Nanoparticles Enhanced Hyperthermia - Intracellular Delivery: Fundamentals and Applications - page 588

Fig. 2 Electromagnetic spectrum
frequency of the heating bands can reach 100 MHz of VHF, while the high
frequency reaches 3,000 MHz. The accepted MW frequencies are generally
2.45 GHz, 915 and 434 MHz.
The wavelength band from 1 mm to 780 nm is infrared light, where IR is below
3,000 nm. The wavelength range of 780 to 380 nm is visible light. The laser heating
method makes use of IR and visible light.
Heating is a process of absorbing energy during spread of electromagnetic wave.
When human is irradiated under the RF field, the free electrons, ions and dipoles,
will move resulting in ohm-heat. At the same time, vibrations among the molecules
produce parts of heat. The principle of MW heating methods is similar to that of
RF, but the vibration heat holds the uppermost.
Ultrasound frequency for heat treatment is 0.5-5 MHz; generally 1 MHz.
Ultrasound wave is a king of mechanical wave. It produces thermal energy accor-
ding to vibration friction. The higher ultrasound intensity is, the faster temperature
rises; and the higher the frequency is, the more heat tissues will absorb. Therefore,
treating superficial tumors uses high-frequency ultrasound to prevent the tissue below
tumor from heating, while deep tumors treatment uses low-frequency to prevent
surface overheating. Besides, the non-thermal effect brought about by ultrasound is
also a research focus.
The domain of action, advantages and disadvantages are considered to deter-
mine the choice among various heating methods (Table 4 ) (Li and Hu 1995 ; Lin
et al. 1997 ; Peng and Zhao 2002 ). In nanoparticle enhanced hyperthermia, the
toxicity, biocompatibility, heat efficiency of the nanoparticles will also affect the
results. Heating methods based on electrothermal needle, high temperature fluids
or thermochemistry are in the initial stage, so there are still many problems asso-
ciated with application need to be clarified.
Although each kind of energy has its advantages, one can still envisage with a
bold hand that there would be a new device which can emit waves with different
frequency energy according to need. That means, we can combine RF and MW
devices into one multifunction device, and then change frequency according to
practical need.