Abstract: Objective To evaluate the application value of region of interest (ROI) selection for intravoxel incoherent motion (IVIM) diffusion-weighted imaging parameters with MVD, VEGF and LVI in rectal cancer. Methods Fifty-four patients with rectal cancer underwent preoperative IVIM and conventional MRI were included in this study. Three methods of ROI measurements (volume ROI, maximum area ROI and small ROI) were used to independently measure the IVIM parameters including pure diffusion coefficient (D), perfusion-related diffusion coefficient (D*), and perfusion fraction (f) values of the rectal cancer. The expressions of VEGF, MVD and LVI were detected by immunohistochemical staining. IVIM parameters were analyzed in the different expressions of VEGF, MVD and LVI in rectal cancers. The receiver operating characteristic (ROC) curve of each parameter of IVIM was analyzed, and the area under the ROC curve (AUC) was calculated to evaluate the diagnostic performance of each parameter for VEGF, MVD and LVI. Results Among the three ROI methods used by 2 doctors to detect each parameter value, the consistency of D value, D* value and f value measured by volume ROI was the best, and the consistency of D value diagnosis among the three parameters of IVIM was generally more advantageous. Among the low and high MVD expressions, only the D value measured by the volume ROI showed a significant difference (P＜0.05). In VEGF negative and positive patients, only the volume ROI and small ROI measured D values were significant (P＜0.05). In LVI-negative and positive patients, only the D value measured by volume ROI had a statistically significant difference (P＜0.05). ROC curve analysis results showed that the D value of volume ROI was better for judging MVD, VEGF and LVI, especially for judging the sensitivity of high MVD expression. The D value of small ROI showed better specificity for diagnosing negative expression of VEGF. Conclusion D value can reflect the angiogenesis of rectal cancer. In particular, D value measured by volume ROI can more objectively and accurately evaluate the MVD, VEGF and LVI before surgery.

Key words: rectal neoplasms, diffusion magnetic resonance imaging, microvessels, vascular endothelial growth factors,  intravoxel incoherent motion, region of interest