In vivo three-dimensional visualization of choroidal neovascularization using gold nanorod-enhanced multimodal photoacoustic microscopy and optical coherence tomography molecular imaging

Early identification of the margins and location of choroidal neovascularization (CNV) is critical for the precise diagnosis and treatment of numerous neovascular eye diseases, including age-related macular degeneration (AMD). Integration of multimodal photoacoustic microscopy (PAM) and optical coherence tomography (OCT) imaging has been developed to complement the strengths of each modality. A major challenge remains in selectively distinguishing CNV from native microvasculature due to the high optical absorption of hemoglobin. To overcome such limitations, RGD targeting peptides conjugated with gold nanorods (GNR-RGD) was used as multimodal contrast agents to increase the sensitivity of PAM and OCT, allowing for enhanced visualization of CNV due to RGD’s selective binding to integrins in neovascularization. The ability of GNR-RGD enhanced PAM and OCT imaging was evaluated in three New Zealand White rabbits with CNV models. The CNV model was created at day 28 post laser-induced retinal vein occlusion. In vivo color fundus photography, fluorescein angiography, PAM, and OCT imaging was acquired before and after intravenous injection of 400 μL GNR-RGD at concentration of 5 mg/mL at days 1, 3, 5, 7, and 14. Longitudinal studies show that GNR accumulated at CNV sites and led the PAM and OCT signal increased by 27.2-fold in PAM and 171.4 % in OCT peaking at 48 h post-injection and decreased at day 14. Histological analysis, TUNEL assay, and liver and kidney function tests show no systemic toxicity of GNR in the retina or vital organs. The above approaches can provide a potential multimodal molecular imaging tool for precise evaluation of CNV in AMD and other neovascular diseases.