Biomech Applications

8/12/2019 Biomech Applications

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Modelling Biomechanics:applications of the FE method on

nonlinear problems


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Modelling BiomechanicsLinear problems

The finite element method is very commonly used in structural problems, and theoriesof solid mechanics can be used to predict deformation or stresses

Most materials have a linear relationship between stress and strain , for smallenough strains. For hard objects (metals, bone, etc), the theory of linear elasticitysuffices.


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Modelling biomechanics:onlinear stress!strain relationships

"n general the relationship bet#een stress and strain is much more comple$.

%tress is a nonlinear function of strain, but can also depend on the history of theloading & unloading ( hysteresis ). The stress!strain relationship may differ in differentdirections in the material ( isotropic vs anisotropic ) The general theory of nonlinear elasticity has to be used when predictingsoft-tissue deformation


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Modelling biomechanics:stages

Generate mesh ! usually generated using a set of M' images ! images need to segmented before mesh generation

Set up equations to be solved ! time!dependent & static & uasi!static ! stress!strain relationship* nonlinear + #hich form anisotropic ! forces + gravity

Apply appropriate boundary conditions ! usually need to apply a fi$ed displacement boundary condition some#here ! fi$ed or ero e$ternal stress boundary conditions else#here ! can be very difficult to determine appropriate boundary conditions..

umerically compute solution ! develop or use a finite element solver, #hich #ill have to include a nonlinear solver


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Modelling biomechanics:-redicting tumour location in the breast

reast cancer diagnosis is hindered by

the fact that the breast shape variesdramatically bet#een mammographyultrasound and M'".

Mammography: breast is compressed(several directions are possible)MRI: -atient lies on bac/Ultrasound: -atient sits upSurgery (biopsy): -atient lies on bac/

Goal: develop a !" computational modelof the breast from M# images$ whichcan be deformed to simulate otherscenarios and aid diagnosis%

00 ML1


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&redicting tumour location in the breast:mesh generation


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&redicting tumour location in the breast:00 to ML1 mammogram simulation


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&redicting tumour location in the breast:00 to ML1 mammogram simulation


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'ardiac electro-mechanical modelling

Electrical activation of cardiac myocytes induces tension generation + electro!mechanics.

2eformation of cardiac tissue has an influence on electrical activity3hilst a great deal of insight can be gained into cardiac activity & pathology & effect ofdrugs using an electro!physiological tissue model, electro!mechanical models are also ofgreat use

Difficulties in simulating cardiac electro-mechanics:! highly nonlinear (computationally intensive)

! highly anisotropic tissue ! active tension ! residual stress ! suitable boundary conditions

Le4rice et. al., Laminar structure of the heart*

5entricular myocyte arrangement andconnective tissue architecture in the dog, 6778


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Model developed at " '"9,%ophia 9ntipolis, France Model developed at Lausanne,%#it erland and Milan, "taly


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Modelling study + iederer et al., Length-dependent tension in the failing heart and

the efficacy of cardiac resynchroni ation therapy , :;66.0ardiac 'esynchroni ation Therapy (0'T) is a method of treating heart failure thatinvolves implantation of a pacema/er #hich resynchroni es activation!contraction

This study investigated the efficacy of 0'T and suggested a lin/ bet#een 0'T!efficacy and Fran/!%tarling mechanism

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Biomech Applications