  Elastic properties of arteries have long been recognized as playing a major
role in the cardiovascular system. However, non-invasive in vivo assessment of
local arterial stiffness remains challenging and imprecise as current
techniques rely on indirect estimates such as wall deformation or pulse wave
velocity. Recently, Shear Wave Elastography (SWE) has been proposed to
non-invasively assess the intrinsic arterial stiffness. In this study, we
applied SWE in the abdominal aortas of rats while increasing blood pressure
(BP) to investigate the dependence of shear wave speed with invasive arterial
pressure and non-invasive arterial diameter measurements. A 15MHz linear array
connected to an ultrafast ultrasonic scanner, set non-invasively, on the
abdominal aorta of anesthetized rats (N=5) was used. The SWE acquisition
followed by an ultrafast (UF) acquisition was repeated at different moment of
the cardiac cycle to assess shear wave speed and arterial diameter variations
respectively. Invasive arterial BP catheter placed in the carotid, allowed the
accurate measurement of pressure responses to increasing does of phenylephrine
infused via a venous catheter. The SWE acquisition coupled to the UF
acquisition was repeated for different range of pressure. For normal range of
BP, the shear wave speed was found to follow the aortic BP variation during a
cardiac cycle. A minimum of (5.06$\pm$0.82) m/s during diastole and a maximum
of (5.97$\pm$0.90) m/s during systole was measured. After injection of
phenylephrine, a strong increase of shear wave speed (13.85$\pm$5.51) m/s was
observed for a peak systolic arterial pressure of (190$\pm$10) mmHg. A
non-linear relationship between shear wave speed and arterial BP was found. A
complete non-invasive method was proposed to characterize the artery with shear
wave speed combined with arterial diameter variations. Finally, the results
were validated against two parameters the incremental elastic modulus and the
pressure elastic modulus derived from BP and arterial diameter variations.
