Surgery Simulation

• In vitro rheology
– can be performed in a laboratory. Technique is mature – Not realistic for soft tissue (perfusion, …)
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Soft Tissue Characterization
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Soft Tissue Characterization
• Biomechanical behavior of biological tissue is very complex • Most biological tissue is composed of several components :
(source, Ayudamos)
Procedure Duration (min)
Surgery Training on a pig at EITS
41-60
61-80
81-100
Total number of patients Resident Training
Goal for simulation : Training versus Rehearsal
• Training: Modelling a standard patient for teaching classical or rare situations • Rehearsal: Modelling a specific patient to plan and rehearse a delicate intervention, and evaluate consequences beforehand
• Deformation Function
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X ∈Ω a φ(X ) ∈ℜ
3
• Displacement Function
Rest Position
Φ
U (X ) = φ ( X ) − X
Deformed Position
Ω
X U(X)
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Basics of Continuum Mechanics • The local deformation is captured by the deformation gradient : ∂φ1 ∂φ1 ∂φ1
∂φ F= ∂X
Rest Position
Ω
Deformed Position
∂X 1 ∂φ ∂φ Fij = i = 2 ∂X j ∂X 1 ∂φ 3 ∂X 1
∂X 2 ∂φ2 ∂X 2 ∂φ3 ∂X 2
∂X 3 ∂φ2 ∂X 3 ∂φ3 ∂X 3
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Soft Tissue Characterization
• Different possible methods
– In vitro rheology – In vivo rheology – Elastometry – Solving Inverse problems
Soft Tissue Characterization
Structural Mechanics Hyperelasticity Elasticity
Linear Elasticity
(Anisotropic, heterogeneous)
Plasticity
Material Modeling: Basics of Continuum Mechanics
Increasing need for training surgeons and residents
• Medical malpractice has become socially and economically unacceptable
Increasing need for objective evaluation of surgeons (see Cordis Nitanol endovascular carotid stent)
Liver Reconstruction
Deformation from a reference model reconstructed from the « Visible Human Project »
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Different Technical Issues
• • • • • • • Mesh Reconstruction from Images Soft Tissue Modeling Tissue Cutting Collision Detection Contact Modeling Surface Rendering Haptic Feedback
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Soft Tissue Characterization
• To characterize a tissue, its stressstrain relationship is studied
Radius r Height h
Strain
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Stress σ =
F πr2
Force F
Radius r*
Average Duration of an hysterectomy with laparoscopy
180 160 120 100 Example of a mechanical simulator
(source, US Surgical Corporation)
140 • Cadavers
80 • Patients 60 40 20 0 1-10 11-20 21-40
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Estimating material parameters
• Complex for biological tissue :
– Heterogeneous and anisotropic materials – Tissue behavior changes between in-vivo and in-vitro – Effect of preconditioning – Potential large variability across population – Ethics clearance for performing experimental studies
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Different Technical Issues
• • • • • • • Mesh Reconstruction from Images Soft Tissue Modeling Tissue Cutting Collision Detection Contact Modeling Surface Rendering Haptic Feedback
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Surgery Simulation
Olivier Clatz
Hervé Delingette
Asclepios Research project INRIA Sophia Antipolis, NhomakorabeaFrance
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Motivations of surgery simulation
• Increasing complexity of therapy and especially surgery
– Fluids : water or blood – Fibrous materials : muscle fiber, neuronal fibers, … – Membranes : interstitial tissue, Glisson capsule – Parenchyma : liver or brain
σ
Unloading
ε Hysteresis
ε
Linear Domain
Slope =Young Modulus
ε
Visco-elasticity
Non-Linearity
Anisotropy
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Continuum Mechanics
Continuum Mechanics
Fluid Mechanics
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Source Echosens, Paris
Soft Tissue Characterization
• Inverse Problems
• well-suited for surgery simulation (computational approach) • requires geometry & BC before and after deformation
Soft Tissue Characterization
• Elastometry (MR, Ultrasound)
• mesure property inside any organ non invasively • validation ? Only for linear elastic materials
X
φ(X)
F(X) is the local affine transformation that maps the neighborhood of X into the neighborhood of φ(X)
Basics of Continuum Mechanics
• Distance between point may not be preserved
Rest Position
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Ω
Deformed Position
X+dX X
φ(X+dX) φ(X)
• Distance between deformed points
(ds )
2
= φ ( X + dX ) − φ ( X ) ≈ dX T ∇φ T ∇φ dX