Viscoelastic Response Ultrasound Detects Increased Degree of Mechanical Anisotropy with Ischemia-Reperfusion Injury in Pig Kidney, In Vivo

Chronic kidney disease is associated with progressive inflammation, which is conventionally assessed by invasive biopsy. A noninvasive alternative is to interrogate the mechanical property alterations that occur with inflammation. This work evaluates the feasibility of using in vivo Viscoelastic Response (VisR) ultrasound for detecting differences in mechanical degree of anisotropy (DoA) associated with inflammation after ischemia-reperfusion injury (IRI) in pig kidney. VisR measurements were validated by histology, Shear Wave Elasticity Imaging (SWEI), and Shearwave Dispersion Ultrasound Vibrometry (SDUV) derived DoA. In 6 pigs, data were acquired in vivo in the kidney following IRI and in the contralateral kidney, which did not undergo IRI and served as a control. VisR (relative elasticity (RE), relative viscosity (RV), and peak displacement (PD)), SWEI (shear elastic modulus (μ)), and SDUV (shear elastic (μ1) and viscous (μ2) moduli) outcomes were evaluated alone and as ratios to reflect DoA (longitudinal over transverse). VisR PD and RE, SWEI μ, and SDUV μ1 demonstrated significantly increased DoA (p<;0.1, Wilcox Ranksum) after IRI in the medulla and cortex (except SWEI μ in cortex). Notably, while elastic DoA increased in both medulla and cortex, the underlying causes differed (cortex: diminished transverse modulus v. medulla: elevated longitudinal modulus). VisR RV indicated decreased viscous DoA in the medulla after IRI. Spatially matched histology indicated mild inflammation in the injured, but not the control, kidneys. These results suggest that VisR noninvasively detects changes in DoA associated with inflammation induced by IRI in a pig model. VisR may be diagnostically relevant to delineating inflammation in human kidney.