Analysis of vascular morphology. A, intravital microscopy image of a representative untreated R-18-GFP tumor. Tumor area is delineated by a solid black line. B, intravital microscopy image of the region highlighted in A. C, vascular mask. D, skeleton of the vascular mask. Vessels with diameter >15 μm are shown in red and vessels with diameter < 15 μm are shown in green. E, color-coded vessel diameter superimposed on the vascular mask. Color bar, vessel diameter scale in μm. Figures C-E refer to the tumor region shown in B. F, sketch of vessel segment. Vessel segment length (SL; red) was defined as the distance between branching points along the vessel, whereas vessel tortuosity (T) was defined as T = (SL – S)· 100% / SL, where SL represents the vessel segment length and S represents the shortest distance between the branching points (S; green).