Supersonic Shear Wave Imaging to Assess Arterial Nonlinear Behavior and Anisotropy: Proof of Principle via Ex Vivo Testing of the Horse Aorta

Abstract

Supersonic shear wave imaging (SSI) is a noninvasive, ultrasound-based technique to quantify the mechanical properties of bulk tissues by measuring the propagation speed of shear waves (SW) induced in the tissue with an ultrasound transducer. The technique has been successfully validated in liver and breast (tumor) diagnostics and is potentially useful for the assessment of the stiffness of arteries. However, SW propagation in arteries is subjected to different wave phenomena potentially affecting the measurement accuracy. Therefore, we assessed SSI in a less complex ex vivo setup, that is, a thick-walled and rectangular slab of an excised equine aorta. Dynamic uniaxial mechanical testing was performed during the SSI measurements, to dispose of a reference material assessment. An ultrasound probe was fixed in an angle position controller with respect to the tissue to investigate the effect of arterial anisotropy on SSI results. Results indicated that SSI was able to pick up stretch-induced stiffening of the aorta. SW velocities were significantly higher along the specimen's circumferential direction than in the axial direction, consistent with the circumferential orientation of collagen fibers. Hence, we established a first step in studying SW propagation in anisotropic tissues to gain more insight into the feasibility of SSI-based measurements in arteries.

A finite element model to study the effect of tissue anisotropy onex vivoarterial shear wave elastography measurements

“…The experimentally measured gauge length at 2 N load was adjusted to 47.87 mm at 0 N by taking into account the curve offset of -4.55 mm. The complete model length was 98.79 mm at 0 N. The thickness and width of the model were 4 mm and 74.2 mm (Shcherbakova et al, 2014). …”

“…In a previous work (Shcherbakova et al, 2014), we demonstrated that SWE can detect stretch-induced stiffening of a slab of ex-vivo equine aortic tissue and pick up the cyclic variation in SWS related to the dynamic stretching of the material. Moreover, we showed SWE to be dependent on the orientation angle of the probe, and hypothesized that the SWS along the presumed fibre orientation exceeded the SWS across the fibres.…”

“…The SWE measurements were performed with an Aixplorer scanner (SuperSonic Imagine, Aix-enProvence, France) with the probe fixed in an angle position controller above the sample. The probe settings were discussed in our previous works (Shcherbakova et al, 2013(Shcherbakova et al, , 2014. The probe was rotated in steps of 30° from 0° to 180°.…”

“…Assessing the anisotropic architecture of arteries with SWE (Chu & Rutt, 1997;Woodrum et al, 2006;Fujikura et al, 2007;Bernal et al, 2011;Ramnarine et al, 2014;Shcherbakova et al, 2014;Widman et al, 2016) could support the diagnosis of early-stage collagen remodelling and atherosclerosis. The potential of SWE to detect tissue anisotropy was previously shown for in-vitro tissue phantoms (Chatelin et al, 2014;Aristizabal et al, 2014) for skeletal and cardiac muscle (Gennisson et al, 2010;Urban et al, 2016;Rudenko & Sarvazyan, 2006;Pernot et al, 2007) and kidneys (Amador et al, 2011).…”

“…In order to complement the previous experimental work and to have a more profound understanding of the nature of SWs propagating in a hyperelastic, anisotropic arterial tissue, we present in this paper a numerical modelling workflow, mimicking the experimental setup described in Shcherbakova et al, 2014. This approach allows to have full control over the arterial architecture, mechanical properties and the excited ARF (Lee et al, 2012;Palmeri et al, 2005;Caenen et al, 2015).…”