Thermal Damage
This node defines a transformation model to account for damage by overheating or freezing in biological tissues. The transformation indicator is computed by a model based either on a temperature threshold or on Arrhenius kinetics.
Damaged Tissue
Three methods are available for the analysis; choose the Transformation model: Temperature threshold (the default), Arrhenius kinetics, or User defined. Depending on the material properties you have access to, you may choose one of the damage models.
The Arrhenius kinetics method is only applicable to hyperthermia analysis.
For Temperature threshold, define the settings for the Hyperthermia Analysis or Cryogenic Analysis. See Temperature Threshold for more details on the parameters of the model.
Hyperthermia Analysis
Enter values for:
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Damage temperature Td, h to define the (high) temperature that the tissue needs to reach to start getting damaged. The default is 323.15 K.
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Damage time td, h to define the time needed for the necrosis to happen while the temperature is above Td, h. The default is 50 s.
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Necrosis temperature Tn, h to define the (high) temperature to be reached for the necrosis to happen instantly. The default is 373.15 K.
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Enthalpy change Ld, h to define the enthalpy variation associated with damage by hyperthermia. The following heat source is added to the right-hand side of the bioheat equation:
Cryogenic Analysis
Enter values for:
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Damage temperature Td, c to define the (low) temperature that the tissue needs to reach to start getting damaged. The default is 273.15 K.
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Damage time td, c to define the time needed for the necrosis to happen while the temperature is below Td, c. The default is 50 s.
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Necrosis temperature Tn, c to define the (low) temperature to be reached for the necrosis to happen instantly. The default is 253.15 K.
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Enthalpy change Ld, c to define the enthalpy variation associated with damage by freezing. The following heat source is added to the right-hand side of the bioheat equation:
Arrhenius Kinetics
For Arrhenius kinetics, define the parameters to compute the degree of tissue injury with the Arrhenius equation (see Arrhenius Kinetics for more details):
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Frequency factor A in the Arrhenius equation. Default is taken From material. For User defined enter a value or an expression.
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Activation energy ΔE in the Arrhenius equation. Default is taken From material. For User defined enter a value or an expression.
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Polynomial order n to define a polynomial Arrhenius kinetics equation.
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Enthalpy change L to define the enthalpy variation associated with damage. The following heat source is added to the right-hand side of the bioheat equation:
User Defined
Enter values or expressions for the Enthalpy change L and the Fraction of transformation θd to define the heat source associated with the transformation as:
As required, also define how to Specify Different Material Properties for healthy and damaged tissue.
Specify Different Material Properties
When the Specify different material properties for damaged tissue check box is selected, choose a Transformed material, which can point to any material in the model. The default uses the Domain material. The healthy tissue properties correspond to the properties specified in the Heat Conduction and Thermodynamics sections. The effective tissue properties change from the healthy tissue properties to the damaged tissue properties as the damage evolves.
Heat Conduction
This section is available when the Specify different material properties for damaged tissue check box is selected.
Select a Thermal conductivity kd — From material (the default) or User defined, to be used for damaged tissue. For User defined choose Isotropic, Diagonal, Symmetric, or Full based on the characteristics of the thermal conductivity and enter another value or expression in the field or matrix.
Thermodynamics
This section is available when the Specify different material properties for damaged tissue check box is selected.
Select a Density ρd and Heat capacity at constant pressure Cp, d — From material (the default) or User defined, to be used for damaged tissue. The heat capacity describes the amount of heat energy required to produce a unit temperature change in a unit mass.
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Theory for Bioheat Transfer
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Biological Tissue
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Bioheat
There are specific predefined materials available in the Bioheat material database. See Materials Overview and Bioheat Materials Database in the COMSOL Multiphysics Reference Manual.
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Modeling a Conical Dielectric Probe for Skin Cancer Diagnosis: Application Library path Heat_Transfer_Module/Medical_Technology/conical_dielectric_probe
Location in User Interface
Context Menus
Bioheat Transfer>Biological Tissue>Thermal Damage
Ribbon
Physics Tab with interface as Heat Transfer in Solids and Fluids, Bioheat Transfer, Heat Transfer in Solids, Heat Transfer in Fluids, Heat Transfer in Porous Media or Heat Transfer in Building Materials selected:
Domains>interface>Biological Tissue>Thermal Damage