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There are numerous velocity criteria published, that can be utilized as a
starting point!   However, it is essential to understand fully the
methodology, angles (not all are at 60 degrees) and examination specifics
applied by the initial investigators in developing these criteria.  For
example:

Dr. Strandness et al, developed their criteria using a 5 mhz pulsed Doppler,
a 1.5mm sample volume, & sampling midstream with a 60-degree angle.  In
addition the stenosis classification applies to the first 3 cm of the ICA!

 Dr. Bluth et al, developed their criteria using 45 - 60 degree angles, a
1.5 mm sample volume in proximal 1/3rd of ICA.

Since NASCET and ACAS studies the number of published criteria has increased
significantly.   All these criteria have been throughly correlated by the
investigators in their institututions with their equipment and personnel.
However, there has been much discussion as to the reasons that these
criterion do not necessarily apply across the spectrum of labs, equipment
and personnel.   Several recent papers have indicated that velocity
measurments may vary between equipment manufacturers.  In addition,
examiners may not be using the criteria as developed by the initial
investigator.  Eg:  using distal ICA velocity as highest rather than the
highest velocity from the first 3 cm.,  using different angles, etc.

I personnally have used four (4) different criteria over the past twenty
years, with great success.  However, I routinely reconcile the velocity
criteria with my image findings.  This has been especially beneficial when
there is a clear discrepancy between image findings and velocity.

Ongoing correlation with a reference study, preferable angiography, is the
only method for examiners to evaluate their accuracy.  From personnal
experience, it is one of the best learning experiences you may ever find.
We learn so much from looking at our mistakes as well as our successes.

Cathy Mankin, LPN, RVT
Au Courant Sonography