Figure 2.

mPAM measurements of sO₂ and blood flow on four orders of artery-vein pairs in the mouse ear. (a) sO₂ mapping from two measurements at 584 and 590 nm. Four different orders of artery-vein pairs are labeled. Scale bar: 125 μm. (b) Profiles of blood flow speed across vessels of different orders measured along the dashed lines in (a) on the basis of PA Doppler bandwidth broadening at 584 nm. Generally, the flow speed decreases from the proximal order to the distal order. However, it also depends on the vessel diameter as a result of the conservation of total flow. Solid circles: experimental data; red curves: fit. (c) Mean sO₂ versus the vessel order, quantified along the centerline of each vessel. The sO₂ values in both the arteries and veins slightly change with the vessel order, especially at distal branches. This is probably due to oxygen diffusion between the arteries and veins, and the inhomogeneous MRO₂. (d) Blood flow rate (in μl/min) versus the vessel order, quantified from the flow speed profiles and vessel diameters. Blood flow in both arteries and veins decreases from the proximal order to the distal order and is conserved between the artery and vein of the same order. The blood fed by the artery is mostly drained by the corresponding vein of the same order. V: vein; A: artery. (Color online only.)