In this study, where was the CCA spectral velocity obtained for conparison
with the ICA for the ICA:CCA ratio? As you know proximal velocities are
generally higher than mid CCA velocities in a non-stenotic CCA.
Zwiebel states that the CCA component of the ratio should be the "peak
velocity obtained in a normal portion on the CCA, proximal to the stenosis (of
the ICA)". This is very non-specific leaving room for great variation in the
ICA:CCA depending on where the CCA is measured. I generally use the mid CCA
for the ratio. I don't know if there are specific guidelines for the place of
aquisition of the CCA or that these guidelines, if they exist, are uniformly
used clinically or in reasearch studies.