Contrast-enhanced ultrasound examination of a stable functioning renal transplant. Pilot study

Objective. The lack of standardized protocols and reference values for quantitative parameters in contrast-enhanced ultrasound (CEUS) of stable functioning renal transplants limits its clinical application. This study aimed to analyze CEUS quantitative parameters in recipients with stable graft function and no significant pathology on protocol biopsy, as well as to assess inter-operator reproducibility.

Materials and Methods. An interventional prospective study was conducted (October 1, 2024 – March 1, 2025). 23 patients were enrolled. CEUS was performed by Resona 7 system (Mindray, China) with a convex probe (1.2–6 MHz) and SonoVue contrast agent (Bracco, Italy). Time-intensity curve (TIC) parameters were analyzed in: ROI₁ (region of interest): cortex, ROI₂: cortex between pyramids (renal columns), ROI₃: pyramids, ROI₄: combined ROI₁+ROI₂+ROI3. Parameters assessed: Ascending Slope (AS), Arrival Time (AT), Area Under the TIC Curve (AUC), Descending Slope (DS), mean TIC intensity (mTIC), Peak Intensity (PI), Rise Time (RT), Time-to-Peak (TTP), Wash-in Area Under the Curve (WiAUC), Perfusion Index (WiAUC/RT), Wash-out AUC (WoAUC). Analysis was performed using Contrast QA software (Mindray). Inter-operator reproducibility was evaluated via intraclass correlation coefficients (ICC) and Bland-Altman analysis (mean difference, limits of agreement).

Results. Mean TIC parameters (averaged between operators) were obtained for all ROIs. ROI₁: excellent/good reproducibility for most parameters; moderate reproducibility for AS and DS (ICC 0.840 [0.662; 0.928] and 0.859 [0.697; 0.938]). ROI₂: Excellent to good reproducibility; moderate for WiAUC (0.848 [0.678; 0.933]), RT (0.877 [0.733; 0.946]), WiAUC/RT (0.835 [0.628; 0.929]), AS (0.836 [0.653; 0.927]), and DS (0.777 [0.537; 0.899]). ROI₃: Higher variability for WiAUC/RT (0.706 [0.418; 0.864]), AS (0.657 [0.351; 0.838]), and DS (0.752 [0.497; 0.887]). ROI₄: Results comparable to ROI₁.

Conclusion. This study is a crucial step toward standardizing CEUS for renal transplants. It establishes the first quantitative CEUS benchmarks for stable allografts without significant pathology on protocol biopsy. The low inter-operator variability supports the clinical feasibility of using absolute TIC parameters (comparison of normal vs dysfunctional grafts) across different ultrasound systems.

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