An optical doppler intravital velocimeter.

A system has been implemented for measurement of red blood cell velocity in microvessels by using an optical Doppler technique. Ronchi rulings are used to stimulate a differential grating to translate red blood cell movement to light intensity variations. These variations are sensed by two photodiodes coupled in a resistive subtraction mode. The nonelectronic subtraction allows high transimpedance gains (2 X 10(9) V/I) while noise is held to a minimum (4.5 mv RMS in a 5-kHz bandwidth). To derive average velocity the average frequency determination of the amplified signal is performed with a thresholding frequency-to-voltage functional block. The velocimeter provides the typical performance features of an optical Doppler system, including high-frequency response, without the need for the complications of the laser Doppler technique or the requirement of custom micro-prism gratings. The device represents a cost-effective approach to intravital work, and offers significant improvements in performance over standard techniques.