005 THE IMPACT OF CALCIUM ON ARFI IMAGING OF ATHEROSCLEROTIC PLAQUES

Cardiovascular risk stratification could be improved by properly delineating the position of calcium deposits relative to other plaque structures in atherosclerosis imaging. ARFI ultrasound has been demonstrated to resolve plaque collagen and elastin composition, in vivo and ex vivo, but its ability to localize calcium deposits has not been thoroughly explored. We here evaluate the impact of calcium deposits on ARFI imaging of atherosclerotic plaques in a familial hypercholesterolemic pig model. I. Introduction: Although coronary calcium deposits are well-established predictors of cardiac morbidity and mortality, the overall role of calcium deposits in atherosclerosis and their contribution to plaque stability remains controversial (1). Recent evidence based on mathematical modeling and postmortem studies supports that when positioned in the plaque shoulder, calcium deposits stabilize plaques. However, when positioned in the fibrous cap, calcium deposits substantially compromise plaque stability (1-3). Even 10-20 µm microcalcifications in thin fibrous caps have been shown to significantly increase plaque rupture potential, while calcium deposits positioned in lipid cores or far from the arterial lumen are reported to have little impact on overall plaque stability (3). These data suggest that improvements in cardiovascular risk stratification may be gained by properly identifying the position of calcium deposits relative to other atherosclerotic plaque structures. Atherosclerotic plaque structure and composition can be assessed noninvasively by Acoustic Radiation Force Impulse (ARFI) ultrasound. We have previously demonstrated ARFI's potential for in vivo delineation of plaque collagen and elastin content and identification of fibrous cap and lipid core structures in a familial hypercholesterolemic pig model (4). However, we have not evaluated ARFI's utility for localizing calcium deposits, nor have we investigated how calcium deposits impact ARFI's ability to resolve other plaque structures. Therefore, we now explore the impact of calcium deposits on ARFI imaging outcomes in a familial hypercholesterolemic pig model, ex vivo and in vivo, with immunohistochemical validation. II. Methods: ARFI imaging was performed using a Siemens SONOLINE Antares™ imaging system equipped for