Monitoring Bevacizumab-Induced Tumor Vascular Normalization by Intravoxel Incoherent Motion Diffusion-Weighted MRI

Background Accurate monitoring of tumor blood vessel normalization progression is beneficial to accurate treatment of patients. At present, there is a lack of safe and noninvasive monitoring methods. Purpose To serial monitor the vascular normalization time window of tumor antiangiogenesis treatment through intravoxel incoherent motion diffusion-weighted imaging (IVIM-DWI) and histopathological methods. Study Type Exploratory animal study. Population Sixty rat C6 glioma models were randomly and equally divided into the control groups (N = 30) and bevacizumab treatment groups (N = 30). Twenty-five for magnetic resonance imaging (MRI) and five for electron microscope testing in each group. Field Strength/Sequence T1-weighted imaging (T1WI), T2WI with a fast spin echo sequence and IVIM-DWI with a spin-echo echo-planar imaging sequence at 3 T. Assessment IVIM-DWI quantitative parameters (f, D, D*, and fD*) were obtained on days 0, 2, 4, 6, and 8 after bevacizumab treatment. After MRI, the microvessel density (MVD), pericyte coverage, and hypoxia-inducible factor-1 alpha (HIF-1 alpha) were assessed. Electron microscope observation was performed at each time point. Statistical Tests One-way analysis of variance and Student's t-tests were used to compare differences within and between groups. Spearman's correlation coefficient (r) assess the correlation between IVIM and pathological parameters. The intragroup correlation coefficient was determined to assess the repeatability of each IVIM parameter. Results The IVIM-DWI perfusion parameters (f and fD*) of the treated group were higher than the control group on days 2 and 4. Compared to the control group, MVD decreased on days 2 and pericyte coverage increased on days 4 in the treatment group. Electron microscopy showed that the tight junctions of the treatment group were prolonged on days 2-4. In the control group, f had the highest correlation with MVD (r = 0.689). In the treated group, f had a good correlation with pericyte coverage (r = 0.557), HIF-1 alpha had a moderately positive correlation with f (r = 0.480) and fD*(r = 0.447). Data Conclusion The vascular normalization time window of bevacizumab treatment of glioma was days 2-4 after antiangiogenesis treatment, which could be monitored noninvasively by IVIM-DWI. Evidence Level 2 Technical Efficacy Stage 3