Arous EJ, Simons JP, Flahive JM, Beck AW, Stone DH, Hoel AW, Messina LM, Schanzer A. National variation in preoperative imaging, carotid duplex ultrasound criteria, and threshold for surgery for asymptomatic carotid artery stenosis. J Vasc Surg. 2015 Oct; 62(4):937-44.