Assessment of Mesorectal Microstructure and Microcirculation with Intravoxel Incoherent Motion MRI

Motivation: To evaluate the mesorectal microenvironment. Goal(s): To assess the mesorectal microstructure and microcirculation of rectal cancer by IVIM-MRI. Approach: 42 patients with semicircular rectal tumors underwent IVIM-MRI with 14 b values before surgery. ROIs were depicted in the mesorectum that surrounded the tumor (MT) and normal rectal wall (MN) respectively. D, D* and f values of ROIs were estimated based on the bi-exponential model. Histopathology served as standard reference. Results: The MT showed lower D but higher D* and f than the MN (P<0.001). A higher D* of MT was observed in patients with pT3 tumors than in patients with pT1~2 tumors (P=0.001). Impact: The mesorectum that surrounded the rectal tumor had a more complex microstructure and a higher microvascular prefusion than that close to the normal rectal wall. The mesorectal microenvironment might be an interesting point for further MRI study in rectal cancer.