FI nanoparticles enhanced multimodal near-infrared photoacoustic microscopy and optical coherence tomography imaging of rat choroid

The choroid is involved in the pathogenesis of several ocular conditions. However, most techniques of fundus imaging have focused on the retinal layer because the choroid is beyond the penetration depth of the detection light. In this study, a multimodal Near-infrared Photoacoustic Microscopy (NIR-PAM) and Optical Coherence Tomography (OCT) system was developed to image choroid. Polyethylene glycol (PEG) modified FI nanoparticles (FINPs) with absorption peak up to 1064 nm were used as a contrast agent to enhance NIR-PAM and OCT for in vivo imaging of choroid. After intravenous injection of PEG-FINPs into Brown Norway (BN) rats (8 weeks), the rat choroid was time-serially monitored with PAM and OCT: 1 min, 3 min, 5 min, 10 min, 15 min, 30 min, and 60 min. Signal increased by 381% in PAM and 109% in OCT at 1 min. The choroidal vessels were clearly visualized in the NIR-PAM compared with that in VIS-PAM imaging using 532 nm light source.