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Hyperthermia and ablation 277

with the reference values σ and ε taken from the well known and cited database
r
(Andreuccetti et al., 1997) at the corresponding working frequency and standard body
temperature.
The results of a numerical experiment documented in Morega et al. (2008) allow
for a comparison between the evolution of highest temperatures in human liver heated
by interstitial mild hyperthermia, performed with one pin-antenna (as shown earlier in
Fig. 8.11 left) fed at 2.45 GHz CW. The numerical analysis was executed as previ-
ously described and the reference dielectric properties for liver-like tissue are:

σ 5 1:69 S=m and ε 5 43. The absorbed power inside the target tissue and the tem-

r
perature distribution were determined for both coupling cases: unidirectional coupling
of the electromagnetic and thermal problems (i.e., constant dielectric properties) and
bidirectional coupling of the two problems (i.e., temperature-dependent dielectric
properties). Figure 8.20 shows the color temperature spectra in the symmetry section
of the coaxial pin-antenna in the two described cases (with constant (A), and
temperature-dependent (B) dielectric properties), while Fig. 8.21 compares tempera-
ture variations with increasing antenna power in the same two cases.

8.4 Magnetic hyperthermia

More recently increased interest is visible in using either gold (Moran et al., 2009)ormag-
netic nanoparticles (Giustini et al., 2010) to enhance and improve the selective heating of
diseased tissue, thereby obtaining improved hyperthermia treatment. Because tumors have
higher heat-sensitivity over normal cells, heating them to 41 C 47 C results in their selec-

tive damage. Moreover, an equivalent therapeutic efficacy was observed when combining a

Figure 8.20 Temperature distribution in the plane of axial-symmetry, for constant (A) versus
temperature-dependent (B) dielectric properties of heated tissue (2.45 GHz, 0.9 W). Adapted from
Morega, M., Neagu, M., Morega, A.M., 2008. Bidirectional coupling of electromagnetic and thermal pro-
cesses in radiofrequency hyperthermia. In: Proceedings of the 12th International Conference on
Optimization of Electrical and Electronic Equipment—OPTIM 2008, Brasov, Romania, pp. 257 262.