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Mohamed El-Haddad, Yuankai Tao; Real-time dynamic depth tracking for arbitrarily long range OCT imaging and surgical instrument tracking using a Fourier domain optical delay line. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4089.
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© ARVO (1962-2015); The Authors (2016-present)
Intraoperative optical coherence tomography (iOCT) allows visualization of tissue microstructure, and provides real-time feedback for clinical decision making during ophthalmic surgery. However, the potential for iOCT-guided surgical maneuvers has been limited both by imaging speed, which can only display single cross-sectional images at video-rates, and imaging range, which is on the order of 2 mm for SDOCT and 8 mm for SSOCT. Last year, we presented novel lateral tracking technology that automatically centered the iOCT scan field on the tip of ophthalmic surgical instruments. Here, we demonstrate a digitally controlled optical delay that allows real-time depth tracking. Integration of automated lateral and depth tracking with iOCT will allow for dynamic three-dimensional field-of-view imaging of ophthalmic surgical dynamics.
A reference arm based on a Fourier domain optical delay line (FDODL), was designed to provide a digitally controlled optical delay for iOCT. A free-space optical delay on a motorized stage was added to the FDODL path to further extend the available tracking range. A control algorithm handles the actuation hand-off between the stage and the FDODL to allow for fast scanning over a short range, and slower scanning over a long range (Fig. 1). The FDODL allowed inter-line depth tracking over >16 mm depth range with a 100 µs small-angle step response (Fig. 1, δz) while the motorized stage allowed for inter-frame scanning over a 100 mm range at speeds up to 100 mm/s (Fig. 1, Δz).
As a demonstration, we imaged a metal surface placed at ~62 deg. to the horizontal (Fig. 1). Without tracking, small part of the surface was visible (Fig. 1b, blue). The FDODL was then scanned by a saw-tooth function, effectively compensating for the tilt (Fig. 1b, red). The A-Scans in the latter represent different depths, in linear proportion to the applied voltage (3.7 mm/volt), which was corrected for in post-processing to reflect the true image over the entire range of the FDODL.
Integrating automated lateral and depth tracking with iOCT will allow real-time imaging of surgical dynamics. Improved understanding of tissue-instrument interactions during conventional ophthalmic surgical maneuvers may elucidate mechanisms of tissue repair, be predictive of clinical outcomes, and lead to novel iOCT-guided surgical techniques.
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