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 ( R 1 ρ and S ρ ), 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, R 1 , R 2 , R 1 ρ , and S ρ showed in IRI compared with contralateral kidneys, with PSR and S ρ exhibiting the most significant changes. In addition, the exchange parameter S ρ dropped by the largest degree among all the MRI parameters, while R 2 * increased significantly. In the ISOM of IRI kidneys, PSR increased while S ρ kept decreasing. R 2 , R 1 ρ , and R 2 * all increased due to more severe
fibrosis in this region. Among MRI measures, PSR and R 1 ρ showed the highest detectability of renal changes no matter whether tubular
atrophy or
fibrosis dominated. R 2 * and S ρ could be more specific to a single pathological event than other MRI measures because only R 2 * increased and S ρ 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.