Forschungszentrum Karlsruhe
Technik und Umwelt
Introduction
Theory
Noninvasive Measurement
of Elastic Properties
of Living Tissue
Methods
Experiments
Results
Application
Summary
Dr. Heiko Maaß
Institut für Angewandte Informatik
Mechanical properties in medicine
Introduction
• Quantification of tissue mechanics
Theory
Methods
• Quantitative evaluation of diagnostical results
Experiments
Results
Application
Summary
• Monitoring of healing processes
• Detection of hardenings or softenings (palpation)
Application of mechanical tissue parameters
Introduction
• simulation of elastic tissue
Theory
Methods
Experiments
• accident research
• product design
Results
Application
Summary
• biophysics
The 'Karlsruhe Endoscopic Trainer'
State of the art
Introduction
vibration
10-1000 Hz
• Elastography
Theory
Methods
• Sonoelastic Imaging
Experiments
Results
Application
• Strain Imaging
deformation
• Magnetic Resonance Elastography
Summary
measurement using Ultrasound
or MR-tomography
Phenomenological model
Introduction
Christoffel-equation:
( Cijkmn j nm   c 2sound   ik ) U k  0
Theory
Methods
general approach
Experiments
Results

  f (  ,csound ,vload , material )
Application
Summary
restricted to soft tissue (no bone or cartilage)
Mechanical properties of biological tissue
stress
Introduction
• non-linear
Theory
• inhomogeneous
Methods
• anisotrop
Experiments
• plastic
Results
• viscous
Application
• incompressible
Summary
• temperature dependent
compression
tension
strain
• dependent on metabolism,
innervation and perfusion
liver
1mm
Acoustical properties of biological tissue
velocity of sound
Introduction
0
Theory
Methods
1000
gases
3000
2000
soft tissue
4000
m/s
bone, cartilage
Experiments
   0 e x
 ~ f
a
25
20
15
10
5
0
4
b
3
2
c
1
0
0
5
10
15
sound frequency in MHz
20
resolution
in mm
Summary
in cm
Application
damping
penetration depth
Results
a: penetration depth
b: lateral resolution
c: axial resolution
Non-invasive testing principle
Introduction
Theory
Methods
Experiments
t
Results
Application
Summary
s
Simulation of the propagation of ultrasound waves
Introduction
Theory
Methods
Experiments
Results
Application
Summary
Assembly used for the non-invasive measurement
tomographical system
graphic workstation
Introduction
Theory
Methods
position sensing system
Experiments
Results
interaction
Application
Summary
ultrasound device
ultrasound head coupled
with position sensor
Performance of the sound speed measurement
Introduction
spatial orientation
image overlay
Theory
Methods
Experiments
Results
Application
Summary
liver
Testing devices
US
Introduction
Theory
F
Experiments
Results
Application
Summary
C = 1540 m/s
F

Pos
Methods

Introduction
Theory
Methods
compressive stress in MPa
Evaluation of the experimental series
0,06
Summary
1: origin tangential gradient
1
 1  EU   d
0,04
0,02
2: parametric regression
0
0
0,2
0,4
compressive strain d
0,6
 2  EP   d  (1  P1   d  P2   d2 )
3: general regression
compressive stress in MPa
Application
2
0,08
Experiments
Results
regression analysis
3
0,1
Fat
0,1
0,08
0,06
0,04
0,02
0
Liver
Muscle
 3  a1   d  a2   d2  a3   d3
Kidney
Spleen
linear
0
0,2
0,4
compressive strain d
0,6
correlation analysis
Correlation analysis results
Theory
Methods
Experiments
Results
Application
Summary
origin tangent EU in MPa
Introduction
0,5
0,45
0,4
0,35
0,3
0,25
0,2
0,15
0,1
0,05
0
1500
parameter EP in MPa
liver tissue
1550
1600
0,5
0,45
0,4
0,35
0,3
0,25
0,2
0,15
0,1
0,05
0
1500
1550
1600
sound speed in m/s
sound speed in m/s
origin tangent
parametric regression
1 = EU d
series intra vitam
2 = 1,2 EP d (1 _ 3d + 17d2)
series post mortem
Ranges of sound speed and origin gradient
origin gradient in MPa (compression)
Introduction
Theory
Methods
Experiments
Results
Application
Summary
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
fat (soft)
fat (harder)
liver
spleen
heart muscle
kidney
post
mortem
fat
liver
spleen
kidney
intra
vitam
1400 1420 1440 1460 1480 1500 1520 1540 1560 1580 1600
sound speed in m/s
Simulation of soft biological tissue
tension
Introduction
  E   t  ( 1  a2 t  a3 t 2  a4 t 3 )
Theory
F(s)
stress 
Methods
Experiments
Results
-1,0
0
Application
Summary
-0,5
compression
0,5
1,0
strain t
• Development and employment of testing devices
• Measurement of tissue parameters intra vitam
Introduction
• Comparison to tisssue properties post mortem
• Simulation of the propagation of sound
Theory
Methods
• Non-invasive differenciation of fat is possible
Experiments
• Curve shapes are specific to the tissue kind
Results
Application
• Curves are independent on stress velocity
• Phenomenological model is not quantifiable
Summary
• Usage of curve approximations in complex simulations
• Development of new non-invasive methods of testing
Introduction
Theory
Methods
Experiments
Results
Application
Summary
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