In vivo DTI assessment of hepatic ischemia reperfusion injury in an experimental rat model

Purpose: To investigate hepatic ischemia reperfusion injury (IRI) using diffusion tensor imaging (DTI). Materials and Methods: Ten Sprague-Dawley rats were scanned at 7 Tesla (T) with DTI using b-value of 1000 s/mm² and 6 gradient directions before, 2 h, and 1 day after 30-min total hepatic IRI. Apparent diffusion coefficient or mean diffusivity (MD), directional diffusivities and fractional anisotropy (FA) were measured. Seven of the animals were also examined with spin-echo echo-planar diffusion-weighted imaging (DWI) with seven b-values up to 2000 s/mm² to estimate the true diffusion coefficient (D), blood pseudodiffusion coefficient (D*), and perfusion fraction (f) using a bi-compartmental model. Results: MD 2 h after IRI (0.77 ± 0.07 × 10^-3 mm²/s) was significantly lower (P < 0.01) than that before (1.03 ± 0.07 × 10^-3 mm²/s) and 1 day after IRI (1.01 ± 0.05 × 10 ^-3 mm²/s). Meanwhile, FA 2 h after IRI (0.33 ± 0.03) was significantly higher (P < 0.01) than that before (0.21 ± 0.02) and 1 day after IRI (0.20 ± 0.02). The bi-compartmental model analysis revealed the transient decrease in D, D* and f 2 h after IRI. Liver histology showed the multifocal cell swelling 3 h after IRI and widespread cell necrosis/apoptosis 1 day after IRI. Sinusoidal narrowing and congestion of erythrocytes were also observed 3 h and 1 day after IRI. Conclusion: DTI can characterize hepatic IRI by detecting the transient change in both MD and FA.