Exploring the value of functional magnetic resonance imaging in assessing subclinical rejection in kidney transplantation

Introduction: Functional magnetic resonance imaging (fMRI) is a promising method to assess kidney injury non-invasively. This study aimed to explore the value of fMRI in assessing subclinical rejection and provide potential monitoring methods for non-invasive rejection screening in kidney transplantation. Methods: Based on the kidney transplantation cohort of the Second Affiliated Hospital of Nanjing Medical University, 46 cases of patients who underwent protocol renal biopsy and fMRI at 3 months or 12months post-transplantation were included in this study. They were divided into the subclinical rejection group and the normal group according to the pathological results. Various fMRI parameters, including blood oxygenation level-dependent (BOLD) imaging, intravoxel incoherent motion (IVIM) imaging, and diffusion kurtosis imaging (DKI), were used to assess the oxygenation, microcirculation perfusion, and tissue microstructural changes of renal grafts. Multivariate analysis was performed to evaluate the role of different imaging parameters in subclinical rejection. Additionally, the receiver operating characteristic (ROC) curve analysis were used to compare the diagnostic performance of imaging parameters, clinical indicators, and the combined model in diagnosing subclinical rejection. Results: Comparing the imaging parameters of 17 cases in the subclinical rejection group with those of 29 cases in the normal group, it was found that there were statistical differences between two groups in cortical apparent transverse relaxation rate (R2*), cortical axial diffusion (Da), cortical axial kurtosis (Ka), medullary fractional anisotropy (FA) and medullary Da. Among them, cortical Ka and medullary Da were independent predictors of subclinical rejection. In the evaluation of diagnostic performance, when MRI parameters were combined with clinical indicators, the AUC increased to 81.3%, which was better than either fMRI parameters (76.1%) or clinical indicators (73%) alone, with a sensitivity of 76.5% and a specificity of 86.2%. Conclusion: fMRI could provide key imaging information for subclinical rejection in kidney transplantation. DKI parameters, cortical Ka, and medullary Da have high diagnostic value for subclinical rejection. Combining fMRI parameters with clinical indicators could further improve the identification of subclinical rejection and provide a new fMRI-based approach for non-invasive rejection screening in kidney transplantation.