{HEAD ~ means} for producing an electrical signal in {TAIL ~ 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 ~ means } for producing an electrical signal in { TAIL ~ 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 OTH OTH OTH OTH OTH OTH 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