Dynamic optical coherence tomography in studies of optical clearing, sedimentation, and aggregation of immersed blood

TLDR

Refractive‑index matching is used to increase the optical penetration depth of whole blood, a concept explored with near‑infrared optical coherence tomography in vitro. Optical clearing of blood depends on refractive‑index matching and changes in red‑blood‑cell size and aggregation, with agents such as 6.5 % glycerol reducing attenuation from 4.2 to 2.0 mm⁻¹ and increasing 820‑nm penetration to 117 %, while other chemicals yield 20–150 % enhancement and oscillatory sedimentation patterns that correlate with aggregation stages, indicating potential for intravascular OCT imaging.

Abstract

The concept of refractive-index matching to enhance the optical penetration depth of whole blood is discussed on the basis of in vitro studies that used the technique of near-infrared optical coherence tomography. It was found that optical clearing of blood is defined not only by refractive-index matching but also by changes in the size of red blood cells and in their aggregation ability when chemicals are added. For example, in whole blood diluted to twice its volume by saline with the addition of 6.5% glycerol, the total attenuation coefficient was reduced from 4.2 to 2.0 mm-1, and the optical penetration at 820 nm was correspondingly increased to 117%. For the other agents tested (glucose, dextrans, propylene glycol, and trazograph) the enhancement of penetration was 20–150.5%. In the blood sedimentation study, regular or irregular oscillations or jumps of the red-blood cell–plasma boundary were observed. The 1-min time period of regular oscillations correlated well with the kinetics of the aggregation process as described by the two subsequent stages of formation of linear and three-dimensional aggregates. The results also showed that optical clearing of blood by osmotic agents is potentially useful not only in blood sedimentation and aggregation studies but also in intravascular optical coherence tomography imaging techniques.