The electric field of polarized light creates a wave signal along a single plane (such as vertical or horizontal). When it is directed at tissue, the electric field is influenced by the microscopic structure and organization of the tissue. Tissues rich in collagen and smooth muscle cells split the beam of light into two rays that diverge into slightly different directions. The researchers could distinguish coronary plaque composition and stability based on the optical effect.
Participants in this study underwent cardiac catheterization including intravascular imaging with optical coherence tomography, to measure the polarization properties of the coronary artery wall. Intravascular imaging uses light in the near infrared range to acquire high-definition, cross-sectional images of the vessel wall. Twelve catheterizations were performed on patients who had been affected by acute coronary syndrome—the higher risk form of the disease, and another 18 on patients with symptoms of stable angina pectoris.
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The 30 catheterizations provided multiple plaque images for each procedure, including 342 cross-sectional plaque images and 244 images from the fibrous caps of the atherosclerotic lesions responsible for high risk or stable symptoms. The high-resolution images enabled the researchers to classify coronary cross-sections into one of seven categories: normal, fibrous, fatty, calcified, thick cap, thin cap, or ruptured cap. Then, the team used the specialized instrument to determine the polarization properties of the coronary arterial wall.
Optical images of arteriesOptical imaging distinguished seven categories of coronary arteries, from left: normal, fibrous, fatty, calcified, thick cap, thin cap, ruptured cap. Credit: Otsuka, K. et al. J Am Coll Cardiol Img. 2019.
“This is the first-in-human pilot study of intravascular polarimetry,” Bouma said, noting that fibrous caps of plaques that are prone to rupture can now be reliably identified using the method. “Intravascular polarimetry may open new avenues for studying plaque composition and detecting high-risk patients.”
The research was supported by in part by grants from the National Institutes of Health, including NIBIB (EB015903) for support of the technical development and methods, and the National Heart, Lung, and Blood Institute (HL-119065).
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