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. Author manuscript; available in PMC: 2012 Aug 1.

Published in final edited form as: Arterioscler Thromb Vasc Biol. 2011 May 26;31(8):1748–1756. doi: 10.1161/ATVBAHA.111.227314

a,b, Image of dilated, fixed and filled pial cortical circulation; higher magnification image showing two collaterals (black dotted lines) and penetrating arterioles (stars) branching from type II (black arrows) and type I (white arrows) distal-most arterioles that either are or are not cross-connected by collaterals, respectively. MCA, ACA, middle and anterior cerebral artery, respectively. c,d, All collaterals interconnecting MCA and ACA trees in both cerebral hemispheres were quantified. Increased collateral tortuosity and resistance of the native collateral circulation with aging (e-h). e,f, Collateral length (l), axial length of pial collateral. Collateral span (L), scalar length connecting both ends of collateral. h, Relative resistance of the pial collateral circulation, calculated as collateral length / (collateral number x diameter⁴), is 6- and 10-fold higher in 24- and 31-months-old groups than 3-months-old group. All collaterals between MCA and ACA in both hemispheres were quantified.

a,b, Image of dilated, fixed and filled pial cortical circulation; higher magnification image showing two collaterals (black dotted lines) and penetrating arterioles (stars) branching from type II (black arrows) and type I (white arrows) distal-most arterioles that either are or are not cross-connected by collaterals, respectively. MCA, ACA, middle and anterior cerebral artery, respectively. c,d, All collaterals interconnecting MCA and ACA trees in both cerebral hemispheres were quantified. Increased collateral tortuosity and resistance of the native collateral circulation with aging (e-h). e,f, Collateral length (l), axial length of pial collateral. Collateral span (L), scalar length connecting both ends of collateral. h, Relative resistance of the pial collateral circulation, calculated as collateral length / (collateral number x diameter⁴), is 6- and 10-fold higher in 24- and 31-months-old groups than 3-months-old group. All collaterals between MCA and ACA in both hemispheres were quantified.