Histological Grading of Hepatocellular Carcinomas with Intravoxel Incoherent Motion Diffusion-weighted Imaging: Inconsistent Results Depending on the Fitting Method

PURPOSE: To compare the abilities of three intravoxel incoherent motion (IVIM) imaging approximation methods to discriminate the histological grade of hepatocellular carcinomas (HCCs). METHODS: Fifty-eight patients (60 HCCs) underwent IVIM imaging with 11 b-values (0–1000 s/mm(2)). Slow (D) and fast diffusion coefficients (D(*)) and the perfusion fraction (f) were calculated for the HCCs using the mean signal intensities in regions of interest drawn by two radiologists. Three approximation methods were used. First, all three parameters were obtained simultaneously using non-linear fitting (method A). Second, D was obtained using linear fitting (b = 500 and 1000), followed by non-linear fitting for D(*) and f (method B). Third, D was obtained by linear fitting, f was obtained using the regression line intersection and signals at b = 0, and non-linear fitting was used for D(*) (method C). A receiver operating characteristic analysis was performed to reveal the abilities of these methods to distinguish poorly-differentiated from well-to-moderately-differentiated HCCs. Inter-reader agreements were assessed using intraclass correlation coefficients (ICCs). RESULTS: The measurements of D, D(*), and f in methods B and C (Az-value, 0.658–0.881) had better discrimination abilities than did those in method A (Az-value, 0.527–0.607). The ICCs of D and f were good to excellent (0.639–0.835) with all methods. The ICCs of D(*) were moderate with methods B (0.580) and C (0.463) and good with method A (0.705). CONCLUSION: The IVIM parameters may vary depending on the fitting methods, and therefore, further technical refinement may be needed.