Fig. 2.

Spatiotemporal traces of the blood cells when the imaging light was focused on different planes. The plots in each row were generated from the videos taken in the same capillary. Left column panels were blood cells traces when the light was focused on the photoreceptor inner segment plane. Due to low absorption and scattering, the leukocyte traces appear as hyper-reflective bands indicated by solid color arrowheads. Right column panels were made from videos with light focused on the capillaries directly. Due to higher scattering rate, the erythrocyte formed hyper-reflective lines separated by narrow dark gaps generated by plasma. When leukocytes pass through the capillary, because of their low absorption and low scattering and confocal rejection of scattering out-of-focus, they appear as broad hypo-reflective bands (pointed by the empty arrowheads) followed by densely packed hyper-reflective lines, which are accumulated erythrocytes. Arrowheads with same color indicate leukocytes in the same capillary. Because the videos were not taken simultaneously, the leukocytes in the same capillary are not the same cells. All images were generated from videos acquired at 800 fps. The spatial (vertical) scale bar is 25 µm and the temporal (horizontal) scale bar is 100 ms.