Multiparametric magnetic resonance imaging in diagnosis of long‐term renal atrophy and fibrosis after ischemia reperfusion induced acute kidney injury in mice.

Tubular atrophy and fibrosis are pathological changes that determine the prognosis of kidney disease induced by acute kidney injury (AKI). We aimed to evaluate multiple magnetic resonance imaging (MRI) parameters, including pool size ratio (PSR) from quantitative magnetization transfer, relaxation rates, and measures from spin‐lock imaging (R1ρ and Sρ), for assessing the pathological changes associated with AKI‐induced kidney disease. Eight‐week‐old male C57BL/6 J mice first underwent unilateral ischemia reperfusion injury (IRI) induced by reperfusion after 45 min of ischemia. They were imaged using a 7T MRI system 56 days after the injury. Paraffin tissue sections were stained using Masson trichrome and picrosirius red to identify histopathological changes such as tubular atrophy and fibrosis. Histology detected extensive tubular atrophy and moderate fibrosis in the cortex and outer stripe of the outer medulla (CR + OSOM) and more prominent fibrosis in the inner stripe of the outer medulla (ISOM) of IRI kidneys. In the CR + OSOM region, evident decreases in PSR, R1, R2, R1ρ, and Sρ showed in IRI compared with contralateral kidneys, with PSR and Sρ exhibiting the most significant changes. In addition, the exchange parameter Sρ dropped by the largest degree among all the MRI parameters, while R2* increased significantly. In the ISOM of IRI kidneys, PSR increased while Sρ kept decreasing. R2, R1ρ, and R2* all increased due to more severe fibrosis in this region. Among MRI measures, PSR and R1ρ showed the highest detectability of renal changes no matter whether tubular atrophy or fibrosis dominated. R2* and Sρ could be more specific to a single pathological event than other MRI measures because only R2* increased and Sρ decreased consistently when either fibrosis or tubular atrophy dominated, and their correlations with fibrosis scores were higher than other MRI measures. Multiparametric MRI may enable a more comprehensive analysis of histopathological changes following AKI. [ABSTRACT FROM AUTHOR]