Factors influencing renal shear wave elastography: effects of probe orientation, respiration, corticomedullary differentiation, and hydration

Aim: To assess how probe orientation, respiratory phase, hydration, and corticomedullary differentiation affect renal two-dimensional shear wave elastography. Material and methods: Prospective single-center study with four independent sub-studies: (1) probe orientation (long vs. short axis; children, n = 35), (2) respiration (quiet breathing vs. brief mid-expiratory breath-hold; children, n = 20), (3) hydration (adults, n = 12; 700 mL water intake; stiffness at baseline, +20, +40 min), and (4) corticomedullary differentiation with depth assessment (children, n = 29). Shear wave elastography was acquired as five- frame series using 5-mm regions of interest. Sub-studies 1–3 sampled the cortex, whereas sub-study 4 sampled the cortex and renal pyramids at matched depths. Outcomes included per-subject median stiffness (kPa) and interquartile-range-to-median ratio (IQR/M). A quality filter (IQR/M ≤0.30) was applied to all sub-studies except the orientation sub-study. Statistical analysis included the Wilcoxon signed-rank test, Friedman test (hydration), and Spearman’s ρ (depth). Results: Long-axis orientation reduced variability within measurement series (lower IQR/M) compared with short-axis orientation (p <0.05). Stiffness during quiet breathing and mid-expiratory breath-hold was comparable. After water intake, stiffness increased (Friedman p <0.05). The cortex was consistently stiffer than the renal pyramids in the same subjects (p <0.05), and no depth-related effect was detected (Spearman’s ρ −0.24 to +0.25; all p ≥0.19). Conclusions: Among the four evaluated factors, probe orientation and hydration influenced renal shear wave elastography, whereas respiratory phase within the tested range did not. Corticomedullary differences should be explicitly reported when standardizing pediatric renal shear wave elastography.