Assessment of diffusion-weighted MR imaging in liver fibrosis

Purpose: To assess whether hepatic fibrosis is associated with a restriction in the diffusion of water that can be analyzed with diffusion-weighted MR imaging (DWI) of the liver. Materials and Methods: DWI was performed in 10 normal rats and 15 rats with liver fibrosis. Echo-planar DWI was performed in the living rats at 1.5 T and repeated immediately after the animals were killed. Afterwards the livers were explanted, fixed in Bouin solution, and imaged with a DW spin-echo sequence at 4.7 T. Fibrosis was quantified by densitometry on Sirius red-stained histological sections. Results: In living rats the apparent diffusion coefficient (ADC) decreased with the severity of liver fibrosis (controls: 1535 +/- 294 mm(2)/second; CCl4 (5 weeks) 1129 +/- 273 mm(2)/second; CCl4 (9 weeks): 943 +/- 132 mm(2)/second; P = 0.002). An inverse correlation between ADC and liver fibrosis volume density was observed (r = -0.712, P < 0.001). In contrast, these findings were not observed in the rats after they were killed or in the fixated livers. Conclusion: Decreased ADC correlated with increased liver fibrosis in living rats, but not after death. These results suggest that restricted water diffusion cannot be assessed by DWI in liver fibrosis. Other factors, such as a decrease of perfusion, may explain the decrease of the hepatic ADC measured in vivo in rats with liver fibrosis.