In Vivo Carotid Plaque Stiffness Measurements with ARFI Ultrasound in Endarterectomy Patients

Acoustic radiation force impulse (ARFI) ultrasound is an elasticity imaging technique that has the potential to identify vulnerable atherosclerotic plaque characteristics. Previous studies have shown that regions of high ARFI-induced displacement correspond to lipid/necrotic areas in plaques, whereas regions of low displacement correspond with fibrotic/calcified areas. In this work, we continue our analysis of ARFI images captured from patients undergoing carotid endarterectomy. ARFI imaging of carotid plaque was performed prior to surgery, and extracted specimens were histologically processed and matched to the ultrasound imaging plane. ARFI images and histological slides were annotated independently for various features including necrotic core, calcification, fibrosis and fibrous cap, and wide hemorrhage. Results are presented for a number of advanced plaque types (Va, Vb, and VI), and ARFI-derived fibrous cap thickness measurements are compared quantitatively to histology. Results suggest ARFI is capable of measuring fibrous cap thickness with a mean positive bias of 0.09 +/- 0.12 mm, and may be capable of identifying ruptured plaque.