Fig. 9

Scar depth angle and thickness measurements should be performed on the axial central slice of the tumour. For scar depth angle measurements of small (< 180°) tumour scars, the endoluminal centre of the scar serves as pivot while the angle lines cross the endoluminal extremities of the scar (in blue). In > 180° scars, the pivot should also be central but the angle lines should cross the endoluminal aspect of the scar at 180° of the rectal circumference and no more than that. The same applies to circumferential scars but in such cases, the pivot should be placed at the most invasive tumour front if there is one, or randomly if there isn´t. The most important thing to keep in mind is measuring at the exact same location in both first and second post-NAT MR imaging examinations. Scar thickness should be measured at pivot level, at the second MR imaging assessment. Measurement corresponds to a line that transverses tumour scar in depth, perpendicularly to it (in yellow), from inner to outer surface, irrespectively of it signal intensity