Ultrasound and MRI Assessment of Cardiovascular Risk

Detection of subclinical atherosclerosis through noninvasive imaging such as ultrasound and magnetic resonance imaging (MRI) can improve cardiovascular risk stratification beyond that based on traditional cardiovascular risk factors. Ultrasound-based measures such as carotid intima-media thickness (CIMT) and presence of plaque (carotid, iliofemoral) have been evaluated and shown to have associations with cardiovascular events. However, given issues with reproducibility and other potential errors related to assessment of CIMT, there is currently a greater focus on use of carotid artery plaque measurement for cardiovascular risk assessment. The Mannheim consensus defined plaque as a focal structure or thickening (1) that is at least 50% greater than the thickness of its surrounding vessel, or (2) encroaches into the arterial lumen by at least 0.5 mm, or (3) demonstrates a CIMT greater than 1.5 mm. Several methods of plaque quantification including plaque score, plaque area, and 3D ultrasound-based plaque volume have been shown to predict cardiovascular outcomes. Additional efforts in characterizing plaque also continue to be evaluated. Carotid MRI is an important diagnostic tool not only to identify plaque burden but also to characterize plaque components including a thin fibrous cap, lipid-rich necrotic core, calcification, and intraplaque hemorrhage. It demonstrates moderate to excellent correlation of different plaque characteristics with histology. Clinical data on the value of MRI in risk prediction are starting to emerge. Numerous prospective and retrospective studies have shown MRI-derived measures of plaque characteristic and burden can identify those at higher risk for future cardiovascular events. At the current time, coronary calcium scoring is the recommended imaging approach in cardiovascular risk stratification. However, as technology continues to advance, the value of ultrasound and MRI in cardiovascular risk stratification will likely increase.