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Gongpu Lan, Alexander Zotov, Skyler Boehm, Kirill Larin, Michael D Twa; Effect of Heartbeat and Respiration on Elastography Measurement Precision. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4338. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Optical coherence tomography (OCT) is commonly used for structural imaging and can resolve micron-scale features. Phase-sensitive detection (useful for elastography imaging) can improve the ability to resolve dynamic surface displacements from micron-scale to sub-nanometer scale. Here we address the impact of normal physiological movements (e.g. heartbeat and respiration) on corneal phase-sensitive OCT elastography (PhS-OCE) measurement precision.
Corneal PhS-OCE elastography imaging was performed with a low-force, micro-air-pulse tissue stimulator and a home-built PhS-OCT to detect sub-micron corneal tissue displacements (0.24±0.07nm with a temporal resolution of 1.5μs). The axial position of the corneal apex was tracked during structural OCT imaging (axial resolution=3.3µm) over a total acquisition time of 2-3 minutes. Dynamic tissue displacements (pointwise, M-mode) were measured at the corneal apex during elastography imaging in two healthy subjects at three different tissue stimulation pressures (20-60 Pa). Similar elastography measurements were performed on tissue phantoms (2% agar) to mimic the effects of breathing (±15 μm amplitude, 0.30 Hz) and oculocardiac pulsations (±5 μm amplitude, 1.4 Hz), with 20Pa tissue stimulation.
Frequency analysis showed that respiratory movements produced larger amplitude lower-frequency eye movements (15.9±10.2µm; 0.16±0.09 Hz) compared to oculocardiac pulsations (4.5±1.1µm; 1.11±0.15Hz). The coefficient of variation (CV) for in vivo measurements of corneal displacement ranged from 8-16% (n=68 total measures) and this was not associated with the magnitude of tissue stimulation or the resulting tissue displacement amplitude (0.22 to 0.65µm; n=58 measures). The observed elastography displacement for 2% agar phantoms that were subjected to simulated breathing motion was (mean±SD) –1.46±0.03 μm; CV: 2.1%. Displacement with simulated oculocardiac pulsation was –1.46±0.04 μm; CV: 2.7%.
Low frequency (1-10 s) large magnitude (5-15 µm) movements have no observable effect on elastography measurement precision. The total acquisition time for PhS-OCE imaging is 1-10 ms duration with a sampling rate of 15µs. This reduces the influence of normal physiological movement artifacts on sub-micron displacement measurements.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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