Quantitative imaging of red blood cell velocity in vivo using optical coherence Doppler tomography

We present particle counting ultrahigh-resolution optical Doppler tomography (pc-mu ODT) that enables accurate imaging of red blood cell velocities (nu(RBC)) of cerebrovascular networks by detecting the Doppler phase transients induced by the passage of a RBC through a capillary. We apply pc-mu ODT to image the response of capillary nu(RBC) to mild hypercapnia in mouse cortex. The results show that nu(RBC) in normocapnia (nu(N) = 0.72 +/- 0.15 mm/s) increased 36.1% +/- 5.3% (nu(H) = 0.98 +/- 0.29 mm/s) in response to hypercapnia. Due to uncorrected angle effect and low hematocrit (e.g., similar to 10%), nu(RBC) directly measured by mu ODT were markedly underestimated (nu(N) approximate to 0.27 +/- 0.03 mm/s, nu(H) approximate to 0.37 +/- 0.05 mm/s). Nevertheless, the measured nu(RBC) increase (35.3%) matched that (36.1% +/- 5.3%) by pc-mu ODT. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4726115]