The significance of BOLD MRI in differentiation between renal transplant rejection and acute tubular necrosis

Background. Blood oxygen level-dependent MRI (BOLD MRI) can be used to assess intra-renal oxygen bioavailability by measuring the R2(*) level, which reflects tissue deoxyhaemoglobin levels. This study was designed to identify the significance of BOLD MRI in differentiation of acute rejection (AR) and acute tubular necrosis (ATN) in patients within 6 months after kidney transplantation. Methods. Eighty-two patients with normal graft function and 28 patients with biopsy-proven AR (n = 21) or ATN (n = 7) were enrolled. Patients with normal functioning allograft underwent BOLD MRI within 2 to 3 weeks post-transplantation, while patients with AR and ATN underwent BOLD MRI within 6 days before or after kidney transplant biopsy. Cortical R2(*) (CR2(*)) and medullary R2(*) (MR2(*)) levels were measured. Results. The mean CR2(*) level was significantly higher in the ATN group (15.25 +/- 1.03/s) compared to the normal group (13.35 +/- 2.31/s, P = 0.028) and AR group (12.02 +/- 1.72/s, P = 0.001). There was a significant difference also between the AR group and normal group on CR2(*) levels (P = 0.013). The mean MR2(*) level was significantly lower in the AR group (14.02 +/- 2.68/s) compared to the normal group (16.66 +/- 2.82/s, P < 0.001) and ATN group (19.47 +/- 1.62/s, P < 0.001). There was also a significant difference between the ATN group and normal group on MR2(*) levels (P = 0.011). There were no correlations between characteristics such as patient age, post-operation time, post-biopsy time, Scr level, HB level, urine output volume, MAP level, CNI trough concentration and R2(*) levels, except between MAP level and CR2(*) level (P = 0.029). Conclusions. BOLD MRI could be a valuable method to discriminate between AR and ATN by measuring tissue oxygen bioavailability in early kidney allograft dysfunction.