Optimizing the contrast agent dose and image acquisition time for renal ultrasound localization microscopy

Objective Renal microvascular assessment is essential for kidney function. Ultrasound localization microscopy (ULM) enables super-resolution imaging of renal microvasculature. However, contrast dose and acquisition time need to be optimized. This study explored the effects of contrast agent dose and acquisition time on renal cortical microvascular imaging. Materials and methods In this prospective study, healthy volunteers underwent renal contrast-enhanced ultrasound (CEUS) using four sulfur hexafluoride microbubbles doses (0.4, 0.6, 0.8, and 1.2 mL). ULM was performed during cortical (peak enhancement), medullary, and delayed phases. Quantitative CEUS perfusion parameters and ULM-derived microvascular metrics were assessed, and the effects of dose and time were evaluated using repeated-measures ANOVA. The minimal effective dose was predefined using repeated-measures ANOVA with Bonferroni correction as the lowest dose without significant benefit from higher doses. Results Twenty-five participants were included. CEUS parameters, including area under the curve, peak intensity, half-time to peak, and acceleration time, demonstrated a clear dose–response relationship, plateauing at doses ≥ 0.6 mL (all p ≤ 0.008). ULM imaging was most favorable during the peak enhancement phase. Four distinct patterns of ULM parameters were identified: dose- and time-dependent, dose-dependent, time-dependent, and stable. Among these, the dose- and time-dependent parameters ( e.g ., vessel ratio, maximum velocity, mean velocity) exhibited the most consistent plateau at 0.6 mL, paralleling the CEUS findings. Conclusion In healthy, non-obese adults, a 0.6-mL dose at peak enhancement reached a plateau in quantitative performance and may represent a practical minimal effective protocol for renal ULM. Key Points Question What are the optimal contrast dose and acquisition time for renal ULM protocols, given that they are not currently standardized? Findings A minimal effective dose of 0.6 mL at peak enhancement in healthy, non-obese adults was found. Multiparametric ULM shows good to excellent intra- and inter-observer repeatability for protocol optimization. Relevance statement Renal ULM enables quantitative assessment of cortical microvascular perfusion. This technique provides a reference for optimizing contrast dose and acquisition time, supporting standardized imaging protocols for kidney function evaluation.