Role of blood oxygen level-dependent MRI in differentiation of acute renal allograft dysfunction

Early graft dysfunction after renal transplantation manifests as acute rejection (AR) or acute tubular necrosis (ATN). Blood oxygen level-dependent (BOLD) magnetic resonance (MR) imaging is a noninvasive method of assessing tissue oxygenation, which may be useful for predicting acute allograft dysfunction. This was a prospective study involving 40 patients scheduled for renal transplantation from August 2012 to August 2014. In addition, 15 healthy donors were also enrolled in this study. All recipients underwent BOLD MR imaging (MRI) and R2* mapping 10-20 days after transplant, and additionally within 48 h of biopsy if there was any evidence of graft dysfunction. The healthy donors underwent BOLD MRI 1-2 days before surgery. The biopsies were grouped into AR, ATN, and no evidence of AR or ATN. The mean medullary R2*, cortical R2*, corticomedullary gradient, and medullary: cortical R2* ratio were compared between groups using one-way analysis of variance. Spearman's correlation and multinomial linear regression were applied to determine the influence factors of R2* value. Overall, nine patients had graft dysfunction. Six were reported as AR, two as ATN, and one as no evidence of ATN or rejection. The mean medullary and cortical R2* were significantly higher in ATN group compared with AR and normal group, whereas the mean medullary and cortical R2* of AR group were significantly lower than normal group. The corticomedullary gradient of AR group was significantly lower compared with ATN and normal group. Medullary R2*:cortical R2* ratio was significantly lower in AR group compared with normal group. No significant difference was noted between the 15 donors and patients with normal graft function. R2* values on BOLD MRI are significantly decreased in AR allografts and increased in an early stage of ATN allografts, suggesting that BOLD MRI can become a valuable tool for discriminating between AR and ATN.