Transcript Presentation

Chen Wu 1 , Zhaolong Han 1 , Shang Wang 1,5 , Jiasong Li 1 ,
Manmohan Singh 1 , Chih-hao Liu 1 , Salavat
Aglyamov 2 , Stanislav Emelianov 2 , Fabrice Manns 3,4 ,
and Kirill V. Larin 1,5,+
1Department
of Biomedical Engineering, University of Houston, 3605 Cullen Boulevard, Houston,
Texas 77204, USA
2Department of Biomedical Engineering, University of Texas at Austin, 107 W Dean Keeton Street,
Austin, Texas 78712, USA
3Ophthalmic Biophysics Center, Bascom Palmer Eye Institute, University of Miami Miller School of
Medicine, 1638 NW 10th Avenue, Miami, Florida 33136, USA
4Biomedical Optics and Laser Laboratory, Department of Biomedical Engineering, University of Miami
College of Engineering, 1251 Memorial Drive, Coral Gables, Florida 33146, USA
5Molecular Physiology and Biophysics, Baylor College of Medicine, One Baylor Plaza, Houston, Texas
77584, USA
 Motivation
 Experimental Setup
 Materials and Samples
 Result and Discussion
 Summary
 Acknowledgements
 The age-related changes in viscoelastic properties of the
crystalline lens play an important role in the development
of presbyopia, which is the progressive, age-related loss of
accommodation of the eye.
 The increase in lens stiffness is generally believed to be
responsible for the progressive loss of the ability of the lens
to change shape leading to presbyopia.
 The location of the crystalline lens inside the eye makes it
challenging to measure its mechanical properties in vivo or
in situ.
 Elastography is an emerging technique that can map the
local mechanical properties of tissues
 Ultrasound elastography (USE)
 magnetic resonance elastography (MRE)
 Relative low spatial resolution pose a limitation
 Brillouin microscopy is a new technique to study
biomechanical property of lens.
 Uncertainty on correlation of brillouin shift to Young’s modulus
 In this study, we combine ultrasound excitation with
Optical coherence elastography (OCE) for investigation of
biomechanical properties of lens.
 spatial imaging resolution, faster acquisition speed, and greater
displacement sensitivity
 Spectral domain OCT
 Laser Source
 Central wavelength
~840nm
 bandwidth~49nm)
 Ultrasound system
 Ultrasound transducer (Model
ISO305HP)
 Frequency~3.7MHz
 Focal length~19mm
 Function Generator
 Power Amplifier
 Gain~40dB
 Adjustable transducer
holder
 TTL trigger signal from the
DAQ.
 The TTL signal trigger the
sinusoidal wave for
ultrasound excitation and
camera recording
simultaneously.
 The sinusoidal wave is set
to be 3.7MHz and the
excitation force can be
changed by adjusting the
voltage.
o Three young rabbit eyes ~ around 2-3 months old.
o Four mature rabbit eyes ~ over 6 months old.
o All the samples were conducted with OCE test, and then
the lenses were dissected out and followed by mechanical
compression tests.
 The phase profile during ultrasound excitation, the phase value
and physical displacement is converted by
 Displacement = wavelength*phase/(4*pi)
 The displacement for young lenses ~ 3.3±0.1 µm & mature lenses
~ 1.6±0.4 µm
 SD for mature ones is much larger.
The simplified kinematical differential equation
can be used to describe the lens’s relaxation
process:
d 2 y (t )
dy (t )
m
c
 ky (t )  0
2
dt
dt
where m is the equivalent mass, c is the viscosity
coefficient and k is the equivalent spring stiffness;
For simplifying and understanding the basic
characteristics of the equation, two parameters, ξ
and ω, are introduced where is the damping ratio
and is the natural frequency of the dynamic
system:
2
d y (t )
dy (t )

2

  2 y (t )  0
2
dt
dt
The analytical solution of equation above is:
y(t )  A(1  b t )et

is the natural frequency of the dynamic system
 Natural frequency
values of the young
and the mature lenses
are 0.8±0.2 kHz and
2.2±0.5 kHz
 Figure a shows typical stress-strain curves for young and
mature sample. Figure b demonstrates the Young’s moduli
calculated from all samples.
 Young’s modulus of Young lens ~ 8.2±1.1 kPa.
 Young’s modulus of mature lens ~ 12.6±1.2 kPa.
Developed a co-focused ultrasound and OCE system to
study the biomechanical property of the rabbit lens;
2) The parameters of maximal displacement, natural
frequency can be used for assessment;
3) Stiffness of the rabbit crystalline lens increases with age;
4) Prospective future work would be to correlate the
relaxation process with a quantitative evaluation of the
lens elasticity and to perform depth-resolved OCE
measurements to map elasticity gradient as a function of
depth.
1)
 This work was supported by the National Institutes of
Health under grants R01EY022362 and R01EY014225.