NDLI: Acoustic-property maps of the cornea for improved high-frequency ultrasound corneal biometric accuracy

Content Provider	IEEE Xplore Digital Library
Author	Rohrbach, D. Lloyd, H.O. Silverman, R.H. Urs, R. Mamou, J.
Copyright Year	2015
Description	Author affiliation: Lizzi Center for Biomed. Eng., Riverside, NY, USA (Rohrbach, D.; Silverman, R.H.; Urs, R.; Mamou, J.) \|\| Dept. of Ophthalmology, Columbia Univ., New York, NY, USA (Lloyd, H.O.)
Abstract	Early diagnosis of keratoconus, a progressive disease characterized by corneal thinning and bulging, is important for avoiding corneal refractive surgery and for treatment planning. Current gold-standard procedures rely on surface topography and corneal-thickness measurements using high-frequency ultrasound (HFU) or optical coherence tomography (OCT). In a previous study of more than 200 normal corneas, OCT measurements of epithelial thickness were systematically thinner than those obtained from 40-MHz HFU measurements. In the present study, acoustic impedance (Z), attenuation (a) and speed of sound (c) of the corneal epithelium and stroma were independently measured using a scanning acoustic microscope (SAM) to investigate the discrepancy in thickness estimates. Corneas of two pigs were snap-frozen and 12-μm thick sections were scanned using a custom-built SAM with an F-1.16, 250-MHz transducer with a 160-MHz bandwidth. 2D maps of c, Z and a, with a spatial resolution of 7 μm were derived. These maps were used to model HFU propagation in silico and to provide more-accurate estimates of corneal and epithelial thicknesses. HFU significantly overestimated epithelial thickness by 1.2 to 2.2 μm because a single value of c (1636 m/s) was used to estimate thickness for all corneal layers. SAM showed that the value of c in the epithelium is substantially lower (i.e., 1539 ± 18 m/s) than the value of c in the stroma (i.e., 1591 ± 28 m/s). After using the SAM-based values in the simulations, no significant difference between HFU and OCT thickness determinations occurred, which showed that the assumption of a constant value of c for all corneal layers is incorrect. SAM permitted obtaining reliable thickness measurements because it provides accurate acoustic-property estimates at fine resolution.
Starting Page	1
Ending Page	4
File Size	1027071
Page Count	4
File Format	PDF
e-ISBN	9781479981823
DOI	10.1109/ULTSYM.2015.0149
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	2015-10-21
Publisher Place	Taiwan
Access Restriction	Subscribed
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Acoustic measurements Thickness measurement Attenuation measurement Optical variables measurement Surgery Surface treatment Acoustics stroma Scanning acoustic microscopy cornea speed of sound epithelium
Content Type	Text
Resource Type	Article

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