Biological Tissue
This node adds the bioheat equation as the mathematical model for heat transfer in biological tissue. This equation can include source terms representing blood perfusion and metabolism using Pennes’ approximation, through the addition of a Bioheat subnode; see Equation 4-19. Optionally it can define a damage model to account for overheating or freezing in tissues.
Heat Conduction, Solid
The default Thermal conductivity k uses values From material. For User defined select Isotropic, Diagonal, Symmetric, or Anisotropic based on the characteristics of the thermal conductivity and enter another value or expression in the field or matrix.
Thermodynamics, Solid
The default Density ρ and Heat capacity at constant pressure Cp are taken From material. See Material Density in Features Defined on the Material Frame if a temperature-dependent density should be set.
The heat capacity describes the amount of heat energy required to produce a unit temperature change in a unit mass.
For User defined enter other values or expressions.
Damaged Tissue
Select the Include damage integral analysis check box to account for overheating or freezing in tissues with a damage model.
Two methods are available for the analysis; choose Damage integral form: Temperature threshold (the default) or Energy absorption. Depending to the material properties you have access to, you may choose one of the damage models.
The Energy absorption method is only applicable to hyperthermia analysis.
For Temperature threshold, define the settings for the Hyperthermia Analysis and Cryogenic Analysis. See First Form Integral for more details on the parameters of the model.
Hyperthermia Analysis
Enter values for:
•
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.
•
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.
•
Temperature of necrosis Tn, h to define the (high) temperature to be reached for the necrosis to happen instantly. The default is 373.15 K.
•
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:
•
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.
•
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.
•
Temperature of necrosis Tn, c to define the (low) temperature to be reached for the necrosis to happen instantly. The default is 253.15 K.
•
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:
For Energy absorption, define the Frequency Factor and Activation Energy to compute the degree of tissue injury with the Arrhenius equation. See Second Form Integral for more details.
Frequency Factor and Activation Energy
Enter values for:
•
Frequency factor A in the Arrhenius equation. Default is taken From material. For User defined enter a value or an expression. The default is 7.39 ⋅ 1039 s–1.
•
Activation energy ΔE in the Arrhenius equation. Default is taken From material. For User defined enter a value or an expression. The default is 2.577 ⋅ 105 J/mol.
•
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:
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 Damaged 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, Solid and Thermodynamics, Solid sections. The effective tissue properties change from the healthy tissue properties to the damaged tissue properties as the damage evolves.
Heat Conduction, Damaged Tissue
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 Anisotropic based on the characteristics of the thermal conductivity and enter another value or expression in the field or matrix.
Thermodynamics, Damaged Tissue
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.
Theory for Bioheat Transfer
Damaged Tissue
When Surface-to-surface radiation is activated, the Opacity subnode is automatically added to the entire selection, with Opaque option selected. The domain selection can’t be edited. To set some part of the domain as transparent, add a new Opacity subnode from the context menu (right-click the parent node) or from the Physics toolbar, Attributes menu.
There are specific predefined materials available in the Bioheat material database. See Materials Overview and Bioheat Materials Database 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
More locations are available if the Heat transfer in biological tissue check box is selected under the Physical Model section. For example:
Heat Transfer in Solids>Biological Tissue
Ribbon
Physics Tab with interface as Heat Transfer, Bioheat Transfer, Heat Transfer in Solids, Heat Transfer in Fluids, Heat Transfer in Porous Media, Heat Transfer in Building Materials, Heat Transfer with Surface-to-Surface Radiation or Heat Transfer with Radiation in Participating Media selected:
Domains>interface>Biological Tissue