Assessing the Stability of Aortic Aneurysms with Pulse Wave Imaging

Purpose: To assess whether the stability of murine aortic aneurysms is associated with the homogeneity of pulse wave propagation within the saccular wall. Materials and Methods: All animal procedures were approved by the institutional Animal Care and Use Committee. Apolipoprotein E and tissue inhibitor of metalloproteinases-1 knockout mice (n = 26) were infused with angiotensin II by using subcutaneously implanted osmotic pumps, with an additional control mouse used for histologic examination (n = 1). Pulse wave imaging (PWI) was performed just before infusion and 15 days after infusion by using 40-MHz ultrasonography at 8000 frames per second (with electrocardiographic gating). Aneurysm appearance on B-mode images was monitored every 2-3 days for 30 days. On the basis of B-mode images obtained after 30 days, aneurysms were deemed to have been unstable if they had ruptured; otherwise, they were deemed stable. Statistical significance was assessed by using two-tailed t tests. Results: In normal aortas, the pulse waves propagated at relatively constant velocities (mean 6 standard deviation, 2.8 m/sec +/- 0.9). Fifteen days after infusion, all mice had developed aneurysms, with significant (P < .001/12) changes in maximum anterior-posterior diameter (increase of 54.9% +/- 2.5) and pulse wave velocity (PWV) (decrease of 1.3 m/sec +/- 0.8). While there was no significant difference in these parameters (P = .45 for diameter and P = .55 for PWV) between stable aneurysms (n = 12) and unstable aneurysms (n = 14), the standard deviation of the high-resolution PWV was significantly higher (P < .001/12) in unstable aneurysms (5.7 m/sec +/- 1.6) than in stable ones (3.2 m/sec 6 0.9). Conclusion: High-resolution PWI was used to measure the local homogeneity of pulse wave propagation within the saccular wall, which is lower in unstable aneurysms than in stable ones. Hence, if proven to add additional information beyond size and appearance in human studies, PWI could potentially be used to assess the stability of aneurysms by providing information that is complementary to the anatomic data obtained with conventional B-mode imaging. (C) RSNA, 2016