Thermal Damage
This node defines a transformation model to take into account damage by overheating or freezing in biological tissues. The transformation indicator is calculated 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 (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:
A user defined value can be set for the initial damaged tissue indicator and the initial instant necrosis indicator used in the hyperthermia analysis. See the Initial Values section for details.
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:
A user defined value can be set for the initial damaged tissue indicator and the initial instant necrosis indicator used in the cryogenic analysis. See the Initial Values section for details.
Arrhenius Kinetics
For Arrhenius kinetics, define the parameters to calculate 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:
A user defined value can be set for the initial damaged tissue indicator of the Arrhenius equation. See the Initial Values section for details.
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 (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.
When the material and spatial frames differ (due to the presence in the model of a Moving Mesh node, or a Solid Mechanics interface for example), you can select on which frame the Thermal conductivity kd is specified.
By default the Deformation model for thermal conductivity is set to Standard. With this option, the thermal conductivity is supposed to be given on the material frame. If the material frame does not coincide with the spatial frame, a conversion is applied to get the variables ht.k_dxx, ht.k_dyy, and so on. This option is often suitable for moderate elastic strains.
By selecting the Large strain option, the thermal conductivity is supposed to be given on the spatial frame. In case of isotropic materials, the thermal conductivity variables ht.k_dxx, ht.k_dyy, and so on, are directly equal to the values you have set. In case of anisotropic materials, the rotation of the material is also taken into account following
where R is the rotation matrix between the material and the spatial frames.
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 (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.
Initial Values
This section is available when the Transformation model is set to Temperature threshold or Arrhenius kinetics. Set a value or expression for the Initial damaged tissue indicator, αinit, to be used as an initial condition for any of the time integral analyses. For the Temperature threshold model, a value or expression for the Initial instant necrosis indicator, αn,init, can be set as well.
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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 Library in the COMSOL Multiphysics Reference Manual.
Hepatic Tumor Ablation: Application Library path Heat_Transfer_Module/Medical_Technology/tumor_ablation
Microwave Heating of a Cancer Tumor: Application Library path Heat_Transfer_Module/Medical_Technology/microwave_cancer_therapy
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