abdominal aortas in vivo

Vascular diseases (e.g., abdominal aortic aneurysm or, AAA) lead to changes in the regional aortic wall mechanical properties. Pulse-Wave Imaging (PWI) was previously developed by our group to map the pulse-wave propagation along the abdominal aorta of mice in vivo. In this study, the feasibility of PWI with real-time scanning is shown in human abdominal aortas in vivo. The abdominal aortas of five normal subjects and one AAA subject were scanned. A Sonix RP system (Ultrasonix Medical Corp., Burnaby, Canada) was employed with a phased array at 3.3 MHz. The beam density of the 2-D echograms was reduced to 32 beams in order to obtain a high frame rate of 180-260 Hz. The real-time scanning reduces the artifacts from respiration and transducer motion. The velocities of the aortic wall were estimated using RF-based speckle tracking. The sequences of PWI images visually depicted the propagation of the pulse wave along the aortic wall. The regional pulse-wave velocity (PWV) was measured and used to estimate the Young´s modulus of the aortic wall. In healthy volunteers (n=5), the propagation was relatively uniform, with a correlation coefficient of 0.97 plusmn 0.01 and a PWV of 3.73 plusmn 0.19 m/s. The Young´s modulus of the aortic wall was 79 plusmn 10 kPa. In the aneurysmal aorta, the propagation of the pulse wave was relatively nonuniform with lower correlation coefficients (r=0.65). The PWV and Young´s modulus of the aneurysmal aorta were both found to be higher than in the normal case. The PWI technique was successfully implemented in both normal and aneurysmal human abdominal aortas and shown to provide regional information on the mechanical properties of the aortic wall in vivo.