Dependence of Intravoxel Incoherent Motion diffusion MR thresholdb-value selection for separating perfusion and diffusion compartments and liver fibrosis diagnostic performance

Purpose To explore how the selection of threshold b -value impacts Intravoxel Incoherent Motion (IVIM) diffusion parameters of PF ( f ), D slow ( D ),and D fast ( D* ) values and their performance for liver fibrosis detection. Materials and Methods Fifteen healthy volunteers and 33 hepatitis-b patients were included. With a 1.5 T MR scanner and respiration gating, IVIM data was acquired with 10 b -values of 10,20,40,60,80,100,150, 200, 400, and 800 s/mm 2 . Signal measurement was performed on right liver. Segmented-unconstrained analysis was used to compute IVIM parameters, and six threshold b -values between 40 and 200 s/mm 2 were compared. PF, Dslow, and Dfast values were placed along the x -axis, y -axis, and z -axis, and a plane was defined to separate volunteers from patients. Results Higher threshold b -values were associated with higher PF measurement; while lower threshold b -values led to higher Dslow and Dfast measurements. The dependence of PF, Dslow, and Dfast on threshold b -value differed between healthy livers and fibrotic livers; with the healthy livers showing a higher dependence. Threshold b -value=60 s/mm 2 showed the largest mean distance between healthy liver datapoints vs. fibrotic liver datapoints in 3-dimensional space. Conclusion For segmented-unconstrained analysis, the selection of threshold b -value=60 s/mm 2 improves IVIM diffusion differentiation between healthy livers and fibrotic livers.