Fibrosis imaging with multiparametric proton and sodium MRI in pig injury models

Chronic kidney disease (CKD) is common and has huge implications for health and mortality. It is aggravated by intrarenal fibrosis, but the assessment of fibrosis is limited to kidney biopsies, which carry a risk of complications and sampling errors. This calls for a noninvasive modality for diagnosing and staging intrarenal fibrosis. The current, exploratory study evaluates a multiparametric MRI protocol including sodium imaging (Na-23-MRI) to determine the opportunities within this modality to assess kidney injury as a surrogate endpoint of fibrosis. The study includes 43 pigs exposed to ischemia-reperfusion injury (IRI) or unilateral ureteral obstruction (UUO), or serving as healthy controls. Fibrosis was determined using gene expression analysis of collagen. The medulla/cortex ratio of Na-23-MRI decreased in the injured kidney in the IRI pigs, but not in the UUO pigs (p = 0.0180, p = 0.0754). To assess the combination of MRI parameters in estimating fibrosis, we created a linear regression model consisting of the cortical apparent diffusion coefficient, Delta R2*, Delta T1, the Na-23 medulla/cortex ratio, and plasma creatinine (R-2 = 0.8009, p = 0.0117). The Na-23 medulla/cortex ratio only slightly improved the fibrosis prediction model, leaving Na-23-MRI in an ambiguous place for evaluation of intrarenal fibrosis. Use of multiparametric MRI in combination with plasma creatinine shows potential for the estimation of fibrosis in human kidney disease, but more translational and clinical work is warranted before MRI can contribute to earlier diagnosis and evaluation of treatment for acute kidney injury and CKD.

Automated summary

Chronic kidney disease has significant implications for health and mortality, and there is a need for a noninvasive method to assess kidney fibrosis. This study explores the potential of a multiparametric MRI protocol, including sodium imaging, in assessing fibrosis. The results suggest that sodium imaging can partially predict fibrosis but its application in kidney disease remains uncertain.