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Tan Liu, Xiaojing Liu, Rong Wen, Yiwen Li, Carmen A Puliafito, Hao F Zhang, Shuliang Jiao; Optical coherence photoacoustic microscopy for in vivo multimodal retinal imaging. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4367.
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To develop a near-infrared (NIR) optical coherence photoacoustic microscopy (OC-PAM) system, which can accomplish optical coherence tomography (OCT) and photoacoustic microscopy (PAM) simultaneously by using a single pulsed broadband near-infrared light source. The ultimate goal of the study is to provide a multimodal in vivo imaging tool that can provide comprehensive and quantitative information about the absorption and scattering properties of the retina.
OC-PAM offers a unique opportunity for studying the scattering and absorption of biological tissues because the simultaneously acquired OCT and PAM signals are generated by the same group of photons. The acquired OCT and PAM images are intrinsically registered in the lateral directions. To make this technique more suitable for eye imaging, i.e more tolerable by human subjects, we built a NIR OC-PAM by using an ultrafast Ti:sapphire laser amplifier operating under an unseeded mode. The light source had a center wavelength of 800 nm with a FWHM bandwidth of 30 nm. The OCT signal was detected in the spectral domain while the photoacoustic signal is detected with an ultrasonic transducer place in contact with the eyelid. The measured depth resolution of OCT and PAM are 9.9 μm (in air) and 46 μm, respectively.
To test the capabilities of the system on multimodal ophthalmic imaging we imaged the retina of pigmented rats. The OCT images showed the retinal structures with quality similar to conventional OCT while the PAM images revealed the distribution of absorbers in the retina, which were confirmed with histology to melanin in the RPE and choroid. Choroidal vessels cast shadows in PAM images. Since the absorption of hemoglobin is relatively weak at around 800 nm, the NIR PAM signals are generated mainly from melanin in the posterior segment of the eye.
We have demonstrated the feasibility of an OC-PAM system working in the near-infrared. By using a single pulsed broadband NIR light source, OC-PAM can image the scattering and absorption contrasts simultaneously. This system can provide both structural information with good depth resolution as conventional OCT and melanin specific absorption contrast of the eye.
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