{HEAD ~ means} for producing {TAIL ~ an electrical signal} in the photodetector having a frequency component proportional to the blood cell velocity in response to autodyne beating of Doppler shifted and non Doppler shifted radiation signals 
for producing
{ HEAD ~ means } for producing { TAIL ~ an electrical signal } in the photodetector having a frequency component proportional to the blood cell velocity in response to autodyne beating of Doppler shifted and non Doppler shifted radiation signals
HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH