Arterial spin labeling combined with T1 mapping for assessment of kidney function and histopathology in patients with long-term renal transplant survival after kidney transplantation.

Background: The long-term survival of kidney transplants is often influenced by various factors, among which renal allograft rejection is the most notable factor. A noninvasive and reliable imaging biomarker correlating with kidney function and histopathology would facilitate longitudinal long-term follow-up of renal allografts. The aim of the study is to investigate the value of arterial spin labeling (ASL) combined with T1 mapping for assessing kidney function in patients with long-term renal transplant survival, and to establish radiological and histopathologic correlations between the magnetic resonance imaging (MRI) measurements and kidney allograft biopsy findings.

Methods: Kidney transplant recipients who were admitted to the Department of Urology in First Affiliated Hospital of Soochow University between January and December 2022 were prospectively consecutively recruited [group A, estimated glomerular filtration rate (eGFR) ≥60 mL/min/1.73 m; group B, 30≤ eGFR <60 mL/min/1.73 m; group C, eGFR <30 mL/min/1.73 m], and part of them underwent biopsies. All patients underwent ASL and T1 mapping. MRI parameters were calculated and analyzed.

Results: A total of 63 patients (Group A, 30 cases; Group B, 20 cases; and Group C, 13 cases) were included in this cross-sectional study. Cortical T1 increased, whereas renal blood flow (RBF) and ΔT1 [100% × (cortical T1 - medullary T1)/cortical T1] decreased with the decrease of eGFR. The RBF, cortical T1, and ΔT1 values were moderately correlated with eGFR (r=0.569, -0.573, and 0.672, respectively). The MRI parameters were moderately correlated with Banff scores, which determined renal allograft rejection and chronicity. The area under the curve (AUC) for the discrimination of groups A versus B and groups A versus C were 0.740 [95% confidence interval (CI): 0.597-0.854, P=0.004] and 0.923 (95% CI: 0.800-0.982, P<0.001), respectively, using ASL; 0.873 (95% CI: 0.749-0.950, P<0.001) and 0.926 (95% CI: 0.803-0.983, P<0.001), respectively, using T1 mapping; and 0.892 (95% CI: 0.771-0.962, P<0.001) and 0.956 (95% CI: 0.846-0.995, P<0.001), respectively, using multi-parameter MRI. The AUC for discrimination between groups B and C was 0.729 (95% CI: 0.546-0.868, P=0.02) using ASL.

Conclusions: The RBF, cortical T1, and ΔT1 can serve as new imaging biomarkers of kidney function and histopathological microstructure.