Contrast-Enhanced Ultrasound to Assess Kidney Quality During Ex Situ Normothermic Machine Perfusion

Normothermic machine perfusion (NMP) provides opportunity for viability assessment of donated kidneys. Diminished microvascular perfusion, despite adequate total blood flow, is a key pathophysiology in ischaemia-mediated acute kidney injury. Contrast-enhanced ultrasound (CEUS) could allow objective assessment of microvascular perfusion during renal NMP. Blood-based NMP was performed on porcine kidneys (circulatory death model) and human kidneys declined for transplant (preclinical). CEUS was performed with a contrast bolus into the NMP circuit arterial limb. Microvascular perfusion quality was quantified and z-score normalisation allowed combination of metrics and regions into an overall "CEUS-score." In porcine kidneys, inferior microvascular perfusion of cortex and medulla correlated with increased urinary NGAL (Neutrophil gelatinase-associated lipocalin) and histological DNA-fragmentation (a hallmark of apoptosis). In human kidneys, CEUS-score at 2 h was correlated with histological DNA-fragmentation (r = -0.937; P = 0.019) and predicted urinary NGAL at 24 h of NMP (r = -0.925; P = 0.024). Total renal flow was not correlated with these outcomes. An open-source web application (stingle.shinyapps.io/Time_intensity_analysis) and R package ("tican") were developed for quantitative time-intensity curve analysis. CEUS allows objective point-of-care microvascular perfusion assessment during NMP. As 2-hour CEUS-score predicts NGAL at 24 h, CEUS warrants future clinical investigation as a potential tool to assess kidney quality in assessment and reconditioning centres.