Sound touch viscosity imaging for chronic kidney disease staging: a novel biomarker for renal fibrosis

The accurate monitoring of chronic kidney disease (CKD) progression is clinically challenging, as conventional shear wave elastography (SWE) only evaluates tissue stiffness by focusing solely on quantifying tissue elasticity, and this parameter is influenced by hemodynamic fluctuations. Sound touch viscosity imaging (STVi) addresses these limitations by simultaneously quantifying both elasticity and viscosity, providing a comprehensive biomechanical profile that better reflects the complex pathophysiology of CKD. This dual-parameter approach enables more reliable disease staging and progression monitoring. This study aimed to investigate whether STVi-derived viscosity parameters outperformed conventional elasticity measurements in CKD diagnosis and staging, establish clinically applicable cut-off values for viscosity to stratify CKD severity, and explore the pathophysiological correlation between viscoelastic properties and renal fibrosis.

In total, 127 CKD patients [staged G1-G5 under the Kidney Disease: Improving Global Outcomes (KDIGO) criteria] and 84 healthy controls (HCs) were prospectively enrolled in this study. Ultrasound viscoelastic imaging was performed using Mindray Resona A20 systems with standardized protocols. Renal viscosity [pascal-seconds (Pa·s)] and elasticity (kPa) were measured simultaneously through Voigt model-based shear wave dispersion analysis. Histopathological correlation was established via image-guided biopsies.

The viscosity parameters showed superior diagnostic performance compared to the elasticity measurements. At the optimal cut-off value of 1.66 Pa·s, the area under the curve (AUC) for the right kidney was 0.95 [95% confidence interval (CI): 0.92-0.99] (sensitivity 94.4%, specificity 96.2%). The viscosity values showed a strong correlation with pathological grading (Spearman's r=0.82, P<0.001) and displayed characteristic stage-dependent progression from G1 (1.71±0.11 Pa·s) to G5 (2.36±0.21 Pa·s), with a notable plateau observed between stages 4 and 5 (left kidney: P=0.87; right kidney: P=0.74). The bilateral consistency of the measurements (intraclass correlation coefficient >0.90) and the significantly higher diagnostic accuracy for detecting inflammatory changes (AUC 0.95 vs. 0.73 for elasticity, P<0.001) suggested that viscosity is a more comprehensive biomarker than conventional elasticity parameters.

STVi imaging provides a novel, non-invasive biomarker for assessing renal fibrosis in CKD that outperforms conventional SWE. The established cut-off values and characteristic progression patterns offer clinically actionable thresholds for early detection and staging. Future multicenter studies should be conducted to validate these findings across diverse populations and etiologies.