Acute cardiovascular events are still the leading cause of morbidity and mortality in the Western world. The rupture of a vulnerable atherosclerotic plaque is the most common cause of an acute cardiovascular event. Vulnerable plaques are characterized by presenting a necrotic core below a thin fibrous cap, and extensive infiltration of macrophages and foam cells. Thus, the degree of macrophage accumulation is an indicator in determining plaque progression and probability of rupture. This work presents a simple and fast image processing method for the identification of agglomerated macrophage/foam-cells regions in intravascular optical coherence tomography (IV-OCT) images that might be used for in-vivo assessment of plaque vulnerability. This method relies on the ratio of the values of either the normalized-intensity standard deviation or the entropy estimated over two axially adjacent regions of interest in IV-OCT images. This method is able of highlighting areas in the IV-OCT images where significant amount of macrophages is localized, and was applied to IV-OCT scans of 26 postmortem coronary segments and validated against histopathological assessment. The accuracy for detecting macrophage/foam-cell was as follows: the normalized standard deviation ratio approach showed an accuracy of 86% and a sensitivity and specificity of 85.8% and 86.1%, respectively; while the entropy ratio led to an accuracy of 86.9% and a sensitivity and specificity of 86.8% and 86.9%, respectively.
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