Effect of diffusion time on liver DWI: An experimental study of normal and fibrotic livers

Abstract

Purpose: To investigate whether diffusion time (Δ) affects the diffusion measurements in liver and their sensitivity in detecting fibrosis. Methods: Liver fibrosis was induced in Sprague-Dawley rats (n = 12) by carbon tetrachloride (CCl4) injections. Diffusionweighted MRI was performed longitudinally during 8-week CCl4 administration at 7 Tesla (T) using single-shot stimulatedecho EPI with five b-values (0 to 1000 s/mm2) and three Ds. Apparent diffusion coefficient (ADC) and true diffusion coefficient (Dtrue) were calculated by using all five b-values and large b-values, respectively.

Results: ADC and Dtrue decreased with D for both normal and fibrotic liver at each time point. ADC and Dtrue also generally decreased with the time after CCl4 insult. The reductions in Dtrue between 2-week and 4-week CCl4 insult were larger than the ADC reductions at all Ds. At each time point, Dtrue measured with long Δ (200 ms) detected the largest changes among the 3 Δs examined. Histology revealed gradual collagen deposition and presence of intracellular fat vacuoles after CCl4 insult.

Conclusion: Our results demonstrated the Δ dependent diffusion measurements, indicating restricted diffusion in both normal and fibrotic liver. Dtrue measured with long Δ acted as a more sensitive index of the pathological alterations in liver microstructure during fibrogenesis.