In vivo assessment of inflammation in carotid atherosclerosis by noninvasive photoacoustic imaging

: Objectives: The objective of this study was to demonstrate the feasibility of using noninvasive photoacoustic imaging technology along with novel semiconducting polymer nanoparticles for in vivo identifying inflammatory components in carotid atherosclerosis and assessing the severity of inflammation using mouse models. Methods and Results: Healthy carotid arteries and atherosclerotic carotid arteries were imaged in vivo by the noninvasive photoacoustic imaging system. Molecular probes PBD-CD36 were used to label the inflammatory cells to show the inflammation information by photoacoustic imaging. In in vivo imaging experiments, we observed the maximum photoacoustic signal enhancement of 4.3, 5.2, 8 and 16.3 times between 24 h post probe injection and that before probe injection in four carotid arteries belonging to three atherosclerotic mice models. In the corresponding carotid arteries stained with CD36, the ratio of 0.043, 0.061, 0.082 and 0.113 was found between CD36 positive (CD36(+)) expression area and intima-media area (P < 0.05). For the CD36(+) expression less than 0.008 in eight arteries, no photoacoustic signal enhancement was found due to the limited system sensitivity. The photoacoustic signal reflects CD36(+) expression in plaques, which shows the feasibility of using photoacoustic imaging for in vivo assessment of carotid atherosclerosis. Conclusion: This research demonstrates a semiconducting polymer nanoparticle along with photoacoustic technology for noninvasive imaging and assessment of inflammation of carotid atherosclerotic plaques in vivo.