Bioelectromagnetics
Principle
Bioelectromagnetics is the study of how electromagnetic fields interact with
and influence biological processes; almost the same as radiobiology of
non-ionizing radiation. Common areas of
investigation include the mechanism of animal migration and navigation using
the geomagnetic field, studying the potential effects of man-made sources of
electromagnetic fields, such as those produced by the power
distribution system and mobile phones (see Mobile phones
radiation hazards), and
developing novel therapies to treat various disorders.
While several treatments based on the use of
magnetic fields have been reported in peer-reviewed journals, the only ones
that have been approved by the US FDA are the use of pulsed magnetic fields to
aid non-union bone fractures. Transcranial magnetic
stimulation (TMS) is currently
under active study in multiple research centers, and will likely become an
approved therapy in the future. Bioelectromagnetics is not to be confused with
bioelectromagnetism (also simply called Bioelectricity), which deals with the ability of life to produce its own
electromagnetism.
Thermal versus nonthermal nature
Most of the molecules that make up the human
body interact only weakly with electromagnetic fields that are in the
radiofrequency or extremely low frequency bands. One basic interaction is the
absorption of energy from the electromagnetic fields, which can cause tissue to
heat up; more intense field exposures will produce greater heating. This heat
deposition can lead to biological effects ranging from discomfort to protein
denaturation and to burns. Many nations and regulatory bodies have established
safety guidelines to limit the electromagnetic fields exposure to a non-thermal
level (see Magnetobiology), which can either be defined as heating only to the
point where the excess heat can be dissipated/radiated away, or as some small temperature
increase(<
Biological effects of weak electromagnetic
fields are the subject of study in Magnetobiology.
Application
TMS
A well known medical application is the various types
of TMS (Transcranial magnetic
stimulation) which attempts to affect brain
functioning and consequently behavior.
Thermotherapy
A completely different application is thermotherapy.
This therapy induces local hypothermia with
temperatures greater than 45 oC and is used as a cancer treatment to kill or weaken tumor
cells, with negligible effects on healthy cells. Tumor cells, with a
disorganized and compact vascular structure, have difficulty dissipating heat.
Hyperthermia may therefore cause cancerous cells to undergo apoptosis in direct
response to applied heat, while healthy cells can more easily maintain a normal
temperature. Even if the cancerous cells do not die outright, they may become
more susceptible to ionizing radiation treatments or to certain chemotherapies,
allowing such therapy to be given in
smaller doses. It is often used for prostate cancer. A non-cancerous
application is rheumatoid arthritis and treatment of atrial fibrillation. Penetration depth are a few mm to a few cm, depending on
the applied frequencies, which are from tens of MHz up to about 6 GHz (the
higher the frequency, the smaller the depth).
High-energy
thermotherapy applies temperatures greater than 70 oC. The radiation is delivered by a probe with a microwave power of some
40 W, a penetration depth of 2-