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Yannis M. Paulus, Adam de la Zerda, Robert Teed, Sunil Bodapati, Yosh Dollberg, Butrus T. Khuri-Yakub, Mark S. Blumenkranz, Darius M. Moshfeghi, Sanjiv S. Gambhir; Ophthalmic Photoacoustic Imaging for Blood Distribution Evaluation. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6573.
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Currently available retinal imaging devices (e.g., OCT) are optically-based and primarily visualize anatomy. Photoacoustic imaging provides physiologic information of optically deep tissue with a high spatial resolution. We demonstrate photoacoustic imaging in pig eyes ex vivo and in living rabbit eyes.
A photoacoustic system is constructed using a tunable, pulsed Nd:YAG laser with a repetition rate of 10 Hz and pulse width of 5 ns. Illumination is provided through a fiber optic ring (mean laser pulse energy density 0.5 mJ/cm^2). Ultrasound transducers with 15 and 25 MHz frequencies acquired both pulse-echo and photoacoustic images, leading to axial resolutions of 83 and 50 µm and lateral resolutions of 200 and 240 µm, respectively. This instrument is used to scan 2 enucleated pig eyes and 5 New Zealand rabbits. A second generation photoacoustic system is developed with improved 35 µm resolution.
We demonstrate co-registered photoacoustic and ultrasound images and visualize the orbit with a high depth of penetration while showing blood distribution. Figure 1 shows external photographic (A), coronal (B) and parasagittal (D) photoacoustic, ultrasonographic (C), and 3D photoacoustic (E) images. The pig eye image was acquired using 8 averages of 63 A-scan lines 250 µm apart. In rabbits, the acquisition consists of 32 averages of a scanned area 12 mm by 8 mm in 250 µm steps. Improved 35 µm resolution is demonstrated with a phantom of two crossing hairs (F).
We developed a novel photoacoustic imaging device to noninvasively image the retina, choroid, and optic nerve. Using safe laser intensity, this system visualizes blood distribution in pig and rabbit eyes. Simultaneously acquired ultrasound images visualize ocular anatomy. Photoacoustic imaging may be used for early detection and improved management of neovascular ocular diseases, including AMD and PDR.
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