High sensitivity Intravascular photoacoustic imaging of macrophages

In atherosclerosis, tracking and locating the activity of macrophages that are highly involved in plaque development will help to identify the pathology of the disease. Intravascular photoacoustic (I VP A) imaging has shown potential to detect atherosclerosis and to determine plaque composition. Furthermore, using optical absorbers as contrast agents, IVPA can also be used for molecular imaging. In this paper, we study the feasibility of using gold nanoparticles as contrast agent for high sensitivity IVPA imaging of macrophages. The artery was modeled using a cylindrical tube made out of polyvinyl alcohol. Within the vessel wall, several compartments were made to mimic plaques. After incubating murine macrophages with 50 nm spherical gold nanoparticles overnight, macrophages loaded with particles were filled into the compartments of the arterial phantoms. Because of the plasmon resonance coupling of aggregated nanoparticles inside the macrophages, these macrophages can be detected by IVPA imaging using 680 nm wavelength. The sensitivity of the molecular IVPA imaging was tested using phantoms with different concentrations of nanoparticles and macrophages. Finally, to address the feasibility of in-vivo IVPA imaging with gold nanoparticles, the viability of the macrophages loaded with nanoparticles exposed to laser irradiation was studied. The results show that IVPA imaging can safely image macrophages loaded with gold nanoparticles with relatively high sensitivity.