Combined EPR and Optical Imaging to Reveal Oxidative Stress and Microstructure in Human Atherosclerotic Plaques

The development of atherosclerosis is driven by inflammation in combination with structural changes and aggregation of certain tissue, ultimately resulting in a plaque. There is an intricate interplay between the structural changes, characterized by the many different structures seen in a plaque, and the inflammation and ensuing cellular responses. To better understand the etiology of atherosclerosis it is necessary to have methods which elucidate the interplay between the structural and inflammatory features. The main aim of this study is to present the combination of electron paramagnetic resonance imaging (EPRI), which images the oxidative stress and compare this with modern optical imaging techniques that can reveal property and microstructure of a variety of biological tissue. Thus, we compare images mapping the inflammatory locations as detected by ROS trapping and EPRI [1] with images obtained from the adjacent sections as obtained by optical methods such as second harmonic generation (SHG), two-photon excitation fluorescence (TPEF) [2] and imaging based on transmission Mueller Matrix Ellipsometry (MME) [3]. The combined images reveal the presence and location of calcified regions, accumulation of cholesterol crystals within the section of the carotid artery. It is concluded that regions of high oxidative stress appears to be associated with regions of calcification and high concentration of cholesterol crystals, and that the combination of the optical and EPR imaging techniques appears to be useful for investigating the spatial and causal relationships between inflammation and structural modifications. References [1] Gustafsson, H., Hallbeck, M., Lindgren, M., Kolbun, N., Jonson, M., Engström, M., de Muinck, E. and Zachrisson, H.; Visualisation of oxidative stress in ex vivo biopsies using electron paramagnetic resonance imaging (EPRI). Magnetic Resonance in Medicine 2014, In Press. [2] Lilledahl, M. B., Haugen, O. A., de Lange Davies, C. and Svaasand, L. O., Characterization of vulnerable plaques by multiphoton microscopy. J. Biomed. Opt. 2007, 12(4), 044005-. doi:10.1117/1.2772652 [3] Ellingsen, P. G., Lilledahl, M. B.; Aas, L. M. S., Davies, C. D. L. and Kildemo, M.; Quantitative characterization of articular cartilage using Mueller matrix imaging and multiphoton microscopy, J. Biomed. Opt., 2011, 16, 116002-.