  Non-invasive measurement of the arterial blood speed gives rise to important
healthinformation such as cardio output and blood supplies to vital organs. The
magnitude andchange in arterial blood speed are key indicators of the health
conditions and development andprogression of diseases. We demonstrated a simple
technique to directly measure the blood flowspeed in main arteries based on the
diffused light model. The concept is demonstrated with aphantom that uses
intralipid hydrogel to model the biological tissue and an embedded glass
tubewith flowing human blood to model the blood vessel. The correlation
function of the measuredphotocurrent was used to find the electrical field
correlation function via the Siegert relation.We have shown that the
characteristic decorrelation rate (i.e. the inverse of the decoherent time)is
linearly proportional to the blood speed and independent of the tube diameter.
This strikingproperty can be explained by an approximate analytic solution for
the diffused light equation inthe regime where the convective flow is the
dominating factor for decorrelation. As a result, wehave demonstrated a
non-invasive method of measuring arterial blood speed without any
priorknowledge or assumption about the geometric or mechanic properties of the
blood vessels.
