Aortic Wall Biomechanical Assessment Depends on Ultrasound Probe Pressure: In-Vivo and In-Silico Insights

Objective: Ultrasound-based aortic stiffness estimation has the potential to improve the diagnosis and prognosis of patients with abdominal aortic aneurysms (AAA), as a complement to routinely used diameter surveillance. However, existing methods have shown limited reproducibility, possibly influenced by the unknown effects of the highly variable ultrasound probe pressure. This proof-of-concept study addressed this gap by analyzing time-resolved ultrasound sequences from AAA patients. Methods: Two-dimensional ultrasound sequences were acquired from 10 AAA patients, applying light and firm probe pressure. Diameter variations and stiffness were evaluated and compared. An in-silico simulation was performed to support the in-vivo observations. Results: Measured stiffness decreased with an increased probe pressure. Specifically, in the most responsive patient group, the cyclic diameter variation between diastole and systole changed from 1 % at light probe pressure to 5 % at firm probe pressure, and the estimated stiffness decreased by a factor of 6.3. Another group of patients showed a marginal increase in the diameter variations and a smaller decrease in stiffness (factor of 1.5) when transitioning from light to firm probe pressure. These two behaviors were reproduced via numerical simulations, showing that the different responses to probe pressure depend on the stress-strain relationship of the wall material. Conclusion: Varying the ultrasound probe pressure can alter the in-vivo mechanics of AAAs. Significance: This proof-of-concept study suggests potential implications for AAA mechanical characterization via ultrasound imaging.