The picture shows a mesenteric arteriole of appr. 20µm and the photosensors. The output of the photodiodes - which is modulated by the streaming cells - is fed to a crosscorrelator with an integrated microcontroller. It processes online the velocity and the correlation factor which reaches up to 70% at stable conditions.
References: Prof. Dr.D. Seiffge, Hoechst Marion Roussel Deutschland, Frankfurt