Multiparametric functional MRI for detection of early renal allograft dysfunction after kidney transplantation: a systematic review and meta-analysis

BACKGROUND: Kidney transplantation is the gold-standard renal-replacement therapy for end-stage kidney disease, yet delayed graft function affects 5-50% of recipients and predicts chronic allograft dysfunction. Functional magnetic resonance imaging (fMRI) offers a non-invasive means to simultaneously assess allograft perfusion, oxygenation, and microstructure. METHODS: We systematically searched PubMed, Web of Science, Cochrane Library, Embase, and MEDLINE for studies evaluating arterial spin labeling (ASL), blood oxygen level-dependent (BOLD), diffusion-weighted imaging (DWI), and intravoxel incoherent motion (IVIM) MRI in kidney transplant recipients. Study quality was appraised with QUADAS-2. Data were pooled using random-effects models, with subgroup analyses by magnetic field strength, post-transplant time, and baseline creatinine. RESULTS: Twenty-eight studies comprising 1,956 recipients were included. ASL-derived cortical renal blood flow (RBF) discriminated normal from impaired renal function (estimated glomerular filtration rate (eGFR) ≥ 60 vs. <60 mL/min/1.73 m²; mean difference (MD) 98.48mL·min⁻¹·100 g⁻¹, 95% confidence interval (CI) 68.66-128.31; P < 0.00001; I²=57%) and correlated with eGFR (r = 0.58). BOLD identified acute rejection (lower R2*; I²=77-86%) but not acute tubular necrosis. IVIM-derived D values showed the strongest discriminatory power (MD 0.14-0.16 × 10⁻³ mm²/s; P < 0.00001; I²=0%). Substantial heterogeneity (I²=18-98%) limited conclusions for some parameters. CONCLUSIONS: Multiparametric fMRI, particularly ASL and IVIM shows promise for detecting early allograft dysfunction. However, marked inter-study heterogeneity underscores the need for standardized protocols before clinical implementation.