Audrey,  I don't know if you found your reference by now or not but I thought
I would pass on to you something I feel strongly about.  Although this
"trick" of tapping on the superficial temporal branch of the ECA can help to
identify the ECA from the ICA, it is not foolproof.  In theory, the tapping
causes a resistance to flow which is transmitted in a retrograde direction to
the ECA where the "tap" is demonstrated as undulations in the spectral
doppler profile.  In practice, however, I have seen the temporal tap elicit a
positive result in both  branches and sometimes in the ICA but not the ECA.
If you are contemplating using this technique, be wary of the pitfalls.  I
recommend you use it as an adjunct to vessel identification only.

Steve Knight BSc, RVT