Figure 4. Example of two locally advanced rectal tumours with (a), (b) high and (c), (d) low permeability. The top images are the anatomical axial T₂ images whilst the lower two demonstrate a "permeability" (capillary leakiness) map overlaying the two tumours. The colour scale is shown on the left of images (b) and (d) and permits an appreciation of the extent of capillary leakiness within individual voxels based on modelling kinetic contrast agent data (in this case Gd-DTPA, gadolinium(III) diethylenetriamine pentaacetic acid). Our results indicate that rectal tumours with a higher permeability (b) are more likely to respond to chemotherapy than those with low permeability (d). Our findings are independent of original tumour size.