Abstract
Optical coherence tomography (OCT) has become a standard-of-care in retinal imaging. OCT allows non-invasive imaging of the tissue structure but lacks specificity to contrast agents that could be used for in vivo molecular imaging. Photothermal OCT (PT-OCT) is a functional OCT-based technique that has been developed to detect absorbers in a sample. We demonstrate in vivo PT-OCT in the eye for the first time on both endogenous (melanin) and exogenous (gold nanorods) absorbers. Pigmented mice and albino mice (n = 6 eyes) were used to isolate the photothermal signal from the melanin in the retina. Pigmented mice with laser-induced choroidal neovascularization lesions (n = 7 eyes) were also imaged after a systemic injection of gold nanorods to observe their passive accumulation in the retina. This experiment demonstrates the feasibility of PT-OCT to image the distribution of both endogenous and exogenous absorbers in the mouse retina.
Highlights
Optical coherence tomography (OCT) is a standard-of-care retinal imaging technique in the clinic, and is widely used to study retinal diseases in pre-clinical research[1]
photothermal OCT (PT-OCT) is an emerging technique that adds functional contrast to traditional OCT imaging. It has been demonstrated in vitro[25], ex vivo[40] and in vivo[37] in the past on contrast agents such as gold nanoparticles[42] and melanin[45]. This was the first time that PT-OCT was demonstrated in the eye, even though OCT is commonly used for retinal imaging in eye research and is a standard of care in ophthalmology[1]
We obtained a statistically significant increase in photothermal signal in pigmented mice, and the signal was located in depth at a retinal layer corresponding to the retinal pigment epithelium (RPE) and choroid
Summary
Optical coherence tomography (OCT) is a standard-of-care retinal imaging technique in the clinic, and is widely used to study retinal diseases in pre-clinical research[1]. A molecular OCT technique that detects endogenous and exogenous contrast agents would provide complimentary information to structural OCT, OCTA, PS-OCT and OCE Such a multifunctional, OCT-based approach would be beneficial for eye imaging since it is impractical to focus multiple instruments at once on the retina, and successive imaging using different instruments increases imaging time and requires image registration. Contrast agents can be used with OCT to increase the backscattered signal in regions of interest[17], but the detection specificity of these contrast agents is poor against a scattering background[18] such as a neovascular lesion in AMD models Techniques such as spectroscopic[19], pump-probe[20, 21], magnetomotive[22], diffusion-sensitive[23]. Since melanin is an absorber in the near-infrared, detection with PT-OCT can be done directly, without the need for additional tags or dyes
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