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.