Imaging carotid wall mechanical heterogeneity in ultrasound image sequences using Eulerian video magnification

Atherosclerosis is a cardiovascular disease causing gradual infiltration of fatty streaks in the arterial wall and eventually plaque build-up that may rupture and cause a stroke. This induces changes in local biomechanics in response to systemic pressure variations. Such mechanical heterogeneities in the carotid arteries can be studied using ultrasound imaging methods. However, in 2-D ultrasound imaging, mechanical heterogeneity may result in both in-plane motions as well as out-of-plane motion, the latter causing intensity variations. Here, we evaluate linear Eulerian video magnification (EVM) processing on carotid ultrasound image sequences, and its ability to image local mechanical heterogeneity. In addition, we explore the method on several ultrasound image sequences from carotid wall tissues at different atherosclerotic disease stages ranging from healthy, early and late atherosclerosis, as well as changes with pharmacological treatment. The results show that linear EVM can be used to magnify motions in carotid ultrasound image sequences, and to derive heterogeneity maps that can visualize mechanical aspects of the carotid walls and its composition. Empirical case study on carotid walls indicate that the heterogeneity maps transition from homogenic to heterogenic pattern with progression of the atherosclerotic disease. The findings of this work show that mechanical heterogeneity imaging may be important in assessing atherosclerotic disease progression and potential risk prediction.