Biomedical Engineering Reference
In-Depth Information
energy directly to the tumor, and this method will probably become a new means
for cancer hyperthermia.
Besides, one can release the heat energy with the help of transportation of
high temperature fluids. It consists of two forms: one is hyperthermia probe technol-
ogy based on closed high-temperature steam heating; another is based on percutane-
ous fluid injection. The former belongs to closed heating, whose purpose is to
transport high-temperature fluid such as steam into the target tumor tissue, while to
protect surrounding healthy tissue with vacuum insulation. Yu et al. developed a new
minimally invasive tumor hyperthermia probe using high temperature water vapor
(Yu et al.
2004
) and evaluated it theoretically and experimentally. The latter directly
injects the high-temperature fluids into the target tissue to raise its temperature.
The nanoparticles have special properties. One can choose some nanoparticles
with better thermal conductivity and load them into the tumor, and then these
nanoparticles could improve the thermal conductivity of the tumor, so that increase
the tumor temperature much faster. In recent years, the thermal conductivity of
nanoparticle-fluid mixture has been reported by many authors (Wang et al.
1999
;
Shalkevich et al.
2010
; Le Goff et al.
2008
; Tian and Yang
2008
). The nanoparticles
can be suspended into heat transfer fluids such as water to increase the thermal
conductivities relative to those of the base fluids. The nanoparticles have been
studied include Al
2
O
3
, CuO (Wang et al.
1999
), Fe
3
O
4
(Tsai et al.
2009
), Cu (Xuan
and Li
2003
), etc., and some of them are safe for human body.
8
Challenging Issues
8.1
Comparison Among Different Heating Strategies
From the above review, it is known that heat generation sources refer to a wide
range of radiation spectrum in the forms of RF, MW, IR, and ultrasound, chemical
reaction, fluids or steam with high temperature. Each method has its own heat
transfer principle, advantages and disadvantages. Facing so many alternatives,
how can the clinicians make the best choice to treat tumor? The answers lie in the
comparisons among these methods.
Figure
2
shows the division of spectrum for the electronic magnetic wave.
The lower the frequency is, the deeper it penetrates into the tissues. Therefore, RF,
which is a subset of electromagnetic radiation with a frequency below 300 MHz,
has largest penetration possibility among the electronic magnetic wave heating
methods. RF is divided by LF, MF, HF, and VHF. For capacitive RF, HF and VHF
can reach any deep tissue of human body; while HF is mainly used on superficial
muscle for inductive heating. LF and MF are applied for interstitial heating. The
usual bands are 40.68, 13.56 and 8 MHz.
MW refers to the wave with a frequency of 300 MHz to 300 GHz, where
UHF is mainly used for heating. The MW and RF have an overlap, and low
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