Quantitative imaging of red blood cell velocity invivo using optical coherence Doppler tomography.

We present particle counting ultrahigh-resolution optical Doppler tomography (pc-μODT) that enables accurate imaging of red blood cell velocities (ν(RBC)) of cerebrovascular networks by detecting the Doppler phase transients induced by the passage of a RBC through a capillary. We apply pc-μODT to image the response of capillary ν(RBC) to mild hypercapnia in mouse cortex. The results show that ν(RBC) in normocapnia (ν(N) = 0.72 ± 0.15 mm/s) increased 36.1% ± 5.3% (ν(H) = 0.98 ± 0.29 mm/s) in response to hypercapnia. Due to uncorrected angle effect and low hematocrit (e.g., ∼10%), ν(RBC) directly measured by μODT were markedly underestimated (ν(N) ≈ 0.27 ± 0.03 mm/s, ν(H) ≈ 0.37± 0.05 mm/s). Nevertheless, the measured ν(RBC) increase (35.3%) matched that (36.1% ± 5.3%) by pc-μODT.