Measurement of Collagen and Smooth Muscle Cell Content in Atherosclerotic Plaques Using Polarization-Sensitive Optical Coherence Tomography

Abstract

The purpose of this study was to investigate the measurement of collagen and smooth muscle cell (SMC) content in atherosclerotic plaques using polarization-sensitive optical coherence tomography (PSOCT). A method capable of evaluating plaque collagen content and SMC density can provide a measure of the mechanical fidelity of the fibrous cap and can enable the identification of high-risk lesions. Optical coherence tomography has been demonstrated to provide cross-sectional images of tissue microstructure with a resolution of 10 mum. A recently developed technique, PSOCT measures birefringence, a material property that is elevated in tissues such as collagen and SMCs. We acquired PSOCT images of 87 aortic plaques obtained from 20 human cadavers. Spatially averaged PSOCT birefringence, Phi, was measured and compared with plaque collagen and SMC content, quantified morphometrically by picrosirius red and smooth muscle actin staining at the corresponding locations. There was a high positive correlation between PSOCT measurements of Phi and total collagen content in all plaques (r = 0.67, p < 0.001) and in fibrous caps of necrotic core fibroatheromas (r = 0.68, p < 0.001). Polarization-sensitive optical coherence tomography measurements of Phi demonstrated a strong positive correlation with thick collagen fiber content (r = 0.76, p < 0.001) and SMC density (r = 0.74, p < 0.01). Our results demonstrate that PSOCT enables the measurement of birefringence in plaques and in fibrous caps of necrotic core fibroatheromas. Given its potential to evaluate collagen content, collagen fiber thickness, and SMC density, we anticipate that PSOCT will significantly improve our ability to evaluate plaque stability in patients.