DWI and IVIM are predictors of Ki67 proliferation index: direct comparison of MRI images and pathological slices in a murine model of rhabdomyosarcoma

Objectives The purpose of this study was to investigate the correlation of diffusion-weighted imaging (DWI) and intravoxel incoherent motion (IVIM) with the Ki67 proliferation index in a murine model of rhabdomyosarcoma. Methods The rhabdomyosarcoma model was established by injecting RD cells into the right hind flank of nude mice. The mice underwent 3.0T magnetic resonance imaging (MRI), including DWI and IVIM. The apparent diffusion coefficient (ADC), D, D*, and f were calculated with the ADW4.7 workstation. A specialized method was employed to ensure the pathological sections corresponded to the correct MRI slices. The Ki67 proliferation index was analyzed by immunohistochemistry, and any possible correlations were assessed between the DWI and IVIM parameters and Ki67 proliferation index. Results Twenty-seven rhabdomyosarcoma mice were established successfully. After 46 days, the average tumor volume reached 1094.78 +/- 678.77 mm(3). The average ADC, D, and D* values were 1.0470 +/- 0.2036 x 10(-3) mm(2)/s, 0.7237 +/- 0.0971 x 10(-3) mm(2)/s, and 4.8497 +/- 1.6293 x 10(-3) mm(2)/s, respectively. The range in f values was 0.102-0.229. The ADC and D values showed a moderate negative correlation with the Ki67 proliferation indexes (r = - 0.543, p = 0.003; r = - 0.491, p = 0.009, respectively). In addition, the f value showed a weak negative correlation with the Ki67 proliferation indexes (r = - 0.151, p = 0.451), while the D* value showed no association with the Ki67 proliferation indexes (r = - 0.037, p = 0.853). Conclusions The ADC value of DWI, along with the D value of IVIM, may be reflective of Ki67 proliferation indexes in murine models of rhabdomyosarcoma.