Extraction of thickness and water content gradients in hydrogel-based, water-backed corneal phantoms via submillimeter wave reflectometry
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Volume Title
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
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Date
2021-11-01
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Mcode
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Language
en
Pages
11
Series
IEEE Transactions on Terahertz Science and Technology
Abstract
Absolute thickness and free-water-content gradients in gelatin-based corneal phantoms with physiologically accurate radii of curvature and aqueous backing were extracted via coherent submillimeter-wave reflectometry at 220-330 GHz. Fourier-domain-based calibration methods, utilizing temporal and spatial gating, were developed and yielded peak-to-peak amplitude and phase clutter of 10-3 and 0.1°, respectively, for signal-to-noise ratios (SNRs) between 40 and 50 dB. Total 12 phantoms were fabricated. Calibration methods enabled quantification of target sphericity that strongly correlated with optical-coherence tomography-based sphericity metrics via image segmentation. The extracted free-water volume fraction varied less than 5% in the five phantoms whose fabrication yielded the most spherical geometry. Submillimeter-wave-based thickness accuracy was better than 111 μm (∼λ/9) with an average of 65 μm (∼λ/17) and standard deviation of 44 μm (∼λ/25) for phantoms with physiologically relevant geometry. Monte-Carlosimulations of measurement noise and uncertainty limits agree with the experimental data analysis and indicate a lower thickness accuracy limit of 33 μm, and water-content sensitivities of 0.5% and 11.8% for the anterior and posterior segments, respectively. Numerical analysis suggests that the measurement fidelity was SNR limited and identified optical path length ambiguities within the cornea where a continuum of thickness/water gradient pairs produces statistically insignificant differences in complex reflection coefficient for finite SNR. This is the first known submillimeter-wave measurement technique, which is able to extract both the thickness and water-content gradients from a soft-tissue phantom, with a water backing, without the need for ancillary measurements.Description
Publisher Copyright: IEEE
Keywords
Cornea, Corneal phantom, gelatin hydrogel, Optical device fabrication, Optical imaging, Optical reflection, optical-coherence tomography, Phantoms, Reflectivity, submillimeter-wave spectroscopy, Thickness measurement
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Citation
Tamminen , A , Baggio , M , Nefedova , I , Sun , Q , Presnyakov , S , Ala-laurinaho , J , Brown , E , Wallace , V , Macpherson , E , Maloney , T , Kravchenko , N , Salkola , M , Deng , S & Taylor , Z 2021 , ' Extraction of thickness and water content gradients in hydrogel-based, water-backed corneal phantoms via submillimeter wave reflectometry ' , IEEE Transactions on Terahertz Science and Technology , vol. 11 , no. 6 , pp. 647-659 . https://doi.org/10.1109/TTHZ.2021.3099058
