Introduction: Ultrasound wall tracking allows assessing the distension of superficial arteries. While the technique is well established in humans, wall tracking is challenging in mice due to the smaller size of the arteries. The aim of this study was to assess the feasibility of sequential distension measurements on the aorta of an aortic aneurysm mouse model.

Methods: In-house bred male ApoE −/− mice were implanted an osmotic pump filled with Angiotensin II. Ultrasound data were obtained with a high-frequency ultrasound apparatus equipped with a linear array probe. All measurements were performed by a single operator. M-mode images of proximal and distal abdominal aorta were obtained in 5 animals on day 1, 6, 14, 30 and 49. Dedicated software was employed for wall tracking using stored demodulated Radio Frequency (RF) data. Resulting curves were processed to calculate the diastolic diameter and the relative (DeltaD/D) arterial diameter distension.

Results: Proximal abdominal aorta diastolic diameter presented higher values than distal abdominal aorta, as expected. However, diameter values in both locations decreased through time, reaching a minimum at day 30. DeltaD/D progressively decreased from baseline until day 14 in both locations, after which values increased to near baseline levels at day 49.

Conclusion: RF-based Vessel wall tracking of the abdominal aorta in an aneurysmatic mouse model is feasible. Our data suggest an initial narrowing and stiffening of the abdominal aorta up to day 14, followed by an increase in diameter and distensibility, a phenomenon that is possibly due to Angiotensin II-induced smooth muscle contraction.