Investigation of water diffusion dynamics in corneal phantoms using terahertz time-domain spectroscopy

Chen, Andrew; Osman, Omar B.; Harris, Zachery B.; Abazri, Azin; Honkanen, Robert; Arbab, M. Hassan

doi:10.1364/boe.382826

Cited by 25 publications

(13 citation statements)

References 34 publications

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“…Thus, phantoms allow for a more static environment to evaluate corneal hydration sensing methods. Some corneal phantoms are accurately characterized, e.g., contact lenses on metal spheres with a known thickness and water content [14].…”

Section: Introductionmentioning

confidence: 99%

Extraction of Thickness and Water-Content Gradients in Hydrogel-Based Water-Backed Corneal Phantoms Via Submillimeter-Wave Reflectometry

Tamminen

Baggio

Nefedova

et al. 2021

IEEE Trans. THz Sci. Technol.

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Absolute thickness and free water content gradients in gelatinbased 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-topeak amplitude and phase clutter of 10 -3 and 0.1°, respectively for signal to noise ratios between 40 dB and 50 dB. Twelve phantoms were fabricated. Calibration methods enabled quantification of target sphericity that strongly correlated with optical coherence tomography-based sphericity metrics via image segmentation. Extracted free water volume fraction varied less than 5 % in the 5 phantoms whose fabrication yielded the most spherical geometry. Submillimeter wave-based thickness accuracy was better than 111 μm (~λ/9) with average of 65 μm (~λ/17) and standard deviation of 44 μm (~λ/25) for phantoms with physiologically relevant geometry. MonteCarlo simulations of measurement noise and uncertainty limits agree with experimental data analysis and indicates 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 measurement fidelity was SNR limited and identified optical path length ambiguities within the cornea where a continuum of thickness/water gradient pairs produce statistically insignificant differences in complex reflection coefficient for finite SNR. This is the first known submillimeterwave measurement technique 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.

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Section: Introductionmentioning

confidence: 99%

Extraction of Thickness and Water-Content Gradients in Hydrogel-Based Water-Backed Corneal Phantoms Via Submillimeter-Wave Reflectometry

Tamminen

Baggio

Nefedova

et al. 2021

IEEE Trans. THz Sci. Technol.

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“…A subsequent study by Chen et al applied the more appropriate diffusion model to represent water content gradients. 321 Corneal tissue water content gradients have been confirmed in cornea. Castoro et al observed a substantial bound water component in ex vivo bovine corneal samples along the optical axis.…”

Section: Corneal Assessmentmentioning

confidence: 86%

Terahertz (THz) biophotonics technology: Instrumentation, techniques, and biomedical applications

Chen

Lindley-Hatcher

Stantchev

et al. 2022

Chemical Physics Reviews

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Terahertz (THz) technology has experienced rapid development in the past two decades. Growing numbers of interdisciplinary applications are emerging, including materials science, physics, communications, and security as well as biomedicine. THz biophotonics involves studies applying THz photonic technology in biomedicine, which has attracted attention due to the unique features of THz waves, such as the high sensitivity to water, resonance with biomolecules, favorable spatial resolution, capacity to probe the water–biomolecule interactions, and nonionizing photon energy. Despite the great potential, THz biophotonics is still at an early stage of development. There is a lack of standards for instrumentation, measurement protocols, and data analysis, which makes it difficult to make comparisons among all the work published. In this article, we give a comprehensive review of the key findings that have underpinned research into biomedical applications of THz technology. In particular, we will focus on the advances made in general THz instrumentation and specific THz-based instruments for biomedical applications. We will also discuss the theories describing the interaction between THz light and biomedical samples. We aim to provide an overview of both basic biomedical research as well as pre-clinical and clinical applications under investigation. The paper aims to provide a clear picture of the achievements, challenges, and future perspectives of THz biophotonics.

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“…Three locations are relevant for coupling a Gaussian beam to aspherical surfaces: at the two solutions to Equation (1), and a third orientation where the corneal apex is coincident with the beam waist. Illuminating the cornea with the beam waist does not produce a curvature match but it's study was motivated results presented in the literature where separate transmitter and receiver paths are coupled through corneal surface at the collocating foci of beams [13], [18]- [20].…”

Section: Surfacesmentioning

confidence: 99%

Quasioptical System for Corneal Sensing at 220–330 GHz: Design, Evaluation, and Ex Vivo Cornea Parameter Extraction

Tamminen

Palli

Ala‐Laurinaho

et al. 2021

IEEE Trans. THz Sci. Technol.

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The design, simulation, and characterization of a quasioptical system for submillimeter-wave quantification of corneal thickness and water content are presented. The optics operate in the 220-330 GHz band and are comprised of two, custom aspheric, biconvex lenses in a gaussian beam telescope configuration. The design produces broad band wavefront curvature matching to 7.5 mm radius of curvature target surfaces thus emulating a plane-wave-on-planar-media condition and enabling application of stratified medium theory to data analysis. Aspheric lens coefficients were optimized with geometric ray tracing subject to optical path length penalties and physical optics simulations showed aspheric designs achieved wavefront coupling to spherical surfaces, superior to equivalent, canonical hyperbolic lenses. The fabricated lens system was characterized in a planar near-field scanner system and demonstrated good agreement to physical-optics simulations. An average central corneal thickness of 652 m and free water content volume of 47 % were extracted from ex vivo sheep corneas via complex s-parameters and agree with literature values. Extracted contact lens thickness and water content agreed with independently validated values. Moreover, the quasioptical system enabled observation of dynamic changes in artificial tear-film, thickness, and water content. This work elucidates two major findings related to submillimeter-wave wavefront matching on spherical surfaces, with wavelength order radii of curvature: (1) An asphere whose sag coefficients are optimized via field phase variation on a spherical surface produces coupling superior to a plano-hyperbolic lens. (2) For most feasible apertures, the Gaussian beam waist is located in the aperture near field, suggesting consideration for operating in the beam near field.

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Investigation of water diffusion dynamics in corneal phantoms using terahertz time-domain spectroscopy

Cited by 25 publications

References 34 publications

Extraction of Thickness and Water-Content Gradients in Hydrogel-Based Water-Backed Corneal Phantoms Via Submillimeter-Wave Reflectometry

Extraction of Thickness and Water-Content Gradients in Hydrogel-Based Water-Backed Corneal Phantoms Via Submillimeter-Wave Reflectometry

Terahertz (THz) biophotonics technology: Instrumentation, techniques, and biomedical applications

Quasioptical System for Corneal Sensing at 220–330 GHz: Design, Evaluation, and Ex Vivo Cornea Parameter Extraction

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