Ocular tissue biomechanics using Brillouin microscopy and optical coherence elastography
Biomechanical properties of the crystalline lens can provide crucial information for early disease detection and guiding precision therapeutic interventions. Early work assessing lens elasticity noninvasively has been limited to global assessments or qualitative measurements. Optical coherence elastography (OCE) can provide quantitative measurements of viscoelasticity rapidly but relies on backscattered light, so imaging transparent samples is a challenge. Whereas, Brillouin microscopy can map the Brillouin frequency shift with micro-scale resolution in transparent samples. However, Brillouin microscopy imaging times are long, and translating the Brillouin frequency shift to quantitative materials parameters is still an open question. In order to overcome the drawbacks of individual optical elastography modalities, we demonstrate a multimodal optical elastography technique combining optical coherence elastography and Brillouin microscopy. The combined system was first validated with tissue-mimicking gelatin phantoms of varying elasticities. The Young’s modulus obtained from OCE was first validated using uniaxial mechanical testing. Then the OCE data was used to calibrate the Brillouin shift measurements to obtain the Young’s modulus of the phantoms. After validation, OCE and Brillouin measurements were performed on ex vivo porcine lens (N=6), and the derived Young’s modulus of the lenses was spatially mapped. We observed a strong correlation between Young’s moduli measured by OCE and longitudinal Brillouin moduli measured by Brillouin microscopy. The correlation coefficients were R=0.98 for the gelatin phantoms and R = 0.94 for the lenses. Based on the correlation between Young’s modulus from OCE and longitudinal Brillouin modulus, we derived the Young’s modulus everywhere along the optical axis of lens. We observed that the nucleus of lens was stiffer compared to anterior and posterior parts. By combining OCE and Brillouin microscopy, we have shown that these techniques can map the Young’s modulus completely noninvasively in transparent tissues such as the crystalline lens.
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Yogeshwari S Ambekar
Department of Biomedical Engineering, University of Houston, Houston, TX, USA
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