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Ruobing Qian, Oscar Carrasco-Zevallos, Lejla Vajzovic, Cynthia A Toth, Joseph A Izatt; Long Working Distance Swept Source Optical Coherence Tomography for Pediatric Imaging. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4094.
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© ARVO (1962-2015); The Authors (2016-present)
Optical coherence tomography (OCT) has become the standard of care for diagnosis of many retinal pathologies. However, current commercial OCT systems require cooperative patients to maintain fixation for several seconds in a chinrest. Handheld OCT systems have also been demonstrated for successful imaging of supine patients, as well as pre-term infants and neonates up to ~1 year old. However, no technology yet exists for OCT in young children due to their lack of attention and cooperation, as well as inherent fear of large objects close to their face. Therefore, we designed and built a novel OCT system with a very long working distance (distance of the last optical component of the system to the subject’s eye) to facilitate imaging of young children.
A novel scanning configuration OCT system was designed to achieve a working distance of 36 cm (Fig. 1) to situate young children at a comfortable distance away during imaging. A 2f scanning configuration, instead of the conventional 4f scheme, was implemented to reduce the footprint and weight of the sample arm. To optimize optical performance at the retinal plane, the 2f system employed two custom-designed lenses (Zemax, Inc; Redmon, WA). A dichroic mirror after the objective enabled co-alignment of a LCD display used for fixation. The monitor displayed videos and targets to aid fixation during imaging.The swept-source OCT system employed a 1060 nm frequency-swept laser (Axsun Tech; Billerica, MA) and a Mach-Zender interferometer. The interferometric signal was detected with a dual-balanced receiver (Thorlabs, Inc.; Newton, NJ) and digitized at 800 MS/s (Alazar Tech Inc; QC, Canada). Custom GPU-based software enabled real-time volumetric imaging at 100,000 A-line/second.
The axial resolution across the 6 mm imaging depth range was measured to be 8.4um and the lateral resolution was measured to be 11-12 um. The peak sensitivity was 99.4 dB with a 3.5 mm -6dB falloff. To prove the feasibility of the system, consented adult subjects were imaged. A representative volumetric and an averaged B-scan image are shown in Fig 2. The subject was situated on a chinrest 36 cm away from the system. The LCD monitor facilitated fixation during imaging.
A novel long working distance OCT system along with the fixation system were designed, built and tested on adult subjects. The future implication is to image the retina of young children.
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