Velocity variation assessment of red blood cell aggregation with spectral domain Doppler optical coherence tomography.

We propose spectral domain Doppler optical coherence tomography (SD-D-OCT) to qualitatively measure red blood cell aggregation. Variance/standard deviation (SD) of the Doppler frequency spectrum in Doppler variance imaging of flowing blood under shearing conditions was developed as a new aggregation index. In in vitro microchannel-flow experiments, porcine blood at various hematocrits with aggregation characteristics induced by dextran 500 or at the presence of plasma fibrinogen was measured by a SD-D-OCT system with a spectrum centered at 1310 nm. The effects of shear rate, hematocrit, aggregation level on the SD values were investigated. The results demonstrate that Doppler variance imaging using the SD value was capable of differentiating the normal and the aggregated blood with hematocrits of 30-55% flowing at a shear rate of 40-60 s(-1). The SD value was found to be nonsignificant hematocrit-dependent. It is also a sensitive and repeatable aggregation index for comparison between nonaggregated and aggregated blood samples.