Assessment of mechanical properties of porcine aortas under physiological loading conditions using vascular elastography

Non-invasive assessment of the elastic properties of the arterial wall is often performed with ultrasound (US) imaging. The purpose of this study is to estimate mechanical properties of the vascular wall using in vitro inflation testing on biological tissue and two-dimensional (2-D) US elastography, and investigate the performance of the proposed methodology for physiological conditions. An inflation experiment was performed on 12 porcine aortas for (a) a large pressure range (0-140 mmHg); and (b) physiological pressures (70-130 mmHg) to mimic in vivo hemodynamic conditions. Two-dimensional radiofrequency (RF) data were acquired for one longitudinal and two transverse cross-sections for both experiments, and were analyzed to obtain the geometry and diameter-time behavior. The shear modulus (G) was estimated from these data for each pressure range applied. In addition, an incremental study based on the static data was performed to (1) investigate the changes in G for increasing mean arterial pressure (MAP) for a certain pressure difference (30, 40, 50 and 60 mmHg); (2) compare the results with those from the dynamic experiment, for the same pressure range. The resulting stress-strain curves and shear moduli G (94 +/- 16 kPa) for the static experimentare in agreement with literature and previous work. A linear dependency on MAP was found for G, yet the effect of the pulse pressure difference was negligible. The dynamic data revealed a G of 250 +/- 20 kPa, whereas the incremental shear modulus (G(inc)) was 240 +/- 39 kPa. For all experiments, no significant differences in the values of G were found between different image planes. This study shows that 2-D US elastography of aortas during inflation testing is feasible and reproducible under controlled and physiological circumstances. In future studies, the in vivo, dynamic experiment should be repeated for a range of MAPs, and pathological vessels should be examined. (C) 2015 Elsevier Ltd. All rights reserved.