Chronic Kidney Disease (CKD) is a major public health issue, leading to high mortality and the necessity for renal replacement therapy. Kidney fibrosis, resulting from chronic damage to kidney tissue, significantly determines CKD outcomes. Kidney biopsy, the gold standard for assessing fibrosis, is invasive and limited in its ability to reflect the heterogeneous nature of fibrosis. Consequently, there is growing interest in noninvasive methods, particularly Magnetic Resonance Elastography (MRE). MRE, which evaluates tissue stiffness, has shown potential for assessing kidney fibrosis. This study aims to use multifrequency MRE to assess renal fibrosis, focusing particularly on the early stages of CKD, to enhance understanding of its progression and relationship to clinical outcomes.

Chronic Kidney Disease (CKD) is a significant public health concern, impacting approximately 10% of the global population. Annually, millions face mortality or require renal replacement therapy due to CKD progression. Kidney fibrosis, a result of chronic parenchymal damage from various glomerular and tubulointerstitial insults, is a primary determinant of outcomes. Accurately assessing the extent and severity of fibrosis is vital for diagnosis and treatment. However, Glomerular Filtration Rate (GFR) may not diminish despite the presence of renal fibrosis, often until extensive damage occurs, owing to the kidney's compensatory abilities. Additionally, GFR reductions may not solely indicate chronic damage or parenchymal fibrosis.

GFR estimates using serum markers offer only rough approximations of kidney fibrosis and can be misleading. The gold standard for assessing kidney fibrosis is a kidney biopsy. However, biopsies are invasive, with potential complications and sampling errors, as they assess less than 1% of the kidney parenchyma. Given the heterogeneous and patchy nature of fibrosis within kidneys, the efficacy of biopsies is further questioned. Serial biopsies to track fibrosis progression are also impractical.

The need for noninvasive, accurate fibrosis assessment has led to research into various imaging techniques. Emerging functional MRI sequences, such as Intravoxel Incoherent Motion (IVIM) and Arterial Spin Labeling (ASL) for perfusion, Blood Oxygen Level Dependent (BOLD) for oxygenation, and T1 mapping for tissue characterization, offer multidimensional insights into renal pathology. Among these, Magnetic Resonance Elastography (MRE) appears particularly promising for directly assessing tissue mechanical properties. MRE, combining MRI with acoustic wave assessment, quantitatively determines tissue viscoelastic properties in response to external mechanical vibration. Initially developed for liver fibrosis assessment, kidney studies have shown that MRE-determined stiffness mildly negatively correlates with CKD stages and positively with fibrosis in renal allografts and diabetic kidneys. While kidney stiffness increases with fibrosis in renal allografts, it decreases with GFR in diabetic nephropathy. In CKD progression, marked by increased fibrosis and decreased GFR, these opposing effects on renal stiffness could limit MRE's applicability in CKD patients. We hypothesize that in early-stage CKD, when GFR is normal or slightly elevated, MRE could effectively determine renal fibrosis severity. To date, no study has specifically explored renal fibrosis and stiffness correlation in early-stage CKD.

Therefore, this study aims to evaluate renal fibrosis using multifrequency 3D-MRE-derived stiffness as a surrogate marker. This involves detecting renal fibrosis prior to CKD changes, distinguishing renal fibrosis from CKD stages, and comparing renal stiffness with clinicopathological correlates in CKD patients. Additionally, we will briefly explore the complementary value of MRE alongside other functional MRI metrics (IVIM, ASL, BOLD, T1 mapping) and investigate their potential efficacy in predicting the prognosis of CKD progression.

Inclusion Criteria:

(1) adults with CKD defined according to the 2024 KDIGO guidelines, with either elevated SCr or abnormal proteinuria ; and (2) renal MRI was performed within 7 days of the renal biopsy.

Exclusion criteria:

(1) genitourinary malignancy, polycystic kidney disease, renal transplantation, or acute renal failure; (2) contraindications for MRI examination; (3) poor image quality; (4) kidney deformity or severe hydronephrosis on MRI; and (5) poorly defined corticomedullary demarcation.

Adult patients with CKD stages 1-5 and healthy age-matched adults as controls