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The role of blood flow during vessel pruning, in which the segment with lower blood flow is pruned. a The diameter of the upper branch and the lower branch is the same before vessel pruning, while the blood flow velocity of the lower branch is lower than that of the upper branch. b Vessel stenosis occurs at the lower branch with low blood flow. c No blood perfusion in the lower branch. d, e The lower branch is pruned, while the upper branch remains
