Exploration of Interstitial Fibrosis in Chronic Kidney Disease by Diffusion-Relaxation Correlation Spectrum MR Imaging: A Preliminary Study.

Background: Renal interstitial fibrosis is one of the most common pathways in the progression of chronic kidney disease (CKD). Noninvasive evaluation of interstitial fibrosis would help monitoring CKD progression and prognosis prediction.

Purpose: To evaluate the severity of renal interstitial fibrosis by diffusion-relaxation correlation spectrum imaging (DR-CSI).

Study Type: Prospective.

Subjects: Forty patients with CKD and 10 healthy controls (average age 49.2 ± 14.8 years, 18 females).

Field Strength/sequence: 3-T, DR-CSI with 36 axial spin-echo echo-planar diffusion-weighted images (6 b-values, 6 echo times).

Assessment: Interstitial fibrosis level (IFL) was assessed from biopsy results (IFL = 1, fibrosis percentage <25%, defined as mild; IFL = 2, 25%-50%, moderate; IFL = 3, >50%, severe). Estimated glomerular filtration rate (eGFR) was calculated using serum creatinine. The regions of interest included cortex for both kidneys. The diffusivity-T2 spectrum was assessed considering three compartments (threshold: T2 30-40 msec, diffusivity 5-9 μm /msec, according to visible peaks): A (low diffusivity, short T2), B (low diffusivity, long T2), and C (high diffusivity). Volume fractions V (i = A, B, C) were calculated.

Statistical Tests: Intra-class coefficient (ICC, >0.6 as good) to assess inter-reader agreement of DR-CSI V . Spearman's correlation to assess relationship of V to IFL and eGFR. Receiver operating characteristic analyses with the area under the curve (AUC) to discriminate patients with moderate-severe fibrosis from mild ones. Statistical significance criteria: P-value <0.05.

Results: ICCs were good for all V . Correlations were found between IFL and V (r = 0.424, significant) and V (r = -0.400, significant), and between eGFR and V (r = -0.303, P = 0.058) and V (r = 0.487, significant). Regarding V and V , the AUCs were 0.903 and 0.824.

Data Conclusion: DR-CSI help distinguish patients with moderate or severe renal interstitial fibrosis from mild ones.

Evidence Level: 2 Technical Efficacy: Stage 2.