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Abstract: PO2224

Longitudinal Assessment of Unilateral Ureteral Obstruction Kidney Injury by Relaxometry and Spin-Lock Exchange MRI

Session Information

Category: Pathology and Lab Medicine

  • 1601 Pathology and Lab Medicine: Basic

Authors

  • Wang, Feng, Vanderbilt University Medical Center, Nashville, Tennessee, United States
  • Otsuka, Tadashi, Vanderbilt University Medical Center, Nashville, Tennessee, United States
  • Takahashi, Keiko, Vanderbilt University Medical Center, Nashville, Tennessee, United States
  • Harris, Raymond C., Vanderbilt University Medical Center, Nashville, Tennessee, United States
  • Takahashi, Takamune, Vanderbilt University Medical Center, Nashville, Tennessee, United States
Background

Non-invasive imaging technique allows longitudinal and repetitive assessment of renal disease progression. In this study, we assessed the utility of a new MRI technique, quantitative relaxometry and Spin-lock exchange MRI, in detecting renal pathology in unilateral ureter obstructed (UUO) kidneys, focusing on destructive tubular injury (dilatation) and renal fibrosis, the pathological changes commonly observed in progressive kidney disease.

Methods

BALB/c mice (n=6-8) were imaged before and after (day 5, 10 and 15) UUO surgery at 7T magnet. Spin-lock images were acquired in a transverse plane using a fast spin echo sequence preceded by a preparatory spin-lock cluster. The dispersion of R1ρ with locking frequency was fit to Chopra model. The fits provided regional values of transverse relaxation rates R2fit, R1ρ at infinite spin-lock frequency (R1ρ∞), and an exchange rate-weighted parameter Sρ. Since cortex and outer stripe of outer medulla (OSOM) were clearly identified with T2-weighted image, even with UUO kidneys, these regions were selected for analysis. Paraffin tissue sections were stained using picrosirius red or anti-collagen I antibody. Histological scores for tubular dilatation and fibrosis, based on luminal space and positive fibrotic areas in sections, were computationally measured and the correlation between MRI parameters and histological scores were assessed.

Results

In histology, evident tubular enlargement was observed at UUO day 5, while tubulointerstitial fibrosis was mild at this stage. Both histological changes became more evident on progression and fibrosis showed larger increases from day 5 to day 15 (tubular dilatation ~25% increase, fibrosis ~3 fold increase). Relaxation rates R1obs, R2obs and R1ρ were progressively dropped (25-50%) in UUO kidneys. Interestingly, R1obs showed the highest sensitivity to tubular dilatation, while Sρ showed the highest correlation with renal fibrosis.

Conclusion

Relaxation parameters showed high detectability to tubular dilatation and overall changes in UUO progression. Sρ best detected fibrotic changes. This would be because it depends mainly on the average exchange rate between water and other chemically shifted resonances such as amides and hydroxyls, sensing collagen accumulations. These new MRI parameters could be used for the assessment of kidney disease progression.

Funding

  • NIDDK Support