93970 / 93971 help

For CPT® 93970 DUPLEX SCAN OF EXTREMITY VEINS INCLUDING RESPONSES TO COMPRESSION AND OTHER MANEUVERS; COMPLETE BILATERAL STUDY - AND - 93971 UNILATERAL OR LIMITED.

CAN ANYONE TELL ME IF BOTH THE DEEP AND SUPERFICIAL SYSTEM MUST BE STUDIED?

WHERE CAN I FIND THIS INFORMATION OUT?

I HAVE TRIED BY REVIEWING THE NCD'S, LCD'S AND CPT® BOOK BUT AM NOT FINDING THE ANSWER ANYWHERE.

YOUR HELP WOULD BE APPRECIATED - THANKS!