Characteristics of Blood Oxygen Level-Dependent and Diffusion-Weighted Magnetic Resonance Imaging in Tubulointerstitial Nephritis: an initial experience
Authors: Su Tao , Yang Xuedong , Wang Rui , Yang Li , Wang Xiaoying 
Published: August 2020

Abstract
Diffusion weighted (DW) and blood oxygen level-dependent (BOLD) magnetic resonance (MR)imaging are basic classical sequences of functional MR (fMR) in clinical application, but the exploration in the field of non-transplanted kidney disease is limited.ObjectsTo analyze the characteristics of global apparent diffusion coefficient (ADC) values and renal oxygenation status by R2* values using DW and BOLD imaging in patients with acute, chronic tubulointerstitial nephritis (ATIN, CTIN) and healthy control. MethodsFour biopsy-proven ATIN, thirteen clinical CTIN patients in stage 2-5 of chronic kidney disease and four controls were enrolled. They underwent fMR imaging with a 3.0-T MR scanner. A multiple gradient-echo sequence was used to acquire 12 T2*-weighted images for calculation of R2* map. DW imaging was acquired by combining a single-shot spin-echo echo planar imaging pulse sequence and the additional motion probing gradient pulses along the x, y, z-axes. We used two different b value groups: 0 and 200 s/mm2 as well as 0 and 800 s/mm2. For ATIN patients, DW and BOLD MR were performed at the time of renal biopsy (T0) and the third month (T3). Serum creatinine levels at the T3 and sixth month (T6) were regarded as indicators of long-term renal prognosis. Pathological changes such as tubular injury, tissue edema, severity of interstitial inflammation or fibrosis were assessed semi-quantitatively. Activity index (AI) and chronic index (CI) were calculated. Correlation analysis were conducted within MR parameters, pathological and clinical indexes.ResultsIn ATIN kidneys, ADCs were significantly lower than control, and showed an obvious remission through three months (both b values, p<0.05). Both cortical R2* values (CR2*) and medullary R2* values (MR2*) were decreased, the difference was significant in the change of MR2*. A rapid recovery of MR2* was also observed at T3. There was no relationship between fMR parameters and histopathological indexes (whether compared separately or as AI and CI). MR2* had a close relationship with eGFR (R=0.682, P=0.001). The change of ADCs (ΔADC) when b value was 0,200 s/mm2 (R=-0.956, P=0.044) and 0, 800 sec/mm2 (R=-0.968, P=0.032) were inversely correlated to ADCs, ΔMR2 (R=0.979, P=0.021) and pathological CI (R=-0.977, P=0.023). Renal long-term prognosis analysis among candidate predictive markers showed no relationship with time-point ADC or R2* values, but ΔMR2* had a significant correlation to Scr levels at T3 (R=-0.959, P=0.041) and T6 (R=0.98, P=0.02). That was, the lower the ADC value (b was 0, 200 sec/mm2), the greater the increase of ADC and MR2* in the next three months, then the subsequent Scr level would be lower. In CTIN group, a low level of MR2* was observed while CR2* remained unchanged.ConclusionsDirect evidence of global ADCs and renal oxygenation were got in TIN patients for the first time. MR2* served as a promising marker reflecting eGFR. A lower ADC value when b was 0, 200 sec/mm2 was a predictive marker to reversible acute injury. The "pseudo normalization" of CR2* in CTIN might be the result of the aggravation of renal ischemic changes, contributing to the progression of CKD.