Hepatic Steatosis Decreases Diffusion Parameters in Diffusion-Weighted Imaging With Monte Carlo Simulation and...

To calibrate the effect of hepatic steatosis on diffusion parameters, including $\mathrm{ADC}$ and pure diffusion coefficient ( $D$ ), by Monte Carlo simulation and phantom studies.

In the simulation study, four types of virtual liver models were constructed by incorporating size, nearest neighbor distance and regional anisotropy of fat droplets. By simulating magnetic field, proton movement and phase accrual, DWI signals were synthesized and analyzed to predict $\mathrm{ADC}$ and $D$ . Correlation analyses were performed to investigate relationships between fat fraction (FF) and diffusion parameters predictions. Bland Altman analysis was conducted to evaluate the effects of virtual liver model, fat susceptibility and proton diffusivity on these predictions. In the phantom study, a fat-water phantom was scanned to investigate the relationships between proton density fat fraction (PDFF) and diffusion parameters.

The simulation study demonstrated that $\mathrm{ADC}$ and $D$ predictions were linearly and negatively correlated with FFs ( $r\le -0.924$ ), unaffected by virtual liver model and fat susceptibility ( $p\ge 0.756$ ). Additionally, proton diffusivity posed positive effects on these predictions. Compared with in vivo calibration, simulations with the virtual liver model incorporating all criteria, fat susceptibility of 0.2 ppm and proton diffusivity of 0.96 μm²/ms can accurately predict the diffusion parameters. The phantom study indicated that $\mathrm{ADC}$ and $D$ measurements were linearly and negatively correlated with PDFF ( $r\le -0.895$ ).

Hepatic steatosis decreases both diffusion parameters and should be calibrated in the DWI-based assessment of liver fibrosis.