Enhancing Kidney Quality Assessment: Power Doppler During Normothermic Machine Perfusion

Objectives: Marginal donor kidneys are increasingly used for transplantation to overcome organ shortage. This study aims to investigate the additional value of Power Doppler (PD) imaging in kidney quality assessment during normothermic machine perfusion (NMP). Methods: Porcine kidneys (n = 22) retrieved from a local slaughterhouse underwent 2 h of NMP. Based on creatinine clearance (CrCl) and oxygen consumption (VO₂) at 120 min, kidneys were classified into Group 1 (n = 7, CrCl > 1 mL/min/100 g and VO₂ > 2.6 mL/min/100 g) and Group 2 (n = 15, CrCl ≤ 1 mL/min/100 g and/or VO₂ ≤ 2.6 mL/min/100 g). PD imaging was performed at 30, 60, and 120 min, and PD metrics, including vascularization index (VI), flow index (FI), and vascularization flow index (VFI) were calculated. Renal blood flow (RBF), CrCl, and VO₂ were measured at the same time points during NMP. The metrics were compared utilizing correlation analysis. Results: FI and VFI moderately correlated with CrCl (r = 0.537, p < 0.0001; r = 0.536, p < 0.0001, respectively), while VI strongly correlated with VO₂ (r = 0.839, p < 0.0001). At 120 min, PD metrics demonstrated the highest diagnostic accuracy for distinguishing between the two groups, with an area under the curve (AUC) of 0.943 for VI, 0.924 for FI, and 0.943 for VFI. Cutoff values of 17% for VI, 50 a.u. for FI, and 9 a.u. for VFI provided 100% specificity and 73% sensitivity in identifying kidneys in Group 2, with an overall diagnostic accuracy of 82%. Baseline kidney biopsies showed moderate acute tubular necrosis in both groups, with no significant differences. Conclusions: PD metrics strongly correlate with renal viability and effectively differentiate kidneys with higher and lower functionality during NMP. PD imaging can be a valuable alternative to RBF during NMP for kidney quality assessment.