Study population

This retrospective study was approved by our Institutional Review Board, and written informed consent was waived. The study included inpatients who sought medical advice in the Department of Nephrology, Cardiology and Endocrinology of our Hospital from October 2019 to January 2020. The clinical manifestations of patients were chronic renal insufficiency, nephrotic syndrome, nephritis syndrome, asymptomatic hematuria and/or proteinuria regardless of eGFR and hypertension or diabetes with impaired renal function (eGFR < 90 ml/min/1.73 m²). The flow chart of study population is presented in Fig. 1.

The flow chart of study population

Patients’ demographics and the closest laboratory values within 3 days of MRI examination were obtained by reviewing electronic medical records, including gender, age, body mass index (BMI), mean arterial blood pressure (MAP), blood glucose, urea, serum creatinine, cystatin C, eGFR, 24-h urine volume, urinary total microprotein (mTP), urinary microalbumin (mALB), urine creatinine and urinary microalbumin/creatinine ratio (UALB/Cr). The eGFR was calculated according to the formula recommended by the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI): GFR = 141 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^−1.209 × 0.993^Age × 1.018 [if female] × 1.159 [if black], where Scr is serum creatinine, κ is 0.7 for females and 0.9 for males, α is -0.329 for females and −0.411 for males, min indicates the minimum of Scr/κ or 1, and max indicates the maximum of Scr/κ or 1 [26]. All subjects were divided into two groups according to the eGFR: group 1, patients with good or stable renal function (eGFR ≥ 60 ml/min/1.73 m²); group 2, patients with moderately or severely impaired renal function (eGFR < 60 ml/min/1.73 m²). If the patient underwent percutaneous renal biopsy under the guidance of B-ultrasound within 1 week of MRI examination, the pathological results were recorded. Interstitial fibrosis was evaluated by using a semi-quantitative assessment method (two-point scale): 0 (mild fibrosis, < 25%), 1 (moderate fibrosis, 25–50%) and 2 (severe fibrosis, > 50%).