Tumor perfusion-related parameter of diffusion-weighted magnetic resonance imaging: Correlation with histological microvessel density

Purpose We obtained intravoxel incoherent motion (IVIM) parameters through biexponential analysis on diffusion-weighted MR imaging (DWI) using multiple b values. Correlation was evaluated between these parameters and histological microvessel density (MVD) for the possibility of noninvasive evaluation of MVD with DWI. Methods Twenty-five nude mice with the HT29 colorectal cancer cells implanted were analyzed after undergoing DWI with multiple b values (0, 50, 100, 300, 500, 700, and 1000 s/mm²). Tissue diffusivity (D_t), pseudo-diffusion coefficient (D_p), and perfusion fraction (f _p) were calculated using a biexponential analysis, and these parameters were correlated with MVD. The MVD was determined with the CD31 stain. For statistical analysis, Spearman's rank correlation was applied. Results The mean value and correlation coefficient with MVD for each IVIM parameter were as follows: D_t = 0.98 ± 0.06 × 10^-3 mm ²/s with r = 0.139 (P = 0.508); D_p = 23.70 ± 7.94 × 10^-3 mm²/s with r = 0.782 (P < 0.001); and f_p = 15.58 ± 5.7% with r = 0.749 (P < 0.001). D_p and f_p showed significant correlation with MVD, but D_t did not. Conclusion The IVIM parameters, D_p and f_p, on DWI might be used in the noninvasive evaluation of MVD.