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  Non-ionizing
radiations are those whose frequency ranges between 100 Khz and 300 GHz;
up to 300 MHz radiations are defined microwaves, beyond this limit they
are defined radiofrequencies.
Such radiations have many uses in the health sector. The most common use
is diathermy, i.e. warming up of superficial tissues by exploitation of
radiofrequencies or microwaves thermic effect.
Radiofrequencies tratment mainly employed in physiotherapy to treat
pathologies of bones and muscles, such as arthropathies, myositis,
neuralgia, etc. The part to be treated (wrist, knee, neck, elbow, etc) is
introduced in a variable electromagnetic field that, by interacting with
tissues, leads to a rise in the local temperature by means of thermic
dissipation phenomena.
Also microwaves tratment is employed in physiotherapy to warm up
biological tissues exposed to an electromagnetic field with microwaves
frequencies.
Further radiofrequencies' uses in the health field include hyperthermia
which is employed as coadjutor in some tumour treatments and in the rapid
warming up of blood and tissues during organ graft.
Finally, radiofrequencies are used in imaging (MRI employes
radiofrequencies of particular frequency in static magnetic fields). In
fact MRI (Magnetic Resonance Imaging) is a methodology that allows us to
obtain bi- and tri-dimensional information of different sections of the
body by employing non-ionizing radiations.
Furthermore the images present a high soft tissue contrast and this
allows us to obtain many information on the conditions of different
organs.
Therefore MRI is particularly indicated for the diagnosis of:
- intracranial pathologies (malformations, vascular pathologies,
neoplasies, etc.);
- spine or spinal cord pathologies (disc prolapse, trauma, neoplasies,
etc.);
- liver, kidney, cardiovascular system and mediastinum diseases.
To obtain images, a magnetic resonance tomograph employes:
- a static magnetic field;
- a magnetic field that varies in space and time;
- a radiofrequencies generator.
The static magnetic field is produced with different types of magnets
permanent, superconducting, ect.); in the last generation instruments,
the most widely employed magnets are superconducting magnets, allowing
the attainment of fields of higher value if compared to the previous
ones. However, their employment makes it compulsory to arrange for
cooling systems and for systems to dissipate the enormous energy stored
up in the case of quenching.
The extension and distribution of the energy absorbed by radiofrequencies
and microwaves is thought to be one of the main factors that influence
the appearance of biological effects; the absorption of such radiations
depends on their frequency (it is highest between 60 and 100 MHz), and on
the shape, dimension and dielectric characteristics of the irradiated
body.
Microwaves are absorbed only superficially, whereas radiations of lower
frequencies (radio waves) are absorbed by the deeper layers.
Their main biological effects depend on the thermical effect and involve
the crystalline lens and the male gonads. The crystalline lens may
present posterior cataract.
The gonadic alterations can lead to infertility, although this is
reversible and object of discussion amongst different authors. Such
alterations involve anomalies of the seminal epithelium and of
spermiogenesis with reduction of the number and mobility of spermatozoa.
Among the non-thermical effects there is the neuroasthenic syndrome which
is characterized by weakness, fatigue, insomnia, bradycardia,
hypotension.
Furthermore haemopoietic effects have been described (reduction of
erythrocytes, tendency to lymphocytosis and eosinophilia) as well as
effects on endocrine function (interference on thyroid, pituitary gland and
suprarenal function). Teratogen and carcinogenic actions, which have been
hypothesized in the past, have not been proved yet.
Finally, it must be mentioned that radiofrequencies and microwaves are
capable of interfering with the activity of heart pacemakers.
The employment of MRI equipment entails further risks relative to:
- interference between the magnet and metallic materials that could be
present inside the subject's body;
- interference between the magnet and ferromafnetic materials that could
be present in the environment (room).
Metallic objects, such as surgical clips, cardiac valves built before
1964 (since 1964 valves have been produced with non-ferromagnetic
materials), orthopaedic implantations, cochlear implantations, foreign
bodies (such as the presence of metallic splinters in the eyes), are
subject to displacement (directly related to the field force) induced by
the magnet. This can provoke torsion and compression of the tissues that
can result in harmful consequences such as vessel breakage following
torsion of intracranial surgical clips employed for aneurysm clamping.
The magnetic field influences also the objects that can be present in the
room. Its force decreases as the distance of the object from the magnet
increases. This is why metallic objects, such as scissors, scalpels,
screwdrivers, if close to the field become attracted towards the centre
of the magnet and behave like bullets that can harm both the patients and
the personnel.
Another risk both for the patients and for the personnel is represented
by the accidental quenching of the magnet, which is usually cooled by
liquid helium; gaseous helium, at room temperature, takes up 700 times
the volume of the same amount of liquid helium. Therefore, an accidental
quenching of the magnet can cause big differences in volume between the
liquid and the gaseous phases and it follows that the container of the
cryogens must be strong enough to contain the increase in pressure. Furthermore,
the room must be equipped with an appropriate ventilation system to allow
the quick expulsion of the gas in the case of its release, in order to
avoid asphyxia risk.
For additional information
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