A harmonic tracking method for improved visualization of arterial structures with acoustic radiation force impulse imaging

Acoustic Radiation Force Impulse (ARFI) imaging has shown improved visualization of arterial structures that may provide for a more reliable assessment of atherosclerotic risk than conventional B-mode imaging. Existing ARFI imaging methods, however, are limited due to the presence of clutter that can increase bias and jitter in estimates of tissue deformation. We have recently developed a novel pulse inversion harmonic tracking method to suppress clutter degradation in ultrasonic tissue displacement estimates. In this work, harmonic B-mode and harmonic ARFI images of in vivo carotid arteries are compared with fundamental images obtained using conventional techniques. A certified reader measured the intima-media-thickness (IMT) in B-mode images and the adventitia-intima-media-thickness (AIMT) in ARFI images. The yield and the length of the artery amenable for analysis were larger in ARFI images compared to B-mode images. Intra-reader measurements of ARFI AIMT in the distal wall were more reproducible than B-mode IMT measurements. Qualitatively, harmonic ARFI images showed improved delineation of the vessel-lumen interface compared to fundamental ARFI images. These results suggest that harmonic ARFI imaging may provide a reliable method for monitoring arterial thickening to predict the occurrence of clinical events.