Arterial Plaque Classification

The goal of this research is to develop and evaluate a non-invasive ultrasound-based technique for in vivo classification of atherosclerotic plaque. The ultimate goal is to develop a screening tool for stroke risk. The technique measures the absolute integrated backscatter (IBS) of arterial wall structures through an intervening inhomogeneous soft tissue layer. The aberrating effect of this tissue layer is minimized by normalizing the measured IBS from the wall region of interest with the IBS from an adjacent range cell in blood.

Stroke is the third largest killer, after heart disease and cancer.  In the US, about 700,000 people suffer strokes each year. About 500,000 of these are first attacks, and 200,000 are recurrent attack. Stroke is estimated to cost $30 to $40 billion per year. As many as 60 – 70% of all strokes are caused by emboli from “vulnerable” plaques in the carotid artery. Treatment regimens are available, such as surgical removal of plaque material (carotid endarterectomy) or carotid artery stenting, a recent procedure where an expandable metal-mesh tube, called a stent, is inserted into the carotid artery to increase blood flow.

Atherosclerotic lesions contain a combination of fatty, fibrofatty, fibrotic and calcified materials, each with different ultrasound backscatter characteristics, and there appears to be a strong correlation between plaque composition and vulnerability/stability of plaque. Thus, morphology and composition of atherosclerotic plaque is predictive of stroke risk, and may be detected ultrasonically.                                                                   

The major challenge with ultrasound-based plaque classification is the phase aberration of the ultrasound beam caused by the soft tissue between the skin surface and plaque region of interest, which modifies echoes from a given vessel wall and plaque in an unpredictable way.

However, this may be overcome by using a reference backscatterer in the immediate vicinity of the plaque or vessel wall: a volume of flowing arterial blood inside the lumen of the carotid artery, adjacent to the plaque region of interest. Arterial blood, however, must be treated as a stochastic scatterer. In our approach, the Integrated backscatter (IBS) of the plaque or wall echoes is normalized with the IBS of an adjacent volume of arterial blood.

This work was started by then MS student in Electrical and Computer Engineering, Ruben Lara-Montalvo, and is being continued by Towa Matsumura, MS student in Electrical and computer Engineering.