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 (IVPA) 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.