Page 279 - Computational Modeling in Biomedical Engineering and Medical Physics

268 Computational Modeling in Biomedical Engineering and Medical Physics

Figure 8.12 Microwave applicators for interstitial hyperthermia of soft tissue—1 W per pin, at 2.45
GHz; dimensions are in meters and temperature is in degrees Celsius. Adapted from Morega, M.,
Mogos, L., Neagu, M., Morega, A.M., 2006. Optimal design for microwave hyperthermia applicator. In:
Proceedings of the 11th International Conference on Optimization of Electrical and Electronic
Equipment—OPTIM 2006, Brasov, Romania, pp. 219 224.

Numerical analysis of heating when blood flow is taken into account

Temperature and target tissue control are best addressed in preinterventional stages by
numerical simulation and analysis. An example of a complex mathematical model is
given further, for coupled electromagnetic and thermal problems, with different con-
ditions for blood flow heat transfer: the cooling effect of blood perfusion in soft tissue
is compared versus more efficient heat extraction due to the presence of large blood
vessels in the interventional tissue volume. Three physical problems are described and
transposed in mathematical formulations (Morega et al., 2014):
1. The EMF problem—electromagnetic waves is emitted by the pin-antennae of the array;
the mathematical expression is given by the waves equation (in terms of either electric
field strength E, or magnetic field strength H). For time-harmonic working conditions
[continuous waves (CW)], the equations are presented in their complex form.

1 1 2
2
r 3 r 3 E 2 ω εE 5 0 for E; or r 3 r 3 H 2 ω μ H 5 0 for H: ð8:10Þ
0
μ 0 ε
The quantities in Eq. (8.1) are explained in Tables 8.4 and 8.5.
For the anatomical domain, a volume of homogeneous material is considered,
with a simple geometrical shape like the representations in Fig. 8.11 (right), or with
an anatomical realistic shape, for example an organ (liver, lung, etc.) reconstructed
from CT or RMN scans. For interstitial microwaves hyperthermia, the EMF prob-
lem is commonly confined to the volume of the organ; the external surface of the