Background. Scleral biomechanical properties may be important in the pathogenesis and progression of glaucoma. The goal of this study is to develop and validate an ultrasound method for measuring cross-sectional distributive strains in the sclera during elevations of intraocular pressure (IOP). Method of Approach. Porcine globes (n = 5) were tested within 24 hs postmortem. The posterior scleral shells were dissected and mounted onto a custom-built pressurization chamber. A high-frequency (55-MHz) ultrasound system (Vevo660, VisualSonics Inc., Toronto) was employed to acquire the radio frequency data during scans of the posterior pole along both circumferential and meridian directions. The IOP was gradually increased from 5 to 45 mmHg. The displacement fields were obtained from correlation-based ultrasound speckle tracking. A least-square strain estimator was used to calculate the strains in both axial and lateral directions. Experimental validation was performed by comparing tissue displacements calculated from ultrasound speckle tracking with those induced by an actuator. Theoretical analysis and simulation experiments were performed to optimize the ultrasound speckle tracking method and evaluate the accuracy and signal-to-noise ratio (SNR) in strain estimation. Results. Porcine sclera exhibited significantly larger axial strains (e.g., −5.1 ± 1.5% at 45 mmHg, meridian direction) than lateral strains (e.g., 2.2 ± 0.7% at 45 mmHg, meridian direction) during IOP elevations (P’s < 0.01). The strain magnitudes increased nonlinearly with pressure increase. The strain maps displayed heterogeneity through the thickness. The lateral strains were significantly smaller in the circumferential direction than the meridian direction at 45 mmHg (P < 0.05). Experimental validation showed that the ultrasound speckle tracking method was capable of tracking displacements at the accuracy of sub-micron to micron. Theoretical analysis predicted the dependence of the strain estimation SNR on the strain level, as well as signal processing parameters such as kernel size. Simulation results showed that ultrasound speckle tracking had a high accuracy for estimating strains of 1–5% and a high SNR for strains of 0.5–5%. Conclusions. A new experimental method based on ultrasound speckle tracking has been developed for obtaining cross-sectional strain maps of the posterior sclera. This method provides a useful tool to examine distributive strains through the thickness of the sclera during elevations of IOP.
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September 2012
Research Papers
Ultrasonic Measurement of Scleral Cross-Sectional Strains During Elevations of Intraocular Pressure: Method Validation and Initial Results in Posterior Porcine Sclera
Junhua Tang,
Junhua Tang
Department of Biomedical Engineering,
Ohio State University
, 1080 Carmack Road, Columbus, OH
43210
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Jun Liu
Jun Liu
Assistant Professor
Department of Biomedical Engineering, Department of Ophthalmology,
Ohio State University
, 1080 Carmack Road, Columbus, OH
43210
Search for other works by this author on:
Junhua Tang
Department of Biomedical Engineering,
Ohio State University
, 1080 Carmack Road, Columbus, OH
43210
Jun Liu
Assistant Professor
Department of Biomedical Engineering, Department of Ophthalmology,
Ohio State University
, 1080 Carmack Road, Columbus, OH
43210J Biomech Eng. Sep 2012, 134(9): 091007 (10 pages)
Published Online: August 29, 2012
Article history
Received:
April 2, 2012
Revised:
August 9, 2012
Posted:
August 17, 2012
Published:
August 29, 2012
Online:
August 29, 2012
Citation
Tang, J., and Liu, J. (August 29, 2012). "Ultrasonic Measurement of Scleral Cross-Sectional Strains During Elevations of Intraocular Pressure: Method Validation and Initial Results in Posterior Porcine Sclera." ASME. J Biomech Eng. September 2012; 134(9): 091007. https://doi.org/10.1115/1.4007365
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