Capillary video red blood cell velocimetry by cross-correlation and spatial filtering.

A spatial filter capillary red blood cell velocimeter was implemented in video format by means of a linear array of video photometric windows whose number could be varied from two to eight. Two windows of the same video linear window array were used to measure velocity by means of the conventional cross-correlation method. The two methods, spatial filtering and cross-correlation, were compared by means of a computer-controlled video test pattern generator designed to simulate red blood cell flow of variable hematocrit and velocity. It was found that at normal microvascular hematocrits, both methods provide essentially identical data. At low hematocrit, if the simulated red blood cell distribution is such that a cell is always present within the array, spatial filtering data processing provides a more stable measurement than does cross-correlation; however, under the same conditions spatial filtering yields measurement directly related to flux (red blood cells per unit time) rather than to velocity.