We have a fail-proof way of vein- mapping---- we first scan leg using gel and
 measure GSV from jx to ankle. If adeq. size we wipe off all gel and rescan
using water. Get cup with water and just dip probe into cup ( not all the
way) and scan trans all the way down marking mid point. Water works great and
allows enough contact w/ skin to visualize it. I use regular marks-alot.

Pattie Shandloff BSN,RVT
Vascular Supervisor
Bethesda Vascular Institue