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首页> 外文会议>Advances in optics for biotechnology, medicine and surgery XV >DYNAMIC OPTICAL COHERENCE ELASTOGRAPHY AND OCULAR BIOMECHANICS
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DYNAMIC OPTICAL COHERENCE ELASTOGRAPHY AND OCULAR BIOMECHANICS

机译：动态光学相干弹性成像和眼球生物力学

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摘要

Microscopic changes in biological tissues leading to pathologies often result in macroscopic changes in tissue biomechanical properties, such as tissue elasticity. It is known, that the biomechanical characteristics of ocular tissues have a profound influence on the health, structural integrity, and normal function of the human eye. Such conditions as presbyopia, corneal ectasia and keratoconus correlate with stiffness of the ocular tissues. Elastography is a general name for a group of diagnostic methods capable of remote evaluation of tissue biomechanical properties based on applying mechanical excitation, measuring tissue response, and interpretation of tissue response to evaluate biomechanical parameters of tissue. Optical Coherence Elastography (OCE) is a branch of elastography that uses Optical Coherence Tomography (OCT) to measure tissue motion in response to external excitation. In comparison with other imaging techniques, such as ultrasound and magnetic resonance imaging, OCT has significant advantages in resolution and accuracy of motion estimation, but limited by the low penetration depth of light. Therefore, OCE is an ideal imaging technique to measure biomechanical properties of the ocular tissues. We have developed noninvasive OCE approaches to measure elastic properties of the ocular tissues using air puff stimulation and acoustic radiation force. The critical step in evaluating the biomechanical properties of tissues is interpretation of the tissue mechanical response based on the appropriate mechanical model. The model dictates how the measured mechanical response relates to elastic parameters. Biomechanical properties are evaluated based on developed mathematical model of the dynamic deformation of the viscoelastic medium. This approach has been successfully tested in phantom, ex-vivo and animal studies. The home-built OCE system was composed of a focused air-pulse delivery system or focused single element transducer and a phase-stabilized swept source optical coherence tomography (PhS-SSOCT) system. The system utilized a broadband swept laser source (HSL2000, Santec, Inc., CA) with a central wavelength of -1310 nm, bandwidth of -150 nm, scan rate of 30 kHz, and experimentally measured phase stability of -40 nm during experiments. We developed a method to assess corneal biomechanics based on the measurements of the elastic wave propagation in the cornea using phase-sensitive OCT imaging system after micro air-puff stimulation of the cornea. The focused air-pulse delivery system was comprised of a controller with a signal input for synchronization, a solenoid-controlled air gate, and an air-pulse port with a flat edge and diameter of-150 μm. The system is capable of delivering a short duration focused air-pulse (≤1 ms) with a Gaussian profile. The modified Rayleigh-Lamb frequency equation was derived and used to calculate the dispersion of the Lamb wave in cornea. The model was tested in phantom and ex vivo studies, and used to quantify the viscoelasticity of in situ porcine corneas in the whole eye-globe configuration before and after CXL. The viscoelasticity of the untreated and CXL-treated eyes was quantified at various lOPs. The results showed that the stiffness of the cornea increased after CXL and that corneal stiffness is close to linear as a function of IOP. The influence of the corneal thickness and curvature on the propagation on the elastic waves was investigated. We have developed acoustic radiation force based approach to assess the biomechanical properties of the lens and applied this approach for measuring biomechanical properties of the lens in intact animal eyes in situ for different ages and lOPs. A 3.7 MHz single element transducer was used to remotely disturb the anterior surface of the animal lenses through the cornea and the aqueous humor. The crystalline lens was modeled as a viscoelastic layer. Ultrasound transducer and OCT system were co-focused, and the measurements of the displacement were performed at the focal point. Results of the measurements demonstrated a significant difference between elastic properties of the young and the mature lenses, as well as, stiffening lens with IOP. In summary, the optical coherence elastography was demonstrated as a promising tool for noninvasive assessment of the biomechanical properties of the ocular tissues.
机译：导致病理的生物组织的微观变化通常会导致组织生物力学特性（例如组织弹性）的宏观变化。众所周知，眼组织的生物力学特性对人眼的健康，结构完整性和正常功能有着深远的影响。诸如老花眼，角膜扩张和圆锥角膜等状况与眼组织的刚度相关。弹性成像技术是一组诊断方法的总称，这些诊断方法可基于施加机械激励，测量组织反应和解释组织反应来评估组织的生物力学参数，从而对组织的生物力学特性进行远程评估。光学相干弹性成像（OCE）是弹性成像的一个分支，它使用光学相干层析成像（OCT）来测量响应外部激发的组织运动。与其他成像技术（例如超声和磁共振成像）相比，OCT在运动估计的分辨率和准确性方面具有明显优势，但受光的低穿透深度限制。因此，OCE是测量眼组织生物力学特性的理想成像技术。我们已经开发出非侵入性的OCE方法，使用吹气刺激和声辐射力来测量眼组织的弹性。评估组织生物力学特性的关键步骤是基于适当的机械模型解释组织的机械反应。该模型决定了所测得的机械响应与弹性参数之间的关系。基于力学模型的粘弹性介质动态变形评估生物力学性能。该方法已在幻影，离体和动物研究中成功测试。家用OCE系统由聚焦的空气脉冲传输系统或聚焦的单元素换能器以及相位稳定的扫频源光学相干断层扫描（PhS-SSOCT）系统组成。该系统使用了宽带扫频激光源（HSL2000，Santec，Inc.，CA），其中心波长为-1310 nm，带宽为-150 nm，扫描速率为30 kHz，在实验过程中实验测量的相位稳定性为-40 nm 。我们开发了一种方法，该方法在微气雾刺激角膜后，使用相敏OCT成像系统，基于弹性波在角膜中传播的测量结果来评估角膜生物力学。聚焦式空气脉冲输送系统包括一个带有同步信号输入的控制器，一个螺线管控制的空气闸门和一个扁平边缘且直径为-150μm的空气脉冲端口。该系统能够以高斯分布传送短时聚焦的空气脉冲（≤1ms）。推导了改进的瑞利-兰姆频率方程，并将其用于计算兰姆波在角膜中的色散。该模型在幻像和离体研究中进行了测试，并用于量化在CXL前后整个眼球配置中原位猪角膜的粘弹性。未经处理和经CXL处理的眼睛的粘弹性在各种LOP下进行了定量。结果表明，CXL后角膜的刚度增加，并且角膜的刚度作为IOP的函数接近线性。研究了角膜厚度和曲率对弹性波传播的影响。我们已经开发了基于声辐射力的方法来评估晶状体的生物力学性能，并将该方法应用于在不同年龄和lOPs的原位动物眼睛中测量晶状体的生物力学性能。使用3.7 MHz单晶元换能器通过角膜和房水远程干扰动物晶状体的前表面。将晶状体建模为粘弹性层。超声换能器和OCT系统共同聚焦，并在焦点处测量位移。测量结果表明，年轻和成熟镜片以及具有IOP的加劲镜片的弹性之间存在显着差异。总之，光学相干弹性成像被证明是一种无创评估眼组织生物力学特性的有前途的工具。

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