Optical coherence elastography to assess biomechanics and detect progression of ocular and other tissues degenerative diseases
An excitation force (internal or external) and phase-sensitive optical coherence elastography (OCE) system, used in conjunction with a data analyzing algorithm, is capable of measuring and quantifying biomechanical parameters of tissues in situ and in vivo. The method was approbated and demonstrated on an example of the system that combines a pulsed ultrasound system capable of producing an acoustic radiation force on the crystalline lens surface and a phase-sensitive optical coherence tomography (OCT) system for measuring the lens displacement caused by the acoustic radiation force. The method allows noninvasive and nondestructive quantification of tissue mechanical properties. The noninvasive measurement method also utilizes phase-stabilized swept source optical coherence elastography (PhS-SSOCE) to distinguish between tissue stiffness, such as that attributable to disease, and effects on measured stiffness that result from external factors, such as pressure applied to the tissue. Preferably, the method is used to detect tissue stiffness and to evaluate the presence of its stiffness even if it is affected by other factors such as intraocular pressure (IOP) in the case of cornea, sclera, or the lens. This noninvasive method can evaluate the biomechanical properties of the tissues in vivo for detecting the onset and progression of degenerative or other diseases (such as keratoconus).
1. A method for measuring tissue stiffness and for differentiating tissue samples using optical coherence elastography, comprising:
inducing elastic waves in the tissue samples;
detecting properties of the waves using interferometry, low coherence interferometry, or optical coherence tomography at different measurement positions along the waves, wherein the detected properties include measured wave velocities and measured wave displacement amplitudes and/or using temporal analysis of the elastic wave displacement profile;
determining elasticities of the tissue samples using the measured wave velocities dispersion, and attenuation;
differentiating the tissue samples having different measured wave velocities;
normalizing the measured wave displacement amplitudes for the tissue samples having similar measured wave velocities and needing further differentiation to produce normalized wave displacement data;
using the normalized wave displacement data to identify tissue samples having faster wave attenuation and slower wave attenuation; and
classifying the tissue samples having faster wave attenuation as tissue sample having increased viscosity and reduced stiffness and the tissue samples having slower wave attenuation as tissue samples having reduced viscosity and increased stiffness.
2. The method of claim 1 , wherein the tissue samples are ocular or any other soft or hard tissue samples.
3. The method of claim 1 , wherein the step of inducing elastic waves is by directing a focused air-pulse on the tissue samples.
4. The method of claim 1 , wherein the step of determining elasticities of the tissue samples is by calculating Young's modulus using the measured wave velocities.
5. The method of claim 1 , wherein the step of normalizing the measured wave displacement amplitudes is by dividing the measured wave displacement amplitudes at the different measurement positions along the waves by the measured wave displacement amplitude at an excitation position.
6. The method of claim 1 , wherein the step of using the normalized wave displacement data to identify tissue samples having faster wave attenuation and slower wave attenuation is by using a customized ratio having a formula of:
r (ND 1 /ND 2 ) =mean( r i )±std( r i ),
wherein
r
i
=
ND
1
i
ND
2
i
and ND1i and ND2i are normalized displacement data at an i th different measurement position for a first and a second tissue sample,
wherein if r (ND1/ND2) is significantly greater than 1, the second tissue sample is identified as having faster wave attenuation and the first tissue sample is identified as having slower wave attenuation, and
wherein if r is significantly less than 1, the first tissue sample is identified as having faster wave attenuation and the second tissue sample is identified as having slower wave attenuation.
7. The method of claim 6 , wherein the step of using the normalized wave displacement data to identify tissue samples having faster wave attenuation and slower wave attenuation is repeated for different tissue samples.
8. A method for quantifying biomechanical properties of a tissue, comprising:
producing an external or internal force to stimulate localized deformation on a surface of the tissue;
using an optical coherence tomography (OCT) or other low-coherence interferometry subsystem to measure an induced displacement profile resulting from the localized deformation on the surface of the tissue; and
quantifying the biomechanical properties of the tissue based on the analysis of the induced elastic wave using an algorithm.
9. The method of claim 8 , wherein the algorithm quantifies one or more of displacement amplitude, natural frequency, Young's modulus, and shear viscosity of the tissue.
10. The method of claim 8 , wherein the step of producing an excitation force is by any internal or external methods such as using an ultrasound/air puff/laser pulse delivery subsystem.
11. A system for quantifying biomechanical properties of tissues, comprising:
an external force delivery subsystem for producing a force to stimulate localized deformation on a surface of the tissues;
an optical coherence tomography (OCT) or other low-coherence interferometry subsystem for measuring an induced displacement profile resulting from the localized deformation on the surface of the tissues; and
a data processor programmed with an algorithm for quantifying the biomechanical properties of the tissues based on the induced displacement profile.
12. The system of claim 11 , wherein the algorithm quantifies one or more of displacement amplitude, natural frequency, Young's modulus, and shear viscosity of the tissues.