Multiparametric MRI Evaluation of Renal Flow Reserve in Response to Oral Protein Loading

Background: Renal flow reserve (RFR), the capacity of the kidneys to increase renal blood flow (RBF) under stress, is a promising marker of early renal dysfunction. While stress testing is well-established in other organs, no standardized kidney stress test exists in clinical practice. Acute protein loading can activate RFR, but current assays rely on global estimates or invasive tests that lack spatial and temporal resolution. This study evaluated the feasibility of using multiparametric MRI to noninvasively characterize the kidney hemodynamic response to an oral protein load in healthy adults and assess its ability to detect RFR activation. Methods: Fifteen adults (29±12 years, 10 females) underwent MRI before ( ≥10-hour fasting, 400mL water intake) and after consuming 0.7 g/kg of tuna(n=15) or tofu (n=5). Imaging was performed on a 3T Siemens Vida, including MRA, 2D PC-MRI, IVIM(D, D*, f), T1, and T2* mapping. In a tuna subset (n=5), renal perfusion was assessed with 3D-pCASL. Results: PC-MRI showed a significant post-tuna RBF increase (+11.8±4.5%, p=0.001), while tofu showed no change (+3.1±13.6%, p=0.62). RFR (peak tuna ΔRBF) correlated with age (R2=0.28,p=0.04) and eGFR (R2=0.29,p=0.04). Medullary D increased (+10.1±1.94%,p=0.001) post-tuna but not in the cortex or with tofu; D* and f did not change significantly. Cortical T2* increased 60-90min post-tuna (+8.5±18.9%,p=0.04) but did not change in the medulla or with tofu. T1 increased only in the cortex 90–120min post-tuna (+4.0±4.5%,p=0.03). Kidney volumes remained stable (+3.4±6.6%,p=0.31). In the pCASL subset, RBF change was not significant (–6.10±8.81%,p=0.11). Conclusion: MRI-based renal stress testing with an oral protein load is feasible and noninvasive. Animal protein elicited hyperemia consistent with RFR activation. Hyperemia occurred without a drop in T2*, suggesting preserved oxygen supply-demand balance. No response was seen with tofu. RFR correlations with age and eGFR suggest sensitivity to subclinical kidney disease. This approach may support future applications in living donor evaluation, CKD staging, and imaging biomarker development. Funding: Other NIH Support - NIH R01-EB033916, TERMINATED 04/25/2025Postprandial RBF Change(left). RFR vs. eGFR Correlation(right)