Page 270 - Computational Modeling in Biomedical Engineering and Medical Physics

Hyperthermia and ablation 259

Table 8.3 Quantities used in the numerical modeling of the RF kidney ablation.
Symbol Property Value
m Fluid consistency coefficient 0.017 Pa n
n Flow behavior index 0.708
_ γ Lower shear rate limit 0.01s -1
κ Porosity 10 29 m 2
Permeability 0.03
ε p
β F Forchheimer drag coefficient 0
Q br Mass source 0
Thermal conductivity, blood 0.543 W/(m K)
k b
k Thermal conductivity, renal tissue 0.4812 W/(m K)
Mass density of blood 1000 kg/m 3
ρ b
ρ Mass density of renal tissue 1000 kg/m 3
Specific heat capacity of blood 4180 J/(kg K)
C p,b
C p Specific heat capacity at constant pressure renal tissue 3771 J/(kg K)
Ta Basal temperature 37 C

3
_ q Specific power (Joule heat source) E J (W/m )
23 -1
ω Blood perfusion rate 3.4 3 10 s
RF, Radiofrequency.
transfer (no conduction) is set for the vein outlet and continuity conditions for the
interfaces. The surface of the kidney is in thermal equilibrium with its surroundings
(adiabatic) throughout the RF process (Fig. 8.3 right). The validity of this hypothesis is
checked throughout the numerical simulation.
In the bioheat transfer (BHT) model, there is no directional hemodynamic flow,
and the kidney is a homogeneous medium with a distributed heat source/sink that
accounts for its contribution (convection) to the heat transfer

@T
ð
ρC p 1 ρ C p;b ω T b 2 T a Þ 5 r 2krTð Þ 1 _q; ð8:9Þ
b
@t
a form of the energy equation. The hemodynamic and thermal properties are presented in
Table 8.3.
For consistency, the input flow rate in the GHT model, related to the renal arterial
inlet velocity (0.1 m/s), is sized to match the BHT perfusion rate, ω. Adiabatic bound-
ary conditions close the BHT model too.

Numerical modeling

The mathematical model (4) (9) was integrated using the finite element method
(FEM) (Peralta et al., 2006; Comsol, 2010 2019). The computational domains are
meshed using tetrahedral, quadratic, Lagrange elements, Fig. 8.4.
In theGHT model, becausethere arenocouplings,the properties aretemperature-
independent, the electrokinetic problem (8.4) and the hemodynamic (8.5) (8.7) problems