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Medical Devices and Systems Exposure and Dosimetry
and/or staff unintentionally to RF stray fields from surgical devices, to RF EMF from
telemetric data transmission from electromedical implants, or to magnetic fields from
incorporated devices, active or nonactive, because of their generation by electric current
flow or by the physical nature of ferromagnetic or superparamagnetic material (e.g.,
magnetic nanoparticles).
Electromagnetic coupling comprises a wide range of frequencies, from static magnetic fields (e.g., MRI, permanent magnets for navigation and tracking) to extremely
low–frequency (ELF) electric and magnetic fields (e.g., magnet therapy), and to RF EMFs
(e.g., diathermy, hyperthermia, and MRI) and microwave radiation (e.g., diathermy and
telemedicine). In addition, it includes fast magnetic field transients (e.g., TMS and MRI).
For clarity, it should be kept in mind that from a physical point of view the umbrella
term electromagnetic could be slightly misleading. In the wide frequency range extending from static fields until microwaves, the physical nature of these fields as well as the
governing mechanisms of interaction and propagation changes. In the static case and
in the ELF range, electric and magnetic fields are decoupled and need to be considered
separately. Only at higher frequencies in the RF range, electric and magnetic fields are
tied together (coupled) and justify the term electromagnetic. Only in close vicinity to
the antenna (in the reactive near field), depending on the kind of antenna (rod or loop
antenna), either electric or magnetic fields may dominate and the counterpart neglected.
For small antenna dimensions, this applies up to a distance of about half the wavelength
of the EMF. Up to frequencies of 500 MHz, this distance is larger than the body diameter
of 30 cm.
6.2 Medical Therapy
In medical therapy, electric fields, magnetic fields, and EMFs are applied to stimulate
nerve and/or muscle cells, induce electric fields to stimulate healing, or deliver heat as
a primary goal or as a vehicle for inducing a secondary effect such as drug delivery or
activation.
6.2.1 Thermotherapy
Excess heating of the target region can be subdivided into the following (Habash et al.
2006):
• Long-term low-temperature diathermia (e.g., elevating temperatures to 40°C–41°C
for 6–72 hours)
• Moderate-temperature hyperthermia (e.g., elevating temperatures to 42°C–45°C
for 15–60 minutes)
• High-temperature hyperthermia or thermal ablation (e.g., elevating temperatures
up to 50°C for 4–6 minutes)
Therefore, these applications differ with regard to amplitude and duration of EMF exposure. The biological interactions may occur at the molecular, cellular, organ, and/or system level. EMF delivers heat by converting EMF energy into kinetic energy of moving
particles. This is achieved by accelerating intracorporal particles by electric or magnetic