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 biomechanical properties of tissues 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 measurement positions along the waves, wherein the measurement positions are the same or different, and wherein detected properties include measured wave velocities, measured wave displacement amplitudes, and measured wave dispersion;
determining biomechanical properties of the tissue samples by using the detected properties to create elastic wave displacement profiles and performing temporal or spatial analysis of the elastic wave displacement profiles or one or more of the detected properties of the elastic waves;
differentiating the tissue samples having different elastic wave displacement profiles or one or more different detected properties;
normalizing the elastic wave displacement profiles 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 any internal or external methods such as using an ultrasound/air puff/laser pulse delivery subsystem.
4. The method of claim 1 , wherein the step of determining biomechanical properties of the tissue samples is by calculating Young's modulus using the detected properties of the elastic waves or the elastic wave displacement profiles.
5. The method of claim 1 , wherein the step of normalizing the elastic wave displacement profiles is by dividing the measured wave displacement amplitudes at 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.