Viscoelastic Response Ultrasound Detects Changes in Degree of Mechanical Anisotropy with Renal Fibrosis in Pig Model

Chronic kidney disease is associated with progressive inflammation and fibrosis, which is conventionally assessed by invasive biopsy. A noninvasive alternative to biopsy may be interrogating elastic and viscous anisotropy. This work evaluates the feasibility of using in vivo Viscoelastic Response (VisR) ultrasound for detecting changes in the elastic and viscous degree of anisotropy (DoA) associated with fibrosis after chronic ischemia-reperfusion injury (IRI) in pig kidney. Histology was used to validate VisR DoA measurements, which were compared to those derived using Shear Wave Elasticity Imaging (SWEI) and Shearwave Dispersion Ultrasound Vibrometry (SDUV). In the injured and contralateral (control) kidneys of 8 pigs, VisR, SWEI, and SDUV-derived elastic DoA, evaluated as the ratio of longitudinal over transverse shear elasticity, was significantly (p<; 0.1, Wilcox Ranksum) decreased in the fibrotic medulla and increased in fibrotic cortex relative to control. Sirius red stain confirmed a significant (p<; 0.1, Wilcox Ranksum) increase in collagen content in the fibrotic medulla and cortex relative to control. These results suggest that VisR noninvasively detects changes in elastic DoA associated with fibrosis induced by chronic IRI in a pig model. VisR may be diagnostically relevant to delineating fibrosis in human kidney.