Validation of the corticomedullary difference in magnetic resonance imaging-derived apparent diffusion coefficient for kidney fibrosis detection: a cross-sectional study.

Background. Kidney cortical interstitial fibrosis (IF) is highly predictive of renal prognosis and is currently assessed by the evaluation of a biopsy. Diffusion magnetic resonance imaging (MRI) is a promising tool to evaluate kidney fibrosis via the apparent diffusion coefficient (ADC), but suffers from inter-individual variability. We recently applied a novel MRI protocol to allow calculation of the corticomedullary ADC difference (Delta ADC). We here present the validation of Delta ADC for fibrosis assessment in a cohort of 164 patients undergoing biopsy and compare it with estimated glomerular filtration rate (eGFR) and other plasmatic parameters for the detection of fibrosis. Methods. This monocentric cross-sectional study included 164 patients undergoing renal biopsy at the Nephrology Department of the University Hospital of Geneva between October 2014 and May 2018. Patients underwent diffusion-weighted imaging, and T1 and T2 mappings, within 1 week after biopsy. MRI results were compared with gold standard histology for fibrosis assessment. Results. Absolute cortical ADC or cortical T1 values correlated poorly to IF assessed by the biopsy, whereas Delta ADC was highly correlated to IF (r= -0.52, P < 0.001) and eGFR (r= 037, P < 0.01), in both native and allograft patients. Delta T1 displayed a lower, but significant, correlation to IF and eGFR, whereas T2 did not correlate to IF nor to eGFR. Delta ADC, Delta T1 and eGFR were independently associated with kidney fibrosis, and their combination allowed detection of extensive fibrosis with good specificity. Conclusion. Delta ADC is better correlated to IF than absolute cortical or medullary ADC values. Delta ADC, Delta T1 and eGFR are independently associated to IF and allow the identification of patients with extensive IF.