Has anyone had any experience discerning the difference between these 2 cpt's and when it is appropriate to use which? I'm of the opinion that there's a very subtle difference beside that fact that 93965 is a bilateral study where they are looking for venous reflux. Plus, I've seen 965 is 'non-invasive' and 971 is duplex doppler and wonder if that' where the distinction is. Thank you !!