As a discipline at the intersection of molecular biology and in vivo imaging, molecular imaging enables the visualization of the cellular function and the follow-up of the molecular processes in living organisms without perturbing them. The multiple potentialities of this field are applicable to the diagnosis and treatment monitoring of diseases such as cancer and neurological and cardiovascular diseases.
We have developed a novel multimodal imaging system for high-speed, high-resolution retinal imaging of larger animals, such as rabbits. The system integrates three state-of-the-art imaging modalities, including photoacoustic microscopy (PAM), optical coherence tomography (OCT), and fluorescence microscopy (FM). The PAM employs a wavelength tunable pulsed laser, a galvanometer, a scan lens, an ophthalmic lens, and an ultrasound transducer. High speed imaging is achieved to visualize individual blood vessels of the eye. Using animal models of abnormal microvasculature and neovascularization coupled with molecular contrast agents, molecular imaging is achieved.
Fig. 1 Integrated photoacoustic microscopy, optical coherence tomography, and fluorescence microscopy for chorioretinal imaging. A: Schematic; B: physical setup. OPO: Optical parametric oscillator; SLD: superluminescent diode; BS: beam splitter; DM: dichroic mirror; DCG: dispersion compensation glass; galvo: galvanometer.
Fig.2 PAM and OCT dual-modality imaging of retinal blood vessels in rabbits. (c) Close-up of the RVs in the white rectangle box in (b). (d) MIP of PAM signals of RVs and choroidal vessels (CVs). (e) 3D volumetric rendering of the PAM image (see Visualization 1). (f) 2D orthogonal slices of the PAM image showing RVs and CVs at different depths. (g) OCT image showing RVs, CVs, NFL, and retinal layers.
Fig. 3 PAM and OCT dual-modality imaging of choroidal blood vessels in rabbits. (c) OCT image showing retinal layers, the choroid, and the sclera. GCL: Ganglion cell layer; IPL: inner plexiform layer; INL: inner nuclear layer; OPL: outer plexiform layer; ONL: outer nuclear layer; OLM: outer limiting membrane; MZ: myoid zone; EZ: ellipsoid zone; OS: outer segment; IZ: interdigitation zone; BM, Bruch’s membrane.