["Spatial shift alignment (SSA)"--a new method for determining blood flow velocity in video capillary microscopy]

A new technique (spatial shift alignment [SSA]) for measuring capillary blood velocity in human capillaries in the skin is described. A capillaroscopic image is digitized by means of a frame grabber. Within the lumen of a suitable capillary limb a region of interest known as a slot is placed. At a frame frequency of 25 per second, this slot is copied in a free part of the frame grabber store along a horizontal axis. A static space-time image with light diagonal bands representing the plasma gaps in their passage through the capillary limb is obtained. By determining the gradient of the diagonal bands, a measure of the capillary blood velocity is obtained. The SSA system was validated by means of a simulated model using known fixed velocities between 0 and 1.0 mm/sec (r = 0.979, n = 24). The procedure can be employed with any image processing systems, and enables continuous monitoring of the velocity measurements. Since it is time-saving and just as accurate as the frame-to-frame method, SSA could be widely applied to the measurement of blood cell velocity in capillaroscopy.