CST SAR and Thermal treatment simulations

Alba Hyperthermia uses the CST (Computer Simulation Technology), world leader company in electromagnetic simulations, Studio Engines to perform SAR (Specific Absorption Rate) and Thermal calculations. For more information about CST www.cst.com.

CST allows to import the 3D segmented patient specific model from the ALBA HTPS previous steps and to position it into the antenna system model resembling accurately the actual treatment position.

The simulation is a two steps procedure:

1) First the Maxwell's equations are solved by the FIT (Finite Integration Technique)

The use of CST simulator gives an important advantage, that is the introduction of the PERFECT BOUNDARY APPROXIMATION (PBA) technology into the Finite Integration Technique which allows a more precise calculation at curved boundary with a minimum number of passes, respect to other conventional numerical methods.

PERFECT BOUNDARY APPROXIMATION

The SAR (Specific Absorption Rate) distribution (W/Kg) is then calculated from the electric field as

SAR distribution formula

Where s (S m-1) and r (Kg/m3) are the tissue electric conductivity and density, respectively.

2) The Temperature distribution is calculated with one of the model most frequently used in hyperthermia simulations, the Bioheat Equation:


the Bioheat Equation

where ρt (kg m-3) is the tissue density, ct (J kg-1 K-1) the tissue specific heat, kt (W m-1 K-1) the thermal conductivity, cb the blood specific heat, Wb the blood volumetric perfusion rate (kg m-3 s-1), Tart the local arterial temperature. Qm(W m-3), Q (W m-3) and T (K) are the metabolic heat generation, the absorbed power density and the local tissue temperature respectively.

The following example, regarding a Radiofrequency liver thermal ablation, shows a CST simulation, highlighting the different result obtained considering or not the blood perfusion.

different result obtained considering or not the blood perfusion

The CST thermal solver allows transient or steady state thermal distribution simulation.

Transient increase of tissue temperature