The Abdominal Aortic Aneurysm (AAA) is a silent and often deadly vascular disease caused by the localized weakening of the arterial wall. Previous work has shown that local changes in wall stiffness can be detected with Pulse Wave Imaging (PWI), which is a noninvasive technique for tracking the propagation of pulse waves along the aorta at high spatial and temporal resolutions. This study aims at assessing the capability of PWI to monitor and stage AAA progression in a murine model of the disease. ApoE/TIMP-1 knockout mice (N = 18) were given angiotensin II for 30 days via subcutaneously implanted osmotic pumps. The suprarenal sections of the abdominal aortas were imaged every 2-3 days after implantation using a 30 MHz Visualsonics Vevo 770 with 115 μm lateral resolution. Pulse wave propagation was monitored at an effective frame rate of 8 kHz by using retrospective electrocardiogram (ECG) gating and by performing 1-D cross-correlation on the radio-frequency (RF) signals to obtain the displacements induced by the waves. In normal aortas, the pulse waves propagated at constant velocities (2.8±0. 9 m/s, r2 = 0.89±0.11), indicating that the composition of these vessels was relatively homogeneous. In the mice that developed AAAs (N = 10), the wave speeds in the aneurysm sac were 45% lower (1.6±0.6 m/s) and were more variable (r2 = 0.66±0.23). Moreover, the wave-induced wall displacements were at least 80% lower within the sacs compared to the surrounding vessel. Finally, in mice that developed fissures (N = 5) or ruptures (N = 3) at the sites of their AAA, higher displacements directed out of the lumen and with no discernible wave pattern (r2 < 0.20) were observed throughout the cardiac cycle. These findings show that PWI can be used to distinguish normal murine aortas from aneurysmal, fissured, and ruptured ones. Hence, PWI could potentially be used to monitor and stage human aneurysms by providing information complementary to standard B-modes.

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