Maybe this will help - sm

Maybe this will help:

"Visualize the arterial system as a tree, with the aorta as its “trunk.”  Branching from the aorta are several smaller arteries, which themselves give rise to lesser branches that, in turn, continue to branch off in a repeated pattern.  

The largest “branches” emerging from the aorta are first-order vessels. Those branches immediately arising from the first-order vessels are second-order vessels, and so on to include third-order vessels and beyond.  During nonselective catheterization, the radiologist stays on the same branch, or moves from a branch toward the trunk (the aorta).  

During selective catheterization, in contrast, the radiologist must make his way from the trunk to a smaller branch, or from one branch to another, threading the catheter through the intervening vessels along the way.  A first-order vessel and all its branches together comprise a vascular family."

http://www.rt-image.com/Quick_Tips_Rules_to_Choose_By_Determining_selective_vs_nonselective_arterial_cat/content=8004J05E48B68484407698744468A0441

Thank you!! NM - Freebie