Diffusion Weighted Imaging and T2 Mapping Detect Inflammatory Response in the Renal Tissue during Ischemia Induced Acute Kidney Injury in Different Mouse Strains and Predict Renal Outcome

Parametric MRI Detects Aristolochic Acid Induced Acute Kidney Injury

Exposure to aristolochic acid (AA) is of increased concern due to carcinogenic and nephrotoxic effects, and incidence of aristolochic acid nephropathy (AAN) is increasing. This study characterizes renal alterations during the acute phase of AAN using parametric magnetic resonance imaging (MRI). An AAN and a control group of male Wistar rats received administration of aristolochic acid I (AAI) and polyethylene glycol (PEG), respectively, for six days. Both groups underwent MRI before and 2, 4 and 6 days after AAI or PEG administration. T₂ relaxation times and apparent diffusion coefficients (ADCs) were determined for four renal layers. Serum creatinine levels (sCr) and blood urea nitrogen (BUN) were measured. Tubular injury scores (TIS) were evaluated based on histologic findings. Increased T₂ values were detected since day 2 in the AAN group, but decreased ADCs and increased sCr levels and BUN were not detected until day 4. Significant linear correlations were observed between T₂ of the cortex and the outer stripe of outer medulla and TIS. Our results demonstrate that parametric MRI facilitates early detection of renal injury induced by AAI in a rat model. T₂ mapping may be a valuable tool for assessing kidney injury during the acute phase of AAN.

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 ( 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, whileR 2 * increased significantly. In the ISOM of IRI kidneys, PSR increased while S ρ kept decreasing. R 2 , R 1 ρ , andR 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 onlyR 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.