Multimodal photoacoustic microscopy and OCT molecular imaging of choroidal neovascularization with gold nanostars

Abstract

Purpose : Choroidal neovascularization (CNV) is a leading cause of blindness worldwide. Early detection in macular degeneration results in improved outcomes. This study describes a multimodal OCT and photoacoustic microscopy (PAM) molecular imaging system using plasmonic gold nanaostars (GNS) conjugated to RDG as contrast agents. GNS have an optical absorption peak in near infrared window (650 nm) at a small size of 30 nm, allowing for contrast where intrinsic tissue PAM signal is low due to the low absorption of hemoglobin.

Methods : CNV was created in 6 New Zealand rabbits though intravenous injection of Rose Bengal (5mg/kg) followed by laser illumination at a power of 300 mW, spot size 70 mm, and 500 ms pulse duration for 40 laser spots on a retinal vessel. The model was monitored using multimodal imaging for 28 days until the CNV had developed. Rabbits were intravenously injected with 400 mL of GNS (2.5 mg/mL) conjugated to RGD. OCT, PAM, FA, ICGA, and fundus imaging were acquired at 1, 2, and 8 hours and 1, 2, 4, 7, 9, 11, and 14 days post-injection to provide visualization of the GNS.

Results : Multimodal OCT and PAM signal peaked at 24 hours after GNS injection with a 24-fold enhancement in PAM and a 180% increase in OCT signal. These values suggest the benefits of using GNS to produce improved visualization by acquiring PAM images at 650 nm where intrinsic tissue signal is low. Histological analysis and TUNEL assay indicated no change in cell morphology or evidence of cell death. GNS-RGD localized at high resolution to CNV and provided molecular imaging.

Conclusions : Multimodal OCT and PAM allows for improved visualization of CNV. The addition of GNS-RGD allows for molecular targeting of CNV for early detection of molecular changes. These results are promising, and future investigations are warranted.

This is a 2020 ARVO Annual Meeting abstract.

 

PAM images at 24 h post GNS injection at exitation wavelengths of 578 nm (a,d,f,g) and 650 nm (b,c,e,h). CNV is noted (c) and (i) by arrows. (g-i) demonstrate the overlaying of GNS with normal vasculature.

 

(a) Schematic setup of multimodal OCT and PAM imaging system. (b) TEM image of the configuration and rotation the GNS. (c) Absorption spectrum of GNS, indicating the optimal wavelength of 650 nm. (d) PAM imaging of cells with GNS and peak at 650 nm. (e-f) Histology analysis of the eye and liver with CNV in (e) noted by arrows.