Evaluation of the flying spot technique as a television method for measuring red cell velocity in microvessels

The success of measuring red cell velocity in microvessels by television methods based on cross-correlation depends to a considerable extent on the optical contrast between red cells and plasma gaps passing through these vessels. Poor optical contrast, such as under conditions of low magnification, may result in deteriorated cross-correlograms and, consequently, in completely erroneous velocity values. The success of measuring velocity by the flying spot technique, however, depends only on the operator's ability (1) to discern the moving red cells, and (2) to match the speed of the spot to that of these cells. We have implemented this technique as a television method and estimated the subjective error involved in this velocity matching. Under a total magnification of 112 X, the estimated relative errors among four observers in the velocity range from 0.10 to 0.57 mm/s varied between 4.4 and 14.9%, while the overall error was 8.7%. It was concluded that this technique can provide, in the range from 0 up to possibly 1-2 mm/s, quick and reliable velocity measurements with a reasonable accuracy. Also, since no sophisticated equipment is required for the implementation, this method, at present, is much less expensive than the other conventional television methods for measuring velocity.