Table S2. MRI feature measurement.

Features	Measurement	Classification
MRI, magnetic resonance imaging; EMVI, extramural venous invasion.
mrT stage	The identification and staging of rectal cancers at MRI is largely based on differences in T2 signal intensity between the tumor, submucosa, muscular layer, and mesorectum on short-axial-T2 weighted images.	T3: Tumor invades through muscularis propria into pericolorectal tissues.
mrN status	Nodes with irregular borders, mixed signal intensity, or both are suspicious, uniform nodes smaller than 10 mm with homogeneous signal intensity are not suspicious.	mrN(+): presence of suspicious nodes; mrN(−): no suspicious nodes.
mrEMVI	Extramural venous invasion, including tumor, positive lymph node, and tumor deposit.	Positive: intermediate signal intensity apparent within vessels, although the contour and calibre of these vessels is only slightly expanded; obvious irregular vessel contour or nodular expansion of vessel by definite tumour signal. Negative: pattern of tumor extension through the muscle coat is not nodular, and there are no vessels adjacent to areas of tumor penetration; minimal extramural stranding/nodular extension, but not in the vicinity of any vascular structure; stranding demonstrated in the vicinity of extramural vessels, but these vessels are of normal calibre, and there is no definite tumor signal within the vessel.