Carotid Artery Ultrasound and MRI Assessment

Ultrasound was also used to assess DC (10⁻³ mmHg^-1), YEM (mmHg), and common carotid artery carotid intima-media thickness (IMT) [19 (link), 20 (link)]. Mean and maximal IMT of the far wall of distal CCA (distal 1 cm, proximal to the carotid bifurcation point, where the distal CCA diameter remains uniform) and the proximal 1 cm of the ICA were measured in triplicate at the University of Wisconsin using a semi-automated border detection program (Syngo Arterial Health package, Siemens Medical Solutions, Malvern, PA) blinded to subject demographic and medical information. For DC and YEM, systolic and diastolic diameters were determined as the largest and smallest diameters during the cardiac cycle. All measurements were performed in triplicate from 2–3 consecutive cardiac cycles to derive mean internal diameter at peak systole and mean internal and external diameters at end-diastole using Access Point Web version 3.0 (Freeland Systems, LLC) [20 (link)]. Thoracic aortic distensibility was measured with magnetic resonance imaging [21 (link)]; small and large artery elasticity were measured using radial pulse contour analyses [21 (link)]. Each of these measurements was calculated using standard formulae and have been previously described in detail within MESA [19 (link)–22 (link)].