Detection of macrophages and lipid using ultrasound guided spectroscopic intravascular photoacoustic imaging.

Abstract

Macrophages and lipid are two key components in the development and characterization of atherosclerotic plaques. Imaging the activity and distribution of macrophages and lipid in the vessel wall would help identify the vulnerable plaques. In this study, spectroscopic intravascular photoacoustic (sIVPA) imaging was used to detect phagocytically active macrophages and deposits of lipid simultaneously. Polyethylene glycol coated spherical gold nanoparticles (Au NPs) were intravenously injected in vivo into an atherosclerotic rabbit allowing phagocytically active macrophages within the plaques to be labeled with Au NPs. Atherosclerotic aorta was harvested and scanned with a bench-top sIVPA imaging system. Au NP-labeled macrophages were detected in the 710–770 nm wavelength range because of the plasmon resonance coupling effect. Lipid was imaged in 1210–1230 nm wavelength range based on the characteristic optical absorption spectrum of fatty acids. An image processing method was developed to identify Au-NP-labeled macrophages and lipid deposits from the multiwavelength IVPA data. Coregistered sIVPA images were combined with corresponding IVUS images to demonstrate the location of Au NP-labeled macrophages and lipid within the vessel wall. Finally, histochemistry stains confirmed that combined sIVPA and IVUS imaging can successfully detect the distribution of phagocytically active macrophages and lipid deposits.