All criteria for ultrasound measurement of degree of stenosis are based on
Velocities (or Frequencies).  Measuring stenosis by ultrasound is notoriously
inaccurate.  Maybe someday there will be validation for power angio to
measure stenosis but the data now is minimal.  To be accurate you have to
measure velocities at 60 deg., do a correlation with angio and then set your
velocity criteria.  Until you establish your own try Strandness' criteria.
Direct measurement of vessels by sono is not an acceptable method.

Mike Ingegno, M.D., RVT
Vascular Surgeon
Miami Vascular Inst.