Purpose
To test the utility of magnetization transfer imaging (MTI) in detection and monitoring the progression of renal fibrosis in mice with unilateral renal artery stenosis (RAS).
Materials and Methods
This prospective study was approved by the Institutional Animal Care and Use Committee. RAS (n=10) or sham surgery (n=5) was performed, and the stenotic and contralateral kidneys were studied longitudinally in-vivo at baseline and 2, 4 and 6 weeks post-surgery. Following a 16.4T MRI exam, magnetization transfer ratio (MTR) was measured as an index of fibrosis (guided by parameters selected in preliminary phantom studies). In addition, renal volume, perfusion, blood flow and oxygenation were assessed. Fibrosis was subsequently measured ex-vivo by histology and hydroxyproline assay. The Wilcoxon rank-sum or signed-rank test was used for statistical comparisons between or within groups, and Pearson’s and Spearman’s rank correlation to compare fibrosis measured in-vivo and ex-vivo.
Results
In the stenotic kidney, the median MTR showed progressive increases from baseline to 6 weeks post-surgery (by 13.7% [P=0.0006] and 21.3% [P=0.0005] in cortex and medulla, respectively), which were accompanied by a progressive loss in renal volume, perfusion, blood flow, and oxygenation. The 6-week MTR map showed good correlation with fibrosis measured ex-vivo (Pearson’s r=0.9038 and Spearman’s ρ=0.8107, P=0.0002 vs. trichrome staining; r=0.9540 and ρ=0.8821, P<0.0001 vs. Sirius red staining; r=0.8429 and ρ=0.7607, P=0.001 vs. hydroxyproline assay).
Conclusion
MT successfully measured and longitudinally monitored the progression of renal fibrosis in mice with unilateral RAS.