First of all, great input!.... Would'nt you agree that if the studies in a particular facility/lab are internally validated as compared to angiography,MRA(yuck), outside studies, serial studies, etc. (regardless of angulation method ie: strict 60 degree vs. 40-50 degree and presuming both are parallel to wall or jet, (no debate please) that consistancy among serial studies needs to happen. In other words, if Mr Smith has a carotid duplex today and sonographer "A" uses a 60 degree angle in the CCA, 50 degree angle in the ICA etc, that when Mr. Smith returns in 6 months the study needs to be reviewed prior to his next scan to use the same angles as on the first study? (you know, manzanas to manzanas) I think this is one of reasons that a standardized angulation is pushed. Other than diagnostic criteria being developed using a particular angle. If internal validation shows 95% + agreement, What is the difference??